Method for treatment of single-crystalline silicon wafer surface

FIELD: semiconductor engineering; chemical treatment of single-crystalline silicon wafer surfaces chemically resistant to open air and suited to growing epitaxial semiconductor films.

SUBSTANCE: proposed method for treatment of single-crystalline silicon wafer surface positioned on Si(100) or Si(111) plane includes cleaning of mentioned surface followed by passivation with hydrogen atoms. Silicon surface is first cleaned twice by means of boiling trichloroethylene solution for 10-20 minutes involving washing with deionized water and then with ammonium-peroxide aqueous solution of following composition: 5 volumes of H2O, 1 volume of 30% H2O2, 1 volume of 25% NH4OH at 75-82 °C or with salt-peroxide aqueous solution of following composition: 6 volumes of H2O, 1 volume of 30% H2O2, 1 volume of 37% HCl at 75-82 °C, followed by three 5- or 10-minute steps of washing with deionized water; passivation with hydrogen atoms is conducted by treatment first with 5-10 mass percent HF solution and then with aqueous solution of NH4OH and NH4F mixture at pH = 7.6-7.7 for 40-60 s followed by washing with deionized water and drying out under normal conditions.

EFFECT: ability of producing wafers capable of retaining their serviceability for long time in storage and in transit, in open air, without oxidizing their surfaces.

1 cl, 3 dwg

 

The invention relates to semiconductor technology, and particularly to a method of chemical treatment of the surface of monocrystalline silicon wafers and can be used in the production of high-quality chemically stable in air of substrates suitable for growing epitaxial semiconductor films and to create semiconductor devices.

One of the significant problems in the technology of silicon wafers with high-purity and high-quality on the structure surface is that the surface layers are oxidized rapidly in air with the formation of oxide layers of silicon, preventing subsequent epitaxial building layers of semiconductors or semiconductor compounds.

Numerous options for fine chemical cleaning (wet chemical cleaning) of the surface of silicon wafers, which are summarized in the monograph:

Handbook of semiconductor wafer cleaning technology (Edited by Wermer Kern) Noyes Publications, New Jersey. USA 1993. 623 R.

Most fully according to the source currently studied the effect of different chemical composition of aqueous solutions containing various amounts of the following components:

- ammonia, hydrogen peroxide and deionized water (NH4OH, H2O2H2O)

- hydrochloric acid, hydrogen peroxide and deionized water (Cl, H2About2N2O),

- solutions of sulfuric (H2SO4) and hydrofluoric (HF) HF acid and other Chemical cleaning of silicon wafers from impurities is characterized by the use of a wide range of solutions, different sequence of stages of purification and varied conditions of the individual stages. From the above monograph also known processing carried out in two stages (steps):

- stage 1 - use standard solution (Standard Clean, abbreviated as SC-1), consisting of the following components: 5 volumes of N2Oh, 1 volume of N2O230%, 1 volume of NH4OH 29%. The process is carried out by heating to 70-80°With subsequent washing of the plates with deionized water. Under this treatment removes organic impurities and desorbers traces of many metals - 2 stage cleaning - use standard solution (Standard Clean, abbreviated as SC-2), consisting of the following components: 6 volumes of N2O, 1 volume of N2About230%, 1 volume of HCl 37% of the Process is carried out by heating to 70-80°With subsequent washing of the plates with deionized water. This removes ions of alkali metals, hydroxides of Al, Fe, Mg and desorbers residual ions of other metals through complexation.

After 2 stages on the surface of the product remains hydrated oxide film. For e the removal or after 1 step, or after 2 stages (preferably after 1 stage) silicon wafer is subjected to additional treatment in the acid, for example a 1%solution of HF (HF:H2O=1:50)for 15 seconds.

From US 6054393, publ. 25.04.2000, H01L 21/306 known various combinations of reagents and sequence of operations of cleaning the surface of silicon wafers using solutions of SC-1, SC-2, and HF and H2O2. The final stage of processing according to well-known solution is drying in the vapor of isopropyl alcohol, providing significant reduction of defects on the surface due to adsorption of water particles.

From US Patent 6514875, publ. 04.02.2003, H01L 21/302 known method for obtaining optically smooth surfaces of silicon wafers based on the methodology of company RCA in combination with etching and 44 wt.% the solution of KOH at 50-90°With subsequent washing in an aqueous solution of acetic acid (20-40 vol.% acid).

The above invention and as many other publications disclose decisions on the development of chemical compositions and conditions fine purification by chemical means, allowing to obtain high-purity, smooth and close to perfect on the structure of surfaces of silicon wafers, which should be immediately after cleaning to go on a technological chain epitaxial produce some or other device the century Otherwise (in the case of storage) surface of a silicon wafer quickly oxidized in the air with the formation of the oxide film of silicon, preventing the buildup of epitaxial layers of semiconductors.

Publications:

1. Handbook of semiconductor wafer cleaning technology (Edited by Werner Kern) Noyes Publications, New Jersey. USA 1993. 623 R.

2. Le Than V. et. al., Fabrication ofSiGe quantum dots on a Si (100) surfaces Phys. Rev. B., 1997,v.56, No. 16, 10505-10509.

3. De Larios J.M. et al., Silicon surfaces cleaning procedures. Appl. Surf. Sci., 1987, v.30, No. 1-4, p.1-30 (Proceedings of the conference on Interfaces).

4. G.S. Higashi et. all., Ideal hydrogen termination of Si (111) surfaces., Appl. Phys. Lett., 1990, v.56, N7, p.656.

5. Jakob P., Y.J. Chabal, Chemical etching of vicinal Si (111): Dependence of the urface structure and the hydrogen termination on the pH of the etching solutions., J. Chem.Phys.,1991, v.95, No. 4, p.2897.

given the following information, which must be set for disclosure of the claimed invention.

1. Disclosed chemical composition and thermal stability of the coatings of the surfaces of Si (100) and Si (111) silicon wafers, mono-, di - and tri - hydrides of silicon, i.e. hydrogen atoms in the processing of wafers aqueous solutions of HF, aqueous buffer solutions on the basis of HF and ammonium fluoride (NH4F).

2. Studies of the influence of pH on the morphology (degree of smoothness and discontinuities) and the chemical composition of the surfaces of Si (100) and Si (111) etching:

in diluted HF (1%, pH 2);

- in mixtures of 50 wt.% aqueous HF solution with 40 wt.% aqueous solution of NH4 F: with different ratio of components:

- in a solution of HF (7:1) with a pH of 4.5-5.0 and the mixture composition: 7 volumes NH4F+1 volume of HF; (of these 1 source s);

- 40 wt.% a solution of NH4F (pH 7.8)(of these 1 source, s Fig and s, Fig).

In the experiments described in the above sources, it was found that increasing the pH of the solution from 2 to 8 accompanied by a significant increase in the rate of etching, chemical composition and morphology of the surfaces of Si (100) and Si (111).

The total output of all research is that:

1) by etching in dilute HF solutions both surfaces of Si (100) and Si (111) become loose (not smooth) and covered with a layer simultaneously mono- (≡Si-H), di (=Si=) and three- (-Si≡) hydrides of silicon;

2) raising the pH to 4.5 to 5.0 when processing wafers with orientation of the Si (100) leads to the coating surface mainly monohydride groups, and the surface morphology remains relatively loose. With limited time (≈1 min) processing the surface of Si (100) in a solution of NH4F (pH 7.8), it becomes nuclear-smooth and covered with dihydrides film, which is completely desorbed in vacuum at ≈400°C;

- when processing the surface of Si (111) in alkaline solutions with pH=9-10, when mixing chloroethanol acid (HCl)and ammonium hydroxide (NH4OH) in different the ratios obtained atomic smooth surface, perfectly covered monohydride silicon (≡Si-H), oriented perpendicular to the surface.

The known method (Le Than V. et. al., Fabrication of SiGe quantum dots on a Si (100) surfaces Phys. Rev. C., 1997, v.56, No. 16, 10505-10509) growing SiGe quantum dots on Si (100)surface. In the specified source of the dependence of the degree of roughness of the surfaces of Si (100); Si (111) and the degree of coverage of their predominantly mono-, di - and trihydrides silicon depending on the chemical compositions and pH (acidity or alkalinity) solutions, which are processed silicon wafer of the substrate. In a well-known source, the following scheme chemical treatment to obtain atomic-smooth Si (100)surface covered with a layer of dihydride silicon.

1. Cleaning solutions that are similar to the compositions of the solutions of SC-1 and SC-2.

2. Treatment in diluted 2-10% solution of HF (1-2 min) or for 1 min in a buffer solution of HF+NH4OH ("buffered" HF aqueous solution: buffered oxide etchant FIRST:7:1, pH 5) to remove from the surface layer of native silicon oxide. However, the surface is rough (not smooth), and covered with a combination of mono-, di - and trihydrides.

3. Treatment in a solution of NH4F (pH 7.8) for about 1 min, in which the surface of Si (100) becomes atomic-smooth and covered only with a layer of dihydride silicon, which is desorbed in vacuum at a temperature of ≈400°C. the ri longer processing surface becomes loose. Gaps and unresolved questions above studies in conservation (passivating) substrates for long-term storage and subsequent epitaxial capacity of semiconductors on silicon wafers - wafers:

- the scratch resistance of the surfaces of Si (100) and Si (111) oxidation, i.e. to the formation of the oxide film of silicon, which prevents epitaxy, not investigated;

- processing wafer-substrates 40 wt.% a solution of NH4F (7,8) is actually a concentrated solution inevitably leaves on the surface of islet precipitation of ammonium fluoride, which prevents further epitaxial extension of the semiconductor layers.

Closest to the claimed solution is the above-mentioned method disclosed in US 6054393, publ. 25.04.2000, H01L 21/306, whereby to clean the surface of the silicon wafer using a solution SC-1, SC-2, and HF and H2O2. The final stage of processing of the known method is drying in the vapor of isopropyl alcohol, providing significant reduction of defects on the surface due to adsorption of water particles. However, the known method does not provide the perfect structure of the plates, as well as their long-term storage without surface oxidation.

The invention aims at eliminating indicated the deficiencies and the development of the method of chemical treatment of the surface of the monocrystalline silicon wafers using aqueous alkaline buffer solution (buffer mixtures) on the basis of ammonium hydroxide (NH 4OH)and ammonium fluoride (NH4F)providing a perfect structure and passivation of the surfaces of Si (111) and Si (100) layer of hydrogen atoms, allowing long time to save and transport the plate - substrate in the air without oxidation of the surface.

The technical result is achieved in that in the method of processing the surface of a monocrystalline silicon wafer, including the effects of chemical reagents, in addition conduct passivating the surface of the wafer by coating the hydrogen atoms. The method includes the stage of cleaning the surface from organic impurities, metal impurities, removing the film native silicon oxide and the final stage of processing alkaline buffer solution of a specific composition containing NH4OH and NH4F followed by rinsing in deionized water.

The method is as follows:

Industrial output plate of monocrystalline silicon cut from a given crystallographic orientation, is subjected to chemical treatment for cleaning the surface from organic impurities, impurities of metals, removal of own film of silicon oxide, for example sequential exposure in the following fluids:

1).

2) standard solution SC-1,

3) standard solution SC-2,

with promisc the th in deionized water after each solution.

Next, the plate is additionally Passepartout first 5 wt.% the HF solution, and then in a mixture of NH4OH and NH4F, followed by rinsing with deionized water and drying in air at normal conditions.

The following examples explain the invention.

Example 1.

Industrially produced single-crystal silicon wafer with orientation of the Si (100) or Si (111) or deviation of a few degrees from the Si (111) sequentially subjected to the following treatments.

1. In a boiling solution of trichloroethylene; 10 min - two-time processing.

2. Rinsing with deionized water for 5-10 minutes after each treatment.

3. In the standard solution SC-1 (5 volumes H2O, 1 volume of N2About230%, 1 volume of NH4OH 29%) when 75-82°C, 10 min, three - time processing.

4. Rinsing with deionized water for 5-10 minutes after each treatment.

5. In the standard solution SC-2 (6 volumes N2Oh, 1 volume of N2About230%, 1 volume of HCl 37%) when heated to 70-80°C, 10 min, three - time processing.

6. Rinsing with deionized water for 5-10 minutes after each treatment.

7. In 5% HF solution at room temperature for 1 minutes

8. In aqueous buffer solution containing NH4OH and NH4F with a pH of 7.6 to 7.7 at room temperature for 40-60 sec.

9. Double rinse with deionized water at room temperature is about 15-20 seconds.

10. Drying under normal conditions

Example 2.

Industrially produced a monocrystalline silicon wafer with orientation of the Si (100) or Si (111) or deviation of a few degrees from the Si (111) is exposed sequentially to all chemical treatments as in example 1 except for stage 8, which is carried out for 1 minute

Example 3

Industrially produced a monocrystalline silicon wafer with orientation of the Si (100) or Si (111) or deviation of a few degrees from the Si (111) is subjected successively to all chemical treatments as in example 1 except for stage 8, which is carried out within 60 seconds

Figure 1 and 2 presents a typical electron diffraction from Si (100) surface and the surface of Si (111) with a deviation of a few degrees after processing, carried out according to the claimed invention (Fig 1) and after storage for 2 weeks (Figure 2). It should be noted that the qualitative picture of electron diffraction in figure 1 and Figure 2 are not changed during storage of silicon wafers in the air, at least for 2 weeks.

Notes to figure 1 and figure 2

1. The signatures indicate the sequence of operations etching of silicon wafers.

2. After each of the first three operations - consistent triple rinsing with deionised water.

3. TAE - trichloroethylene (in temp, boiling); "NH3" (H2O:sub> 2O2:NH3=5:1:1)for 10 min at 80-84°; "HCl (H2O:H2O2:HCl=6:1:1)for 10 min at 80-84°C; 5% HF for 1 min at room temp.; in a solution with a pH of 7.64 or pH 7,73 for 1 min at room temp.; 2 k - double rinsing for 15 seconds deionized water at room temp.

4. On the first three stages of the surface of the wafer in the solution is directed downward ("h"), and upon etching in HF and at pH of 7.64; 7,73 and subsequent leaching in water - up ("in").

5. 2-12 - number of silicon wafers.

6. Si (111)4gr, ie (Si (111)4°.

Figure 3 shows a typical electronography epitaxial film of silicon carbide (SiC) grown on plates - monocrystalline silicon substrates prepared in example 1 and example 2.

Epitaxial growth of SiC films was observed on the si wafers stored in air for 3-4 weeks.

Notes to Figure 3

1. The signatures indicate the sequence of operations etching of silicon wafers.

2. After each of the first three operations - consistent triple rinsing with deionised water.

3. TAE - trichloroethylene (in temp. boiling); "NH3" (H2O:H2About2:NH3=5:1:1)for 10 min at 80-84°; "HCl(H2O:H2O2:HCl=6:1:1)for 10 min at 80-84°C; 5% HF for 1 min at room temp.; in a solution with a pH of 7.64 or pH 7,73 for 1 min at room temp.; 2 k - double rinsing for 15 seconds deionized water at room temp.

4. N the first three stages of the surface of the wafer in the solution is directed downward ("n"), while etching in HF and at pH of 7.64; 7,73 and subsequent leaching in water - up ("in").

5.03-05 - the number of silicon wafers

The method of processing the surface of a monocrystalline silicon wafer, oriented along the plane of the Si(100) or Si(111), including the specified cleaning the surface with subsequent passivation by hydrogen atoms, characterized in that the surface cleaning of silicon carried out first in a boiling solution of trichloroethylene in 10-20 min - dual treatment with rinsing with deionized water for 5-10 minutes after each treatment, and then in an aqueous ammonia-peroxide solution composition: 5 volumes of N2Oh, 1 volume of N2O230%, 1 volume of NH4OH 25% 75-82°or in aqueous hydrochloric peroxide solution composition: 6 volumes of N2Oh, 1 volume of H2O230%, 1 volume of HCl 37% at 75-82°With subsequent speed triple rinse with deionized water for 5-10 min at each step and the passivation by hydrogen atoms is performed by the first processing 5-10 wt.% the HF solution, and then an aqueous solution of a mixture of NH4OH and NH4F with a pH of 7.6 to 7.7 for 40-60 with subsequent washing with deionized water and drying under normal conditions.



 

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2 cl, 4 dwg

FIELD: technology for producing semi-penetrable membranes for molecular filtration of gas flows and for division of reaction spaces in chemical reactors.

SUBSTANCE: method for producing gas-penetrable membrane includes two-sided electro-chemical etching of monocrystalline plate made of composition AIIIBV of n conductivity type or of semiconductor AIV with width of forbidden zone E≥1,0 electron volts and alloying level 1017-1020 1/cm3. Modes of aforementioned etching are set, providing for generation of simultaneously porous layers, while etching process is performed until moment of spontaneous stopping of electro-chemical process and generation of solid separating layer of stationary thickness on given part of plate area, determined using sharp bend on the curve of temporal dependence of anode current.

EFFECT: gas membrane, produced in accordance to method, has increased penetrability for molecules of light gases and increased selectivity characteristics at room temperature.

2 cl, 3 dwg, 3 ex

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