JPS60241287A - Manufacture of high-density lattice pattern - Google Patents

Abstract

PURPOSE:To obtain the titled pattern without the need of an interferometer by a method wherein the whole is irradiated with the light from a light source having a plurality of line spectra from the direction of the Bragg angle of a diffraction grating pattern in the state that a mask and a substrate are kept warm in adhesion, and is exposed to this light. CONSTITUTION:The mask 1 is with the recording of a previously formed lattice pattern keeps the lattice plane in adhesion to a photoresist 2 applied on the substrate 3. On irradiation with substantially coherent light frim the direction of the Bragg angle of the mask 1 lattice in this state, the primary diffracted light 6 generates in addition to a direct transmitted light 5. Interference fringes are formed by both lights, and a lattice of the same period (d) as that of the mask is recorded to the photoresist 2.

Description

Detailed Description of the Invention (#Tojo Field of Application) The present invention relates to a method for manufacturing a high-density grating pattern, particularly for DFB (Distributed Chit Feedback) type semiconductor lasers and DBR (Distributed Feedback) type semiconductor lasers. The present invention relates to a method of manufacturing a dense grating pattern with a grating period of 0.5 μm or less, which can be applied to a Chitto-Bragg reflector (2 distributed Bragg reflector) type semiconductor laser.

(Prior Art) The periodic structure required in a DFB type semiconductor laser or an HR type semiconductor laser is a very dense diffraction grating (hereinafter abbreviated as a grating). For example, the Bragg condition for a DFBffi semiconductor laser is λ0 = 2n6 d/m
(11) where λ is the oscillation wavelength, no is the refractive index of the crystal, d is the lattice period, and m (integer) is the diffraction order.

m=1. λ as n=3.56. = 1.5 μm, d = 0.21 μm, resulting in an extremely dense grid. Such dense grids are widely used in the literature, e.g. by Mikami, Nakagome, and Kobe in Technical Report 0QE81 of the Electronics Association Society.
-Volume 77, pages 23-28 1.5 μm band GaI
It can be fabricated using holographic techniques as described in a paper entitled ``nABP/InP Distributed Feedback Laser''. For example, if an interferometer is constructed using the emitted light of a He-Od laser with a wavelength of 325 nm, and two beams of light are caused to interfere at an incident angle of ±507°,
This results in dry #stripe of d=0.21 μm.

This interference/product is recorded on a photoresist coated on the semiconductor laser crystal. Thereafter, the photoresist i is developed and the crystals are etched to obtain the desired periodic structure.

(Problems with the prior art) The prior art as described above corrects the following problems. The interference M used in the prior art requires a high degree of stability, has to be constructed on a cutting table, and has the disadvantage that the device is large and expensive. Also, He-C
The oscillation wavelength of the d laser is stable, but the oscillation position changes due to temperature fluctuations within the laser oscillator, and the incident angle of the two beams changes due to slight mechanical fluctuations in the optical system jig that makes up the interferometer. However, there was a drawback that it was not possible to produce a good harvest of lattices with good reproducibility and the same pitch. Because of this problem, it was also necessary to maintain the interferometer for each required grating period, which was a major problem. We aim to provide a simple method for producing high-density lattice patterns.

Another object of the present invention is to provide a method for manufacturing a high-density grating pattern, which eliminates the above-mentioned drawbacks and allows gratings with the same pitch to be manufactured with good reproducibility.

(Structure of the Invention) The present invention includes a step of bringing a mask on which a diffraction grating is formed into close contact with a substrate coated with photoresist using a combination of heating and pressure, and a step of bringing the mask and the substrate into close contact with each other and keeping the temperature of the substrate. , a step of irradiating and exposing the diffraction grating pattern with light from a light source having a plurality of bright line spectra from the Bragg angle direction; and after cooling the mask in the close contact state and peeling off the mask from the substrate, developing and etching the photoresist. (Detailed explanation of N formation) The present invention solves the problems of the prior art by adopting the above-mentioned structure. When irradiation is performed from the Bragg angle direction using a grating pattern formed in advance as a mask, first-order diffracted light is generated in addition to directly transmitted light. Therefore, if the irradiation light is coherent light, the directly transmitted light and the first-order diffracted light interfere, producing interference fringes. A high-density lattice pattern can be produced by recording these interference fringes on a first photoresist directly under a mask.

Conventionally, photolithography, which has been used to produce 10 patterns, is used to print a ball onto a substrate covered with photoresist.
The mask was placed under pressure and exposed to light using an ultra-high-pressure water lamp from the vertical direction of the mask. Furthermore, in an improved method, Deep
Methods have been used to improve the adhesion between the mask and the resist using UV resists, and expose them to approximately 250 nm light from a mercury-xenon lamp, but the line width obtained with current technology is at most 0.5 μm. , converted to the grid pitch is 1
Only patterns larger than μm can be produced one inch at a time.As a grating manufacturing method relatively similar to this method, there is a hologram duplication method. In invention, Coheren)
A method of reproducing holograms on new photographic materials using IT monochromatic light is disclosed. However, [-1] When attempting to produce a high-density grating pattern using the disclosed method, not only the sensitivity of the photoresist is low, but also the output power of the laser, which is sensitive to the photoresist, is low, so a long exposure time is required. productivity is low. Furthermore, it is necessary to keep the mask and photoresist stable during exposure.

In addition, as another method, Kashihara, Nishihara, and Koyama published a paper titled "Optimal conditions for hologram replication using the Chi-attached method" in Miyako Communication Society Transactions Vol. J59-0, No. 7, pages 443-450. There is a method disclosed. Based on this paper, it is possible to create a replica of a hologram by selecting the angle of incidence under a super-infrared mercury lamp, but since there are multiple emission line spectra, the hologram, which is a mask, and the photoreceptor must be in close contact with each other. 11. ing. Therefore, with the close contact method disclosed in this paper, it is not possible to produce a high-density grating with a pitch of 05 μm or less, which is the object of the present invention. Therefore, in the present invention, a very good 1x grating can be manufactured by adhering the mask and photoresist as follows (7
After applying the photoresist to the substrate, bake it at 4C for 1 hour at 40℃ or at 60℃ for 2 hours.
Use a photoresist that has been baked for about 0 minutes and has not yet been dried. Temperature: 80-120℃ when in close contact with the mask
Heat and pressurize the mask.

So, the mask and photoresist are stuck together? 16r- did. Once stuck, peeling will not occur as long as the temperature is kept above 50°C. After exposure, the mask is peeled off from the photoresist by air cooling or forced air cooling.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. The figure is a sectional view showing one embodiment of the present invention. The dimensions of the grid are larger than the other dimensions for illustrative purposes.

In the figure, a mask 1 on which a preformed lattice pattern is recorded has its lattice surface deposited on a photoresist 2I coated on a substrate 3. In this case, when the practically coherent foC element 4 is irradiated from the Black angle direction of the grating of the mask 1, first-order diffracted light 6 is generated between directly transmitted light 5 and the like. When the incident angle of the irradiated light is υi and the pitch of the grating is d and 1, the diffraction angle θd is as follows. The angle of incidence on the photoresist 2 is θl, and the angle of incidence of the diffracted light 6 is
Since θd, the interference fringes are again formed according to equation (2), and a grating with the same period d as the mask is also recorded on the photoresist 2. Therefore, regardless of the wavelength λ, a grating is always formed that has the same grating period d of the mask. Utilizing this characteristic, in the present invention, it is possible to fabricate a grating even if an ultra-high pressure mercury lamp, which does not have a wavelength of light, is used as a light source. The light of the ultra-high pressure water GL lamp is a large number of #! Although it has a line spectrum and a coherence length (coherence length) of about 0.2 km, such a light source is sufficient for this method.

In the present invention, the fact that an ultra-high pressure mercury lamp with a large output optical power can be used as a light source is a major advantage. In addition, if a laser having a plurality of oscillation wavelengths such as an argon laser is used and oscillated at all wavelengths simultaneously, the exposure time can be shortened. As for the material of the mask, a holographic dry plate, a chrome dry plate, glass, etc. can be used. As a holography dry plate, a Kodak 120-t)1 dry plate was used. Masu, He-Ne laser (wavelength 63'8 n
m) Using an interferometer with a P light source, two beams of light are interfered at an incident angle of ±45°, and one holographic dry plate has a grating period of 0.
．． A 447 μm gray scale grid was recorded. Using this grid as a mask5, we used an ultra-high-pressure mercury lamp with the configuration shown in the figure at an incidence angle of approximately 2.
Photoresist 2 (0.3 μm thick Hoechst AZ-1350 photoresist) was exposed at 4° and was 0447 μm thick.
I was able to create a pitch grid.

In the example using a chrome dry plate, an interferometer with a He-Cd laser (wavelength λ = 325 n, m) as a light source was used to cause two beams of light to interfere at an incident angle of ±50.7° and onto a chrome dry plate. A grating with a pitch of 0.21 μm was recorded on the applied A, Z-1350 photoresist film with a thickness of 02 μm. After developing the photoresist, the chromium was etched using a commercially available chrome etching solution to form a grating on the chromium film. ,
The photoresist was then removed. Using the chrome dry plate produced in this way as a mask, it was exposed to light at an incident angle of approximately 45°C using a mercury-xenon lamp as a light source in the configuration shown in the figure, to a thickness of 0.
A grating with a pitch of 0.21 μm was fabricated on the 2 μm photoresist 2.

In the example in which glass was used as the mask material, as in the example in which a chrome dry plate was used, a grid with a pitch of 0.21 μm was recorded on the photoresist coated on the glass, and the photoresist was viewed and imaged. He is tetrafluoromethane (
cF4) Glass was etched vertically using an ion beam to form a lattice with a pitch of 0.21 μm on the glass surface. Thereafter, the photoresist was removed to form a mask. If the etching depth of the glass is set to about 0.2 μm, the intensity of the directly transmitted light and the first-order diffracted light at the black angle of incidence can be almost rounded, and the intensity of the 1st-order diffracted light can be relatively improved. I was able to fabricate a photoresist lattice with easy control of +11.

(Effects of the Invention) According to the present invention, a dense layer grating pattern can be manufactured without requiring every 1 [11 interferences: 1], and gratings with the same pitch can be formed with good reproducibility.

[Brief explanation of the drawing]

The figure shows the primary example of Kiseiaki's Tk plane. With all due respect, 1... Mask, 2... Photoregis 1.
3... Board, 4... Terumi, ° light, 5.
...iα tangent passing light, 6...1st-order diffracted light. Susumu Uchihara, patent attorney

Claims (1)

[Claims] (b) A step of bringing the mask on which the diffraction grating is formed into close contact with the substrate ζ coated with photoresist using both heating and pressure, and with the mask and the substrate being kept under constant vigilance and kept warm, the diffraction grating is A step of irradiating and exposing the photoresist with light from a light source having a bright silk spectrum of m number from the Bragg angle direction of the pattern, and a step of developing and etching the photoresist after cooling it in the contact state and peeling off the mask from the substrate. t
A method for producing a convex density lattice pattern characterized by the fact that N(!:) is minimized.