This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). Responsibility for the views, information or advice expressed herein is not accepted by the Australian Government.

1. Experimental Setup
<ol>
	<li>Locate a suitable fume hood for the measurement technique, and remove any irrelevant equipment to allow better air flow and reduce cluttering. Do not use any chemicals other than hydrofluoric acid (HF) in the fume hood.</li>
	<li>Test the quality of the deionized (DI) water from the tap within the fume hood using a conductivity meter. Ensure that the DI water has a conductance of at most 0.055 &#181;S/cm at a temperature of 20 &#176;C.</li>
	<li>Place a minority carrier lifetime tester into the fume hood. Connect the cables to a computer, which is situated on a table outside of the fume hood.</li>
	<li>Switch on the computer and lifetime tester. Open the lifetime tester file on the computer and click the &#39;measure&#39; button to ensure correct communication between computer and the lifetime tester. The light source on the lifetime tester should flash if the computer and tester have been connected correctly.</li>
	<li>Place a halogen lamp inside the fume hood. Position the lamp such that it can illuminate the lifetime tester stage where the sample will be located.</li>
	<li>Connect the halogen lamp to a power source which should be situated outside of the fume hood. When the halogen lamp is switched on, its intensity should be at least 0.02 W/cm2 on the lifetime tester stage.</li>
</ol>
2. Preparing the 15% HF Solution
Note: HF is a dangerous chemical and must be treated with care. It causes slow, sustained, and deep damage to the body following exposure. HF does not readily burn the skin like other acids - rather it absorbs quickly into the skin and causes deep blistering and damage to bones. This means that bones become brittle and blistered as the fluorine reacts with calcium. HF also binds with free calcium which is used in nerve regulation and osmotic cell balance, so binding of free calcium in the body can be fatal. It is paramount that the user follows laboratory safety protocols when using HF, and ensures they know the location of the HF first aid kit and hexafluorine (or calcium gluconate gel).
<ol>
	<li>Place a chemically cleaned round plastic container (H: 55 mm, D: 170 mm) into the fume hood (same as in Section 1). The container must have a clear plastic lid. See Section 6 on how to chemically clean the container prior to use.</li>
	<li>Clear the area around the plastic container in the fume hood so the HF solution can be prepared without any obstructions nearby.</li>
	<li>Apply all personal protection equipment (PPE).</li>
	<li>CAUTION: Add 50 ml of HF to 100 ml DI water (H2O) in the container.</li>
	<li>CAUTION: Add 20 ml of hydrochloric acid (HCl) to the container and mix the H2O : HF : HCl solution using plastic tweezers. Rinse the tweezers thoroughly afterwards.</li>
	<li>CAUTION: Place the lid on the plastic container and allow the solution to settle for 1 hr. During this time, HF fumes will condense on the lid.</li>
	<li>Adequately label the container, and make it clear that it contains HF. 
	Note: The HF solution will last 1-2 months with heavy usage. Therefore there is no need to replace the solution each time a measurement is to be performed.</li>
</ol>
3. Calibration of the Lifetime Tester
<ol>
	<li>Locate at least 6 silicon wafers of known resistivity and conductance. Ideally the resistivity range should span 0.1-100 &#937;-cm.</li>
	<li>On the computer, open the lifetime tester calibration file. Enter the resistivity of each wafer in the table and then click &#39;Update # of wafers&#39;.</li>
	<li>Click the &#39;Get data&#39; button in the calibration file and enter the details of the lifetime tester.</li>
	<li>Apply all necessary PPE.</li>
	<li>CAUTION: Place the plastic container filled with the HF solution on the lifetime tester stage and position it over the inductive coil (blue circle region).</li>
	<li>When prompted to measure the &#39;air voltage&#39; on the computer, measure the voltage of the HF solution by clicking the &#39;Ok&#39; button. In this case, the air has been replaced by the conductance of the HF solution.</li>
	<li>CAUTION: Carefully remove the container filled with HF from the stage and place it on the fume hood bench. Carefully remove the lid.</li>
	<li>CAUTION: When the lid has been removed from the container, immerse the first silicon wafer into the HF solution using plastic tweezers. Place the lid back on the container.</li>
	<li>CAUTION: Place the plastic container back onto the lifetime tester stage and position it over the inductive coil. Ensure the silicon wafer is centered over the coil (blue circle region).</li>
	<li>When prompted to measure the &#39;sample voltage&#39; on the computer, click the &#39;Ok&#39; button once again. Remove the container from the stage and place it on the fume hood bench.</li>
	<li>CAUTION: Carefully remove the silicon wafer from the HF solution using plastic tweezers and rinse the wafer in the dedicated rinse beakers. Do a final rinse under the tap in the fume hood.</li>
	<li>CAUTION: Place the lid back onto the container, and position the container back onto the lifetime tester stage.</li>
	<li>Repeat steps 3.6 to 3.12 until all samples have been measured.</li>
	<li>Once all of the samples have been measured, click the &#39;Fit data&#39; button in the calibration file. This will fit a parabolic curve to the measured data and provide calibration coefficients A, B and C which are specific to this setup.</li>
	<li>On the computer, open the lifetime tester file and click on the &#39;settings&#39; tab. Enter in the new calibration coefficients A, B and C for the HF setup. Save the file under a new name. 
	Note: The HF setup only requires a calibration every 6 months. Therefore there is no need to calibrate the setup each time a measurement is to be performed.</li>
</ol>
4. Wet Chemical Treatment of Silicon Wafers Prior to Measuring
<ol>
	<li>Prepare standard clean 1 (SC 1).
	<ol>
		<li>CAUTION: In an alkaline allocated fume hood, add 185 ml of ammonium hydroxide (NH4OH) to 1,295 ml of DI water in a 2 L glass beaker.</li>
		<li>CAUTION: Place the beaker onto a hot plate and heat the H2O : NH4OH solution to a temperature of ~50 &#176;C. Use a watch glass to cover the beaker.</li>
		<li>CAUTION: Once the H2O : NH4OH solution has reached a temperature of ~50 &#176;C, add 185 ml of hydrogen peroxide (H2O2) and continue to heat until the temperature reaches ~75 &#176;C. This H2O : NH4OH : H2O2 solution is known as SC 1. 
		Note: SC 1 should be changed daily to effectively clean silicon wafers.</li>
	</ol>
	</li>
	<li>Prepare standard clean 2 (SC 2).
	<ol>
		<li>CAUTION: In an acid allocated fume hood, add 185 ml of HCl to 1,295 ml of DI water in a 2 L glass beaker.</li>
		<li>CAUTION: Place the beaker onto a hot plate and heat the H2O : HCl solution to a temperature of ~50 &#176;C. Use a watch glass to cover the beaker.</li>
		<li>CAUTION: Once the H2O : HCl solution has reached a temperature of ~50 &#176;C, add 185 ml of H2O2 and continue to heat until the temperature reaches ~75 &#176;C. This H2O : HCl:H2O2 solution is known as SC 2. 
		Note: Change SC 2 daily to effectively clean silicon wafers.</li>
	</ol>
	</li>
	<li>Prepare the silicon etching solution.
	<ol>
		<li>In an alkaline allocated fume hood, add 1,600 ml of tetramethylammonium hydroxide (TMAH) to a chemically clean 2 L glass beaker. Please see Section 6 on how to chemically clean the beaker prior to use.</li>
		<li>Place the beaker onto a hot plate and heat the TMAH solution to a temperature of ~85 &#176;C. Use a watch glass to cover the beaker. 
		Note: The TMAH solution will not need changing until it starts to crystallize, i.e., after 1 month.</li>
	</ol>
	</li>
	<li>Perform the wet chemical treatment.
	<ol>
		<li>Load samples into a quartz cradle and place them in a communal HF solution in the lab. The concentration is not critical.</li>
		<li>After ~10 sec or once the samples become hydrophobic (pull dry), remove the cradle from the HF solution and rinse using 3 beakers filled with DI water.</li>
		<li>Transport the cradle of wafers to the fume hood where SC 1 has been prepared. When SC 1 has stabilized at ~75 &#176;C, slowly immerse the cradle of wafers into SC 1.</li>
		<li>Clean the wafers in SC 1 for 10 min.</li>
		<li>After 10 min has elapsed, remove the cradle of wafers from SC 1 and rinse them using three 2 L glass beakers filled with DI water. Chemically clean these glass beakers prior to filling them with DI water. Please see Section 6 on how to chemically clean the beakers.</li>
		<li>After rinsing, place the samples into a HF solution which is dedicated only for post SC 1 processing. The concentration is not critical.</li>
		<li>After ~10 sec or once the samples become hydrophobic (pull dry), remove the cradle from the HF solution and rinse using 3 beakers filled with DI water. Use the same beakers as in step 4.4.5.</li>
		<li>Transport the cradle of wafers to the fume hood where SC 2 has been prepared. When SC 2 has stabilized at ~75 &#176;C, slowly immerse the cradle of wafers into SC 2.</li>
		<li>Clean the wafers in SC 2 for 10 min.</li>
		<li>After 10 min has elapsed, remove the cradle of wafers from SC 2 and rinse them using 3 beakers filled with DI water. Use the same beakers as in step 4.4.5. 
		Note: The cradle of wafers could be stored in one of the rinse beakers filled with DI water until the following day.</li>
		<li>After rinsing, place the samples into a HF solution which is dedicated only for post SC 2 processing. The concentration is not critical.</li>
		<li>After ~10 sec or once the samples become hydrophobic (pull dry), remove the cradle from the HF solution and rinse using 3 beakers filled with DI water. Use the same beakers as in step 4.4.5.</li>
		<li>Transport the cradle of wafers to the fume hood where the TMAH solution has been prepared. When the TMAH solution has stabilized at ~85 &#176;C, slowly immerse the cradle of wafers into the TMAH solution.</li>
		<li>Etch the wafers in TMAH for 5 min. This will remove ~5 &#181;m of silicon.</li>
		<li>After 5 min has elapsed, remove the cradle of wafers from the TMAH solution and rinse them using 3 beakers filled with DI water. Use the same beakers as in step 4.4.5. More than 3 rinses might be required as TMAH is quite &#39;sticky&#39;.</li>
		<li>Transport the cradle of wafers in DI water to the fume hood where the experiment has been setup. See section 1.1.</li>
		<li>Measure the prepared silicon wafers within 2 hr after step 4.4.16.</li>
	</ol>
	</li>
</ol>
5. Measurement Procedure
<ol>
	<li>Apply all necessary PPE.</li>
	<li>Fill two 2 L plastic beakers with DI water and place them in the fume hood. These will be used for rinsing the silicon samples post measurement.</li>
	<li>Place plastic tweezers into an empty 500 ml plastic beaker and place inside the fume hood near the rinse beakers. These tweezers will be used to handle the silicon samples.</li>
	<li>On the computer, open the lifetime tester file. Make sure the file contains the correct calibration coefficients for the HF measurement setup. See section 3.</li>
	<li>In the lifetime tester file, select the &#39;Transient&#39; mode. Enter the details of the silicon wafer to be measured, for example, thickness, resistivity and dopant type.</li>
	<li>CAUTION: Place the container (lid on) filled with HF onto the stage of the lifetime tester and center it over the inductive coil (blue circle region). Let the solution settle for 1 min.</li>
	<li>On the computer, click on the &#39;Zero instrument&#39; button in the lifetime tester file. This will measure the voltage of the solution. 
	Note: Over time, the solution voltage will decrease because the composition of the solution changes with time. Irrespective of this, the HF solution does not show any degradation in its passivating quality, which is why the solution can be used for 1-2 months without being changed.</li>
	<li>CAUTION: Carefully remove the container from the lifetime tester stage and place it on the fume hood bench.</li>
	<li>CAUTION: Carefully remove the lid from the container filled with the HF solution. If there is some condensation on the lid, carefully rinse the lid in DI water using the tap in the fume hood.</li>
	<li>CAUTION: Carefully immerse the first silicon wafer into the HF solution. Using the plastic tweezers, lightly press down on the silicon wafer to ensure it is sitting on the bottom of the container.</li>
	<li>Rinse the tweezers and place them back into the empty 500 ml plastic beaker.</li>
	<li>CAUTION: Carefully place the lid back on the container and then place the container on the lifetime tester stage. Ensure the silicon wafer is positioned over the inductive coil (blue circle region).</li>
	<li>Rinse and dry your gloves. Remove them before operating the computer.</li>
	<li>If the fluorescent light in the fume hood is on, it must be switched off before a measurement is to be conducted. Minimum light is required during the measurement.</li>
	<li>Switch the halogen lamp on, and ensure it is illuminating the silicon wafer through the lid of the plastic container. Time for 1 min (the exact time is not critical).</li>
	<li>During the illumination period, click the &#39;Measure&#39; button in the lifetime file on the computer. A small window labeled &#39;Taking data&#39; will appear.</li>
	<li>In the &#39;Taking data&#39; window, type in a name for the file. Under &#39;sample averaging&#39; select 10.</li>
	<li>When the silicon wafer has been illuminated for 1 min, switch the halogen lamp off and immediately click the &#39;Average&#39; button in the &#39;Taking data&#39; window. The lifetime tester will flash 10 times and average the lifetime measurements. 
	Note: Once the halogen lamp is switched off, the passivation of the silicon wafer will start to degrade, and thus it is important to measure immediately after illumination to achieve the best results.</li>
	<li>When the averaging is complete, click the &#39;Ok&#39; button in the &#39;Taking data&#39; window.</li>
	<li>If another measurement is required, repeat steps 5.15-5.18.</li>
	<li>CAUTION: Once the measurement is complete, remove the container from the lifetime tester stage and place it on the fume hood bench.</li>
	<li>CAUTION: Carefully remove the lid from the container filled with the HF solution. If there is some condensation on the lid, carefully rinse the lid in DI water using the tap in the fume hood.</li>
	<li>CAUTION: Carefully remove the silicon wafer from the HF solution using plastic tweezers and rinse the wafer in the dedicated rinse beakers. Do a final rinse under the tap in the fume hood.</li>
	<li>If more samples are to be measured, repeat steps 5.10-5.23.</li>
	<li>Once all samples have been measured, ensure the lid is placed on the container and store the HF solution in the fume hood. Make sure the container is adequately labeled.</li>
	<li>Rinse all beakers and tweezers and store them in their allocated spots in the laboratory.</li>
	<li>Allow the lifetime tester to remain in the fume hood for 1 hr after use and then remove it from the fume hood.</li>
</ol>
6. Chemical Cleaning of Beakers and Containers
<ol>
	<li>In an alkaline allocated fume hood, prepare an SC 1 solution as outlined in sections 4.1.1-4.1.4.</li>
	<li>To chemically clean beakers and containers, pour the SC 1 solution into the beakers/containers. The beakers can only be cleaned one at a time.</li>
	<li>Let the solution clean the beaker/container for 10 min. If the beaker/container is plastic, it cannot be placed on a hot plate, and therefore the SC 1 solution will cool during the clean. This will not affect the cleaning process.</li>
	<li>After 10 min, pour the SC 1 solution into another beaker/container if they require cleaning also. Otherwise let the SC 1 solution cool in a large beaker. Once cooled, SC 1 can be poured down the sink with running water.</li>
	<li>Rinse SC 1 cleaned beaker/container in DI water.</li>
	<li>In an acid allocated fume hood, prepare an SC 2 solution as outlined in sections 4.2.1-4.2.4.</li>
	<li>Pour the SC 2 solution into beaker/container from step 6.5. Allow the solution to clean the beaker/container for 10 min.</li>
	<li>After 10 min, pour the SC 2 solution into another beaker/container if they require cleaning also. Otherwise let the SC 2 solution cool in a large beaker. Once cooled, SC 2 can be poured down the sink with running water.</li>
	<li>Rinse SC 2 cleaned beaker/container in DI water. The beaker/container is now chemically cleaned.</li>
</ol>

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B. 73 ((1-3)), 178-183 (2000).</li><li>Bertagna, V., Plougonven, C., Rouelle, F., Chemla, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=p-+and+n-type+silicon+electrochemical+properties+in+dilute+hydrofluoric+acid+solutions.">p- and n-type silicon electrochemical properties in dilute hydrofluoric acid solutions.</a> J. Electrochem. Soc. 143 (11), 3532-3538 (1996).</li><li>Bertagna, V., Erre, R., Rouelle, F., Chemla, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionic+components+dependence+of+the+charge+transfer+reactions+at+the+silicon/HF+solution+interface.">Ionic components dependence of the charge transfer reactions at the silicon/HF solution interface.</a> J. Solid State Electrochem. 4 (1), 42-51 (1999).</li><li>Kolasinski, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanism+of+Si+etching+in+fluoride+solutions.">The mechanism of Si etching in fluoride solutions.</a> Phys. Chem. Chem. Phys. 5 (6), 1270-1278 (2003).</li><li>Trucks, G. W., Raghavachari, K., Higashi, G. S., Chabal, Y. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanism+of+HF+etching+of+silicon+surfaces:+A+theoretical+understanding+of+hydrogen+passivation.">Mechanism of HF etching of silicon surfaces: A theoretical understanding of hydrogen passivation.</a> Phys. Rev. Lett. 65 (4), 504-507 (1990).</li><li>Zhang, X. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electrochemistry of silicon and its oxide. , (2001).</li></ol>

The authors have nothing to disclose.

The successful implementation of the bulk silicon lifetime measurement technique described above is based on three critical steps, (i) chemically cleaning and etching the silicon wafers, (ii) immersion in a 15% HF solution and (iii) illumination for 1 min17,18,19. Without these steps, the bulk lifetime cannot be measured with any certainty.
As the measurement technique is conducted at RT, the surface passivation quality is highly susceptible to surface contamination (metals, organic...

High lifetime (&#62;1 msec) monocrystalline silicon is becoming ever more important for high efficiency solar cells. Understanding the recombination characteristics of embedded impurities has been, and remains an important topic. One of the most widely used techniques to examine the recombination activity of grown-in defects is by a photoconductance method1. By this technique it is often difficult to completely separate surface from bulk recombination, thus making it difficult to examine the recombination characteristics of grown-in defects. Fortunately there exist several dielectric films which can achieve very low effective surface recombination velocities (Seff) of &#60; 5 cm/sec, and thus effectively inhibit surface recombination. These are, silicon nitride (SiNx:H)2, aluminum oxide (Al2O3)3 and amorphous silicon (a-Si:H)4. The deposition and annealing temperatures (~400 &#176;C) of these dielectric films are considered to be low enough not to permanently deactivate the recombination activity of the grown-in defects. Examples of this are the iron-boron5 and boron oxygen6 defects. However, recently it was found that vacancy-oxygen and vacancy-phosphorus defects in n-type Czochralski (Cz) silicon can be completely deactivated at temperatures of 250-350 &#176;C7,8. Similarly a defect in float-zone (FZ) p-type silicon was found to deactivate at ~250 &#176;C9. Therefore, conventional passivation techniques such as plasma enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) may not be suitable for inhibiting surface recombination to examine grown-in bulk defects. Furthermore, SiNx:H and a-Si:H films have been shown to deactivate bulk silicon defects through hydrogenation10,11. Therefore to examine the recombination activity of grown-in defects, a RT surface passivation technique would be ideal. Wet chemical surface passivation fulfils this requirement.
In the 1990s Horanyi et al. demonstrated that immersion of silicon wafers in iodine-ethanol (I-E) solutions provides a means to passivate silicon wafers, achieving Seff &#60; 10 cm/sec12. In 2007 Meier et al. showed that iodine-methanol (I-M) solutions can reduce the surface recombination to 7 cm/sec13, while in 2009 Chhabra et al. demonstrated that Seff of 5 cm/sec can be attained by immersing silicon wafers in quinhydrone-methanol (Q-M) solutions14,15. Despite the excellent surface passivation achieved by I-E, I-M and Q-M solutions, they do not provide adequate surface passivation (Seff &#60;5 cm/sec) to measure the bulk lifetime of high purity silicon wafers.
Another means to achieve a high level of surface passivation is by immersing silicon wafers in HF acid. The notion of using HF to passivate silicon wafers was first introduced by Yablonavitch et al. in 1986, who demonstrated a record low Seff of 0.25&#177;0.5 cm/sec16. Although excellent surface passivation was attained on high resistivity wafers, we have found the technique to be non-repeatable, thus adding a large uncertainty to the lifetime measurement. Therefore to limit the uncertainty by consistently achieving a very low Seff (~1 cm/sec), we have developed a new HF passivation technique that incorporates three critical steps, (i) chemically cleaning and etching of silicon wafers, (ii) immersion in a 15% HF solution and (iii) illumination for 1 min17,18. This procedure is both simple and time efficient in comparison to the traditional PECVD and ALD deposition techniques listed above.

<table><tbody><tr><td>Hydrofluoric acid (48%)</td><td>Merck Millipore,&amp;nbsp; &amp;nbsp;http://www.merckmillipore.com/AU/en/product/Hydrofluoric-acid-48%25,MDA_CHEM-100334</td><td>1003340500</td><td>Harmful and toxic. Any supplier could be used provided the chemical is Analytical Reagent (AR) grade.</td></tr><tr><td>Hydrochloric acid 32%, AR</td><td>ACI Labscan, http://www.rcilabscan.com/modules/productview.php?product_id=1985</td><td>107209</td><td>Harmful and toxic. Any supplier could be used provided the chemical is Analytical Reagent (AR) grade.</td></tr><tr><td>Ammonia (30%) Solution AR</td><td>Chem-supply, https://www.chemsupply.com.au/aa005-500m</td><td>AA005</td><td>Harmful and toxic. Any supplier could be used provided the chemical is Analytical Reagent (AR) grade.</td></tr><tr><td>Hydrogen Peroxide (30%)</td><td>Merck Millipore, http://www.merckmillipore.com/AU/en/product/Hydrogen-peroxide-30%25,MDA_CHEM-107209</td><td>1072092500</td><td>Harmful and toxic. Any supplier could be used provided the chemical is Analytical Reagent (AR) grade.</td></tr><tr><td>Tetramethylammonium hydroxide (25% in H&lt;sub&gt;2&lt;/sub&gt;O)</td><td>J.T Baker, https://us.vwr.com/store/catalog/product.jsp?product_id=4562992</td><td>5879-03</td><td>Harmful and toxic. Any supplier could be used provided the chemical is Analytical Reagent (AR) grade.</td></tr><tr><td>640 ml round plastic container</td><td>Sistema, http://sistemaplastics.com/products/klip-it-round/640ml-round</td><td></td><td>This is a good container for storing the 15% HF solution in.</td></tr><tr><td>WCT-120 lifetime tester</td><td>Sinton Instruments, http://www.sintoninstruments.com/Sinton-Instruments-WCT-120.html</td><td></td><td></td></tr><tr><td>Dell workstation with Microsoft Office Pro, Data acquisition card and software including Sinton Software under existing license.</td><td>Sinton Instruments, http://www.sintoninstruments.com</td><td></td><td></td></tr><tr><td>Halogen optical lamp, ELH 300 W, 120 V</td><td>OSRAM Sylvania, http://www.sylvania.com/en-us/products/halogen/Pages/default.aspx</td><td>54776</td><td>Any equivalent lamp could be used.</td></tr><tr><td>Voltage power source</td><td>Home made power supply</td><td></td><td>Any power supply could be used provided it can produce up to 90 Volts and 1-5 Amps.</td></tr><tr><td>Conductivity meter</td><td>WTW, http://www.wtw.de/uploads/media/US_L_07_Cond_038_049_I_02.pdf</td><td>LF330</td><td></td></tr></tbody></table>

light enhanced hydrofluoric acid passivation: a sensitive technique for detecting bulk silicon defects

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when immersing the wafers in hydrofluoric acid (HF) is presented. By this procedure three critical steps are required to attain the bulk lifetime. Firstly, prior to immersing silicon wafers into HF, they are chemically cleaned and subsequently etched in 25% tetramethylammonium hydroxide. Secondly, the chemically treated wafers are then placed into a large plastic container filled with a mixture of HF and hydrochloric acid, and then centered over an inductive coil for photoconductance (PC) measurements. Thirdly, to inhibit surface recombination and measure the bulk lifetime, the wafers are illuminated at 0.2 suns for 1 min&#160;using a halogen lamp, the illumination is switched off, and a PC measurement is immediately taken. By this procedure, the characteristics of bulk silicon defects can be accurately determined. Furthermore, it is anticipated that a sensitive RT surface passivation technique will be imperative for examining bulk silicon defects when their concentration is low (&#60;1012 cm-3).

Figure 1a shows a schematic and Figure 1b shows a photograph of the experimental setup. When a silicon wafer is immersed into the HF solution, subsequently placed onto the lifetime tester stage and a measurement is performed (before illumination), a lifetime curve which is limited by surface recombination will result, as shown by the blue triangles in Figure 2. However, when the sample is illuminated for 1 min&#160;(while immersed in HF), as shown in Figure 1</st...

Watch this Scientific Journal Video about Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects at JoVE.com

Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

A RT liquid surface passivation technique to investigate the recombination activity of bulk silicon defects is described. For the technique to be successful, three critical steps are required: (i) chemical cleaning and etching of silicon, (ii) immersion of silicon in 15% hydrofluoric acid and (iii) illumination for 1 min.

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when ...

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9.2K Views.  Australian National University. A RT liquid surface passivation technique to investigate the recombination activity of bulk silicon defects is described. For the technique to be successful, three critical steps are required: (i) chemical cleaning and etching of silicon, (ii) immersion of silicon in 15% hydrofluoric acid and (iii) illumination for 1 min.

Video: Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Utilization of Microscale Silicon Cantilevers to Assess Cellular Contractile Function In Vitro

The development of more predictive and biologically relevant in vitro assays is predicated on the advancement of versatile cell culture systems which facilitate the functional assessment of the seeded cells. To that end, microscale cantilever technology offers a platform with which to measure the contractile functionality of a range of cell types, including skeletal, cardiac, and smooth muscle cells, through assessment of contraction induced substrate bending. Application of multiplexed cantilever arrays provides the means to develop moderate to high-throughput protocols for assessing drug efficacy and toxicity, disease phenotype and progression, as well as neuromuscular and other cell-cell interactions. This manuscript provides the details for fabricating reliable cantilever arrays for this purpose, and the methods required to successfully culture cells on these surfaces. Further description is provided on the steps necessary to perform functional analysis of contractile cell types maintained on such arrays using a novel laser and photo-detector system. The representative data provided highlights the precision and reproducible nature of the analysis of contractile function possible using this system, as well as the wide range of studies to which such technology can be applied. Successful widespread adoption of this system could provide investigators with the means to perform rapid, low cost functional studies in vitro, leading to more accurate predictions of tissue performance, disease development and response to novel therapeutic treatment.

Utilization of Microscale Silicon Cantilevers to Assess Cellular Contractile Function In Vitro

This protocol describes the use of microscale silicon cantilevers as pliable culture surfaces for measuring the contractility of muscle cells in vitro. Cellular contraction causes cantilever bending, which can be measured, recorded, and converted into readouts of force, providing a non-invasive and scalable system for measuring contractile function in vitro.

The development of more predictive and biologically relevant in vitro assays is predicated on the advancement of versatile cell culture systems which ...

Bioengineering

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, ...

Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery

With the advent of gene therapy, the development of an effective in vivo nucleotide-payload delivery system has become of parallel import. Fusogenic porous silicon nanoparticles (F-pSiNPs) have recently demonstrated high in vivo gene silencing efficacy due to its high oligonucleotide loading capacity and unique cellular uptake pathway that avoids endocytosis. The synthesis of F-pSiNPs is a multi-step process that includes: (1) loading and sealing of oligonucleotide payloads in the silicon pores; (2) simultaneous coating and sizing of fusogenic lipids around the porous silicon cores; and (3) conjugation of targeting peptides and washing to remove excess oligonucleotide, silicon debris, and peptide. The particle&#8217;s size uniformity is characterized by dynamic light scattering, and its core-shell structure may be verified by transmission electron microscopy. The fusogenic uptake is validated by loading a lipophilic dye, 1,1&#39;-dioctadecyl-3,3,3&#39;,3&#39;-tetramethylindocarbocyanine perchlorate (DiI), into the fusogenic lipid bilayer and treating it to cells in vitro to observe for plasma membrane staining versus endocytic localizations. The targeting and in vivo gene silencing efficacies were previously quantified in a mouse model of Staphylococcus aureus pneumonia, in which the targeting peptide is expected to help the F-pSiNPs to home to the site of infection. Beyond its application in S. aureus infection, the F-pSiNP system may be used to deliver any oligonucleotide for gene therapy of a wide range of diseases, including viral infections, cancer, and autoimmune diseases.

We demonstrate the synthesis of fusogenic porous silicon nanoparticles for effective in vitro and in vivo oligonucleotide delivery. Porous silicon nanoparticles are loaded with siRNA to form the core, which is coated by fusogenic lipids through extrusion to form the shell. Targeting moiety functionalization and particle characterization are included.

With the advent of gene therapy, the development of an effective in vivo nucleotide-payload delivery system has become of parallel import. Fusogenic ...

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

A protocol for metal-assisted chemical imprinting of 3D microscale features with sub-20 nm shape accuracy into solid and porous silicon wafers is presented.

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is ...

Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

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Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Utilization of Microscale Silicon Cantilevers to Assess Cellular Contractile Function In Vitro

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery

Rendering SiO₂/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers