JPH08264498A - Silicon wafer cleaning method - Google Patents

Abstract

PURPOSE: To remove various kinds of metal elements seized in a naturally oxidized film by washing a silicon wafer with a cleaning liquid including hydrogen peroxide and then rinsing the wafer with a rinsing solution formed of ultrapure water containing ozone and hydrofluoric acid of such concentration that do not perfectly dissolve the formed naturally oxidized film. CONSTITUTION: In view of cleaning the surface of a silicon wafer, it is then washed with a cleaning solution including hydrogen peroxide to remove fine particles and form a naturally oxidized film. Thereafter, the etching effect of the hydrofluoric acid is improved with ozone and then executing the linsing with a rinsing solution formed of the ultrapure water to etch off the naturally oxidized film at the area near the surface and to reflectively bleaching impurity leaving the layer near silicon. Cleaning effect for contamination by addition of ozone is never found but it is remarkably improved when HF is added thereto and when HF is 100ppm, an ordinary cleaning effect can be obtained. HF in the rinsing solution never gives adverse effect on the silicon surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a silicon wafer in a silicon wafer manufacturing process and a device manufacturing process, and more particularly to a method for producing a surface-cleaned silicon wafer containing hydrogen peroxide. To obtain a hydrophilic surface composed of a natural oxide film formed by cleaning the silicon wafer with a cleaning solution that is used, and then rinse with a rinse solution composed of ultrapure water to which ozone (O ₃ ) and hydrofluoric acid (HF) have been added. The present invention relates to a method for cleaning a silicon wafer in which a trace metal element is removed by etching to such an extent that the oxide film is not completely dissolved and recontamination is difficult.

[0002]

2. Description of the Related Art In recent years, as the degree of integration of liquid crystals and semiconductor elements (LSI) has been improved, the influence of contamination of a substrate such as a silicon wafer with a trace amount of substances has become a serious problem.

The cause of such contamination is caused by fine particles (even fine particles having a particle size of 0.1 μm poses a problem, and includes microorganisms themselves and decomposed products thereof), and metal (especially Na as an alkali metal, Heavy metals such as Fe, Cu, Ni, Cr, etc., other Zn, Ca, M
g, Al, etc.), by organic (lithographic materials in the ambient air, the plastic plasticizer, machine oil, etc.), by anion _{^{(PO 4 2-, BF 2 -}} , SO 4 2-, C
l ^-, and the like).

Several cleaning methods have been used in the past for these various forms of contamination.

For example, an aqueous cleaning solution containing ammonium hydroxide and hydrogen peroxide (generally called SC-1),
From aqueous cleaning solution containing hydrochloric acid and hydrogen peroxide (generally called SC-2), cleaning solution consisting of sulfuric acid and hydrogen peroxide (sulfuric acid: hydrogen peroxide (30%) = 1: 3), diluted hydrofluoric acid Cleaning liquid (usually HF: H ₂ O = 1: 50 to 200,
(Generally referred to as DHF).

A typical composition of the SC-1 cleaning solution is 1 volume of ammonia water (28% by weight) + hydrogen peroxide (30% by weight).
1 volume + 5 volumes of ultrapure water.

Further, since the SC-1 cleaning has an etching action on the wafer, the silicon surface recedes while forming a natural oxide film (about 10 Å) during the SC-1 cleaning.

Therefore, at this time, the surface of the wafer is hydrophilic.

SC-1 cleaning is the only cleaning method capable of efficiently removing fine particles, and has a particularly strong cleaning power for fine particles derived from microorganisms. In addition, organic substances, metals that make complex ions,
It also has a high detergency against anions.

However, in the above-mentioned typical composition, fine irregularities (microroughness) may occur on the silicon surface to deteriorate the oxide film breakdown voltage characteristic.

By the way, Fe and Al are contained in the SC-1 cleaning solution.
If a very small amount is present, these are easily incorporated into the natural oxide film unless assisted by a chelating agent or the like.

When Fe or Al is present at 0.1 ppb,
About 10 ¹¹ atoms / cm ² is adsorbed on the wafer. In particular, Fe is a level at which the wafer becomes defective. Further, Zn, Ca, Mg and the like also cause such a contamination phenomenon depending on the conditions.

Therefore, even if an ultrahigh-purity reagent is used as the SC-1 cleaning liquid, these cleaning liquids are not thrown away after each wafer carrier treatment in a normal cleaning device, so the cleaning liquid is gradually added. Will be polluted by.

Further, even if an element such as Cu has a relatively high cleaning power, the cleaning power is about 95%, so that, for example, 10 ¹² atoms / c which can occur in a normal semiconductor process.
In case of contamination of about m ² , 5 × 10 ¹⁰ atoms / cm ²
The degree remains.

Therefore, in the SC-1 cleaning, usually about 5 to 10 × 10 ¹⁰ atoms / cm ² of metal remains on the wafer.

The SC-2 cleaning has no etching action but has a cleaning power against metal contamination, a natural oxide film is formed even on the exposed silicon surface, and the wafer surface is hydrophilic. Cleaning with a cleaning solution composed of sulfuric acid and hydrogen peroxide has a strong decomposing power for organic substances, especially for photoresists. In addition, it has cleaning power against metal contamination. Since this cleaning method is performed at about 130 ° C., the exposed silicon surface produces a relatively thick natural oxide film (about 15 Å) and the wafer surface is hydrophilic.
As described above, SC-1 cleaning, SC-2 cleaning, sulfuric acid
In the case of cleaning with a cleaning liquid composed of hydrogen peroxide, a natural oxide film is formed, so that the natural oxide film acts as a protective function, and the contamination of the wafer with fine particles is less likely to occur.

On the other hand, in the DHF cleaning, the natural oxide film on the wafer is dissolved and removed to remove the impurities taken in the natural oxide film. Therefore, the surface of the wafer is exposed to silicon (called bare) and is hydrophobic.

In this DHF cleaning, metal contamination can be efficiently removed. For example, when Fe is 100 ppb in ultrapure water, the amount of Fe adsorbed on the wafer is 10 ⁹ ato.
It is less than ms / cm ^2, which is not a practical problem.
Also, similar behavior is exhibited for Al, Zn, Ca, and Mg. However, most of Cu in the natural oxide film remains due to the ionization tendency. Therefore, in order to remove Cu, cleaning with hydrogen peroxide hydrofluoric acid in which hydrogen peroxide is added to dilute hydrofluoric acid has also been proposed. Silicon wafer is exposed on the wafer surface even after cleaning with hydrofluoric acid and hydrogen peroxide (bare)
And is hydrophobic.

The above-mentioned cleaning treatment with the cleaning liquid is one step of the cleaning, which is combined with the rinse treatment with the ultrapure water after that. This is because the surface of the wafer is deteriorated by the corrosive action of the cleaning liquid unless the cleaning liquid is completely removed.

Further, as described above, each cleaning method has its own characteristics, and one cleaning method has poor oxide film characteristics and PN.
It is not possible to sufficiently remove the contaminating factors that cause device failure due to defective joining characteristics and the like. Therefore, normally, a cleaning method by RCA cleaning in which each cleaning method is combined is used.

That is, the cleaning method is, for example, SC-1 cleaning → DHF cleaning → SC-2 cleaning.

First, fine particles, organic substances, metal forming complex ions, anions and the like were removed by SC-1 cleaning, and then the natural oxide film was dissolved and removed by DHF cleaning and incorporated into the natural oxide film. Impurities (Fe, Al, Zn, Ca
Etc.) are removed. And finally Cu by SC-2 cleaning
The wafer is cleaned by removing various metals including.

However, the bare surface easily attaches fine particles, and therefore DHF cleaning makes it difficult to remove the fine particles generated from the wafer carrier or the cleaning tank in which the cleaning liquid is stored, by adhering them to the wafer. Further, since the SC-2 cleaning has a weak ability to remove fine particles, there is a problem that fine particles remain after cleaning.

Therefore, the order of RCA cleaning is changed to D
Cleaning may be performed as HF cleaning → SC-1 cleaning → SC-2 cleaning.

This is done by first removing most of the metal contamination by DHF washing, then fine particles by SC-1 washing,
The organic substance is removed, and finally SC-2 cleaning is performed. In SC-1 cleaning, Fe, Al, Zn, etc. in the cleaning liquid are taken into the natural oxide film, which can be removed by SC-2 cleaning. There is a problem that there is no.

Therefore, further SC-1 cleaning → DHF cleaning → SC-2 cleaning → DHF cleaning (or hydrofluoric acid hydrogen peroxide cleaning) or DHF cleaning → SC-1 cleaning → SC-2 cleaning → D
There is also a method of removing Fe, Al, Zn, etc. taken in the natural oxide film by removing the natural oxide film again in the last step like HF cleaning (or hydrogen peroxide cleaning). However, this also causes a problem that the fine particles generated from the wafer carrier or the cleaning tank accumulating the cleaning liquid are attached to the wafer to make it difficult to remove. Naturally, although measures have been taken to suppress the generation of these fine particles as much as possible, there is still a problem that the bare surface is contaminated with fine particles during transportation and an incomplete natural oxide film is generated due to contact with air, resulting in defects.

In order to solve such a problem, a method for forming a clean oxide film by applying a treatment with pure water containing ozone immediately after a series of cleaning has been filed (Japanese Patent Laid-Open No. 6-2).
44174).

However, if 100 ppt of Fe is present in the ultrapure water, the treatment with ozone water for 10 minutes gives 5 × 10 ⁹ to
It has been confirmed by a tracer experiment using ⁵⁹ Fe that Fe of about 1 × 10 ¹⁰ atoms / cm ² is reversely adsorbed on the wafer. Of course, there is no cleaning action for such contamination. Similarly, since a metal element such as Al also has such an adsorption effect and a cleaning effect cannot be expected, it is necessary to strictly control the purity particularly when treating a wafer with ozone water.

According to this method, the structure of the cleaning device is SC-1 tank → rinse tank → DHF tank → rinse tank → SC-2.
There are 8 tanks, rinsing tank, DHF tank, and ozone water rinsing tank, and the equipment becomes large-scale at the present when the diameter of the wafer is increasing. In addition, there is a problem that the number of processes increases, so that the chance of contamination during transportation increases.

Therefore, the following method for shortening the washing step has been proposed (Japanese Patent Laid-Open No. 6-216098).

That is, a cleaning liquid (SC- consisting of alkali, hydrogen peroxide and water capable of removing fine particles and organic substances)
In the cleaning by 1), Fe, Zn, Ca are used with a complexon type chelating agent such as EDTA or TTHA.
Fe, Zn, C in the cleaning liquid by chelating etc.
The natural oxide film formed is prevented from adhering to the wafer as much as possible, and the formed natural oxide film is cleaned as much as possible, and then rinsed with pure water containing a slight amount of HF to remove the metal captured in the natural oxide film. It begins to melt with a part of.

However, in order to sufficiently remove the residual metal only by rinsing with pure water to which a trace amount of HF is added, it is necessary to heat the rinsing liquid to about 50 ° C. or set the HF concentration to about 1000 ppm.

Under these conditions, the HF concentration in the atmosphere around the rinsing tank rises and selectively adheres strongly to the wafer surface, causing the wafer to corrode. Is required.

Further, it has been clarified that when a trace amount of organic substances remain on the wafer, the oxide film characteristics are deteriorated in the case of an ultra-high performance LSI. Therefore, even if a trace amount of an organic chelating agent is added to SC-1, it adsorbs on the wafer and deteriorates the oxide film characteristics. Therefore, it must be sufficiently removed. Therefore, HF was added. There has been a problem that the rinse with pure water has to take a long time, which is not practical.

[0035]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of many conventional cleaning methods, and reduces residual fine particles on a wafer and naturally preserves a natural oxide film. It is an object of the present invention to provide a method for cleaning a silicon wafer which removes various metals trapped in an oxide film and makes re-contamination by these metals less likely to occur.

[0036]

A method of cleaning a silicon wafer according to the present invention is a method of cleaning a silicon wafer with a cleaning liquid containing hydrogen peroxide, and then removing ozone and hydrofluoric acid at concentrations that do not completely dissolve the formed natural oxide film. The method is characterized by including a step of rinsing with a rinsing liquid containing ultrapure water.

As the above cleaning solution, any one of (a) hydrogen peroxide and alkali, (b) hydrogen peroxide and acid (preferably hydrochloric acid), and (c) hydrogen peroxide and acid (preferably sulfuric acid) is used. It is desirable to contain. Further, it is desirable to add a cleaning process using ultrapure water after the above process. The average concentration of ozone in the rinse liquid is 0.5.
10 to 10 ppm, and the average concentration of hydrofluoric acid is 1 to 100 p
pm is preferred. In the present invention, the cleaning solution containing hydrogen peroxide is most preferably one that can obtain a strong hydrophilic surface composed of hydrogen peroxide, alkali and water. The _{alkali, NH 4 OH, N (CH} 3) 4 ·
OH, N (CH ₃ ) ₃ (CH ₂ CH ₂ OH) · OH and the like can be used, and these have high ability to remove fine particles.
Further, a cleaning liquid composed of hydrogen peroxide, hydrochloric acid and water and a cleaning liquid composed of sulfuric acid and hydrogen peroxide can also be used. As for the composition of the cleaning liquid containing hydrogen peroxide that constitutes the present invention, 1 volume of aqueous ammonia (28% by weight) + 1 volume of hydrogen peroxide (30% by weight) + 5 volumes of ultrapure water, which is a general composition, are sufficient. In Although,
More preferably, 1 volume of ammonia water (28% by weight) +1 volume of hydrogen peroxide (30% by weight) +10 to 30 volumes of ultrapure water is preferable. The washing temperature is preferably in the range of about 60 to 80 ° C. Furthermore, the wafer cleaning method is such that a sufficient cleaning effect can be obtained by simply immersing the wafer.

In the rinse liquid according to the present invention, the average concentration of ozone is 0.5 to 10 ppm, and the average concentration of hydrofluoric acid is 1 to 100 ppm, more preferably the average concentration of ozone is 1 to 2 ppm. The average concentration of hydrofluoric acid is 10
It is good that it is 100 ppm. In addition, the rinse liquid has a sufficient cleaning effect at room temperature. In addition, it is desirable that the rinse form of the wafer is constantly overflowed in the immersed state. Of course, you can use a spray or a shower. The cleaning liquid constituting the present invention and the ultrapure water used for cleaning the wafer should have a general standard purity of 18 MΩ or more in specific resistance. Especially, since the rinse liquid itself has a strong cleaning power, it is within the specifications. In that case, it is a feature of the method of the present invention that no special maintenance is required.

The natural oxide film remaining after the rinse step is an element
Approximately 5-10 on according to the analysis and measurement result by interference light
It's about Gstrom .

[0040]

In the present invention, in order to clean the surface of the silicon wafer, the silicon wafer is washed with a cleaning liquid containing hydrogen peroxide to remove fine particles and form a clean natural oxide film, and then to remove ozone. To improve the etching action of hydrofluoric acid to etch off near the surface of the natural oxide film, and leave the layer close to silicon effectively to reach the impurities. Rinsing is performed with a rinse liquid made of water to remove contaminants containing various metals trapped in the native oxide film to a range that does not cause device failure, while preserving a part of the native oxide film.

Even if hydrofluoric acid is added to ozone-added water to rinse the silicon surface, HF molecules are difficult to adhere to the surface if there is a natural oxide film. Normal high performance gate oxide pretreatment D
After immersion in HF, HF molecules are of course adsorbed on the silicon surface. This F is said to be easily removed during the subsequent final ultrapure water rinse, but the radioactive tracer ¹⁸ F
When we trace this behavior by labeling hydrofluoric acid in HF,
It can be seen that 5 × 10 ¹³ atoms / cm ² or more of F atoms remain on the silicon surface even after rinsing with ultrapure water for 10 minutes.

However, in the case of the present invention, the maximum amount of 100 p
Even if pm is in the rinsing solution, the F atoms remaining on the silicon surface after rinsing are 10 ¹³ / cm ² or less, which is smaller than in the conventional case and HF in the rinsing solution does not adversely affect the silicon surface.

[0043]

EXAMPLE Since the feature of the present invention relates to the property of the silicon surface, instead of conducting the experiment on the silicon wafer, the experiment was conducted on the chip of 2 cm × 2 cm cut out from the silicon wafer. All of these silicon wafers were (100), p-type was used in Examples 1 and 2, and n-type was used in Example 3. The specific resistance is all several Ωcm.

All these experiments were carried out by the tracer method using radioisotopes.

[0045] Cu is used copper acetate, copper atoms ⁶⁴ Cu
(The following ⁶⁴ Cu is Cu labeled with ⁶⁴ Cu.
Means an atom. ). Fe is an iron chloride, the iron atoms ⁵⁹ are labeled with Fe (hereinafter ⁵⁹ Fe means a Fe atom labeled with ⁵⁹ Fe.). Also, tracer experiments with HF is the fluorine atom is ¹⁸ is labeled with F (hereinafter ¹⁸ F means labeled F atoms ¹⁸ F.).

For the addition of ozone, an ozone supply device (manufactured by Permelek Electrode Co., Ltd.) of the type in which ozone generated by pure water electrolysis is added to pure water in a dissolution module was used. At this time, a silent discharge ozone generator may be used. Even with the bubbling method, the dissolution of ozone in pure water is good,
Poor stability. If it is a dissolution pump, it can be stably supplied.

10 to 15p generated from the ozone supply device
Add about pm of ozone to an auxiliary tank containing ultrapure water,
At the same time, hydrofluoric acid was added to a predetermined concentration and immediately sent to a quartz rinsing bath to dip the PFA carrier-containing chip at room temperature. Two auxiliary tanks were provided to allow continuous overflow rinsing.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.

[0049] (Example 1) ⁵⁹ Fe SC-1 solution was added to the iron chloride so is 1 ppb (aqueous ammonia (2
8 wt%) 1 volume + hydrogen peroxide (30 wt%) 1 volume + water 5
When the silicon chip is dipped in a container) at 70 ° C. for 10 minutes, a contaminated sample in which Fe is adsorbed on a natural oxide film of about 10 ¹² atoms / cm ² is obtained. This radiation dose (A: cpm
Accurately) with a scintillator.

The ozone concentration in the auxiliary tank is always 1 to 2 pp.
The ozone-added water (room temperature) was poured into a quartz rinse tank containing three chips, and the overflow rinse was performed.

After the lapse of 1 minute, 3 minutes, and 10 minutes, the chips were pulled up one by one, and the respective radiation doses (B: cpm) were measured.

By obtaining B / A for each of them, the residual rate showing the cleaning efficiency can be obtained.

Next, HF was added at 1 ppm, 10 ppm, 10
The same measurement was performed by sequentially adding 0 ppm. As a comparative example, the same experiment was conducted by adding only 10 ppm of HF without adding ozone.

The experimental results are shown in FIG. It can be seen that the addition of ozone alone does not have a cleaning effect on Fe contamination, but the addition of HF significantly improves the cleaning effect, and 100 ppm of HF has the same effect as a normal cleaning agent.

(Example 2) The above silicon chip was immersed in a fluorinated ammonium buffered hydrofluoric acid solution containing the above copper acetate so that ⁶⁴ Cu became 3 ppb at room temperature for 10 minutes, and after standing for 24 hours, SC-2 solution ( Immersion in hydrochloric acid (37% by weight) + hydrogen peroxide (30% by weight 1 volume + water 5 volumes) at 70 ° C for 10 minutes resulted in about 10 ¹² att of Cu with a natural oxide film.
A contaminated sample adsorbed by oms / cm ² is obtained.

The same experiment as in Example 1 was conducted on this sample.

The experimental results are shown in FIG. It can be seen that the cleaning effect is remarkably improved by adding ozone and HF to Cu. Moreover, the cleaning effect reaches a considerable level in about 3 minutes. Therefore, if the remaining 7 minutes is changed to the flow of ultrapure water, even a slight amount of water containing hydrofluoric acid does not remain in the cleaning system, and thus the problem of rusting can be avoided.
In actual use, the concentration of hydrofluoric acid in the rinse solution does not need to be constant. For example, 100 for a short time
The concentration may be increased to 0 ppm, and in short, if the average concentration is within a predetermined range, the purpose can be achieved.

(Example 3) H ¹⁸ F was added to 0.1 ppm, 1 ppm, 10 ppm, 1 of pure water added with 1 ppm of ozone.
Make a sample added with 00ppm, SC-1 for each
A silicon chip treated with (the same composition as in Example 1) to make the surface hydrophilic was immersed at room temperature for 10 minutes, and the amount of ¹⁸ F adsorbed on the silicon surface at that time was measured by radioactive measurement.
The result is shown in FIG. HF in rinse solution is 100pp
Adsorption is 10 ¹³ a when the silicon surface is hydrophilic even at m
It can be seen that there is no problem, since it is below toms / cm ² . In addition, although the example using the silicon chip as the sample has been described in the above examples, the cleaning effect on the natural oxide film by the rinse liquid made of ultrapure water to which ozone and hydrofluoric acid are added in the present invention is The etching effect of hydrofluoric acid is significantly improved by the addition of ozone, the hydrophilicity of the natural oxide film itself is significantly increased, and the rinse liquid is soaked into the natural oxide film that has a rough crystal structure, and the impurities in the film are leached well. Therefore, the present invention can be applied to the cleaning of not only the silicon surface but also the surface of a thermal oxide film, a CVD oxide film, another crystalline silicon film, and the like.

[0059]

The combination of the cleaning with the cleaning liquid containing hydrogen peroxide according to the present invention and the rinse with the rinse liquid consisting of ozone and hydrofluoric acid-added ultrapure water is required in the semiconductor process. Metal adhesion level 10 ⁹ at
Since it is possible to achieve oms / cm ² and has the ability to remove both ozone and hydrofluoric acid against microorganisms and organic substances, there is an effect that the number of remaining fine particles can be further reduced. Further, there is an effect that the cleaning process is simplified and the productivity is remarkably improved.

[Brief description of drawings]

FIG. 1 shows the relationship between the rinsing time at HF 0 to 100 ppm and the Fe residual ratio after rinsing when ozone is not added (H
F represented by 10 ppm).

FIG. 2 shows the relationship between the rinsing time at HF 0 to 100 ppm and the Cu residual rate after rinsing when ozone is not added (H
F represented by 10 ppm).

FIG. 3 is a diagram showing a relationship between a rinsing time at HF 0.1 to 100 ppm and adsorption of F atoms on a silicon surface after rinsing.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C11D 7:18 7:06) (C11D 7/60 7:18 7:08) (72) Inventor Yoshiharu Ota Kanagawa 2-9-8 Okada, Atsugi-shi, Japan Nomura Micro Science Co., Ltd. (72) Inventor Yuji Fukasawa 1 Komukai-Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (4)

[Claims] 1. Washing with a washing liquid containing hydrogen peroxide,
Next, a method of cleaning a silicon wafer, which comprises a step of rinsing the formed natural oxide film with a rinse liquid composed of ultrapure water containing ozone and hydrofluoric acid at concentrations that do not completely dissolve it. 2. The method for cleaning a silicon wafer according to claim 1, wherein the cleaning liquid contains (a) hydrogen peroxide and alkali, and (b) hydrogen peroxide and acid. 3. The method for cleaning a silicon wafer according to claim 1, wherein the step further includes a cleaning step with ultrapure water. 4. The average concentration of ozone in the rinse liquid is 0.5 to 10 ppm, and the average concentration of hydrofluoric acid is 1 to 1
It is 00 ppm, The cleaning method of the silicon wafer of Claim 1 characterized by the above-mentioned.