KR19990010190A - Uniform Planar Waveguide Manufacturing Method - Google Patents

Abstract

The present invention relates to a method of manufacturing a uniform planar optical waveguide, the method of manufacturing a uniform planar optical waveguide includes a first step of depositing a lower cladding layer on a substrate and then polishing the deposited surface; Depositing a core layer on the resultant of the first step and then polishing the deposited surface; A third step of patterning the surface polished core layer in a second step to create an optical waveguide; And a fourth step of depositing an upper cladding layer on the optical waveguide patterned and generated in the third step and then polishing the deposited surface.

According to the present invention, the surface planarization process is added to increase the thickness uniformity of the optical waveguide, so that the effective refractive index in the optical waveguide is uniform and a more precise optical device can be manufactured. Especially for AWG DeMUX, phase difference in each channel Crosstalk is reduced by matching the desired value.

Description

Uniform Planar Waveguide Manufacturing Method

The present invention relates to a method for manufacturing an optical waveguide, and more particularly to a method for manufacturing a uniform planar optical waveguide.

Planar lightwave circuits have been developed to compensate for the shortcomings of the micro-optic method for fabricating optical communication devices and for mass production. 1A to 1C illustrate a conventional planar optical waveguide manufacturing process. FIG. 1A illustrates a process of depositing a lower cladding layer 102 and a core layer 104 on a substrate 100. 1B illustrates a pattern process step of forming the waveguide 106 in the core layer of FIG. 1A, and FIG. 1C illustrates a process of depositing and packaging an upper cladding layer 108 on the waveguide formed in FIG. 1B. Is not made).

FIG. 1D is a flowchart illustrating the manufacturing method of FIGS. 1A to 1C. The method of manufacturing the planar optical waveguide according to FIG. 1D is as follows. First, the lower cladding and the core layer are deposited by the film deposition process (step 112). Film deposition includes spin coating for organic materials such as polymer, chemical vapor deposition (CVD) for inorganic materials, modified CVD, flame hydrodeposition (FHD), etc. Is done. At this time, there is a slight difference depending on the film deposition method and conditions, there is a non-uniform thickness. Spin coating is a method of synthesizing organic materials, adjusting the concentration and viscosity using a predetermined solvent, spraying on a spin coater, and then rotating at high speed to form an organic film of several micrometers (μm). to be. The CVD method is a method of forming a film on a substrate by injecting a gas of a material that is a raw material of a film to be deposited to give energy in a reactor. Modified CVD includes low pressure CVD (Atmosphere Pressure CVD), plasma enhanced CVD (PECVD) and the like. FHD is a method of synthesizing a reaction gas using hydrogen and oxygen flame to make small particles and depositing them on a substrate. In each film deposition process, a silicon substrate is mainly used, and oxides of group III-V compounds such as quartz, aluminum oxide (Al ₂ O ₃ ), gallium arsenide (GaAs), and indium phosphide (InP) are used. Substrates are used.

Pattern production takes place in a clean room. After the film is deposited, the wafer is cleaned and dried, followed by photoresist (PR) spin coating (step 116). In this case, a metal mask may be deposited between etching steps 112 and 116 according to etching conditions (step 114). After the PR spin coating, the PR pattern is baked to be solid (step 118), and the design pattern is transferred onto the wafer using a mask aligner, and then ultraviolet rays are irradiated (step 120). When the pattern is formed by UV irradiation, the unreacted PR is peeled off using a developer (step 122), and dry etching (step 124). The etching method may be ionization coupled plasma or reactive ion beam etching. After etching, the material (PR or metal film) used as the pattern mask is removed (step 126), post-annealed (step 128), and an upper cladding is formed by a film deposition process (step 130). ). When this process is completed, the wafer process is completed, cut into each device unit, and then packaged to complete the device.

As described above, in the conventional planar optical waveguide fabrication method, a process of depositing a film is basically repeated three times, and more than that is required when making a device having a multi-layer structure. In this case, even if the film deposition conditions are optimized, the uniformity of the thickness is about 2 to 3%. If the thickness of the film is not constant, the thickness of the waveguide made based on it is also uneven, which leads to non-uniformity of device characteristics. FIG. 2A shows a cross section of an optical waveguide of non-uniform thickness, and FIG. 2B shows a side cross section of an optical waveguide of non-uniform thickness. Reference numeral 200 denotes a substrate, 202 a core layer and 204 a cladding layer, d denotes an optical waveguide thickness, w denotes an optical waveguide width, and l denotes an optical waveguide length. The influence of the above-described thickness nonuniformity on the characteristics of the device is as follows. For example, an arrayed waveguide demultipler (AWG DeMUX) separates the wavelength of an incoming optical signal into multiple independent channels. At this time, the phase difference of each channel Should be set at regular intervals, and this phase difference When this path difference, β is the propagation index of the waveguide, Is given by The propagation index β of the waveguide is when k ₀ is the wave factor, d is the thickness of the waveguide, and θ is the angle of incidence. If the waveguide is not uniform, d is changed during light propagation, and thus crosstalk is increased because it is not separated into a specific wavelength desired at each end of the channel. This is a problem in actual cauterization.

This problem can occur in devices based on optical waveguides as well as AWG DeMUX devices. Basically, if the error caused by this falls within the allowable range, it can be used, but in the case of a device that requires more precise optical signal control due to the multilayer structure, more accurate optical waveguide is required.

The technical problem to be achieved by the present invention is to add a surface planarization process to solve the thickness nonuniformity of the upper and lower cladding layer, core layer 2 to 3% by uniform surface optical waveguide to increase the surface uniformity by minimizing the difference in film thickness To provide a manufacturing method.

1A to 1C illustrate a conventional planar optical waveguide fabrication process.

1D is a flowchart illustrating a conventional method for fabricating a planar optical waveguide.

2A is a cross-sectional view of an optical waveguide having a non-uniform thickness.

2B is a side cross-sectional view of an optical waveguide having a non-uniform thickness.

3 is a flowchart illustrating a method of manufacturing a uniform planar optical waveguide according to the present invention.

4A-4C illustrate the surface planarization process.

In order to achieve the above technical problem, a method for manufacturing a uniform planar optical waveguide according to the present invention includes a first step of depositing a lower cladding layer on a substrate and then polishing the deposited surface; A second step of depositing a core layer on the resultant of the first step and then polishing the deposited surface; a third step of patterning the surface polished core layer in the second step to generate an optical waveguide; And depositing an upper cladding layer on the optical waveguide patterned in the third step, and then polishing the deposited surface.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. 3 is a flowchart illustrating a method of manufacturing a uniform planar optical waveguide according to the present invention. The method of manufacturing a uniform planar optical waveguide according to FIG. 3 includes a lower cladding layer deposition step 300, a first surface polishing system 310, and a core. The layer deposition step 320, the second surface polishing step 330, the patterning step 340, the upper cladding layer deposition step 350, and the third surface polishing step 360 are performed.

The film deposition steps 300, 320 and 350 of the upper and lower cladding layers and the core layer may use one of the above-described spin coating, CVD, low pressure CVD, PECVD, APCVD, and FHD. As the substrate, one of the above-described oxides such as silicon, quartz, Al ₂ O ₃ , GaAs, InP, and a group III-V compound semiconductor substrate is used.

The first, second and third surface polishing steps 310, 330, and 360 are processes for planarizing the surface. Surface polishing includes mechanical and chemical polishing methods. Mechanical polishing is a method of physically scraping a surface by using a material that is more than the hardness of the surface material to be polished, and chemical polishing reacts with the surface. It is a method of melting the surface little by little using chemicals. Chemical Mechanical Polishing, which combines the two polishing methods described above, may also be used. Mechanochemical polishing method is a method of improving the mechanical polishing efficiency by changing the properties of the surface by chemical reaction with the surface to be polished using chemicals, especially a semiconductor process capable of mass production process using wafers and fine surface polishing Used a lot for 4A to 4C illustrate the above-described mechanochemical polishing method, in the drawings,? Denotes an abrasive and? Denotes a chemical. FIG. 4A shows an unpolished deposition surface, 400 in FIG. 4A shows a substrate, and 402 shows a deposited film. FIG. 4B illustrates a polishing process using a polishing apparatus, an abrasive, and chemicals of 404. FIG. 4C is a view showing that the surface is uniform after polishing.

For example, in the case of the silica optical waveguide, the surface polishing target is BPSG (Borth Phosporous Silica Glass), and since the main component is silicon oxide (SiO ₂ ), KOH, which is one of the alkali (Alkali, OH) reacting thereto, is added. If abrasives (SiO ₂ fine particles, ceramic fine particles, etc.) are used, the surface properties of the silica glass are different, and the mechanical polishing efficiency is enhanced due to the surface properties of the film which are changed by the chemical reaction.

On the other hand, the operation principle of the present invention is as follows. First, the lower cladding layer film is deposited (step 300), and the surface polishing operation is performed by the method described above (step 310). The core layer film is deposited thereon (step 320), and the surface polishing operation is performed again (step 330). When the deposition and surface polishing of the core layer is completed, patterning is performed (step 340).

The patterning process is as follows. First, after the wafer is cleaned, PR spin coating is performed (step 342). Before performing step 342, a metal mask may be deposited according to an etching condition (step 341). After the PR spin coating, the PR pattern is baked to be solid (step 343), and the design pattern is transferred onto the wafer, followed by irradiation with ultraviolet light (step 344). When the pattern is formed by UV irradiation, the unreacted PR is removed using a developer (step 345), and dry etching (step 346). Etching methods use ionized plasma or reactive ion beam etching. After etching, the material (PR or metal film) used as the pattern mask is removed (step 347), and then heat-treated (step 348) to complete the patterning process.

After patterning, the upper cladding is formed by the film deposition process (step 350), and the surface polishing operation is performed (step 360).

When all of the above processes are completed, these processes may be repeated to fabricate a multi-layered device.

In the case of the single mode silica waveguide polished by the above-described method, the thickness variation of the waveguide is reduced to within 500 mW. In the case of the single mode silica waveguide, the thickness of the core layer is about 8 μm, so the thickness variation ratio is 0.6%, and the uniformity is improved by 3 to 5 times compared to the conventional 2 to 3%. In the case of multimode, the waveguide becomes larger in size and the thickness variation does not change, thereby reducing the variation rate. Therefore, the present invention can be used for devices that handle multiple wavelengths, devices with a long propagation length of light, or devices having multiple waveguides.

According to the present invention, the surface planarization process is added to increase the thickness uniformity of the optical waveguide, so that the effective refractive index in the optical waveguide is uniform and a more precise optical device can be manufactured. Especially for AWG DeMUX, phase difference in each channel Crosstalk is reduced by matching the desired value.

Claims (9)

Depositing a lower cladding layer on a substrate and then polishing the deposited surface; A second step of depositing a core layer on the resultant of the first step and then polishing the deposited surface; A third step of patterning the surface polished core layer in the second step to create an optical waveguide; And And depositing an upper cladding layer on the optical waveguide patterned and generated in the third step, and then polishing the deposited surface. The method of claim 1, wherein the material of the substrate Method of manufacturing a uniform planar optical waveguide, characterized in that any one of silicon, quartz, aluminum oxide, gallium arsenide and indium phosphide. The method of claim 1, wherein the lower cladding layer deposition is A method for manufacturing a uniform planar optical waveguide, comprising any one of spin coating, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, atmospheric chemical vapor deposition, and flame hydrolysis. The method of claim 1, wherein the polishing is A method of manufacturing a uniform planar optical waveguide, characterized by using any one of mechanical polishing, chemical polishing and mechanical chemical polishing. The method of claim 1 wherein the core layer deposition is A method for manufacturing a uniform planar optical waveguide, comprising any one of spin coating, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, atmospheric chemical vapor deposition, and flame hydrolysis. The method of claim 1 wherein the upper cladding layer deposition is A method for manufacturing a uniform planar optical waveguide, comprising any one of spin coating, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, atmospheric chemical vapor deposition, and flame hydrolysis. The method of claim 1, wherein the patterning step Photoresist spin coating; A baking step of applying heat to harden the photoresist pattern; Transferring the design pattern to the photoresist to align the mask and irradiate ultraviolet rays; Dipping the unresponsive photoresist pattern by soaking in a predetermined developer; An etching step of etching the material according to the design pattern and then removing the material used as the pattern mask; And Method for producing a uniform planar optical waveguide, characterized in that it comprises a post-heat treatment step. The method of claim 7, wherein And depositing a metal mask prior to the photoresist spin coating step. The method of claim 7, wherein the etching is A method for fabricating a uniform optical waveguide, characterized in that the method is performed using any one of an ionization coupled plasma method and a reactive ion beam matching method.