JP7456416B2 - Evaluation method of alkali ion concentration in environmental atmosphere - Google Patents

Description

The present invention relates to a method for evaluating the concentration of alkali ions contained in an environmental atmosphere.

With the evolution of electronic devices, very strict requirements are being placed on the cleanliness of substrate surfaces. In particular, surface contamination includes metal contamination, organic matter contamination, alkali contamination, and the like, which cause deterioration of device characteristics, so it is essential to reduce the level of surface contamination. In particular, alkaline contamination can cause pattern defects in the lithography process for chemically amplified resists, and if sulfate ions are present in the presence of ammonia ions or amine ions, ammonium sulfate salts and amine sulfate salts are generated, resulting in the formation of wafers. It is known that spiders occur, so controlling the components in the ambient air and collecting methods are important.

Alkali ions in the environmental atmosphere include ammonia and amines, and a method for evaluating these components is, for example, as shown in Figure 11, by bubbling the environmental atmosphere into an impinger containing pure water using an air pump or the like. However, there is a method in which the components are dissolved in pure water and measured using an ion chromatograph. In addition, as shown in Figure 12, the environmental atmosphere is sucked through an absorption tube filled with an adsorbent such as TENAX using an air pump, etc., and the components desorbed by heating the absorption tube are measured using a gas chromatograph or gas chromatograph mass spectrometer. There is a way to do it. Furthermore, there is a method shown in FIG. 13 in which components in the environmental atmosphere are collected using a diffusion scrubber method and analyzed using an ion chromatograph or the like. Furthermore, there is a method shown in FIG. 14 in which a silicon wafer or the like coated with an acid or alkaline solution and dried is exposed to the ambient atmosphere to be adsorbed, extracted with hot water, and then analyzed by ion chromatography. In addition, as shown in FIG. 15, the wafer was immersed in sulfuric acid/hydrogen, hydrochloric acid/hydrogen, and nitric acid, then washed with water, and then exposed to the environmental atmosphere in a dry surface state, and the components adsorbed on the wafer surface were extracted with hot water, and the wafer was subjected to ion chromatography. There is a way to analyze it.

Japanese Patent Application Publication No. 11-142381

The impinger method has the problem of low absorption rate for alkali ions such as ammonia and amines, and the absorption tube collection method is an effective method for organic matter analysis, but alkali ions cannot be absorbed by thermal decomposition etc. It has an impact and is unsuitable. Although the diffusion scrubber method has a high absorption rate for alkali ions, it is difficult to separate components using ion chromatography analysis, and the detection sensitivity for amines is low. These methods are methods in which components in the ambient atmosphere are directly taken into a solvent and the concentration of the components in the ambient atmosphere is analyzed by analyzing the solvent.
In addition, the wafer exposure method (including the selective collection method) described in Patent Document 1 uses the phenomenon of physical adsorption or chemical adsorption of components in the environmental atmosphere to the wafer to indirectly measure the concentration of components in the environmental atmosphere. This is a method of analyzing Both methods are evaluation methods that focus on the concentration in the environmental atmosphere.

On the other hand, although there is a rule of thumb that indicates that higher alkali gas concentrations in the environmental atmosphere result in more pattern defects and cloud formation, the relationship between the alkali gas concentration and cloud formation has not been quantitatively demonstrated, and empirically, the environmental atmosphere The current situation is to set allowable concentrations within the range.

The present invention has been made in view of the above-mentioned problems, and provides a method capable of evaluating the alkali ion concentration in an environmental atmosphere.

In order to achieve the above object, the present invention provides a method for evaluating an alkali ion concentration in an environmental atmosphere, comprising the steps of:
a correlation acquisition step of exposing a preliminary test wafer that has been previously subjected to SPM cleaning to an environmental atmosphere to contaminate the wafer surface with an amount of alkali ions, and then measuring the alkali ion concentration on the wafer surface of the preliminary test wafer and the reflection intensity on the wafer surface to acquire a correlation between the alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface;
The present invention provides a method for evaluating an alkali ion concentration in an environmental atmosphere, comprising: an alkali ion concentration evaluation step of: exposing a test wafer that has been SPM cleaned to an evaluation environment atmosphere for a predetermined period of time, measuring the reflection intensity of the wafer surface of the test wafer, estimating the alkali ion concentration of the wafer surface of the test wafer from the measurement results of the reflection intensity of the wafer surface using the correlation acquired in the correlation acquisition step, and evaluating the alkali ion concentration in the evaluation environment atmosphere from the estimated alkali ion concentration of the wafer surface.

With such an evaluation method of the present invention, it is possible to accurately evaluate the alkali ion concentration in the environmental atmosphere. In turn, this can be useful for preventing pattern defects in the lithography process and cloud formation on the wafer surface.
In addition, although the reflection intensity of the wafer surface of the test wafer exposed to the environment to be evaluated is measured, the evaluation can be performed without actually measuring the alkali ion concentration, which is simpler than conventional methods.

When contaminating the preliminary test wafer by spreading the amount of contamination by alkali ions on the wafer surface, this can be done by changing the exposure time in the same environmental atmosphere or by making the exposure time the same in different environmental atmospheres.

In this way, it is easy to contaminate the preliminary test wafers with various amounts of contamination.

The alkaline ion concentration on the wafer surface can also be measured using a capillary electrophoresis device.

In this way, the alkali ion concentration on the wafer surface of the preliminary test wafer can be measured more easily.

Furthermore, the alkali ion concentration on the wafer surface can be measured for one or more of ammonia, methylamines, and ethanolamines.

In this way, it is possible to evaluate things that particularly affect the occurrence of pattern defects in the lithography process, haze on the wafer surface, and the like.

When measuring the reflection intensity of the wafer surface, a wafer film thickness measuring device is used to measure the maximum reflection intensity and background intensity of the reflected light with a spectral wavelength of 400-500 nm obtained by vertically incident light on the wafer surface. By measuring the difference, a value based on a wafer not exposed to an environmental atmosphere can be determined as the reflection intensity of the wafer surface.

If the reflection intensity of the wafer surface determined in this manner is used, there is a better correlation with the alkali ion concentration of the wafer surface, and therefore more accurate evaluation can be performed.

With the method of evaluating the alkali ion concentration in the environmental atmosphere of the present invention, the evaluation can be performed more accurately and more easily than before.

It is a flowchart which shows an example of the process of the evaluation method of the alkali ion concentration in an environmental atmosphere of this invention. It is an explanatory diagram showing an example of a correlation acquisition process (condition setting process) which is a preliminary test in the present invention. It is an explanatory diagram showing an example of an alkali ion concentration evaluation process (main process) which is the main test in the present invention. 2 is a graph showing the correlation between total alkali ion concentration and reflection intensity in Experimental Example 1. 3 is a graph showing the relationship between wafer exposure time and reflection intensity in Experimental Example 1. 3 is a graph showing the correlation between total alkali ion concentration and reflection intensity in Experimental Example 2. 3 is a graph showing the correlation between ammonia concentration and reflection intensity in Experimental Example 2. 3 is a graph showing the correlation between methylamine concentration and reflection intensity in Experimental Example 2. 3 is a graph showing the correlation between ethanolamine concentration and reflection intensity in Experimental Example 2. It is a graph showing the relationship between the total alkali ion concentration (actually measured value) in the environmental atmosphere and the haze value on the wafer surface. FIG. 1 is an explanatory diagram showing a method for evaluating component concentrations in an environmental atmosphere using an impinger method. FIG. 2 is an explanatory diagram showing a method for evaluating component concentrations in an environmental atmosphere using an absorption tube collection method. FIG. 2 is an explanatory diagram showing a method for evaluating component concentrations in an environmental atmosphere using a diffusion scrubber method. FIG. 2 is an explanatory diagram showing a method for evaluating component concentrations in an environmental atmosphere using a wafer exposure method. FIG. 2 is an explanatory diagram showing a method for evaluating component concentrations in an environmental atmosphere using a wafer exposure method (selective collection method).

As mentioned above, there is a need for a method that can evaluate the concentration of alkali ions in an environmental atmosphere. The inventor of the present invention conducted extensive research and discovered that there is a correlation between the reflection intensity of the surface of a wafer left exposed in an ambient atmosphere and the concentration of alkali ions in the ambient atmosphere adsorbed on the wafer surface. Ta. Then, by measuring the reflection intensity of the wafer surface left and exposed in the environmental atmosphere of the evaluation target and using the above correlation, we can estimate the alkali ion concentration on the wafer surface and, by extension, the alkali ion concentration in the environmental atmosphere. The present invention was completed based on the discovery that evaluation can be performed with high accuracy and more easily than before.

Hereinafter, the present invention will be explained in detail with reference to the drawings, but the present invention is not limited thereto.
An embodiment of a method for evaluating alkali ion concentration in an environmental atmosphere according to the present invention will be described. FIG. 1 shows a flowchart that is an example of the process of the present invention. Broadly speaking, it consists of a correlation acquisition step (also called a condition setting step), which is a preliminary test, and an alkali ion concentration evaluation step (also called a main step), which is a main test. Moreover, FIG. 2 is an explanatory diagram of a preliminary test, and is an explanatory diagram of the procedure for measuring the alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface by exposing the wafer in an environmental atmosphere. Figure 3 is an explanatory diagram of this test, and shows the estimation of the alkali ion concentration on the wafer surface from the reflection intensity of the wafer surface (also referred to as wafer reflection intensity) due to exposure of the wafer in the evaluation environment atmosphere. FIG. 3 is an explanatory diagram of the procedure for evaluating the alkali ion concentration in the sample.

In addition, in the present invention, there is no particular restriction on the size of the wafer (preliminary test wafer, main test wafer) used in the preliminary test and main test, and a single wafer may be used as is, or a wafer piece cut from the wafer may be used. Applicable. Furthermore, in order to measure the reflection intensity on the wafer surface, the surface is required to have the same smoothness as a PW wafer. On the other hand, as for the material of the wafer, a silicon wafer is suitable, but any substrate that is smooth and does not interact with sulfate ions or alkali ions, such as a glass substrate, can be used. . In order to make the conditions the same, it is preferable to use the same wafer for the preliminary test and the wafer for the main test.

(Correlation acquisition process)
In the preliminary test correlation acquisition step, first, the prepared preliminary test wafer is cleaned with sulfuric acid and hydrogen peroxide (SPM). The SPM cleaning can be carried out, for example, by immersing it in a water tank at 120° C. for 10 minutes in a 1:1 liquid composition of 96% sulfuric acid and 35% hydrogen peroxide.
Thereafter, the wafer for preliminary testing is washed with water and dried.
Then, two of the preliminary test wafers are left and exposed in the environmental atmosphere to be measured.
After exposure for a certain period of time, the alkali ion concentration on the surface of one of the two wafers for preliminary testing is measured. For example, it is possible to seal the wafer together with an extraction liquid in a polypropylene bag, extract the components adsorbed on the wafer surface, and measure the alkali ion concentration using a capillary electrophoresis device. For the other preliminary test wafer, the reflection intensity on the wafer surface is measured.

In the above procedure of exposure to the environmental atmosphere, the wafer surface is contaminated by varying the amount of contamination by alkaline ions. For example, this can be done by varying the exposure time in the same environmental atmosphere (changing the exposure time), or by making the exposure time the same in different environmental atmospheres (changing the exposure environmental atmosphere). In this way, contamination can be easily achieved with various contamination amounts. However, the method of distribution is not limited to this as long as it is possible to vary the amount of contamination.
The exposure time is not particularly limited, but in order to more reliably obtain a correlation between the exposure time, which affects the alkali ion concentration on the wafer surface, and the reflection intensity, the exposure time is preferably 3 to 48 hours. When evaluation is performed by changing the exposure environment, taking into consideration the measurement of exposed wafers in a highly clean environmental atmosphere, the exposure time is more preferably about 24 hours.

Here, measurement of the alkali ion concentration and reflection intensity on the wafer surface will be explained.
First, the measurement of alkali ion concentration is not particularly limited, as long as the concentration of alkali ions on the wafer surface can be measured. Although other methods such as ion chromatography can be used, an example in which a capillary electrophoresis device is used will be described here. A capillary electrophoresis device utilizes a phenomenon in which components are separated due to differences in their mobility by applying a high voltage to a hollow quartz capillary and flowing a sample solution, and uses a UV detector. This method calculates components and concentrations from the migration time and detection intensity of the obtained chromatogram (electropherogram) based on a calibration curve. This allows easy calculation.

Further, the measurement of the wafer reflection intensity is not particularly limited, and it is sufficient that the reflection intensity of the wafer surface can be measured. For example, it can be measured using a wafer film thickness measuring device. This is a method in which light is incident perpendicularly to the wafer surface and the resulting reflected light intensity is measured. The optical constants, integration time, and background conditions are held constant, and the maximum reflection intensity of the reflected light at a spectral wavelength of 400 nm to 500 nm is measured. Obtain the difference between this maximum reflected intensity and the background intensity. Here, we use the value based on the reflection intensity of the surface of a wafer that has not been exposed to the environmental atmosphere (unexposed wafer) as the reflection intensity of the wafer surface used to obtain the correlation with the measured value of alkali ion concentration. It can be used as a measurement value. To explain with a more specific example, when an unexposed wafer is used as a reference, the difference (reduction value) between the reflection intensity due to the unexposed wafer and the reflection intensity due to the exposed wafer is calculated. For convenience, it is assumed that the state of the unexposed wafer is 10,000, and the value obtained by subtracting the above reduction value from 10,000 can be used as the reflection intensity of the wafer surface.
The reflection intensity measured in this way becomes reflection intensity data that has a higher correlation with the alkali ion concentration on the wafer surface. That is, a better correlation can be obtained, and a more accurate evaluation can be obtained.
Note that the numerical value of the spectral wavelength used in the measurement is not particularly limited, and can be appropriately determined depending on the type of wafer used and the like.

As described above, preliminary test wafers with various amounts of contamination (various exposure conditions such as changing the exposure environment atmosphere and exposure time) were measured, and the concentration of alkali ion components adsorbed on the wafer surface and the wafer at that concentration were measured. The reflection intensity of the surface is obtained, and the correlation between the alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface is obtained. Note that the number of patterns of exposure conditions and the number of measurements to be made are not particularly limited and can be determined as appropriate.

(Alkali ion concentration evaluation process)
Next, in the alkali ion concentration evaluation step of the main test, the prepared test wafer is subjected to SPM cleaning, water washing, and drying in the same manner as the correlation acquisition step.
Then, after exposing the main test wafer to an unknown environmental atmosphere to be evaluated (environmental atmosphere to be evaluated) for a predetermined period of time, the reflection intensity on the wafer surface is measured.
Note that the length of this exposure time is not particularly limited, but may be, for example, the same exposure time as in the correlation acquisition step. Having the same length enables more accurate evaluation.

Using this measurement result of reflection intensity and the correlation between the alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface, which was determined in advance in the correlation acquisition process, the wafer surface of the main test wafer exposed to the environment atmosphere to be evaluated is calculated. Estimate the alkali ion concentration of
Then, the alkali ion concentration in the environment to be evaluated is evaluated from the estimated value.

With such an evaluation method of the present invention, it is possible to evaluate the alkali ion concentration in the environmental atmosphere with high accuracy, and it is possible to evaluate with accuracy at least as good as conventional evaluation methods. It can also be used to prevent pattern defects in lithographic processes and cloudiness on the wafer surface caused by alkali ions.
In particular, in the measurement of the alkali ion concentration described above, it is extremely effective to measure one or more of ammonia, methylamines, and ethanolamines, since these have a particular influence on the above problem. It is more preferable to measure all of these and use the total concentration (total alkali ion concentration).

Furthermore, in the evaluation method such as the conventional wafer exposure method shown in FIG. 15, it is necessary to perform ion chromatography measurement every time the wafer is exposed to the environment to be evaluated to measure the components adsorbed on the wafer surface, which is complicated. Met. However, in the present invention, such component measurement (measurement of alkali ion concentration) is unnecessary in the alkali ion concentration evaluation step of this test, and it can be estimated from the measured value of the reflection intensity on the wafer surface using the above correlation. It's simple.

EXAMPLES Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.
(Example)
As a correlation acquisition step (preliminary test) in the present invention, in Experimental Example 1, which will be described later, correlations obtained under different exposure times in the same environmental atmosphere are acquired. Further, in Experimental Example 2, correlations obtained in different environmental atmospheres and the same exposure time are obtained. Then, as an alkali ion concentration evaluation step (main test), the evaluation method of the present invention is carried out using the correlation of either Experimental Example 1 or 2 (here, the correlation of Experimental Example 2 is used).

First, we will summarize the preliminary test wafers and main test wafers used, as well as the method for measuring the alkali ion concentration and reflection intensity on the wafer surface.
The wafer used for exposure in the environmental atmosphere was a CZ silicon single crystal PW with a diameter of 200 mm. There are no particular restrictions on the wafer surface condition, and as long as the surface condition is smooth, it may be a bare Si surface or a SiO ₂ surface. Here, a bare Si surface was used.

This was cleaned with SPM (sulfuric acid and hydrogen peroxide) for 10 minutes at 120°C using a 1:1 ratio of 96% sulfuric acid and 35% hydrogen peroxide, and then rinsed with ultrapure water for 10 minutes. went. After washing with water, spin drying was performed.
Two SPM-cleaned wafers were exposed to the ambient atmosphere while being held vertically, thereby using both sides of the wafers as adsorption surfaces.

After the exposure, one exposed wafer was sealed in a polypropylene bag with 20 mL of ultrapure water, and the components adsorbed on the wafer surface were extracted for 20 minutes while heating at 80° C. in a water bath. The concentrations of ammonia and amines in the extracted solution were measured using a capillary electrophoresis device (Agilent 7100).

The remaining exposed wafer was measured using a wafer film thickness measuring device (Filmetrics F20), with the film structure set to SiO ₂ (natural oxide film), the optical constants fixed, and the incident light intensity constant at an arbitrary value. At that time, the difference between the maximum reflection intensity at a spectral wavelength of 400 nm to 500 nm and the background intensity was measured as the reflection intensity of the wafer surface. Regarding this reflection intensity, in order to use the reflection intensity of the surface of an unexposed wafer as a reference value, for convenience, it was assumed that the numerical value of the reflection intensity of the surface of an unexposed wafer, which serves as a reference, is 10,000.
More specifically, the incident light was continuous tungsten halogen light with a wavelength of 375 nm to 3000 nm, and the spectral wavelength of the reflected light used for reflection intensity measurement was 420 nm to 430 nm.

<Experiment example 1>
Next, as Experimental Example 1, using preliminary test wafers, the reflection intensity on the surface of the exposed wafer and the total amount of alkali ions (total alkali ions This section describes the process of obtaining the correlation between
Multiple sets of two wafers are prepared in the environmental atmosphere at location A for an exposure time of 3 to 48 hours, and as described above, one of each set is exposed to the adsorbed components of the wafer. was extracted and measured using a capillary electrophoresis device. In the other set of each set, the reflection intensity of the wafer surface was measured using a wafer film thickness measuring device. Regarding these measurement results, FIG. 4 shows the correlation between the reflection intensity of the wafer surface and the total amount of alkali ions. Further, FIG. 5 shows the relationship between the reflection intensity of the wafer surface and the exposure time of the wafer.
Table 1 also shows the concentrations of ammonia, methylamines, and ethanolamines, their total value (total alkali ion concentration), and the reflection intensity of the wafer surface at each exposure time.

There is a strong correlation between the total alkali ion concentration and the reflection intensity on the wafer surface due to exposure to the environmental atmosphere; the longer the exposure time, the lower the reflection intensity, and the higher the total alkali ion concentration, the lower the reflection intensity. Intensity decreases. This is because many sulfate ions are distributed on the wafer surface due to SPM cleaning, and when they combine with ammonia and amines in the environment, they become sulfide salts and precipitate on the wafer surface, and this depends on the exposure time. It is thought that this increases the amount of precipitation, causing clouding and reducing the reflection intensity on the wafer surface.

<Experiment example 2>
Next, as Experimental Example 2, using a preliminary test wafer, the correlation between the concentration of ammonia, methylamines, ethanolamines, and total alkali ions and the reflection intensity on the wafer surface was determined by exposure for 24 hours. This section describes the process of obtaining .
Wafers were exposed for 24 hours in the same manner as in Experimental Example 1 to the environmental atmospheres of five different locations (locations A to E), and one of each set was used to extract the adsorbed components of the wafer. It was measured using a capillary electrophoresis device. In the other set of each set, the reflection intensity of the wafer surface was measured using a wafer film thickness measuring device. Regarding these measurement results, FIG. 6 shows the relationship between the reflection intensity of the wafer surface and the concentration of total alkali ions. Further, FIG. 7 shows the relationship between the reflection intensity on the wafer surface and the ammonia concentration. Further, FIG. 8 shows the relationship between the concentration of methylamines and the reflection intensity on the wafer surface. Further, FIG. 9 shows the relationship between the concentration of ethanolamines and the reflection intensity on the wafer surface.
Table 2 also shows the reflection intensities of ammonia, methylamines, ethanolamines, total alkali ions, and wafers for locations A to E during a 24-hour exposure time.

As can be seen from the correlation coefficients (coefficients of determination) between the ammonia concentration, methylamine concentration, ethanolamine concentration, and total alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface, the total alkali ion concentration and The correlation coefficient with the wafer reflection intensity is closer to a straight line, indicating a better correlation.

These results show that there is a correlation between the alkali ion concentration (concentration of various alkali ions and total alkali ion concentration) and the reflection intensity of the wafer surface in wafers cleaned and exposed to SPM (especially is between the total alkali ion concentration and the reflection intensity of the wafer surface). Therefore, from the correlation between the alkali ion concentration and the reflection intensity of the exposed wafer (calibration curve), using the calibration curve, it is possible to determine the alkali ion concentration on the surface of the exposed wafer from the reflection intensity of the wafer exposed to an unknown environmental atmosphere. The concentration can be estimated and thus the alkali ion concentration in an unknown environmental atmosphere can be evaluated.

Therefore, an evaluation of an unknown environmental atmosphere was conducted as follows.
Wafers for this test were prepared, and the wafers after SPM cleaning were exposed to unknown environmental atmospheres (locations F to J) for 24 hours in the same manner as in Experimental Example 2. After exposure, the reflection intensity on the wafer surface was was carried out under the same conditions as Experimental Example 2.
Next, based on the previously determined calibration curve (correlation between total alkali ion concentration and reflection intensity in Experimental Example 2), total alkali ions on the wafer surface are calculated from the reflection intensity of the wafer surface after exposure. The concentration of the same species was estimated. Table 3 shows the results of evaluating the total alkali ion concentration in the unknown environmental atmosphere.
Here, for the sake of simplicity, the estimated value of the total alkali ion concentration on the wafer surface of the exposed wafer is evaluated as the total alkali ion concentration in the environmental atmosphere.
In addition, in Table 3, the estimated total alkali ion concentration and the total estimated concentration of each alkali ion do not match, but this is because the concentration can be calculated from the reflection intensity based on the calibration curve obtained in Figure 6-9. This is because conversion (estimation) is performed, and the estimated value of the total alkali ion concentration is not the sum of the estimated values of the concentrations of each alkali ion.

(Comparative example)
Next, as a comparative example, an evaluation was performed using the evaluation method of Patent Document 1 (conventional wafer exposure method (selective collection method)).
The wafer used for exposure in the environmental atmosphere was a CZ silicon single crystal PW with a diameter of 200 mm, as in the example. The acid treatment of the wafer was SPM (sulfuric acid hydrogen peroxide) cleaning, followed by rinsing with pure water. After drying the wafer, it was exposed to the same environmental atmosphere (locations F to J) as in the example for 24 hours, and the exposed wafer was sealed in a polypropylene bag with ultrapure water, heated and extracted, and the extract was subjected to ion chromatography. Measured using a graph (DX-500 manufactured by Dionex) (actual value). The measurement results are shown in Table 4.
The fact that the total alkali ion concentration deviates from the total concentration of each alkali ion by 0.1 ng/cm ² at location F in Table 4 is only a display problem due to rounding.

(Comparison of results between Example and Comparative Example)
A comparison of the example (item of estimated total alkali ions in Table 3) and the comparative example (item of total alkali ions in Table 4) reveals that the two exhibit roughly equivalent values. That is, it can be seen that the present invention allows evaluation to be performed with as much accuracy as the conventional method.
Further, in the comparative example, when evaluating the concentration in the environmental atmosphere, it is necessary to perform an ion chromatography measurement step to actually measure the alkali ion concentration each time, which is very complicated. On the other hand, in the present invention, there is no need to measure the alkali ion concentration on the wafer surface in this test, and the alkali ion concentration can be estimated from a relatively simple measurement of the light reflection intensity, and the alkali ion concentration in the environmental atmosphere can be evaluated. So it's really advantageous.

(Relationship with haze value)
In addition, since haze on the wafer surface can be detected as haze, the wafer surface was measured using an SP3 wafer surface inspection device manufactured by KLA TENCOL. Regarding the inspection values obtained from the surface haze map, the environmental atmosphere of the five locations (locations A to E) in Experimental Example 2 and the five locations The numerical values of the above unknown environmental atmosphere (locations F to J) were standardized.
Then, the actual measured value of the total alkali ion concentration of the wafer exposed in each environmental atmosphere (the value is a comparative example, but as mentioned above, it is comparable to the estimated value of the example of the present invention), the haze value, Table 5 and FIG. 10 show the results of visual inspection of the presence or absence of spiders under a condensing light.

As the total alkali ion concentration in the environmental atmosphere increases, the haze value also increases, but the haze becomes visible as a cloud when the total alkali ion concentration in the environmental atmosphere is approximately 100 ng/cm2 ^or more ( More precisely, at least 98.8 ng/cm ² at location J).
In other words, if the total concentration of alkali ions in the environmental atmosphere after 24-hour exposure is kept to less than 100 ng/cm ² (more precisely, less than 98.8 ng/cm ² ), clouds will not form on the wafer surface. It is suggestive. In addition, it is considered that if the amount is suppressed to 80.6 ng/cm ² or less at location A, the generation of spiders can be more reliably prevented.
Although the explanation has been given here using the actual measured values of the comparative example, instead, by selecting the evaluated environmental atmosphere using the measured values in the preliminary test and the estimated values in the main test in the corresponding present invention, It is possible to prevent the occurrence of spiders or to predict the occurrence of spiders.

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. within the technical scope of the invention.

Claims (5)

An evaluation method for evaluating alkali ion concentration in an environmental atmosphere, the method comprising:
A preliminary test wafer that has been subjected to SPM cleaning is exposed to an environmental atmosphere and the wafer surface is contaminated by alkali ions, and then the alkali ion concentration on the wafer surface and the wafer surface concentration are determined. a correlation obtaining step of measuring the reflection intensity and obtaining a correlation between the alkali ion concentration on the wafer surface and the reflection intensity on the wafer surface;
After the main test wafer that has been SPM cleaned is exposed to the evaluation environment atmosphere for a predetermined period of time, the reflection intensity of the wafer surface of the main test wafer is measured, and from the measurement results of the reflection intensity of the wafer surface, the above correlation is determined. Estimating the alkali ion concentration on the wafer surface of the main test wafer using the correlation acquired in the relationship acquisition step, and evaluating the alkali ion concentration in the evaluation target environment atmosphere from the estimated alkali ion concentration on the wafer surface. A method for evaluating an alkali ion concentration in an environmental atmosphere, the method comprising: a step of evaluating an alkali ion concentration in an environmental atmosphere. A claim characterized in that when the preliminary test wafer is contaminated by spreading the amount of contamination by alkali ions on the wafer surface, it is carried out by varying the exposure time in the same environmental atmosphere or by making the exposure time the same in different environmental atmospheres. Item 1. The method for evaluating alkali ion concentration in an environmental atmosphere as described in Item 1. 3. The method for evaluating alkali ion concentration in an environmental atmosphere according to claim 1, wherein the alkali ion concentration on the wafer surface is measured using a capillary electrophoresis device. The environment according to any one of claims 1 to 3, wherein the alkali ion concentration on the wafer surface is measured for one or more of ammonia, methylamines, and ethanolamines. Method for evaluating alkali ion concentration in the atmosphere. When measuring the reflection intensity on the wafer surface, use a wafer film thickness measuring device to measure the difference between the maximum reflection intensity at a spectral wavelength of 400-500 nm of the reflected light obtained by vertically incident light on the wafer surface and the background intensity. The alkali in the environmental atmosphere according to any one of claims 1 to 4, wherein a value based on a wafer not exposed to the environmental atmosphere is determined as the reflection intensity of the wafer surface. Method for evaluating ion concentration.