JPS6337194B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for accurately determining the end point of etching in a dry etching apparatus such as a plasma etching apparatus or an ion beam etching apparatus.

In etching performed when manufacturing semiconductor devices, etc., it is usually important to completely remove the exposed etched area and form the masked remaining area with precision.
It is necessary to quickly stop the etching process when the etching removal is just completed. If the etching process is stopped too early, an etched layer will naturally remain in the removed area, especially at the boundary between the etched removed area and the remaining area, and on the other hand, if the etching process is performed excessively, the boundary area will be over-etched. This is because the etching progresses to the remaining area, making it impossible to perform patterning with high accuracy.

This kind of problem tends to be particularly severe in wet etching, and the dry etching method was developed to avoid it.Although there are some differences, the same tendency exists in the dry etching method as well. As the density increases, detecting the end point of etching has become the most important issue in order to achieve higher precision. For this reason, various methods for detecting the end point of etching have been devised in the dry etching method. A method for determining the end point by detecting changes in the reflected light has been put into practical use. However, it is sometimes difficult to make a correct judgment with either method; the former method, which uses the emission spectrum, has difficulty distinguishing it from the emission spectrum of gases other than the reaction product gas, and the latter method, which uses reflected light, has little change in the amount of light. Moreover, since the observation is localized, errors are likely to occur.

The purpose of the present invention is to propose an accurate etching end point detection method that does not have such drawbacks.The feature is that a light-receiving surface is provided on the sample mounting table, and the amount of transmitted light from the sample to be etched is measured on the back surface of the sample. This is an end point detection method that focuses and detects light.

Hereinafter, the present invention will be explained in detail by way of examples with reference to the drawings. FIG. 1 shows a schematic sectional view of the plasma etching apparatus, in which a sample 1 is held on a sample mounting table 2, and a reaction gas is introduced through a ring-shaped thin tube 3 provided around the mounting table 2. A counter electrode 4 is provided opposite to the mounting table 2, and a high frequency power of 13.56 MHZ and 500 to 800 W is applied between the mounting table 2 and the counter electrode. The sample substrate to which the present invention is applied is a material that transmits the emission spectrum, such as a glass plate (photomask plate) coated with a chromium film, and when etching chromium, carbon tetrachloride (CCl ₄ ) and oxygen (O ₂ ) are used. Plasma etching is performed by injecting a mixed gas with a vacuum of about 0.4 Torr.

In such an etching apparatus, according to the present invention, the sample mounting table 2 is formed to have a structure as shown in the cross-sectional view of FIG. 2, for example. That is, a material 21 having good thermal conductivity and electrical conductivity is formed into a concave shape, and the concave surface is polished to a mirror surface and plated. A transparent medium 22 is fitted into that part, and a light-receiving end of an optical fiber 23 is provided on the focal side of the concave mirror to receive the reflected light from the concave mirror. Photon (e.g. phototransistor) 24
and detects changes in the amount of light.

As shown in the figure, the sample 1 is placed on a transparent medium 23, and a resist film mask 13 is formed on the surface of the chromium 12 deposited on the glass substrate 11, and etching is performed using the above-mentioned reaction gas. The chrome area covered by mask 13 remains unchanged, but
The exposed chrome areas are etched and gradually removed, allowing transmitted light to reach the concave mirror.
As shown in the diagram in Figure 3, the amount of light is extremely small at the beginning of the etching time, _T1 , but as the etching progresses, at _T2 , it gradually increases, and at _T3 , when etching is nearing completion, it increases slightly, and eventually the light amount increases. is constant. Therefore, the end point of etching can be correctly detected by determining the differential amount of the light intensity curve 1.

This detection method detects the amount of light on the entire surface of the sample, regardless of whether the etching pattern on the sample is formed densely or sparsely. Compared to the conventional method of detecting the light quantity ratio, which is easily affected by the density of the etching, the etching end point can be detected much more accurately because this method measures the absolute value of the light quantity.

The transparent medium 23 described above may be a liquid such as silicone oil, but is preferably an organic material such as polyimide or a solid such as quartz, which has relatively good thermal conductivity, and the sample mounting table 2 should be on the ground side of the power source. It is often more convenient. Further, as shown in FIG. 2, the sample mounting table 2 is cooled, and the transparent medium 23 preferably has excellent thermal conductivity and electrical conductivity, but this is not a necessary condition.

Although the above is an example, it is also within the scope of the present invention to use a method of arranging a photo cell or the like on the back surface of the sample 1 to collect light and detecting the amount of light.

As described above, the present invention enables a dry etching apparatus to accurately detect the end point of etching on a sample substrate through which luminescent plasma is transmitted, and greatly contributes to improving the quality of semiconductor integrated circuits and the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a plasma etching apparatus, FIG. 2 is a diagram of an embodiment of a sample mounting table according to the present invention,
FIG. 3 is a graph showing the relationship between etching time and amount of transmitted light according to the present invention. In the figure, 1 is a sample, 2 is a sample mounting table, 11 is a glass substrate, 22 is a transparent medium, 23 is an optical fiber,
24 indicates a photoreceptor.

Claims (1)

[Claims] 1. In a dry etching device that emits light, a light-receiving surface is provided on the sample mounting table, the amount of transmitted light from the sample to be etched is collected and detected on the back surface of the sample, and the etching end point is detected based on the change in the amount of transmitted light. An etching end point detection method characterized by: