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 ...

<ol>
	<li>Sinton, R. A., Cuevas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contactless+determination+of+current-voltage+characteristics+and+minority-carrier+lifetimes+in+semiconductors+from+quasi-steady-state+photoconductance+data.">Contactless determination of current-voltage characteristics and minority-carrier lifetimes in semiconductors from quasi-steady-state photoconductance data.</a> Appl. Phys. Lett. 69 (17), 2510-2512 (1996).</li><li>Wan, Y., McIntosh, K. R., Thomson, A. F., Cuevas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+surface+recombination+velocity+by+low-absorption+silicon+nitride+on+c-Si.">Low surface recombination velocity by low-absorption silicon nitride on c-Si.</a> IEEE J. Photovoltaics. 3 (1), 554-559 (2013).</li><li>Hoex, B., Schmidt, J., Pohl, P., van de Sanden, M. C. M., Kessels, W. M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silicon+surface+passivation+by+atomic+layer+deposited+Al2O3.">Silicon surface passivation by atomic layer deposited Al2O3.</a> J. App. Phys. 104 (4), 044903 (2008).</li><li>Dauwe, S., Schmidt, J., Hezel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Very+low+surface+recombination+velocities+on+p.-+and+n.-type+silicon+wafers+passivated+with+hydrogenated+amorphous+silicon+films.">Very low surface recombination velocities on p.- and n.-type silicon wafers passivated with hydrogenated amorphous silicon films.</a> , 1246-1249 (2012).</li><li>Macdonald, D., Cuevas, A., Wong-Leung, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capture+cross-sections+of+the+acceptor+level+of+iron-boron+pairs+in+p-type+silicon+by+injection-level+dependent+lifetime+measurements.">Capture cross-sections of the acceptor level of iron-boron pairs in p-type silicon by injection-level dependent lifetime measurements.</a> J. App. Phys. 89 (12), 7932-7339 (2001).</li><li>Schmidt, J., Bothe, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+transformation+of+the+metastable+boron-+and+oxygen-related+defect+center+in+crystalline+silicon.">Structure and transformation of the metastable boron- and oxygen-related defect center in crystalline silicon.</a> Phys. Rev. B. 69 (2), 024107 (2004).</li><li>Rougieux, F., Grant, N., Murphy, J., Macdonald, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=D.+Influence+of+Annealing+and+Bulk+Hydrogenation+on+Lifetime+Limiting+Defects+in+Nitrogen-Doped+Floating+Zone+Silicon.">D. Influence of Annealing and Bulk Hydrogenation on Lifetime Limiting Defects in Nitrogen-Doped Floating Zone Silicon.</a> IEEE J. Photovoltaics. 5 (2), 495-498 (2014).</li><li>Zheng, P., Rougieux, F., Grant, N., Macdonald, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+vacancy-related+Recombination+Active+Defects+in+as-grown+n-type+Czochralski+Silicon.">Evidence for vacancy-related Recombination Active Defects in as-grown n-type Czochralski Silicon.</a> IEEE J. Photovoltaics. 5 (1), 183-188 (2014).</li><li>Grant, N. E., Rougieux, F. E., Macdonald, D., Bullock, J., Wan, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Grown-in+point+defects+limiting+the+bulk+lifetime+of+p.-type+float-zone+silicon+wafers.">Grown-in point defects limiting the bulk lifetime of p.-type float-zone silicon wafers.</a> J. App. Phys. 117 (5), 055711 (2015).</li><li>Hallam, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+passivation+of+B-O+defects+in+Czochralski+silicon.">Hydrogen passivation of B-O defects in Czochralski silicon.</a> Energy Procedia. 38, 561-570 (2013).</li><li>Hallam, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advanced+bulk+defect+passivation+for+silicon+solar+cells.">Advanced bulk defect passivation for silicon solar cells.</a> IEEE J. Photovoltaics. 4 (1), 88-95 (2014).</li><li>Hornyi, T. S., Pavelka, T., Ttt, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+bulk+lifetime+measurement+on+silicon+with+a+chemically+passivated+surface.">In situ bulk lifetime measurement on silicon with a chemically passivated surface.</a> App. Surf. Sci. 63 (1-4), 306-311 (1993).</li><li>Meier, D. L., Page, M. R., Iwaniczko, E., Xu, Y., Wang, Q., Branz, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+surface+recombination+velocities+for+thermal+oxide+and+amorphous+silicon+on+float+zone+silicon.">Determination of surface recombination velocities for thermal oxide and amorphous silicon on float zone silicon.</a> , (2007).</li><li>Chhabra, B., Bowden, S., Opila, R. L., Honsberg, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+effective+minority+carrier+lifetime+on+silicon+substrates+using+quinhydrone-methanol+passivation.">High effective minority carrier lifetime on silicon substrates using quinhydrone-methanol passivation.</a> App. Phys. Lett. 96 (6), 063502 (2010).</li><li>Chhabra, B., Weiland, C., Opila, R. L., Honsberg, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+characterization+of+quinhydrone-methanol+and+iodine-methanol+passivated+silicon+substrates+using+X-ray+photoelectron+spectroscopy.">Surface characterization of quinhydrone-methanol and iodine-methanol passivated silicon substrates using X-ray photoelectron spectroscopy.</a> Phys. Stat. Sol. (a). 208 (1), 86-90 (2011).</li><li>Yablonovitch, E., Allara, D. L., Chang, C. C., Gmitter, T., Bright, T. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unusually+low+surface+recombination+velocity+on+silicon+and+germanium+surfaces.">Unusually low surface recombination velocity on silicon and germanium surfaces.</a> Phys. Rev. Lett. 57 (2), 249-252 (1986).</li><li>Grant, N. E., McIntosh, K. R., Tan, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+the+bulk+lifetime+of+silicon+wafers+by+immersion+in+hydrofluoric+acid+and+illumination.">Evaluation of the bulk lifetime of silicon wafers by immersion in hydrofluoric acid and illumination.</a> J. Solid State Sci. Technol. 1 (2), P55-P61 (2012).</li><li>Grant, N. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light+enhanced+hydrofluoric+acid+passivation+for+evaluating+silicon+bulk+lifetimes.">Light enhanced hydrofluoric acid passivation for evaluating silicon bulk lifetimes.</a> 28.th. European Photovoltaic Solar Energy Conference. , 883-887 (2013).</li><li>Grant, N. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Surface passivation and characterization of crystalline silicon by wet chemical treatments. , (2012).</li><li>Kern, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+evolution+of+silicon+wafer+cleaning+technology.">The evolution of silicon wafer cleaning technology.</a> J. Electrochem. Soc. 137 (6), 1887-1892 (1990).</li><li>Angermann, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wet-chemical+passivation+of+atomically+flat+and+structured+silicon+substrates+for+solar+cell+application.">Wet-chemical passivation of atomically flat and structured silicon substrates for solar cell application.</a> App. Surf. Sci. 254 (12), 3615-3625 (2008).</li><li>Angermann, H., Henrion, W., Rseler, A., Rebien, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wet-chemical+passivation+of+Si(111)-+and+Si(100)-substrates.">Wet-chemical passivation of Si(111)- and Si(100)-substrates.</a> Mat. Sci. Eng. 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 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,&#160; &#160;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 H2O)</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></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>640 mL round plastic container</td>
			<td>Sistema, http://sistemaplastics.com/products/klip-it-round/640ml-round</td>
			<td>N/A</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>N/A</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>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Halogen optical lamp, ELH 300W, 120V</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>N/A</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 ...

The overall goal of this procedure is to use a room temperature surface passivation method in order to inhibit surface recombination, such that bulk silicon defects can be accurately characterized. This method can help us understand what defects will limit the lifetime of high-purity silicon wafers, which are required for very high efficiency solar cells. The main advantage of this technique is that it can be performed at room temperature, meaning the recombination activity of bulk silicon defects will not change during the measurement.The implications of this technique extend towards measuring the recombination activity of bulk silicon defects that exist in low concentrations which otherwise would be very difficult to measure by other techniques. Generally, individuals new to this method will struggle because a requirement for high purity DI water and chemical cleaning procedures is not initially understood, thus it's imperative the procedure is followed step-by-step. Solution preparation, including vital notes on hydrofluoric acid preparation, as well as general setup and equipment calibration instructions are all provided in the text protocol.With those objectives achieved, proceed with cleaning the silicon wafers using chemical treatments. Begin with loading the samples into a quartz cradle. Then, transfer the cradle into a hydrofluoric acid bath meant for general use.After about 10 seconds, the samples will be hydrophobic. Remove them from the bath, and rinse them off by passing them through three deionized water baths. Next, in a fume hood, slowly immerse the cradle in the SC1 solution, which has been maintained at a temperature of 75 degrees Celsius.Let the treatment go for 10 minutes. And meanwhile, fill three chemically cleaned two-liter beakers with deionized water. After the SC1 treatment, rinse the samples off by passing them through the three water baths.Next, dip the samples into a dedicated hydrofluoric acid bath for about 10 seconds. Then rinse the samples off using three fresh deionized water baths. Now, move the samples to the fume hood where the SC2 solution was prepared, and heated to a stable 75 degrees Celsius.Immerse the samples in the SC2 solution for 10 minutes. After the SC2 treatment, rinse off the samples using the three deionized water baths. If needed, let the samples stay in the last water bath overnight.After the rinse, dip the samples in another dedicated hydrofluoric acid bath for 10 seconds. Again, rinse the samples by passing them through three fresh deionized water baths. Now, take the samples to the fume hood where the TMAH solution is stably heated to about 85 degrees Celsius, and slowly immerse the samples into the TMAH solution to etch the wafers.Let them react for five minutes to remove about five microns of silicon. Next, rinse off the tacky TMAH solution using at least three deionized water baths. The same rinse beakers can be re-employed here.Once rinsed, proceed with taking measurements within two hours. This process is conducted under a fume hood. In preparation, fill two two-liter plastic beakers with deionized water.Also prepare some plastic tweezers in the hood to handle the samples. On the computer, open the Lifetime Tester file, which contains the correct calibration coefficients for the hydrofluoric acid measurement setup. Select transient from the mode options, and enter a description of the wafer's variables.Now, carefully secure the lid on the hydrofluoric acid container, and move it onto the Lifetime Tester stage, centered over the blue circle, which represents the position of the inductive coil. Let the solution settle for about a minute before proceeding. Then, on the computer, click the Zero Instrument button to measure the voltage of the solution.After taking the measurement, carefully return the hydrofluoric acid container to the fume hood bench. There, remove the lid, and rinse off any condensation on the lid with DI water from the fume hood's water tap. Now, using tweezers, transfer one wafer into the hydrofluoric acid bath.Lightly press the wafer down to the bottom of the bath. Then, replace the lid and carefully carry the container back to the Lifetime Tester stage. Center the wafer over the inductive coil.Before taking a measurement, make sure the fume hood lights are switched off. Now, switch on the halogen lamp to illuminate the silicon wafer, and keep it on for about a minute. During the illumination period, in the software, click the Measure button.The software will then begin taking data. Fill in the prompt with a file name, and set the Sample Averaging option to 10. After about a minute of illumination, switch the lamp off, and immediately click the Average button on the Taking Data window.The software will perform 10 measurements. Then, click OK.Now, carefully return the container to the fume hood bench, cautiously remove the lid, and carefully remove the wafer. Rinse the tested wafer off in the dedicated rinse beakers, followed by a final rinse using the DI water tap in the fume hood.Then, store the tested wafer, and repeat the process for each silicon wafer to be measured. After the experiment, follow the clean up instructions provided in the text protocol. Following the described protocol, whereby silicon wafers were treated, etched, immersed in hydrofluoric acid, and measured using the photoconductance tool, a lifetime curve, which is limited by surface recombination results, as seen by the blue triangles.When the silicon wafer immersed in the hydrofluoric acid bath is illuminated by a halogen lamp for one minute, and then a photoconductance measurement is performed directly after illumination, a significant increase in the lifetime will occur, as seen by the red circles. This increase in lifetime is due to a reduction in surface recombination. The surface passivation began to degrade within seconds of turning off the halogen lamp.The blue circles show the consequence of waiting for one minute post-illumination. After watching this video, you should have a good understanding of how to measure the bulk lifetime of silicon wafers using a hydrofluoric acid bath, specifically how to treat the wafers before the measurement, how to activate the surface passivation by using a light source, and how to measure the lifetime immediately after illumination. Once mastered, this technique can be performed in two to three minutes per wafer.However, it will take an hour to prepare the wafers for the measurement, and thus it's time efficient to measure batches of wafers. While attempting this procedure, it's important to remember that the silicon wafers must be kept clean in order to consistently achieve very good surface passivation, and thus be able to detect and characterize bulk defects. Don't forget that working with hydrofluoric acid can be extremely hazardous, and precautions such as wearing personal protection equipment, and following procedure step-by-step should always be taken while performing this technique.

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Research

JoVE Journal

Engineering

9.2K ビュー.  Australian National University. The overall goal of this procedure is to use a room temperature surface passivation method in order to inhibit surface recombination, such that bulk silicon defects can be accurately characterized. This method can help us understand what defects will limit the lifetime of high-purity silicon wafers, which are required for very high efficiency solar cells. The main advantage of this technique is that it can be performed at room temperature, meaning the recombination activity of bulk silicon de...