CN103676487B - A kind of workpiece height measurement mechanism and bearing calibration thereof - Google Patents

Abstract

A workpiece height measuring device and its correction method, comprising: the light emitted by a light source passes through a slit and is divided into a slit beam, obliquely incident on a workpiece to form an incident beam, and then irradiated to a measurement spot and reflected by the workpiece to form a reflected beam and pass through a mirror group to form a parallel beam ; The beam splitter divides the parallel beam into first and second measuring beams; the first and second measuring beams respectively pass through the first and second detection mirror groups and are received by the first and second linear array charge-coupled devices to form first and second measuring beams respectively. , the second image. When the workpiece is at the zero position, the first and second images are stitched together to calculate the zero distance of the sub-spots; when the workpiece is out of focus, the obtained first and second images are stitched together to calculate the defocus distance of the sub-spots; Calculate the displacement of each sub-spot according to the zero-position distance and defocus distance, and use the average value as the average value of the spot displacement to calculate the defocus amount of the workpiece. The invention has high measurement precision and strong process adaptability.

Description

A workpiece height measuring device and its calibration method

technical field

The invention relates to the field of object height measurement and correction, in particular to a device for measuring the height of a workpiece by light and a correction method thereof.

Background technique

The exposure device is a device that projects the pattern on the mask onto the surface of the workpiece through the projection objective lens. In projection exposure equipment, factors such as workpiece thickness deviation, surface undulation, and inaccuracy and non-repeatability of the focal plane position of the projection objective lens will cause defocus or inclination of the workpiece relative to the focal plane. If the defocus or inclination of the workpiece Making certain areas in the exposure field of view outside the effective depth of focus will seriously affect the measurement accuracy.

U.S. Patent US5118957 proposes a non-contact photoelectric measurement technology. This technology uses the light beam emitted by a high-brightness light source to pass through the condenser to illuminate the focusing mark with multiple pinholes. The pinhole focusing mark passes through the imaging system and the turning mirror. Projected on the workpiece, the pinhole image on the workpiece is located in the center of the exposure field of view, while other measurement points are distributed around. After being reflected by the workpiece, the image is enlarged and imaged on the area array CCD (charge-coupled device) by the imaging system. When the workpiece is in the focal plane of the projection objective lens, the focusing mark forms an optical conjugate relationship with the area array CCD after two imaging, then the defocus and tilt of the workpiece will cause the incident position of the pinhole imaging beam on the CCD to change, through signal processing The amount of defocus and tilt of the workpiece can be obtained. However, because the CCD is limited by the resolution, it is impossible to accurately calculate the defocus and tilt.

Contents of the invention

The technical problem to be solved by the invention is the restriction of the resolution of the charge-coupled device on the measurement accuracy of the defocusing amount of the workpiece. In order to solve the above technical problems, the present invention provides a workpiece height measuring device, comprising:

Light source, lighting mirror group, slit, projection mirror group, the light emitted by the light source passes through the lighting mirror group and the slit in turn, and is divided into several beams of light, and the several beams of light pass through the projection mirror After being assembled, it is obliquely incident on the workpiece located on the workpiece table to form incident light, and the incident light is reflected by the workpiece to form reflected light;

It is characterized in that it also includes:

A mirror group, the reflected light rays form several parallel light beams after passing through the mirror group;

a beam splitter for dividing the parallel beam into a first measurement beam and a second measurement beam perpendicular to the first measurement beam;

The first detection mirror group and the first linear array charge-coupled device, the first linear array charge-coupled device receives the first measuring beam after passing through the first detection mirror group, and obtains the first image;

The second detection mirror group and the second linear charge-coupled device, the second linear charge-coupled device receives the second measuring beam behind the second detection mirror group to obtain a second image;

The distance between the first detection mirror group and the second detection mirror group and the beam splitter is the same, and the first linear charge-coupled device and the first detection mirror group and the second linear charge-coupled device are connected to the The distances of the second detection mirror group are the same, the magnifications of the first detection mirror group and the second detection mirror group are the same, and the parameters of the first linear charge-coupled device and the second linear charge-coupled device Similarly, the second linear charge-coupled device is placed opposite to the first linear charge-coupled device.

Preferably, the light source is an LED or a halogen lamp.

The present invention also provides a height calibration method of a height measuring device, comprising the following steps:

Step 1, when the workpiece table is at the zero position, obtain the first image and the second image from the first linear charge-coupled device and the second linear charge-coupled device respectively;

Step 2, according to the obtained first image and the second image, calculate the distance between the sub-spot centers on the same projection plane;

Step 3, acquiring images of the first linear charge-coupled device and the second linear charge-coupled device under the condition that the workpiece surface is defocused;

Step 4, according to the obtained first image and the second image, calculate the distance between the centers of the sub-spots on the same projection plane;

Step 5, according to half of the change value of the center distance of each sub-spot, calculate the corresponding position change of each sub-spot, and then calculate the average value of the displacement of the light spot;

Step 6, calculating the defocus amount of the workpiece surface.

Further, the calculation formula of the defocusing amount of the workpiece is , where Z is the defocus amount of the workpiece, Hccd is the average value of the spot displacement, is the incident angle of the incident ray, and are the magnifications of the reflecting mirror group and the detecting mirror group, respectively.

Further, the calculation of the sub-spot center distance includes the following steps:

Combining the first image and the second image into one image;

Preprocessing the synthesized image, including eliminating the background of the image and removing the noise of the image itself;

Convert the image into a grayscale curve, and obtain the edge information of the light spot according to the curve;

According to the edge information of the light spot, the central position of the sub-spot on the first linear charge-coupled device and the central position of the sub-spot on the second linear charge-coupled device are obtained by positioning;

Subtracting the center positions of the sub-spots at the same position on the projection plane to obtain the distance between the centers of the sub-spots on the same projection plane;

Further, the image background elimination is to subtract the collected image from the background image of the charge-coupled device, so as to eliminate the influence of the background noise of the charge-coupled device on the image.

The advantage of the present invention is that by calculating the images of the two linear array CCDs and the displacement of each sub-spot, the influence of the different topography of the upper surface of the workpiece on the defocus amount is reduced, the influence of the CCD resolution on the measurement is weakened, and the Errors in the measurement process can effectively improve the accuracy of defocus measurement. The invention only needs to measure the height of the workpiece at the best focal plane, and also avoids the influence of workpieces with different shapes on the defocusing amount, and has good process adaptability.

Description of drawings

The advantages and spirit of the present invention can be further understood through the following detailed description of the invention and the accompanying drawings.

Fig. 1 is the structural representation of workpiece height measuring device of the present invention;

Fig. 2 is the distribution figure of spot neutron spot on the projection surface;

Fig. 3 is the gray value map of the image formed by measuring the light spot on the first linear array charge-coupled device;

Fig. 4 is the gray value map of the image formed by measuring the light spot on the second linear array charge-coupled device;

Fig. 5 is a geometric relationship diagram between the position change of the light spot on the linear array charge-coupled device and the defocusing amount of the workpiece;

6 is a mosaic diagram of images formed by the first and second linear charge-coupled devices;

Fig. 7 is a flow chart of the workpiece height correction method of the present invention;

FIG. 8 is a flow chart of calculating the sub-spot distance in FIG. 7 .

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

Referring to FIG. 1 , the workpiece height measuring device of the present invention is located between the projection objective lens 9 and the workpiece 22 in the scanning exposure equipment. The mask stage 3 is located above the projection objective lens 9 , the mask 21 with a pattern is placed on the mask stage 3 , and the workpiece 22 is placed on the workpiece stage 8 . The pattern of the mask 21 is projected onto the surface of the workpiece 22 through the projection objective lens 9 . The workpiece 22 may be a silicon wafer or a glass substrate.

The workpiece height measuring device includes a first linear array charge-coupled device (linear array CCD) 1, a first detection mirror group 2, a second linear array charge-coupled device 4, a second detection mirror group 5, a beam splitter 6, a mirror group 7, Projection mirror group 10 , slit 11 , illumination mirror group 12 , light source 13 . The light emitted by the light source 13 is divided into several bundles of light after passing through the illumination mirror group 12 and the slit 11 in sequence. After passing through the projection mirror group 10, the several bundles of light will be obliquely incident on the workpiece 22 at a certain angle, forming incident light. The light source is LED or halogen lamp. The incident light is reflected by the workpiece 22 to form reflected light. After the reflected light passes through the mirror group 7, several parallel bundles of light are formed. The parallel light rays are evenly divided into two groups after passing through the beam splitter 6. One group passes through the beam splitter 6 and continues to exit along the original direction. After being reflected by the beam splitter 6, it enters the second detection lens group 5, and then enters the second linear array CCD4. In this embodiment, the included angle between the light reflected by the beam splitter 6 and the parallel light is selected to be 90°.

Wherein, the magnifications of the first detecting mirror group 2 and the second detecting mirror group 5 are the same, the parameters of the first linear array CCD1 and the second linear array CCD4 are the same, can be selected as 2048 pixels, and the data output is 12bit. The second linear array CCD4 is placed in reverse, and the distances from the first linear array CCD1 and the second linear array CCD4 to the first detection mirror group 2 and the second detection mirror group 5 are the same. The mirror distance is also the same. The working principle of the workpiece height measuring device is: the linear array CCD can image the light spot image on the workpiece, and calculate the height of the workpiece through the different parts of the light spot in the image.

Referring to Figure 2, the figure shows the position of the spot on the projection plane, the projection plane is perpendicular to the main optical axis of the focusing and leveling (FLS), the plane where the slit 11 is located, and the Y axis is the measurement direction of the FLS, The X-axis is the non-measurement direction of the FLS. A group of measurement spots consists of three measurement sub-spots (sub-spot u, sub-spot c and sub-spot d), the size of which is L in the measurement direction, and SP in the non-measurement direction. The centers of the sub-spots are all located on the Y axis, and the distance is DP.

Figure 3 shows the gray value of the measurement spot imaged by the first linear CCD1, where the ordinate is the gray value of the image, and the abscissa is the pixels on the linear CCD, and one time from left to right is the low pixel point The highest pixel point, Du, Dc, and Dd are the positions of the centers of the three sub-spots in the spot on the CCD, Huc is the distance between spot u and spot c, and Hcd is the distance between spot c and spot d. After passing through the equidistant slits, theoretically, the spacing between the sub-spots is the same, that is, Huc=Hcd, but due to the influence of the surface topography and inclination of the workpiece, the distance between the two edge sub-spots and the central sub-spot Not the same. When the workpiece table is at zero position, that is, at the best focal plane, the central sub-spot c should be at the center of the image, that is, Dc=1024 in this embodiment.

Fig. 4 has shown the gray scale value that measurement light spot is imaged in the second line array CCD4, and the second line array CCD4 is reversely placed, so this figure and Fig. 3 are two images reversed, namely in Fig. 3, from the left To the right, the order of the sub-spots is: u, c, d. In Figure 4, the order of the sub-spots is: d, c, u.

As shown in Figure 5, due to the defocusing amount of the workpiece 22, the spot position detected by the linear array CCD will change, and the relationship between the spot position change Hccd and the workpiece position can be expressed as:

(1)

The above formula characterizes the relationship between the defocus amount Z of the workpiece and the spot position change Hccd detected by the linear array CCD, where is the incident angle of the incident light in the projection light path, and are the magnifications of the reflecting mirror group 7 and the detecting mirror group respectively, and their values are fixed. when the incident angle When the magnification of the detection mirror group and mirror group 7 is 75o, the magnification of the workpiece defocus detection can be regarded as 13.523, that is, the defocus corresponding to one pixel is 73.95nm. Theoretically, the spot position change Hccd detected by the first linear array CCD1 and the second linear array CCD4 should be the same, but in practice, because the first and second detection mirror groups cannot be exactly the same, the angle of the beam splitter and other reasons, will be slightly different.

Figure 6 shows the spliced images of the images detected by the first and second line array CCDs, the left side is the image detected by the first line array CCD1, and the right side is the image detected by the second line array CCD4. The solid line in the figure is the image detected when the workpiece table is at the original position, the dotted line is the image obtained after the workpiece table is moved down Z as shown in Figure 5, H1 is the distance between the sub-spots c at the original position, and H2 is the workpiece The distance between the two sub-spots c after the stage moves, so the following relationship can be obtained:

(2)

The Hccd calculated by the above formula is actually the average value of the spot position changes detected by the two linear array CCDs. When the original position of the workpiece table is at zero, formula (2) can be transformed into:

(3)

in, Be the pixel value of linear array CCD, be the fixed parameter, in the present embodiment =2048. When the workpiece table moves down, the distance between two images formed by the same sub-spot on the projection plane increases, and when the workpiece table moves up, the distance between two images formed by the same sub-spot on the projection plane decreases Small.

Referring to Fig. 7, the workpiece height correction method of the present invention includes the following steps:

Step 1, when the workpiece table is at zero position, acquire the images in the two linear array CCDs at this time;

In step 2, the two acquired images are stitched together, and the distances Hu0, Hc0, and Hd0 of the same sub-spots on the projection surface are calculated. Theoretically, when the workpiece table is at the zero position, the central sub-spot will be at the center of the image, but this cannot be realized in the actual device, and the distance between the actual sub-spots needs to be measured and calculated at the zero position of the workpiece table;

Step 3, acquiring the image of the linear array CCD under the condition that the workpiece surface is out of focus, wherein the defocus can be caused by the upward or downward movement of the workpiece table;

Step 4, splicing the two acquired images, and calculating the distance Hu1, Hc1, Hd1 of the center of the same sub-spot on the projection surface;

Step 5, according to the formula (2), the corresponding position changes Hccdu, Hccdc, and Hccdd of the three sub-spots can be calculated, and the formula is:

(4)

Then the average Hccd of the spot displacement can be calculated, namely

(5)

Step 6, according to the formula (1), the defocus amount of the workpiece surface can be calculated:

(6)

This embodiment adopts three sub-spots as a preferred embodiment, and the number of sub-spots in the measurement spot in the present invention should be at least 2.

In the above correction method, the measuring the spacing of the same sub-spots includes the following steps:

Step 1, combining the images obtained by the two linear array CCDs into one image;

Step 2, preprocessing the synthesized image, including two steps of image background elimination and image smoothing and filtering. Eliminate the background is to subtract the collected image from the background image of the CCD to eliminate the influence of the background noise of the CCD on the image. The smoothing filter is to eliminate the noise of the image itself while retaining the characteristics of the image. This step can reduce the influence of noise and background on the image and reduce the measurement error;

Step 3, convert the image into a grayscale curve as shown in Figure 6, and obtain the information of the edge of the spot according to the curve, that is, the area where there is a grayscale change in the adjacent pixels in the curve;

Step 4, according to the edge area of the light spot in step 3, the central positions Du, Dc, Dd of the sub-light spots on the first line array CCD and the center positions Du', Dc', Dc', Dd';

Step 5, subtracting the center positions of the same sub-spots on the projection surface can obtain the spacing of the same sub-spots on the same projection surface:

(5)

What is described in this specification is only preferred specific embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit the present invention. All technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments according to the concept of the present invention shall fall within the scope of the present invention.

Claims (4)

1. A height correction method for a height measurement device, comprising the steps of:

step 1, when a workpiece table is positioned at a zero position, a first image and a second image are respectively obtained from a first linear array charge coupled device and a second linear array charge coupled device;

step 2, calculating the distance between the centers of the sub light spots on the same projection plane according to the obtained first image and the second image;

step 3, obtaining images of the first linear array charge coupled device and the second linear array charge coupled device under the condition that the surface of the workpiece is out of focus;

step 4, calculating the distance between the centers of the sub light spots on the same projection plane according to the obtained first image and the second image;

step 5, calculating to obtain the corresponding position change of each sub-light spot according to a half of the change value of the center distance of each sub-light spot, and then calculating to obtain the average value of the light spot displacement;

and 6, calculating the defocusing amount of the surface of the workpiece.

2. The correction method according to claim 1, wherein the defocus amount of the workpiece is calculated by the following formulaWherein Z is the defocusing amount of the workpiece, Hccd is the displacement average value of the light spots,is the angle of incidence of the incident light rays,andthe magnification ratios of the reflector group and the detection lens group are respectively.

3. The correction method according to claim 2, wherein the sub-spot center-to-center distance calculation comprises the steps of:

combining the first image and the second image into one image;

preprocessing the synthesized image, including eliminating the image background and eliminating the noise of the image;

converting the image into a gray curve, and acquiring light spot edge information according to the curve;

according to the light spot edge information, positioning to obtain the central position of the sub light spot on the first linear array charge coupled device and the central position of the sub light spot on the second linear array charge coupled device;

and subtracting the center positions of the sub light spots at the same position in the projection plane to obtain the center distance of the sub light spots on the same projection plane.

4. The correction method of claim 3, wherein the background image is subtracted from the acquired image to eliminate the influence of the background noise of the CCD on the image.