JPS62200742A - Wafer shape measuring device - Google Patents

Abstract

PURPOSE:To enable the resist shapes to be judged easily and accurately by a single picture image by a method wherein the attention is paid to the standing waves produced in the exposure development in the wafer manufacturing process to judge the resist shapes by measuring the gaps in the standing waves. CONSTITUTION:A scanning type electronic microscope 15 for inputting picture images, a picture image memory 16 for storing the input picture images, a standing waves extracting algorism for the input picture images 17 and a judging means 18 to judge the acceptability of wafer shapes are provided in the title wafer shape measuring device. Where, the standing waves represent the ruggedness 30 on a resist 27 side produced by exposure development in the wafer manufacturing process. When the resist 27 not to be developed is irradiated with light in case of exposing the resist 27, if the irradiation is excessive, needless part thereof is developed. Such defects are represented by the fluctuation in gaps of standing waves, in other words, any excessive development extends the gap in standing waves making it feasible to judge such defects.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wafer shape measuring device used for shape inspection of semiconductor wafers.

[Conventional technology]

FIG. 7 is a system configuration diagram of a conventional wafer shape measuring device. In the figure, 1 is a scanning electron microscope (SEM) for capturing images, and 2 is an A for converting analog image signals into digital signals. /D converter, 3 is an input interface for importing image signals into a computer, 4 is an image memory for storing image signals, 5 is a CPU for processing data on the memory 4, 6 is a processing result. This is a CRT shown in FIG.

Next, the operation will be explained using FIGS. 8 and 9.

Here, FIG. 8 is a flowchart of the operation using the system with the above configuration, and FIG. 9 shows the measurement principle (triangulation principle). First, an image signal of the wafer surface is obtained using a scanning electron microscope (SEM) 1 (step 7), and the signal is
/D converter 2 to digitize step 8),
Store image data in image memo IJ 4 (step 9)
. Also, tilt the SEMI sample stage by θ degrees (steps 10 and 1).
1) The image data of the same location is stored in the image memory 4 again (steps 7 to 9). Next, pixels that are considered to be at the same location are found for the image first obtained in the image memory 4 and the image obtained when the sample stage is tilted by θ degrees (step 12). When the corresponding points are found, the height H is determined using the formula % in FIG. 9 (step 13). Based on this height information, the quality of the resist shape is determined (step 14).

[Problem that the invention seeks to solve]

Conventional wafer shape measuring equipment is configured as described above, so it is necessary to input images of the same location by changing the tilt of the sample stage, and it is difficult to search for corresponding points in two images. This is difficult, and there are problems such as areas that are not common to each other appearing in both images.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a wafer shape measuring device that can easily determine the shape without the need to input multiple images.

By the way, if we consider the resist exposure and development process during the wafer manufacturing process, generally speaking, when resist is exposed and developed, the light incident on the resist and the light reflected within the resist cause interference, resulting in changes in the intensity of the light. For example, in the case of a resist that remains exposed to light during development, the areas that are weakly exposed to light are developed more than the areas that are more strongly exposed, resulting in unevenness (standing waves) on the sides of the resist.

Now, if unnecessary portions remain in the resist, the interval between the standing waves will be larger than the interval when it is normal. Therefore, if the wafer shape is measured using the interval between these standing waves, it is thought that the shape of the resist can be easily determined using a single image.

[Means for solving problems]

Therefore, the wafer shape measuring device according to the present invention includes: an image input means for inputting an image of the wafer surface; an extraction means for extracting and measuring the interval of standing waves from the image signal of the wafer surface; and determining means for determining.

[Effect]

In this invention, we focused on the standing waves created during the exposure and development process during the wafer manufacturing process, and determined the resist shape by measuring the interval between these standing waves. The resist shape is determined.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of the overall configuration of a wafer shape measuring device according to an embodiment of the present invention, in which 15 is a scanning electronic device for inputting images; 16 is a scanning type electronic device for inputting images; 17 is an extraction means for extracting standing waves from the input image, and 18 is a judgment means for judging whether the shape of the wafer is good or bad. Note that the system configuration diagram of the present invention is the same as the conventional system shown in FIG. 7, so a description thereof will be omitted.

Next, the operation will be explained. FIG. 2 shows a flowchart of the operation using the system configured as described above.

First 1. An image signal is obtained using a scanning electron microscope (SEM) 15 (step 19). Converting the image signal into an 8-bit digital signal (step 20), image memory 16
The image is stored in (step 21).

At this time, the image is composed of 256 x 256 pixels.

Next, the standing wave in this image is extracted. Here, the standing wave is shown in Fig. 3(a).
(As shown in bl, when performing exposure and development during the wafer manufacturing process, the incident light 28 on the resist 27 and the reflected light 29 inside the resist 27 interfere, causing the intensity of the light to change. For example, in the case of a resist that remains after development where it is exposed to light, the unevenness 30 on the side of the resist 27 is created because the areas where the light is weaker are developed more than the areas where the light is stronger.Image Inside, the standing waves appear as brightness and darkness as shown in Figure 4 (al).

First, we will show a method for extracting this standing wave. FIG. 4, which is stored from the image memory 16 (
+1) Take out the image (original image) shown in Figure 5, and use an edge emphasis filter to take out pixels with sharp changes in brightness. This is done by creating an image on the image memory 16 using the brightness of the eight pixels around it, such that the value is 0 (step 22).

If we create a histogram of the values of each pixel for this image, we get
The graph will have peaks in areas where the brightness of the original image changes drastically and areas where it does not. A binary image as shown in FIG. 4 (bl) is created in the memory 16 by setting the value between these two peaks as a boundary value, and setting the brightness of points with pixel values higher than that as 1, and the brightness of other points as O. (Step 23)
. If you create an image like this, you will get an image where the light-to-dark and dark-to-bright changes of the standing wave become 1, that is, the two ends of the bright standing wave appear as lines. This determines the direction in which the standing wave will appear (step 24).
).

Add the brightness of the original image for a certain length along this direction to create a projection diagram as shown in Figure 4 (C1) with the horizontal axis perpendicular to the standing wave. , peaks appear in the projection diagram.By finding the distance between these peaks, the interval between the standing waves can be found (step 25).

For example, if the resist is not developed in the areas exposed to light during resist exposure, if too much light is applied, unnecessary areas will remain as shown in FIG. 6 when developed. Such defects appear as a change in the interval between standing waves. In other words, it can be determined that a defect has occurred because the interval between standing waves becomes larger when unnecessary parts remain.

In the apparatus of this embodiment as described above, the shape of the resist is determined from the interval of the standing waves, so the shape of the resist can be determined easily and accurately with one image input, and it is possible to easily and accurately determine the shape of the resist, and it is possible to easily and accurately determine the shape of the resist from the interval between the standing waves. This eliminates the need for a mechanism for tilting the device, making it possible to reduce the cost of the device.

In the above embodiment, a scanning electronic w is used as an image input device.
Although a device equipped with 4im is shown, it may be any input device that allows the surface of the wafer to be observed (the same effect as in the above embodiment can be achieved).

Furthermore, in the above embodiment, the image signal was converted to an 8-bit digital signal and processing was performed using 256 gradation brightness values, but this is a bit number that is sufficient to extract the brightness and darkness of the standing wave. The same effect as in the above embodiment can be achieved.

〔Effect of the invention〕

As described above, the wafer shape measuring device according to the present invention is configured to measure the standing wave width to determine the resist shape, so that the resist shape can be easily and accurately determined with a single image. This also has the effect of making the device cheaper.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the configuration of a wafer shape measuring device according to an embodiment of the present invention, FIG. 2 is a diagram showing a flowchart of the operation of the device, and FIG. 4 (a) to (C), 5 and 6 are diagrams for explaining the operation of the above device, and FIG. 7 is an overall configuration diagram of the conventional device, Fig. 8 is a flowchart showing the processing process of the conventional device, and Fig. 9 is a diagram for explaining the measurement principle of the conventional device. 1 is a scanning electron microscope (image input means), 2 is an A/D conversion 3 is an input interface, 4 is an image memory, 5 is a CPU (extraction means 1 judgment means), 6 is a CRT, 15 is a scanning electron microscope, 16 is an image memory, 17 is an extraction means, and 18 is a judgment means. Note that the same symbols in the figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) An image input means for inputting an image of the wafer surface; an extraction means for extracting and measuring the interval between the irregularities on the side surface of the resist on the wafer surface from the input image signal of the wafer surface; A wafer shape measuring device characterized by comprising: determining means for determining a shape. (2) The wafer shape measuring device according to claim 1, wherein the image input means is a scanning electron microscope. (3) The wafer shape measuring device according to claim 1, wherein the functions of the extracting means and the determining means are realized by a CPU.