JP2737815B2 - Laminar type diffraction grating fabrication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method for forming a diffraction grating (laminar type diffraction grating) having a flat top and bottom surface of a grating groove by an ion beam etching method.

[0002]

2. Description of the Related Art In order to form a diffraction grating by an etching method, a mask of a grid pattern made of a resist layer is formed on a grid material, and portions exposed from the mask of the grid material are removed by ion beam etching. The lattice grooves are formed by going. Conventionally, a reactive ion beam etching method using a reactive gas has been used for this ion beam etching. When ion beam etching is performed while covering the lattice material with a lattice pattern mask, the mask itself is also etched, so the mask is less likely to be etched with respect to the lattice material, that is, it is necessary to select an etching method with a smaller etching rate. is there. As such an etching method, a material containing SiO ₂ as a main component, such as a Si-based inorganic material such as quartz or glass, or S
Reactive ion beam etching using an i-pure product and using a carbon fluoride or a hydrocarbon fluoride such as CHF ₃ or CF ₄ as an etching gas as an etching gas is used.

In the laminar type diffraction grating, it is desirable that the top surface of the ridge forming the grating and the bottom of the grating groove are each horizontal, and both side surfaces of the ridge, that is, both sides of the grating groove are vertical. When such a groove is formed by ion beam etching, the etching rate of the lattice material with respect to the resist layer needs to be sufficiently large. In other words, when the lattice pattern of the resist uses a photoresist as a resist and the lattice pattern is printed by a holographic exposure method, the cross section of the resist mask is mountain-shaped, and the height of the mountain becomes lower as the etching progresses. At the same time, both side edges disappear, and the width of the lattice of the mask gradually narrows. For this reason, the width of the exposed portion of the lattice material is increased, and both sides of the lattice groove are inclined surfaces. The reactive ion beam etching method using CHF ₃ or CF ₄ can increase the etching rate of the grating material with respect to the resist, but when making a laminar type diffraction grating, the verticality of both sides of the grating groove is made satisfactory. It was difficult. In addition, in the reactive ion beam etching method using these reactive gases, carbon is deposited, and impurities in the chamber are sputtered and adhere to the bottom of the groove. When used in a vacuum ultraviolet region, light scattering due to the rough surface is large, stray light level is increased, and performance as a diffraction grating is insufficient.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a laminar type diffraction grating manufactured by reactive ion beam etching, in which the verticality of both sides of the grating groove is enhanced, and a smooth groove bottom is obtained without roughness of the groove bottom. It is intended to obtain a desired etching method.

[0005]

According to the present invention, there is provided a grid material having an S shape.
Using an inorganic material mainly composed of iO ₂ and forming a diffraction grating pattern by a photoresist layer thereon,
And from the vertical direction to the lattice material surface using a mixed gas of Ar as an ion beam etching in F _3.

[0006]

When CHF ₃ is used as a reactive gas for reactive ion beam etching, the etching rate ratio of the SiO ₂ -based inorganic material to the resist layer becomes relatively high. The etching rate is reduced, and the etching rate ratio can be further increased. This effect becomes more pronounced mixing Ar in CF _4. In addition, the incorporation of Ar removes precipitated carbon generated in the case of using only the hydrocarbon fluoride, so that the etched surface is less rough and a smooth, groove bottom is obtained as compared with the case of using only the hydrocarbon fluoride.

[0007]

FIG. 1 shows the progress of the steps of the method of the present invention in the order of A, B, C. In the figure, 1 is a quartz glass lattice material,
As shown in FIG. 1A, a photoresist OFRP5
000 layer 2 to a thickness of 0.4 μm. Then, as shown in FIG. 1B, 441.6n by He-Cd laser
An interference fringe due to two-beam interference of light having a wavelength of m is projected and exposed on the photoresist layer 2 and developed to form a mask of a lattice pattern of the photoresist 2. The interference fringes exposed to the photoresist have a sinusoidal cross section due to development, and the photoresist is left in a half sinusoidal cross section on the surface of the grating material 1 by adjusting the exposure time and the development time. Thereafter, reactive ion beam etching is performed. At this time, the ion beam irradiation direction is perpendicular to the surface of the lattice material 1, CHF ₃ is used as a reactive gas, and the mixing ratio with Ar is 70.
% To 30%. A lattice groove is formed by this etching, and the depth of the groove is controlled by the etching time while keeping the ion beam current per area constant. In this way, a lattice groove is formed as shown in FIG. 1C. In this process, the progress of etching of the photoresist 2 depends on the S of the lattice material.
Since it is much slower than iO ₂ , the width of the photoresist mask hardly decreases, and both sides of the groove are almost vertical. When the groove reaches a predetermined depth, stopping the etching, the remaining photoresist 2 is incinerated out by plasma etching of O _2, the number of grooves are coated with Al layer 3 on the surface as the subsequent Figure 1E 1200 A laminar type diffraction grating of 本 / mm is completed. The etching rate ratio (selection ratio) with respect to the resist layer according to the present invention, and the etching rate ratio when reactive ion beam etching is performed with a mixed gas of 50% CF _{4 and} 50% Ar using CF ₄ as the reactive gas. Is shown in Table 1. The numerical values in the above table indicate the etching rates (all in the unit (nm / min) / (mA / cm ² )), and the mixing ratio with Ar is the ratio at which the etching rate in the reactive gas is maximized. From this result, it can be seen that the use of a mixed gas of CHF ₃ and Ar improves the etching rate ratio by a factor of three or more compared to the use of a mixed gas of CF ₄ and Ar.

The lattice substrate in the above embodiment may be made of ordinary glass instead of quartz glass.

[0009]

[Effect] In reactive ion beam etching using CHF ₃ , by mixing Ar, the etching rate ratio between the resist and the lattice material is increased, and a lattice groove having a steep ridge is obtained. Since the deposition of carbon is prevented and the groove bottom is smoothed, the performance of the laminar type diffraction grating is improved. In particular, it was confirmed that the etching rate ratio was improved by three times or more as compared with the case of using a mixed gas of CF ₄ and Ar. Further, since the deposited carbon on the inner surface of the etching apparatus is also removed by the wiping action of Ar, the frequency of maintenance of the etching apparatus itself is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing each step of a process according to an embodiment of the present invention. 1 lattice material 2 photoresist 3 Au coating

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Claims (1)

(57) [Claims] 1. A grating material is formed by using an inorganic material mainly composed of SiO ₂ as a grating material, a diffraction grating pattern is formed by a photoresist layer thereon, and a gas obtained by mixing Ar with CHF ₃ is used on the grating material surface. A laminar type diffraction grating manufacturing method, wherein a grating groove is formed by performing ion beam etching from a vertical direction.