JPH0367101A - Precision grating plate - Google Patents

Abstract

PURPOSE:To obtain the grating optimum as a standard prototype by using the resist patterns formed by a holographic exposing method as a mask and forming grating grooves by reactive ion beam etching on a substrate. CONSTITUTION:A glass plate 1 is used as the substrate and a novolak photoresist is coated by spin coating as the photoresist 2 to be baked with interference patterns. After the interference patterns are baked, a photoresist layer 2 is made to remain in the form of a half-wave sinusoidal shape by devel opment. The exposed part of the glass plate 1 is etched by the reactive ion beam etching using CHF3 for a reaction gas with the above-mentioned photoresist pattern as a mask, by which the grooves 3 are formed. The grooves are then formed by the ion beam etching and thereafter, the resist pattern is ashed and removed by a barrel type plasma etching device using O2 plasma to obtain the grating. The high-density grating of several hundred to several thousand pieces/mm grating grooves is obtd. in this way.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is useful for verifying the magnification of scanning electron microscopes and scanning tunneling microscopes, for determining the units of length in images produced by these, and for determining the units of length in horizontal and depth directions. This invention relates to a precision grid plate such as a reference grid plate used for calibration, etc. when simultaneously and accurately measuring dimensions.

(Prior art) In a scanning electron microscope (SEM), vertical tunneling microscope (STEM), or stylus type surface roughness meter, even if the same object is measured, the measurement conditions and measurements at that time are different. Measured values vary depending on the method, etc., and will deviate from the true value if used for a long time. For this reason, it is necessary to determine a reference standard and calibrate the magnification, dimensional units, etc. of the image as needed or for each measurement. Conventionally, as a reference standard used for the above-mentioned calibration, a metal deposited on a glass substrate with steps formed by chemically etching, a diffraction grating, etc. have been used.

<Problems to be Solved by the Invention> Diffraction gratings have high precision as reference standards, but even so, periodic errors in the grating pitch cannot be avoided when the grating grooves are mechanically cut.

Furthermore, when measuring the difference in magnification in the X and Y directions of an image or the distortion of an image using SEM or STEM, conventional parallel groove gratings can only measure the length in one direction. It is necessary to rotate the grid by 90" and measure it twice. This problem can be solved by using an orthogonal grid, but with a machine-cut grid, the shapes of the grid intersections are distorted, making it difficult to obtain a good grid.

Diffraction gratings using the holographic exposure method have no grating pitch errors due to mechanical precision, and both parallel gratings and orthogonal gratings can be made without shape distortion, and in practice, the grating pitch error can be considered zero. However, since the cross-sectional shape of the groove is sinusoidal, it is difficult to clearly determine where on the grid lines the measurement points should be, which leads to errors in actual measurement operations. Furthermore, since the lattice grooves do not have horizontal surfaces, it is difficult to use them as a measurement standard in the depth direction. Blazed diffraction gratings, whose grating patterns are formed by holographic exposure and ion beam etching, have grating grooves with sawtooth cross sections, so they do not have the above-mentioned problem as a measurement standard in the horizontal direction. Therefore, it is difficult to use it as a measurement standard in the depth direction.

The present invention is applicable to SEM or STEM magnification verification, image distortion measurement,
The purpose of this invention is to provide a grid plate that is easy to use as a reference standard for calibration in dimension measurements using these methods, and serves as an ultra-precise reference both in the horizontal direction and in the depth direction. (Means for solving the problem) A uniformly spaced interference pattern based on three-beam interference is printed on a resist layer on a substrate, and using this resist pattern as an etching mask, reactive ion beam etching (REBE) is applied to the top and bottom surfaces of the convex portions of the substrate. Both were flat, and a lattice groove with a step of a constant height was formed between the two.

(Operation) When two mutually coherent parallel light beams are irradiated onto the surface of one substrate from two directions, a parallel and equally spaced interference pattern is formed. The lattice spacing of this interference pattern is determined by the wavelength of the light used and the angle of incidence of the three beams of light onto the substrate surface, and is completely equidistant without mechanical errors. Therefore, the grating obtained by the holographic exposure method does not have any pitch error of the grating unlike the mechanically cut grating.

Further, during holographic exposure, an orthogonal lattice pattern can be easily created by rotating the substrate 90' and performing three-day exposure to create an interference pattern of parallel stripes.

In the present invention, the substrate is etched using a resist pattern formed by holographic exposure as a mask, so a grating with no pitch error can be obtained, and the grating grooves are created by reactive ion beam etching, which is different from chemical etching. , only the parts exposed from the mask pattern are selectively etched, and the etching progresses only in the irradiation direction of the ion beam, and the etching depth can be controlled in units of IOA. A lattice groove having a convex top surface and a groove bottom with clearly angular sides on both sides can be obtained. Therefore, the problems associated with using a conventional holographic diffraction grating with a sinusoidal cross-section as a standard standard are eliminated, and an optimal grating can be obtained as a standard standard for simultaneous measurements in the horizontal and depth directions.

(Example) Fig. 1 is an enlarged view of one embodiment of the grating according to the present invention.This embodiment is an example of a parallel groove grating plate.The characteristics of the grating according to the present invention are as shown in the figure. Both the top surface of the embankment and the bottom surface of the ditch are flat, and the shape of the bay is clearly angular.

FIG. 2 shows a holographic optical system for printing a grating pattern. 10 is a laser using a He-Cd laser, and the wavelength is 4416A. The luminous flux obtained from this laser is split into two by a semi-transparent mirror 11, and each luminous flux passes through a mirror 12, is converted into a spherical wave luminous flux by a subbasial filter 13, and then its cross section is divided by an off-axis parabolic mirror 14. It is reconverted into an enlarged parallel light beam, is reflected by a plane mirror 15, and is then reflected onto the substrate 1.
6 from two directions to form an interference pattern on the substrate surface. The pitch d of the interference pattern is given by 2 dsinθ=λ, where θ is the angle of incidence of each light beam onto the substrate surface.

FIG. 3 shows the groove machining process.

A glass plate 1 was used as the substrate 16, and a nopolac photoresist was coated with a spin cord to a thickness of 2500 mm as the photoresist 2 on which the interference pattern was printed (FIG. 3A). After the interference pattern is printed and developed, the photoresist layer 2 is left in a half-sine wave shape as shown in FIG. 3B. The photoresist's photosensitive density is sinusoidal, but if the exposure amount or development time is set appropriately, the width of the photoresist removed area is gradually expanded; The width ratio of the masked portion and the unmasked portion can be changed. In the example shown in this figure, this width ratio was set to 1:1. Using the photoresistor pattern in Figure 3B as a mask, CHFa
Using reactive ion beam etching (RIBE), the exposed portion of the glass substrate is etched to form #3 as shown in FIG. 3C. At this time, etching selectively proceeds only in the exposed portion of the glass substrate in the ion irradiation direction. The depth of the groove is controlled by time. In this example, the groove depth was 1000A. After forming grooves by ion beam etching, the resist pattern is ashed and removed using 02 plasma using a barrel type plasma etching device, and finally, cleaning is performed to obtain the grating shown in the third diagram. By this method, l) a high-density grating with several hundred to several thousand grating grooves/mm can be obtained;

FIG. 4 shows another embodiment of the invention. This embodiment consists of two sets of orthogonal grids *G1. The soil surface of the rectangular convex part P surrounded by G2 is a flat surface, and both grooves Gl, which are the base surfaces of this convex part, and the bottoms of G2 form a common plane, and the top surface of the convex part P and the base A certain level difference is formed between the surface and the surface.

This grid is manufactured in exactly the same way as in the previous example.

The apparatus shown in FIG. 2 is used to expose the grating pattern, and after exposing the parallel stripe interference pattern in one direction, the substrate 16 is
” Rotate and expose the same interference pattern again. After printing the orthogonal lattice pattern in this way, by developing it, a mask with 7 photoresists R remaining in the shape of rectangular islands is formed on the substrate as shown in Figure 5. 1. After forming a mask consisting of a two-dimensional array of rectangular island patterns in this way, parts other than the island parts are etched by the same reaction 11 ion beam etching as in the previous example to form orthogonal patterns. The base surfaces of the grating grooves are formed, and the island portions of the photoresist are left as convex portions P to obtain an orthogonal grating.

(Effects of the Invention) According to the present invention, since the grating pattern is a closely-transferred interference pattern formed by a holographic exposure method, there is no error in the grating bitches due to mechanical causes, and the groove cross section has a concave shape. Both the top surface of the convex part and the bottom of the groove are flat, and the groove depth is etched with an accuracy of about 10A, and the bay is formed in a steep shape. At the same time, a grid plate is obtained that can be used as a reference for measurements of .

[Brief explanation of drawings]

FIG. 1 is an enlarged perspective view of an embodiment of a grating plate obtained by the present invention, FIG. 2 is a plan view of a holographic optical system used in an embodiment of the present invention, and FIG. 3 is a grating of the above embodiment. 4 is a perspective view of a grating surface of a grating according to another embodiment of the present invention, and FIG. 5 is a perspective view of a resist pattern formed on a substrate in this embodiment. 1...Glass substrate, 2...Photoresist, 3...
・Groove, 10... Laser, 13... Special filter, 14... Parabolic mirror, 16... Substrate.

Claims (1)

[Claims] An interference pattern is printed onto a resist layer on a substrate using a holographic exposure method, and after the resist layer is developed, the upper surface of the convex portion is etched by reactive ion beam etching of the substrate using the lattice resist pattern formed according to the interference pattern as a mask. A precision lattice plate characterized by etching so that the and base surfaces are both flat.