JPH0848996A - Cleaning fluid for silicon wafer and silicon oxide - Google Patents

Abstract

PURPOSE:To obtain a high-precision product in the production of a silicon semiconductor or a semiconductor device. CONSTITUTION:This cleaning fluid, which is significantly effective for removing a fouling metal and adherent particles, is an aqueous solution containing 0.001 to less than 1.00mol/l hydrofluoric acid and 0.05 to less than 0.25mol/l ammonium fluoride and having a pH of 1.5 to less than 7.0.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cleaning solution for silicon and silicon oxide.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, semiconductor wafers, and glass wafers, a cleaning process is performed before and after various processes. As a method for cleaning these wafers, for example, for a silicon wafer, cleaning for removing organic substances and adhered fine particles is performed by so-called SC-1 cleaning using an alkaline cleaning solution which is a mixed aqueous solution of hydrogen peroxide solution and ammonia water.

However, this cleaning solution inevitably causes contamination by trace impurities Fe, Zn, and Al in the solution, and therefore SC is required for wafers requiring removal of metal impurities.
-1 After cleaning, acid cleaning is performed.

Although the acid cleaning liquid is excellent in the ability to remove surface impurity metals, it has a drawback that suspended particles in the liquid adhere to the wafer due to cleaning. Therefore, a cleaning technique capable of removing metal contamination and having few adhered particles. Are required in the semiconductor device industry and the silicon wafer industry.

The same is true of the technology for cleaning silicon oxide such as quartz glass wafers.

As a typical conventional method relating to the acid cleaning technique, for example, a mixed solution of hydrofluoric acid, sulfuric acid and hydrogen peroxide is disclosed in JP-A-58-30135, and JP-A-2-10032.
Japanese Unexamined Patent Application Publication No. HEI 0-32242 discloses a combination of a mixed aqueous solution of ammonia and hydrogen peroxide and a mixed aqueous solution of hydrochloric acid and hydrogen peroxide.
-273629 discloses a mixture of hydrochloric acid and hydrogen peroxide, and JP-A-4-177725 discloses a combination of treating with a hydrogen peroxide solution after washing with an aqueous solution of hydrofluoric acid.
No. 8 discloses a method of using a solution containing a strong acid and a very small amount of a fluorine-containing compound, and a method of washing with 0.5% hydrofluoric acid and an aqueous solution of 0.1 to 1% hydrogen peroxide at room temperature (for example, " Tribologist "Vol. 37, No. 3, 1992 2
18-224), 0.27 to 10.3 mol /
A method called buffered hydrofluoric acid in which 1.0 to 2.7 mol / liter of hydrofluoric acid is added to less than 1 liter of ammonium fluoride (for example, IEEE TRANSACTION)
SONS EMICONDUCTOR MANUFAC
TURING, VOL. 4, NO. 1, FEBRU
ARY 1991, p26), JP-A-4-45531.
A method in which hydrogen peroxide is added to buffered hydrofluoric acid is known in the publication.

The above-mentioned ,,, and, although seemingly similar to the cleaning solution of the present invention, are not similar.

The cleaning solution of the invention described above is intended to suppress degreasing, heavy metal removal and etching (removal of a grinding layer) of a semiconductor wafer which is an object to be treated at the same time. However, the purpose of the invention and the industrial usage are different from those of the cleaning liquid of the present invention.

The etching amount of the cleaning liquid of the invention is on the order of micrometers as illustrated in the specification, but in the present invention, the etching amount is on the order of angstroms.

In the invention, the composition of the cleaning liquid is not described in the claims, but the "HF mixing ratio" in the specification is 1.5.
It is stated that the range is less than or equal to%, and "H
It is shown that the "etching amount of the semiconductor wafer" becomes zero when the "F mixture ratio" is around 0.1%.

From this, the "HF mixing ratio" is 0.1-0.1%.
It is considered to be 1.5%, and the concentration of hydrofluoric acid is clearly different from that of the cleaning solution of the present invention by an order.

According to the description in the specification, the method of the invention is "washing with a mixed solution of hydrofluoric acid, sulfuric acid and hydrogen peroxide water", and as described above, "the mixing ratio of HF" is Since it is 1.5% or less, the concentration of sulfuric acid and / or hydrogen peroxide in the cleaning liquid should be extremely high, and in this respect as well, the composition is different from that of the cleaning liquid of the present invention.

In the present invention, the main constituent of the cleaning liquid is a concentrated acid, and the typical cleaning liquid composition is shown in Table 1 of the examples.

The sulfuric acid concentration is all 88.9% by weight. On the other hand, in the present invention, as is clear from the claims and Examples, the main component of the cleaning liquid is water. Therefore, the invention differs from the present invention.

The invention is similar to the cleaning liquid of the present invention in that the cleaning liquid contains hydrofluoric acid and hydrogen peroxide, but the concentration of hydrofluoric acid is clearly different from that of the present invention.

The invention is not only different in composition from the present invention, but also does not contain ammonium fluoride. Therefore, the cleaning liquid of the present invention is completely different from the cleaning liquid of the present invention in terms of composition and action.

The invention is similar to the cleaning solution of the present invention in that the cleaning solution contains hydrofluoric acid and ammonium fluoride, but the concentrations of hydrofluoric acid and ammonium fluoride are clearly different from those of the present invention.

Further, the main purpose is etching of the oxide film, which is different from the present invention.

Like the invention, the invention is similar to the cleaning liquid of the invention in that it contains hydrofluoric acid and ammonium fluoride, but the concentrations of hydrofluoric acid and ammonium fluoride are clearly different from those of the invention.

Further, since the main purpose is etching of the oxide film, the etching rate is also large and different from the present invention.

[0021]

As described above, in the production of semiconductor devices, semiconductor wafers, and glass wafers, there is a demand for a wafer cleaning technique capable of removing metal contamination and having less adhered fine particles.

With the progress of industry, it is becoming more and more difficult to reduce the amount of metal contamination and adhered particles, and it has become impossible to achieve this target level with conventional cleaning techniques.

The object of the present invention is to provide a new high-performance cleaning solution which can significantly reduce the surface impurity metal level of the wafer and the number of adhered fine particles in such a situation.

[0024]

The cleaning solution of the present invention is 0.0
An acidic aqueous solution having a pH of 2 or more and less than 7 containing 01 mol / l to less than 1.0 mol / l hydrofluoric acid and 0.05 mol / l to less than 0.25 mol / l ammonium fluoride. It is a characteristic cleaning solution for silicon wafers and silicon oxides. By cleaning, it reduces the amount of contaminating metals in the silicon wafer that is the object to be cleaned, and provides a surface with very few adhered particles.

The acidic aqueous solution may contain, in addition to hydrofluoric acid and ammonium fluoride, one or more of acids, salts and bases, and the acid is a group consisting of phosphoric acid, sulfuric acid, nitric acid and hydrochloric acid, and the above salts. May be selected from the group consisting of ammonium salts and amine salts, and ammonia and amines as bases. Further, ozone and hydrogen peroxide may be added to the aqueous solution.

[0026]

By cleaning the silicon semiconductor with the cleaning solution of the present invention, a natural oxide film is not formed on the surface of the object to be cleaned, and a very clean surface with a small number of metal impurities and adhered fine particles can be obtained.

The washing temperature is preferably in the range of 25 to 60 ° C. The washing time is preferably in the range of several minutes to 30 minutes.

As will be apparent to those skilled in the industrial field related to the present invention, these cleaning conditions have many factors, such as cleanliness of the object to be cleaned before cleaning, surface properties, manufacturing cost, and throughput. It cannot be decided unconditionally because it is influenced by, etc.

The reason why the concentration range of hydrofluoric acid in the cleaning liquid of the present invention is 0.001 mol / liter or more and less than 1.0 mol / liter is as follows.

When the amount of hydrofluoric acid is less than 0.001 mol / liter, the recombination lifetime becomes short, that is, the removability of surface metal impurities deteriorates. When the amount of hydrofluoric acid is 1.0 mol / liter or more, the number of adhered fine particles after washing increases.
Although such an increase in the number of adhered fine particles can be suppressed to some extent by lowering the cleaning temperature, the number of adhered particles is still considerably higher than that of the cleaning liquid of the present invention.

Therefore, in order to reduce the amount of contaminating metal on the surface of the object to be cleaned by cleaning and to significantly reduce the adhesion of suspended particles in the liquid during cleaning, the concentration range of hydrofluoric acid is 0.001 mol. / Liter or more to 1.0 mol /
Must be less than liter.

Therefore, in the cleaning liquid of the present invention, the concentration range of hydrofluoric acid was set to 0.001 mol / liter or more and less than 1.0 mol / liter.

The reason for setting the concentration range of ammonium fluoride in the cleaning liquid of the present invention to 0.05 mol / liter or more and less than 0.25 mol / liter is as follows.

This is because when the amount of ammonium fluoride is 0.25 mol / liter or more, adhesion of fine particles suspended in the liquid increases, and it is economically disadvantageous to increase the concentration of ammonium fluoride.

When the amount of ammonium fluoride is less than 0.05 mol / liter, the adhesion of fine particles suspended in the liquid is suppressed, but the amount of contaminating metal on the surface of the object to be cleaned increases.

From the above, in the cleaning liquid of the present invention, the concentration range of ammonium fluoride is set to 0.05 mol / liter or more and less than 0.25 mol / liter. Ammonium fluoride may be prepared by mixing hydrofluoric acid and ammonia.

In the cleaning liquid of the present invention, the pH range is 1.
The reason why it is set to 5 or more and less than 7.0 is as follows.

Even if the concentration of hydrofluoric acid and hydrogen peroxide is in the range defined by the cleaning solution of the present invention, if the pH is less than 1, the number of adhered fine particles after cleaning will remarkably increase.

When the pH is 7 or more, the recombination lifetime becomes short and the removability of surface metal impurities deteriorates.

Therefore, in order to reduce the amount of contaminating metals on the surface of the object to be cleaned and to significantly reduce the adhesion of fine particles suspended in the liquid during cleaning, the pH range should be 1.5 to less than 7.0. There must be.

Further, even if the silicon wafer is cleaned with the cleaning liquid of the present invention, the wafer is not fogged after cleaning.

The cleaning liquid of the present invention is suitable for cleaning silicon semiconductor wafers and glass wafers, but its characteristics are not impaired by the shape of the object to be cleaned, and it can be used in any shape.

Cleaning using the cleaning liquid of the present invention may be performed in combination with other cleaning steps. Even if the object to be cleaned is shaken by ultrasonic waves during cleaning, the characteristics of the cleaning liquid of the present invention are not impaired.

It should be noted that when cleaning the silicon wafer with the cleaning solution of the present invention, side effects such as increase of surface irregularities and deterioration of electrical breakdown characteristics of the high temperature oxide film do not occur.

The cleaning liquid of the present invention may contain, in addition to the specified concentrations of hydrofluoric acid and ammonium fluoride, one or more of an acid, a salt and a base. As the acid, phosphoric acid or sulfuric acid may be used. , Nitric acid, trichloroacetic acid, dichloroacetic acid, hydrochloric acid, monochloroacetic acid, acetic acid, the salt may be selected from the group consisting of ammonium salts and amine salts, and the base may be selected from the group consisting of ammonia and amine salts.

In the examples of Table 1, phosphoric acid, sulfuric acid, nitric acid, trichloroacetic acid, cyclochloroacetic acid, hydrochloric acid, monochloroacetic acid,
The case where acetic acid, ammonium chloride, ammonium nitrate, choline chloride, ammonia, and choline were added was shown.

In either case, the amount of contaminating metal on the surface of the object to be cleaned is reduced by cleaning, adhesion of fine particles suspended in the liquid during cleaning is extremely reduced, and the hydrophobicity of the surface is maintained even after cleaning. It is clear that it will not be damaged.

As is apparent from the fact that the characteristics of the cleaning solution of the present invention are not impaired even if a large variety of acids and bases are added as described above, the acids, salts, and salts added to the cleaning solution of the present invention,
And the base is not limited to the types noted herein.

The cleaning liquid of the present invention may contain ozone in addition to the specified concentrations of hydrofluoric acid and ammonium fluoride.

By adding ozone, the ability to decompose and oxidize organic substances can be enhanced, and therefore the ability to remove metal contamination is enhanced.

Ozone may be generated by electrolyzing water, or ozone gas may be introduced into the liquid for bubbling. The ozone concentration is 1 ppm or more and 15p
pm is preferred.

Further, the cleaning liquid of the present invention maintains the characteristics of the cleaning liquid of the present invention even when hydrogen peroxide is added in addition to the specified concentrations of hydrofluoric acid and ammonium fluoride. The hydrogen peroxide concentration is preferably 0.3% by weight or more and less than 20.0% by weight.

It has been found that the cleaning liquid of the present invention differs from the conventional cleaning liquid in the following points. JP-A-3-273629
The publication describes the characteristics of a mixed solution of hydrochloric acid and hydrogen peroxide, and according to FIG. 1, the number of adhered particles (the number of adhered fine particles in the liquid after cleaning) starts to increase at pH 5 or lower,
It is remarkable at pH 3 or less.

On the other hand, in the cleaning liquid of the present invention, the adhered number of suspended fine particles in the liquid after cleaning is small even when the pH is in the range of 1.5 to less than 7.

Further, in FIG. 2 of JP-A-3-273629, it can be seen that the amount of adhered particles increases as the cleaning temperature rises, especially at 60 ° C. or higher.

Comparative Examples 7 to 8 in Table 1 described in the present invention correspond to the cleaning liquid described in JP-A-3-278629, but the number of adhered fine particles in the liquid after cleaning is 170 pieces / cm. ² or more.

On the other hand, the cleaning liquid of the present invention has a cleaning temperature of 6
Even at 0 ° C or higher, the number of adhered fine particles in liquid is very small.

From the above, it is clear that the cleaning solution of the present invention is also greatly different from the conventional cleaning solution in terms of action.

[0059]

[Example] Ammonia water having a concentration of 28%, hydrogen peroxide water having a concentration of 31%, and pure water were mixed so that a volume ratio was 1: 1: 5, and a silicon wafer or a glass wafer was immersed therein to 70 ° C. After washing for 5 minutes with water, rinsing in pure water for 5 minutes and drying with a spin dryer, a surface with few adhered particles can be obtained.

This method is called APM cleaning.
Although there are few adherent particles in PM cleaning, it is known that the impurity metal during cleaning easily adheres to the wafer surface and the concentration of impurity metal on the surface is high.
There is dilute hydrofluoric acid cleaning (referred to as DHF cleaning) in which the surface oxide film and the surface metal are removed by immersion for a minute.

The APM and DHF cleaning was carried out as a treatment before cleaning with the cleaning liquid of the present invention. Next, the cleaning liquid of the present invention was used for cleaning under the conditions shown in Table 1.

Two methods were used to evaluate the amount of surface-contaminated metal after cleaning. One is the measurement of recombination lifetime, and it can be judged that the larger this value is, the smaller the amount of contaminating metal on the surface is.

A microwave reflection type lifetime measuring device was used for the measurement, and 1000 ° C., 70
Therefore, high temperature oxidation is performed in dry oxygen to form an oxide film of about 500 Å.

Atomic absorption spectrometry was used for another evaluation of the amount of surface contaminant metals after washing. This is a method of dissolving and recovering the contaminated metal on the wafer surface with a mixed acid of hydrofluoric acid and nitric acid, and quantifying the metal concentration in the recovered liquid by atomic absorption spectrometry to convert it into the surface contaminant concentration. The lower limit of quantification of this method is about 8 × 10 ⁹ a
It is toms / cm ² .

The method for evaluating the adhesion property of the fine particles suspended in the liquid was as follows. First, after cleaning a clean wafer with APM, a silicon wafer or a glass wafer was cleaned with the cleaning liquid of the present invention under the conditions shown in Table 1.

At this time, the washing liquid contains 1.5 × 10 ⁵ pieces /
Polystyrene latex fine particles of L concentration (diameter 0.35
2 μm) is dispersed in advance.

After washing, the plate was rinsed in pure water for 2 minutes and dried with a spin dryer. Surface foreign matter meter (light scattering method) for measuring polystyrene latex particles adhering to the wafer
Was used to measure the number of adhered fine particles having a diameter of 0.33 μm or more, and converted per unit area.

Table 1 collectively shows the number of fine particles adhered by the cleaning solution of the present invention, the recombination lifetime, and the atomic absorption analysis result.

As a comparative example, Table 1 also shows the results of cleaning with a cleaning solution having a hydrofluoric acid concentration, a hydrogen peroxide concentration, and a pH different from those of the cleaning solution of the present invention, and a cleaning solution containing no hydrofluoric acid. .

The cleaning method and the evaluation method are the same as in the case of the present invention. It can be seen that the cleaning liquid of the present invention provides a surface having a low amount of contaminating metals on the surface of the silicon semiconductor and the silicon oxide after cleaning and having very little adhered fine particles in the liquid.

On the other hand, when the cleaning liquid shown in the comparative example is used, the number of adhered contaminant metals or fine particles suspended in the liquid cannot be used for the purpose of the present invention.

When the treatment with the cleaning liquid of the present invention was carried out, no oxide film was formed on the surface and all were hydrophobic.

[0073]

[Table 1]

[0074]

[Table 2]

[0075]

[Table 3]

[0076]

[Table 4]

[0077]

As described above in detail, in the production of semiconductor devices, semiconductor wafers and glass wafers, the cleaning liquid of the present invention can be used to obtain a product with less metal contamination and adhered particles.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Sachi, 1618 Ida, Nakahara-ku, Kawasaki City, Advanced Technology Research Laboratories, Nippon Steel Corporation (72) Inventor Shuji Sohei, 3434, Shimada, Hikari City, Yamaguchi Prefecture Nittetsu Denko Incorporated (72) Inventor Toyoshi Ogura 3434 Shimada, Hikari-shi, Yamaguchi Nittetsu Denshi Co., Ltd. (72) Inventor Haruki Tanaka 3434 Shimada, Hikari-shi Shin Nippon Steel Co., Ltd.

Claims (5)

[Claims] 1. The pH of an aqueous solution containing 0.001 mol / liter to less than 1.00 mol / liter hydrofluoric acid and 0.05 mol / liter to less than 0.25 mol / liter ammonium fluoride has a pH of 1. A cleaning solution for a silicon wafer and a silicon oxide, which is 5 or more and less than 7.0. 2. The acidic aqueous solution contains, in addition to hydrofluoric acid and ammonium fluoride, one or two of acids, salts and bases.
The cleaning liquid according to claim 1, containing one or more kinds. 3. The cleaning liquid according to claim 1, wherein the acid is selected from the group consisting of phosphoric acid, sulfuric acid, nitric acid and hydrochloric acid, the salt consisting of ammonium salts and amine salts, and the base consisting of ammonia and amines. 4. A cleaning liquid comprising ozone added to the aqueous solution according to claim 1. 5. A cleaning liquid comprising hydrogen peroxide added to the aqueous solution according to claim 1.