JP2003218085A - Cleaning method of semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method for a semiconductor substrate for preventing fluorine from remaining on a substrate surface, after the cleaning treatment of the semiconductor substrate and for preventing particles from adhering, even in a cleaning method of the semiconductor substrate using a cleaning liquid of fluorine-ozone water. <P>SOLUTION: Even the cleaning method for cleaning the semiconductor substrate by a chemical liquid comprises a first cleaning process for cleaning the semiconductor substrate by a mixed solution containing fluorine-ozone water in a composition for preventing fluorine from remaining, and a second cleaning process for cleaning the semiconductor substrate by the ozone water in a composition for successively making the surface of the semiconductor substrate hydrophilic. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate cleaning method.

[0002]

2. Description of the Related Art It is widely known that particles (dust) and metals adhering to the surface of a semiconductor substrate cause wiring failure and electrical characteristic deterioration in the semiconductor manufacturing process. Therefore, conventionally, chemical cleaning for removing these contaminants has been frequently used.

As typical chemicals, ammonia-hydrogen peroxide mixture (APM), hydrochloric acid-hydrogen peroxide mixture (HPM), sulfuric acid-hydrogen peroxide mixture (SPM), dilute hydrofluoric acid solution. (DHF) and the like. Further, recently, new chemical solutions such as hydrofluoric acid-hydrogen peroxide water mixed solution (FPM) and hydrofluoric acid (HF) -ozone water are being used.

Then, in order to remove organic substances, particles, impurity metals, oxide films, etc. on the surface of the semiconductor substrate, the semiconductor substrate surface is cleaned by a cleaning step in which these chemicals are combined to obtain a semiconductor having a target cleanliness. Getting the board.

As a typical conventional method relating to the acid cleaning technique, for example, (a) Japanese Patent Application Laid-Open No. 58-30135 discloses a mixed solution of hydrofluoric acid, sulfuric acid and hydrogen peroxide, and (b) Japanese Patent Application Laid-Open No. Hei 5 (1999). -100320, a combination of a mixed aqueous solution of ammonia and hydrogen peroxide and a mixed aqueous solution of hydrochloric acid and hydrogen peroxide, (c) Japanese Patent Laid-Open No. 3-273629 discloses a mixed solution of hydrochloric acid and hydrogen peroxide, (d) ) JP-A-4-177725
JP-A-4-234008, a method of using a solution containing a strong acid and a very small amount of a fluorine-containing compound, and (f) ) 0.5% hydrofluoric acid and 0.1-1
% Aqueous solution of hydrogen peroxide at room temperature (for example, "Tribologist" Vol. 37, No. 3, 199).
2 years, pages 218-224) are known. Also,
(G) A cleaning method in which ozone gas is supplied to a hydrofluoric acid solution described in JP-A-7-6993, and (h) JP-A-8-4588.
JP-A-10-98018 discloses a cleaning liquid in which ozone gas is directly dissolved to a saturated solubility in a hydrofluoric acid solution.
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a cleaning method using hydrofluoric acid-ozone water. (J) Further, Japanese Patent Laid-Open No. 8-250460 discloses a treatment method in which the etching rate of silicon and that of oxide film are made equal by using hydrofluoric acid-ozone water.

The cleaning solution of the invention of (a) is one for simultaneously performing a degreasing process, a heavy metal removing process, and an etching (removing a grinding layer) process on a semiconductor wafer which is an object to be processed,
It is not intended to suppress the adhesion of fine particles that occur during cleaning.

In the invention (e), 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 concentrations are all 88.9% by mass.

The invention (g) is characterized in that ozone gas is supplied into the hydrofluoric acid aqueous solution for processing.
Neither hydrofluoric acid concentration nor ozone concentration is specified, and it is stated in the specification that the substance is not contaminated by a natural oxide film or the like. Further, it is characterized by having a high decontamination capability for metals having a smaller ionization tendency than silicon, particularly copper.

The invention (h) is characterized in that it is a cleaning liquid in which ozone gas is directly dissolved to a saturated solubility in a hydrofluoric acid solution. Dissolving ozone to saturation solubility is very time consuming and costly. Further, in order to dissolve to the saturated solubility, ozone gas or the like must be directly dissolved as described in the specification.

In the invention of (i) above, the composition of hydrofluoric acid-ozone is specified so that the surface of the wafer after processing becomes hydrophilic, but with this composition, fluorine remains on the surface of the wafer.

In the invention of (j) above, there is shown a method in which after the hydrofluoric acid-ozone water treatment, ozone water is introduced and replaced in the same tank. In this method, the wafer is made hydrophilic. A hydrofluoric acid-ozone composition that becomes hydrophilic is inevitably formed and fluorine remains.

Of these chemicals, hydrofluoric acid has the ability to dissolve and remove the silicon oxide film, and it is possible to completely remove the impurity metal contained in the oxide film. However, among the impurity metals, a metal such as copper having a high redox potential has a problem that even if it is once removed with hydrofluoric acid, it is likely to be redeposited on the surface of the semiconductor substrate. To solve this problem, by making the redox potential of the cleaning liquid higher than the redox potential of the impurity metal, reattachment of the impurity metal to the semiconductor substrate can be prevented. To increase the redox potential of the cleaning liquid, it is effective to add a water-soluble oxidizing agent.
As the oxidizer, ozone is attracting attention because it can provide a high addition effect even at a small amount at room temperature. Then, as the development of an ozone water production apparatus capable of producing clean ozone water progresses, studies using a cleaning solution of hydrofluoric acid-ozone water for cleaning a semiconductor substrate have become widespread.

In such cleaning with hydrofluoric acid-ozone water,
By combining the concentration of hydrofluoric acid and the concentration of ozone, it is possible to control the surface state of the semiconductor substrate after the cleaning treatment to be hydrophilic or hydrophobic. Specifically, when a silicon wafer is used as a semiconductor substrate, if the hydrofluoric acid concentration is lowered or the ozone concentration is raised, an oxide film is formed on the surface of the silicon wafer after cleaning, and the surface state becomes hydrophilic. Tends to become. On the contrary, when the concentration of hydrofluoric acid is increased or the concentration of ozone is decreased, the oxide film is easily removed, and the state of the surface of the silicon wafer after cleaning tends to be hydrophobic. When the surface of the silicon wafer after the hydrofluoric acid-ozone water cleaning treatment becomes hydrophobic, the subsequent rinsing step, drying step,
Particles are easily attached to the particles during the transportation process and the storage process. Therefore, in the cleaning solution of hydrofluoric acid-ozone water,
The concentration composition that makes the surface state of the silicon wafer after the cleaning treatment hydrophilic is generally used from the viewpoint of preventing particle adhesion.

[0014]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
For the cleaning solution of ozone water, it is desirable to use a cleaning solution having a concentration composition in which the surface state of the semiconductor substrate after the cleaning treatment becomes hydrophilic, but the surface of the semiconductor substrate finished to a hydrophilic surface with a cleaning solution of hydrofluoric acid-ozone water. Has a problem that fluorine remains. Similar to the problem that residual chloride ions react with residual ammonium ions in the atmosphere in the storage container to deposit as ammonium chloride on the semiconductor substrate, fluorine remaining on the surface of the semiconductor substrate becomes ammonium fluoride as the semiconductor substrate. Fluorine may be deposited on the surface of the semiconductor substrate and may cause generation of particles. Therefore, it is necessary to prevent fluorine from remaining on the surface of the semiconductor substrate.

On the other hand, in the cleaning solution composition of hydrofluoric acid-ozone water in which the surface of the semiconductor substrate is hydrophobic, there is a problem that particles are likely to adhere, as described above.

Therefore, even if the present invention is a method of cleaning a semiconductor substrate using a cleaning solution of hydrofluoric acid-ozone water, the above-mentioned problems do not occur. It is an object of the present invention to provide a method for cleaning a semiconductor substrate, in which particles do not remain and the adhesion of particles can be prevented.

[0017]

The present inventors systematically studied cleaning of semiconductor substrates using a cleaning solution of hydrofluoric acid-ozone water in which hydrofluoric acid concentration and ozone concentration were changed, and As a result of investigating the relationship of residual fluorine on the substrate surface,
Hydrofluoric acid that makes the semiconductor substrate surface hydrophobic-With a cleaning liquid composition of ozone water, it is found that there is a range where fluorine does not remain on the semiconductor substrate surface, and if the hydrophobic surface without residual fluorine is made hydrophilic, We found that particles could not be attached and a clean surface condition could be maintained,
The present invention has been completed.

That is, the gist of the present invention is (1) a cleaning method for cleaning a semiconductor substrate with a chemical solution, wherein the semiconductor substrate is a mixed solution containing hydrofluoric acid and ozone water having a composition such that fluorine does not remain on the surface of the semiconductor substrate. A cleaning step for cleaning the semiconductor substrate, and a second cleaning step for cleaning the semiconductor substrate with an oxidizing solution having a composition that makes the surface of the semiconductor substrate hydrophilic. (2) The second cleaning step is a step of immersing the semiconductor substrate in the oxidizing solution, supplying pure water thereto, and replacing the oxidizing solution with pure water without taking out the semiconductor substrate. The method of cleaning a semiconductor substrate according to (1), (3) the supply of pure water is
The method for cleaning a semiconductor substrate according to (2), which is started within 10 seconds after the semiconductor substrate is immersed in an oxidizing solution, and (4) the second cleaning step is after the semiconductor substrate is immersed in pure water. The method for cleaning a semiconductor substrate according to (1), which is a step of supplying an oxidizing solution and replacing pure water with the oxidizing solution without removing the semiconductor substrate, and (5) supplying the oxidizing solution. The method for cleaning a semiconductor substrate according to (4), which is started within 10 seconds after immersing the semiconductor substrate in pure water, (6)
The method for cleaning a semiconductor substrate according to any one of (1) to (5), wherein the oxidizing solution in the second cleaning step is a solution containing at least one of ozone water and hydrogen peroxide water. 7) The oxidizing solution in the second cleaning step is a solution containing ozone water, and the concentration of the ozone water is 1 p
The method for cleaning a semiconductor substrate according to any one of (1) to (5), wherein the hydrofluoric acid-ozone water in the first cleaning step is 0.1 to 1.0 mass. % Of hydrofluoric acid and ozone satisfying the following conditional expression (1)
A method of cleaning a semiconductor substrate according to

[0019]

[Equation 2]

(9) The method for cleaning a semiconductor substrate according to any one of (1) to (8), wherein the semiconductor substrate is a silicon wafer.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The present invention is a cleaning method for cleaning a semiconductor substrate with a chemical solution, which comprises a first treatment step of cleaning with hydrofluoric acid-ozone water having a composition that does not leave fluorine, and subsequent cleaning with ozone water that becomes hydrophilic. And a second processing step for cleaning the semiconductor substrate. Here, the cleaning tanks used in the first processing step and the second processing step need to be independent cleaning tanks. This is because when the cleaning tank containing the hydrofluoric acid-ozone water in the first treatment step is replaced by supplying the ozone water used in the second treatment step, the supply of ozone water dilutes the hydrofluoric acid. As the ozone becomes thicker with it, as will be described in detail below, during the replacement of hydrofluoric acid-ozone water with ozone water, hydrofluoric acid-ozone water having a concentration composition that forms a hydrophilic surface ends up being formed. This is because the fluorine in the liquid adheres to the surface of the semiconductor substrate which has been made hydrophilic. Further, even when the hydrofluoric acid-ozone water is drained from the cleaning tank and then the ozone water is poured, the hydrofluoric acid unavoidably remains in the cleaning tank to form a hydrophilic surface. Are generated, and the adhesion of fluorine to the semiconductor substrate cannot be prevented.

For example, the above (j) JP-A-8-25046.
In JP-A-0, no consideration is given to whether the surface of the wafer is hydrophilic or hydrophobic, and since the wafers are all treated in a single tank, the liquid composition that makes the wafer hydrophilic is Inevitably formed, fluorine remains.

The hydrofluoric acid used in the first cleaning step is 0.1-0.1%.
It is necessary that the concentration range is 1.0% by mass. When the concentration of hydrofluoric acid is less than 0.1% by mass, the components of the acidic solution are too dilute, so the ability to dissolve the oxide film on the surface of the semiconductor substrate and the ability to remove metals are reduced, and the waiting time during and between cleanings (holding time) In addition, the fluctuation of the hydrofluoric acid concentration becomes large, which is not preferable. On the other hand, if it exceeds 1.0 mass%, the etching force of the surface of the semiconductor substrate due to hydrofluoric acid becomes too strong, which causes problems such as surface roughness of the surface of the semiconductor substrate, which is not preferable.

Further, ozone in the first cleaning step needs to be in a concentration range that satisfies the following expression (1).

[0026]

[Equation 3]

When the ozone concentration is less than 0.1 ppm, the ability to form an oxide film is lowered and the adhesion of metal is increased, which is not preferable. In particular, when the oxide film formation decreases and the cleaning time becomes long, copper or the like having a high redox potential redeposits on the surface of the semiconductor substrate. In addition, ozone concentration (pp
When m) exceeds 900 × [hydrofluoric acid concentration (mass%)] ² , fluorine remains on the surface of the semiconductor substrate, which is not preferable.
FIG. 1 is an example of the result of investigating the residual state of fluorine on the wafer surface when a silicon wafer was immersed in hydrofluoric acid-ozone water of various concentrations. The circles show the wafer surface with no residual fluorine, and the circles show the wafer surface with no residual fluorine.
Shown respectively. The cleaning test method and the fluorine determination method for evaluating the residual amount of fluorine used in this investigation will be described in detail in Examples. The boundary line shown in FIG. 1 is [ozone concentration (ppm)] = 900 × [hydrofluoric acid concentration (mass%)] ² , and the state of the semiconductor substrate surface in hydrofluoric acid-ozone water is hydrophobic and hydrophilic. It corresponds to the area that changes to. From this, when the oxide film that becomes hydrophilic is formed, the fluorine in the solution is taken into the oxide film,
It is presumed that fluorine remains on the surface of the semiconductor substrate.

The washing temperature in the first washing step is not particularly limited, but is preferably 10 to 30 ° C. If the cleaning temperature is lowered too much, the cleaning efficiency may decrease. On the other hand, if the cleaning temperature is too high, the cleaning efficiency is improved, but the dissolved concentration of ozone may not be secured.

The washing time in the first washing step is not particularly limited, but is preferably 1 to 10 minutes. If the cleaning time is too short, there is a possibility that the cleaning ability will not be fully exerted. On the other hand, if the cleaning time is too long, the cleaning ability is improved, but the etching amount may be too large.

The solution pH in the first washing step is not particularly limited, but within the concentration range specified in the present invention.
It is about 3 to 7. However, there is a possibility that the metal removing ability can be further enhanced by adding a strong acid such as hydrochloric acid, nitric acid or sulfuric acid to further lower the pH and increase the acidity. In addition, weak acids such as phosphoric acid and carbonic acid, and oxalic acid,
The cleaning ability may be improved by adding an organic acid such as citric acid.

Note that these additional conditions such as temperature, washing time, pH, additives, etc. vary due to various factors and cannot be determined unconditionally.

Next, the cleaning liquid in the second cleaning step is
An oxidizing solution that can make the hydrophobic surface of the semiconductor substrate hydrophilic after the first cleaning step is used. The oxidizing solution preferably contains at least one of ozone water and hydrogen peroxide water, and ozone water is particularly preferable.

The case where ozone water is used in the second cleaning step will be described in more detail below.

The dissolved ozone concentration in the second cleaning step needs to be in the concentration range of 1 ppm or more.
If the ozone concentration is less than 1 ppm, the ability to form an oxide film is insufficient, so that the surface of the semiconductor substrate cannot be made sufficiently hydrophilic, particles adhere to the surface of the semiconductor substrate, or water marks are generated during drying, and the surface is It deteriorates the quality. The upper limit of the dissolved ozone concentration is not particularly limited, but it is preferably 50 ppm or less. That is, when the concentration exceeds 50 ppm, a huge device is required to dissolve a large amount of ozone, and it takes time to produce ozone water. More preferable ozone concentration is 3 to 30 ppm, and further preferable concentration is 5 to 20 ppm.
It is ppm.

The treatment time of the second cleaning step is not particularly specified, but is preferably 10 seconds to 5 minutes. If it is less than 10 seconds, the ability to form a sufficient oxide film on the wafer surface is poor. Further, even if it is continued for longer than 5 minutes, the effect of making the surface of the wafer hydrophilic and the removal of fluorine are not enhanced, so that it is preferably within 5 minutes in consideration of the throughput of the cleaning step.

Regarding the processing time of the second cleaning process, the chemical composition of the first cleaning process, the dissolved ozone concentration of the second cleaning process, the ozone water supplied in the second cleaning process, and the ultrapure water. The optimum processing time range fluctuates depending on the flow rate, and therefore cannot be determined unconditionally.

By the way, it is important that the hydrofluoric acid-ozone water used in the first cleaning step is not brought into the second cleaning step and accumulated therein. That is, it is desirable that the concentration of hydrofluoric acid in the second cleaning step be suppressed to 10 ppm or less. If hydrofluoric acid is present in the second cleaning step in excess of this concentration, as described above, it tends to be incorporated into the oxide film as fluorine when the oxide film is formed by ozone on the semiconductor substrate surface, which is not preferable.

Therefore, in order to prevent the chemical solution from being brought into the second cleaning step from the first cleaning step, the shape of the substrate holder or the transfer jig for transferring the semiconductor substrate is devised so that the liquid cannot be accumulated. It is essential to However, such as when the chemical liquid attached to the semiconductor substrate itself is brought in,
Since there is a limit to the carry-in of chemicals only with the above device,
It is important to take additional measures to prevent the concentration due to the accumulation of hydrofluoric acid in the second washing step.

There are the following three methods for hydrophilicizing a semiconductor substrate with ozone water in the second cleaning step. (A) a method of immersing a semiconductor substrate in ozone water and then supplying the ozone water to replace the cleaning liquid without taking out the semiconductor substrate; (b) immersing the semiconductor substrate in the ozone water and then supplying pure water, A method of replacing ozone water with pure water without taking out the semiconductor substrate, (c) A method of immersing the semiconductor substrate in pure water, supplying ozone water, and replacing pure water with ozone water without taking out the semiconductor substrate Is.

The method (a) of immersing the semiconductor substrate in the ozone water and then supplying the ozone water is most effective for making the surface of the semiconductor substrate hydrophilic, that is, sufficiently forming an oxide film. When the amount of chemical liquid brought in from the first cleaning step increases, fluorine may remain.

When fluorine remains by the method (a), it is desirable to adopt the method (b) of immersing the semiconductor substrate in the ozone water and then supplying pure water. this is,
This is because the adhesion of fluorine can be suppressed by shortening the time of contact with ozone water. It is desirable to supply ozone water before the pure water is supplied.
It is not particularly limited. The time from the immersion of the semiconductor substrate in ozone water to the start of the supply of pure water is preferably 10 seconds or less. This is because if the time to start the supply of pure water is too long, it may not be possible to sufficiently suppress the adhesion of fluorine. However, the optimum time for starting the supply of pure water differs depending on the carry-in amount of the chemical solution from the first cleaning step and the concentration of the ozone water to be immersed, and therefore the optimum value cannot be unconditionally determined.

After immersing the semiconductor substrate in pure water (c),
The method of supplying ozone water can further reduce the amount of residual fluorine. The time from the immersion of the semiconductor substrate in pure water to the start of the supply of ozone water is preferably within 10 seconds. By delaying the start of ozone water supply, the residual amount of fluorine can be suppressed to a low level, but if the semiconductor substrate surface is hydrophobic and immersed in pure water for a long time, particle adhesion will increase. . Pure water may or may not be supplied before the supply of ozone water. When pure water is supplied during the time until ozone water is supplied, the residual amount of fluorine becomes lower, but the possibility of particle adhesion also increases. On the other hand, if pure water is not supplied before the supply of ozone water, the possibility of particles adhering decreases, but there is a slight disadvantage with respect to residual fluorine.

Regarding the method of replacing the liquid in the tank in the second cleaning step, the residual amount of fluorine is reduced to the utmost limit, the amount of adhering particles is reduced to the utmost limit, or a condition that balances the two is adopted, It may be determined according to the purpose of.

Other cleaning processes (APM, HPM, SPM, DHF, FPM, etc.) may be incorporated before the cleaning step of the present invention. In particular, the inclusion of a process having a high particle removal capability is effective because the work load on particles in the cleaning method of the present invention can be reduced. Also,
A rinse step may be incorporated in the latter stage.

The present process can be applied to all semiconductor substrates, but its action and effect are excellent especially for silicon wafers.

[0046]

EXAMPLES (Example 1) A method for evaluating the fluorine adhesion to the wafer surface by cleaning with an HF / ozone composition range in which no fluorine remains will be described. After immersing a clean silicon wafer in the first cleaning tank containing the hydrofluoric acid-ozone cleaning solution prepared in various compositions for 5 minutes, it was immersed in the 5 ppm ozone water prepared in the second tank, and immediately immersed in ultrapure water for 5 minutes. A water overflow rinse was performed. The rinsed wafer was dried with a spin dryer. The wafer after this treatment was sealed in a bag together with 50 ml of ultrapure water, and was placed in a water bath at 95 to 100 ° C. for 3 days.
The wafer was kept for 0 minute to extract the fluorine remaining on the wafer. With this method, both sides of the silicon wafer (mirror side and back side)
Fluorine remaining on the surface will be extracted. The concentration of fluorine contained in this extract was analyzed by an ion chromatograph analyzer. The lower limit of fluorine determination for this method is 1
× 10 ¹² atoms / cm ² .

A hydrofluoric acid-ozone cleaning solution having a different composition was prepared in the range of hydrofluoric acid concentration of 0.01 to 0.5 mass% and ozone concentration of 2.5 to 30 ppm, and the solution was placed in the first cleaning tank and the above-mentioned solution was prepared. Treated and evaluated. The result is shown in FIG.

Specified with the hydrofluoric acid-ozone cleaning solution of the present invention,

[0049]

[Equation 4]

In the range satisfying the conditional expression of, the residual fluorine concentration was 2 × 10 ¹² atoms / cm ² or less (FIG. 1).
(○ mark). On the other hand, in the region where this conditional expression is not satisfied, the residual fluorine concentration is 50 × 10 ¹² atoms / cm 3.
It became ² or more (marked with ● in Fig. 1).

Differences in wafer surface properties between the case of treatment with a cleaning solution of hydrofluoric acid-ozone composition in which fluorine remains and the case of treatment with a cleaning solution of hydrofluoric acid-ozone composition in which fluorine does not remain are as follows. I verified it by such a method. After treating with a hydrofluoric acid-ozone cleaning solution of each composition, overflow rinse was performed for 5 minutes only with ultrapure water containing no ozone, and the contact angle between the mirror surface of the wafer dried by a spin dryer and the water droplet was measured. As a result, the hydrofluoric acid-ozone cleaning solution of the present invention was defined,

[0052]

[Equation 5]

In the range satisfying the conditional expression of, the contact angle is 20
Was ~ 30 °. On the other hand, in the range where this conditional expression was not satisfied, the contact angle was 0 to 4 °. From this result, it can be inferred that the residual fluorine is related to the contact angle between the wafer surface and water, that is, the state of the oxide film on the wafer surface, such as the thickness and density of the oxide film.

Immediately after the wafer was subjected to the first cleaning treatment with the hydrofluoric acid-ozone cleaning solution having the various compositions described above, and subsequently, ozone water having a concentration of 10 ppm was put in the second cleaning tank and the wafer was immersed in the ozone water. Ultrapure water was introduced into the above, and after performing an overflow rinse for 3 minutes, an ultrapure water rinse was performed and the product was dried with a spin dryer. As a result, no change was found in the residual fluorine concentration on the wafer surface before and after cleaning with ozone water.

(Example 2) A method for evaluating the ability to remove contaminant metals on the surface of impurities metal removal ability will be described. APM in which the volume ratio of ammonia water with a concentration of 29%, hydrogen peroxide water with a concentration of 31%, and pure water is set to 1: 1: 5.
After further mixing iron and copper as impurities in the cleaning liquid,
The clean silicon wafer was immersed at 80 ° C. for 5 minutes. Then, after rinsing in pure water for 5 minutes to confirm the hydrophilicity of the surface, it was dried with a spin dryer. Hereinafter, this method is referred to as IAP contamination. Due to the IAP contamination, heavy metal impurities in the cleaning liquid adhere to the surface of the wafer to contaminate the surface. Flameless atomic absorption spectrometry was used for the evaluation of the amount of metal polluting the surface. Contaminant metals on the wafer surface were recovered with a mixed acid of hydrofluoric acid and nitric acid, and the metal concentration in the recovered liquid was quantified by flameless atomic absorption spectrometry and converted into the surface contaminant concentration.

The metal concentration adhered to the wafer surface by the IAP contamination treatment was 3 × 10 ¹¹ atoms / cm ^{2 of} Fe,
Cu was at a level of 6 × 10 ¹¹ atoms / cm ² .

The IAP-contaminated wafers thus produced were prepared using different hydrofluoric acid concentrations and ozone concentrations.
After cleaning with the ozone cleaning liquid, the amount of metal remaining on the wafer surface was compared. The amount of metal remaining on the wafer surface is
It was analyzed by the frameless atomic absorption spectrometry method described above. In addition,
The lower limit of quantification of metals by this method is that Fe is 2 × 10 ⁸ a
toms / cm ² , Cu is 1 × 10 ⁹ atoms / cm ^2.
Is.

Specifically, after immersing in the hydrofluoric acid-ozone cleaning solution prepared in the first tank for 5 minutes, 5 p prepared in the second tank
Immersed in pm ozone water and immediately subjected to ultrapure water overflow rinse for 5 minutes. The rinsed wafer was dried with a spin dryer.

The composition of hydrofluoric acid-ozone subjected to the cleaning test is as follows: hydrofluoric acid concentration of 0.05 to 1% by mass, ozone concentration of 0 to 3
It is in the range of 0 ppm. After cleaning the IAP-contaminated wafer with a hydrofluoric acid-ozone cleaning solution of each composition, the results of analyzing the amount of metal adhering to the wafer surface with a flameless atomic absorption spectrometer are shown in FIGS. 2 and 3.

As shown in FIG. 2, the ozone concentration is 0 ppm.
Dilute hydrofluoric acid of 10 ¹¹ atoms irrespective of the hydrofluoric acid concentration
/ Cm ² level Cu remains, but ozone concentration is 1
At 0 ppm or more, if the hydrofluoric acid concentration is 0.1% by mass or more, the detection limit of the analyzer is 1 × 10 ⁹ atom.
It can be seen that s / cm ² or less is removed.

As shown in FIG. 3, with respect to Fe as well, in the case of dilute hydrofluoric acid having 0 ppm ozone, 10 ¹⁰ atoms / cm ² level of Fe remains regardless of the hydrofluoric acid concentration, but the ozone concentration is 10 ppm or more. In the case of a hydrofluoric acid concentration of 0.1 mass% or more, it is removed up to a level of 10 ⁹ atoms / cm ² , and in the hydrofluoric acid-ozone composition range defined by the present invention, the removal ability is particularly high and the contamination metal It was found that the residual concentration can be set to 10 ⁹ atoms / cm ² level or less.

Further, the above IAP-contaminated wafer was subjected to a first cleaning treatment with a hydrofluoric acid-ozone cleaning solution having various compositions, and subsequently, ozone water having a concentration of 10 ppm was put into a second cleaning tank, and the wafer was immersed in the ozone water. Immediately after that, ultrapure water was introduced, overflow rinse was performed for 3 minutes, ultrapure water rinse was performed, and the product was dried with a spin dryer. As a result, no change was found in the residual metal concentration on the wafer surface before and after cleaning with ozone water.

Example 3 Effect of Ozone Concentration in Rinse Step (Particle Removal Ability) A clean p-type 8 inch (200 mm) wafer was used in the cleaning test. APM cleaning and ultrapure water rinsing were performed, followed by hydrofluoric acid-ozone cleaning in the first cleaning step, ozone water cleaning in the second cleaning step, and then ultrapure water rinsing and spin drying. The hydrofluoric acid-ozone cleaning liquid in the first cleaning step is selected from the hydrofluoric acid-ozone composition range specified in the present invention, and has a hydrofluoric acid concentration of 0.3 to 1.0 mass% and an ozone concentration of 10 to 20 ppm. It was used. Second
The concentration of the ozone water in the cleaning step was changed from 0 to 20 ppm, and ultrapure water was introduced immediately after being immersed in the ozone water of each concentration and overflowed for 3 minutes. A surface foreign matter meter (laser light scattering method) was used to measure the number of particles adhering to the wafer surface. FIG. 4 shows the difference in the number of particles increased depending on the ozone concentration in the second cleaning step.

When the ozone water concentration in the second cleaning step was less than 1 ppm, the number of particles of 0.28 μmφ or more increased by several hundreds. Since the hydrophilicity of the wafer surface (that is, the growth of the oxide film) due to the cleaning with ozone water is insufficient, it is considered that a large amount of particles adhered in the subsequent drying process, transporting process and the like. In contrast, ozone water concentration is 1p
If it is set to pm or more, increase in the number of particles of 0.28 μmφ or more is 3 or less per wafer, and the average number of increase is 1.7 /
It can be suppressed to a wafer. It is considered that, by increasing the concentration of ozone water, the surface of the wafer was made hydrophilic, that is, the oxide film was sufficiently grown, so that particle adhesion could be prevented in the subsequent steps. By the way, AP
In the wafer subjected to only M cleaning, the increase in the number of particles of 0.28 μmφ or more can be suppressed to 3 or less, and the average increase in number is 1.7, but metal contamination cannot be prevented.

After the first cleaning step of the present invention, the residual fluorine concentration is 2% in any concentration of ozone water cleaning.
It was less than or equal to × 10 ¹² atoms / cm ² . From this, it was found that the concentration of ozone water did not affect the residual fluoride.

[0066]

According to the cleaning method of the present invention, in the production of semiconductor substrates, particularly silicon wafers, it is possible to remove metal contamination, prevent particles from adhering, and ensure the hydrophilicity of the surface. It can contribute to the development of the semiconductor industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a hydrofluoric acid concentration and an ozone concentration of a cleaning liquid in a first cleaning step of the present invention and a residual state of fluorine on a wafer surface after processing.

FIG. 2 is a diagram showing a hydrofluoric acid concentration and an ozone concentration of a cleaning liquid and an analysis value of Cu remaining on a wafer surface after processing in a first cleaning step of the present invention.

FIG. 3 is a diagram showing a hydrofluoric acid concentration and an ozone concentration of a cleaning liquid and an analysis value of Fe remaining on a wafer surface after processing in a first cleaning step of the present invention.

FIG. 4 is a diagram showing the relationship between the ozone concentration in the second cleaning step and the increase / decrease of particles before and after the processing in the wafer which has undergone the first cleaning step of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Uemura             3434 Shimada, Waka, Hikari City, Yamaguchi Prefecture             NSC Co., Ltd. F-term (reference) 4H003 BA12 DA15 DB01 EA05 EA20                       ED02 EE04 FA21

Claims (9)

[Claims] 1. A cleaning method for cleaning a semiconductor substrate with a chemical solution, comprising a first cleaning step of cleaning the semiconductor substrate with a mixed solution containing hydrofluoric acid-ozone water having a composition in which fluorine does not remain on the surface of the semiconductor substrate. A second step of subsequently cleaning the semiconductor substrate with an oxidizing solution having a composition that makes the surface of the semiconductor substrate hydrophilic
And a cleaning step for cleaning the semiconductor substrate. 2. The second cleaning step is a step of immersing the semiconductor substrate in the oxidizing solution, supplying pure water, and replacing the oxidizing solution with pure water without taking out the semiconductor substrate. The method for cleaning a semiconductor substrate according to claim 1, wherein 3. The method for cleaning a semiconductor substrate according to claim 2, wherein the supply of the pure water is started within 10 seconds after the semiconductor substrate is immersed in the oxidizing solution. 4. The second cleaning step is a step of immersing the semiconductor substrate in pure water, supplying an oxidizing solution, and replacing the pure water with the oxidizing solution without taking out the semiconductor substrate. The method of cleaning a semiconductor substrate according to claim 1. 5. The method for cleaning a semiconductor substrate according to claim 4, wherein the supply of the oxidizing solution is started within 10 seconds after the semiconductor substrate is immersed in pure water. 6. The cleaning of a semiconductor substrate according to claim 1, wherein the oxidizing solution in the second cleaning step is a solution containing at least one of ozone water and hydrogen peroxide water. Method. 7. The oxidizing solution in the second cleaning step is a solution containing ozone water, and the concentration of the ozone water is 1
The method for cleaning a semiconductor substrate according to any one of claims 1 to 5, which has a ppm or more. 8. The composition according to claim 1, wherein the hydrofluoric acid-ozone water in the first cleaning step contains 0.1 to 1.0% by mass of hydrofluoric acid and ozone satisfying the following conditional expression. Semiconductor substrate cleaning method. [Equation 1] 9. The method of cleaning a semiconductor substrate according to claim 1, wherein the semiconductor substrate is a silicon wafer.