JPH08128962A - Method for examining trace contaminated state - Google Patents

Abstract

PURPOSE: To examine a contamination with a high sensitivity by arranging a silicon substrate in a space to be examined, allowing it to stand for a fixed period, exposing the surface to water, and detecting the particles adhered to the surface. CONSTITUTION: A beaker 2 containing a contaminant 5 is arranged in a vessel 1, and a bare silicon wafer 3 is arranged with the polished surface toward the material 5. The vessel 1 is allowed to stand for about 18 days after sealed by a lid 4, and the particles on the wafer surface are counted in the state where the wafer is taken out from the vessel 1, the state after it is rinsed with pure water, and the state after it is brush-scrubbed, respectively. The wafer is once taken out, for example, on the first, third, and seventh days after it is left, and returned into the vessel 1 after particle counting. Depending on the kind of the material 5, throughout these measurements, there are cases where the particles are increased but cart be removed pure water rinsing, and cases where the particles are never increased in the left state out increased after brush scrubbing. Thus the contaminated state of the environment in which the wafer is left can be known by counting these particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for investigating a trace amount of pollution, and more particularly to a method for investigating the status of contamination in a clean room.

[0002]

2. Description of the Related Art A clean room is usually supplied with air from which particles in the outside air have been removed by a filter. For example, the air is adjusted so that 100 particles or less having a diameter of 0.1 μm or more per 1 m ³ .
Various processing apparatuses are arranged in the clean room, and particles or gas are often generated depending on the content of the processing. These cause pollution in the clean room.

Conventionally, as a method for measuring the contamination state of a clean room, a method of absorbing air in the environment with a solvent such as pure water and analyzing the absorbing solution by liquid chromatography, atomic absorption or plasma emission spectroscopy, A method for directly analyzing a gas by infrared spectroscopy or mass spectrometry,
After the test piece is left in the environment, the surface of the test piece is analyzed by ESCA (electron spectroscopy for chemical analysis) or etching, and the gas in the environment is adsorbed and concentrated for analysis. A method, a method of performing temperature rising desorption of a gas adsorbed on a wafer, and performing mass spectrometry are known.

By the above method, it is possible to know the pollutant and the pollutant concentration.

[0005]

Although it is possible to know the pollutant and the pollutant concentration by the above method, the detection sensitivity is not sufficient to detect the pollutant in the clean room for semiconductor device manufacturing. In addition, sophisticated measuring technology and expensive measuring equipment are required.

An object of the present invention is to provide a method for investigating the pollution state of the environment with high sensitivity and in a simple manner.

[0007]

A method for investigating a contamination state according to the present invention comprises a step of placing a silicon substrate in a space where the contamination state is to be investigated and leaving it for a certain period of time, and a step of exposing the surface of the silicon substrate to water. And detecting particles adhering to the surface of the silicon substrate.

In the step of exposing to water, the surface of the silicon substrate may be physically rubbed while being exposed to water. In the step of exposing to water, the surface of the silicon substrate may be exposed to water and the surface of the silicon substrate may be scrubbed with a brush.

The surface of the silicon substrate may be a bare silicon surface, a thermal oxide film surface, a silicon oxide film surface deposited by CVD, a silicon nitride film surface, or a polysilicon film surface.

In the step of leaving, the air may be forcedly sent to the surface of the silicon substrate.

[0011]

When a wafer surface left in a contaminated environment is exposed to water, contaminants may increase particles on the surface. By detecting these particles, it is possible to know the pollution state of the environment. Even if the contaminant cannot be identified, the degree of contamination can be detected with high sensitivity.

Particles are easily generated when the wafer surface is physically rubbed while being exposed to water. Therefore, even if the particles cannot be detected only by exposing them to water, there are cases where the particles can be detected by physically rubbing. By physically rubbing in this way, the detection sensitivity can be increased.

The generation of particles after exposure to water is
It also depends on the surface characteristics of the silicon wafer. By using wafers with different surface characteristics, different contamination states are expected to be detected.

Further, if the air is forcibly blown to the wafer surface while the wafer is left standing, the wafer surface is more likely to be contaminated.
Therefore, it is expected that particles will be detected even if the standing period is shortened.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to FIG. 1, a phenomenon which is a basis of a method for investigating a trace amount of pollution according to an embodiment of the present invention will be described.

FIG. 1 (A) shows a schematic sectional view of an apparatus used for a confirmation experiment of a phenomenon which is a basis of a method for investigating a trace pollution state. A beaker 2 containing a contaminant 5 is placed in a container 1. In addition, a bare silicon wafer 3 that has been subjected to hydrogen peroxide-based RCA cleaning is placed in the container 1 so that the polishing surface faces the contaminant 5.

The space inside the container 1 in which the silicon wafer 3 and the contaminants 5 are arranged is almost closed by the lid 4.
It was left for 18 days after being sealed. After that, the particles on the wafer surface in the state of being taken out from the container, after being rinsed with pure water, and after being rubbed with a brush scrubber were counted. The wafers were once taken out on the first, third, and seventh days after standing, and the particles on the surface of the wafer were counted and returned to the container again.

FIG. 1B shows an outline of the brush scrubbing process. The silicon wafer 3 is fixed on the rotating disk 6 and rotated about the central axis. While supplying pure water from the nozzle 8 to the surface of the silicon wafer 3, the brush 9 is rotated to rub the surface of the silicon wafer 3. By rotating the brush 9 and translating it at the same time, the entire surface of the wafer can be rubbed.

FIG. 1C schematically shows a method of counting particles. Silicon wafer 3 on the mounting table 10
Is placed, and the surface of the wafer 3 is irradiated with Ar laser. The scattered light scattered from the surface of the wafer 3 is detected by the integrating sphere 11 and converted into an electric signal by the photomultiplier 12.

The pollutant 5 is a typical pollutant such as a dust-proof coating, dioctyl phthalate (DOP), and a silicone sealant, and hexamethyldisilazane (HMDS) used as a resist adhesive, and a resist (THMR-). Experiments were carried out for 5 types of ip2100).

For counting particles, a detection sensitivity of 0.1
A μm optical wafer dust detection device (WM-1010, manufactured by Topcon) was used. As the brush scrubber, C / T-SS-2 brush scrubber manufactured by Tokyo Electron Ltd. was used.

Table 1 shows, for each pollutant, 1, 3, 7,
The number of detected particles on the wafer surface on the 18th day, after the pure water rinse, and after the brush scrub treatment is shown.

[0023]

[Table 1]

When the pollutant was a dustproof paint, particles were observed on the orientation flat portion on the 7th day, and particles were observed on the entire surface on the 18th day.
These particles could be almost removed by rinsing with pure water.

In the case of DOP, no increase in particles was observed from day 1 to day 18. Although no significant change in the number of particles was observed after the pure water rinse, an increase in the number of particles was observed in the central portion of the wafer after the brush scrub treatment.

In the case of the silicone sealant, almost no increase in particles was observed. In the case of HMDS, as in the case of DOP, there was almost no increase in particles from day 1 to day 18. No significant change in the number of particles was observed even after rinsing with pure water, but the number of particles increased sharply after the brush scrub treatment. At this time, many particles were observed in the central portion and the peripheral portion of the wafer.

In the case of the resist, almost the same tendency as in the case of the dustproof paint was exhibited, and an increase of particles was observed on the 7th and 18th days. These particles could be almost removed by rinsing with pure water.

From the above experimental results, the contamination of the wafer surface has increased particles, but it can be removed by rinsing with pure water, and no increase in particles is observed in the state of being left standing. It can be seen that there are two types of cases where particles increase.

The reason why particles increase when brush scrubbing the wafer surface contaminated with DOP or HMDS is considered to be that the gas or the like adsorbed on the surface is hydrolyzed to become solid and detected as particles. By counting the particles, it is possible to know the contamination state of the wafer surface and thus the contamination state of the environment where the wafer is left.

The surface contaminated with HMDS was superhydrophobic, and even if pure water was treated with a spinner, pure water did not spread over the entire surface of the wafer. Next, a first embodiment of the present invention will be described with reference to FIGS.

A silicon wafer having a 100 nm thick SiO ₂ film formed on its surface by CVD (chemical vapor deposition)
It was left in multiple places in a clean room. After the lapse of 1, 3, and 7 days, the wafer surface was subjected to a brush scrub treatment, and the number of particles on the surface was measured by a wafer dust detection device.

FIG. 2 shows the increased number of particles on the wafer surface after being left at each of the leaving locations. There are 10 places of leaving, A to J, and the measurement results of two wafers are shown for each place. The data for the first wafer is shown in the left half and the data for the second wafer is shown in the right half in the graphs of each abandoned place. For each wafer,
Left, center, and right bar graphs are for the first day after leaving, 3
The number of particles after the brush scrub on the 7th day is shown.

It can be seen that the number of particles is remarkably increased in the wafers at the leaving places B, C and D. In the abandonment place B, almost no increase in particles is observed when the number of days left is 3 days or less. When the number of days left is 7 days, the number of particles increases rapidly, and the first wafer has about 40 particles.
The number of 00 wafers and the number of second wafers is about 10,000.

In the abandoned place C, the number of particles increases with the passage of days. In the first wafer, the number of particles increases to about 1,900 after standing for 3 days and to about 4,600 after standing for 7 days. For the second wafer, leave it for about 3 days for about 900
Particles increase to about 2000 when left for 7 days.

In the abandoned place D, as in the abandoned place C, the number of particles increases with the passage of days. With the first wafer, about 1200 wafers are left for 3 days, and about 310 wafers are left for 7 days.
Particles increase to 0. For the second wafer,
The particles increase to about 5,700 after standing for 3 days and to about 6,300 after standing for 7 days.

At other locations, no particularly problematic increase in particles was detected. FIG. 3 shows a particle map of the surface of the wafer on which particles are generated.

FIG. 3 (A) shows a particle map of the first wafer left for one day in the left place C after brush scrubbing. There is almost no increase in particles compared to before leaving.

FIG. 3B shows a particle map after the brush scrubbing of the first wafer left in the left place C for 7 days. It can be seen that particles are concentrated and generated on the upper and lower sides of the wafer surface in the figure. this is,
When holding the wafer in the wafer carrier, the second wafer was inserted adjacent to the front side of the first wafer,
It is considered that the upper side and the lower side of the surface of the first wafer were exposed to more contaminants.

The particle map of the first wafer in the leaving places B and D also shows the same tendency as in FIG. 3 (B). FIG. 3C shows a particle map of the second wafer left for 7 days in the left place C after the brush scrub treatment. It can be seen that particles are concentrated in the center of the wafer.

FIG. 3D shows a particle map of the second wafer left in the left place B for 7 days after the brush scrub treatment. It can be seen that the particles are distributed radially from the center of the wafer.

As shown in FIGS. 3 (C) and 3 (D), it is not clear why particles are concentrated in the center of the wafer or generated radially from the center, but the frictional characteristics during brush scrubbing are different. It is presumed that the wafer surface is not uniform but has variations.

FIG. 4 shows a change in film thickness formed on the surface of the wafer left in the left place D of FIG. The horizontal axis represents the number of days left to stand, and the vertical axis represents the film thickness in nm. The film thickness is measured by ellipsometry.

Symbols □, ○, and ▲ in the figure respectively indicate the film thicknesses of the orientation flat portion, the central portion, and the numbering portion. The symbols Δ and ■ indicate the film thickness at the intermediate portion between the orientation flat portion and the central portion and at the intermediate portion between the central portion and the numbering portion, respectively. Also, the symbol * is other 20
The average film thickness of the points is shown.

The film thickness increases relatively rapidly on the first 5 days and gradually increases after the 5th day. After 20 days, the film thickness hardly increases. Since a silicon oxide film having a thickness of about 100 nm is formed on the wafer surface in the initial state by CVD, it is unlikely that the increase in the film thickness is due to the natural oxide film. Therefore, although it cannot be specified, it is considered that some kind of film is formed on the surface or that the surface state is changed by adsorbing contaminants and the refractive index is changed.

By brush scrubbing the thus-changed wafer surface and detecting particles by the wafer dust detector, the change of the wafer surface state can be visualized as a particle map and quantified as the number of particles. .

As described in the first embodiment, the surface of the wafer left in the clean room is subjected to the brush scrubbing process and the particles are detected by the wafer dust detecting device to easily detect the environmental pollution state with high sensitivity. Can be investigated.

Incidentally, even if the particles are left in the abandoned places B, C and D and the number of particles is remarkably increased, it is often the case that almost no impurities can be detected by the conventional elemental analysis.
Therefore, the above-mentioned processing has very good detection sensitivity. Particles once generated are difficult to remove by brush scrubbing or the like. However, particles are removed by hydrofluoric acid treatment and ammonium peroxide treatment. From this result, it is presumed that the particles are silanol-based substances.

By forcibly blowing air on the surface of the wafer, the number of days left until particle detection may be shortened. Next, referring to FIG. 5 and FIG.
An example will be described.

In the phenomenon confirmation experiment described in FIG. 1, a bare silicon wafer was used as a wafer to be left unattended. Further, in the first embodiment, the thickness of the surface is 100 n by CVD.
A silicon wafer having a SiO ₂ film of m was used.
In this example, the influence of the surface characteristics of a wafer to be left on generation of particles will be described.

FIG. 5 (A) is a wafer in which a thermal oxide film having a thickness of 100 nm is formed on the surface of a silicon wafer, FIG. 5 (B).
Shows a particle map when a bare silicon wafer is used. Both of them are left in the same environment for one week, and the state of particle generation is observed by a wafer dust detection device after the brush scrub treatment.

The numbers of particles of the wafer on which the thermal oxide film was formed and the bare silicon wafer were about 7700 and 1100, respectively. As described above, although the environment in which the particles are left is the same, the generation state of particles is greatly different depending on the surface characteristics of the wafer.

FIGS. 6A and 6B are wafers each having a SiN film with a thickness of 150 nm formed on the surface of a silicon wafer.
(C) and (D) show particle maps when a wafer on which a polysilicon film having a thickness of 100 nm is formed is used. Along with this, the particles were left in the same environment for 10 days or more, and after the brush scrub treatment, the state of particle generation was observed by the wafer dust detection device.

6A and 6C are SSW-629 brush scrubbers manufactured by Dainippon Screen Mfg. Co., Ltd. using a rayon brush, and FIGS. 6B and 6D are polyvinyl alcohol (PVA) brushes. Brush scrubbing using a C / T-SS-2 brush scrubber using.

The number of particles in FIGS. 6A to 6D is
They are about 900, 2100, 1500 and 200, respectively. 6 (A) and (C), or FIG. 6 (B) and (D)
From the comparison, it can be seen that the generation state of particles is different between the surface of the SiN film and the surface of the polysilicon film.

Further, FIGS. 6A and 6B or FIG.
Comparing (C) and (D), it can be seen that the generation state of particles also differs depending on the brush scrubber that performs the brush scrubbing process.

As described above, since the generation state of particles varies depending on the surface characteristics of the silicon wafer left in the environment, by leaving the silicon wafers having various surface characteristics in the same place, the contamination state can be detected with higher sensitivity. Expected to be investigated.

Since the generation state of particles also differs depending on the brush scrubber, it is preferable to use a brush scrubber that is more likely to generate particles.
Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 7A is a particle map of the initial state of a silicon wafer having a SiN film formed on its surface.
FIG. 7B shows a particle map of a wafer obtained by dropping several drops of pure water onto the wafer in the state of FIG. The number of particles before dropping pure water is about 1200, and the number of particles after dropping pure water and spin drying is also about 1200.
Therefore, there is almost no change in the number of particles.

FIG. 7C is a particle map of a silicon wafer having a SiN film formed on the surface thereof after being left in a clean room for a certain period of time. FIG. 7D is a pure map of the wafer in the state of FIG. 7C. 3 shows a particle map of a wafer obtained by spin-drying a few drops of water. The water droplets dropped on the wafer surface move to the outer peripheral portion of the wafer while drawing an arc by centrifugal force, and are scattered from the outer peripheral edge to the periphery.

As shown in FIG. 7D, particles are generated along the trajectory of the water droplet. It is considered that this is because the contaminants adsorbed on the wafer surface were hydrolyzed to generate particles. As described above, under a certain condition, particles are generated only by exposing the surface of the abandoned wafer to water without brush scrubbing.

When the generation of particles is not sufficient just by exposing to water, it is considered that hydrolysis is promoted and the generation of particles is amplified by physically rubbing by brush scrubbing or the like.

As described in the first to third embodiments, according to the embodiment of the present invention, the wafer left in the clean room is exposed to water or brush scrubbed, and the number of particles is detected by the wafer dust detector. By measuring, it is possible to know the state of pollution of the environment. Although it is not possible to specify the pollutant and the pollutant concentration, it is possible to easily and easily investigate the pollutant that is a problem in the manufacturing process of the semiconductor device.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0064]

As described above, according to the present invention,
It is possible to easily and easily investigate the pollution state of the environment. This makes it possible to improve the yield of semiconductor devices.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus used for an experiment for confirming a phenomenon which is a basis of a method for investigating a trace amount of pollution according to an embodiment of the present invention.

FIG. 2 is a graph showing the increased number of particles on the surface of an abandoned wafer according to the first embodiment.

FIG. 3 is a plan view of the wafer showing a particle map on the surface of the wafer observed in the first embodiment.

FIG. 4 is a graph showing changes in the film thickness on the wafer surface observed in the first example.

FIG. 5 is a plan view of the wafer showing a particle map on the surface of the wafer observed by the second embodiment.

FIG. 6 is a plan view of the wafer showing a particle map on the surface of the wafer observed by the second embodiment.

FIG. 7 is a plan view of the wafer showing a particle map on the surface of the wafer observed by the third embodiment.

[Explanation of symbols]

 1 Container 2 Beaker 3 Wafer 4 Lid 5 Contaminant 6 Rotating Disk 8 Nozzle 9 Brush 10 Mounting Table 11 Integrating Sphere 12 Photomaru

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadamitsu Wada 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (6)

[Claims] 1. A step of placing a silicon substrate in a space where a contamination state is to be investigated and leaving it for a certain period of time, a step of exposing the surface of the silicon substrate to water, and removing particles adhering to the surface of the silicon substrate. A method for investigating a contamination state including a step of detecting. 2. The contamination state investigating method according to claim 1, wherein in the step of exposing to water, the surface of the silicon substrate is physically rubbed while being exposed to water. 3. The surface of the silicon substrate is one of a bare silicon surface, a thermal oxide film surface, a silicon oxide film surface deposited by CVD, a silicon nitride film surface, an amorphous silicon film surface, and a polysilicon film surface. A method for investigating a pollution state according to any one of claims 1 to 2. 4. A plurality of the silicon substrates are arranged, and the surfaces of the silicon substrates are a bare silicon surface, a thermal oxide film surface, a silicon oxide film surface deposited by CVD, a silicon nitride film surface, an amorphous silicon film surface, and The contamination state investigation method according to any one of claims 1 and 2, wherein a combination of a plurality of types of the surface of the polysilicon film is used. 5. The method for investigating a contamination state according to claim 1, wherein the step of leaving is a step of forcibly sending air to the surface of the silicon substrate. 6. The contamination state investigating method according to claim 1, wherein in the step of detecting the particles, scattered light is measured to optically detect the particles.