KR20180125216A - Method and apparatus for calculating diffraction grating depth - Google Patents

Abstract

According to the present invention, provided are a method for calculating the depth of a diffraction grating that can quickly and precisely determine the depth of a grating using a photodiode scanning method and an apparatus thereof. The apparatus for calculating the depth of a diffraction grating includes: a laser part for outputting a test light to a diffraction grating having a grating of a concavo-convex shape on its surface; a photodiode part for measuring the intensity of diffracted light by the diffraction grating; and a grating depth calculating part for calculating the depth of the grating based on the intensity of the diffracted light measured by the photodiode part.

Description

[0001] The present invention relates to a diffraction grating depth calculation method and apparatus,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating used in an optical element, and more particularly to a technique for evaluating a diffraction grating.

The linear encoder is a length measuring system that converts a linear displacement amount into an electrical digital signal by using a linear solid scale (diffraction grating, diffraction scale) in which a scale is artificially recorded.

Linear encoders have been improved in resolution, precision and responsiveness in response to demands for machine tools and measuring instruments. However, the linear encoders have been rapidly upgraded in performance in recent years, reaching a level comparable to a laser length measuring machine.

FIG. 1 and FIG. 1A are diagrams showing a diffraction phenomenon due to a square lattice.

Referring to FIG. 1 and FIG. 1A, a rectangular grid is shown in which slits of width W periodically lie at intervals p.

When a square wave is Fourier-unfolded, it is expressed as the sum of sinusoids of various frequencies. Therefore, the square lattice is regarded as a superposition of a plurality of sinusoidal gratings, and generates a plurality of diffracted light corresponding to each frequency component.

Of these, using the 0th order and ± 1st order diffracted light is equivalent to using the above sinusoidal grating. In addition, although light has been used to transmit a lattice, the same principle holds for a reflective lattice. Furthermore, although the amplitude distribution of light is given by the change of the transmittance of the grating, the same diffraction light can be obtained also by the change of the optical path length by the sublattice (called a phase grating).

The amplitude of the interference light changes to a complete sinusoidal wave due to the phase of the grating. All recent products use the interference of ± 1st order light. The output of the photodetector is the average intensity of the interference light,

Can be expressed by Equation (1).

&Quot; (1) "

Here, T _D is an average time greater than the time constant of the photodetector. As a result, when the intensity of the + 1st-order diffracted light and the -1st-order diffracted light are detected to detect the intensity, the output changes to a complete sinusoidal wave with one cycle of p / 2. Since it is not a pseudo-sinusoidal wave like the conventional scale, according to the present principle, the limit of the interpolation error or the interpolation resolution is determined only by the SN ratio of the output signal.

Although a high-precision linear encoder has been in the application range of the laser length measuring device, the basic functions of both are the same. The laser length measuring instrument uses the wavelength of light as a scale as a standard for measuring length (measurement reference unit). However, since the wavelength of light depends on the air refractive index, precision fluctuates due to air fluctuation in the optical path.

When a highly controlled environment, but you can measure the length variations (± 2σ) of the measured values ± 1 × 10 ^-7 for the measurement length, wherein the general greenhouse the ± 1 × 10 ^- it is difficult to obtain the stability of the ^6. On the other hand, in a high-precision linear encoder, the scale temperature is easily stable in terms of the heat capacity, the interval of the scale can be maintained, and a relatively stable length measurement is possible.

The arrangement of the length measuring system in the direct-drive system is easy to arrange based on the Abbe's principle or in relation to other elements, and each of the high-precision linear encoder and the laser length measuring instrument has advantages and disadvantages. In terms of price, there is a problem that the laser length measuring device is still expensive.

It is necessary to thoroughly study the high performance of high-precision linear encoders in terms of resolution, precision, responsiveness, and basic elements (scale, interpolation circuit, transmission circuit).

2 is a block diagram of a system (error evaluation device) for evaluating a linear encoder.

Referring to FIG. 2, the linear encoder error evaluation apparatus is composed of a 40-nm sensor and a stage.

The "ruler" part (scale, substrate with scale on the surface) of the linear encoder to be evaluated is provided on a stage that moves in the horizontal direction. The interval of the scale in the reader (head) You can read, and obtain the electrically divided scale. The reading of the linear encoder and the measurement of the moving distance of the stage by the sensor of the stage are simultaneously performed, and the measured results are compared to evaluate the performance.

3 is a plan view of a diffraction grating used in an optical field, such as a linear encoder, and Fig. 4 is a cross-sectional view of a diffraction grating.

3 and 4, the precision of the high-precision linear encoder is generally determined by the scale pitch accuracy of the scale (diffraction grating). However, in order to achieve high precision, the scale material processing technique before scaling, Technology is important. It is a matter of course that the pitch accuracy is precisely produced at the time of scale creation, and the good planarity of the reference surface and the scale surface of the scale material is a necessary condition for reproducing the pitch precision at the scale generation.

Since both transmissive gratings and reflective gratings are used in both scales (diffraction grating), as shown in Fig. 4, a transmissive grating is made of a glass / quartz grating and a reflective grating is made of glass / quartz And silicon wafers can be manufactured by using a lattice.

Meanwhile, the diffraction grating is formed by sequentially forming a dielectric film and a photoresist film on a semiconductor substrate, exposing the photoresist film by an optical holography method, developing and patterning the photoresist film, patterning the dielectric film by a reactive ion etching method using the patterned photoresist film as a mask , Anisotropically etching the semiconductor substrate by a reactive ion etching method using the dielectric film as a mask to form a diffraction grating, and removing the dielectric film.

At this time, the pitch interval of the diffraction grating is made relatively constant, but the depth of the grating may not be constant during the etching.

Therefore, there is a demand for a technique for quickly measuring and evaluating the depth of a lattice. Conventionally, after the diffraction grating is cut, a method of measuring the depth of the grating using a scanning electron microscope (SEM) or the like is used.

In the case of the conventional method, expensive equipment for precisely cutting the diffraction grating is required and the measurement speed is very slow.

KR 10-0169836 B

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the above-

A diffraction grating depth calculation method and apparatus capable of quickly and precisely checking the depth of a grating by a photodiode scanning method are provided.

According to an embodiment of the present invention, there is provided a laser processing apparatus comprising: a laser unit for outputting a test light source to a diffraction grating having a grating of a concavo-convex shape on its surface; A photodiode section for measuring the intensity of the diffracted light by the diffraction grating; And a grating depth calculating unit for calculating a grating depth based on the intensity of the diffracted light measured by the photodiode unit.

In addition, the lattice-

The depth (t) of the lattice is calculated by applying Equations (2) and (3).

&Quot; (2) "

&Quot; (3) "

a: b is the duty ratio

sinc x = [sin (x)] / (x)

t: thickness difference of grid

N: number of grid

λ: wavelength of light

?: diffraction angle of light

I: diffracted light intensity of light

m: Number of times

Further, the diffraction grating may be formed of a transmissive substrate or a reflective substrate.

Further, the photodiode part measures the diffracted light by the diffraction grating while moving in the horizontal direction.

According to another embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: outputting a test light source with a diffraction grating in which a grating of a concave- Measuring the intensity of the diffracted light by the diffraction grating in the photodiode part; And calculating a depth of the grating on the basis of the intensity of the diffracted light measured by the photodiode part in the grating depth calculating part.

The step of calculating the depth of the grating may include:

The depth (t) of the lattice is calculated by applying Equations (2) and (3).

&Quot; (2) "

&Quot; (3) "

a: b is the duty ratio

sinc x = [sin (x)] / (x)

t: thickness difference of grid

N: number of grid

λ: wavelength of light

?: diffraction angle of light

I: diffracted light intensity of light

m: Number of times

The step of measuring the intensity of the diffracted light is characterized by measuring the diffracted light by the diffracting grating while moving the photodiode part in the horizontal direction.

The method and apparatus for calculating the diffraction grating depth according to the embodiment of the present invention can confirm the depth of the grating quickly and precisely by the photodiode scanning method.

Conventionally, there are direct measurement methods using SEM, AFM or the like, although the geometrical shape measurement of um or less is very expensive,

The indirect optical measurement method according to the present invention is an inverse conversion method of a theoretical expression based on the principle of distribution of light intensity according to a geometrical shape change of a lattice of um or below, and is very inexpensive, The caustic rain is very high.

1 and 1A are views showing a diffraction phenomenon by a rectangular lattice.
Fig. 2 is a block diagram of a system (error evaluation device) for evaluating a linear encoder
3 is a plan view of a diffraction grating used in an optical field, such as a linear encoder,
4 is a cross-sectional view of the diffraction grating
5 is a diagram of a diffraction grating depth calculation apparatus according to an embodiment of the present invention
6 is a diagram illustrating a diffraction grating depth calculation method according to an embodiment of the present invention.
7 is a view showing the behavior of diffracted light in the diffraction grating;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order to facilitate a person skilled in the art to easily carry out the technical idea of the present invention.

5 is a configuration diagram of a diffraction grating depth computing apparatus according to an embodiment of the present invention.

The diffraction grating depth computing apparatus according to the present embodiment includes only a simple structure for clearly explaining the technical idea to be proposed.

5, the apparatus for calculating the diffraction grating depth includes a laser unit 10, a diffraction grating 20, a photodiode unit 30, and a grating depth calculating unit 40. [

The detailed configuration and main operation of the diffraction grating depth computation apparatus constructed as above will be described below.

The laser unit 10 outputs a test light source to a diffraction grating 20 having a concave-convex type grating formed on its surface.

The laser section 10 is operated to output a test light source of a predetermined wavelength, and the wavelength of the test light source can be adjusted within a predetermined range.

The diffraction grating 20 may be made of a transmissive substrate or a reflective substrate.

That is, the transmissive substrate may be formed by forming a concave-convex grid on a transparent glass substrate or a quartz substrate,

The reflection type substrate may be formed by forming a convex-concave grating using a transmission type substrate, then depositing a metal thin film, or by forming a concave / convex type grating on an opaque substrate such as a silicon substrate.

In this embodiment, it is assumed that the pitch of the grating formed on the diffraction grating 20 is constant, and the process of verifying the depth value of the grating proceeds.

The photodiode section 30 measures the intensity of the diffracted light by the diffraction grating 20.

The photodiode unit 30 measures the diffracted light by the diffraction grating 20 while moving in the horizontal direction, and then transfers the measurement result to the grating depth calculation unit 40. [

The grating depth calculating section 40 calculates the depth of the grating based on the intensity of the diffracted light measured by the photodiode section 30. The lattice depth calculating unit 40 may be defined by a computer or a control unit and may control the operations of the photodiode unit 30 and the laser unit 10. [

That is, the lattice depth calculating unit 40 is configured to control the scan speed, the scan range, and the scan number of the photodiode unit 30, and to control the wavelength of the light source output from the laser unit 10.

FIG. 6 is a view illustrating a method of calculating a diffraction grating depth according to an embodiment of the present invention, and FIG. 7 is a diagram showing the behavior of diffraction light of a diffraction grating.

6 and 7, the diffraction grating depth calculating method includes:

A step of outputting a test light source to a diffraction grating 20 in which a grating of a concavo-convex form is formed on the surface of the laser part 10, a step of measuring the intensity of the diffracted light by the diffraction grating 20 in the photodiode part 30 , And calculating the depth of the grating based on the intensity of the diffracted light measured by the photodiode unit 30 in the grating depth calculating unit 40. [

The step of calculating the depth of the grating is configured to calculate the depth t of the grating by applying Equation 2 and Equation 3 in the grating depth calculating unit 40. [

&Quot; (2) "

&Quot; (3) "

a: b is the duty ratio

sinc x = [sin (x)] / (x)

t: thickness difference of grid

N: number of grid

λ: wavelength of light

?: diffraction angle of light

I: diffracted light intensity of light

m: Number of times

That is, the intensity (I) of the diffracted light by the diffraction grating 20 is measured while the photodiode section 30 moves in the horizontal direction,

The grating depth calculating section 40 calculates the depth t of the grating based on the intensity I of the diffracted light measured by the photodiode section 30.

At this time, it is preferable that the pitch (P, pitch) of the lattice is assumed to be constant, and it is processed with a constant to calculate the depth (t) of the lattice.

The method and apparatus for calculating the diffraction grating depth according to the embodiment of the present invention can confirm the depth of the grating quickly and precisely by the photodiode scanning method.

Conventionally, there are direct measurement methods using SEM, AFM or the like, although the geometrical shape measurement of um or less is very expensive,

The indirect optical measurement method according to the present invention is an inverse conversion method of a theoretical expression based on the principle of distribution of light intensity according to a geometrical shape change of a lattice of um or below, and is very inexpensive, The caustic rain is very high.

Thus, those skilled in the art will appreciate that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

10: laser part
20: diffraction grating
30: Photodiode part
40: Grating depth calculating unit

Claims (7)

A laser part for outputting a test light source to a diffraction grating having a concave-convex lattice on its surface;
A photodiode section for measuring the intensity of the diffracted light by the diffraction grating; And
A grating depth calculating unit for calculating a grating depth based on the intensity of the diffracted light measured by the photodiode unit;
And a diffraction grating depth computing unit for computing a diffraction grating depth.
The method according to claim 1,
The lattice-
Wherein the depth (t) of the grating is calculated by applying Equation (2) and Equation (3).
&Quot; (2) "

&Quot; (3) "

a: b is the duty ratio
sinc x = [sin (x)] / (x)
t: thickness difference of grid
N: number of grid
λ: wavelength of light
?: diffraction angle of light
I: diffracted light intensity of light
m: Number of times
The method according to claim 1,
Wherein the diffraction grating is made of a transmissive substrate or a reflective substrate.
The method according to claim 1,
Wherein the photodiode unit measures the diffracted light by the diffraction grating while moving in the horizontal direction.
Outputting a test light source with a diffraction grating in which a grating of a concave-convex shape is formed on a surface of the laser part;
Measuring the intensity of the diffracted light by the diffraction grating in the photodiode part; And
Calculating a depth of the grating on the basis of the intensity of the diffracted light measured by the photodiode part in the grating depth calculating part;
And calculating a diffraction grating depth.
6. The method of claim 5,
The step of calculating the depth of the grating may include:
Wherein the depth (t) of the grating is calculated by applying Equations (2) and (3).
&Quot; (2) "

&Quot; (3) "

a: b is the duty ratio
sinc x = [sin (x)] / (x)
t: thickness difference of grid
N: number of grid
λ: wavelength of light
?: diffraction angle of light
I: diffracted light intensity of light
m: Number of times
6. The method of claim 5,
Wherein the step of measuring the intensity of the diffracted light includes measuring the diffracted light by the diffracting grating while moving the photodiode part in the horizontal direction.

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