JP2977868B2 - Liquid management method for surface treatment agent - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing a surface treating agent comprising a mixed solution of sulfuric acid and hydrogen peroxide used for cleaning a semiconductor wafer in a process of manufacturing a semiconductor device.

[Prior art and solutions]

Conventionally, in the process of manufacturing a semiconductor device, various methods for removing metal ions, organic substances, and the like attached to the surface of a semiconductor wafer have been studied. Among them, in the so-called wet method, sulfuric acid and hydrogen peroxide are used. Is effective not only for removing metal ions, but also for removing and removing organic substances such as a photoresist film. Particularly, treatments such as high-temperature treatment and ion implantation are effective. It is difficult to completely remove the resist modified by other general organic solvents, and the actual situation is that the resist is modified by a treatment method using a mixed solution of sulfuric acid and hydrogen peroxide.

However, since the decomposition rate of a mixed solution of sulfuric acid and hydrogen peroxide varies depending on the purity of the liquid, the liquid temperature, the material of the apparatus, the cleanliness of the processed wafer, and the like, the concentration of the liquid must be controlled. It is difficult to control the liquid based on the elapsed time after preparing the mixed liquid or the number of processed wafers. In this method, the mixed solution must be discarded in a state where hydrogen peroxide still remains sufficiently in order to keep the effects of cleaning, stripping and removal constant, thereby increasing the amount of chemical solution used. Further, since the liquid must be replaced frequently, the proportion of the liquid preparation time occupied in the process increases, which is a major factor in reducing the throughput.

In view of the above, in recent years, attempts have been made to automatically manage such a mixed solution.For example, a flow of the mixed solution is created, and organic substances decomposed by the above-mentioned processing solution are forcibly forced into the line. A method has been proposed in which liquids are controlled by measuring the transparency of the mixed liquid with a measuring instrument located downstream, and evaluating the detergency of the processing liquid from the output thereof (Japanese Patent Laid-Open No. 63-189496). ).

However, since this method is performed by adding an organic substance such as a photoresist for evaluating the cleaning power of the liquid, this alone leads to contamination and deterioration of the cleaning liquid, and is not a very good method.

[Problem to be solved]

A main object of the present invention is to provide a method for performing liquid management using a simple liquid replenishment method and extending the life as a surface treatment agent.

[Means for solving the problem]

The inventors of the present invention conducted a systematic study by changing various conditions such as a temperature and a mixing ratio of a sulfuric acid-hydrogen peroxide-based mixed solution. The evaporation rate of water in the liquid is well balanced,
Just replenish the same amount of hydrogen peroxide as the amount of evaporated water at any time,
The present inventors have found that the liquid amount and the liquid composition can be kept constant, and have reached the present invention.

That is, the present invention uses a mixture of concentrated sulfuric acid and hydrogen peroxide at a mixing volume ratio of concentrated sulfuric acid to hydrogen peroxide of 1.9 to 2.1, a liquid temperature of 125 to 130 ° C., and metal concentration in the liquid. When performing a surface treatment of a semiconductor wafer under a use condition in which the total ion concentration is 100 ppb or less, a reduction amount of a liquid caused by carry-out by the wafer and evaporation of water is calculated by a replenishment formula [I]
And a liquid management method for a surface treating agent, characterized in that concentrated sulfuric acid and hydrogen peroxide are replenished according to [II] and the amount and composition of the solution are adjusted to be constant.

Formula [I] [Amount of replenishment of concentrated sulfuric acid ()] = [Amount of solution taken out by processing wafer ()] x 2/3 Formula [II] [Amount of replenishment of hydrogen peroxide ()] = [Amount of solution by processing wafer] Take-out amount ()] x 1/3 + (1-10 ^-0.0004t ) x [ ^Bath amount of mixed solution ()] [where t represents the elapsed time (minutes) from liquid adjustment] The first term in the replenishment formula [I] and the replenishment formula [II] for hydrogen peroxide is for replenishing the liquid taken out by the processing wafer for each liquid,
The amount of liquid taken out is equal to the amount obtained by subtracting the evaporation amount of water from the reduction amount of the mixed liquid after the treatment. The second term in the hydrogen peroxide replenishment formula [II] expresses the amount of evaporation of water from the mixed solution as a function of the time elapsed since the adjustment of the solution, and indicates the decrease in the concentration of hydrogen peroxide in the mixed solution. It is for adjusting the minute.

By the way, the loss of water in the prepared mixture is
It changes at a constant rate over time after the preparation of the mixture,
As a result of the experiment, it was found that the rate of change was represented by a straight line as shown in FIG.

From the results of these experiments, the above formula of the replenishing amount is derived. Based on the formulas [I] and [II], concentrated sulfuric acid and hydrogen peroxide are respectively replenished as needed to adjust the liquid amount and the liquid composition to be constant. Is what you can do.

In general, a method for building a sulfuric acid-hydrogen peroxide-based mixed solution is performed by injecting hydrogen peroxide into concentrated sulfuric acid contained in a container. At the time of mixing, the following equilibrium reaction occurs while the liquid temperature rises to a considerably high temperature due to heat of dissolution and the like.

If the H ₂ SO ₄ + H ₂ O ₂ = H ₂ SO ₅ + H ₂ O solution is extremely hot or if the mixture contains transition metal ions, hydrogen peroxide is decomposed as shown in the following formula. To produce water.

H ₂ O ₂ → H ₂ O + 1/2 O ₂ Also, if organic matter such as photoresist exists in the solution,
Organic substances carbonized by sulfuric acid are oxidized to generate water and carbon dioxide gas, and hydrogen peroxide is consumed by a reaction represented by the following formula.

Organic substance + H ₂ O ₂ → CO ₂ + H ₂ O The mixing volume ratio of concentrated sulfuric acid and hydrogen peroxide is 1 hydrogen peroxide.
Concentrated sulfuric acid is generally 1 to 10.

The mixing volume ratio of concentrated sulfuric acid and hydrogen peroxide is 1% for hydrogen peroxide.
If the concentration of concentrated sulfuric acid is lower than 1, the temperature of the solution becomes higher than 160 ° C during the preparation of the solution, not only is the consumption of hydrogen peroxide decomposed intensely, but also the concentration of sulfuric acid is so low that organic substances such as photoresist Can not obtain a sufficient effect, on the other hand, the volume mixing ratio of concentrated sulfuric acid and hydrogen peroxide,
If the concentration of sulfuric acid is higher than 5 with respect to 1 hydrogen peroxide, the hydrogen peroxide becomes stable, sufficient active oxygen effective for cleaning cannot be obtained, and organic substances such as photoresist removed and removed by sulfuric acid are oxidized. This is not preferable because it is difficult to accumulate in the system.

The surface treatment of a semiconductor wafer with a mixed solution of concentrated sulfuric acid and hydrogen peroxide is performed by setting a required number of semiconductor wafers to be processed in a carrier such as Teflon or the like, usually 25, and immersing the semiconductor wafer in the mixed solution. However, in order to increase the processing effect, it is desirable that the temperature of the processing liquid is high.

However, under the present circumstances, surface treatment is generally performed while the temperature of the solution decreases over time, without using the heat generated during the preparation of the solution and controlling the temperature of the particular solution. According to such a method, the mixed liquid immediately after the bathing and the mixed liquid before the liquid disposal have a very large difference in the concentration composition of the active ingredient in the liquid and the liquid temperature at the time of processing, and as a result, the wafer surface treatment It can greatly affect the effect. This is not preferable because it affects the yield in manufacturing the semiconductor device.

In the present invention, the mixed liquid is treated at a liquid temperature of 125 to 130 ° C. with a volumetric mixing ratio of concentrated sulfuric acid and hydrogen peroxide to hydrogen peroxide of 1 to 1.9 to 2.1. This is not only a condition capable of keeping the liquid concentration composition constant by constantly replenishing the same amount of hydrogen peroxide as the amount of evaporated water in the mixed liquid, but also maintaining the liquid temperature at a constant temperature. A sufficient surface treatment effect can be maintained. Regarding impurities in the mixture, the total of metal ions is 20
Exceeding 0 ppb extremely accelerates the decomposition of hydrogen peroxide,
It was confirmed that the range was negligible below 100 ppb. As a surface treatment agent, if there are too many metal ions in the solution, secondary contamination due to re-adhesion can be considered.
0 ppb or less is a desirable range.

Further, the rate of decrease in the concentration of hydrogen peroxide is also affected by the concentration of organic substances in the mixture because it is consumed for oxidation. The removal and removal of the photoresist is the most typical process. However, if the processing speed of the resist removal is 0.5 g (resist) / (liquid amount) · hr or less, the liquid can be sufficiently controlled under the above conditions. It was confirmed that we could do it. The resist stripping rate is 6 per hour when the liquid volume is 10.
This is equivalent to processing about 300 inch wafers. If the use conditions of the mixed liquid are out of the above range, the amount of evaporated water and the replenishment amount of hydrogen peroxide are not well balanced, and it is extremely difficult to keep the liquid amount and the liquid composition constant at the same time.

 Hereinafter, an example will be described in detail.

98.5% concentrated sulfuric acid 6 and 31.0% hydrogen peroxide 3 were put in the quartz container of Example 10 and mixed well to prepare a mixed solution. The liquid temperature at this time was 130 ° C. When the mixture was analyzed, the concentration of all peroxides was 7.1 wt% as hydrogen peroxide. This mixture was host-baked at 180 ° C in advance.
Twenty-five 6-inch wafers coated with a positive resist having a thickness of 1.2 μm were immersed in a Teflon wafer carrier, and after confirming that they were completely peeled off, the carrier was pulled up. The time required for peeling by immersion was 6 minutes. While maintaining the liquid temperature at 130 ° C., immersion of the wafer, stripping of the resist, and pulling up of the wafer were performed in a cycle of 6 minutes, and a total of 250 wafers were processed in one hour. When the surface of the processed wafer was visually observed, the resist was successfully removed. When the concentration of all peroxides immediately after the treatment was analyzed, the concentration was 6.2 wt% as hydrogen peroxide, and the liquid volume was reduced to 7.9. Therefore, according to the replenishment formulas (I) and (II), concentrated sulfuric acid was added.
41, after replenishing hydrogen peroxide 0.69 each,
As a result of a concentration analysis, the concentration of all peroxides was 7.1 wt%, which was the same as in the bath.

〔The invention's effect〕

By carrying out the liquid management method of the surface treatment agent according to the present invention, the surface treatment agent can be effectively used without reducing the amount of the liquid used, and by maintaining the liquid concentration composition and the liquid temperature constant. In addition, variations in surface treatment conditions can be extremely reduced.

[Brief description of the drawings]

FIG. 1 shows the elapsed time after the preparation of the mixed solution and the change in the water loss.

Continuation of the front page Examiner Mitsuru Suzuki (56) References JP-A-61-281532 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/304

Claims (1)

(57) [Claims] 1. A mixture of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of hydrogen peroxide to hydrogen peroxide of 1 to 1.9 to 2.1, a liquid temperature of 125 to 130 ° C., and metal ions in the liquid. The sum of the concentrations
When performing a surface treatment of a semiconductor wafer under a use condition of 100 ppb or less, the amount of liquid reduction due to carry-out by the wafer and evaporation of water is determined by the following replenishment formulas [I] and [I].
A liquid management method for a surface treatment agent, comprising replenishing concentrated sulfuric acid and hydrogen peroxide in accordance with I) to adjust the amount and composition of the solution to be constant. Formula [I] [Amount of replenishment of concentrated sulfuric acid ()] = [Amount of solution taken out by processing wafer ()] x 2/3 Formula [II] [Amount of replenishment of hydrogen peroxide ()] = [Amount of solution by processing wafer] Amount taken out ()] x 1/3 + (1-10 ^-0.0004t ) x [ ^Bath amount of mixed solution ()] [where t represents the elapsed time (minutes) from liquid adjustment]