JPH03219000A - Etching method and washing method for silicon wafer - Google Patents

Abstract

PURPOSE:To extremely decrease metallic contaminating materials contg. Fe by etching a silicon wafer with an etching soln. prepd. by adding a complexing agent which forms a complex compd. with the metallic contaminating materials to an aq. alkaline soln. CONSTITUTION:The silicon wafer is etched or washed by using the etching liquid or washing liquid or the etching liquid or washing liquid added with the complexing agent (e.g.: citric acid) which forms the complex compd. with an extremely slight quantity of the metallic contaminating material, for example, Fe, existing on the surface of the silicon wafer at the time of etching or washing the silicon wafer by using the aq. alkaline soln., for example, an aq. KOH soln. and ammonia-aq. hydrogen peroxide soln. The degradation in the quality of the silicon wafer is averted in this way and the deterioration in the electrical characteristics when the silicon wafer is used for highly integrated devices is averted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an etching or cleaning method for bringing the surface of a silicon wafer into a highly clean state. Background of the Invention In recent years, as devices have become more highly integrated, there has been a strong desire to further clean the surfaces of silicon wafers that serve as their substrates. In general, a silicon wafer is cut into a disk shape from a single-crystal silicon ingot, and then undergoes lapping, etching, polishing, and cleaning steps to create a product with a smooth surface that is free from processing distortion and contaminants. However, if there is a problem with processing distortion or the etching or cleaning that removes contaminants, particulate contaminants (also called particles) such as silicon particles and dust, and metal contaminants will remain on the silicon wafer surface. The presence of particulate contaminants causes disconnections and short circuits in device wiring, and the presence of metal contaminants causes problems such as the generation of oxidation-induced m-layer defects and shortened lifetimes. Therefore, it is necessary to reduce these pollutants as much as possible. Conventional methods for etching silicon wafers include: (1) etching with a caustic alkaline aqueous solution (hereinafter referred to as alkaline etching method), and (2) etching with a mixed acid aqueous solution containing nitric acid and hydrofluoric acid as main components. Among the conventional etching methods, method (■) often uses an aqueous solution of potassium hydroxide. However, even if special grade potassium hydroxide is used, ppm or sub-pp
In addition to containing m-order metal contaminants,
The silicon surface etched with an alkaline aqueous solution is Fe
There is a problem in that it is extremely susceptible to contamination with metal-based contaminants such as. Conventional methods for cleaning silicon wafers include: ■ Cleaning with a dilute hydrofluoric acid solution (hereinafter referred to as the hydrofluoric acid method); ■ Cleaning with a mixed aqueous solution of hydrochloric acid or sulfuric acid and hydrogen peroxide (hereinafter referred to as the hydrofluoric acid method). (referred to as hydrochloric acid hydrogen peroxide method or sulfuric acid hydrogen peroxide method), ■ method of washing with a mixed aqueous solution of ammonia and hydrogen peroxide (hereinafter referred to as ammonia hydrogen peroxide method), and ■ organic method of quaternary ammonium hydroxide. Alkali, such as [(CH3)3NCH,CH,OH
] The chemical formula of OH is used for washing with a mixed aqueous solution of an organic alkali called choline and hydrogen peroxide or a surfactant (hereinafter referred to as the choline-hydrogen peroxide method). The cleaning liquid used in each of these cleaning methods uses high-purity chemicals and water that contain as little particulate contaminants and metal contaminants as possible. It has the ability to dissolve naturally intoxicated films in which contaminants usually exist in a thickness of about 10λ, and is highly effective in removing metal contaminants in oxide films, but it is difficult to reduce particulate contaminants. ① utilizes the high dissolving ability of hydrochloric acid or sulfuric acid for metal contaminants, but it does not have the ability to dissolve oxidized particles.For this reason, it is not effective in removing metal contaminants on the oxide film. is high, but its effectiveness in removing metal contaminants present in the oxide film and at the interface between the oxide film and silicon is low. However, the oxide film formed in the alkaline cleaning solution has the property of easily absorbing metal contaminants, etc. in the cleaning solution, and there is a high possibility that the silicon wafer will be re-contaminated. This method is widely used by wafer manufacturers and device manufacturers because it is highly effective in removing fine particles. ■ is more alkaline than ammonia, so it dissolves silicon fine powder better. Also, because it has a strong destructive effect on bacteria, other This method is effective in removing adhered bacteria that are difficult to remove with cleaning methods.However, since the cleaning solution is strongly alkaline, it tends to absorb metal contaminants in the cleaning solution, as in (2), and silicon wafers may be recontaminated. Problems to be Solved by the Invention Methods for evaluating the cleanliness of silicon wafer surfaces include a method of analyzing metal contaminants using flameless atomic absorption;
There is a way to check the lifetime (hereinafter referred to as recombination lifetime) using microwave reflection method. The inventor is
Using these methods, the cleanliness was evaluated by examining the Fe contamination on the surface of silicon wafers by alkaline etching and the recombination lifetime of silicon wafers cleaned by the various cleaning methods described above. The alkaline etching method uses approximately 100 PPb impurity Fe.
The amount of Fe contamination on the W surface of a silicon wafer etched at 80°C for 15 minutes with a 5% potassium hydroxide aqueous solution containing
The problem of contamination with Fe at a high concentration of 1015 atoms/cm2 was clarified. In addition, as a result of evaluating the recombination lifetime of silicon wafers cleaned by the various cleaning methods mentioned above, as illustrated in Table 1, silicon wafers cleaned by the ammonia hydrogen peroxide method and the choline hydrogen peroxide method We clarified the problem that the recombination lifetime is considerably inferior to that of those cleaned using this method. As a result of the inventor's investigation into the cause of this problem, it was found that the cause was a trace amount of Fe originally contained in potassium hydroxide, aqueous ammonia, aqueous choline solution, and aqueous hydrogen peroxide. According to the inventor's analysis, although there are differences depending on the chemical manufacturer and manufacturing loft, potassium hydroxide has a concentration of about 70 ppb, and ammonia water has a concentration of 0.06 to 0.0 ppb.
．． About 25 ppb, 0.13 to 0.3 for hydrogen peroxide solution
About 2ppb, 10p for choline (0.5% aqueous solution)
It contained approximately pb of Fe. In addition, quartz glass cleaning tanks and heaters used for etching or cleaning also contain Fe as an impurity, and its elution is promoted by heating the cleaning solution, so that the Fe content in the etching solution is approximately 100 PPb. If the Fe content in the cleaning solution is o. s
It is not uncommon for it to be around ppb. In the alkali etching method, as mentioned above, about 1
The surface of a silicon wafer etched with a 5% potassium hydroxide aqueous solution containing 00 ppb of impurity Fe is approximately 4
Contaminated with 10" atoms/cm2 of Fe. Also, in the ammonia hydrogen peroxide method, Fe is contaminated in the cleaning solution.
Even if it exists in a trace amount of 0.5 ppb, 8 x 10
It is known that Fe with a concentration of about C12 adheres to the silicon wafer surface, contaminates the silicon wafer surface, and reduces the recombination lifetime (Otsuka et al., Proceedings of the 34th Semiconductor and Integrated Circuit Technology Symposium, 1888 year, p. 37)
The purpose of the present invention is to improve the alkaline etching method among conventional etching methods for silicon wafers, and to provide a new etching method in which metallic contaminants including Fe are extremely reduced. In addition, among conventional silicon wafer cleaning methods, we have improved the ammonia hydrogen peroxide method or the choline hydrogen peroxide method, which is highly effective in removing particulate contaminants, to achieve high cleanliness that significantly reduces metal contaminants including Fe. The purpose of this study is to provide a new cleaning method that can obtain silicon wafers. Means and Action for Solving the Problems The present inventor has discovered that in the conventional alkaline etching method, ammonia hydrogen peroxide method, or choline hydrogen peroxide method, the surface of the silicon wafer is The reason for the contamination is that Fe in alkaline etching and cleaning solutions is ferric hydroxide F, which is insoluble in water.
It is assumed that this is because Fe is dispersed in a colloidal form as e(OH)s, and the surface is dissolved and adsorbed to the activated silicon wafer. We investigated ways to prevent adsorption by using different compounds. The present invention was made based on this idea, and its gist is as follows: 1. When etching a silicon wafer using an alkaline aqueous solution as an etching solution, metals present on the surface of the silicon wafer or in the etching solution are removed. 2. A method for etching a silicon wafer, comprising etching with an etching solution in which a complexing agent that forms a complex compound with a contaminant is added to the etching solution; 2. When cleaning a silicon wafer using an alkaline aqueous solution as a cleaning liquid, the silicon wafer is cleaned with a cleaning solution in which a complexing agent that forms a complex compound with the surface of the silicon wafer or a metal contaminant present in the cleaning liquid is added to the cleaning liquid. This is a method for cleaning silicon wafers. Etching of silicon wafers by the conventional alkaline etching method is generally performed in KOH aqueous solution II at 85°C. Cleaning of silicon wafers by the conventional ammonia hydrogen peroxide method uses NH40H: 0.5 to 5% by weight, 1702:
It is generally carried out in an aqueous solution containing 4 to 6% by weight and at a temperature of 70 to 85°C. Cleaning of silicon wafers by the conventional choline hydrogen peroxide method is [(C}I3)3MCI12CH20H]OH:
1-38% by weight, H, 02: 0-3% by weight, temperature 30
It is generally carried out in an aqueous solution at ~70°C. In the method of the present invention, a complexing agent is added to the etching solution of the conventional alkaline etching method, the ammonia hydrogen peroxide method, or the choline hydrogen peroxide method, and the solution is used as the etching solution or cleaning solution. The complexing agent to be added is one that reacts with metal contaminants present on the surface of the silicon wafer or in the etching solution or cleaning solution to form a stable complex compound, and in particular reacts with Fe to form a stable Fe@ compound. It must form a In particular, the ammonia hydrogen peroxide cleaning solution has a PR of about 10 to 12.
The choline hydrogen peroxide cleaning solution is also strongly alkaline with a pH of 12 or higher, contains hydrogen peroxide, a strong oxidizing agent, and is heated to high temperatures, so the complexing agent must be one that will not be decomposed by oxidation. You need to choose. In the present invention, as the complexing agent that forms a complex compound with a metal contaminant, one or more of the following can be used. (1) Hydroxycarboxylic acids in which the two oxygen atoms of the donor atoms that participate in the reaction with metals are converted into a hydroxyl group and a carpoxyl group. For example, citric acid, tartaric acid, malic acid, 4,6-dihydroxy-10-toluic acid, zincone, and other hydroxycarboxylic acids. (2) Compounds in which two oxygen atoms, which are donor atoms that participate in reactions with metals, are also converted into hydroxyl groups. For example, catechol, resorcinol, pyrogallol, orcine, gluconic acid, 4,2-pyridylazoresorcinol,
4.5-dihydroxybenzene-1,3-disulfonic acid (thyrone). (3) Compounds in which the two oxygen atoms of the donor atoms that participate in the reaction with the metal are also a hydroxyl group and a carbonyl group. For example, tropolones, 2-hydroxy-1,4-benzquinone, 2-hydroxy-1,4-naphthoquinone, 5
Hydroxyquinones such as -hydroxy-1,4-naphthoquinone, 1-hydroxy-8, ]0-anthraquinones, 4-hydroxyquinones such as 3-hydroxy-4-pyrone (pyromeconic acid), kojic acid, comenic acid, maltol, etc. Pyrones. (0β-diketones. For example, acetylacetone, thenoyltrifluoroacetone, etc.) (5) Amines used in amine groups in which nitrogen is the second donor atom that participates in the reaction with metals. For example, ethylenediamine, trifluoroacetone, etc. Ethanolamine, etc. (6) Polyaminocarboxylic acids containing an amino group in which one of the two donor atoms participating in the reaction with a metal is nitrogen, and the other is a carpoxyl group, in which the other is oxygen. For example, ethylenediamine diacetic acid, ethylenediamine 4
Acetic acids, etc. and other polyaminocarboxylic acids. (7) Compounds in which one nitrogen of the two donor atoms participating in the reaction with the metal is a ditro group, and the other oxygen is a hydroxyl group. For example, cuperone, nitroso R salt, etc. In the present invention, the lower limit of the amount of these complexing agents added cannot be determined unconditionally because it varies depending on the type of complexing agent and the component and amount of impurity metal in the etching solution or cleaning solution. 1% by weight or more, 0 in cleaning solution
．． It is desirable that the amount be 0l% by weight or more. In addition, no effect is observed even if the amount added is increased, so there is no particular upper limit to the upper limit, but depending on the type of complexing agent added to the cleaning solution, bumping may occur due to a rapid exothermic reaction (for example, nitroso R salt). ．． Also, from the point of view of economy, it is desirable that the amount be 1% by weight or less. When silicon wafers are etched or cleaned using the method of the present invention, due to the dissolving action of silicon itself, which is a characteristic of an alkaline aqueous solution, it is highly effective in removing particulate contaminants from the wafer surface, and at the same time, a trace amount of Fe is contained in the etching solution or cleaning solution. Even if the ferric hydroxide is present, it becomes an Fe complex compound due to the action of the complexing agent, so the colloid of ferric hydroxide is not adsorbed onto the activated wafer surface, which prevents Fe contamination, which was a problem in the past. This avoids a decrease in the recombination lifetime. Furthermore, depending on the type of complexing agent, M, Ca. Cr.
Cu. Metals such as Ng and Xi also form complex compounds, so
When etching or cleaning silicon wafers contaminated with trace amounts of these metals, or when using etching solutions or cleaning solutions contaminated with trace amounts of these metals, problems of contamination due to these metal substances and metal contamination may occur. Reduction of recombination lifetime due to substances is avoided. Note that the cleaning method of the present invention may be performed in combination with conventionally known cleaning methods. For example, it is effective to perform the method of the present invention after removing an oxide film on the surface of a silicon wafer using a dilute hydrofluoric acid method. As an etching example, an n-type silicon wafer with a diameter of 5 inches was immersed in an aqueous solution of KOH: 5% by weight with or without addition of various complexing agents at 80° C. for 15 minutes. Etched. After etching, the silicon wafer was immediately rinsed with running water for at least 5 minutes twice in ultrapure water, dried using a spin dryer, and then flameless atomic absorption spectroscopy was performed to determine the F content on the silicon wafer surface.
We analyzed e. In addition, NIL in the table indicates that it is less than 0.2X 10"atoms/cm2, which is below the lower limit of analytical quantification. Table 2 shows the test results. As is clear from Table 2, in the example of the present invention, , Fe contamination is extremely reduced. As cleaning, NH40H: 3.7% by weight, H,02
: 4.9% by weight ammonia hydrogen peroxide cleaning solution,
80% cleaning solution with or without various complexing agents added
℃ and 5 inch diameter nfi and p! ! ! The silicon wafer was immersed and cleaned for 10 minutes. Also, [(C
H3)sNcTocH,OH]OH = 0.5% by weight. III, Mo2 N-type and p-type silicon wafers with a diameter of 5 inches are immersed in a 3.0% by weight choline-hydrogen peroxide cleaning solution with or without addition of various complexing agents and maintained at 70°C. and washed for 3 minutes. After cleaning, the silicon wafers were immediately rinsed with running water for 5 minutes or more twice in ultrapure water, dried with a spin dryer, and then subjected to evaluation tests. The results are shown in Table 3. The Fe ion addition amounts of 5 and 10 ppb in the table were intentionally added to the cleaning solution. After drying, some of the wafers were checked for the number of contaminant particles using a wafer surface particle counting device, and the remaining wafers were dry oxidized for 25 minutes at 1000°C in an oxidation furnace, leaving about 2.
An oxide film with a thickness of 80 people was formed. The recombination lifetime of the oxidized wafer was measured by microwave reflection method. The number of contaminant particles was less than 10 per wafer in all cases.
Furthermore, as is clear from Table 3, in the examples of the present invention, metal contaminants are extremely reduced, resulting in silicon wafers with excellent recombination lifetimes. No. 3 in Table 3. 01, No. 02. No
．． 07. No. 11 No. 12, No. 22.
No. 24, No. About 25, diameter l~6m
A NOS diode with an aluminum electrode of m was fabricated, and the oxidized H# pressure and generation lifetime were measured. Oxidation voltage withstand voltage is applied electric field 0-25V/cm step, judgment current 1
#LA/cm2 condition
NvlCI1 or less, B mode (caused by weak spots in the oxide film due to metal contaminants, etc.) for n-type wafers 4~? ．． 5MV/c■, p-type wafer 4-8. ON
V/c group C mode (dielectric breakdown inherent to oxide film) is 7.5NV/cm+ or more for n-type wafers and 8.5NV/cm+ for p-type wafers. OMV
/cm or more, and evaluated based on the C mode rate. As a result, as shown in Table 4, silicon wafers cleaned by the method of the present invention have excellent oxide film breakdown voltage and generation lifetime. (Left below) Effects of the Invention When silicon wafers are etched by the method of the present invention, highly clean silicon wafers with significantly reduced Fe contamination can be obtained. Furthermore, when a silicon wafer is cleaned by the method of the present invention, a highly clean silicon wafer with extremely reduced levels of both metal-based contaminants and particulate contaminants can be obtained.
This avoids deterioration in the quality of silicon wafers, such as the occurrence of oxidation-induced stacking faults and shortened lifetimes, as well as the deterioration of electrical characteristics when used in highly integrated devices.

Claims (1)

[Claims] 1. When etching a silicon wafer using an alkaline aqueous solution as an etching solution, a complexing agent that forms a complex compound with a metal contaminant present on the surface of the silicon wafer or in the etching solution is added to the etching solution. A silicon wafer etching method characterized by etching with an etching solution added to a silicon wafer. 2. When cleaning a silicon wafer using an alkaline aqueous solution as a cleaning liquid, it is recommended to clean the silicon wafer with a cleaning solution containing a complexing agent that forms a complex compound with the surface of the silicon wafer or a metal contaminant present in the cleaning liquid. Characteristic silicon wafer cleaning method.