JPS6025761B2 - Manufacturing method of holographic grating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blazed holographic grating.
This invention relates to a manufacturing method for in-bags.

In recent years, holographic gratings (diffraction gratings) have higher precision in groove spacing than regular machine-cut gratings, making it easier to narrow the groove spacing and easily obtain grooves with the desired oriented angle. It has attracted a lot of attention because it has many advantages, such as being able to save time and cost in manufacturing, and its manufacturing technology has made remarkable progress, and many techniques have been developed and devised.

FIG. 1 schematically shows a typical conventional method for manufacturing a glazed holographic grating (Samuraiko Showa 55-14 Urinu No. 6).

A diffraction grating 3 of parallel grooves with a predetermined interval is formed on a photoresist layer 2 coated on a substrate 1 by holography (by a method of recording two-light east interference fringes such as a laser and developing it). Figure 1-1). Using the diffraction grating 3 made of this photoresist as a mask, the ion beam 4 is irradiated diagonally above the substrate surface and from a direction in which the component projected onto the grating is not parallel to the grooves of the grating, thereby etching the substrate 1 itself ( Figures 1-2). As a result, a grating consisting of sawtooth grating grooves 5 with a lasing angle of 8 is obtained in the substrate (FIGS. 1-3). By the way, in the above conventional manufacturing method in which a diffraction grating made of photoresist is used as a mask and the substrate is etched with an ion beam through this mask, the etching rate ratio between the substrate and the photoresist is an important condition, and an appropriate There is a restriction that the combination of materials must have an etching rate.

In other words, if the substrate is made of a material (e.g. quartz, glass, etc.) that has a lower etching rate than the photoresist (e.g. AZ1350), the photoresist mask will etch faster and the blaze angle of the grating formed on the substrate will be smaller. Control becomes extremely difficult. Therefore, it is necessary to use a substrate made of a material having a higher etching rate than the photoresist (for example, PMMA.C ship, etc.). Therefore, for example, even if it is desired to use a substrate made of another material in order to suppress an increase in stray light caused by etching, there is a restriction that it cannot be used due to the etching rate conditions with the photoresist mask. On the other hand, recently, due to advances in replica technology, most of the gratings used are plastic gratings, and it is also easy to create replicas from replica gratings. Therefore, it is not always necessary to form a grating directly on the substrate except for special applications. In view of the above, the present invention has been developed through extensive research and development into the production of holographic gratings.

As a result, by forming sinusoidal grating grooves in the photoresist layer on the substrate using holography, and etching the sinusoidal grating grooves themselves with an ion beam, we were able to remove the loose serrated gratings blazed into the photoresist itself. It was found that a grating consisting of the following can be obtained.
The present invention is based on the above knowledge, and will be explained below using the attached drawings.

Figures 2-1 and 2-2 schematically illustrate the manufacturing method of the present invention. As shown in FIG. 211, parallel grating grooves 6 having a sinusoidal cross section are formed in the photoresist layer 2 on the substrate 1 by holography, and the projected components on the grating are formed diagonally upward and onto the grating grooves. The ion beam 4 is irradiated at an angle in a direction that is not parallel to the groove, for example, at an incident angle of about 30 degrees with respect to the substrate surface. The etching rate of a photoresist by an ion beam depends on the incident angle of the ion beam with respect to the normal to the photoresist surface. Experimentally, the etching rate reaches a maximum at an incident angle of around 600 degrees, and decreases even when the angle of incidence is greater than this. will also decrease. Since this has already been confirmed experimentally, the details will be omitted. The angle of incidence of the ion beam with respect to the groove surface of the grating is maximum at the apex of the grating groove, decreases towards the middle, and increases again after passing the middle. Therefore, the etching rate is fastest near the apex of the lattice groove, and becomes slower toward the middle. Once it passes halfway down, the ion beam is prevented from being irradiated by the ion beam by an adjacent mountain, and as the mountain gets etched and gets lower, it is irradiated, so etching is delayed the most at the bottom of the product. Based on this process, after a certain period of time, the initial sinusoidal grooves transform into lattice grooves 5 whose cross section is almost serrated, as shown in Figure 2-2, and are blazed. A grating is obtained. At this time, the blaze angle 0 is determined by the depth of the sinusoidal grating grooves 6 initially formed in the photoresist layer, the number of grooves per unit length, that is, the grating constant, and the incident angle of the ion beam. Therefore, by appropriately selecting these conditions, a holographic grating having a desired blaze angle can be manufactured. Hereinafter, the present invention will be explained in detail with reference to Examples.

Shipley's positive photoresist (AZ-1350J
) was applied to a glass substrate with a spinner to a thickness of 0.8 mm, exposed to laser light using a conventional method, and developed to form parallel grating grooves with a sinusoidal cross section (120 mm/mm). candle)
Ion etching was performed on the formed surface. Etching conditions: Ion etching with argon. Incident angle of the ion beam with respect to the substrate surface: 6r. Voltage and current density of ion beam: 50 positive V-0.7 A' skin. The following table shows experimental data regarding the efficiency of each grating sample obtained.

As is clear from this table, in the measurement of stray light at a wavelength of 24, there is no significant change regardless of whether the etching time is long or short.

It is also clear that the grating obtained by the present invention is superior in that it has less stray light than a commercially available grating made by another company with 1200 grooves per sail produced by machine cutting. 3, 4, and 5 are scanning electron micrographs (magnification: 1 pi) of samples a, b, and f in the above table.

As is clear from these figures, according to the present invention, the third
It is clearly shown that the grating grooves, which are approximately sinusoidal in the figures, are formed into approximately serrated grating grooves in FIGS. 4 and 5. However, compared to FIG. 4, the lattice grooves in FIG. 5 seem less clear. FIG. 6 shows the wavelength efficiency characteristics of samples a to f in the above table.

As is clear from this figure, sample d has the highest diffraction efficiency at short wavelengths, and the efficiency of samples d, e, and f changes uniformly from short wavelengths to long wavelengths. From the above results, the holographic material manufactured by the present invention
Although the efficiency of gratings varies depending on the length of the etching time, etc., by controlling the etching time, it can be put to practical use, and the manufacturing process is also more flexible than the conventional process. There are advantages such as being able to be selected, and the industrial value of the present invention is very high.

[Brief explanation of the drawing]

1-1 to 1-3 are schematic diagrams for explaining the conventional manufacturing method, and FIGS. 2-1 and 2-2 are vague diagrams for explaining the manufacturing method of the present invention. Figures 3 to 5 are scanning electron micrographs of holographic gratings obtained in Examples of the present invention, and Figure 6 shows wavelength efficiency characteristics of holographic gratings obtained in Examples of the present invention. graph. Codes in the figure: 1...Substrate, 2...Photoresist layer, 3...Diffraction grating, 4...
・Ion beam, 5... Serrated lattice groove, 6...
...Sinusoidal grating groove, a...Blaze angle. Figure 1-1 Figure 1-2 Figure 1-3 Figure 2-1 Figure 2-2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. Parallel grating grooves with a sinusoidal cross section are formed in the photoresist layer on the substrate by holography, and the ion beam is directed into the grating grooves so that the ion beam is directed diagonally above the substrate surface and the projected component onto the grating is the same as the grating grooves. A method for manufacturing a holographic grating, characterized in that serrated grating grooves are formed in a photoresist layer by etching the photoresist layer with irradiation from non-parallel directions.