JPS5858740A - Measuring device for warp of semiconductor wafer - Google Patents

Abstract

PURPOSE:To easily measure the warp of a semiconductor wafer by a method wherein the focusing of an optical microscope magnifying a part of the optical image of a pattern in an integrated circuit is automatized. CONSTITUTION:A semiconductor wafer 1 is mounted on a reference plate 2 and the reference plate 2 is fixed to a scanning stage mechanism 3. A TV camera 5 is installed on the ocular section 13 of the optical microscope 4. The image signal from the camera 5 is sent to a picture image processing section 9. The processing in the processing section 9 is performed by the kind and condition decided by a control section 10. The control section 10 controls an objective lens driving mechanism 7 and a scanning driving mechanism 8. The number of pulses sent to the mechanisms 8, 7 from the control section 10 corresponds to the moving distances of the wafer 1 and the lens 6. This information is sent to a data processing section 11 and is converted into the warp value and the position coordinate on the wafer 1 measured the warf value.

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 maintain yield improvement, 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,
(Moiré method, various interferometers, microscope depth of focus 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 density as the manufacturing process progresses. In other words, in the microscope depth of focus method, the measurement end is not in contact with the sample. If the magnification is increased, the two-dimensional resolution becomes smaller, making it easier to apply semiconductor wafers having fine and complex patterns, and the depth of focus becomes deeper, which 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 air pressure that blows deforms the semiconductor wafer to be measured, making it impossible to measure warpage. Another reason for the difficulty in automating measurements 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.

That is, even if the surface of the sample stage that contacts 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 position is corrected using this tilt angle. In order to eliminate the need for this correction, the surface of the sample stage must be made a reliably horizontal plane, but the 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. 1(a) is a schematic diagram of the configuration of a semiconductor wafer warpage measuring device of the present invention, FIGS. 1(b) and 1(c) are partial perspective views for explaining the function and operation, and FIG. 1(c) 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 scanning stage mechanism 8. An optical microscope 4 is provided above the semiconductor wafer 1, and a television camera 5 is attached to its eyepiece 1B. The video signal from the television camera 6 is sent to an image 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 1. Further, the control section 10 controls one of the optical microscopes 4.
It drives and controls an objective lens driving mechanism 7 that vertically moves the position of an objective lens 6, which is a section, and a scanning stage mechanism 8 that moves the semiconductor wafer 1 and reference plate 2 in the X-Y direction. Although neither of the scanning stage machine tR8 and the objective lens drive mechanism 7 are shown, a stepping motor moves the semiconductor wafer l and the reference plate 2 in the −
In the Y direction, the objective lens 6 can be moved stepwise and repeatedly over small distances in two directions, up and down. The 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. From the control section 10 to the scanning stage mechanism 8
The number of drive pulses sent to the stepping motor of the objective lens drive mechanism 7 is
This corresponds to information on the movement distance and the vertical movement distance of the objective lens 6. This information is sent from the control unit 10 to the data processing unit 11, where the information about the vertical movement is converted into a warpage value.
Further, information regarding the X-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. This binarization determines the bright/dark level range such that only the edge of the pattern 1a of the semiconductor wafer l is at the "l" level or the "θ" level when the focal point 12 of the objective lens 6 is focused on one surface of the semiconductor wafer. This is done using two thresholds, an upper limit and a lower limit. This threshold only needs to be set once. The same image processing unit 9 is designed to be able to measure the relative area (area ratio) occupied by the l'' level or the 0'' level in the area of the binarized image. The relative area becomes maximum when the focal point '12 is connected to one surface of the semiconductor wafer. When the focal point 12 is shifted above or below the surface of the semiconductor wafer 1, 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 the objective lens drive section 7 to move the objective lens 6 from above to below at the same time.
If the movement of the objective lens 6 is stopped at the position where the relative area becomes the maximum, the focal point 12 is automatically brought to the surface of the semiconductor wafer. This method of automating focusing is described in detail in Japanese Patent Application No. 177800/1983. 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 Zf of the objective lens 6. Therefore, objective lens 6
If you count the number of pulses to the stepping motor of the objective lens drive unit 7 required to move the objective lens 6 downward until the focal point 12 matches the surface of the semiconductor wafer after moving it to the top end, the focal point Objective lens 6 at the end of alignment
The position (Zsi) of can be known in a constant manner.

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 the control section 10
A pulse signal for X-Y movement is sent to the scanning stage mechanism 8 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 based on the position coordinates (X
i.

This is done by sending the number of pulses corresponding to Y i) to the X and Y stepping motors of the scanning stage mechanism 8. The warpage measurement point may be any arbitrary point on the semiconductor wafer 1, and its positional coordinate values are set in advance by the control section 10, and this positional 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. This is 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 values such that a part 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. Since the stepped portion of the pattern 2b of the reference plate 2, that is, the pattern edge, is optically equivalent to the pattern edge of the semiconductor wafer 1, the reference plate 2
It is also possible to automate the focusing as explained in FIG. It can be known from (Xi, Yi). 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 l 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 section 11, and the position (Zoi) information of the objective lens 6 with respect to the semiconductor wafer 1 that has already been sent is sent to the data processing section 11.
The position (Zsi) information of each measurement point (Xi, Y
i), it is possible to determine the warpage value of the semiconductor wafer l 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, the absolute value of the position of the objective lens 6 (Z
si, Zoi), the absolute value of the position coordinates of the measurement point (Xi
, Yi) and the difference in the position of the objective lens 6 at each position coordinate (Xi, Yi) δ1(lZsi-Zo i
1), check the minimum value δ of the difference δi, and then find (Δ
1=ai-Jm), this Δi becomes the warpage value of the measurement point at the position (Xi, Yi) on one surface of the semiconductor wafer. Note that during data processing in the data processing unit 11, the position coordinates (Xi
, Yi), the position (Zoi) of the objective lens 6 with respect to the main surface 2a of the reference plate 2,
Since the inclination angle θ of 2a is determined, the warp value Δi can be determined more accurately. Also (Xi, Yi
, Δi), the warped state of the semiconductor wafer can be clearly seen.

Such data processing, focusing, and x-y 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 is determined by the objective lens drive mechanism 7.
The combination of gears can be made into an extremely small unit, and the step d of the pattern on the reference plate 2 can be made small as long as the pattern can be identified optically. Furthermore, according to recent polishing techniques, the variation in the thickness of the raw wafer of the semiconductor wafer 1 is small, and the warpage that occurs during the high-temperature heat treatment process and film formation process, which cause warpage problems, is larger than the variation in thickness. Further, among the patterns 1a of a large number of integrated circuits etc. formed on the semiconductor wafer l, the control unit 10 controls the measurement points so that only the same pattern portions are measured even if the integrated circuits etc. are different.
6. By setting the position coordinate information, 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. 8 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 expose grain boundaries 21b. Since the grain boundaries 21b are small in size and can be easily observed with an ordinary metallurgical microscope as is well known, they have the same effect as the level plate 2 described in FIG. 2.

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 for manufacturing the semiconductor wafer 11 or a similar type of mask. If many types of masks are required for manufacturing, just one of them will suffice. The main surface 22a of this reference plate 22 is of course flat, and the pattern 1a of the integrated circuit etc. of the semiconductor wafer 1 is
Since the pattern 22b corresponding to one of these types is formed of, for example, a chrome film or the like, it has the same effect as the reference plate 2 described in FIG. 2.

[Brief explanation of the drawing]

1(a), 1(b), and 1(c) are a schematic configuration diagram, a partial perspective view, and a partial sectional view for explaining the warp measuring device of the present invention, respectively, and FIGS. 2, 8, and 4 are FIG. 3 is a partial perspective view showing an example of a reference plate used in the present invention. 1 is a semiconductor wafer, 2 is a reference plate, 8 is a scanning stage mechanism, 4 is an optical microscope, 6 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 10 is a control section, and 11 is a data processing section. In the drawings, the same reference numerals indicate the same or corresponding parts. Agent Makoto Kuzuno - Figure 1 (α) Figure 2 Figure 1 Figure 3 Figure 4 Procedural amendment (spontaneous) To the Director of Patent f'l 1, Matter (Indication of 'I' Patent application 157757-1972)
No. 2, Name of the invention Electrodynamic device of semiconductor wafer 3, Relationship with the case of the person making the amendment Special feature 11' ``Applicant δ, Detailed description of the invention of the subject matter of NI Positive 6, Amendment Content

Claims (1)

[Scope of Claims] (In a semiconductor wafer warpage measuring device in which the same pattern of integrated circuits, etc. is repeatedly arranged and formed, a reference plate on which a semiconductor wafer is placed, the semiconductor wafer and the reference plate, A scanning stage mechanism that moves the dimension, an optical microscope that magnifies a part of the optical image of the pattern, a television camera that photoelectrically converts the expanded optical image, and binarization of the video signal of the television camera and a binarized image. “ within the plane”
an image processing unit capable of measuring the relative total area of the 1" or "0" level region, capable of moving the objective lens position of the optical microscope stepwise upward or downward by repeating a certain minute movement distance, and An objective lens driving mechanism having a stopper for setting the uppermost position of the objective lens, the scanning stage mechanism, an image processing section and a control section for operating and controlling the objective lens driving mechanism, positional coordinates on the semiconductor wafer surface, and the like; A semiconductor wafer warpage measurement device comprising a data processing unit that calculates and displays the second position, etc. (2) The reference plate has a flat main surface provided with a pattern such as a grid. Claim No. (
1) The semiconductor wafer warpage measuring device described in item 1). (3) Measurement of warpage of a semiconductor wafer according to claim (1), wherein the reference plate is made of metal and has a flat main surface that exposes grain boundaries due to corrosion or the like. Device. (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.