CN117666288A - Focusing and leveling measuring device - Google Patents

Abstract

The invention provides a focusing and leveling measuring device which comprises an illumination unit, a projection unit and a detection unit, wherein the illumination unit emits incident light rays which are projected on a region to be measured through the projection unit to form at least two sub-light spots, reflected light of the at least two sub-light spots carries at least two surface information of the region to be measured to enter the detection unit, and the position information of the region to be measured is obtained by utilizing the at least two surface information. According to the invention, at least two sub-light spots are formed in different areas of the area to be measured, or at least two sub-light spots with different light wave bands are formed in the area to be measured, so that when more comprehensive surface information of the area to be measured is obtained, the sensitivity of different sub-light spots to different process pieces can be utilized, and the adaptability of the focusing and leveling measuring device to different processes is improved.

Description

Focusing and leveling measuring device

Technical Field

The invention relates to the technical field of semiconductors, in particular to a focusing and leveling measuring device.

Background

In today's scanning projection lithography apparatuses, optical measurement methods are mostly used to realize focusing and leveling measurement on silicon wafers, and triangulation principles are mostly utilized. The basic principle of the conventional optical measurement method is that an optical illumination system and a projection system are utilized to irradiate light spots on the surface of a workpiece, and an imaging and detecting system is utilized to detect the light spots reflected by the workpiece. When the height and the inclination of the surface of the workpiece change, the position of the light spot reflected from the surface of the workpiece also changes, or the light spot detection signal law changes, and the height or the overall definition of the surface of the workpiece can be determined by detecting the change information of the position of the light spot or the light spot detection signal law information.

But when focusing and leveling are carried out on workpieces (different process pieces) of different process procedures, the reflection signals of light spots not only carry the position information of the workpiece surface, but also are easily influenced by the surface structure or the substrate structure of the region to be measured, so that the adaptability of focusing and leveling to different processes is influenced. The surface structure, such as the surface of the area to be measured, is provided with grooves, is plated with a metal film layer, and the substrate structure is a transparent substrate, a bonding substrate (bonding sheet), a resin substrate or the like.

Disclosure of Invention

The invention aims to provide a focusing and leveling measuring device, which is used for improving the adaptability of the focusing and leveling measuring device to different processes.

In order to solve the technical problems, the invention provides a focusing and leveling measurement device, which comprises an illumination unit, a projection unit and a detection unit, wherein the illumination unit emits incident light rays which are projected on a region to be measured through the projection unit to form at least two sub-light spots, reflected light of the at least two sub-light spots carries at least two surface information of the region to be measured to enter the detection unit, and the position information of the region to be measured is obtained by utilizing the at least two surface information.

Optionally, the projection unit includes a light path shaping lens set, a slit and a projection lens set that are sequentially arranged.

Optionally, one or more of the sub-light spots form one or more groups of measurement light spots, and any two of the sub-light spots in each group of measurement light spots have unequal intervals; or any of the sub-spots of each set of measurement spots may have a different size.

Optionally, the multi-band light source device further comprises a multi-band segmentation unit, and the multi-band segmentation unit is arranged between the illumination unit and the projection unit, wherein the illumination unit is a wide spectrum light source, the multi-band segmentation unit comprises a filtering runner, and the detection unit is a multi-band detection unit.

Optionally, the focusing and leveling measurement device includes a first projection branch and a second projection branch, the first projection branch and the second projection branch are both provided with the illumination unit and the projection unit, the first projection branch and the second projection branch form a first measurement light spot and a second measurement light spot which are staggered in the region to be measured, and the first measurement light spot and the second measurement light spot respectively include at least one sub-light spot.

Optionally, the first measurement light spot is located at a middle position of the area to be measured, the first reflected light of the first measurement light spot enters the detection unit, the second measurement light spot is located at an edge area of the area to be measured, and the second reflected light of the second measurement light spot enters the detection unit.

Optionally, the first measurement light spot is a light spot in a visible light band, and the second measurement light spot is a light spot in an infrared band.

Optionally, the method further comprises a controller configured to:

opening the first projection branch, closing the second projection branch to acquire first surface information carried by the first measuring light spot;

opening the second projection branch, closing the first projection branch to acquire second surface information carried by the second measuring light spot;

judging whether the information intensity of the first surface information is larger than a preset information intensity or not;

if the information intensity of the first surface information is larger than the preset information intensity, the first surface information and the second surface information are utilized to obtain the position information of the area to be detected;

and if the information intensity of the first surface information is smaller than or equal to the preset information intensity, acquiring the position information of the region to be detected by using the second surface information.

Optionally, the focusing and leveling measurement device includes a third projection branch, where the third projection branch is provided with the illumination unit and the projection unit, and the third projection branch is on the area to be measured and at least forms a third measurement light spot and a fourth measurement light spot in sequence, where the third measurement light spot and the fourth measurement light spot have different light wave bands, and the third measurement light spot and the fourth measurement light spot each include at least one sub-light spot.

Optionally, the method further comprises a controller configured to:

starting the third projection branch to form the third measuring light spot so as to acquire third surface information of the region to be measured;

starting the third projection branch to form the fourth measuring light spot so as to acquire fourth surface information of the region to be measured;

and comparing the information intensity of the third surface information and the fourth surface information, and outputting the position information corresponding to the larger information.

In summary, the focusing and leveling measurement device provided by the invention comprises an illumination unit, a projection unit and a detection unit, wherein at least two sub-light spots are formed in different areas of a region to be measured, or at least two sub-light spots with different light wave bands are formed in the region to be measured, so that surface information of different areas or different light wave bands is obtained, when more comprehensive surface information of the region to be measured is obtained, the sensitivity of different sub-light spots to different process sheets can be utilized, the adaptability of the focusing and leveling measurement device to different processes is improved, and the effect and efficiency of focusing and leveling measurement are improved.

Drawings

It will be appreciated by those of ordinary skill in the art that the drawings are provided for a better understanding of the present invention and are not to be construed as limiting the present invention in any way. Wherein:

fig. 1 is a block diagram of a focusing and leveling measurement device provided in the first embodiment;

FIG. 2 is a schematic diagram of a first measurement spot and a second measurement spot on a region to be measured according to the first embodiment;

FIG. 3 is a measurement flow chart provided in accordance with one embodiment;

fig. 4 is a gray threshold image obtained by the multiband detection unit provided in the first embodiment;

fig. 5 is a partial gray threshold image obtained by the multiband detection unit according to the first embodiment;

fig. 6 is a structural diagram of a focusing and leveling measurement device provided in the third embodiment;

fig. 7 is a measurement flow chart provided in the third embodiment.

In the accompanying drawings:

10-a workpiece; 11-an area to be measured; 20-a first projection branch; 21-a first lighting unit; 22-a first multi-band splitting unit; 23-a first projection unit; 23 a-a first optical path shaping lens group; 23 b-a first slit; 23 c-a first projection lens group; 24-a first measurement spot; 30-a second projection branch; 31-a second lighting unit; a second multi-band splitting unit; 33-a second projection unit; 33 a-a second optical path shaping lens group; 33 b-a second slit; 33 c-a second set of projection lenses; 34-second measurement spot 40-detection branch; a 41-multiband detection unit; 42-detecting lens group; 50-a third projection branch; 51-a third lighting unit; 52-a third multi-band splitting unit; 53-a third projection unit; 53 a-a third optical path shaping lens group; 53 b-a third slit; 53 c-a third set of projection lenses.

Detailed Description

The invention will be described in further detail with reference to the drawings and the specific embodiments thereof in order to make the objects, advantages and features of the invention more apparent. It should be noted that the drawings are in a very simplified form and are not drawn to scale, merely for convenience and clarity in aiding in the description of embodiments of the invention. Furthermore, the structures shown in the drawings are often part of actual structures. In particular, the drawings are shown with different emphasis instead being placed upon illustrating the various embodiments.

It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on, connected to, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on" …, "directly connected to" another element or layer, there are no intervening elements or layers present. Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. Spatially relative terms, such as "under … …," "below," "lower," "above … …," "upper," and the like, may be used herein for convenience of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "under" … … "," below "and" beneath "would then be oriented" on "other elements or features. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

The invention provides a focusing and leveling measuring device, which comprises an illumination unit, a projection unit and a detection unit, wherein the illumination unit emits incident light rays which are projected on a region to be measured through the projection unit to form at least two sub light spots, and reflected light (including specularly reflected light and/or diffusely reflected light) of the at least two sub light spots carries at least two surface information of the region to be measured to enter the detection unit, and the position information of the region to be measured is obtained by utilizing the at least two surface information.

The position information of the workpiece table is simulated by acquiring the position information of at least three areas to be detected which are not on the same straight line on the workpiece table (platform), and the position adjustment or the posture adjustment of the workpiece table can be completed by matching with a corresponding adjusting mechanism. The focusing and leveling measuring device provided by the invention can be suitable for any suitable workpiece (workpiece stage), such as an exposure platform of a lithography device, a laser scanning annealing slide stage and the like. In addition, in the step exposure process of the lithography equipment, the position information of the area to be exposed can be measured in real time before exposure, so that the exposure accuracy is improved.

Example 1

Fig. 1 is a block diagram of a focusing and leveling measurement device according to a first embodiment.

As shown in fig. 1, the focusing and leveling measurement device provided in this embodiment includes a first projection branch 20, a second projection branch 30 and a detection branch 40, where the first projection branch 20 and the second projection branch 30 are located on one side of a region 11 to be measured on a workpiece 10, and the detection branch 40 is located on the opposite side of the region 11 to be measured. The light beam exiting from the first projection branch 20 forms a first measurement light spot on the area to be measured 11, and a first reflected light of the first measurement light spot enters the detection branch 40. The light beam exiting from the second projection branch 30 forms a second measurement light spot on the area to be measured 11, and the second reflected light of the second measurement light spot enters the detection branch 40.

The first projection branch 20 includes a first illumination light source 21, a first multiband splitting unit 22, and a first projection unit 23 sequentially disposed along an optical path, and the first projection unit 23 includes a first optical path shaping lens group 23a, a first slit 23b, and a first projection lens group 23c sequentially disposed. Similarly, the second projection branch 30 includes a second illumination light source 31, a second multiband splitting unit 32, and a second projection unit 33 sequentially disposed along the optical path, and the second projection unit 33 includes a second optical path shaping lens group 33a, a second slit 33b, and a second projection lens group 33c sequentially disposed. The detection branch 40 includes a detection lens group 42 and a multiband detection unit 41, which are sequentially arranged.

Specifically, the first illumination light source 21 and the second illumination light source 31 may be broad spectrum light sources, and cover the visible light to infrared light bands. The first slit 22 and the second slit 32 may each include one or more groups (at least two) of sub-slits arranged at unequal intervals, wherein any two sub-slits of each group of sub-slits have unequal intervals, or any sub-slits of each group of sub-slits have different sizes, and the light beam passing through the sub-slits is thus loaded with unique preset information of the corresponding sub-slits. Thus, the light beam forms one or more sub-light spots in the area to be measured 11 through the sub-slits via the projection unit, so as to correspondingly form one or more groups of measurement light spots, wherein any two sub-light spots in each group of measurement light spots are arranged at unequal intervals, or the sub-light spots in each group of measurement light spots have unique (respectively different) sizes, and the reflected light of each measurement light spot carries the surface information of the area to be measured 11 and then enters the detection branch 40. The multiband detection unit 41 may include a multi-line scanning sensor, each for scanning spot information (surface information) of a different wavelength band, thereby calculating positional information, such as a height or inclination, of the region 11 to be detected.

Particularly, when grooves, protrusions or other structures (the surface state is relatively complex) which are easy to cause abnormal reflectivity are arranged on the surface of the region to be measured 11, only part of sub-light spots or part of the size of a certain sub-light spot in the measurement light spot can be caused, and the unique preset information of the corresponding sub-light spot can be obtained by utilizing the characteristic that each sub-light spot has a unique size, so that the position information of the region to be measured 11 is obtained from the part of the measurement light spot. Furthermore, each sub-spot of the first measurement spot may also be unique with respect to each sub-spot in the second measurement spot. Of course, in this embodiment, the sub-light spots may be strip-shaped, each sub-light spot may have the same length, but the widths of the sub-light spots are different, and the uniqueness of the size is reflected by using the difference of the widths of the sub-light spots.

The first and second measuring light spots can be formed at different positions of the region 11 to be measured by utilizing different incident angles of the first and second projection branches 20 and 30, and the first and second measuring light spots can be staggered from each other in the length direction and the width direction of the sub-light spots so as to improve the distinction degree of the multi-band detection unit during measurement. As shown in fig. 2, in a preferred embodiment, the first measuring spot 24 is located at a middle position (may be referred to as a main measuring spot) of the area under test 11, the reflected light (specular reflection) of the first measuring spot 24 enters the detection branch 40 for obtaining the most representative surface information of the area under test 11, the second measuring spot 34 is located at an edge position (may be referred to as a sub-measuring spot) of the area under test 11, and the second reflected light (similar to diffuse reflection) of the second measuring spot 34 enters the detection branch 40 for obtaining the general representative surface information of the area under test 11. It should be appreciated that the information intensity of the most representative surface information is high, but at the same time is relatively easily affected by the surface state of the area to be measured 11, whereas the information intensity of the generally representative surface information is low, but at the same time is affected only to a limited extent by the surface state of the area to be measured 11. The information intensity may be a gray threshold of the sub-light spot detected by the multi-band detection unit, taking the shape of the area 11 to be detected as a circle as an example, and the area covered by the circle with a radius of 0.5 times may be referred to as a middle position of the circle, and the other areas except the middle area may be referred to as edge positions of the circle.

The focusing and leveling measurement device of the present embodiment further includes a controller for controlling the first projection branch 20, the second projection branch 30, and the detection branch 40 to perform focusing and leveling. Compared to the case where the reflected light (the first reflected light and the second reflected light) of the first measurement light spot 24 and the second measurement light spot 34 enter the detection branch 40 at the same time, the first measurement light spot 24 and the second measurement light spot 34 are preferably measured step by step in the present embodiment, so as to improve the measurement accuracy of the line scanning sensor and facilitate the calculation. Specifically, the controller may be configured to measure the process as shown in fig. 3:

s11: opening the first projection branch 20, and closing the second projection branch 30 to obtain first surface information carried by the first measurement light spot;

s12: opening the second projection branch 30, and closing the first projection branch 20 to obtain second surface information carried by the second measurement light spot; the method comprises the steps of,

s13: judging whether the information intensity of the first surface information is larger than the preset information intensity; if so, the first surface information and the second surface information are utilized to obtain the position information of the region 11 to be detected; if not, the second surface information is used to obtain the position information of the area to be measured 11.

In steps S11 and S12, the first projection branch 20 or the second projection branch 30 can be controlled by controlling the first lighting unit 21 or the second lighting unit 31 to be turned on and off, respectively. The first measurement spot 24 and the second measurement spot 34 may both belong to the same visible band for subsequent calculations. The first surface information and the second surface information may each comprise intensity information representing the intensity of their information, e.g. the gray threshold of the sub-spot.

In step S13, if the information intensity of the first surface information is greater than the preset information intensity, it is indicated that the first surface information is less affected by the surface state of the area 11 to be measured, and it can be determined that the data validity of the first surface information is higher, that is, the first surface information is mainly used, and the second surface information is assisted, so as to comprehensively calculate and obtain the position information of the area 11 to be measured, and improve the data reliability of the obtained position information. If the information intensity of the first surface information is smaller than or equal to the preset information intensity, it indicates that the first surface information is greatly affected by the surface state of the area 11 to be measured, the surface state of the area 11 to be measured is complex, and the data validity of the first surface information can be considered to be low, that is, the position information of the area 11 to be measured can be obtained by calculating the second surface information.

Referring to fig. 4, fig. 4 is a gray threshold image (intensity information image) of the first measurement spot obtained by the multi-band detection unit. In fig. 4, the first measurement light spot includes four sub-light spots, the sub-light spots are similar to pulses, a dotted line L is a gray threshold line (preset information intensity), a width of the sub-light spots below the gray threshold line is a width W of the sub-light spots, and a top of the sub-light spots exceeds the gray threshold line to indicate that the information intensity exceeds the preset information intensity. Of course, the first measurement spot comprises only one effective sub-spot, or a partial pattern of one effective sub-spot, the gray threshold image of which in the multi-band detection unit may be, for example, the image shown in fig. 5.

In this embodiment, the first projection branch 20 and the second projection branch 30 are not provided with multi-band dividing units, and a detection unit (non-multi-band detection unit) with corresponding bands is also possible.

Example two

An embodiment II provides a focusing and leveling measurement device, where the focusing and leveling measurement device in this embodiment is the same as the focusing and leveling measurement device in embodiment I, and each focusing and leveling measurement device has a first projection branch, a second projection branch and a detection branch, where a first measurement light spot formed by the first projection branch in a region to be measured is located at a middle position of the region to be measured, and the first measurement light spot belongs to a visible light band, a second measurement light spot formed by the second projection branch in the region to be measured is located at an edge position of the region to be measured, and the second measurement light spot belongs to an infrared band, and the insensitive characteristic of the light spot of the infrared band to part of materials is utilized, so that the data reliability of the obtained position information is improved.

Taking the photoresist layer as an example to cover the surface of a workpiece, focusing and leveling measurement is carried out on the surface of the photoresist layer when a measuring light spot in a visible light wave band is incident on the surface of the photoresist layer, and the photoresist layer is covered on the surface of the workpiece in a shape-following manner and may have different thicknesses in different areas to be measured, so that the position information of the photoresist layer and the position information of the workpiece are not completely identical. When the near infrared band is adopted to form a second measuring light spot, the second measuring light spot can at least partially penetrate through the photoresist layer and then reflect (scatter) to enter the detection branch, so that the second measuring light spot is utilized to obtain the position information of a workpiece under the photoresist layer, the accuracy of focusing and leveling measurement is improved, and better process adaptability is achieved.

Example III

The third embodiment provides a focusing and leveling measurement device, which is similar to that of the first embodiment. As shown in fig. 6, the focusing and leveling measurement device of the present embodiment includes a third projection arm 50 and a detection arm 40, and the setting of the third projection arm 50 and the detection arm 40 may be the same as the setting of the first projection arm and the detection arm of the first embodiment. Unlike the first embodiment, in this embodiment, a projection branch (a third projection branch) is adopted to sequentially form a plurality of (at least two) measurement light spots with different optical bands on the area to be measured, where each measurement light spot includes at least one sub-light spot, so as to improve measurement accuracy by using reflectivity differences (sensitivity degrees) of different optical bands on different materials and different surface states, and further improve adaptability to different process slices.

In this embodiment, taking two measurement light spots as an example, the controller of the focusing and leveling measurement device may be configured to perform the measurement steps as shown in fig. 7:

s21: starting a third projection branch to form a third measuring light spot so as to acquire third surface information of the area to be measured;

s22: starting a third projection branch to form a fourth measuring light spot so as to acquire fourth surface information of the area to be measured;

s23: and comparing the information intensity of the third surface information and the fourth surface information, and outputting the position information corresponding to the larger information.

In steps S21 and S22, the third measuring spot and the fourth measuring spot may be preferably disposed at the middle position of the area to be measured, that is, the reflected light of the third measuring spot and the fourth measuring spot is similar to the first reflected light (specular reflected light) of the first embodiment, so as to improve the information intensity. The light beam emitted from the third illumination unit 51 (wide spectrum light source) is split (e.g. filtered) by the third multiband splitting unit 52 of the third projection branch 50 to output measurement light spots with different wavelength bands, so as to obtain surface information with different wavelength bands of the area to be measured.

In step S23, there is a certain difference in reflectivity difference (sensitivity) between the areas to be measured with different materials and different surface conditions in different optical bands, and the measuring light spot with the highest information intensity can be selected from the difference, and the position information calculated by the optical band is used as the position information of the area to be measured.

In summary, the focusing and leveling measurement device provided by the invention comprises an illumination unit, a projection unit and a detection unit, wherein at least two sub-light spots are formed in different areas of a region to be measured, or at least two sub-light spots with different light wave bands are formed in the region to be measured, so that surface information of different areas or different light wave bands is obtained, when more comprehensive surface information of the region to be measured is obtained, the sensitivity of different sub-light spots to different process sheets can be utilized, the adaptability of the focusing and leveling measurement device to different processes is improved, and the effect and efficiency of focusing and leveling measurement are improved.

The above description is only illustrative of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, and any alterations and modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the appended claims.

Claims (10)

1. The focusing and leveling measuring device is characterized by comprising an illumination unit, a projection unit and a detection unit, wherein the illumination unit emits incident light rays which are projected to a region to be measured through the projection unit to form at least two sub-light spots, reflected light of the at least two sub-light spots carries at least two surface information of the region to be measured to enter the detection unit, and the position information of the region to be measured is obtained by utilizing the at least two surface information.

2. The focus leveling measurement device according to claim 1, wherein the projection unit includes an optical path shaping lens group, a slit, and a projection lens group arranged in sequence.

3. The focusing and leveling measurement device according to claim 1, wherein one or more of the sub-spots form one or more sets of measurement spots, any two of the sub-spots of each set of measurement spots having a non-equidistant spacing therebetween; or any of the sub-spots of each set of measurement spots may have a different size.

4. The focus leveling measurement device of claim 1, further comprising a multi-band splitting unit disposed between the illumination unit and the projection unit, wherein the illumination unit is a broad spectrum light source, the multi-band splitting unit comprises a filter wheel, and the detection unit is a multi-band detection unit.

5. The focusing and leveling measurement device according to any one of claims 1 to 4, wherein the focusing and leveling measurement device comprises a first projection branch and a second projection branch, the first projection branch and the second projection branch are both provided with the illumination unit and the projection unit, the first projection branch and the second projection branch form a first measurement light spot and a second measurement light spot which are staggered in the region to be measured, and the first measurement light spot and the second measurement light spot each comprise at least one sub light spot.

6. The focus leveling measurement device of claim 5, wherein the first measurement spot is located at an intermediate position of the area to be measured, a first reflected light of the first measurement spot enters the detection unit, the second measurement spot is located at an edge area of the area to be measured, and a second reflected light of the second measurement spot enters the detection unit.

7. The focus leveling measurement device of claim 6, wherein the first measurement spot is a visible band spot and the second measurement spot is an infrared band spot.

8. The focus leveling measurement device of claim 6 or 7, further comprising a controller configured to:

opening the first projection branch, closing the second projection branch to acquire first surface information carried by the first measuring light spot;

opening the second projection branch, closing the first projection branch to acquire second surface information carried by the second measuring light spot;

judging whether the information intensity of the first surface information is larger than the preset information intensity, if the information intensity of the first surface information is larger than the preset information intensity, obtaining the position information of the region to be detected by using the first surface information and the second surface information, and if the information intensity of the first surface information is smaller than or equal to the preset information intensity, obtaining the position information of the region to be detected by using the second surface information.

9. The focusing and leveling measurement device according to any one of claims 1 to 4, comprising a third projection branch provided with the illumination unit and the projection unit, the third projection branch forming at least a third measurement spot and a fourth measurement spot sequentially on the area to be measured, the third measurement spot and the fourth measurement spot being different in optical band, the third measurement spot and the fourth measurement spot each comprising at least one of the sub-spots.

10. The focus leveling measurement device of claim 9, further comprising a controller configured to:

starting the third projection branch to form the third measuring light spot so as to acquire third surface information of the region to be measured;

starting the third projection branch to form the fourth measuring light spot so as to acquire fourth surface information of the region to be measured;

and comparing the information intensity of the third surface information and the fourth surface information, and outputting the position information corresponding to the larger information.