JPH0126529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a diffraction grating on a semiconductor surface.

Diffraction gratings are used to obtain spectra by diffracting light, and up until now, they were made by moving the grating material at regular intervals using a high-precision feeding mechanism and carving fine grooves with a diamond cutting tool. Recently, holographic diffraction gratings that utilize laser light diffraction and interference and photolithography have been developed, and are used for distributed feedback (DFB) lasers, grating lenses, and laser-waveguide coupling, and will be used in optical integrated circuits in the future. It will contribute to manufacturing and development.

However, in this method of manufacturing a diffraction grating using photolithography, the process of creating a mask using photoresist is unreliable, and the photoresist mask must be removed after the diffraction grating is created. Applying photoresist to the semiconductor surface as a grating material, baking, etching, and removing the photoresist as described above will affect the composition, crystallinity, etc. of the semiconductor surface. Quality crystallization is difficult to do.

As described above, the method of manufacturing a diffraction grating using photolithography is not economical because it requires many processes, and there are also problems with the obtained product.

Furthermore, it is known that when a semiconductor or dielectric material is irradiated with powerful laser light (laser annealing), periodic damage is formed on the irradiated surface.
In other words, for a linearly polarized single laser beam emitted by a YAG laser, etc., the wavelength of the laser beam is λ, and the angle of incidence of the laser beam on the substrate surface is θ.If the electric field of the laser beam is parallel to the laser incidence plane, then In other words, in the case of P-polarized light, two types of fringes with different periods given by Λ±=λ/(1±sinθ) are observed in a direction substantially perpendicular to the electric field direction of the laser beam. When the electric field is perpendicular to the laser incidence plane, i.e.
In the case of S-polarized light, the damage period is Λ ₀ = λ/cosθ
is given by

As mentioned above, the method of creating a periodic structure using a powerful laser beam that melts the semiconductor surface is impractical because the composition and crystallinity of the semiconductor are impaired.
Furthermore, in the case of compound semiconductors such as gallium arsenide and indium phosphide, the vapor pressures of their constituent elements vary considerably, so irradiation with powerful laser light evaporates elements with high vapor pressure, while elements with low vapor pressure evaporate on the surface. For example, in the case of a gallium arsenide compound semiconductor, arsenic evaporates and only gallium remains, making it impossible to obtain a perfect periodic structure.

An object of the present invention is to provide a method for forming a periodic structure as described above on a semiconductor surface without impairing the composition and crystallinity of the semiconductor to form a diffraction grating.

In order to achieve the above object, the method for manufacturing a diffraction grating according to the present invention includes irradiating a semiconductor surface in a photochemical etching solution with a single linearly polarized laser beam to form a large number of uneven stripes parallel to the semiconductor surface. It is characterized by

The present invention will be explained with reference to the accompanying drawings. By irradiating a single linear laser beam 1 onto a semiconductor substrate 2 in a photochemical etching solution 3, an incident light beam is induced on the semiconductor surface by the incident light on the substrate surface. A diffraction grating pattern is formed based on the interference of surface electromagnetic waves, and areas of the semiconductor surface where the electric field is strong are etched more quickly than areas where the electric field is weaker, forming an uneven striped pattern with the same spacing as the diffraction grating pattern. I will do it. The depth and shape of the grooves to be formed are determined by the output of the laser beam, the irradiation time, the etching liquid, the type of semiconductor, etc.
The depth of the unevenness is approximately 0.01 to 1.0 μm, and the interval between the grooves of the formed unevenness is λ/n in the case of vertical incidence, where n is the refractive index of the etching liquid and λ is the wavelength of the laser beam. It can be controlled by changing the wavelength of light. Further, if the angle at which the semiconductor substrate receives the irradiated laser light is changed, the interval between the uneven grooves to be formed also changes, and the interval between the diffraction gratings can be adjusted.

Semiconductors used as lattice materials include Si,
These include group semiconductors such as Ge and -group compound semiconductors, which have particularly high electron mobility and are easily diffracted against gallium arsenide, which is composed of elements with different vapor pressures and is used in optical and electronic device materials. A grid can be formed.

As the photochemical etching solution, a solution having a composition normally used for photochemical etching of semiconductors can be used, and the solution is selected as appropriate depending on the semiconductor used as the grating material. The laser used may be a laser that emits a single linearly polarized laser beam, such as a YAG laser, a helium neon laser, an argon laser, or a krypton laser.

As mentioned above, a semiconductor substrate is immersed in a photochemical etching solution, and a linearly polarized single laser beam with an output of about 0.1 to 100 W/cm ² is applied to the substrate.
λ/n on the semiconductor substrate by irradiating for ~10 minutes
A diffraction grating with a height of about 0.1 to 0.2 μm is formed with unevenness at intervals.

FIG. 2 shows a method of forming a plurality of diffraction gratings with locally different spacing or directions on a semiconductor substrate,
A photochemical etching solution 3 is contained in the container 4, and the semiconductor substrate 2 is supported by a rotating support shaft 5 so as to be able to move up and down and rotate in the etching solution 3. A transparent window 6 is provided on one side of the container 4, and a 1/2 wavelength plate 7 is rotatably provided outside the window 6.

A laser beam 1 from a laser is adjusted to a specific size by a lens 8, and then passes through a wavelength plate 7 and a window 6 to irradiate the semiconductor substrate 2 in an etching solution 3. The semiconductor substrate 2 is positioned in advance by driving the rotary support shaft 5 so that the position where the diffraction grating is to be formed is irradiated with the laser beam, and is fixed for a predetermined period of time.
After the diffraction grating is formed by irradiating the laser beam, the irradiation of the laser beam is stopped, the semiconductor substrate is moved, and the next position where the diffraction grating is to be formed is irradiated with the laser beam. At this time, the interval between the formed diffraction gratings can be controlled by changing the angle at which the semiconductor substrate receives the laser beam.

Furthermore, if the wave plate 7 provided outside the window 6 is rotated by 45 degrees, the direction of the diffraction grating formed on the semiconductor substrate will change by 90 degrees. Therefore, the direction in which the diffraction grating is formed can be arbitrarily set by rotating the wave plate, and a plurality of diffraction gratings with different sizes, intervals, and directions can be easily formed at any position within one semiconductor substrate. can be produced, such as gallium arsenide,
Even when forming a diffraction grating on a compound semiconductor containing an arsenic component that easily evaporates, it is manufactured by irradiating a very weak laser beam in a solution, which prevents evaporation of arsenic and reduces the component ratio. A semiconductor with an unchanging diffraction grating can be obtained.

As is clear from the above description, the present invention makes it possible to form diffraction gratings with different spacing and directions at arbitrary positions on the semiconductor surface without using a mask, and makes a significant contribution to the construction of optical integrated circuits. Become.

Next, embodiments of this invention will be described. _{H2SO4 :}
GaAs (3 mm x 3 mm) is immersed in a photochemical solution with a composition of H ₂ O ₂ :H ₂ O of 1:1:30, and laser light (wavelength 0.53 μm) from a YAG laser is irradiated from above.
As a result of irradiation for 10 minutes at an output of 1 W/cm ² , uneven lines with a height of 0.02 μm were formed at equal intervals of 0.4 μm over the entire semiconductor surface, and the formed uneven lines could be used as a diffraction grating.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of the method for manufacturing a diffraction grating according to the present invention, and FIG. 2 is a sectional view showing another example of the method for manufacturing a diffraction grating according to the invention. In the figure, 1 is a laser beam, 2 is a semiconductor substrate, and 3 is a photochemical etching solution.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a diffraction grating, which comprises irradiating a semiconductor surface in a photochemical etching solution with a single linearly polarized laser beam to form a large number of uneven lines parallel to the semiconductor surface. 2. The method for manufacturing a diffraction grating according to claim 1, wherein the semiconductor is gallium arsenide.