JPH01195342A - Measuring method for fine grain in solvent - Google Patents

Abstract

PURPOSE:To efficiently execute an exact measurement by diluting a solvent by superpure water, converting it to aerosol, measuring the grain diameter and the number of pieces of a solid fine grain by a light-scattering fine grain counter and subtracting the number of pieces of only superpure water from this measured value. CONSTITUTION:A solvent is diluted in a suitable ratio by superpure water, mixed and injected with clean air A which has passed through a filter 2 and becomes aerosol, and a droplet exceeding a prescribed grain diameter is eliminated by a droplet separator 4. A droplet being smaller than said droplet goes into a cavity 6 together with air, and also, water content is eliminated by a heater 7. Subsequently, said aerosol is cooled and dehumidified by a cooler 9 and fed to a light-scattering fine grain counter 10. The counter 10 divides fine grains into each grain diameter and counts the number of pieces. Next, by subtracting the number of pieces of only superpure water from the count number, the number of pieces of solid fine grains of the solvent itself is derived. In such a way, an exact measurement can be executed efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for measuring solid fine particles contained in a cleaning solvent used in the manufacture of semiconductors.

[Background Art] In the manufacturing process of semiconductor products, various surface treatments are performed on a substrate such as a silicon wafer or a photomask that serves as a matrix thereof, and necessary cleaning is performed each time the treatment is performed. For cleaning, in addition to ultrapure water, a water-soluble and volatile solvent such as isopropyl alcohol, which is effective against various inorganic and organic substances adhering to the substrate, is used. During cleaning, it is necessary that no particles of solid foreign matter such as dust remain after cleaning, which deteriorates the performance of the semiconductor, and it is important that not only ultrapure water but also various solvents do not contain impure solid particles. is necessary.

With the recent increase in the density of semiconductors, the number of microparticles contained in ultrapure water per meter is strictly limited. However, there are not necessarily strong restrictions on solvents, and in reality, the number of fine particles contained in ultrapure water is far greater than that in ultrapure water, and there is also a lack of efficient measurement methods for this. It is a fact.

Generally, fine particles in a liquid are measured by a method of measuring the collected particles using a microscope. This method allows the size and number of particles to be measured accurately, but it requires time and skill, so it is not efficient as a measurement method at sites such as semiconductor manufacturing factories. An optical method can be considered in which light is irradiated onto the particle and the light scattered by the particles is measured, but the size of the particles that can be detected is too large due to interference such as bubbles in the solvent or reflections from the container, making it impractical.

[Problems to be solved] In response to the above situation, it is possible to measure fine particles in the aerosol using the conventional method of measuring fine particles such as dust in the air by aerosolizing the solvent using clean air. This is considered to be effective as it allows measurements to be taken without the influence of air bubbles, containers, etc. However, there are difficulties in aerosolizing volatile solvents, and it is costly to directly aerosolize expensive solvents. On the other hand, since the solvent contains a large number of impure particles as described above, it is appropriate to dilute the solvent in an appropriate proportion with ultrapure water and then aerosolize it before performing the above measurements.

However, there is a problem with the ultrapure water used for dilution in the above. In other words, soluble impurities are more or less dissolved in ultrapure water, and when the droplets evaporate when ejected, they form residual particles, which cannot be distinguished from the target microscopic solid particles. , resulting in measurement errors. There is a need for a method that can solve these problems and efficiently and accurately measure solid particles such as dust and dirt in a solvent at sites such as semiconductor factories.

This invention was made in view of the above circumstances, and the solvent is diluted with ultrapure water at an appropriate ratio and aerosolized with clean air, thereby eliminating the influence of impurity residues in the ultrapure water. The object of the present invention is to provide a method for efficiently measuring scattered light generated by solid particles contained in a solvent using a light scattering particle counter.

[Means for Solving the Problems] The present invention is a method for measuring fine particles contained in a water-soluble solvent for cleaning the surface of a silicon wafer or the like during a semiconductor processing process. First, a solvent is diluted with ultrapure water at an appropriate ratio to obtain a diluted solvent, which is mixed with clean air and sprayed through a spray nozzle to form an aerosol. A droplet separator installed immediately after the injection nozzle removes droplets larger than a certain particle size contained in the aerosol, and heats and dries the aerosol containing droplets with a smaller particle size. Evaporate moisture. After further cooling and dehumidifying, the aerosol was mixed with clean air to dilute it, and the number of solid particles was measured using a light scattering particle counter for this aerosol. From this, the dilution ratio of ultrapure water was determined to be 0%. That is, by subtracting the measured number of ultrapure water alone, the particle size and number of solid particles such as dust contained in the solvent are determined.

In the above, the lower limit of the particle size of the droplets removed by the droplet separator is that impurities dissolved in the droplets become residual particles by vaporization, so the size of the residual particles must be below the detection limit of the light scattering particle counter. The settings are as follows.

[Function] In the method for measuring fine particles in a solvent of the present invention with the above configuration, the diluted solvent diluted with ultrapure water at an appropriate ratio is mixed with clean air by the injection nozzle to form an aerosol, and the Among the droplets, droplets with a certain particle size or more are removed by a droplet separator. This aerosol is heated, dried, cooled and dehumidified, and then the particle size and number of solid particles are counted in a light scattering particle counter. This count includes the amount in ultrapure water for dilution, so by measuring only the number of ultrapure water with a dilution ratio of 0% and subtracting it, you can change the number of solid particles relative to the solvent. It is something that can be done. In this case, the dilution ratio with ultrapure water is adjusted depending on the number of fine particles in the solvent, and if necessary, clean air is mixed in at the aerosol stage to finely adjust the dilution ratio.

The droplet separator mentioned above removes droplets with a larger size than the droplet size determined by the droplet speed, size, aerosol speed, etc., and allows droplets with a smaller size to pass through. It is something. − On the other hand, impurities dissolved in the droplet (
(originated from ultrapure water for dilution) is left behind due to vaporization of moisture during the heating and drying process, but the particle size of the droplets must be adjusted so that this size is below the detection limit of the light scattering particle counter. The particle size is determined by the method described below, and various constants of the droplet separator are set for the particle size. This eliminates the influence of dissolved impurities on the measurement of the target solid particles.

In the above, a method for determining the particle size of a droplet such that it is below the detection limit of the light scattering particle counter will be described below.

Generally, the particle size of the droplet is XI, and the residue produced when it evaporates is 5
When the grain size of z is represented by X, there is the following hour wheel relationship between the two.

XI = kCJ X, ・
...... (1) Here, C is the concentration of the solution, and k is influenced by the heating drying process, but in principle,
.

k= (ρ 1/ρ g )”
--- (2) where ρ1 is the density of the droplet and ρ is the density of the impurity residue. Therefore, using C and k for specific impurities dissolved in the ultrapure water for dilution, and assuming that the detection limit of the light scattering particle counter is X, the particle size X1 of the droplet to be removed is determined.

Next, the above-mentioned light scattering particle counter uses what is called a dust monitor that detects solid particles such as dust in the air, which is already in practical use.

The detection limit of dust monitors varies depending on the model, but is 0.1
The number of particles can be counted by dividing fine particles of .mu.m or more or 0.05 .mu.m or more into sizes. Therefore, the size of the above-mentioned dissolved impurity residue is set to be 0.1 μm or less or 0.05 μm or less corresponding to one model, and this is defined as X3 in the above formula.

As described above, the influence of impurities dissolved in the ultrapure water used for dilution is eliminated while the dilution solvent is in an aerosolized state, and solid particles such as dust particles are continuously measured.

Note that the data obtained from this measurement naturally includes the number of solid particles in the ultrapure water used for dilution, so measure the number of solid particles in the ultrapure water at the appropriate time with the dilution ratio set to 0%. , it is necessary to subtract this from the above measurements.

[Example] Figure 1 is a diagram showing the configuration of an example of the method for measuring fine particles in a solvent according to the present invention.The solvent is diluted in advance with ultrapure water at an appropriate ratio, and the diluted solvent 1 is poured into a container 1'. The liquid level is maintained at a constant height by the discharge pipe 1''.The diluted solvent is atomized by the injection nozzle 3 using clean air A from which dust fρ has been removed by the filter 2, and becomes an aerosol. As a result, droplets larger than a certain size are removed by the droplet separator 4. Droplets smaller than this enter the next cavity 6 with air, and are then heated and dried in a heater 7 to vaporize the water in the droplets. The temperature of the aerosol is kept constant by the operation of the temperature sensor 8a provided at the outlet of the heater 7 and the '1lfl unit 8b.Then, the aerosol is cooled and dehumidified in the cooler 9, and cleaned if necessary. Air A is mixed and diluted and sent to the light scattering particle counter 10.The above-mentioned dust monitor is used for the light scattering particle counter!O, and the particles are divided into sizes and counted. By subtracting the number of particles measured using only ultrapure water for dilution from this count number, the number of solid fine particles relative to the solvent itself can be determined, and furthermore, the number relative to the undiluted solution can be determined from the dilution ratio. be.

An experiment with the above configuration was carried out, and when a sample of isopropyl alcohol diluted with ultrapure water was tested, the number of solid fine particles obtained by particle size differed depending on the quality grade of the sample, but in all cases, ultrapure water was used. It has been confirmed that the average number of solvents themselves is proportional to the dilution ratio of the sample, that is, the concentration.

Since the number is proportional to the concentration in this way, it can be considered as proof that the influence of impurity residues dissolved in the ultrapure water for dilution has been eliminated, albeit indirectly.

In addition, the condensation nucleus counter 11 indicated by a dotted line in FIG.
This is related to Jikai's ``Method for Measuring Impurities in Liquid and Its Upwelling Apparatus'' (Sho 62-22214), which uses minute impurities as nuclei, mixes them with high-temperature saturated steam such as water, and condenses the steam. The particle size is enlarged and counted optically. However, although this is not related to the structure of the present invention,
This is described for convenience in explaining the performance of the droplet separator described below.

Now, the principle and operation of the droplet separator, which plays an important stage in the above, will be explained with reference to FIGS. 2(a) and 2(b). In figure (a), the droplet separator consists of a nozzle N and a collision plate M, and droplets larger than a certain size among the droplets in the aerosol injected from the nozzle collide with the collision plate as indicated by the arrow ρ. However, if the small particles collide toward the periphery as shown by arrow q, they do not collide, that is, the droplets are separated depending on their size. However, this separation does not clearly separate particles above and below a certain particle size, but rather separates particles above and below that particle size with a certain efficiency. This separation effect is analyzed using the equation of motion of fine particles in a viscous gas, and
The results have been applied and put to practical use in powdered woodworking characters and aerosolue characters.

In Fig. 2 (1), the length of the straight part of the nozzle N is T,
Assume that the inner diameter is D, and that there is a distance sG:i [M]. Let the velocity of the aerosol passing through the nozzle be U,
The density and particle size of fine particles (droplets) are respectively ρ3. d, the density and viscosity of air are ρr and η, respectively, then the Reynolds number Re, which characterizes the flow of air, and the Stokes number θ, which defines the movement of particles in the fluid, are determined by the following equations.

Re==uDρ, /η...----(3) θ=
Cc p r du /9 ri D
−・−=−=−(4).

However, Cc is Cunningham's correction coefficient.

The separation effect on the particle size of fine particles changes depending on the two numbers Re and θ and the nozzle shape and size ratio (T/D, S/D). Figure 2 (b) shows the separation efficiency for a circular nozzle. The group of zero curves showing the theoretical curves shows the particle separation efficiency in % when the Reynolds number Re is used as a parameter and the square root FT of the Stokes number θ is plotted on the horizontal axis. Therefore, the lower limit of the particle size d of the droplets to be removed can be set by giving the nozzle shape, size ratio, various constants, and appropriate separation efficiency.

FIG. 3 is one experimental data showing the branch performance of the droplet separator. In the experiment, a potassium chloride solution with a concentration of 1/1000 was used as a sample, and the solution was made into an aerosol using the configuration shown in FIG.
The measured values are subjected to necessary processing and converted into droplet diameters. The horizontal axis is the droplet diameter in μm, and the vertical axis is the droplet separator, which represents the distribution of the number of droplets per unit volume of the solution (number concentration) on an arbitrary logarithmic scale. 1 for data “0” when not used
We used a droplet separator with μm as the separation boundary.
The data shows that most of the droplets larger than 1 μm are removed;
The results show that the effective separation efficiency is close to 100%.

In this invention, the purpose of removing large droplets is to remove large droplets when the water in large droplets is vaporized by heating and drying as described above, and impurities dissolved in the ultrapure water for dilution are left behind.
This is to prevent them from remaining as solid particles and causing measurement errors because they cannot be distinguished from solid fine particles. Therefore, the particle size of the residue
3 below the detection limit of the light scattering particle counter (in the case of the above-mentioned dust monitor, the detection limit is 0.1 μm or below, or 0.
．． 05 μm or less), and the type and concentration of impurities are specified based on the relationship between the particle size X3 of the residue and the particle size Particle size d(x
1). Further, the droplet separator having this d as the branch boundary is set according to the above equations (3) and (4).

[Effects of the Invention] As is clear from the above explanation, the method for measuring fine particles in a solvent according to the present invention involves diluting the solvent to be measured with ultrapure water at an appropriate ratio, aerosolizing this, and producing light-scattering fine particles. It is measured using a counter, and by removing large droplets from the aerosol with a droplet separator, the size of the remaining impurities dissolved in the ultrapure water for dilution due to the vaporization of the droplets can be measured by light scattering. This is below the detection limit of the particle counter, eliminating measurement errors. By applying this method to semiconductor manufacturing factories, etc., the particle size and number of harmful solid particles contained in various solvents for cleaning semiconductors can be efficiently and accurately measured. be.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an embodiment of the method for measuring fine particles in a solvent according to the present invention, and Figures 2 (a) and (b) are
Figure 3 is an explanatory diagram of the principle and operation of the droplet separator shown in Figure 2.
It is a curve diagram showing IN. 1...-diluent solvent, 1'...container, 2...
-filter, 3...-injection nozzle. 4...-droplet separator, l", 5... discharge pipe,
6...-cavity, 7... heater, 8a...
-・Temperature sensor, 8b...Temperature controller, 9-・-
Cooler, 10...Light scattering particle counter. ! 1-.-Condensation nucleus counter.

Claims (2)

[Claims] (1) A water-soluble solvent for cleaning surfaces such as silicon wafers in the semiconductor manufacturing process is diluted with ultrapure water at an appropriate ratio to obtain a diluted solvent, and the diluted solvent is mixed with clean air and sprayed with a spray nozzle. to form an aerosol, and a droplet separator provided immediately after the injection nozzle removes droplets of a certain particle size or more contained in the aerosol,
The aerosol containing droplets with a certain particle size or less is heated and dried to vaporize the moisture in the droplets, further cooled and dehumidified, and if necessary, clean air is mixed to dilute the aerosol and light scattering is applied to the aerosol. The number of solid fine particles such as dust contained in the solvent is measured by subtracting the number of solid fine particles measured with the dilution ratio of the ultrapure water being 0% from the number of solid fine particles measured by a particle counter. and
Method for measuring particulates in solvents. (2) By vaporizing the droplets, the size of the residue of impurities dissolved in the droplets is set to the above-mentioned constant particle size that is less than the lower limit of the detection performance of the light scattering counter, and the droplets having the above-mentioned particle size are The method for measuring fine particles in a solvent according to claim 1, wherein the droplet separator to be removed is used as a droplet separator.