JPH1079365A - Method of washing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of washing effect with time in washing with a solution using sulfuric acid, hydrogen peroxide water and a fluorine-containing compound. SOLUTION: When a semiconductor substrate is washed with chemicals comprising sulfuric acid, hydrogen peroxide water and a fluorine-containing compound, the concentration of sulfuric acid in the chemicals is set to a concentration by which no concentration of hydrofluoric acid is altered at the degrees of the evaporation of hydrofluoric acid and water from the chemicals with the change of time. Specifically the concentration of sulfuric acid in the chemicals is set to approximately 36%. The chemicals are driven by a pump 4 and returned to a treating tank 1 through a filter 5, so that washing is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning technique for removing contamination, particles and the like in the manufacture of semiconductor devices.

[0002]

2. Description of the Related Art In recent years, the diameter of silicon wafers for forming semiconductor devices has tended to increase from 6 inches to 8 inches and 12 inches. As the size increases, the cleaning cost increases. In addition, since semiconductor devices have been highly integrated and miniaturized, a cleaning process with less adhesion of particles has been desired.

Hereinafter, an example of the above-described conventional cleaning apparatus and its method will be described with reference to the drawings.

FIG. 5 is a schematic view showing the structure of a conventional cleaning apparatus. In FIG. 5, reference numeral 14 denotes a cleaning tank, which is provided with a heating means depending on a chemical used. Reference numeral 15 denotes a washing tank in which only pure water flows. The washing tank 14 and the washing tank 15 are used as a pair, and a plurality of the washing tanks are often arranged in the order of chemical solution treatment. Numeral 16 denotes a wafer drying means, for example, spin drying, IPA vapor drying, or the like.

[0005] Using the cleaning apparatus constructed as described above, sulfuric acid, hydrogen peroxide and fluorine as disclosed in, for example, JP-A-4-234118 or JP-A-5-63701. Cleaning using a mixed solution of hydrofluoric acid is performed. The chemical solution conventionally used for cleaning is, for example, one in which the volume ratio of sulfuric acid and hydrogen peroxide is in the range of 3: 1 to 5: 1 and 0.01% of hydrofluoric acid is added.

[0006]

However, the above structure has a problem that the etching rate decreases with time and the cleaning effect is not stable. It is considered that the decrease in the etching rate is caused by evaporation of hydrofluoric acid. The present invention has been made in view of the above problems, and has as its object to provide a cleaning method in which a decrease in an etching rate is small.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a cleaning method according to the present invention provides a method for cleaning a substrate with a chemical solution containing sulfuric acid, hydrogen peroxide and a fluorine-containing compound.
The sulfuric acid concentration in the chemical solution is configured so that the degree of evaporation of hydrofluoric acid and water from the chemical solution with time changes does not cause a change in hydrofluoric acid concentration. The accompanying change in the etching rate can be minimized.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cleaning apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a cleaning apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a Teflon processing tank provided with an outer tank for circulating a chemical, 2 denotes a carrier containing a wafer to be cleaned, 3 denotes a heat exchange unit for heating the chemical, and 4 denotes a processing tank. A pump 5 for circulating the liquid inside the filter, a filter 5 for removing particles in the circulated liquid, and a heater 8 for heating. In the present embodiment, the concentration of sulfuric acid is 0 wt% or more.
A solution changed to 48 wt% is used. A chemical solution having a constant concentration of about 5 wt% of hydrogen peroxide solution and about 1 wt% of hydrofluoric acid is used.

The operation of the cleaning apparatus configured as described above will be described below with reference to FIGS.

(Embodiment 1) First, FIG. 1 shows a state of cleaning in Embodiment 1 of the present invention. A carrier containing a wafer 2 is put into a processing tank 1 by means such as a transfer robot. Can be The chemical solution in the treatment tank 1 is adjusted to a temperature of about 70 ° C. by adding hydrofluoric acid as a fluorine-containing compound to an aqueous solution of sulfuric acid and hydrogen peroxide at about 1.0 wt%. The chemical is driven by the pump 4 and returned to the processing tank 1 through the filter 5 to perform cleaning.

When the cleaning is completed, the wafer is conveyed from the cleaning tank 1 to the washing tank by means of a robot or the like, and QDR rinsing is performed to remove the chemical solution, as in the prior art. Thereafter, drying is performed using a drying means such as a spin dryer. Here, QDR rinsing is a method of quickly overflowing and draining pure water using a washing tank having a mechanism for draining pure water in the tank at high speed. Rinsing is completed).

FIG. 2 shows the dependence of the etching rate of the oxide film on the elapsed time as a function of the sulfuric acid concentration. About 36%
The etching rate tends to increase with time when the sulfuric acid concentration decreases at the border of sulfuric acid, and the etching rate tends to decrease when the sulfuric acid concentration increases (so-called conventional chemical solution concentration).

In another experiment, the etching rate decreases with time at about 70% sulfuric acid because the hydrofluoric acid evaporates with the passage of time, and the evaporation of hydrofluoric acid depends on the sulfuric acid concentration. I knew it was there.

From FIG. 2, it can be seen that the time variation of the etching rate is substantially equal at each of the sulfuric acid concentrations of 0%, 12% and 24%. It is considered that the etching rate is controlled not by the evaporation of hydrofluoric acid but by the evaporation of water in the case of sulfuric acid having a low concentration of 24% or less. That is, the evaporation amount of water is larger than the evaporation of hydrofluoric acid over time, and as a result, the concentration of hydrofluoric acid in the chemical increases. Therefore, it can be expected that the optimum sulfuric acid concentration changes depending on the temperature used.

The oxide film etching rate in the present embodiment is about 50 nm / min to 300 nm / min. As is apparent from FIG. 2, the initial oxide film etching rate varies depending on the sulfuric acid concentration. I understand.
Although the cause of this has not been elucidated yet, it is necessary to pay attention to the sulfuric acid concentration from this point as well.

FIG. 3 shows the effect of removing metal impurities (iron and copper) when 39% sulfuric acid is used. Both iron and copper impurities are below the detection limit (<1.0 × 10 ¹⁰ atoms / cm ² )
It can be seen that it has decreased to Thus, it can be seen that the chemical solution used in the present embodiment can be used for removing metal impurities even if the sulfuric acid concentration is reduced as compared with the conventional one.

In the present embodiment, a concentration of 1% was selected as the concentration of hydrofluoric acid in order to evaluate the time dependency of the etching rate. However, in actual cleaning, the substrate surface may be etched from 3 nm to 4 nm. When the sulfuric acid concentration is 36%, the oxide film is etched by 4 nm.
It was 1 wt%. Excessive etching of the surface causes variations in film thickness and roughness, and less etching makes it difficult to remove particles on the surface. Therefore, since the etching rate depends on the concentration of sulfuric acid, it is necessary to optimize the concentration of hydrofluoric acid according to the concentration of sulfuric acid used.

The time-dependent change in the etching rate with the change in the concentration of sulfuric acid in the chemical solution used for cleaning has been described above with reference to FIG. 2. By changing the concentration of the sulfuric acid, the change in the etching rate with time changes. The drop can be prevented. Specifically, the concentration of sulfuric acid may be lower than that of a conventionally used chemical solution. However, if the sulfuric acid concentration is too low, the etching rate will increase with time, and consequently the degree of evaporation of hydrofluoric acid and water from the chemical solution will not change the hydrofluoric acid concentration as much as possible. If the sulfuric acid concentration is set so as not to occur, the change with time of the etching rate can be minimized. It is considered that the specific sulfuric acid concentration is preferably about 36%.

With a conventional cleaning solution using a high concentration of sulfuric acid, the etching rate decreases with time, so that it is necessary to additionally supply hydrofluoric acid at regular intervals. However, as in the present invention, the degree of evaporation of hydrofluoric acid and water from the chemical solution is adjusted to a sulfuric acid concentration such that a change in the hydrofluoric acid concentration does not occur as much as possible, whereby a decrease in the etching rate can be sufficiently suppressed. This eliminates the need for the above-described additional supply means, which is advantageous in terms of cost.

(Embodiment 2) Hereinafter, Embodiment 2 of the present invention.
Will be described with reference to the drawings. The cleaning device is the same as in the first embodiment,
About 2.3% fluorosulfuric acid is used as the fluorine-containing compound instead of the hydrofluoric acid. The treatment temperature was 90 ° C. and the sulfuric acid was varied from 0% to 71%. When the sulfuric acid concentration is 24% or less, the amount of water in the chemical solution becomes too large, and it is impossible to evaluate the time dependency due to evaporation of water. Therefore, the data of 0% sulfuric acid is for the case where the processing temperature is 70 ° C. As shown in FIG. 4, as in the case of hydrofluoric acid, the time change of the etching rate changes from increasing to decreasing with an increase in the sulfuric acid concentration.

Considering the similarity with hydrofluoric acid, 48
% Sulfuric acid sharply reduces the oxide film etching rate, but in the case of hydrofluoric acid, if the processing temperature is 70 ° C.
Since the decrease in the etching rate is suppressed to a practical level, it can be considered that 48% sulfuric acid is a usable concentration depending on the temperature. Similarly, a treatment temperature of 24% sulfuric acid is 9
Although it is impossible to use at 0 ° C., it is considered that it can be used by lowering the temperature.

If the variation of the etching rate is within ± 10%, only one batch can be processed in about 10 minutes with 48% or more sulfuric acid, while about 30% with 36% sulfuric acid.
Minutes, three times the effect. In addition, it is clear that optimizing the sulfuric acid concentration increases the processable time.

In this embodiment, as in the first embodiment, the degree of evaporation of hydrofluoric acid and water from the chemical solution is determined by the concentration of sulfuric acid such that the hydrofluoric acid concentration does not change as much as possible. By doing so, the change with time of the etching rate can be minimized. It is considered that the specific sulfuric acid concentration is preferably about 36%.

As described above, according to the present invention, if the concentration of sulfuric acid is optimized, the etching rate in the conventional cleaning decreases with time, and the reduction in the etching rate can be suppressed even if the cleaning effect is deteriorated. The cleaning effect can be maintained for a long time.

In the present invention, hydrogen peroxide solution is used as an oxidizing agent. However, as will be apparent to those skilled in the art, adding ozone as an oxidizing agent to the solution has the same effect. Furthermore, although the description has been made mainly on the etching rate of the oxide film, it is known that the silicon substrate and the like can be etched with the cleaning liquid of the present invention, and thus it is understood that the cleaning of the substrate is effective.

In the present invention, the processing temperature is 70 ° C.
And 90 ° C., but above 90 ° C., the evaporation of water is intense, and substantial washing is impossible depending on the sulfuric acid concentration. On the other hand, if the temperature is lower than 70 ° C., the chemical reactivity decreases,
It has been found that removal of organic matter becomes difficult.

By extending the life of the chemical, the amount of the chemical used can be reduced. In addition, since the amount of the chemical solution used is reduced, the burden of the waste liquid treatment can be reduced.

In a chemical solution using sulfuric acid at a high concentration, the viscosity of sulfuric acid is high, so that the pump and the filter tend to have a short life due to the high viscosity. However, the chemical solution of the present invention has a viscosity close to that of water, When a filter is used, the circulation amount increases, and particles in the chemical solution can be removed in a short time. Further, when the circulation amount is set to be the same, the apparatus can be made compact and the footprint of the apparatus can be reduced, so that there is a cost advantage.

[0030]

As described above, according to the present invention, the change with time of the etching rate can be suppressed by optimizing the sulfuric acid concentration, so that the life of the chemical solution can be extended and the frequency of replacing the chemical solution can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a processing tank that performs cleaning according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an elapsed time and an oxide film etching rate in Embodiment 1 of the present invention.

FIG. 3 is a diagram showing a change in the amount of metal impurities on a wafer before and after cleaning according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an elapsed time and an oxide film etching rate according to the second embodiment of the present invention;

FIG. 5 is a schematic diagram of a conventional cleaning device.

[Explanation of symbols]

 1 Processing tank 2 Carrier 3 Heater 4 Pump 5 Filter

Claims (4)

[Claims] A semiconductor device cleaning method for cleaning a substrate with a chemical solution containing sulfuric acid, a hydrogen peroxide solution and a fluorine-containing compound, wherein the concentration of sulfuric acid in the chemical solution is changed over time by changing the concentration of sulfuric acid from the chemical solution. A method for cleaning a semiconductor device, wherein a degree of evaporation of hydrofluoric acid and water is set to a concentration that does not cause a change in hydrofluoric acid concentration. 2. The method according to claim 1, wherein the concentration of sulfuric acid in the chemical is about 36%. 3. The method according to claim 1, wherein the fluorine-containing compound is at least one of hydrofluoric acid and fluorosulfuric acid. 4. A substrate is immersed in a chemical solution, and the chemical solution is heated to 70.degree.
2. The method for cleaning a semiconductor device according to claim 1, wherein the treatment is performed in a temperature range of not less than 90.degree.