JPS6137779B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a fine and highly accurate metal pattern having a thickness of 0.5 μm or more.

In recent years, with the miniaturization of semiconductor devices, there has been a need to form fine patterns with high precision. especially,
In the X-ray lithography technology, which is attracting attention as a new technology that enables high-precision transfer of fine patterns including line widths of around 1 μm or less, any transfer pattern including the above-mentioned fine patterns can be transferred, for example. An X-ray lithography mask made of a metal such as Au that absorbs soft X-rays and has a thickness of at least 0.5 μm is essential. Conventionally, the transfer pattern on an X-ray lithography mask is created by sequentially depositing an X-ray absorbing layer consisting of a metal layer and a resist film on an X-ray lithography mask substrate, and using an electron beam exposure method or a normal photolithography technique. A desired pattern is formed by drawing or transferring it onto the resist film, and the exposed area of the metal layer is etched away by ion milling using this resist pattern as a mask, or by electron beam exposure. X using the method
After forming a resist pattern on a line lithography mask substrate, depositing a metal as an X-ray absorbing layer on the resist pattern by vacuum evaporation method,
A so-called lift-off method is used in which the resist pattern is removed and the metal deposited in the openings of the resist pattern is left behind to form a desired pattern, or a conductive metal is placed on the X-ray lithography mask substrate in advance. A thin metal film is deposited, a resist pattern complementary to the desired transfer pattern is formed on the metal thin film using electron beam exposure or photolithography, and this resist pattern is used as a mask to form the resist pattern. One of two methods was used: depositing metal on the openings of the substrate by electroplating and removing the resist pattern to form a desired metal pattern. Among these, metal patterns formed by pattern forming methods using ion milling have the disadvantage that the slope of the sidewalls is gentle. This method is inappropriate as a method for forming a transfer pattern of an X-ray lithography mask which requires a sidewall having a large diameter. In addition, in the case of the lift-off method, in order to obtain a desired transfer pattern made of metal, a resist pattern with a thickness greater than that of the metal pattern to be formed is formed, and its cross section exhibits an inverted trapezoidal shape. In other words, it must be formed in a so-called undercut state. wavelength is 4000
The cross-sectional shape of the resist pattern formed by ordinary photolithography technology using ultraviolet rays of about 100 Å as the transfer medium is trapezoidal or has a wide base.
It is almost impossible to apply photolithographic techniques to the lift-off method. In order to avoid this difficulty, when forming a metal pattern using the lift-off method, the resist pattern is formed using an electron beam exposure method, which reduces the scattering of the electron beam in the resist and the scattering of the electron beam from the substrate. Use this to obtain a pattern that is rather undercut. Although it is certainly possible to form a metal pattern with steep sidewalls in this way, it has the drawback of requiring a long exposure time. Also,
In the transfer pattern forming method using the electroplating method described above, the shape of the metal pattern deposited using the resist pattern as a mask already faithfully reflects the shape of the resist pattern, so as in the case of the lift-off method, Conventional photolithography techniques cannot achieve the desired pattern precision. Therefore, conventionally, when forming fine and highly accurate metal patterns by electroplating, electron beam exposure is used to strictly control the electron beam diameter, current amount, accelerating voltage, development conditions, etc. The first problem was to form a resist pattern with walls perpendicular to the substrate. However, in the electron beam exposure method, the energy of the electron beam that irradiates the resist film is several times
It is very large, ranging from KeV to several tens of KeV, and has a large scattering effect in the resist and from the substrate, so it is not easy to form a desired pattern shape in a thick resist layer with good reproducibility. Also,
The electron beam exposure method requires a long exposure time, which is a major drawback in terms of productivity.

An object of the present invention is to provide a method in which the formation of thick film fine metal patterns, which has conventionally been accompanied by many difficulties, can be easily and reproducibly performed as described above. To achieve this objective, it is important to faithfully convert a fine resist pattern formed by electron beam exposure or optical exposure into a thick metal pattern. In order to solve this problem, the present invention employs the following steps. That is, first, a conductive metal thin layer is deposited on a substrate, a silicon nitride layer having a thickness of 0.5 μm or more is deposited on the conductive metal thin layer by a plasma CVD method, and a silicon nitride layer is deposited on the silicon nitride layer. A resist is applied to the surface, the resist film is formed into a desired pattern by an electron beam exposure method or an optical exposure method, and the portions of the silicon nitride layer exposed in the openings of the resist pattern are etched using the resist pattern as an etching mask. A part of the surface of the conductive metal thin layer is exposed by etching and removal using a dry etching method such as plasma etching or reactive sputter etching, and the silicon nitride layer is deposited on the exposed surface of the conductive metal thin layer. The procedure is to deposit a desired metal by plating so as to fill the opening, and then remove the remaining resist pattern and silicon nitride layer by etching.

Hereinafter, a typical embodiment of the present invention will be described in detail using the drawings.

First, as shown in FIG. 1, a conductive metal thin layer 12 of, for example, Au is deposited on the surface of a substrate 11 on which a desired thick film fine metal pattern is to be formed by RF sputtering, vacuum evaporation, or ion plating. tens of Å to several hundred Å depending on thin film formation methods such as
The film is formed to have a film thickness of . Next, as shown in FIG. 2, plasma is applied onto the surface of the conductive metal thin layer 12.
A silicon nitride layer 13 with a thickness of 0.5 μm or more is deposited by CVD. Next, as shown in FIG. 3, a resist is applied onto the surface of the silicon nitride layer 13, and a predetermined fine pattern is drawn or transferred onto the resist layer by electron beam exposure or optical exposure. form. Next, as shown in FIG. 4, using the resist pattern 14 as a protective film, the openings of the resist pattern are exposed by a dry etching method such as a plasma etching method using CF ₄ gas or a reactive pattern etching method. The silicon nitride layer is etched away to expose the surface of the conductive layer 12.
In this dry etching step, it is important to faithfully convert the planar dimensions and shape of the resist pattern 14 into a silicon nitride pattern 13'. It is easy to obtain good results using a parallel plate type plasma etching apparatus. Silicon nitride deposited by plasma CVD is generally hydrogen fluoride or _CF4
The etching rate of dry etching methods such as plasma etching and reactive sputter etching using fluorine compound gases is high, and the etching rate is several to several tens of times that of silicon nitride deposited by vapor phase growth. Because it is etched at a speed several times faster than silicon dioxide formed by thermal oxidation, thick silicon nitride layers can be patterned as desired while preserving the shape of the resist pattern used as a protective film for etching. , is advantageous for the purposes of the invention. The present invention actively utilizes this property. By doing so, a sufficiently thick silicon nitride layer 13 can be patterned with extremely high precision. The thus obtained thick film pattern 13' has a rectangular cross-sectional shape, and its planar dimensions are the same as those of the resist pattern 14. As shown in FIG. 5, a thick film pattern 1 formed of the silicon nitride
Using mask 3', a desired metal is formed by plating to fill the opening of the thick film pattern 13' to a desired thickness. As a plating method, an electroplating method is usually used, but it is of course possible to use an electroless plating method. Since the metal layer deposited in this manner almost directly reflects the cross-sectional shape of the pattern used in the mask, a thick film fine metal pattern 15 having a rectangular cross-sectional shape complementary to the pattern can be easily formed. After that, the resist pattern 1 used as a mask
4 is removed using a predetermined resist stripping solution, an organic solvent, or the like, or by plasma etching using oxygen gas. Next, the thick film pattern 13' formed of silicon nitride is removed by wet etching using hydrofluoric acid or phosphoric acid, or by plasma etching using fluorine compound gas such as _CF4 or reactive sputter etching. The etching is removed by a dry etching method such as the method.
At this time, the previously formed metal pattern 15 is hardly etched and remains as it is. FIG. 6 shows this state. If the conductive metal layer used as the base layer is an obstacle during plating, it can be etched away by reactive sputter etching or plasma etching using a gas such as CCl ₂ F ₂ or the like. It can be etched away by ion beam etching using an inert gas such as Ar. The thickness of the conductive metal layer to be etched at this time is at most several tenths of the thickness of the metal pattern 15.
5 can be removed without damaging the shape.

[Brief explanation of the drawing]

Each figure from FIG. 1 to FIG. 6 is a schematic cross-sectional view of a workpiece showing each manufacturing process in a typical embodiment of forming a thick film fine metal pattern according to the present invention. . In the figure, 11 is a substrate, 12 is a conductive metal thin layer, 1
3 is a silicon nitride layer formed by a plasma CVD method, 13' is a pattern formed from a part of the silicon nitride layer 13, 14 is a resist pattern, 15
indicate the desired thick-film fine metal pattern, respectively.

Claims (1)

[Claims] 1. A step of depositing a conductive metal thin layer on a substrate, a step of depositing a silicon nitride layer having a thickness of 0.5 μm or more on the conductive metal thin layer by plasma CVD method, and a step of depositing a silicon nitride layer with a thickness of 0.5 μm or more on the conductive metal thin layer. A step of applying a resist on the layer and forming the resist film into a desired pattern by an electron beam exposure method or an optical exposure method; etching away a part of the surface of the conductive metal thin layer by dry etching using the etching mask as an etching mask, and patterning the silicon nitride layer on the exposed surface of the conductive metal thin layer. The method is characterized by comprising the steps of depositing a desired metal by plating so as to fill the opening, and etching away the remaining resist pattern and silicon nitride layer. A method for forming thick film fine metal patterns.