WO2004081493A1 - Method of measuring accurate parallelism - Google Patents

Abstract

The present invention relates to a measuring technique and especially relates to a method of accurately measuring the parallelism. The method is used to measure the relative parallelism which a flat surface of measured object M opposite to a reference plane W. Firstly, the measured object M is installed on a platform having rotating axis Z. The rotating axis Z is perpendicular to with the reference plane W; A measuring apparatus comprise a optical source 1 and a camera 2 so that the lens 3 of the camera 2 aligns the side surface of said measured object to imaged a reflecting beam from which projected to the side surface of said measured object M; A lateral coordinate axis u and a longitudinal coordinate axis u are a image's coordinate system of formed image. An origin of the coordinate system is defined at the center of the formed image. The measured point is the point that the higher or lower surface of said measured object intersect with its side face of throgh the longitudinal coordinate axis v; When said measured object M rotated around the rotating axis, the parallel state of the surface of said measured object M was depict relatively that of the reference plane by detecting the position of image of measured point on the successive survey, so that determined non parallelism and adjusted position of said measured object M relative to the reference plane W. The invention can depict the parallel relationship between said measured object M with reference plane W and having high adjusting precision.

Description

 TECHNICAL FIELD

 The invention relates to measurement technology, and in particular to a precise parallelism measurement method. Background technique

 Precision parallelism measurement is a key technology for precision (sub-micron) inspection and attitude adjustment operations in the large-scale integrated circuit (IC) manufacturing industry. In a typical IC process, a mask and a wafer are positioned in parallel. After the positioning is completed, the wafer is exposed. Traditional methods use precision distance sensors (such as capacitive, optical ranging, and electromagnetic methods) to measure the distance from the measured plane (such as a wafer, defined as M) to a reference plane (such as a template mounting plane, defined as W). The relative distance of a few positions is limited. When the flatness of the wafer surface cannot meet the required measurement accuracy, the measurement data of these measurement points cannot accurately reflect the parallel relationship between M and W at a higher technical level. Limits the accuracy of IC processing. Summary of the Invention

 The object of the present invention is to provide a precise parallelism measurement method that can accurately reflect the parallel relationship between the measured object and the reference plane and adjust the accuracy 髙, that is, a method for measuring the relative parallelism between the flat surface of the measured object and the reference plane.

 In order to achieve the above object, the specific technical solution of the present invention is: Let M be the measured object, W be the reference plane, Z be the rotation axis, and mount the measured object M on a platform having a rotation axis Z, which can be rotated around the rotation axis Z Rotate, the axis of rotation Z is perpendicular to the reference plane W; Equipped with a beam of light and a camera as a measuring device, the camera lens is aimed at the side of the object M to be imaged by the reflected light that can be received and projected on the side of the object M ; Let the horizontal axis u and the vertical axis V be the image coordinate system after imaging, and the origin point is at the center of the imaged image, where the intersection point between the upper or lower plane of the measured object M and its side through the vertical axis V is on the side of the measured object M; Detection point A of the image; When the measured object M rotates about the rotation axis Z, through continuous image acquisition, the image position measurement value of the detection point A is used to describe the parallel state of the plane of the measured object M with respect to the reference plane W, thereby determining Non-parallelism and adjusted position of the measured object M relative to the reference plane W;

When the positions of the light source and the camera remain unchanged, when the sampling rate is much greater than the rotation speed of the measured object M, the detection position of the detection point A is a discrete quantity that changes approximately continuously; when the measured object M and the reference plane W are not When parallel, the position detection value of the detection point A will show an offset change curve during the rotation period. When the curve measured during the rotation period is approximately parallel and straight, the two planes, namely the measured object M plane and the reference plane W, are approximately parallel;

 The offset change curve quantitatively reflects the angular position of the non-parallel amplitude and the maximum deviation amplitude of the measured object M plane and the reference plane W, and the vertical axis of the offset change curve indicates that the measured object M has a rotation angle of Θ Where the X represents the maximum inclination; the horizontal axis represents the rotation angle Θ, where Y is the angle Θ rotated relative to the starting position of rotation at the maximum inclination X; the reference plane may be located above the measured object M Or below.

 The invention has the following advantages:

 1. Based on its principle and reasonable design, the present invention can detect the non-parallelism of the measured object (such as a wafer) relative to the reference system as a whole, so it has a more obvious technical advantage than the existing technology, that is, : Can accurately reflect the parallel relationship between the measured object and the reference plane, at the same time easy to operate, and also has achievability.

 2. The present invention is an optical measurement method, which is not only free of electromagnetic pollution (such as electromagnetic interference), but also has high adjustment accuracy. The measurement accuracy depends on the image resolution and can reach more than 0.1 micron.

 3. The present invention is based on the optical imaging position measurement method, and realizes the parallelism detection between two planes, that is, the measured plane and the reference plane on the sub-micron level, so as to achieve ultra-precision positioning detection during IC processing and improve IC. The integrated circuit processing level and integration further improve the existing IC processing technology. Attached picture

 Figure 1 shows the measurement principle and measurement structure.

 Fig. 2 is a reflection image of the side of the wafer which enables the camera to receive the illumination light source.

 Fig. 3 is a graph showing the change in the displacement of the position detection value of the imaging detection point A on the side of the measured plane M in the rotation period. detailed description

Let M be the measured object, W be the reference plane, be located below the reference plane W, and Z be the rotation axis. The measured object M is mounted on a platform with a rotation axis Z and can be rotated about the rotation axis Z. The rotation axis Z and The reference plane W is vertical; it is equipped with a beam of illumination light source and a camera (a CCD camera is used in this embodiment) as a measuring device, so that the camera lens is aligned with the side of the object M to be measured. Reflective imaging, that is, the imaging of the reflected light projected on the side of the measured object on the camera; set the horizontal axis 11 and the vertical axis V as the image coordinate system after imaging, and the origin is at the center of the image after imaging, where the measured object M is below versus The intersection point A whose side passes through the vertical axis v is the detection point of the side image of the measured object M; when the measured object M rotates around the rotation axis Z, continuous image acquisition is used to describe the image position measurement value of the detection point A The parallel state of the plane of the measured object M with respect to the reference plane W, so as to determine the non-parallelism and the adjusted position of the measured object M with respect to the reference plane W;

 When the position of the light source and the camera is unchanged, when the sampling rate is much greater than the rotation speed of the measured object M, the detection position of the detection point A is a discrete quantity that changes approximately continuously; when the measured object M is not parallel to the reference plane W , The position detection value of the detection point A will show an offset change curve during the rotation period. When the curve measured in a rotation period is approximately parallel straight lines, the two planes are the measured object M plane and the reference. The plane W is approximately parallel;

 The offset change curve quantitatively reflects the angular position of the non-parallel amplitude and the maximum deviation amplitude of the plane of the measured object M and the reference plane W, and the vertical axis of the offset change curve represents the measured position of the measured object M when the rotation angle is Θ. The inclination amplitude, where X represents the maximum inclination amplitude; the horizontal axis represents the rotation angle 6, and Y represents the angle Θ that has been rotated relative to the starting position of rotation at the maximum inclination amplitude X.

 The specific operation of the parallelism measuring method is as follows: the measured object M is rotated around the rotation axis Z axis, and the CCD is used to continuously acquire images, and the image position of the imaging detection point A on the side of the measured object M is detected as a continuous image; When the position of the light source and the CCD is constant, when the sampling rate is much greater than the rotation speed of the measured object M, the detection position of the detection point A is a discrete quantity that changes approximately continuously; when the measured object M is not parallel to the reference plane W, The position detection value of the detection point A will show an offset change curve during the rotation period, see FIG. 3 (FIG. 3 reflects the tilt curve of the measured plane M relative to the reference plane W; the vertical axis indicates that the measured object is at The inclination amplitude when the rotation angle is Θ represents the required adjustment amount; where X is the maximum inclination amplitude of the measured plane M relative to the reference plane W; the horizontal axis is the rotation angle Θ, which represents the position to be adjusted in the measured plane M; Where Y is the rotation angle Θ at the detection point A). When the curve measured in a rotation period is approximately parallel straight line, the two planes are the measured object M plane and the reference plane W Approximately parallel.

 Measuring principle: As shown in Figure 1 (where: 1 is the light source, 2 is the CCD camera, 3 is the camera lens, and 4 is the reflection field), the measured object M is a wafer, and it is mounted on a rotating shaft. On the platform of Z, the rotation axis Z is perpendicular to a given reference plane W. A mask is installed on the reference plane W. Assuming that the reference plane W is parallel to the template, if the measured object M and the reference plane W can be measured, The flatness and the attitude between the two can be adjusted as required. Through this measurement and adjustment, the parallelism measurement and adjustment of the template and the wafer can be achieved. The detection accuracy depends on the position resolution of the measurement system.

Measurement imaging mechanism: Let M be the measured object, W be the reference plane, and Z be the rotation perpendicular to the reference plane W Rotation axis, the measured object M can rotate around the rotation axis Z axis. When a CCD camera and a lighting source are used in the configuration shown in FIG. 1, the reflection imaging that enables the CCD to receive illumination light and project it on the side of the wafer is shown in FIG. 2. Among them, A (the intersection point of the lower plane of the measured object M and its side passing the V axis) is the detection point defined on the side of the measured object M, u and V are image coordinate systems; 5 is the side of the measured plane M Imaging in the reflection domain, 6 for background domain imaging.

 Parallelism measurement mechanism: The core idea of the present invention is to describe the parallel state of the plane of the measured object M with respect to the reference plane W by measuring the image position measurement value of the detection point A, including the inclination width and the maximum inclination distance from the starting position. The rotation angle determines the non-parallelism of M and W and the adjustment position.

In this embodiment, the resolution of the CCD is 1000, and the magnification of the lens is 50. The resolution of the measurement system is 1000 X 50 = 5 X 10 ⁴ , and the field of view is 5 mm (that is, the actual height range of the scene included in the image). Then the measurement accuracy is 5mm / (5 X 10 ⁴ ) = l X l (T ⁴ min = 0.1 μηι. During the experiment, take the X value as the adjustment range, adjust its value to (toward) 0, and the adjustment position is shown by Υ The rotation angle Θ is determined.

 Analysis of the accuracy of parallelism: The detection accuracy of the non-parallelism of the present invention depends on the image resolution. When the image resolution is less than micron (sub-micron), the non-parallel state reflected by the measurement curve of the detection point A can be achieved. Sub-micron level. Since the field of view of the CCD can be designed to include only the area near the detection point A, the magnification of the lens can also be sufficiently large, so the image resolution can be sufficiently high, and theoretically the limit of the combination of the lens and the CCD resolution can be reached. In this way, when the resolution of the CCD imaging system is sufficiently high, precise measurement of the non-parallelism of the measured object M and the reference plane W can be achieved. According to scientific research experience, a linear high-resolution CCD camera can be used, and the magnification of the lens can be taken as required. After image processing, it can meet the measurement accuracy of 0.1 micron or more. Noise signal will appear on the measurement curve of the position of detection point A due to noise (caused by the unevenness of the boundary between the wafer surface and the side) at the measured edge. Therefore, technical processing such as smoothing filtering (conventional technology) needs to be added to correctly obtain The accurate position measurement curve of the detection point A, so as to accurately give non-parallel parameters for mechanism adjustment.

Claims

Thorn request 1. A precise parallelism measuring method, characterized in that: the measured object M can be rotated around a rotation axis Z, and is mounted on a platform having a rotation axis Z, the rotation axis Z is perpendicular to the reference plane W; equipped with a light source The camera and the camera are used as measuring devices, and the camera lens is aligned at the side of the object M to be imaged by the light source reflection that can be received and projected at the side of the object M. Let the horizontal axis u and the vertical axis V be the image coordinate system after imaging The origin is at the center of the imaged image, where the intersection of the upper or lower plane of the measured object M and its side through the longitudinal axis V is the detection point A on the side image of the measured object M; when the measured object M rotates around the rotation axis Z The parallel state of the plane of the measured object M with respect to the reference plane W is described by continuous image acquisition, using the image position measurement value of the detection point A, so as to determine the non-parallelism of the measured object M with respect to the reference plane W and the adjusted position.  2. The precise parallelism measuring method according to claim 1, characterized in that: when the position of the light source and the camera is unchanged, when the sampling rate is much greater than the rotation speed of the measured object M, the detection position of the detection point A Is a discrete quantity that changes approximately continuously; when the measured object M is not parallel to the reference plane W, the position detection value of the detection point A will show an offset change curve in the rotation period, and when measured in a rotation period When this curve is approximately parallel and straight, the two planes, namely the measured object M plane and the reference plane W are approximately parallel.  3. The method for measuring precision parallelism according to claim 2, characterized in that: said offset variation curve quantitatively reflects the angular position of the non-parallel amplitude and the maximum deviation amplitude of the measured object M plane and the reference plane W, which The vertical axis represents the inclination of the measured object M when the rotation angle is Θ, where X represents the maximum inclination; the horizontal axis is the rotation angle Θ, where Y represents the angle θ that has been rotated relative to the starting position of rotation at the maximum inclination X. .  4. The method for measuring precision parallelism according to claim 1, wherein the reference plane is located above or below the measured object M.