JPH05275410A - Evaluation method for organic compound adhering to wafer surface - Google Patents

Abstract

PURPOSE:To evaluate the cleanliness of a clean room by simplify evaluating an organic matter adhering to a wafer surface in a non-destructive manner and by simply determining the adhering state of a contaminant organic compound, when a wafer is stored in the clean room. CONSTITUTION:The difference between film thickness before and after the adhesion of a contaminant organic compound to a wafer surface is measured by ellipsometry and the change of a contact angle is also measured simultaneously so that the quantitative and qualitative analysis of the contaminant are performed by a non-destructive inspection. For example, after SCI cleaning of the wafer surface, a film thickness is measured and, after a predetermined period of time, the wafer surface is cleaned by a surfactant and the film thickness is measured. The degree of organic-matter contamination is determined by the difference between these measured values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating an organic compound adhering to a wafer surface for determining the amount and properties of an organic material adhering to the wafer surface and impairing the quality of a semiconductor wafer.

[0002]

2. Description of the Related Art Contaminants that have once adhered to semiconductor wafers or remain after cleaning remain in a form that is difficult to remove by any subsequent cleaning process depending on the content thereof, and eventually lead to impaired device performance in many cases. .. Therefore, the recognition that it does not contaminate the wafer surface is very important. In particular, it is necessary to pay close attention to wafer contamination during storage after the completion of all wafer processes. This is because, for example, organic contaminants inhibit the growth of an oxide film in a low temperature process, or make the wafer surface water-repellent to make it difficult to remove metallic contaminants. Qualitative analysis of contaminants attached to the wafer after the cleaning, particularly organic compounds, has been performed by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (ATR), or the like.

[0003]

However, in all of these methods, substantially all of these methods must take the form of destructive inspection, and the wafer itself cannot be reused. That is, no evaluation technique has been established for simultaneously performing the qualitative and quantitative analysis of the attached organic compound by the nondestructive method. Therefore, the cleanliness in the clean room is quantitatively analyzed not only by the organic compounds in the clean room, but especially by the wax, oil, resin, etc. The method of checking was not established.

The present invention is capable of easily inspecting the state of adhesion of organic compounds on the surface of a wafer in a non-destructive state and, for example, it is possible to evaluate the degree of contamination in a clean room. The purpose is to propose an evaluation method.

[0005]

Such objects are achieved by the present invention described below. That is, in the present invention, by measuring the increase / decrease in the film thickness of the deposits deposited on the wafer surface at a predetermined time after cleaning with a liquid obtained by diluting NH ₄ OH and H ₂ O ₂ with H ₂ O, and / Alternatively, the organic compound attached to the wafer surface is evaluated by measuring the change in contact angle.

In the present invention, first, the wafer surface is cleaned with an SC1 cleaning solution. As the SC1 cleaning liquid, for example, H
₂ O: H ₂ O ₂ : NH ₄ OH = 5: 1: 1 (volume ratio) is used. Then, the film thickness of the organic substance attached to the wafer surface immediately after this cleaning is measured by, for example, an ellipsometer. Alternatively, pure water is dropped on the surface of the wafer and the contact angle is measured. Then, the wafer after the measurement is stored in, for example, a clean room or a storage clean case for a predetermined time (several hours), and the contact angle measurement and the film thickness measurement by ellipsometry are performed again. Then, by obtaining the difference between the measured value immediately after cleaning and the measured value after storage, the degree of contamination by organic substances on the wafer surface, that is, the degree of contamination in the clean room or storage case is evaluated.

Further, the specific constitution of the present invention will be described in detail. Prepare a dummy wafer for contamination degree evaluation in a clean room, form a thermal oxide film on this wafer, and then perform S
C1 cleaning is performed. The thickness of the oxide film is 100 in consideration of the ease, certainty, sensitivity, etc. of ellipsometry measurement.
It is preferably about 0 angstrom. And
The film thickness of the organic substance of the dummy wafer after this cleaning and the contact angle of the pure water drop dropped on the surface thereof are measured. The film thickness may be measured by a usual ellipsometry method, and the contact angle may be measured by a usual method. The dummy wafer having this thermal oxide film formed is stored in a clean room for a predetermined number of days. The number of days should be 1 to 10 days, with 1 in between.
By measuring about 5 points, it is possible to appropriately follow up and evaluate the increase in pollutants.

For example, the film thickness of the dummy wafer after 3 days is measured by ellipsometry, and the difference from the film thickness immediately after the oxide film is formed 3 days before is obtained to quantify the organic compound deposited on the wafer. be able to. Then, the smaller the difference between the film thicknesses, the higher the cleanliness in the clean room can be determined. Further, the contaminants can be qualitatively determined by obtaining the difference in contact angle between the dummy wafers. Especially when the difference is zero, it is possible to confirm that the cleanliness of the dummy wafer is completely maintained, so that the contact angle measurement immediately after the formation of the thermal oxide film is effective. Moreover, as shown in FIGS.
Is small when the DUT 3 is a hydrophilic substance and is large when the DUT is a hydrophobic substance. Therefore, the nature of the deposit can be specified by the size of the contact angle of the droplets 1 or 2. That is, when the contact angle is large (in the case of b), the presence of an organic compound, particularly wax, resin, etc. is presumed, and when the contact angle is small (in the case of a), in addition to the organic compound, an inorganic compound It is estimated that there is a pollution source. Further, since the contact angle varies depending on the type of organic compound, more rigorous qualitative analysis can be performed. Since the evaluation method of the present invention can perform quantitative and qualitative analysis of polluted organic compounds at the same time in this manner, it is possible to more reliably evaluate the cleanliness in the clean room and to identify the type of contaminants. , It is useful for estimating the source of pollution, planning measures to improve cleanliness, and planning recleaning. Further, the evaluation method of the present invention is a non-destructive inspection, which is advantageous in terms of cost. If the dummy wafers used in the present invention are mixed in a plurality of real wafers placed in the wafer cassette 4 as shown in FIG. 8, the contamination degree of the real wafers can be evaluated in the same atmosphere. So it is more effective.

[0009]

EXAMPLES Example 1 After forming a SiO ₂ film on _two silicon wafers, S
After C1 cleaning, contact angle measurement and film thickness measurement by ellipsometry were performed. The thickness of the thermal oxide film was 995 Å. Next, this wafer was stored in two types of clean rooms. Here, the wafer A was stored in a clean room not using the organic substance removing filter, and the wafer B was stored in a clean room using the organic substance removing filter. Then, the adhesion state of the organic compound due to the change with time was measured, and the difference from the above measurement was obtained. The result of the film thickness measurement is shown in FIG. 1, and the result of the contact angle measurement is shown in FIG.
From this result, it is clear that the evaluation method of the present invention is effective.

Two wafers were prepared in the same manner as in Example 2 , the wafer C was covered with a case and the wafer D was exposed to the atmosphere and stored in a clean room. The change over time is shown in FIGS. From this result, the effectiveness of the evaluation method of the present invention was confirmed.

Example 3 Next, the wafer was stored in a clean room in which the amount of organic substances was the same, while changing only the humidity. Wafer E has a humidity of 30R
H% and wafer F were stored in a humidity of 50 RH% and the same measurement was performed. The results are shown in FIGS. From this, the evaluation method of the present invention is effective.

[0012]

According to the method of the present invention, the organic contamination can be easily measured without destroying the wafer. Therefore, the wafer to be measured can be reused by washing with pure water. Further, as a result, it is possible to measure the cleanliness of an atmosphere such as a clean room and evaluate the result of cleaning with a surfactant. Moreover, by forming the thermal oxide film, the influence of the natural oxide film can be eliminated and the measurement can be performed accurately. Further, by using the film thickness measurement and the contact angle measurement together, the quantitative and qualitative analysis of contaminants can be performed at the same time. It is the most suitable method to evaluate the cleanliness of each process or clean room.

[Brief description of drawings]

FIG. 1 is a graph showing a change with time in a film thickness of a wafer when a storage location is changed in the method for evaluating an organic compound attached to a wafer surface according to Example 1.

FIG. 2 is a graph showing changes in the contact angle.

FIG. 3 is a graph showing changes over time in the film thickness of an attached organic compound with and without a case according to Example 2.

FIG. 4 is a graph showing changes in the contact angle of the same.

FIG. 5 is a graph showing changes with time in film thickness when the humidity of the clean room according to Example 3 is changed.

FIG. 6 is a graph showing changes in the contact angle of the same.

7A and 7B are schematic diagrams showing the degree of change in contact angle when pure water is dropped on a hydrophilic substance and a hydrophobic substance.

FIG. 8 is a schematic diagram showing another example of a method of using a dummy wafer in the present invention.

[Explanation of symbols]

 1, 2 Pure water 3 Wafers 4 Wafer cassette θ Contact angle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuro Morita 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Central Research Laboratory, Mitsubishi Materials Corporation (72) Inventor Takayuki Shingouchi 1-297 Kitabukuro-cho, Omiya-shi, Saitama Central Research Laboratory of Materials Co., Ltd.

Claims (1)

[Claims] 1. An increase / decrease in film thickness of deposits deposited on a wafer surface at a predetermined time after cleaning (hereinafter referred to as SC1 cleaning) with a solution obtained by diluting NH ₄ OH and H ₂ O ₂ with H ₂ O is measured. And / or by measuring the change in the contact angle, the evaluation of the organic compound attached to the wafer surface is performed.