Dual-wavelength surface profiler and measurement method

Abstract

The present invention discloses a dual-wavelength surface profiler and a measurement method, belonging to the technical field of interference measurement. The profiler includes a first laser light source and a second laser light source. On the propagation path of the light emitted by the first laser light source, a first beam splitter prism, a first attenuator, a first reflector, a first spatial filter, a first beam expander collimator, a second reflector, a third reflector, a fourth reflector, and a second beam splitter prism are sequentially provided to form a reference optical path; on the propagation path of the light emitted by the second laser light source, a first beam splitter prism, a second attenuator, a second spatial filter, a second beam expander collimator, and a second beam splitter prism are sequentially provided to form an object optical path. The measurement method of the present invention has high measurement accuracy and fast measurement speed. It is a non-contact measurement method and will not cause any damage to the measured object; since it is a synthetic wavelength generated by two wavelengths, when the difference between the two wavelengths is small, the measurable size of the measured object can be increased, having the advantage of a wider measurement range.

Description

Technical Field

[0001] The present invention relates to a dual-wavelength surface profiler and a measurement method, belonging to the technical field of interference measurement. Background Art

[0002] At present, the measurement of the object surface mainly includes two categories: contact type and non-contact type. Contact measurement generally uses a probe for scanning measurement. Such instruments are flexible to use and convenient to operate, but at the same time, their disadvantages are also obvious. Contact measurement has high requirements for the environment, slow measurement speed, and is likely to cause damage to the surface to be measured. Therefore, its application range is relatively limited. Non-contact measurement usually takes the interference of laser as the principle. This measurement technology has the advantages of high precision and fast speed, and as a non-contact measurement, it will not cause damage to the object to be measured. Currently, the commonly used optical measurement methods include: laser speckle measurement, digital holographic interference measurement technology, etc. However, traditional interference measurement technologies are all carried out under single-wavelength conditions. Due to the limitation of the wavelength size of the laser light source itself, traditional interferometers can only measure small surface profiles. When encountering larger surface profiles, the application range of traditional interferometers will be limited. Summary of the Invention

[0003] [Technical Problem]

[0004] The problem to be solved by the present invention is that the existing interference measurement device can only measure small surface profiles, and its application range is limited.

[0005] [Technical Solution]

[0006] The present invention provides a dual-wavelength surface profiler and a measurement method, which are applicable to the technical field of interference measurement. The profiler has a fast measurement speed, high measurement accuracy, and broadens the application range of high-precision interference measurement.

[0007] On the one hand, the present invention provides a dual-wavelength surface profiler, which includes a first laser light source and a second laser light source. On the propagation path of the light emitted by the first laser light source, a first beam splitter prism, a first attenuator, a first reflector, a first spatial filter, a first beam expander-collimator, a second reflector, a third reflector, a fourth reflector, and a second beam splitter prism are sequentially arranged as a reference optical path; on the propagation path of the light emitted by the second laser light source, a first beam splitter prism, a second attenuator, a second spatial filter, a second beam expander-collimator, and a second beam splitter prism are sequentially arranged as an object optical path.

[0008] In an embodiment of the present invention, the first laser light source and the second laser light source are respectively controlled by switches, the wavelength of the first laser light source is λ1, and the wavelength of the second laser light source is λ2.

[0009] In an embodiment of the present invention, λ1 is not equal to λ2.

[0010] In an embodiment of the present invention, the first attenuator and the second attenuator can respectively control the light intensity of the reference optical path and the object optical path.

[0011] In an embodiment of the present invention, the first spatial filter includes a first objective lens and a first pinhole, the first beam expander and collimator includes a first lens, the second spatial filter includes a second objective lens and a second pinhole, the second beam expander and collimator includes a second lens, the first pinhole and the second pinhole are respectively located at the rear focal planes of the first objective lens and the second objective lens, the first pinhole and the second pinhole are used for filtering high-frequency noise, and the first lens and the second lens are used for beam expansion and collimation to emit parallel light.

[0012] In an embodiment of the present invention, it further includes a third lens and a charge-coupled device. The object optical path irradiates the object to be measured through the second beam splitter prism. The laser beam is reflected back by the object to be measured and interferes with the reference light, and is imaged on the charge-coupled device through the third lens.

[0013] In an embodiment of the present invention, a first polarizer and a second polarizer are respectively arranged between the first attenuator and the first mirror, and between the second attenuator and the second objective lens.

[0014] On the other hand, the present invention provides a dual-wavelength surface measurement method. The dual-wavelength surface measurement method is measured by using a dual-wavelength surface measuring instrument, and includes the following steps:

[0015] Step 1: Only turn on the first laser light source. Place a cardboard between the second lens and the second beam splitter prism to block the object optical path. Adjust the first attenuator to a position where the light intensity is not overexposed. Collect the reference light intensity through the charge-coupled device and record it as I R1 ;

[0016] Step 2: Only turn on the first laser light source. Place a cardboard between the second mirror and the third mirror to block the reference optical path. Adjust the second attenuator to the same position as the reference light intensity. Collect the object light intensity through the charge-coupled device and record it as I O1 ;

[0017] Step 3: Only turn on the first laser light source. Remove the cardboard and directly collect the interference image through the charge-coupled device and record it as I λ11 ;

[0018] Step 4: Only turn on the second laser light source. Place a cardboard between the second lens and the second beam splitter prism to block the object optical path. Adjust the first attenuator to a position where the light intensity is not overexposed. Collect the reference light intensity through the charge-coupled device and record it as I R2 ;

[0019] Step 5: Only turn on the second laser source, place a cardboard between the second mirror and the third mirror to block the reference optical path, adjust the second attenuator to the position with the same intensity as the reference light, and collect the intensity of the object light through the charge-coupled device and record it as I O2 ;

[0020] Step 6: Only turn on the second laser source, remove the cardboard, and directly collect the interference image through the charge-coupled device and record it as I λ22 ;

[0021] Step 7: Calculate the interference fringe intensity distribution I containing the information of the object to be measured according to the images collected in Steps 1 to 6;

[0022] Step 8: Calculate the height difference h of the object to be measured according to the interference fringe intensity distribution I of the object to be measured information calculated in Step 7.

[0023] In an embodiment of the present invention, calculating the interference fringe intensity distribution I containing the information of the object to be measured through Step 7 specifically includes the following steps:

[0024] Step1. Under the illumination of two laser sources with different wavelengths, the object light and the reference light interfere, and their intensities are respectively expressed as:

[0025]

[0026]

[0027] Step2. Under the illumination of two laser sources with different wavelengths, the interference fringe intensity distribution eliminating the influence of the object light and the reference light is:

[0028] I λ1 =I λ11 -I R1 -I O1 ;

[0029] I λ2 =I λ22 -I R2 -I O2 ;

[0030] Step3. Subtract the above-obtained interference fringe intensity distributions, simplify through the formula, and then the interference fringe intensity distribution I after the sum-to-product transformation is:

[0031]

[0032] Since the intensity differences of I O1 、I R1 、I O2 、I R2 are not large, let

[0033] Again

[0034]

[0035] Among them, I λ11 is the interference fringe intensity distribution under the condition of wavelength λ1, I O1 is the object light intensity distribution under the condition of wavelength λ1, I R1 is the reference light intensity distribution under the condition of wavelength λ1, is the phase under the condition of wavelength λ1; I λ22 is the interference fringe intensity distribution under the condition of wavelength λ2, I O2 is the object light intensity distribution under the condition of wavelength λ2, I R2 is the reference light intensity distribution under the condition of wavelength λ2, is the phase under the condition of wavelength λ2.

[0036] In an embodiment of the present invention, the step eight of calculating the height difference h of the object to be measured specifically simplifies the interference fringe intensity distribution in step seven through the formula of the synthetic wavelength, and then the height difference can be obtained after shifting by Λ / 2;

[0037] Since sin(h(λ1 + λ2)*π / λ1λ2) in step seven cannot be resolved on the charge-coupled device, therefore:

[0038]

[0039] Again

[0040]

[0041] After h is shifted by Λ / 2,

[0042] I / II = tan(h*π / Λ);

[0043]

[0044] Among them, I represents the interference fringe intensity distribution of the object to be measured, II represents the interference fringe intensity distribution after the object to be measured 12 is shifted by Λ / 2, Λ represents the synthetic wavelength, and h refers to the height difference of the object to be measured.

[0045] Beneficial effects

[0046] (1) The dual-wavelength surface profiler of the present invention switches the on-off states of the laser light sources of two wavelengths. Since it is a composite wavelength generated by two wavelengths, when the difference between the two wavelengths is small, the measurable size of the object to be measured can be increased, and it has the advantage of a wider measurement range. The obtained composite wavelength expands the range of measurable surface profiles. It is a non-contact measurement method that will not cause any damage to the measured object and has the advantages of high precision and fast measurement speed.

[0047] (2) The dual-wavelength surface profiler of the present invention divides the object light and the reference light into two beams, and attenuators are respectively placed in the two optical paths to achieve the effect of separately adjusting the light intensities of the two paths, which greatly improves the fringe quality of the interference pattern.

[0048] (3) The dual-wavelength surface measurement method of the present invention eliminates the influence of the object light and the reference light and has the advantage of high measurement precision.

[0049] (4) The dual-wavelength surface measurement method of the present invention uses the method of approximate processing and utilizing the displacement of height h, and has the advantage of a simple measurement method. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0051] Figure 1 It is a schematic structural diagram of the dual-wavelength surface profiler according to Embodiment 1 of the present invention;

[0052] Figure 2 It is a schematic structural diagram of the dual-wavelength surface profiler according to Embodiment 3 of the present invention;

[0053] Figure 3 It is a schematic structural diagram of the dual-wavelength surface profiler according to Embodiment 4 of the present invention;

[0054] In the figure, 1. First laser light source; 2. First beam splitting prism; 3. First attenuator; 4. First reflector; 5. First objective lens; 6. First pinhole; 7. First lens; 8. Second reflector; 9. Third reflector; 10. Fourth reflector; 11. Second beam splitting prism; 12. Object to be measured; 13. Second laser light source; 14. Second attenuator; 15. Second objective lens; 16. Second pinhole; 17. Second lens; 18. Third lens; 19. Charge-coupled device; 20. First polarizer; 21. Second polarizer. Detailed Embodiments

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0056] Embodiment 1:

[0057] As Figure 1 shown, this embodiment discloses a dual-wavelength surface profiler, which includes a first laser light source 1 and a second laser light source 13. On the propagation path of the light emitted by the first laser light source 1, a first beam splitter prism 2, a first attenuator 3, a first mirror 4, a first spatial filter, a first beam expander collimator, a second mirror 8, a third mirror 9, a fourth mirror 10, and a second beam splitter prism 11 are successively arranged as a reference optical path; on the propagation path of the light emitted by the second laser light source 13, a first beam splitter prism 2, a second attenuator 14, a second spatial filter, a second beam expander collimator, and a second beam splitter prism 11 are successively arranged as an object optical path.

[0058] Furthermore, the first laser light source 1 and the second laser light source 13 are respectively controlled by switches. The wavelength of the first laser light source 1 is λ1, and the wavelength of the second laser light source 13 is λ2, and λ1 is not equal to λ2. Optionally, in this embodiment, the first laser light source 1 is a He-Ne laser with a wavelength λ1 equal to 632.8 nm, and the second laser light source 13 is a diode laser with a wavelength λ2 equal to 637.33 nm.

[0059] Optionally, the first attenuator 3 and the second attenuator 14 can respectively control the light intensity of the reference optical path and the object optical path.

[0060] Optionally, the first spatial filter includes a first objective lens 5 and a first pinhole 6, the first beam expander collimator includes a first lens 7, the second spatial filter includes a second objective lens 15 and a second pinhole 16, the second beam expander collimator includes a second lens 17. The first pinhole 6 and the second pinhole 16 are respectively located at the rear focal planes of the first objective lens 5 and the second objective lens 15. Since the pinhole itself is a low-pass filter, high-frequency noise can be filtered out, and then after being expanded and collimated by the first lens 7 and the second lens 17 respectively, it becomes parallel light and is emitted.

[0061] Further, it also includes a third lens 18 and a charge-coupled device (CCD) 19. The object light path irradiates the object to be measured 12 through the second beam splitter prism 11. The laser beam is reflected back by the object to be measured 12 to the second beam splitter prism 11 and interferes with the reference light, and is imaged on the charge-coupled device 19 through the third lens 18. Place the object to be measured 12 at a fixed position, respectively collect two interference patterns generated by lasers of different wavelengths through the charge-coupled device 19, then subtract the collected object light and reference light intensity patterns respectively to obtain two interference patterns eliminating the influence of background light, subtract these two interference patterns, and then simplify the height h displacement of Λ / 2 to obtain the height difference.

[0062] Embodiment 2:

[0063] This embodiment provides a dual-wavelength surface measurement method. The dual-wavelength surface measurement method uses the dual-wavelength surface measuring instrument provided in Embodiment 1 for measurement, and includes the following steps:

[0064] Step 1: Only turn on the first laser light source 1, place a cardboard between the second lens 17 and the second beam splitter prism 11 to block the object light path, adjust the first attenuator 3 to a position where the light intensity does not overexpose, and collect the reference light intensity through the charge-coupled device 19 and record it as I R1 ;

[0065] Step 2: Only turn on the first laser light source 1, place a cardboard between the second mirror 8 and the third mirror 9 to block the reference light path, adjust the second attenuator 14 to the same position as the reference light intensity, and collect the object light intensity through the charge-coupled device 19 and record it as I O1 ;

[0066] Step 3: Only turn on the first laser light source 1, remove the cardboard, and directly collect the interference image through the charge-coupled device 19 and record it as I λ11 ;

[0067] Step 4: Only turn on the second laser light source 13, place a cardboard between the second lens 17 and the second beam splitter prism 11 to block the object light path, adjust the first attenuator 3 to a position where the light intensity does not overexpose, and collect the reference light intensity through the charge-coupled device 19 and record it as I R2 ;

[0068] Step 5: Only turn on the second laser light source 13, place a cardboard between the second mirror 8 and the third mirror 9 to block the reference light path, adjust the second attenuator 14 to the same position as the reference light intensity, and collect the object light intensity through the charge-coupled device 19 and record it as I O2 ;

[0069] Step 6: Only turn on the second laser light source 13, remove the cardboard, and directly collect the interference image through the charge-coupled device 19 and record it as I λ22 ;

[0070] Step 7: Calculate the interference fringe intensity distribution I containing the information of the object to be measured 12 based on the images collected in Steps 1 to 6;

[0071] Step 8: Calculate the height difference h of the object to be measured 12 based on the interference fringe intensity distribution I of the information of the object to be measured 12 calculated in Step 7.

[0072] Furthermore, calculating the interference fringe intensity distribution I containing the information of the object to be measured 12 obtained through Step 7 specifically includes the following steps:

[0073] Step1. Under the illumination of two laser light sources with different wavelengths, the object light and the reference light interfere, and their intensities are respectively expressed as:

[0074]

[0075]

[0076] Step2. Under the illumination of two laser light sources with different wavelengths, the interference fringe intensity distribution after eliminating the influence of the object light and the reference light is:

[0077] I λ1 = I λ11 - I R1 - I O1 ;

[0078] I λ2 = I λ22 - I R2 - I O2 ;

[0079] Step3. Subtract the obtained interference fringe intensity distributions, simplify through the formula, and the interference fringe intensity distribution I after sum-to-product transformation is:

[0080]

[0081] Since the intensity differences of I O1 , I R1 , I O2 , I R2 are not large, let

[0082] Also

[0083]

[0084] Among them, I λ11 is the interference fringe intensity distribution under the condition of wavelength λ1, I O1 is the object light intensity distribution under the condition of wavelength λ1, I R1is the reference light intensity distribution under the condition of wavelength λ1, is the phase under the condition of wavelength λ1; I λ22 is the interference fringe intensity distribution under the condition of wavelength λ2, I O2 is the object light intensity distribution under the condition of wavelength λ2, I R2 is the reference light intensity distribution under the condition of wavelength λ2, is the phase under the condition of wavelength λ2.

[0085] Further, the specific calculation of the height difference h of the object 12 to be measured in step eight is to simplify the interference fringe intensity distribution in step seven through the formula of the synthetic wavelength, and then the height difference can be obtained after shifting by Λ / 2;

[0086] Since sin(h(λ1 + λ2)*π / λ1λ2) in step seven cannot be resolved on the charge-coupled device 19, therefore:

[0087]

[0088] Also

[0089]

[0090] After h is shifted by Λ / 2,

[0091] I / II = tan(h*π / Λ);

[0092]

[0093] wherein, I represents the interference fringe intensity distribution of the object 12 to be measured, II represents the interference fringe intensity distribution of the object 12 to be measured after being shifted by Λ / 2, Λ represents the synthetic wavelength, and h refers to the height difference of the object 12 to be measured.

[0094] Embodiment 3:

[0095] As Figure 2 shown, this embodiment provides a second dual-wavelength surface profiler. The difference between this embodiment and Embodiment 1 is the way to obtain the laser light sources of two wavelengths. That is, in this embodiment, the second laser light source 13 in Embodiment 1 is not set, and the first laser light source 1 emits light of two different wavelengths. The feature of this embodiment is that the single-wavelength laser light source can slightly change the wavelength of the laser through a translator. Since the formula of the synthetic wavelength is Λ = λ1λ2 / (λ1 - λ2), when the difference between λ1 and λ2 is very small, the synthetic wavelength Λ will increase, so that the surface profile of the non-optical surface can be measured through the synthetic wavelength. The dual-wavelength surface profiler provided in this embodiment can also be measured by using the dual-wavelength surface measurement method disclosed in Embodiment 2.

[0096] Example 4:

[0097] As Figure 3 shown, this embodiment provides a third dual-wavelength surface profiler. The difference between this embodiment and Embodiment 1 is that: in this embodiment, a first polarizer 20 and a second polarizer 21 are respectively arranged between the first attenuator 3 and the first mirror 4, and between the second attenuator 14 and the second objective lens 15. The feature of this embodiment is that the first laser light source 1 with wavelength λ1 and the second laser light source 13 with wavelength λ2 can be turned on simultaneously. Since the two beams of light irradiate on the first polarizer 20 and the second polarizer 21, but only one kind of beam can pass through, the charge-coupled device 19 can be used to collect images respectively, and then the measurement of the surface profile can be realized. The third dual-wavelength surface profiler provided by this embodiment can also be measured by using the dual-wavelength surface profiling method disclosed in Embodiment 2.

[0098] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dual-wavelength surface profile measurement method, which is performed using a dual-wavelength surface profile measuring instrument, and is characterized in that, The dual-wavelength surface profiler includes a first laser light source and a second laser light source. On the propagation path of the light emitted by the first laser light source, a first beam splitter prism, a first attenuator, a first reflector, a first spatial filter, a first beam expander and collimator, a second reflector, a third reflector, a fourth reflector and a second beam splitter prism are successively provided to form a reference optical path; on the propagation path of the light emitted by the second laser light source, a first beam splitter prism, a second attenuator, a second spatial filter, a second beam expander and collimator and a second beam splitter prism are successively provided to form an object optical path; The first spatial filter includes a first objective lens and a first pinhole. The first beam expander and collimator includes a first lens. The second spatial filter includes a second objective lens and a second pinhole. The second beam expander and collimator includes a second lens. The first pinhole and the second pinhole are respectively located at the rear focal planes of the first objective lens and the second objective lens. The first pinhole and the second pinhole are used to filter high-frequency noise. The first lens and the second lens are used to expand and collimate the light into parallel light for emission; It further includes a third lens and a charge-coupled device. The object optical path irradiates the object to be measured through the second beam splitter prism. The laser beam is reflected back by the object to be measured to the second beam splitter prism and interferes with the reference optical path, and is imaged on the charge-coupled device through the third lens; The dual-wavelength surface profiling method includes the following steps: Step 1: Only turn on the first laser light source. Place a cardboard between the second lens and the second beam splitter prism to block the object light path. Adjust the first attenuator to a position where the light intensity is not overexposed. Collect the reference light intensity through a charge-coupled device and record it as I R1 ; Step 2: Only turn on the first laser light source, place a cardboard between the second mirror and the third mirror to block the reference optical path, adjust the second attenuator to the position where the intensity is the same as that of the reference light, and collect the intensity of the object light through the charge-coupled device and record it as I O1 ; Step 3: Only turn on the first laser source, remove the cardboard, and directly collect the interference image through a charge-coupled device, denoted as I λ11 ; Step 4: Only turn on the second laser source. Place a cardboard between the second lens and the second beam splitter prism to block the object light path. Adjust the first attenuator to a position where the light intensity is not overexposed, and collect the reference light intensity through a charge-coupled device and record it as I R2 ; Step 5: Only turn on the second laser source, place a cardboard between the second mirror and the third mirror to block the reference optical path, adjust the second attenuator to the position where the intensity is the same as that of the reference light, and collect the intensity of the object light through the charge-coupled device and record it as I O2 ; Step 6: Only turn on the second laser source, remove the cardboard, and directly collect the interference image through the charge-coupled device, denoted as I λ22 ; Step 7: Calculate the interference fringe intensity distribution I containing the information of the object to be measured according to the images collected in Steps 1 to 6; Step 8: Calculate the height difference h of the object to be measured according to the interference fringe intensity distribution I of the information of the object to be measured calculated in Step 7.

2. The dual-wavelength surface measurement method according to claim 1, wherein The first laser light source and the second laser light source are respectively controlled by switches. The wavelength of the first laser light source is λ1, and the wavelength of the second laser light source is λ2.

3. The dual-wavelength surface measurement method according to claim 2, characterized in that The λ1 is not equal to λ2.

4. The dual-wavelength surface measurement method according to claim 1, wherein The first attenuator and the second attenuator can respectively control the light intensity of the reference optical path and the object optical path.

5. The dual-wavelength surface measurement method according to claim 4, wherein A first polarizer and a second polarizer are respectively provided between the first attenuator and the first reflector, and between the second attenuator and the second objective lens.

6. The dual-wavelength surface measurement method according to claim 3, wherein, The specific steps for calculating the interference fringe intensity distribution I containing the information of the object to be measured through Step 7 are as follows: Step 1. Under the illumination of two laser light sources with different wavelengths, the object light and the reference light interfere, and their intensities are respectively expressed as: Step 2. Under the illumination of two laser light sources with different wavelengths, the interference fringe intensity distribution after eliminating the influence of the object light and the reference light is: I λ1 = I λ11 -I R1 -I O1 ; I λ2 = I λ22 - I R2 - I O2 ; Step 3. Subtract the interference fringe intensity distributions obtained above, simplify through the formula, and then perform the sum-to-product transformation to obtain the interference fringe intensity distribution I as: Since I O1 、I R1 、I O2 、I R2 have little difference in strength, let Also Among them, I λ11 is the intensity distribution of the interference fringes under the condition that the wavelength is λ1, I O1 is the intensity distribution of the object light under the condition that the wavelength is λ1, I R1 is the intensity distribution of the reference light under the condition that the wavelength is λ1, is the phase under the condition that the wavelength is λ1; I λ22 is the intensity distribution of the interference fringes under the condition that the wavelength is λ2, I O2 is the intensity distribution of the object light under the condition that the wavelength is λ2, I R2 is the intensity distribution of the reference light under the condition that the wavelength is λ2, is the phase under the condition that the wavelength is λ2.

7. The dual-wavelength surface measurement method according to claim 6, wherein The specific calculation of the height difference h of the object to be measured in Step 8 is to simplify the interference fringe intensity distribution in Step 7 through the formula of the synthetic wavelength, and then shift by Λ / 2 to obtain the height difference; Since sin(h(λ1 + λ2)*π / λ1λ2) in Step 7 cannot be resolved on the charge-coupled device, therefore: Also After the h displacement of Λ / 2, I / II = tan(h*π / Λ); Wherein, I represents the interference fringe intensity distribution of the object to be measured, II represents the interference fringe intensity distribution after the object to be measured (12) is displaced by Λ / 2, Λ represents the synthetic wavelength, and h refers to the height difference of the object to be measured.

Images