JPS60107836A - Method of forming pattern - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pattern forming method. More specifically, the present invention relates to a pattern forming method capable of forming four turns of projections and depressions on the surface of a substrate with high precision by corroding the substrate material with ions.

Here, ``4 turns of unevenness'' refers to topographic features to be formed on the surface of the substrate.
ature).

[Conventional technology]

In the field of integrated optics, it has been discovered that three-dimensional patterns (features) can be reliably and reproducibly formed on a microscopic scale. In integrated optics, the edge roughness of the pattern to be formed must be small compared to the optical wavelength over a relatively large area.

[Problem that the invention seeks to solve]

As is clear from the above, there is a desire in the field of integrated optics to provide a method for manufacturing fine, highly accurate three-dimensional/e-turns with good reproducibility. This is the problem that the present invention seeks to solve.

[Means for solving problems]

According to the present invention, the above-mentioned problems can be solved by a method of forming a concavo-convex pattern on the surface of a substrate. The VF includes a milling step, and the masking cutter is made of a mask material having strong ion beam properties.
This problem can be solved by a pattern forming method.

In another aspect of the present invention, this pattern forming method is a method for forming a concavo-convex pattern on the surface of a substrate, the method comprising forming polyimide masking pieces or turns corresponding to the concave-convex pattern on the surface of the substrate, and The method of forming a pattern includes the step of ion beam milling the surface of the substrate through masking.

The term “ion beam resistant” as used herein refers to substrates, particularly lithium niobate (t,
tNbb,) is understood to mean a mask material that reproduces and preserves precise edge resolution during ion beam milling of a substrate.

As is well known, ion beam milling is the process of immersing material of a substrate from an area of the substrate defined by a pattern of masking material overlying the substrate and having appropriate properties i'+'! It refers to the means to do L. This technique can be used to /IP turn gold, insulating materials or semiconductors (including chemically inert materials). One of the most important points in this ion beam milling method is the selection of masking material.

That is, the masking material used must meet the requirements listed below: (1)
The masking material must have a low erosion rate due to the ion bombardment used to mill the substrate. (11
) The masking material must be stable when deposited to the required film thickness without decomposition, loss of adhesion to the substrate, or geometric deformation. (iii) Disintegration of the masking layer must not occur until the / pattern is formed on the substrate.

As an example of applying ion beam milling to integrated optics,
Lithium niobate (L) can act as an optical waveguide mirror.
iNbO3) ion beam milling process on the substrate,
Another example is ion beam milling of grooves (channels) in lithium niobate and precisely placing optical fibers in the grooves for coupling to optical integrated circuits.

The present inventors have recently discovered that it is appropriate to use polyimide as a mask material when ion milling lithium niobate.

Polyimide is produced by a condensation reaction between a diamine and a polycarboxylic acid or an acid anhydride thereof. First, an acid dianhydride and a difunctional base are thermally condensed.
Polyamic acid is formed by polymerization. For example, pyromellitic dianhydride (PDMA) in a suitable solvent
) and 4,4-diaminodiphenyl ether (DADPE
) to produce a polyamic acid resin. The polyamine compound is then converted to polyimide at a temperature high enough to remove the solvent and initiate ring closure of the imide. A common solvent is 1-methylpyrrolidone with aromatic hydrocarbons.

In the course of studying polyimide curing, it was discovered that the final crosslinking is a function of temperature, and that optimal film properties are obtained when the film is completely crosslinked.
There was found. At temperatures above 500°C, polyimide collapse occurred. When the repeating unit of a general polymer is represented by a structural formula, it has the following formula: 0 Below margin As understood from the above, the repeating unit of a polymer contains molecular water. In addition, two molecules of water are generated per one repeating unit of the polymer.

As a result, the amount of water per repeating unit of the polymer increases from 6 to 8 inches, depending on the average weight of the polymer. During curing, water is lost, which means that there is a significant loss of solvent from the film. It should be noted that partially cured films are hygroscopic, so atmospheric moisture must be excluded from the curing film for optimal results. This means that it will not happen. If we use a kotatsu to remove water like this,
Collapse due to high temperatures will occur before final crosslinking occurs.

Polyimide is suitable for use as an ion beam milling mask material over lithium niobate due to the following properties: (1) polyimide is used to remove lithium niobate; The rate of attack by argon ions is lower than that of most other materials.

(ii) =+? Reimirr can be deposited to a minimum film thickness of 10tIfn by spin-coding, drying and curing. The formed layer has a flat surface even if the surface of the substrate is uneven. (After ID curing, polyimide is chemically inert and has elasticity that can absorb the stresses of various thermal expansions. Polyimide is therefore suitable for withstanding a wide range of physical and chemical processes.) The polyimide is rapidly eroded by oxygen ion bombardment, allowing for easy patterning or final removal.

Margins [Example] Next, an example in which polyimide is used as a mass material for ion beam milling will be described in order with reference to FIGS. 2 to 12, which relate to the processing of an optical waveguide mirror.

In a first processing step (FIG. 2), a polyimide layer 1 is applied to the substrate 2 of the planar waveguide made of lithium niobate. The polyimide layer 1 usually has a film thickness of 10
#I and formed via spin cord, drying and curing. A thin charge diffusion layer 3, generally made of gold and having a thickness of 200X, is applied to this polyimide (
Figure 3).

Next, an electron beam resist 4 such as PMlvlA (polymethyl methacrylate) is applied to the charge diffusion layer 3 to a thickness of 1 μm.
Coat with a film thickness of (Figure 4). This resist is betatized and then exposed to electron beam (directly written with an electron beam) and developed to form undercut portion 7''4'' portion 5 (Fig. 5). Titanium 6 is deposited on the substrate processed in step 1 (FIG. 6). The resist 4 and the titanium 6 deposited thereon are then lifted off using a solvent, for example MI BK (FIG. 7).

As a result of the processing up to this point, high quality edges are formed in the titanium film 6 on the polyimide 1. Next, a replica of the nine turns thus formed on the titanium film 6 is formed in the polyimide layer 1 by bombarding oxygen ions through the titanium film 6 constituting the titanium mask (main turning of the polyimide layer). ) (Figure 8). The exposed charge diffusion layer is removed during this oxygen ion bombardment, ie reactive ion etching (RIE) with oxygen. The thus exposed lithium niobate is ion-beam milled to the required depth through a polyimide mask etched into a mother-turn shape (FIG. 9). This step is accomplished using inert argon ions or, alternatively, by using reactive ions derived from e.g. fluorinated or chlorinated hydrocarbons (reactive ion etching). be able to.

The substrate processed in this way is metallized (10th
figure).

This metallization step can be achieved, for example, by depositing aluminum 7 until the wall surface of the uneven pattern (groove 8) is covered with a film thickness of, for example, about 1000×. Normal ion etching is then used on the main surface of the substrate to remove the aluminum from all of the horizontal surfaces of the substrate, while leaving the aluminum on the vertical walls of the substrate (11th figure). Polyimide 1 is subsequently removed from the lithium niobate by using oxygen plasma stripping. As can be understood from the steps shown in FIGS. 10 to 12, polyimide P has a dual process of preserving selected portions of lithium niobate during metallization of the exposed ion beam milling process. Plays a secondary role. However, d? The main role of polyimide is to transfer the precise mechanical turns given by electron beam turning to the substrate without losing the minute details.

In the above processing, writing was performed using an electron beam during patterning of polyimide. However, other writing schemes may alternatively also be used. For example, a combination of UV radiation and a suitable organic photoresist, such as AZ1350H from Sizzole, is one possibility.

The processing steps of this method are substantially the same as those previously described with reference to FIGS. 2-12. However, this method does not require a charge diffusion layer, and baking the photoresist includes a first bake followed by a rinse in chlorobenzene, followed by a second bake. moreover,
Inorganic resist can be used. Gene or A
When g2Se/GeSe films are used as inorganic resists, very high resolution can be obtained compared to standard organic materials, and these resists are of great interest for dense patterning processes.

Heg2se/GeSe resist is an amorphous chalcosinide film. These films, when exposed to UV or electron beams, suffer from a "photodoping" effect, so that silver (Ag) diffuses into the GeSe matrix. As shown in Figure 1, when irradiated with ultraviolet rays, electron-hole pairs are formed in GeSe, and the holes migrate to the Ag 2 Se layer, where silver ions and elements It is thought that selenium is formed in the form of selenium.

Charge neutrality is achieved as a result of the trapping of electrons at defect sites in the lattice and the migration of silver ions towards these trapped electrons. The typical sensitivity of this resist to electron beam irradiation (10 kV) is in the range of 10-5-10-'C/cm2. Higher sensitivity is achieved at lower accelerating voltages because the probability of interaction between the thin film and low energy electrons (stopping probability) increases. Furthermore, when resists are combined as described above, it is possible to reduce the gloximity deformation effect that has been a hindrance to standard thick film organic resists at high exposure energies.

Inorganic resists are subject to higher levels of development and have also been found to be non-swellable, non-deformable, non-contrastive, compatible with dry processes, and at their inherent limits. It can be resolved with a certain 1ooXt. GeSe or GeSe/Ag25o inorganic resist is
It is resistant to oxygen plasma and therefore allows ultra-fine patterns in a thin inorganic resist layer to be formed in the thick film below that layer. The IJ imide layer can be accurately transferred by oxygen RIEK, thus allowing high aspect ratio vertical/
A 4' turn can be formed.

Inorganic resists allow the use of many exposure regimes due to their sensitivity to UV, electron beams and X-rays. However, in the case of electron beam 7i light, the 1E charge diffusion layer that was required on polyimide when using an organic resist is unnecessary when using an inorganic resist, and therefore this point combines with the ease of oxygen RIE. As a result of this, the processing process becomes advantageous. eye? A'turning the reinforcing layer using Gene inorganic resin simply applies Gene to the polyimide by vapor deposition, then exposes Ga55 through a suitable photomask, plasma develops, and removes any unwanted particles. It consists only of the step of removing polyimide by oxygen RIE. Therefore, when compared to organic resinous processes as described above, at least three processing steps can be omitted: baking, titanium deposition, and lift-off in a solvent.

The method of the present invention has been described above with respect to a double ring of a desired shape using ring graphie. From the above description, it will be understood that various modifications and improvements in the arrangement and arrangement on the substrate surface may be made when carrying out the method of the invention.
Additionally, the use of polyimide can provide superior edge quality compared to conventional methods.

[Brief explanation of the drawing]

FIG. 1 shows Ag 2 S e/Ge S according to the present invention.
A schematic cross-sectional view showing "photodoping" of the e-resist and FIGS. 2 to 12 are cross-sectional views sequentially illustrating the manufacturing of an optical waveguide mirror according to the present invention. In the figure, 1 is a 29141 layer, 2 is a LiNbO3 substrate, 3 is a charge diffusion layer, 4 is an electron beam resist layer, 5 is an undercut, 6 is a titanium evaporated film, 7 is an aluminum evaporated N film,
And 8 is a groove. Patent Applicant International Standard Electric Corporation Patent Attorney Akira Ikuki Patent Attorney Kazuyuki Nishidate Patent Attorney (1) Yukio Patent Attorney Akira Yamaguchi Patent Attorney Masaya Nishiyama 2h”+ Ag2 Se - Ichibutsu 2Ag ”+ Se~・
1. Nata > Katsuchiko Kagami Grain

Claims (1)

[Claims] 1. A method for forming a concavo-convex pattern on the surface of a substrate, the method comprising forming a masking/mother turn on the surface of the substrate, and then ion beam milling the surface of the substrate through nine turns of the masking. 1. A method for forming a main turn, the method comprising: a step of forming a main turn, wherein the masking turn is made of a mask material having ion beam resistance. 2. The pattern forming method according to claim 1, wherein the mask material is polyimide. 3. The pattern forming method according to claim 1 or 2, wherein the substrate is lithium niobate (LjNbO,). 4. A layer of polyimide is attached to the surface of the substrate, a resist layer is applied to the formed polyimide layer, and a desired polyimide mask P No. 4? is applied to the resist layer. The pattern forming method according to claim 2 or 3, characterized in that the polyimide masking pattern is characterized by providing a notch turn corresponding to the turn and transferring the masking toe turn to the polyimide layer. . 5. The IQ turn forming method according to claim 4, wherein the resist layer is made of an organic resist material. 6. Apply nine turns of the masking pattern to the titanium layer using a patterned organic resist layer, and reactively ion-etch the polyimide layer with oxygen through the formed titanium mask to convert the masking pattern into polyimide. The pattern forming method according to claim 5, wherein the pattern is transferred to a layer. 7. The four-turn forming method according to claim 5 or 6, wherein the organic resist material is polymethyl methacrylate and the resist material is exposed by electron beam irradiation. 8. The mother turn forming method according to claim 5 or 6, wherein the organic resist material is a photoresist, and the resist material is exposed to ultraviolet irradiation. 9. The turn forming method according to claim 4, wherein the resist layer is made of an inorganic resist material. 10. The inorganic resist material is Ga5e or Ga55/
The method for forming a groove or turn according to claim 9, which is made of Ag 2 Se. 11. The method according to claim 9 or 10, wherein a pattern is formed on the inorganic resist material by exposing the inorganic resist material to electron beams, ultraviolet rays or X-rays, and performing plasma development. How to form a turn. 12. The pattern forming method of claim 11, wherein the pattern is transferred from the developed inorganic resist material to the polyimide layer by reactive ion etching of the polyimide with oxygen. 13. The method for forming a /stone according to any one of claims 1 to 12, wherein the ion beam milling of the substrate comprises bombardment with argon ions. 14. The four-turn forming method according to any one of claims 1 to 12, wherein the ion beam milling of the substrate comprises bombardment with reactive ions. 15. The pattern forming method according to any one of claims 2 to 14, wherein the polyimide masking pattern is removed with oxygen plasma after ion beam milling. 16. Irregularities formed on the substrate after ion beam milling Any one of claims 2 to 14, wherein at least one surface of the turn is metallized to have a mirror surface.
・The method for forming a turn as described in Section 1.