JPH02188702A - Formation of diffraction grating - Google Patents

Abstract

PURPOSE:To improve the stability of pattern dimension accuracy by removing an etching mask layer with a liquid developer for a photoresist layer or the resist pattern of the photoresist layer by an etching means with resistance. CONSTITUTION:Etching mask layers 11 and 12 are laminated on a substrate 10, the upper layer is the photoresist layer 12, and the lower etching mask layer 11 is removed with the liquid developer for the photoresist layer 12 or the resist pattern 13 of the photoresist layer 12 is removed by the etching means with resistance. In this case, the photoresist 12 is only microposit 1400-17 or alkali development type photoresist. Further, a etc., is usable as the lower etching mask layer 11 as long as the material can be etched with an alkali liquid developer for photoresist. Consequently, the dimension accuracy of the pattern is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a diffraction grating, and more particularly to a method for producing an etching mask for producing a diffraction grating.

(Prior Art) Diffraction gratings are used in various optical circuit elements such as filters, optical couplers, distributed feedback lasers, and distributed Bragg reflector lasers in optical ICs.

The period of the diffraction grating used in optical integrated circuits is approximately 0.1.
μ plow ~ 1.0μ■, mainly made by holographic method.

The principle of the holographic exposure method is to make a coherent light beam emitted from a single light source into a uniform parallel beam, split it into two beams with equal amplitude and intensity using a beam splitter, and make the split beams incident on the photoresist surface at an intersection angle of 2θ. let The two beams generate interference fringes on the photoresist surface and sensitize the photoresist according to the light intensity distribution of the interference fringes.

Next, an etching mask is formed by developing the photoresist.

In recent years, dry processes have become mainstream for submicron pattern etching, and resist patterns must be able to withstand this processing process.

Among these, anisotropic etching methods such as sputter etching, ion beam etching, and ion milling can faithfully realize pattern shapes. The pattern shape obtained by this method is determined by the etching selectivity ratio between the mask material and the sample. If the etching rate is 3 times or more, a diffraction grating with a shape close to a square wave will be obtained, but if the difference in etching speed is small, the resist will also be etched at the same time. This results in a sinusoidal etched shape. Therefore, a resist with sufficient resist thickness and a vertical cross-sectional shape is required.

A conventional method for creating an etching mask will be explained using drawings.

In the first method, as shown in FIG. 3, a photoresist is coated on the surface of the substrate 1, and after prebaking, a photoresist layer 2 is obtained (FIG. 3a). Next, He-Cd laser (λ-
325 nm) using a two-beam interference method (FIG. 3b), and development to form a desired resist pattern 3 (FIG. 3C). Furthermore, dry etching is performed using the resist pattern 3 as a mask, and the substrate 1 is etched in a third manner.
Figure 3d) Finally, the resist is removed to form the diffraction grating 4 (Figure 3e).

In the second method, as shown in FIG. 2, a second etching mask layer 6 (organic or metal) is formed on F of the substrate 5 by coating or vapor deposition (FIG. 2a). A photoresist is then applied and, after blibration, a photoresist layer 7 is obtained (FIG. 2b).

Next) 2 using Ie-Cd laser (λ-325nm)
The resist pattern 8 is exposed using a beam interferometry (FIG. 2 c), and then developed to form a desired resist pattern 8 (FIG. 2 d).
. Further, wet etching is performed using the resist pattern 8 as a mask to etch the second etching mask layer 6 (FIG. 2e). A multilayer etching mask is thus formed, and dry etching is performed using the resist pattern 8 and the second etching mask layer 6 as masks to etch the substrate 5 (FIG. 2f), and finally the resist is removed to form the diffraction grating 9. (Figure 2g).

(Problems to be Solved by the Invention) The method for creating an etching mask for a diffraction grating described above has the following problems. That is, in the first method, the layer thickness of the single layer resist, which is related to pattern uniformity and resist cross-sectional shape, cannot be made thicker than the pattern line width, and the cross-sectional shape of the resist may be sinusoidal or S-shaped. Therefore, the cross-sectional shape of the pattern etched using this resist as a mask has a tapered shape. Also,
If the pattern line width is, for example, 0.2 μm, the resist layer thickness is also limited to 0.2 μm, so dry etching also progresses etching of the photoresist mask, making it impossible to form deep grooves. It was not possible to form a thick square wavy pattern, which is desirable for pattern transfer of radiance.

In the second method, the thickness and shape of the first etching mask layer are improved, but in patterning the second etching layer 6, after patterning the photoresist layer 7, this resist pattern 8 is used as a mask for etching. A special etching process is required when forming the pattern of the etching mask layer (2), which increases the number of pattern forming processes and reduces the dimensional density, making it impossible to create a good diffraction grating. ．． In the production of 0 μm diffraction gratings, the yield was low, which was a big problem.

Other methods for creating a diffraction grating include direct writing using an electron beam exposure method and maskless processing using a focused ion beam. Since these are charged beams, it is possible to focus the beam diameter to 0.1 μω or less, and it is possible to directly write fine patterns with high precision, but on the other hand, there is a proximity effect, 0.3 μ due to back scattering
- It is difficult to write diffraction gratings with periods below on thick resists and thick substrates. Furthermore, as patterns become finer, there is a problem in that throughput and yield decrease.

[Means to solve the problem]

The present invention has been made to solve the problems of the prior art described above, and its purpose is to provide a method for creating an etching mask for creating a diffraction grating with a fine period.

In the present invention, a plurality of etching mask layers are laminated on a substrate, the uppermost layer of the plurality of etching mask layers is a photoresist layer, this photoresist layer is exposed and developed to form a resist pattern, and the resist A method for forming a diffraction grating in which a diffraction grating is formed on a substrate by etching the substrate using a pattern as a mask, the etching mask layer other than the photoresist layer being removable with a developer for the photoresist layer, or The method of forming a diffraction grating is characterized in that the resist pattern of the photoresist layer is made of a composition that can be removed by a resistant etching means.

In particular, the plurality of etching mask layers are two layers consisting of a photoresist layer as an upper layer and an etching mask layer as a lower layer that is soluble in a photoresist developer, and the exposure is performed by two-beam interference using an ultraviolet laser. This method of forming a diffraction grating is characterized in that a resist pattern is formed on the photoresist layer by etching and developing with a developer, and at the same time, the underlying etching mask layer is etched with the developer.

That is, one aspect of the present invention is to have a two-layer structure using a photoresist layer as an upper layer as an etching mask, and to expose the upper resist layer to holographic light by two-beam interference using an ultraviolet laser and develop it, and use the resist pattern as a mask. This is achieved by etching the lower etching mask layer that is soluble in the developer using the developer, that is, by performing development and etching in the same process.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram showing a method for producing a diffraction grating according to the present invention.

First, the semiconductor substrate IO is wiped and cleaned with a surfactant, then ultrasonic cleaning with an organic solvent is repeated 2 to 3 times, dried with N2 blow, and heat treated at 200° C. for 30 minutes. Next, a desired dilution of polyimide (trade name: PIX-LIIO, manufactured by Hitachi Chemical Co., Ltd.) was applied to the entire surface to seal the etching mask for the lower layer, and the polyimide layer was dried at 80°C to evaporate the residual solvent. 11 (Fig. 1a).

The appropriate thickness is about 2,000 to 4,000 people.

When a polyimide LB layer was used instead of PIX-LIIG, good results with less side etching were obtained with a layer thickness of 200 to 500 layers.

The appropriate thickness of the lower layer of the photoresist layer strongly depends on the method of forming the layer, but in general, a thinner layer is preferable if durability in subsequent steps is sufficient. - In terms of numbers, it will be around 100 to 5,000 people.

Furthermore, on top of this is a photoresist layer 1 for two-beam interference exposure.
2 (trade name: Microbosito-1400-17 manufactured by Nijibray Co., Ltd.) was diluted as desired and coated on the entire surface.
Drying is carried out at 10°C (Fig. 1b). The appropriate thickness of the photoresist is about 600 to 800 layers.

Next, the photoresist layer 12 is exposed by two-beam interference exposure using a He-Cd laser (λ-325) (FIG. 1C). Next, by developing with a developer exclusively for the photoresist layer 12 (product name Microposit 450 developer: Sibley), the resist pattern 13 is formed according to the degree of sensitivity according to the intensity distribution of interference fringes generated by interference exposure. is formed first, and by further progressing the development, the exposed polyimide layer II is etched using the resist pattern 13 as a mask, and a two-layer diffraction grating pattern of polyimide and photoresist is formed (first
Figure d). Next, heat treatment is performed to transform the polyimide layer 12 into a medium. At this time, the diffraction grating pattern of the photoresist is also heat-treated at the same time to form an etching mask pattern.

Next, using the two-layer etching mask pattern as a mask, the semiconductor substrate 1O is dry etched (Fig. 1e).
Finally, by removing the etching mask layer, a diffraction grating pattern 14 of the semiconductor substrate is obtained (FIG. 1f).

The present invention is not limited to this embodiment, and for example, the type and wavelength of the ultraviolet laser for interference exposure may be determined according to specifications.

Further, although a semiconductor substrate is used in this embodiment, glass or optical glass may be used. Further, although Microposit-1400-17 was used as the photoresist, any positive or negative type photoresist may be used as long as it is an alkaline development type photoresist. Furthermore, although the polyimide layer 11 is used as the lower etching mask layer, it is not limited thereto, and any material that can be etched with the alkaline developer of the photoresist used may be used, for example, the metal layer AI, Mo or the oxide layer ITO1.
Furthermore, the LB layer may be made of polyimide or the like, and the layer thickness in this case may be determined depending on the etching rate with the alkaline developer used. In addition, although dry etching is used for etching the semiconductor substrate in this embodiment, wet etching may also be used if the good acid resistance of polyimide is utilized.

(Effects of the Invention) As explained above, the present invention has the following advantages: (1) Shortening of the process, (2) Etching masks can be multi-layered (mask thickness can be increased), and (3) Stability of pattern dimensional accuracy is improved. The effect is brought about.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the steps of an embodiment of the present invention. FIGS. 2 and 553 are cross-sectional views showing the steps of a conventional method for forming a diffraction grating. 1 Substrate 2 Photoresist layer 3 Resist pattern diffraction grating substrate Second etching mask layer Photoresist layer Resist pattern diffraction grating substrate Polyimide layer Photoresist layer Resist pattern diffraction grating

Claims (2)

[Claims] (1) A plurality of etching mask layers are stacked on a substrate, however, the top layer of the plurality of etching mask layers is a photoresist layer, and this photoresist layer is exposed and developed to form a resist pattern. A method for forming a diffraction grating in which a diffraction grating is formed on a substrate by etching the substrate as a mask, the etching mask layer other than the photoresist layer being removable with a developer for the photoresist layer or etching the photoresist layer. A method for forming a diffraction grating, characterized in that the resist pattern of the resist layer has a composition that can be removed by a resistant etching means. (2) The plurality of etching mask layers are two layers consisting of a photoresist layer as an upper layer and an etching mask layer soluble in a photoresist developer as a lower layer, and the exposure is performed by two-beam interference using an ultraviolet laser. 2. The method for forming a diffraction grating according to claim 1, wherein a resist pattern is formed on the photoresist layer by conducting and developing with a developer, and at the same time etching the underlying etching mask layer with the developer.