TWI575221B - Surface roughness measurement system and method using the same - Google Patents

Description

Surface roughness detecting system and method thereof

A surface roughness detecting system and method thereof, in particular, a surface interference detecting method composed of a differential interference measuring, a four-phase polarizing photosensitive element and an axial dispersion module, and a system used therefor.

In the existing optoelectronic industry, the initial detection of wafers or grains is coarseness detection, which can be divided into contact measurement or non-contact measurement. The contact measurement system is measured by a single-point probe architecture, and the roughness data is measured by the XYZ three-axis movement amount. The non-contact measurement system is measured by an optical probe, which uses the interference and confocal measurement technology to perform the Z-axis vertical scanning movement to perform the topography measurement.

However, the above-mentioned contact measurement and non-contact measurement have their own problems. The speed of contact measurement is very slow, and it takes a long time to perform large-area measurement. Non-contact measuring system and area measurement to speed up the measurement speed, but the measurement fashion needs to perform Z-axis scanning, so it can not be used for measurement on the production line.

The invention provides a surface roughness detecting system, comprising: a first light source; a spectral control unit; an optical collimating module; An axial dispersion module; a first optical unit; a second optical unit; an optical guiding module; a third optical unit; a fourth optical unit; a second light source; and a four-phase polarization The first light source provides a light beam to the optical collimation module, and the light beam is formed into a first group of detection beams through the optical alignment module, and the axial dispersion module is located at the first a set of detection beam travel paths, the first set of detection beams forming a third set of detection beams through the axial dispersion module; the second source providing a second set of detection beams, the fourth optical unit and the The optical guiding module is located in a traveling path of the second group of detecting beams; the first optical unit is located at an intersection path of the third group of detecting beams and the second group of detecting beams, and the third group of detecting beams and the first The two sets of detection beams are combined to form a fourth set of detection beams; the second optical unit is located in the travel path of the fourth set of detection beams, and the fourth set of detection beams are formed into a fifth Detecting a light beam; a test object is disposed on a traveling path of the fifth group of detecting beams, wherein the object to be tested reflects a fifth group of detecting beams to form a first group of reflected beams, and the first group of reflected beams are reflected to The second optical unit is configured to form a second set of reflected light beams; the second set of reflected light beams are passed through the first optical unit to form a third set of reflected light beams and a fourth set of reflected light beams; and the third set of reflected light beams Passing through the axial dispersion module to form a fifth set of reflected beams; the fifth set of reflected beams passing through the optical collimation module to be received by the spectral control unit; the fourth set of reflected beams passing through The optical guiding module and the third optical unit form a sixth set of reflected light beams, and the sixth set of reflected light beams are received by the four-phase polarized photosensitive element.

The invention provides a method for detecting a surface roughness, comprising the steps of: adjusting a phase of a differential interference fringe and a differential interference image, generating a differential interference fringe and a differential interference image, adjusting the phase of the differential interference, and difference The sub-interference image is adjusted to a clear focus focal length position, the clear focus focal length position is a differential interference focal plane; the position of the focused spot is adjusted to the center position of the differential interference image, which is a first focus, a second focus And adjusting a third focus to a center position of the differential interference image; monitoring a reflection signal of the object to be tested received by the axial dispersion module, and causing the differential interference focal plane to be within a focus and focus range, the first focus and the third focus The distance between the focal points constitutes a focus and focus range, the differential interference focal plane is located within the focus and focus range; the distance between the object to be measured and the differential interference focal plane is found, and the differential interference focal plane corresponds to a surface of the object to be tested; and a four-phase differential interference image is obtained, and the topography data is calculated to evaluate the roughness, the differential interference focal plane is regarded as a basis, the first focus, the second focus, and the third The focus position of the surface of the object to be tested is changed according to the fluctuation of the surface of the object to be tested, and the four-phase polarized photosensitive element obtains at least one four-phase difference according to the change. Related image information to derive a topography, the topography-based information can be used to evaluate the surface roughness of the material under test.

10‧‧‧First light source

11‧‧‧Spectrum Control Unit

12‧‧‧Optical collimation module

120‧‧‧First fiber collimating mirror

121‧‧‧Second fiber collimating mirror

123‧‧‧1 pair of 2 optical coupling fibers

124‧‧‧First set of detection beams

13‧‧‧Axial Dispersion Module

130‧‧‧First convex lens

131‧‧‧First concave lens

132‧‧‧second convex lens

133‧‧‧third convex lens

134‧‧‧second concave lens

135‧‧‧4th convex lens

136‧‧‧The third set of detection beams

137‧‧‧ first mirror

138‧‧‧Second mirror

139‧‧‧The fifth set of reflected beams

14‧‧‧First optical unit

140‧‧‧Fourth set of test beams

142‧‧‧The third set of reflected beams

143‧‧‧Fourth set of reflected beams

15‧‧‧Second optical unit

150‧‧‧Fifth Group Detection Beam

151‧‧‧Second set of reflected beams

16‧‧‧Optical guidance module

160‧‧‧Differential Interference

161‧‧‧Mirror

162‧‧‧beam splitter

17‧‧‧ Third optical unit

170‧‧‧ sixth set of reflected beams

18‧‧‧Fourth optical unit

19‧‧‧second light source

190‧‧‧Second set of detection beams

20‧‧‧Four phase polarized photosensitive element

30‧‧‧Test object

300‧‧‧First set of reflected beams

A‧‧‧Dispersive light source focus sequence

B‧‧‧Axial dispersion range

C‧‧‧ first focus

D‧‧‧second focus

E‧‧‧ third focus

F‧‧‧Differential Interferometric Focal Plane

S1~S6‧‧‧Steps

FIG. 1 is a schematic diagram of a surface roughness detecting system according to an embodiment of the present disclosure.

FIG. 2 is a schematic diagram of a surface roughness detecting system according to still another embodiment of the present disclosure.

FIG. 3 is a schematic diagram of an axial dispersion module according to an embodiment of the present disclosure.

FIG. 4 is a schematic diagram showing an operation of performing Z-axis moving chasing to obtain an interference image by a four-phase polarizing photosensitive element according to an embodiment of the present disclosure.

5A-5D are schematic diagrams of a four-phase differential interference image according to an embodiment of the present disclosure.

Figure 6 is a schematic diagram of a four-phase differential interference image after reconstruction.

FIG. 7 is a flow chart of a surface roughness detecting method according to an embodiment of the present disclosure.

The embodiments of the present disclosure are described in the following by means of a plurality of specific embodiments, and those skilled in the art can easily understand other advantages and functions of the disclosure by the contents disclosed in the specification.

Referring to the embodiment shown in FIG. 1 , the embodiment is a surface roughness detecting system including a first light source 10 , a spectral control unit 11 , an optical collimating module 12 , and an axial dispersion mode . Group 13, a first optical unit 14, a second optical unit 15, an optical guiding module 16, a third optical unit 17, a fourth optical unit 18, a second light source 19 and a four-phase bias Photosensitive element 20.

The optical collimation module 12 has a first fiber collimating mirror 120 and a second fiber collimating mirror 121.

The first light source 10 and the spectrum control unit 11 are coupled to the first fiber collimating mirror 120 by a pair of two optical coupling fibers 123. The first light source 10 is a continuous light source. The first source 10 provides a beam of light to the first fiber collimating mirror 120, which passes through an optical collimation module 12 that forms a first set of detection beams 124.

The axial dispersion module 13 is located in the path of travel of the first set of detection beams 124. The axial dispersion module 13 has a first convex lens 130, a first concave lens 131, a second convex lens 132, a third convex lens 133, a second concave lens 134 and a fourth convex lens 135. The first set of detection beams 124 form a third set of detection beams 136 through the axial dispersion module 13. The first convex lens 130, the first concave lens 131 and the second convex lens 132 can be regarded as a first mirror group 137. The third convex lens 133, the second concave lens 134, and the fourth convex lens 135 can be regarded as a second mirror group 138.

The second source 19 is a single wavelength source. The second source 19 provides a second set of detection beams 190. The fourth optical unit 18 and the optical guiding module 16 are located in the traveling path of the second group of detecting beams 190. The fourth optical unit 18 is a collimating mirror. The optical guiding module 16 has a beam splitter 162, a mirror 161 and a differential interference (DIC) 稜鏡 160, and the differential interference 稜鏡 160 is, for example, Wollaston Prism. The second set of detection beams 190 are sequentially passed through the fourth optical unit 18, the beam splitter 162, the mirror 161, and the differential interference 稜鏡160.

The first optical unit 14 is located at a intersection of the third set of detection beams 136 and the second set of detection beams 190, and the third set of detection beams 136 are combined with the second set of detection beams 190 to form a fourth set of detection beams. 140. The first optical unit 14 is a beam splitter.

The second optical unit 15 is located in the traveling path of the fourth group of detecting beams 140, and the fourth group of detecting beams 140 is formed into a fifth group of detecting beams 150 after passing through the second optical unit 15. The second optical unit 15 is a microscope objective.

Referring to the embodiment shown in FIG. 2, a test object 30 is disposed on a traveling path of the fifth group of detecting beams 150, and the object to be tested 30 reflects the fifth group of detecting beams 150 to form a first group of reflections. Light beam 300. The first set of reflected beams 300 are reflected to the second optical unit 15 to form a second set of reflected beams 151.

The second set of reflected beams 151 pass through the first optical unit 14 to form a third set of reflected beams 142 and a fourth set of reflected beams 143. The third set of reflected beams 142 pass through the axial dispersion module 13 to form a fifth set of reflected beams 139, and the fifth set of reflected beams 139 pass through the optical collimation module 12 to be received by the spectral control unit 11.

The fourth set of reflected beams 143 pass through the optical guiding module 16. As further explained, the fourth set of reflected beams 143 sequentially pass through the differential interference 稜鏡160, the mirror 161 and the beam splitter 162.

The third optical unit 17 is a focusing mirror, the third optical unit 17 is located in the traveling path of the fourth group of reflected light beams 143, and the fourth group of reflected light beams 143 is passed through the third optical unit 17 to form a sixth group of reflected light beams 170. The four-phase polarized photosensitive element 20 is located in the path of travel of the sixth set of reflected light beams 170.

Please refer to the embodiment shown in FIG. 7. This embodiment is a method for detecting the surface roughness, and the steps include:

In step S1, the phase of the differential interference fringe and the differential interference image are adjusted. In the embodiment shown in FIG. 1, the second source 19 provides a second set of detection beams 190, and the second set of detection beams 190 sequentially passes through the fourth optical unit 18 and the optical guide module 16. The second set of detection beams 190 passing through the differential interference 稜鏡160 are viewed as a differential interference fringe, and the differential interference 稜鏡160 adjusts the phase of the differential interference fringes to 0 degrees.

The second set of detection beams 190 are guided by the first optical unit 14 to the second optical unit 15, and the second set of detection beams 190 are projected onto the surface of the object to be tested 30 by adjusting the surface of the object to be tested 30 to the Z axis. a position of the differential interference fringe on the surface of the object to be tested 30, forming a differential interference image, and adjusting the differential interference image to a clear focus focal length position, as in the embodiment shown in FIG. 3, The clear focus focal length position can be regarded as a differential interference focal plane F.

In step S2, the position of the focused spot is adjusted to the center position of the differential interference image. Referring to the embodiments shown in FIGS. 1 and 3, the first light source 10 provides a light beam, and the light beam sequentially passes through the optical collimation module 12, and the light beam forms a first set of detection beams 124.

In the embodiment shown in FIG. 3, when the first group of detection beams 124 pass through the first mirror group 137, the dispersion order of the first group of detection beams 124 is in focus order A, for example, from red, green and blue, from inside to outside. distributed.

The first set of detection beams 124 pass through a second set 138, and the first set of detection beams 124 are formed as a third set of detection beams 136. After the third set of detection beams 136 pass through the first optical unit 14, the third set of detection beams 136 are formed into a fourth set of detection beams 140. After the fourth set of detection beams 140 pass through the second optical unit 15, the second optical unit 15 is capable of elongating the focus range of the fourth set of detection beams 140 to a desired size. The axial dispersion module 13 is capable of changing the direction of the focused optical signal of the third set of detection beams 136, for example, from blue to red. It can be designed according to different characteristics of each light measurement and analysis.

The axial dispersion range B of the fourth group of detection beams 140 forms at least a first focus C, a second focus D and a third focus E. The first focus C, the second focus D, and the third focus E are sequentially distributed along one axial direction. The first focus C is, for example, the focus of blue light. The second focus D is, for example, the focus of green light. The third focus E is, for example, the focus of red light. The fourth set of detection beams 140 are combined with a second set of detection beams 190 to form a fifth set of detection beams 150.

The first focus C, the second focus D, and the third focus E are at a center position of the differential interference image.

Step S3, monitoring the reflected signal of the object to be tested received by the axial dispersion module, so that the difference The interference focal plane is within a focus and focus range. The axial dispersion range B in the embodiment as shown in Fig. 3.

As shown in FIG. 3, the distance between the first focus C and the third focus E can constitute a focus and focus range. The differential interference focal plane F is located between the first focus C and the third focus E, that is, within the focus and focus range.

If the second optical unit 15 is used as the basis of the differential interference, the light source of the axial dispersion module 13 and the light source of the differential interference are shared by the first optical unit 14. The light source of the differential interference is the light source from the optical guiding module 16 in the embodiment shown in FIG.

The axial dispersion module 13 achieves axial dispersion by a plurality of sets of optical mirrors, the first mirror set 137 and the second mirror set 138 as described above, and is imaged by the second optical unit 15.

At this time, the light source of the continuous band will be focused to a plurality of depth positions according to different wavelengths, such as the first focus C to the third focus E shown in FIG. The axial dispersion module 13 can enable the surface roughness detection system of the present invention to obtain the current height information in time, thereby performing focusing and chasing functions, and using the wavelength information of the reflected optical signal as the basis for judging the height, and then performing the Z-axis. Quickly chase the focus, and record the amount of Z-axis distance moved by each point (such as the above focus) due to the height change, as the coplanarity calculation information, as described below.

In step S4, the distance between the object to be tested and the differential interference focal plane is found, and the differential interference focal plane corresponds to the surface of the object to be tested. The differential interference focal plane F as shown in Fig. 3 still has a distance from the surface of the object to be tested 30 as shown in Fig. 1, finds the distance, and records the distance. The differential interference focal plane F is then corresponding to the surface of the object 30 to be tested.

In step S5, a four-phase differential interference image is obtained, and the topography data is calculated to evaluate the roughness. As in the embodiment shown in Fig. 4, the surface of the object to be tested 30 has a plurality of undulations. The differential interference focal plane F can be regarded as a basis. The focus position of the first focus C, the second focus D, and the third focus E on the surface of the object to be tested 30 changes depending on the fluctuation of the surface of the object to be tested 30. The object to be tested 30 reflects the fifth detection beam 150 to form a first group of reflected beams 300.

As in the embodiment shown in FIG. 2, the first set of reflected beams 300 includes the above The focus position changes the image information of the differential interference focal plane F with the first focus C to the third focus D. The first set of reflected beams 300 are reflected to the second optical unit 15 to form a second set of reflected beams 151.

The second set of reflected beams 151 pass through the first optical unit 14 to form a third set of reflected beams 142 and a fourth set of reflected beams 143. The third set of reflected beams 142 pass through the axial dispersion module 13 to form a fifth set of reflected beams 139. The fifth set of reflected beams 139 are passed through the optical collimation module 12 to be received by the spectral control unit 11, and the spectral analysis unit 11 analyzes the spectra of the fifth set of reflected beams 139 and records the spectral data. The spectral data is used to determine the above-mentioned focus data.

The fourth set of reflected beams 143 pass through the optical guiding module 16 and the third optical unit 17 to form a sixth set of reflected beams 170. The sixth set of reflected beams 170 are received by the four-phase polarized photosensitive element 20. The four-phase polarized photosensitive element 20 generates at least one four-phase interference image based on the sixth set of reflected light beams. As shown in Figures 5A-5D, it is a four-phase interference image.

A plurality of four-phase interference images obtain a topographical information that can be used to evaluate the surface roughness of the object to be tested 30.

As described above, the axial dispersion module 13 enables the spectrum control unit 11 to obtain the surface information of the current object 30 to perform focusing and tracking functions. The spectrum control unit 11 performs the Z-axis fast tracking by using the wavelength information of the reflected optical signal as the basis for determining the height, and simultaneously records the Z-axis distance between the points due to the height change, and calculates the coplanarity. News.

As shown in the embodiment of Fig. 4, the correspondence between the wavelength of the reflected light and the change in the measured height is expressed as a quadratic curve, a, b and c are curve parameters, and λ is a respective wavelength.

Z=a λ ² +b λ+c (1)

After fast tracking in each measurement position, differential interference image capture is performed, and the four-phase polarization sensor 20 is used to cause differential interference images to produce four different interference phase changes.

As shown in the fifth embodiment of the fifth embodiment, the four-phase polarization detecting element 20 obtains four sets of interference images I ₁ , I ₂ , I ₃ and I ₄ , and the phase difference change relative value α is 90° (Φ + 0°, Φ+90°, Φ+180°, Φ+270°), and calculate the phase change Φ by the four-step phase shift algorithm (2)(3), and then transform the shape height by phase change .

I ₁ = I '+ I "cosΦ I ₂ = I '+ I "cos(Φ+α) I ₃ = I '+ I "cos(Φ+2α) I ₄ = I '+ I "cos(Φ+3α ) (2)

The four-phase image reconstructs the height profile as shown in Fig. 6.

This embodiment uses the four-phase polarized photosensitive element 20, but the present invention is not limited thereto. For example, in an embodiment, an N-phase polarized array photosensitive element may be used, wherein N is greater than 2, and the phase difference varies relative value α. It is also not limited to 90°.

In step S6, the multi-area measurement is moved, and the surface height change of each area is recorded to evaluate the flatness information of the object to be tested. The surface of the object to be tested 30 is divided into a plurality of regions, and the above-mentioned steps S4 and S5 are repeated in each region to obtain surface height variations of the respective regions, and the surface height changes are recorded. The surface height changes recorded are then evaluated to evaluate the surface information of the object 30 to be tested.

In summary, the exposure time of the four-phase polarized photosensitive element 20 can determine the measurement speed between the above-mentioned regions, so the present disclosure can achieve fast and instantaneous roughness measurement, and can make the differential interference measurement can be performed on the regional range. The roughness measurement and accurate measurement of the height variation of each area. Moreover, the present disclosure has the advantages of a non-coaxial focusing device, which can accurately detect the focusing plane of the four-phase polarizing photosensitive element 20, and allow the four-phase polarizing photosensitive element 20 to obtain a clear interference image for roughness measurement.

The specific embodiments described above are only used to exemplify the features and functions of the present invention, and are not intended to limit the scope of the present invention, and may be used without departing from the spirit and scope of the invention. Equivalent changes and modifications made to the disclosure of the invention are still covered by the scope of the following claims.

10‧‧‧First light source

11‧‧‧Spectrum Control Unit

12‧‧‧Optical collimation module

120‧‧‧First fiber collimating mirror

121‧‧‧Second fiber collimating mirror

123‧‧‧1 pair of 2 optical coupling fibers

124‧‧‧First set of detection beams

13‧‧‧Axial Dispersion Module

130‧‧‧First convex lens

131‧‧‧First concave lens

132‧‧‧second convex lens

133‧‧‧third convex lens

134‧‧‧second concave lens

135‧‧‧4th convex lens

136‧‧‧The third set of detection beams

137‧‧‧ first mirror

138‧‧‧Second mirror

14‧‧‧First optical unit

140‧‧‧Fourth set of test beams

15‧‧‧Second optical unit

150‧‧‧Fifth Group Detection Beam

16‧‧‧Optical guidance module

160‧‧‧Differential Interference

161‧‧‧Mirror

162‧‧‧beam splitter

17‧‧‧ Third optical unit

18‧‧‧Fourth optical unit

19‧‧‧second light source

190‧‧‧Second set of detection beams

20‧‧‧Four phase polarized photosensitive element

30‧‧‧Test object

Claims (14)

A surface roughness detecting system comprising: a first light source; a spectral control unit; an optical collimation module; an axial dispersion module; a first optical unit; a second optical unit; a third optical unit; a fourth optical unit; a second light source; and a four-phase polarized photosensitive element; wherein the first light source provides a light beam to the optical collimating module, the light beam The optical alignment module is formed as a first group of detection beams, and the axial dispersion module is located in a path of the first group of detection beams, and the first group of detection beams passes through the axial dispersion module. Forming a third set of detecting beams; the second light source is provided with a second set of detecting beams, and the fourth optical unit and the optical guiding module are located in a traveling path of the second group of detecting beams; the first optical unit Between the third set of detection beams and the second set of detection beams, the third set of detection beams are combined with the second set of detection beams to form a fourth set of detection beams; the second optical unit Located in the The fourth group of detection beams travels through the second optical unit to form a fifth group of detection beams; a sample to be detected is disposed on the path of the fifth group of detection beams, Measuring a fifth set of detection beams to form a first set of reflected beams, the first set of reflected beams being reflected to the second optical unit to form a second set of reflected beams; the second set of reflected beams Passing through the first optical unit to form a third set of reflected light beams and a fourth set of reflected light beams; the third set of reflected light beams passing through the axial dispersion module to form a fifth set of reflected light beams; The reflected beam passes through the optics a collimating module is received by the spectral control unit; the fourth set of reflected beams passes through the optical guiding module and the third optical unit to form a sixth set of reflected beams, the sixth set of reflected beams It is received by the four-phase polarized photosensitive element. The surface roughness detecting system of claim 1, wherein the optical collimating module has a first fiber collimating mirror and a second fiber collimating mirror, and the beam sequentially passes through the first fiber. A collimating mirror and the second fiber collimating mirror form the first set of detecting beams. The surface roughness detecting system of claim 1, wherein the first light source and the spectral control unit are coupled to the optical collimating module by a pair of two optical coupling fibers. The surface roughness detecting system of claim 1, wherein the axial dispersion module has a first mirror group and a second mirror group, and the first detecting beam sequentially passes through the first mirror group. And the second mirror group to form the third group of detection beams. The surface roughness detecting system of claim 4, wherein the first lens group has a first convex lens, a first concave lens and a second convex lens; the second lens group has a third convex lens, a second concave lens and a fourth convex lens. The surface roughness detecting system of claim 1, wherein the first light source is a continuous light source; and the second light source is a single wavelength light source. The surface roughness detecting system of claim 1, wherein the first optical unit is a beam splitter; the second optical unit is a microscope objective; the third optical unit is a focusing mirror; The four optical unit is a collimating mirror. The surface roughness detecting system according to claim 1, wherein the optical guiding module has a beam splitter, a mirror and a differential interference 稜鏡, and the second group of detecting beams sequentially passes the first a fourth optical unit, the beam splitter, the mirror and the differential interference 稜鏡; a fourth set of reflected beams sequentially passes through the differential interference 稜鏡, the mirror, the beam splitter and the third optical unit. A surface roughness detecting method, the steps of which include: Adjusting the phase of the differential interference fringe and the differential interference image to generate a differential interference fringe and a differential interference image, adjusting the phase of the differential interferometric modulation, and adjusting the differential interference image to a clear focus focal length position, the clear focus focal length position a differential interference focal plane; adjusting the position of the focused spot to the center position of the differential interference image, which adjusts a first focus, a second focus, and a third focus to a center position of the differential interference image; The axial dispersion module receives the reflected signal of the object to be tested, so that the differential interference focal plane is within a focus and focus range, and the distance between the first focus and the third focus constitutes a focus and focus range, the difference The interference focal plane is located in the focus and focus tracking range; the distance between the object to be tested and the differential interference focal plane is found, and the differential interference focal plane corresponds to the surface of the object to be tested; and the four-phase differential interference image is obtained, and Calculating the topography data to evaluate the roughness, the differential interference focal plane being regarded as a basis, the first focus, the second focus, and the third focus The focus position of the surface of the object to be tested is changed according to the fluctuation of the surface of the object to be tested, and a four-phase polarized photosensitive element obtains at least one four-phase differential interference image according to the change to obtain a topographical information. The topographical information can be used to evaluate the surface roughness of the test object. The surface roughness detecting method according to claim 9, further comprising a moving multi-area measurement, and recording a surface height change of each region to evaluate flatness information of the object to be tested, which is The surface of the object to be tested is divided into a plurality of regions, and the distance between the object to be tested and the differential interference focal plane is repeated in each region, and the differential interference focal plane corresponds to the surface of the object to be tested, and the step A four-phase differential interference image is obtained, and the topography data is calculated to evaluate the roughness step to obtain the surface height variation of each region, and the surface height changes are recorded. The surface height changes recorded are then evaluated to evaluate the surface information of the object to be tested. The surface roughness detecting method according to claim 10, wherein in the step of adjusting the phase of the differential interference fringe and the step of the differential interference image, a second The light source provides a second set of detecting beams, and the second set of detecting beams sequentially passes through a fourth optical unit and an optical guiding module, and the second group of detecting beams passing through the differential interference is a differential interference fringe The differential interference 稜鏡 adjusts the phase of the differential interference fringe to 0 degrees; the second set of detection beams is guided by a first optical unit to a second optical unit, and the second set of detection beams are projected to the The surface of the object is measured, and the surface of the object to be tested is adjusted to a position of a Z-axis, and the differential interference fringe is formed on the surface of the object to be tested to form the differential interference image. The surface roughness detecting method according to claim 11, wherein in the step of adjusting the position of the focused spot to the center position of the differential interference image, a first light source provides a light beam, and the light beam is The sequence passes through an optical collimation module, and the beam forms a first group of detection beams. When the first group of detection beams passes through a first mirror group, the dispersion order of the first group of detection beams is focused by a red light. , the green light and the blue light are distributed from the inside to the outside, the first group of detection beams pass through a second mirror group, the first group of detection beams are formed as a third group of detection beams, and the third group of detection beams pass the first After the optical unit, the third group of detecting beams is formed as a fourth group of detecting beams, and the axial dispersion range of the fourth group of detecting beams forms the first focus, the second focus and the third focus, the first a focus, the second focus and the third focus are sequentially distributed from the top end to the bottom end in an axial direction, the first focus is the focus of the blue light, the second focus is the focus of the green light, and the third focus is Focus of red light; the fourth Detection beam is combined with the second set of beam-based detection, to form a fifth group of the detection beam. The surface roughness detecting method according to claim 12, wherein in the step of finding a distance between the object to be tested and the differential interference focal plane, and allowing the differential interference focal plane to correspond to the surface of the object to be tested, The differential interference focal plane still has a distance from the surface of the object to be tested, finds the distance, and records the distance, and then the differential interference focal plane corresponds to the surface of the object to be tested. The method for detecting a surface roughness according to claim 13 , wherein the fourth phase differential interference image is obtained, and the topography data is calculated to evaluate the roughness, and the object to be tested reflects the first Five sets of detection beams to form the a first set of reflected beams, the first set of reflected beams being reflected to the second optical unit to form a second set of reflected beams, the second set of reflected beams passing through the first optical unit to form a third set a reflected beam and a fourth set of reflected beams, the third set of reflected beams passing through the axial dispersion module to form a fifth set of reflected beams, the fifth set of reflected beams passing through the optical collimating module Received by a spectral control unit; the fourth set of reflected beams passes through the optical guiding module and a third optical unit to form a sixth set of reflected beams, and the sixth set of reflected beams are biased by the four phases The photosensitive element is received.