JPH0482750A - Silicon substrate having porous silicon oxide layer - Google Patents

Abstract

PURPOSE:To form a porous silicon oxide layer partially at a surface layer part while minimizing a local warping on the rear side thereof by forming a periphery of a layer comprising outward. CONSTITUTION:A silicon substrate 30 has a POS layer 31 formed partially at a surface layer part thereof 30. A planar shape of the POS layer 31 is made square with corners thereof rounded. A periphery of the POS layer 31 is so formed as to be thinner outward. As the silicon substrate 30 is so formed that an outer circumference of the POS layer 31 gets thinner outward, an internal stress associated with an increase in volume is not concentrated on one part in the formation of the POS layer 30 but it is dispersed in a wide range, which allows the silicon substrate 20 to become gentle in the warping on the rear side thereof. This enables the fixing of the silicon substrate 30 accurately with a vacuum chuck and further makes it practicable without fear of breaking when it contacts a photo mask.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to substrates for thermal heads, optical ICs, optical switches, etc. that constitute thermal transfer printers and thermal printers;
In other words, it relates to a silicon substrate that can be suitably used as a substrate that requires both heat insulation and heat dissipation properties, and a method for manufacturing the same, in particular a silicon substrate in which the heat storage layer, heat insulation layer, etc. of the thermal head is formed of porous silicon oxide. The present invention relates to a substrate and a method for manufacturing the same.

"Conventional technology" FIG. 1O shows a conventional thermal head.

This thermal head has a heat storage layer &j2 made of glass glaze partially formed on an alumina substrate l.

A heating resistor layer 3 is formed on the heat storage layer 2 and the substrate l. On this heating resistor layer 3, this s3
A conductor layer 4 is formed for supplying current to. The conductor layer 4 and the resistor layer 3 form a heat generating portion 6 in the shape of a dot. A protective layer 5 is laminated on these to protect them from oxidation and wear.

This thermal head is used in contact with a recording medium (not shown) such as an ink ribbon or thermal paper.

When a current is applied to the heat generating section 6 of the thermal head to generate heat, the ink on the ink ribbon can be thermally transferred or the recording medium can be colored.

As the second method for improving the thermal efficiency of the thermal head, there is a method of increasing the heat storage amount by increasing the heat capacity by thickening the heat storage layer 2 made of glass glaze.

However, when the heat storage layer 2 made of glass glaze is made thicker in this manner, the time required for the temperature to drop after heat generation becomes longer, resulting in a problem that the thermal responsiveness of the thermal head is impaired.

In order to improve the thermal efficiency of the thermal head while avoiding such problems, it is preferable to provide a heat storage layer with low thermal conductivity and low heat capacity.

As a material that can form such a heat storage layer, porous silicon oxide (Porous Oxidized 5il) is used.
icon (hereinafter abbreviated as POS) is known. P.O.
S has high heat resistance and sufficient mechanical strength.

As a thermal head in which a heat storage layer is formed using POS, there is one proposed in JP-A-63-257652. This thermal head, as shown in Fig. 11,
The heat storage layer 12 formed by POS is attached to the silicon substrate 1.
It is formed over the entire surface of 1. And this P
A non-porous silicon oxide layer 1 is provided on the heat storage layer 12 made of O5.
3. A heating resistor layer 3, a conductor layer 4, and a protective layer 5 are sequentially laminated.

As a method for manufacturing the silicon substrate 11 that forms this thermal head, an electrolytic solution consisting of hydrofluoric acid, alcohol, and water (
The silicon substrate 11 is anodized in a hydrofluoric acid aqueous solution to form porous silicon.
A method is known in which a layer made of PS (hereinafter abbreviated as PS) is formed and then this layer made of PS is thermally oxidized.

By the way, in the silicon substrate 11, the volume increases by about 22 times when PS is thermally oxidized to PO3, so internal stress (compressive stress) remains in the formed heat storage layer I2, and the silicon substrate +1 There is a problem that it warps greatly.

When the substrate 11 is actually manufactured, a layer (
When the heat storage layer 12) is formed to have a thickness of 25 μm, the substrate 11
warps 1 mm per inch. This warpage is about 10 times that of a commercially available alumina ceramic substrate. Because such large warpage occurs, the silicon substrate 11 lacks practicality.

The inventors of the present invention have conducted extensive research to solve this problem, and have discovered that the problem can be solved by interspersing the surface of the silicon substrate 11 with a layer made of porous silicon oxide.

FIG. 12 shows a silicon substrate for a thermal head that was initially produced by the inventors.

In this silicon substrate, a porous silicon oxide layer (hereinafter referred to as PO3 layer) 26 having a rectangular planar shape is partially formed on the surface of the silicon substrate 20.

This silicon substrate 20 has a portion where a POS layer is to be formed (
The silicon substrate 20 is manufactured by covering the surface of the silicon substrate 20 with a mask made of tantalum oxide or the like, except for a portion to be processed (hereinafter referred to as a treated portion), and anodizing the mask in an aqueous hydrofluoric acid solution.

If the heating resistor layer 3, conductor layer 4, and protective layer 5 are sequentially laminated on this silicon substrate 20, the thermal head shown in FIG. 13 can be obtained.

The silicon substrate 20 has the advantage that warping of the entire substrate can be significantly improved.

However, in the silicon substrate 20, 208 layers 2
6..., and if the width of the porous silicon oxide layer 26 becomes 0.5 mm or more or the thickness becomes 10 μm or more, as shown in FIG. The back side of 20 is a porous silicon oxide layer 26
There is a large depression at the outer periphery of... For this reason, this silicon substrate 20 may not be fixed by a vacuum chuck during exposure processing or the like. Also, if the photomask comes in contact with the photomask during exposure, the silicon substrate may crack.

SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon substrate in which a porous silicon oxide layer is partially formed on the surface layer, and the local warpage on the back side is also extremely small.

"Means for Solving the Problems" A silicon substrate having a porous silicon oxide layer of the present invention is formed such that the peripheral edge of the layer made of porous silicon oxide becomes gradually thinner toward the outside. be.

The method for manufacturing this silicon substrate is to cover the surface of the silicon substrate with a mask except for the portion to be treated for forming the 208 layer, and then anodize the silicon substrate in an aqueous solution of hydrofluoric acid. A preferred method is to generate porous silicon in the uncovered portion to be treated, and then oxidize the formed porous silicon.

As the mask, a photoresist or an oxide film is preferably used.

As the photoresist, one with excellent acid resistance is used. Photoresists with excellent acid resistance are mainly composed of cyclized hydrocarbon polymers such as cyclized butadiene rubber-based polymers (e.g., cyclized polybutane) and cyclized isoprene rubber-based polymers (e.g., cyclized polyisoprene). A negative resist for mesa etch or the like is preferably used. When this type of organic film is used, the adhesion of the organic film to the silicon substrate is moderately weak, so some electrolyte may enter under the mask during anodization, causing the anodization to occur shallowly below the edge of the mask. Ru. As a result, a porous silicon oxide layer is naturally formed whose peripheral edge becomes gradually thinner toward the outside.

Further, as the oxide film, tantalum oxide (TayOs) is used.
A film made of chromium oxide (crzos) or a film made of chromium oxide (crzos) are preferably used. This type of film has strong adhesion to the silicon substrate, and the electrolyte does not penetrate under the mask during anodization, so it is necessary to obtain a porous silicon oxide layer whose peripheral edge gradually becomes thinner toward the outside. It is preferable to form a thin layer on the surface of the silicon substrate that is easily anodized or eroded during anodizing treatment.

The method of oxidizing porous silicon to make porous silicon oxide involves heating the substrate to 850°C or more in an atmosphere containing oxygen.
A thermal oxidation method in which the substrate is heated to ~1000°C or a method in which the substrate is exposed to plasma can be suitably used.

Note that materials that can be used as a mask when manufacturing the silicon substrate of the present invention include the tantalum oxide, chromium oxide,
The material is not limited to photoresist, and various passive films and insulators that are not attacked by hydrofluoric acid, such as silicon nitride and sialon, can also be used. When a silicon nitride film or a sialon film is used as a mask, pattern formation and removal of the silicon nitride can be performed by dry etching. In addition, materials for masks that are not attacked by hydrofluoric acid include molybdenum (Mo) and tungsten (
W) can also be used. When Mo or W is used as a mask material, it is desirable to form the mask thick.

"Function" In the silicon substrate of the present invention, the layer made of PO5 is formed so as to gradually become thinner toward the outside, so that the internal stress due to the increase in volume when forming the 208 layer is reduced to 1. It is released over a wide area without being concentrated in one spot.

"Example" (Example) FIG. 1 shows an example of a silicon substrate of the present invention.

This silicon substrate 30 has a POS layer 3I partially formed on the surface layer of the silicon substrate 30. The planar shape of this PO8 layer 31 is a rectangle with rounded corners. As shown in an enlarged view in FIG. 3, the peripheral edge of this PO9 layer 31 is formed so as to become gradually thinner toward the outside.

Next, a method for manufacturing this silicon substrate 30 will be explained with reference to FIGS. 4 to 7.

(2) To manufacture this silicon substrate 30, first, the silicon substrate 30 shown in FIG. 4 was prepared. As this substrate 30, a P-type substrate with a resistivity of 0.01ΩcIIl was used.

5 Next, as shown in FIG.
1: manufactured by Nippon Synthetic Rubber Co., Ltd.) was applied and patterned by photolithography.

■ Next, a 20vt% hydrofluoric acid aqueous solution was placed in an electrolytic cell with a platinum plate as a cathode, and anodization was performed for 16 minutes at a current density of 50 mA/cm'' DC with the silicon substrate 30 as an anode. As shown in the figure, the depth at the opening of the photoresist 32 is 32 μm, and the porosity is 80.
% PS layer 33 was formed.

The periphery of the formed PS layer 33 slightly invaded the portion covered with the photoresist 32. The depth of this part is
The depth gradually became shallower as the distance from the opening of the photoresist 32 increased.

(2) Next, the photoresist 32 was removed to obtain the state shown in FIG. The photoresist 32 could be easily removed using a commercially available stripping solution, hot sulfuric acid (sulfuric acid + hydrogen peroxide solution).

■ After this, thoroughly wash and store in humidified oxygen for 85 minutes.
Thermal oxidation was performed at 0°C to 1000°C to oxidize the PS layer 33. This oxidation increased the volume of the PS layer 33 and formed a 208 layer 31 protruding from the surface of the substrate 30 (number ff in the first figure). The periphery of this POS113I gradually became thinner toward the outside. The height of the PO5 layer 31 is 3
It was ~5 μm.

Further, on the surface of the silicon substrate 30 around this POS layer 31, as shown in FIG. 3, a 5IO2 layer 24 having a thickness of 0.2 to 0.5 μm was formed.

After that, a heating resistor layer 3, a conductor layer 4,
By sequentially laminating the protective layers 5, the thermal head shown in FIG. 8 is obtained.

In this silicon substrate 30, since the outer peripheral portion of the 208 layer 31 is formed so as to become gradually thinner toward the outside, internal stress due to the increase in volume when forming the PO9 layer 30 is absorbed in one place. It is not concentrated in one area but is dispersed over a wide area. Therefore, this silicon substrate 20 has a gentle warpage on the back surface side. This silicon substrate 30 can be reliably fixed by a vacuum chuck, and is practical because there is no fear of it breaking when a photomask is brought into contact with it.

(Other Manufacturing Example 1) Next, another example of the method for manufacturing the silicon substrate shown in the above embodiment will be described.

In this manufacturing method, first, as shown in FIG. 9, a thin damaged layer 35 is formed on the surface of a prepared silicon substrate 30. The damaged layer 35 can be formed by irradiating ions of an inert gas such as argon. Specifically, the pressure is 1.0
In an argon atmosphere of about
It can be formed by sputtering the surface of the silicon substrate 30.

After forming the damage &i30 in this way, a mask made of tantalum oxide is formed, and then the same processing as Moeki's process ① to ② is performed, and the silicon substrate 2 shown in FIG. 1 is formed.
0 can be manufactured.

In this manufacturing method, since there are many lattice defects in the damaged layer 35, the damaged layer 35 is severely eroded during the anodization treatment, and a portion below the peripheral edge of the mask is also anodized. Therefore, according to this manufacturing method, even if a mask made of tantalum oxide with strong adhesion to the substrate 30 is used,
It is possible to manufacture a silicon substrate 30 of.

Note that in this manufacturing method, as a means for forming the damaged layer 35, a method of exposing the silicon substrate 30 to plasma of argon or oxygen ions, a method of irradiating the silicon substrate 30 with an ion beam, etc. can also be adopted.

Furthermore, as a mask, one made of chromium oxide, a negative resist film, etc. can be used.

Furthermore, in addition to the above-mentioned argon, helium, neon, etc. can also be used as the inert gas.

(Other Manufacturing Example 2) In this manufacturing method, the surface of a prepared silicon substrate 30 is first doped with holon or aluminum at a high concentration to form a layer.

A method of doping the surface of the silicon substrate 30 with poron is to dope the surface of the silicon substrate 300 with poron. The surface of the silicon substrate 30 is coated with a high-concentration diffusion agent of poron (for example, PBP coating liquid manufactured by Tokyo Ohka Co., Ltd.), and
Holon oxide (B) generated on the surface after diffusion at 00℃
, o 3) There is a method to remove the film.

Further, as a method of diffusing aluminum onto the surface of the silicon substrate 30, sputtering etc. can be used to spread aluminum to a thickness of 500 to 5000
After forming a human aluminum film, it was heated for 70 minutes in a vacuum.
Heat to 0-1200°C to diffuse aluminum,
A preferred method is to then remove the aluminum remaining on the surface.

After forming the fco layer doped with poron or aluminum in this manner, a mask is formed and anodization treatment is performed in the same manner as in the manufacturing method described above.

In this manufacturing method, the surface doped with boron or aluminum has a small resistance value and is preferentially anodized.
The lower portion of the peripheral edge of the mask, which has strong adhesion to the silicon substrate 30, is also shallowly anodized. As a result, according to this manufacturing method, even if a tantalum oxide mask or the like is used, a silicon substrate 20 having 108 layers 26 whose outer periphery gradually becomes thinner toward the outside can be manufactured.

Effects of the Invention-1 As explained above, the silicon substrate having the porous silicon oxide layer of the present invention is formed such that the peripheral edge of the layer made of porous silicon oxide becomes gradually thinner toward the outside. Therefore, the internal stress that accompanies the increase in volume when forming the porous silicon oxide layer is not concentrated in one place but is dispersed over a wide range.

Therefore, the silicon substrate of the present invention has a small warp on the back side. Moreover, the silicon substrate of the present invention can be securely fixed by a vacuum chuck, and is also practical because there is no fear of it breaking when a photomask is brought into contact with it.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a silicon substrate having a porous silicon oxide layer according to the present invention. FIG. 2 is a plan view showing the same embodiment. FIG. 3 is an enlarged view showing section A in FIG. 1. 4 to 7 are cross-sectional views for explaining each step of a method for manufacturing a silicon substrate having a porous silicon oxide layer according to an embodiment. FIG. 8 is a cross-sectional view showing one thermal head manufactured using the silicon substrate of the embodiment. FIG. 9 is a sectional view showing the - step of (Other Manufacturing Example 1). FIG. 10 is a sectional view showing a conventional thermal head formed of a heat storage layer or glass glaze. FIG. 11 is a sectional view showing a conventional thermal head in which the heat storage layer is formed of porous silicon oxide. FIG. 12 is a sectional view showing a silicon substrate previously proposed by the present inventors. FIG. 13 is a sectional view showing a thermal head using the same silicon substrate. FIG. 14 is a cross-sectional view illustrating problems with conventional silicon substrates. 30...Silicon substrate, 31...Porous silicon oxide layer (POS layer). Figure 4

Claims (1)

[Scope of Claims] A silicon substrate having a porous silicon oxide layer in which a layer made of porous silicon oxide is partially formed on a surface portion of the silicon substrate, wherein a peripheral portion of the layer made of porous silicon oxide is A silicon substrate having a porous silicon oxide layer formed so as to gradually become thinner toward the outside.