JPS629217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a warpage measuring device using a microscope depth of focus method used for semiconductor wafers having patterns such as integrated circuits. In recent years, in the manufacture of integrated circuits and the like, large-diameter semiconductor wafers are used and fine patterns are used to achieve high integration in order to improve yields. On the other hand, however, increasing the diameter causes problems such as the occurrence and increase of warpage due to high-temperature heat treatment processes, etc., and a corresponding decrease in pattern overlay accuracy in the photolithography process. Therefore, in order to ensure an improvement in yield, it is necessary to take measures against warping of semiconductor wafers during the manufacturing process, and to provide a warpage measuring device for this purpose.

Currently, such warpage measurement devices are mechanical (dial gauge, etc.), electrical (capacitance meter, etc.), optical (optomicrometer, Moire fringe method, various interferometers,
(microscopic focus depth method, etc.). However, the optical microscope depth of focus method is an excellent method for measuring warpage of semiconductor wafers that have fine patterns such as integrated circuits, patterns that increase in variety and become denser as the manufacturing process progresses. In other words, the microscope depth of focus method requires that the measurement end is not in contact with the sample, that increasing the magnification reduces the two-dimensional resolution, making it easier to apply to semiconductor wafers with fine and complex patterns, and that the depth of focus is deep. This has the advantage of improving sensitivity.

However, the conventional warpage measuring device using the microscope depth of focus method has the drawback that it is difficult to automate the measurement. One reason for this drawback is that it is difficult to automate the alignment of the focal position of the objective lens with the surface of the sample to be measured, that is, to automate focusing. This difficulty is manifested as a weakness in that the measurement mode of the warpage measuring device using the microscope depth of focus method is mainly a manual single point measurement type. There is also a method of using an air micrometer to automate focusing, but the semiconductor wafer to be measured is deformed by the air pressure, making it impossible to measure warping. Another reason for the difficulty in automating measurement is that it is complicated to ensure that the surface of the sample stage on which the semiconductor wafer is placed is horizontal, and to make corrections based on the angle of inclination. In other words, even if the surface of the sample stage that comes into contact with the back surface of the semiconductor wafer of the sample to be measured is flat, if it is tilted from the horizontal plane,
The warpage value cannot be determined unless the focal point position is corrected using this inclination angle. In order to eliminate the need for this correction, the surface of the sample stage must be made a reliably horizontal plane, but this leveling adjustment is extremely complicated in order to perform satisfactory warpage measurements on large-diameter wafers. In addition, when correcting by tilt angle, it is necessary to measure the tilt angle, and if the microscope depth of focus method is applied to this measurement, the above-mentioned weak point will appear, and if other measurement methods are used, the tilt angle measurement for this measurement More equipment is required.

In view of the above points, the present invention measures the warpage of semiconductor wafers more accurately and easily than conventional devices by combining an image processing unit for automating focusing, a reference plate for automating tilt angle correction, etc. The aim is to provide a device that can do this.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor wafer warpage measuring apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1a is a schematic diagram of the configuration of a semiconductor wafer warp measuring apparatus according to the present invention, FIG. 1b is a partial perspective view for explaining the function and operation, and FIG. 1c is a partial sectional view.

In the figure, a semiconductor wafer 1 is placed on a reference plate 2, and the reference plate 2 is placed on or fixed to a skinning stage mechanism 3. An optical microscope 4 is provided above the semiconductor wafer 1, and a television camera 5 is attached to its eyepiece 13.
The image signal of the television camera 5 is sent to a video processing section 9. Image processing in the image processing section 9 is performed under the type and conditions determined by the control section 10, and the image-processed data is taken into the control section 10. Also, the control section 10
drives and controls an objective lens drive mechanism 7 that moves the objective lens 6, which is a part of the optical microscope 4, up and down, and a scanning stage mechanism 3 that moves the semiconductor wafer 1 and the reference plate 2 in XY.
The scanning stage mechanism 3 and the objective lens drive mechanism 7 each include a stepping motor (not shown), which moves the semiconductor wafer 1 and the reference plate 2 through mechanical transmission such as gears, pinions, racks, etc. in the XY direction, and the objective lens 6 can be moved stepwise and repeatedly over small distances in the up and down Z direction. Objective lens drive mechanism 7
has a stopper 8 that stops the movement of the objective lens 6 when it moves to the uppermost end. Stepping and control of the scanning stage mechanism 3 and objective lens drive mechanism 7 from the control unit 10
The number of drive pulses sent to the motor corresponds to information on the XY movement distance of the semiconductor wafer 1 and the vertical movement distance of the objective lens 6, respectively. This information is sent from the control unit 10 to the data processing unit 11, where information regarding vertical movement is added to the warpage value and
Information regarding the Y movement is converted into positional coordinates on the surface of the semiconductor wafer at the location where the warpage value was measured.

Automation of focusing is performed as follows. An electrical image obtained by photoelectrically converting an enlarged optical image of the pattern 1a of the semiconductor wafer 1 by the optical microscope 4 by the television camera 5 is converted into a binarized image by the image processing section 9. In this binarization, when the focal point 12 of the objective lens 6 is focused on the surface of the semiconductor wafer 1, only the edge of the pattern 1a of the semiconductor wafer 1 becomes "1".
This is done using two threshold values, an upper limit and a lower limit, which determine the range of light and dark levels that will be the level or "0" level. This threshold only needs to be set once. The same image processing section 9 is configured to be able to measure the relative area (area ratio) occupied by the "1" level or the "0" level in the binarized image area.

Here, the principle of focusing will be explained using FIG. 5. 5a shows the case where the focal point 12 of the objective lens 6 of the optical microscope 4 is below the surface of the semiconductor wafer 1, and FIG. c is focal point 12
2A and 2B are side views respectively showing cases in which the semiconductor wafer 1 is located above the surface of the semiconductor wafer 1. FIG. Further, d to f in the same figure are plan views corresponding to a to c in the same figure, respectively.

By the way, when light enters the surface of the semiconductor wafer 1 perpendicularly, the pattern 1a and the parts other than the pattern 1a are generally different in material, size, shape, etc., so the incident light is scattered by the edge 1b of the pattern 1a and The amount of reflected light returning to the lens 6 is small. When the focal point 12 is focused on the surface of the semiconductor wafer 1 as shown in figure b, the optical imaging conditions are satisfied, so the edge 1b is the darkest and clearest image, as shown in figure e. (solid line). However, when the focal point 12 is located above and below the surface of the semiconductor wafer 1 as shown in a and c in the figure, the imaging conditions are not satisfied, so the edge portion 1b is shifted to the position e in the figure as shown in d and f in the figure. The resulting image (diagonal lines) is brighter and less clear than the edge portion 1b shown. This phenomenon is
When using an optical microscope, it is common to experience that the image becomes blurred when the focus moves away from the sample surface.

Next, let the maximum value of the brightness level in pattern 1a be Lmax, and the level width obtained by dividing Lmax into n equal parts is Δ
L, and the brightness and darkness levels are (i-1)ΔL and iΔL
When the area of the image between (i=1,...n) is expressed as Si- ₁ as the relative area (area ratio) occupied in the binary image area of pattern 1a, the area ratio S and the brightness level L are Assuming that the focal point 12 is fixed at an appropriate vertical position, the relationship is distributed as shown in g in the figure. This distribution shape is based on the semiconductor wafer 1 at the focal point 12.
It varies depending on the deviation f from the surface.

Figure h is actual measurement data showing this situation.
Here, the brightness level L is normalized by Lmax. As can be seen from this figure, in all cases where the deviation f is ±1 micron, the focus 12 deviates to a greater brightness level than when it coincides with the surface of the semiconductor wafer 1. This phenomenon corresponds to the phenomenon in which the intensity, contrast, and sharpness of an optical microscope change depending on the position of the section 12. Therefore, the level value (level 35 in FIG. 5 h) and level range ( By setting the level width, upper and lower thresholds (level width 30 to 40 in Fig. 5h), and measuring the relative area (area ratio) while displacing the focal point 12, the relative area can be calculated as follows: It is maximum when tied to one surface of the wafer. focus 1
2 is shifted above or below the surface of the semiconductor wafer, the brightness level of the pattern edge shifts to the brighter side, so that the brightness level range between the two thresholds is "1" or "0". ”
The relative area occupied by the level becomes smaller. Therefore, the control section 10 causes the image processing section 9 to measure the relative area and moves the objective lens 6 from above to below through the objective lens drive section 7 at the same time. If the movement of the objective lens 6 is stopped at position 6, the focal point 12 will be automatically focused on the surface of the semiconductor wafer. The stopper 8, which operates when the objective lens 6 moves to the uppermost end, sets this uppermost end as the origin of the position Zi of the objective lens 6. Therefore, the number of pulses to the stepping motor of the objective lens driving unit 7 required to move the objective lens 6 downward until the focal point 12 coincides with the surface of the semiconductor wafer after the objective lens 6 is moved to the uppermost end. If you count
Position of objective lens 6 at the end of focusing (Zsi)
can be known quantitatively.

Position information on the position (Zsi) of the objective lens 6 obtained by focusing at one location on the surface of the semiconductor wafer 1 is sent to the data processing section 11. and,
A pulse signal for XY movement is sent from the control unit 10 to the scanning stage mechanism 3 to move the semiconductor wafer 1 together with the reference plate 2, and similar operations are performed at other locations on the surface of the semiconductor wafer 1. X-
Y movement is movement on a two-dimensional plane, and movement to the measurement point of the warp, that is, the focusing point, is performed by the number of pulses corresponding to the position coordinates (Xi, Yi) of that point set in the control unit 10. This is done by sending the X and Y stepping motors of the scanning stage mechanism 3. The warpage measurement point may be any arbitrary point on the semiconductor wafer 1, and its position coordinate values are set in advance by the control section 10, and this position information is sent to the data processing section 11.

Next, the semiconductor wafer 1 is removed and the same operation is performed on the reference plate 2.

FIG. 2 is a partial perspective view showing an example of the reference plate 2. FIG. The main surface 2a of the reference plate 2 is flat, and the semiconductor wafer 1 is placed on this main surface 2a. A concave lattice pattern 2b is formed on the main surface 2a, and the concave step d corresponds to a certain minute movement distance of the objective lens 6 by the objective lens drive mechanism 7 in FIG. The unit of movement of the objective lens 6 is made smaller than the unit of movement of the objective lens 6 when the stepping motor of the mechanism 7 is driven by one pulse. Dimensions a, b, and c of the pattern 2b are set to such values that a portion of the pattern 2b is always within the field of view of the television camera 5 even when the optical microscope 4 is at the maximum possible magnification. The material of the reference plate 2 is preferably optically opaque and has high hardness. Such a stepped portion of the pattern 2b of the reference plate 2,
In other words, since the pattern edge is optically equivalent to the pattern edge of the semiconductor wafer 1, it is possible to automate the focusing with respect to the reference plate 2 as explained in FIG. 2
The position (Zoi) of the objective lens 6 at the end of focusing can be known from the same position coordinates (Xi, Yi) as the measurement location on the semiconductor wafer 1. The data group of the position (Zoi) of the objective lens 6 in the case of this reference plate 2 is based on the inclination angle (θ) of the main surface 2a from the horizontal plane, since the main surface 2a in contact with the back surface of the semiconductor wafer 1 is flat. It contains information about. Therefore, the position (Zoi) information of the objective lens 6 with respect to the reference plate 2 is sent to the data processing unit 11, and this and the position (Zsi) information of the objective lens 6 with respect to the already sent semiconductor wafer 1 are sent to the position of each measurement point. By comparing (Xi, Yi), it is possible to determine the warpage value of the semiconductor wafer 1 at each measurement location, taking into account the inclination angle θ. That is, in the data processing section 11, the number of pulses to each stepping motor is determined by the absolute value of the position of the objective lens 6 (Zsi,
Zoi), convert it into the absolute value (Xi, Yi) of the position coordinates of the measurement point, find the difference δi (lZsi−Zoil) in the position of the objective lens 6 at each position coordinate (Xi, Yi), and calculate the difference δi (lZsi−Zoil).
After checking the minimum value δmin of i, (Δi=δi−δ
min), this Δi becomes the warpage value of the measurement point at the position (Xi, Yi) on the surface of the semiconductor wafer. Note that during data processing in the data processing unit 11, from the position (Zoi) of the objective lens 6 with respect to the main surface 2a of the reference plate 2 at the position coordinates (Xi, Yi) of at least three measurement points, the main Since the inclination angle θ of the surface 2a is determined, the warp value Δi can be determined more accurately. Furthermore, by drawing a three-dimensional curved surface using the values of (Xi, Yi, Δi), the warpage state of the semiconductor wafer can be clearly seen.

Such data processing, focusing, and XY movement can be automatically and quickly performed by the computer functions of the image processing section 9, the control section 10, and the data processing section 11.

The minute movement distance of the objective lens 6 can be made into an extremely small unit by a combination of gears of the objective lens drive mechanism 7, and the step d of the pattern of the reference plate 2
can be made small as long as the pattern can be identified optically. Furthermore, according to recent polishing technology, the variation in the thickness of the raw material wafer of the semiconductor wafer 1 is small;
The warpage that occurs during the high-temperature heat treatment process and film formation process that causes warpage is larger than the variation in thickness. Also, among the patterns 1a of a large number of integrated circuits etc. formed on the semiconductor wafer 1, position coordinate information is set in the control unit 10 so that only the same pattern part is measured even if the integrated circuits etc. are different. By doing so, it is possible to eliminate the influence of uneven steps on the surface of the semiconductor wafer 1 on the warpage value. Therefore, according to the present device, it is possible to know the warpage value with sufficient accuracy to take measures to improve the manufacturing yield of integrated circuits and the like.

FIG. 3 is a partial perspective view showing another example of the reference plate 2. FIG. This reference plate 21 is made of metal, and has a flat main surface 21a subjected to corrosion treatment to form grain boundaries 21b.
has been exposed. Since the grain boundaries 21b are small in size and can be easily observed with an ordinary metallurgical microscope as is well known, the reference plate 2 illustrated in FIG.
It has the same effect as.

FIG. 4 is also a partial perspective view showing another example of the reference plate 2. As shown in FIG. This reference plate 22 is a mask used to manufacture the semiconductor wafer 1 or a similar type of mask. If many types of masks are required for manufacturing, only one type of mask is sufficient. The main surface 22a of the reference plate 22 is, of course, flat, and the pattern 22b corresponding to one of the patterns 1a of the integrated circuits, etc. of the semiconductor wafer 1 is formed of, for example, a chrome film. It has the same effect as the reference plate 2 explained in FIG.

[Brief explanation of the drawing]

Figures 1a, b, and c are a schematic configuration diagram, a partial perspective view, and a partial perspective view, respectively, for explaining the warp measuring device of the present invention.
FIG. 2, FIG. 3, and FIG. 4 are partial perspective views showing examples of reference plates used in the present invention, and FIG. 5 is a diagram illustrating the principle of focusing in the present invention. 1 is a semiconductor wafer, 2 is a reference plate, 3 is a scanning stage mechanism, 4 is an optical microscope, 5 is a television camera, 6 is an objective lens, 7 is an objective lens drive mechanism, 8 is a stopper, 9 is an image processing section , 10
1 is a control section, and 11 is a data processing section.
In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a semiconductor wafer warpage measurement device that uses an enlarged optical image of a pattern/edge portion of a semiconductor wafer on which patterns of the same integrated circuit, etc. are repeatedly arranged/formed, an optically opaque device is used. a reference plate on which the semiconductor wafer is placed; a scanning stage mechanism for two-dimensionally moving the semiconductor wafer and the reference plate; and an optical image of the pattern. An optical microscope that magnifies a part of the image, a television camera that photoelectrically converts the expanded optical image, binarization of the video signal of the television camera, and relative measurement of the "1" or "0" level area within the binarized image plane. an image processing unit capable of measuring the total area of the optical microscope; the scanning stage mechanism, the image processing section and the control section for operating and controlling the objective lens drive mechanism, the upper reference plate, and the position information of the objective lens relative to the semiconductor wafer. It is comprised of a data processing section that has a function of comparing the plane position coordinates on the reference plate surface and the semiconductor wafer surface, and calculates and displays the position coordinates on the semiconductor wafer surface, the amount of warpage, etc. Features: Semiconductor wafer warpage measuring device. 2. The semiconductor wafer warpage measuring device according to claim 1, wherein the reference plate has a pattern such as a grid pattern on its flat main surface. 3. The semiconductor wafer warpage measuring device according to claim 1, wherein the reference plate is made of metal and has a flat main surface with grain boundaries exposed due to corrosion or the like. 4. The semiconductor wafer warpage measuring device according to claim 1, wherein the reference plate is a mask used to manufacture a semiconductor wafer as a sample to be measured or a mask of the same type.