CN1300550C - Device and method for measuring surface profile of object to be measured - Google Patents

Abstract

The present invention relates to a device and method for measuring the surface profile of an object to be measured, which detects the change of the interference intensity distribution of the broadband light by searching the interference intensity of broadband light, and converts the interference intensity distribution of at least one specific wavelength included in the broadband light to obtain a phase distribution diagram of at least one specific wavelength, and then performs phase restoration processing on the phase distribution diagram of at least one specific wavelength to obtain a phase restoration diagram of at least one specific wavelength. Finally, the phase restoration diagram of at least one specific wavelength is converted from phase to physical scale to obtain the surface profile of the object to be measured.

Description

Device and method for measuring surface profile of object to be measured

technical field

The invention relates to a device and method for measuring the surface profile of an object to be measured, especially a device and method for analyzing white light interference fringes to measure the surface profile of the object to be measured.

Background technique

Measuring the surface profile of the object to be tested allows the user to know whether the surface profile of the object to be tested is normal or in line with the user's expectations. However, the current technology for measuring the surface profile of the object to be tested uses white light vertical scanning interferometry (vertical scanning interferometry) analysis method. White light refers to broadband light with a wavelength of 400-700 nanometers (nm). Since the length required for mutual interference of white light is extremely short, about 8-10 nanometers, the optical path difference must be smaller than the length required for mutual interference to produce obvious interference. Therefore, this method can be used to observe changes in a very small range, and can provide accurate measurement of the surface profile of the object to be tested.

White light vertical scanning analysis can be divided into two major technologies: peak-sensing analysis and spectrum analysis. Both of these two methods use light-splitting elements to divide white light into measurement light and reference light. The light is used to be incident on the surface of the object to be measured, and the reference light is used to be incident on the standard reference surface. By adjusting the optical path difference between the measurement light and the reference light in the measurement light path and recording the change of the interference intensity, the record produces the maximum position during interference contrast, thereby establishing a three-dimensional surface profile.

US Patent No. 4340306, title of the invention, [Optical system for surfacetopography measurement], which uses peak sensing analysis to detect where the maximum interference contrast (intensity) occurs to reconstruct the surface profile of the object to be measured. However, in order to maintain a certain measurement accuracy when measuring a large-order high-level surface profile, a large amount of measurement time is often consumed.

As shown in Figure 1, U.S. Patent No. 5398113, the name of the invention [Method and apparatus for surface topography measurement by spatial-frequency analysis of interferograms], which uses spectrum analysis and uses Fourier Transform (FourierTransform) and least square fitting method to obtain the corresponding white light The initial phase difference of different wavelengths is used to reconstruct the height of the surface profile of the object to be measured. However, this technology performs Fourier transformation on multiple continuous wavelengths. Assuming that if there are N scan data for a single pixel, the number of operations required to complete the Fourier transformation is at least N*10g ₂ *N times, and the least square fitting must be completed The calculation of N times is required, and the number of operations required to complete a single pixel is at least N ² *10g ₂ *N times. Therefore, when measuring the profile of a large-order high surface, a large amount of computing time and memory space will still be consumed because the amount of required computing data and the number of computing operations cannot be effectively reduced.

Since the above two techniques for measuring the height of the surface profile of the object to be tested require a large amount of computing time and memory space, there is no relatively fast and efficient improvement method, which will not be able to meet the needs of users.

Contents of the invention

The main purpose of the present invention is to provide a device for measuring the surface profile of the object to be measured, so as to quickly obtain the surface profile of the object to be measured, and effectively simplify the system structure and cost.

Another object of the present invention is to provide a method for measuring the surface profile of the object to be measured, so as to quickly obtain the surface profile of the object to be measured, effectively reducing the memory space and the required number of calculations.

To achieve the above object, the present invention discloses a device for measuring the surface profile of an object to be measured, including: a broadband light source for providing broadband light, the broadband light includes light waves of at least one specific wavelength; a beam shaping system for Receive the broadband light and output the broadband light; the beam splitter is used to receive the broadband light output by the beam shaping system and output it, and is used to receive the interference broadband light and output it; the reference mirror is used to enter the reference light , and reflect it; the light splitting element is used to divide the broadband light output by the beam splitter into measurement light and reference light. The measurement light is used to enter the surface of the object to be measured and reflect it. The reflected measuring light and the reference photosynthetic light are outputted as interference broadband light; the shifter is used to adjust the distance between the split-combining element and the reference mirror and the distance between the split-combining element and the object to be measured; and the array intensity detector, It is used to receive the interference broadband light reflected by the spectroscope, and analyze the light wave of at least one specific wavelength to obtain the surface profile of the object to be measured.

In order to achieve the above object, the present invention discloses a method for measuring the surface profile of an object to be measured, which includes the following steps: (A) retrieving the interference intensity of the broadband light; (B) detecting the change of the interference intensity distribution of the broadband light; (C ) converting the interference intensity distribution of at least one specific wavelength included in broadband light to obtain a phase distribution diagram of at least one specific wavelength; (D) performing phase reduction processing on the phase distribution diagram of at least one specific wavelength to obtain at least one a phase restoration map of a specific wavelength; and (E) performing phase-physical scale conversion on the phase restoration map of at least one specific wavelength to obtain a surface profile of the object to be tested.

Description of drawings

1 is a schematic diagram of an existing device for measuring the surface profile of an object to be measured;

Fig. 2 is a schematic diagram of the device for measuring the surface profile of the object to be measured according to the present invention;

Fig. 3 is a flow chart of the method for measuring the surface profile of the object to be measured according to the present invention;

Fig. 4 is a waveform diagram of white light vertical scanning interference intensity variation;

Figure 5 is a plan view of the phase distribution of a specific wavelength;

Figure 6 is a phase restoration diagram of a specific wavelength;

Fig. 7 is a schematic diagram of the surface profile of the object to be measured.

Detailed ways

The device and method for measuring the surface profile of the object to be measured in the present invention is to perform Fourier transformation on a plurality of specific single-wavelength interference signals to obtain a complex number of specific single-wavelength initial phase distributions, and then use single-wavelength or multi-wavelength phase shift interference The method of phase restoration in , thus reconstructing the surface profile of the object under test. Since the method for measuring the surface profile of the object to be tested requires less memory space, number of operations, and operation time than the prior art, it can be directly applied to surfaces that combine single-wavelength phase-shift interference and white light vertical scanning interference On the profile interferometer device, at the same time, the phase restoration algorithm in the single-wavelength phase-shift interferometry can be used to process the interference signal of the white light vertical scanning interferometry.

As shown in Figure 2, the device for measuring the surface profile of the object to be measured in the present invention includes the following elements: a broadband light source 12, a beam shaping system 14, a beam splitter 16, an array intensity detector 18, a displacement device 20, and an optical splitting and combining element 22. With reference to the mirror surface 24 and the object under test 26, the description of the above components is as follows:

The broadband light source 12 is used to provide broadband light, ie white light, to the beam shaping system 14 . The beam shaping system 14 is used for uniformly incident the broadband light provided by the broadband light source 12 to the beam splitter 16 .

The beam splitter 16 is used to reflect the broadband light incident by the beam shaping system 14 to the splitting and combining element 22 , and transmit the interference broadband light incident to the splitting and combining element 22 to the array intensity detector 18 .

The splitting and combining element 22 divides the broadband light incident by the beam splitter 16 into measuring light and reference light. The measuring light is used to be incident on the surface of the object 26 to be measured and reflected; the reference light is used to be incident on the reference mirror 24 , and reflect it. After the reflected measuring light and the reference light are combined by the light splitting and combining element 22 , the interference broadband light is formed, and then the interference broadband light is incident to the array intensity detector 18 . At this time, the interference intensity distribution of the two beams (interfering broadband light) is expressed as follows:

I=I _DC .[1+V.cos(φ)] represents the interference phase difference between the two beams. The user changes the interference phase difference  between the two beams sequentially by moving the displacement device 20 vertically in the direction of the optical axis, and then records the change of the interference intensity through the array intensity detector 18 to know the object under test. The change diagram of white light vertical scanning interference intensity at any point on the surface (as shown in Figure 4). The change of the overall interference intensity will change with the wave packet form of the homology function V.

Since the double-beam interference of broadband light can be regarded as a collection of multiple single-frequency light double-beam interferences at the same time, the distribution of broadband light double-beam interference intensity can be expressed as follows:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{<span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; d\&sigma;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

σ is the reciprocal of the wavelength (1/λ), also known as the wave number: (σ, x, y,) =  ₀ (σ, x, y,) + Δ(σ, x, y,) means Corresponding to the interference phase difference of each single-frequency light; (x, y) represents the position of the measurement point (in pixel), and is represented by the plane space position of the array type intensity detector 18, which can correspond to the a point on the surface of an object. Since the double-beam interference of broadband light can be regarded as a collection of multiple single-frequency double-beam interferences at the same time, the user can select a specific wavelength λ1 as the basis for the above measurement. Figure 5 is a plan view of the phase distribution of a specific wavelength λ1. Perform Fourier transform on the interference intensity change data of a specific wavelength λ1, and perform an arctangent (tan ^-1 ) operation on the converted real part and imaginary part, and then obtain a specific wavelength λ1 pair measurement point (x, y) The phase distribution plan of the interference, after completing the above calculations for all measurement points (x, y) in sequence, the phase distribution plan shown in FIG. 5 can be obtained. Then, through the phase restoration algorithm in the single-wavelength phase-shift interferometry to operate on all the measurement points (x, y), the phase restoration diagram of a specific wavelength can be obtained, as shown in FIG. 6 . Since the relationship between wavelength and phase is equivalent, at this time, the phase-physical scale conversion is performed on the phase restoration diagram of a specific wavelength, and the surface profile of the object to be measured can be obtained, as shown in Figure 7. Since the phase restoration algorithm and the phase-physical scale conversion in single-wavelength phase-shift interferometry are known techniques, no further description is given here.

The method for measuring the surface profile of the object to be measured in the present invention comprises the following steps:

Step S30: Retrieve the interference intensity of the broadband light. After the broadband light provided by the broadband light source 12 is transmitted to the beam shaping system 14, the beam splitter 16, and the splitting and combining element 22, the splitting and combining element 22 divides the broadband light into measuring light and reference light, and the measuring light is used for The light is incident on the surface of the object to be measured 26 and reflected; the reference light is used to be incident on the reference mirror 24 and reflected. After the reflected measuring light and reference light are combined by the optical splitter 22, the interference broadband light is formed, and then the interference broadband light is incident on the array type intensity detector 18, and the optical axis direction is adjusted by the displacement device 20. By vertical sweeping, the vertical scanning interference intensity distribution (interference information) of white light (broadband light) at any point on the surface of the object to be measured can be obtained. And by vertically sweeping the displacementr 20 in the direction of the optical axis, the optical path difference between the two beams (measurement light and reference beam) can be changed, and the interference phase difference between the two beams of broadband light can be obtained.

Step S32: Detect changes in the interference intensity distribution of the broadband light. The array intensity detector 18 detects the change of the interference intensity between the two beams of broadband light, so that the distribution of the white light vertical scanning interference intensity at any point on the surface of the object to be measured can be obtained.

Step S34: Convert the interference intensity distribution of the specific wavelength to obtain the phase distribution of the specific wavelength. Since the double-beam interference of broadband light can be regarded as a collection of multiple single-frequency light double-beam interference at the same time, a specific wavelength λ1 can be selected as the basis for measurement, and the interference intensity change data of this specific wavelength λ1 can be Fourier transformed, and The arctangent operation is performed on the converted real part and imaginary part, and the phase distribution of the interference of a specific wavelength λ1 with the measurement point (x, y) can be obtained. After the above calculations of all measurement points (x, y) are completed in sequence, the phase distribution diagram of a specific wavelength can be obtained.

Step S36 : performing a phase restoration process on the phase distribution diagram of the specific wavelength to obtain the phase restoration diagram of the specific wavelength. Then, through the phase restoration algorithm in the single-wavelength phase-shift interferometry, the phase restoration operation is performed on all the measurement points (x, y) to obtain the phase restoration diagram of a specific wavelength.

Step S38: performing phase-physical scale conversion on the phase restoration map of a specific wavelength to obtain the surface profile of the object to be measured. Since the relationship between wavelength and phase is equivalent, if the phase restoration diagram of a specific wavelength is converted from phase to physical scale, the surface profile of the object to be measured can be obtained.

The device and method for measuring the surface profile of the object to be measured according to the present invention not only have the advantage of fewer operations, but also can perform the traditional single-wavelength phase-shifting interferometry without additional filters when using a broadband light source, which can be more effective Simplify system architecture and cost.

The above-mentioned embodiments are only examples for convenience of description, and the scope of rights claimed by the present invention is not limited to the above-mentioned embodiments.

Claims (4)

1. A device for measuring the surface profile of an object to be measured, characterized in that it comprises: A broadband light source is used to provide a broadband light, the broadband light includes light waves of at least one specific wavelength; A beam shaping system is used to receive the broadband light and output the broadband light; A beam splitter is used to receive the broadband light output by the beam shaping system and output it, and is used to receive an interference broadband light and output it; A reference mirror is used to incident a reference light and reflect it; A light splitting and combining element is used to split the broadband light output by the beam splitter into a measuring light and the reference light, the measuring light is used to be incident on the surface of the object to be measured and reflected, the split The light-combining element combines the reflected measuring light and the reference light to output the interference broadband light; a displacement device to adjust the distance between the splitting and combining element and the reference mirror and the distance between the splitting and combining element and the object; and An array type intensity detector is used to receive the interference broadband light reflected by the beam splitter, and analyze the light wave of at least one specific wavelength to obtain the surface profile of the object to be measured; Wherein, the analysis of the light wave of at least one specific wavelength by the array type intensity detector includes: performing Fourier transformation on the interference intensity change data of the specific wavelength, and performing an arctangent operation on the converted real part and imaginary part, And cooperate with the phase restoration algorithm to obtain the phase restoration diagram of the at least one specific wavelength, and then perform phase-physical scale conversion. 2. A method for measuring the surface profile of an object to be measured, characterized in that it comprises the following steps: (A) retrieving the interference intensity of a broadband light; (B) detecting changes in the interference intensity distribution of the broadband light; (C) performing Fourier transformation on the interference intensity distribution of at least one specific wavelength included in the broadband light, and performing an arctangent operation on the transformed real part and imaginary part to obtain a phase distribution diagram of the at least one specific wavelength ; (D) performing phase restoration processing on the phase distribution map of the at least one specific wavelength to obtain the phase restoration map of the at least one specific wavelength; and (E) performing phase-physical scale conversion on the phase restoration map of at least one specific wavelength to obtain the surface profile of the object under test. 3. The method according to claim 2, wherein said step (A) further comprises dividing the broadband light zone into a measuring light and a reference light, the measuring light is used to be incident on the surface of the object to be measured , and reflected, the reference light is used to be incident on a reference mirror and reflected, and the reflected measurement light and the reference light are combined by a light splitting element to retrieve the interference intensity of the broadband light . 4. The method according to claim 2, wherein said step (B) further comprises adjusting the optical path of the measurement light to the surface of the object under test and the reference light to the reference mirror by a phaser difference to obtain changes in the interference intensity distribution of the broadband light.

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