JPS6291842A - Method for evaluating cleanliness - Google Patents

Abstract

PURPOSE:To detect the foreign matter sticking onto a substrate with high sensitivity by coating the surface of the substrate with a material having >=70% reflectivity to light. CONSTITUTION:Al is deposited by sputter evaporation to about 50nm (91% reflectivity to He-Ne laser light) on the mirror surface side of, for example, an Si wafer (about 4 inch diameter) of which at least one face is finished to the specular surface. Such wafer is immersed into a standard particle suspension (for example, 10<5> pieces/ml particle concn. and 0.33mum particle size) and after drying, the number of the foreign matter on the wafer is measured by using an instrument for measuring the stuck foreign matter (using the He-Ne laser). The particles of the respective particle sizes on the Si wafer can be detected with the detection voltage lower by about 110V than on the Al deposited wafer. The 0.109mum particles cannot be detected on the Si wafer but can be detected at about 1,300V on the Al deposited wafer. The very small foreign matter on the substrate is, therefore, detected with the high accuracy by covering the substrate surface with the material having >=70% reflectivity to light.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the evaluation of the cleanliness of a substrate surface that needs to be treated cleanly in a clean space, and particularly to the evaluation of the cleanliness of a substrate surface that needs to be treated cleanly, and in particular to increase the detection sensitivity of foreign substances attached to the substrate surface. This invention relates to a cleanliness evaluation method suitable for

[Background of the invention]

Conventionally, the cleanliness of environments such as clean rooms has long been evaluated using dust counters that utilize light scattering to measure the concentration of suspended dust. However, from the viewpoint of improving the quality of LSI, what is actually a problem is not the concentration of floating dust but the number of foreign particles adhering to the substrate. As this evaluation method, Hitachi Review Vol. 65, p-39 (198
As shown in 3), the number of foreign particles attached to the Si wafer was measured using an attached particle measurement device that uses light scattering to a total of 1111'.
A method has been proposed to evaluate cleanliness by

However, when a Si wafer is used in the above method, the minimum detectable particle size is limited to about 0.17 μm. The detected particle size is determined by the performance of the laser and photomultiplier used, except for the wafer used.

In order to obtain performance equivalent to that of the present invention described below, it is necessary to increase the laser output approximately three times, but (1) the noise also increases according to the output, and the S/N ratio is not improved much. (2) Problems arise, such as the price becoming more than an order of magnitude higher.

[Purpose of the invention]

An object of the present invention is to provide a cleanliness evaluation method that can measure foreign substances on a wafer with high sensitivity by covering the wafer surface with a substance having a higher light reflectance than Si.

[Summary of the invention]

The inventor I゛) conducted a detailed study on the dependence of the detected particle size on the underlying material using an attached foreign matter 4 (1) machine. As a result, the following was clarified. (1) As shown in Fig. 1. As shown, when using AQ (film)-'i, : 50 nm), a detection voltage that is approximately [10 .mu.m] lower is required than when using Sl as the F base material for particles of the same particle size. (2)
As shown in FIG. 2, the signal voltage from the particles is about three times higher in AQ (film thickness: 50 nm) than in Si.

This result can be used for cleanliness evaluation targeting finer particles.

[Embodiments of the invention]

Example 1 Examples of the present invention will be described below.

AQ, approximately 50 nm (Hp - N e
(Reflectance to laser beam = 91%) Sputter deposition was performed.

This wafer was mixed with a standard particle suspension (particle degree: 105 particles/
mQ, particle size: 0.3 μm) and dried,
The number of foreign particles on the wafer was measured using a 1lIII constant machine (using a He-Ne laser). Is the relationship between detection voltage and particle size the same as in Figure 1? ') can be done. The detection voltage of each particle size on the Si wafer is
It was possible to detect the culm at a voltage 110 μ lower than that of the culm. moreover,
0.109 μm particles could not be detected on the Si wafer, but could be detected at about 1300 V on the AQ debo wafer. Therefore, according to this embodiment, it is possible to measure and evaluate foreign matter attached to a wafer with high sensitivity without improving the foreign matter adhesion measurement device. Further, similar effects can be obtained using gold (reflectance: 92%) and copper (reflectance: 93%). Note that in the range of 10 to 500 nm, the deposited film thickness does not change the flatness or reflectance of the surface, and the effect of improving detection sensitivity remains the same. However, when the thickness of the deposited film is thin, the reflectance decreases rapidly and the effect is lost. In addition, if it is thick, the surface becomes uneven and causes diffuse reflection, making it impossible to distinguish it from particles.

Example 2 Silver (Ag) was coated to a thickness of about 200 nm (reflectance:
(approximately 98%) was sputter deposited. This wafer was mixed with a standard particle suspension (particle concentration: 105 particles/mQ, particle size 2.9
The number of foreign particles on the wafer was measured using a measuring device.The results are obtained in the same manner as in FIG. 1.

The detection voltage on the Si wafer is about 770V, but A
On the g-deposited wafer, particles could be detected at a voltage as low as about 140V, about 630V. Furthermore, particles of 0.109 μm, which could not be detected on Si, could be detected at about 1300 V on the Ag-deposited wafer. According to this embodiment, it is possible to measure and evaluate foreign matter adhering to a wafer with high sensitivity without improving the foreign matter adhesion measurement device.

Note that this evaluation method can be applied not only to semiconductors but also to optical disks, magnetic bubbles, etc.

〔Effect of the invention〕

According to the present invention, the intensity of scattered light from foreign particles adhering to the wafer can be made three times stronger by 11 A (detection voltage 1''0) than the conventional method, so that foreign particles can be detected with high sensitivity.

[Brief explanation of drawings]

Figure 1 shows the relationship between the number of detected 0.546 μm particles and the detection voltage (
Figure 2 shows the relationship between the light scattering signal voltage from particles and the detection voltage (Si wafer and A12 non-evaporated 50nm wafer).
m) Comparison with wafer).

Claims (1)

[Claims] 1. In a method of evaluating cleanliness by irradiating light having a specific wavelength onto minute foreign particles attached to a substrate and detecting scattered light, the surface of the substrate is exposed to the light. A method for evaluating cleanliness characterized by covering the surface with a substance having a reflectance of 70% or more. 2. The cleanliness evaluation method according to item 1 above, using a metal film as the substance with a reflectance of 70% or more.