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SG194085A1 - Low temperature deposition of silicon oxide films - Google Patents

Low temperature deposition of silicon oxide films Download PDF

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Publication number
SG194085A1
SG194085A1 SG2013074265A SG2013074265A SG194085A1 SG 194085 A1 SG194085 A1 SG 194085A1 SG 2013074265 A SG2013074265 A SG 2013074265A SG 2013074265 A SG2013074265 A SG 2013074265A SG 194085 A1 SG194085 A1 SG 194085A1
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SG
Singapore
Prior art keywords
wafer
silicon oxide
oxide film
deposition
silicon
Prior art date
Application number
SG2013074265A
Inventor
Curtis Dove
Baljit Singh
Eduard Gil Paran Tesnado
Mehdi Balooch
Original Assignee
Asia Union Electronic Chemical Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asia Union Electronic Chemical Corp filed Critical Asia Union Electronic Chemical Corp
Publication of SG194085A1 publication Critical patent/SG194085A1/en

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104Forming layers
    • H01L21/02107Forming insulating materials on a substrate
    • H01L21/02225Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/02227Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process
    • H01L21/0223Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate
    • H01L21/02233Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer
    • H01L21/02236Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer group IV semiconductor
    • H01L21/02238Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer group IV semiconductor silicon in uncombined form, i.e. pure silicon
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10FINORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F71/00Manufacture or treatment of devices covered by this subclass
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10FINORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00Constructional details of devices covered by this subclass
    • H10F77/30Coatings
    • H10F77/306Coatings for devices having potential barriers
    • H10F77/311Coatings for devices having potential barriers for photovoltaic cells
    • H10F77/315Coatings for devices having potential barriers for photovoltaic cells the coatings being antireflective or having enhancing optical properties
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Photovoltaic Devices (AREA)
  • Formation Of Insulating Films (AREA)
  • Surface Treatment Of Glass (AREA)
  • Paints Or Removers (AREA)

Abstract

Deposition of silicon oxide films at low temperature by using wet chemistry techniques. The wet chemistry solution may be a mixture of sodium hypochloride (NaOCl), tetra methyl ammonium hydroxide (TMAH) and hydrated silicate, such as silicic acid. The resulting silicon oxide films provide excellent anti-reflective coatings for solar cells and the like.

Description

LOW TEMPERATURE DEPOSITION OF SILICON OXIDE FIL.MS
FIELD OF THE INVENTION
(001) The present invention relates to methods of depositing silicon oxide films at low temperature using wet chemistry techniques.
BACKGROUND OF THE INVENTION
(002) Silicon oxide films are deposited onto silicon surfaces for use in many applications, including as masking layers for semiconductor manufacturing and as anti- reflective coatings for solar cells. There are a number of chemical vapor deposition (CVD) techniques that have been used, particularly in the semiconductor industry, to produce thin oxide films. In general, CVD processes form the oxide film by exposing the substrate to one or more volatile precursors that react with or decompose onto the substrate surface to produce the desired oxide film. The CVD processes in use differ in how the chemical reactions are initiated (e.g. activation process) and by the process conditions employed. For example, atmospheric pressure CVD (APCVD), ultrahigh vacuum CVD (UHCVD), plasma enhanced CVD (PECVD) and atomic layer CVD (ALCVD) are some of the CVD techniques used to deposit oxide films. (003) Silicon dioxide (Si0,) may be deposited using a CVD technique, by using any one of several source gas precursor combinations. One such combination uses silane and oxygen according to the following reaction formula.
SiH, (gas) + Op => SiO; (solid) + 2H,
A second combination uses oxygen dichlorosilane (SiCloH;) and nitrous oxide (N>O) according to the following reaction formula.
SiCl,H; + 2N,O => SiO; + 2N, + 2HCI
Another possible precursor source gas 1s tetraethylorthosilicate (TEOS: Si(OC,Hs)s) according to the following reaction formula.
Si(OC;H;s)4) = SiO, + byproducts (004) The choice of source gas depends on the thermal stability of the substrate. In particular, silane deposits between 300°C and 500°C, dichlorosilane deposits at about 900°C and TEOS deposits between 650°C and 750°C. Deposition times generally last for about fifteen minutes, with the full heating and cooling cycle lasting about forty five minutes. (005) The known oxide deposition processes have several disadvantages. These processes require high temperatures and vacuum processing before introduction of the precursor gases, particularly those that are hazardous. Further, the deposition equipment is expensive, has a relatively low wafer throughput, requires frequent cleaning and maintenance and demands highly trained operators. As a result, deposition of silicon oxide films demands substantial capital and operating expense, which increases overall device cost, for example the cost for creating anti-reflective coatings in the photovoltaic industry. Also, backside contact printing, with aluminum or aluminum/gold, is normally performed after the deposition of the oxide, and therefore requires higher temperatures for diffusion of the contacts and reduction in proper contact which could interfere with the overall efficiency of the device. (006) There remains a need in the art for improvements to methods of depositing oxide films, such as silicon oxide films.
SUMMARY OF THE INVENTION
(007) The present invention provides low temperature methods of depositing silicon oxide films using wet chemistry.
BRIEF DESCRIPTION OF THE DRAWINGS
(008) Figure 1 is a graph showing the reflectance of p-type textured silicon wafers following processing according to the present invention. (009) Figure 2 is a graph showing the reflectance textured silicon wafers doped with phosphor following processing according to the present invention. (010) Figure 3 is a graph showing the reflectance of textured multi-crystalline silicon wafers following processing according to the present invention
DETAILED DESCRIPTION OF THE INVENTION
(011) The present provides methods of depositing silicon oxide films at low temperature using wet chemistry techniques. In accordance with the present invention, a wet chemistry mixture of sodium hypo chloride (NaOCl), tetra methyl ammonium hydroxide (TMAH) and hydrated silicate (such as silicic acid) is used for the low temperature oxide deposition. (012) NaOCl is a strong oxidizing agent that ionizes in water to give hypochlorous acid (HOCI) and hypochlorite ions (OCI). If applied to a silicon substrate, the silicon etching rate is low because of the relative lack of availability of OH ions. However, the silicon does react with the hypochlorite ions to form Si10,. The process of forming a SiO; film using a NaOCl solution alone is a slow process and the film produced is of poor quality.
Further this film does not adhere strongly to the silicon substrate. A summary of the reaction sequence is set forth below.
NaOCl <-> Na’ + OCI (1) 20CI' + HO <-> HOCI + OCI’ + OH 2)
Si + 20CH €—> SiO, + 2CI (3)
Diluted TMAH (and other hydroxide solutions such as KOH and NaOH) exhibit strong silicon etch rates. As an initial step, the TMAH is reduced to form hydroxyl ions. This is followed by reaction of the hydroxyl ions with silicon atoms at the substrate surface to form oxidized silicates, such as Si (OH),”" and four electrons are injected from each silicon atom into the conduction band. Therefore, the overall reaction must balance the ions and the electrons. Simultaneously, water is reduced to provide more hydroxyl tons which in turn are bonded to the silicates formed in the second step. This reaction produces soluble silicic acid, with hydrogen gas as a by-product. Using the TMAH solution alone, unlike NaOCl, would result in etching of the silicon substrate rather than deposition of an oxide film. This reaction sequence is set forth below. (CH3)4NOH €~> (CH3lN" + OH 4)
Si + 20H €-> Si(OH)™ + 4e (5)
Si(OH),> + de + 4H,0 <-> Si(OH)s* + 2H, (6) (013) By combination of the above solutions, the deposition of an oxide can be accomplished at low temperatures. In particular, By combining dilute TMAH (or another hydroxide solution) having the capability to etch the silicon substrate, with NaOCl] that is capable of forming a oxide, and silicate that provides an additional source of silicon for oxidation and deposition, in appropriate amounts, according to the present invention and applying such mixture to a silicon substrate, simultaneous etching of the silicon substrate and deposition of oxide can be accomplished at temperatures between 60°C and 90°C.
The oxide coatings produced according to the present invention have the proper texture and properties to serve as anti-reflective coatings for solar cells. The thickness of the oxide coating can be adjusted by changing temperature or chemical exposure times to obtain optimal coatings that have low reflectance of visible light. This results in the ability of devices with these coatings to capture the appropriate solar spectrum with increased efficiency of the solar cell. (014) The present invention will be described in greater detail with reference to the following examples. Initially, a single crystal Si (100) wafer may be textured using either
KOH+IPA, TMAH+IPA or acid solutions such as nitric acid mixed with hydrofluoric acid. The native oxide of the wafer is first removed in a 4% HF solution for several minutes. The wafer is then exposed in accordance with the present invention to a solution of NaOCl, TMAH and extra dissolved Si or added silicic acid. This exposure results in a coating of hydride silica (Polymerized) which when dry heated forms silica having an index of refraction close to SiO;; i.e. about 1.45. (015) Figure 1 shows the reflectance properties of p-type silicon wafers as a function of exposure at 75°C to the solution mixture according to the present invention described above. As can be seen, reflectance is significantly reduced with as little a five minutes exposure, while even better results are achieved with thirteen minutes of exposure. In simulations, the average oxide build-up is 63 nm for five minutes exposure, 93 nm for eight minutes exposure and 120 nm for thirteen minutes exposure. (016) Wafers that were phosphor-diffused using POCI; were treated according to the present invention using the solution mixture noted above, i.e. a solution of NaOCl,
TMAH and extra dissolved Si or added silicic acid. The results are shown in figure 2. In particular, while the high doping concentration slowed the deposition rate, the significant reduction in reflectance was still achieved. The rate of deposition on highly phosphor doped substrates was reduced by a factor of up to two compared to deposition rates on low boron doped (p-type) substrates. (017) In a similar manner multi-crystalline (c-Si) silicon surfaces were treated according to the present invention with a solution of NaOCl, TMAH and extra dissolved
Si or added silicic acid. Figure 3 compares the reflectance properties of the me-Si surface prior to treatment and after exposure for ten minutes at 80°C. The reflectance properties shown in Figure 3 are averaged over a few grains orientation. However, it appears the value does not change appreciably with the location on the wafer. These results suggest that the deposition rate of oxide coating is weakly dependent on the crystalographic orientation of Si wafer exposed. Therefore, it is believed that the coating method of the present invention can be applied to mc-Si as well a single crystal silicon substrates. (018) The present invention of depositing silicon oxide coatings by exposure to wet chemical solutions, has several advantages of the CVD deposition techniques used in the prior art. In particular, the present invention can be carried out at low temperatures and provides faster deposition rates. In addition, the pressent invenition is a simpler process and requires less expensive equipment and fewer utility costs. Moreover, the present invention does not requires any hazardeous gaseous precursur chemicals. The results of the using the present invention are lower reflectance in the high energy wavelength band of natural light and overall reduced light reflectance when integrated across the light spectrum of 400nm to 1000 nm. The present invention is particularly advantageous in solar cell application, where the deposition of oxide anti reflective coating by wet chemistry can be carried out before as well as after contact print film deposition. The solutions used in the present inventino do not significantly etch either the aluminum or gold used for contacts. This results in better contact between the Al or AI/Ag contacts and the dopped silicon and therefore improves the electrical properties of the solar cell.
(019) Tt will be understood that the embodiments described herein are merely exemplary and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the present invention.
All such variations and modifications are intended to be included within the scope of the invention as described above.
Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.

Claims (17)

CLAIMS What is claimed 1s:
1. A method of depositing a silicon oxide film comprising: exposing a silicon wafer to a wet chemical solution of sodium hypochloride, tetramethylammonium hydroxide and a hydrated silicate to form a layer of hydride silica on the surface of the wafer; and dry heating to form a silicon oxide film.
2. The method of claim] wherein the hydrated silicate is silicic acid.
3. The method of claim 1 wherein the deposition is accomplished at temperatures between 60°C and 90°C.
4. The method of claim 1 wherein in the wafer is a solar cell wafer and the silicon oxide film is an anti-reflective coating.
5. The method of claim 1 further comprising adjusting the thickness of the silicon oxide film by changing temperature or exposure time.
6. The method of claim 1 wherein the wafer is a single crystal Si (100) wafer.
7. The method of claim 1 wherein the wafer is a multi-crystalline wafer.
g. The method of claim 1 wherein the wafer is a phosphor doped wafer.
9. The method of claim 1 further comprising exposing the wafer to the wet chemical solution contact print film deposition is performed on the wafer.
10. A silicon oxide film deposited by the method comprising exposing a silicon wafer to a wet chemical solution of sodium hypochloride, tetramethylammonium hydroxide and a hydrated silicate to form a layer of hydride silica on the surface of the wafer; and dry heating to form the silicon oxide film.
11. The silicon oxide film of claimlo wherein the hydrated silicate is silicic acid.
12. The silicon oxide film of claim 10 wherein the wafer is a solar cell wafer and the silicon oxide film is an anti-reflective coating.
13. The silicon oxide film of claim 10 having a thickness of 63 nm to 120 nm.
14. The silicon oxide film of claim 10 wherein the wafer is a single crystal Si (100) wafer.
15. The silicon oxide film of claim 10 wherein the wafer is a multi-crystaliine wafer.
16. The silicon oxide film of claim 10 wherein the wafer is a phosphor doped wafer.
17. The silicon oxide film of claim 10 wherein the oxide film is deposited after contact print film deposition is performed on the wafer.
SG2013074265A 2011-04-12 2012-03-29 Low temperature deposition of silicon oxide films SG194085A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201161474415P 2011-04-12 2011-04-12
PCT/US2012/031122 WO2012141908A1 (en) 2011-04-12 2012-03-29 Low temperature deposition of silicon oxide films

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SG194085A1 true SG194085A1 (en) 2013-11-29

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EP (1) EP2697826A4 (en)
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TW (1) TW201307610A (en)
WO (1) WO2012141908A1 (en)

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Publication number Priority date Publication date Assignee Title
DE102013004611B4 (en) * 2013-03-14 2014-12-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Coating, process for its preparation and its use

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JP2721632B2 (en) * 1992-02-25 1998-03-04 松下電工株式会社 Processing method of copper circuit of circuit board
US5616233A (en) * 1996-05-01 1997-04-01 National Science Council Method for making a fluorinated silicon dioxide layer on silicon substrate by anodic oxidation at room temperature
US20020106865A1 (en) * 2001-02-05 2002-08-08 Tai-Ju Chen Method of forming shallow trench isolation
EP1293488A1 (en) * 2001-09-12 2003-03-19 Toyo Gosei Kogyo Co., Ltd. Coating solution and method for forming transparent coating film
CN1875325B (en) * 2003-10-29 2011-01-26 马林克罗特贝克公司 Alkaline post plasma etch/ash residue remover and photoresist stripping composition containing metal halide corrosion inhibitor
KR100971658B1 (en) * 2008-01-03 2010-07-22 엘지전자 주식회사 Texturing Methods of Silicon Solar Cells

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EP2697826A4 (en) 2014-10-22
WO2012141908A1 (en) 2012-10-18
WO2012141908A8 (en) 2012-11-22
EP2697826A1 (en) 2014-02-19
TW201307610A (en) 2013-02-16

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