Name: light enhanced hydrofluoric acid passivation: a sensitive technique for detecting bulk silicon defects
Uploaded: 2016-01-04T14:00:01
Description: Watch this Scientific Journal Video about Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects at JoVE.com

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. 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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 ...

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