JPH0613444A - Evaluation of cleanliness of wafer heattreatment furnace - Google Patents

Abstract

PURPOSE:To provide a method for evaluating a cleanliness of a wafer heat treatment furnace with the advancement of a quality of a semiconductor device. CONSTITUTION:This is a method for evaluating a cleanliness of a wafer heat treatment furnace. A wafer is preliminarily heat-treated at 600-900 deg.C for 4 hours or longer to precipitate interstitial oxygen on the entire wafer. After that, the wafer is heat-treated in a wafer heat treatment furnace and the life time of the wafer is measured. By this method, the time required for evaluating the cleanliness of the wafer heat treatment furnace is shortened and the sensitivity of evaluation is increased.

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 the cleanliness of a wafer heat treatment furnace which is accompanied by the improvement of the quality of semiconductor devices.

[0002]

2. Description of the Related Art Generally, as a method for evaluating the in-furnace cleanliness of a wafer heat treatment furnace, an unprocessed wafer is heat-treated in an O ₂ atmosphere for several hours in a wafer heat treatment furnace, and then the wafer lifetime (minority carrier recycle Combined lifetime: τ
The cleanliness of the wafer heat treatment furnace is evaluated by the _r- value (for example, VLSI process data handbook (SCIENCE FORU
M company, published in 1990, pp.474-477)), and then a micro-defect is investigated by an etching method to finally evaluate the cleanliness.

At that time, a wafer microwave method is generally used for the lifetime measurement. This method irradiates the surface of the wafer with a pulsed laser and detects changes in the concentration of minority carriers that occur as changes in the reflection intensity of microwaves. Information up to 30 μm (mainly information on deep level oxygen precipitates, heavy metals, etc.) can be obtained.

A method is also known in which the cleanliness is evaluated by the yield of device elements actually manufactured by using a wafer heat treatment furnace.

[0005]

However, in the former case of the above-mentioned conventional evaluation method, the microdefects in the subsequent etching method are examined, and the cleanliness is low enough to detect the microdefects. There is a problem in that the evaluation cannot be performed, and the defect due to the actual device element forming process (for example, oxide film dielectric breakdown voltage defect) is not at a level that can be prevented in advance by the cleanliness evaluation of the wafer heat treatment furnace.

Further, in the latter case in which the cleanliness is evaluated by the yield of the device elements actually manufactured by using the wafer heat treatment furnace, there is a problem that the evaluation requires a long period of 2-3 months. An object of the present invention is to provide a method for evaluating the cleanliness of a wafer heat treatment furnace, which solves the problems of the conventional techniques as described above.

[0007]

The present invention is a method for evaluating the cleanliness of a wafer heat treatment furnace, wherein
Cleanliness of the wafer heat treatment furnace characterized by measuring the lifetime after heat treatment at a low temperature of 600 to 900 ℃ for 4 hours or more to deposit interstitial oxygen on the entire wafer and then heat treatment in the wafer heat treatment furnace This is an evaluation method.

[0008]

[Operation] According to the present invention, a wafer is preliminarily 600-900
Heat treatment at low temperature for 4 hours or more for a long time to deposit interstitial oxygen on the entire wafer, and then heat treat the wafer in the wafer heat treatment furnace, if there is any contamination in the wafer heat treatment furnace, Compared to the unprocessed wafers, the wafers that have been subjected to the precipitation treatment have oxygen precipitates on the entire wafer, so contamination can be easily captured and the lifetime value appears sensitively, so minute defects can be detected by the etching method. At the above levels, the wafer heat treatment furnace can be evaluated by the lifetime.

The reason why the low temperature range of 600 to 900 ° C. is desirable is that interstitial oxygen does not precipitate below 600 ° C. On the other hand, when it exceeds 900 ° C., interstitial oxygen precipitated on the wafer is removed. By separating. The reason why the treatment time is set to 4 hours or longer is that precipitation of interstitial oxygen is not sufficient when the treatment time is shorter than 4 hours. The upper limit of the time depends on various factors such as the apparatus and equipment used and the cost, but normally, the treatment for about 8 hours is required.

[0010]

Example According to the present invention, a wafer was preliminarily heat-treated in a N ₂ atmosphere at a low temperature of 800 ° C. for 8 hours in a clean state of a wafer heat treatment furnace to prepare a wafer in which precipitation was caused on the entire wafer. Here, the clean state of the wafer heat treatment furnace is a state in which the yield of device elements actually manufactured using this wafer heat treatment furnace is the best.

Using the wafer of the method of the present invention and the untreated wafer of the conventional method prepared under the above conditions, the wafer microwave lifetime measurement value (μsec) of the wafer heat treatment furnace and the wafer heat treatment in that state MOS which is one of the device elements after the device elements are manufactured using the furnace
The relationship between the yield of the diodes (C-mode pass rate (%) of the dielectric breakdown voltage of the oxide film) is shown in comparison with FIG. Here, the heat treatment in the wafer heat treatment furnace for evaluation by the wafer microwave method lifetime measurement was performed at 1150 ° C. for 2 hours in an O ₂ atmosphere.

As a result, when the unprocessed wafer of the conventional method is used, 80% of the C-mode pass rate of the MOS diode is obtained.
At the above times, almost no difference was found in the measured values of the wafer microwave lifetime. In addition, when the C-mode pass rate of the MOS diode was 80% or more, a microdefect was examined by the etching method, but no microdefect was detected. On the other hand, when the wafer according to the method of the present invention in which precipitation is caused on the entire wafer is used, it is confirmed that when the C-mode pass rate of the MOS diode is improved, the lifetime value is obviously increased. It can be seen that the condition of the heat treatment furnace is improved by using the method of the present invention.

[0013]

As described above, according to the present invention, the wafer is preliminarily heat-treated at a low temperature of 600 to 900 ° C. for a long time of 4 hours or more to precipitate interstitial oxygen on the entire wafer, Since the wafer was heat-treated in the wafer heat treatment furnace and the lifetime thereof was measured, it is possible to shorten the time required to evaluate the cleanliness of the wafer heat treatment furnace and to achieve high sensitivity of the evaluation.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a C mode acceptance rate of a wafer and a lifetime value.

Claims (1)

[Claims] 1. A method for evaluating the cleanliness of a wafer heat treatment furnace, wherein the wafer is preheated at a low temperature of 600 to 900.degree.
A method for evaluating cleanliness of a wafer heat treatment furnace, which comprises performing heat treatment for at least an hour to precipitate interstitial oxygen on the entire wafer, then performing heat treatment in a wafer heat treatment furnace, and measuring the lifetime thereof.