JPS59210403A - Manufacture of diffraction grating - Google Patents

Abstract

PURPOSE:To obtain a precise saw-tooth wave type diffraction grating by forming a photoresist pattern on a glass or metallic substrate by an interference exposing method, etc. and forming recessed parts by etching, and forming a mask displaced to one side of the recessed parts by slanting vapor deposition and then carrying out etching again. CONSTITUTION:The photoesist layer 2 is formed on the glass or metallic substrte 1, and a latent image is formed on the layer 2 by the interference exposing method or electron beam lithography method and then developed to obtain a diffraction grating pattern 3 whose section is in a sine wave shape. The substrate is etched and the resist 4 is removed to form recesses 4 in the substrate 1 in the since wave shape. Then, Cr is vapor-deposited slantingly to form the mask 5 displaced to one side of the recesses 4. The substrate 1 is further etched in an HF solution until even the lower part of the part covered with the mask 5 is etched to further recess slanting surfaces which are not covered with the mask 5. Then, the mask 5 is removed to point peaks of projection parts 7, thus obtaining the saw-tooth type diffraction grating which has higher efficiency than before.

Description

[Detailed Description of the Invention] Conventionally, methods for providing a diffraction grating on a substrate such as glass or metal include: C) a method of performing interference exposure or electron beam writing on a substrate coated with a photoresist and developing it; (b) A method using mechanical cutting; (c) A method in which a diffraction grating is fabricated on a substrate such as glass or metal by a method such as etching as a resist; (d) A method in which a grating is formed on a resist at a certain angle with respect to the substrate. A method of exposure and development using standing waves.

(e) Ion beam etching method etc.

In (a), when a substrate coated with a positive photoresist is irradiated with two coherent plane waves or spherical waves, interference fringes are recorded in the photoresist, and when it is subsequently developed, the intensity of the recorded interference fringes is The photoresist is dissolved approximately in proportion to the distribution (sinusoidal), and grating grooves are formed. In this method, the cross-sectional shape of the grooves of the diffraction grating is generally sinusoidal, and it is not possible to freely create grooves with a sawtooth cross-section as in the case of mechanical cutting, so a diffraction grating with high diffraction efficiency cannot be obtained.

(b) is a method of mechanically cutting the substrate, and since it is possible to freely create grooves with a sawtooth cross-sectional shape of the diffraction grating, it is possible to increase the diffraction efficiency itself. However, it is limited by the shape of the substrate surface, i.e., whether it is flat, spherical, or aspherical, and it is also easily affected by vibration, so it is impossible to create a diffraction grating with a completely uniform period, and it is difficult to create a diffraction grating with a completely uniform period. It has a drawback that it is not possible to provide various imaging characteristics by providing or arranging them at unequal intervals.

In (c), since the cross-sectional shape of the diffraction grating is close to a sine wave or rectangular, a diffraction grating with high diffraction efficiency cannot be obtained when the groove depth is shallow.

(d) In C2, when a coherent parallel light beam is incident from both sides of a substrate such as a flat glass substrate coated with a photoresist, a standing wave is generated in the photoresist, and a certain angle θ is formed with the substrate surface. This results in a cylindrical surface. When this is developed, the dissolution of the photoresist stops at the cylindrical surface, and a groove having a triangular cross section with an inclination angle (blaze angle) θ is formed. However, with this method, the blaze wavelength of the diffraction grating remains constant regardless of the incident angle.

Therefore, the only way to create planar diffraction gratings with various blaze wavelengths is to change the laser wavelength, but since photoresist is not sensitive to long wavelength light, it is difficult to obtain high diffraction efficiency in the visible region. be.

For example, (e) is a method that uses a device consisting of an ion source chamber and a processing chamber, and is usually carried out after etching using argon ions. It is important to The ion beam etching method is electrically controlled.

Since the grooves are processed and formed using ions that are easily detected, it is extremely easy to control the shape of the grooves, and there is also the advantage that the diffraction grating with any groove spacing can be made into a sawtooth shape with any angle. However, in this method, the sample substrate must be made of a material with a sufficiently faster etch rate than the diffraction grating used as a mask, and it is not possible to directly blaze quartz or glass, which has a slow etch rate, using a photoresist as a mask. It has the disadvantage of being difficult.

As mentioned above, there are methods (b) and (c) for directly producing a diffraction grating on a substrate such as glass or metal.
Of these, (t7) is machine cut, so the period of the diffraction grating cannot be made accurate. In e'), although the period of the diffraction grating can be manufactured with very high precision, the cross-sectional shape cannot be controlled, so the diffraction efficiency cannot be increased.

Further, in (e), although a diffraction grating with good diffraction efficiency and period accuracy can be produced, it cannot be produced directly on the substrate.

As mentioned above, in order to improve the precision of the period of the diffraction grating, the best method is to use the interference exposure method, and in order to increase the diffraction efficiency, the cross-sectional shape of the diffraction grating should be made into a sawtooth shape [ However, with conventional methods, it is difficult to simultaneously satisfy period accuracy and desirable cross-sectional shape.

The present invention solves the above-mentioned drawbacks of the prior art, and the method for manufacturing a diffraction grating of the present invention involves forming a diffraction grating pattern made of hardened photoresist on a glass or metal substrate, and then etching it. Then, oblique evaporation is performed to form a mask unevenly distributed on one side of the recess, and then etching is performed using the mask as a resist. It is characterized by removal.

First, in order to form a diffraction pattern made of a hardened photoresist on a glass or metal substrate 1, for example, as shown in FIG. By exposing the resist layer 2 to light by interference exposure or electron beam lithography to generate a latent image, and then developing it using a predetermined developer,
As shown in FIG. 1 (bl), a diffraction grating pattern 3 made of hardened photoresist is formed.

Next, etching is performed using the diffraction grating pattern 6 as a resist, and after etching, when the resist is removed, the first
As shown in FIG. 0, a recess 4 corresponding to the diffraction grating pattern 6 having a sinusoidal cross section is formed on one surface.

FIG.
As shown in dl, a mask 5 made of a gold R thin film such as Cr is formed only on the slopes in one direction of the four parts by oblique evaporation. The material of this mask 5 is selected so that it will serve as a resist for the substrate 1 during the next etching process.

Next, etching is performed using the formed mask 5 as a resist. Preferably, side etching is also performed on the portions covered with the manno 5, and as shown in FIG. Then, by removing the mask 5 by etching or the like, a diffraction grating having a cross-sectional shape where the top of the convex portion 7 is pointed as shown by +f+ in FIG. 1 is obtained. It will be done.

According to the method of the present invention, each step itself can be performed using existing equipment, and the period of the diffraction grating is determined by the first exposure, so accuracy is high. In particular, the accuracy is extremely high during interference exposure.

There is an advantage in that a diffraction grating having a sawtooth cross-sectional shape with the peaks of the convex portions being pointed can be obtained by the grating operation.

Example A photoresist pattern was formed on a glass substrate by interference exposure method, and then etched with an HF aqueous solution.
A diffraction grating with a sinusoidal cross section was fabricated, and then an Or thin film was formed on the substrate using an oblique evaporation method. Furthermore, the substrate was etched with an HF aqueous solution using the above Or thin film as a resist mask, and then the Or thin film was peeled off to obtain a sawtooth diffraction grating.

The period of this diffraction grating was 3 μm, and a diffraction efficiency of 45 to 50 cm was obtained for incident light with a wavelength of 665 nm. The maximum diffraction efficiency of a normal thin phase-type diffraction grating is 66.9% as a theoretical value, and the wooden design sufficiently exceeds this value.

[Brief explanation of drawings]

FIG. 16) to (fl are cross-sectional views for showing each step of the present invention. 1.........--...Substrate 2...
・・・・・・・・・・・・Photoresist layer 3・
・・・・・・・・・・・・・・・・・・Diffraction grating pattern 4・・・・・・・・・・・・・・・・・・Concavity 5...
・・・・・・・・・・・・Mask 6・・・・・・
・・・・・・・・・・・・Slope 7 on the unmasked side ・・・・・・・・・・・・・・・Convex fangs 1
Figure 1

Claims (1)

[Claims] A diffraction grating pattern made of hardened photoresist is formed on a glass or metal substrate, then etched to form a recess corresponding to the pattern, and then oblique evaporation is performed to form a recess on one side of the recess. 1. A method for producing a diffraction grating, which comprises forming a unevenly distributed mask, etching the mask using the mask as a resist, and then removing the mask.