JPH06267926A - Etching process and electrostatic micro switch using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] An etching process of an electrostatic microswitch using a silicon nitride film that is strong against temperature changes and temperature stimuli and has high resistance to etching by hydrofluoric acid and mechanical stimuli, and the process. The electrostatic microswitch with good reproducibility and flexibility obtained by [Structure] The stress of the silicon nitride film is set to 3 × 10 ⁹ dyn /
A step of forming a patterned silicon oxide film and a patterned polycrystalline silicon film on the substrate at a cm ² or less, and etching the silicon oxide film using the silicon nitride film formed under the silicon oxide film as an etching stop layer (and the silicon oxide film). The film is formed by the sputtering method, or the silicon nitride film is formed by the low pressure chemical vapor deposition method), thereby providing an electrostatic microswitch with good reproducibility and flexibility.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a specific etching process used to obtain an electrostatic microswitch and an electrostatic microswitch obtained using the process.

[0002]

2. Description of the Related Art Conventionally, extremely small mechanical sensors, actuators, etc. have been formed on a semiconductor substrate by using a semiconductor process such as photolithography. A typical micromachine is a micromotor (M. Mehregany et al.
al., “Operation of microfabricated harmonic and
ordinary side-drive motors ”, Proceedings IEEE Mic
ro Electro Mechnical Systems Workshop 1990 pp.1-8
) And linear microactuator (WCTang et a
l., “Laterally Driven Polysilicon Resonant Microst
ructures ”, Senser and actuator 20 (1989) pp.25-32
) Etc. have been proposed. By using these micromachines, arraying and cost reduction are facilitated, and higher precision is possible.

In order to form these micromachines, the sacrificial layer etching technique is a characteristic and important technique for manufacturing an actuator or the like, which is not found in the semiconductor process. Several μ
The sacrifice layer undercut having a thickness of about m is etched to reach the bottom of the structure and be removed.

At present, in order to form a polycrystalline silicon structure like the above actuator, a method using a silicon oxide film as a sacrificial layer and hydrofluoric acid as an etching solution, and a micromirror using an aluminum structure as a resist are used. As a sacrifice layer, a method for producing by removing oxygen plasma ashing (Japanese Patent Laid-Open No. 2-8812) and a method for producing a switching element with a silicon oxide structure, a single crystal silicon as a sacrifice layer, and potassium hydroxide as an etching solution (KEPetersen “Dynamic Micromechanics Silicon: Te
chniques and Devices ”vol.ED-25 no.10 (1978) p.124
1) (Fig. 10) and the like have been proposed. The material of the structure used in each case determines what is used for the sacrificial layer and the etching solution.

Of these, the polycrystalline silicon structure is suitable for micromachines such as actuators because it is relatively easy to form a fine structure and has a large Young's modulus and yield stress. Usually, when forming a polycrystalline silicon structure, silicon oxide is used for the sacrificial layer, the sacrificial layer is removed by hydrofluoric acid, and a silicon nitride film is used as the sacrificial layer etching stop layer.

This silicon nitride film has the advantages of serving as an etching stop layer, preventing the diffusion of moisture and Na ⁺ , having a good insulating property, and having a good film uniformity. However, on the other hand, there is a drawback that the internal stress is large.
For this reason, when the temperature is not sufficiently controlled during lamination or sacrifice layer etching, the nitride film is cracked or peeled off due to external stimuli such as thermal stress due to the difference in thermal expansion coefficient from other laminated films. There was a problem of doing.

Further, after the completion of etching, the cracks may spread or peel off due to latent microcracks in the film, stimulation by running water during cleaning, temperature change, or the like. Therefore, it is difficult to manufacture a polycrystalline silicon structure having a high yield and good reproducibility because the silicon oxide film as an insulating layer is also etched or the film is peeled off together with the polycrystalline silicon structure.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to avoid the above-mentioned problems, to be resistant to temperature changes and temperature stimuli, and to withstand etching by hydrofluoric acid and mechanical stimuli. An object of the present invention is to provide an etching process of an electrostatic microswitch using a resistant silicon nitride film and an electrostatic microswitch obtained by using the etching process.

[0009]

In order to achieve the above-mentioned object, the present invention has the following constitution. That is, a first aspect of the present invention is an etching process using a silicon nitride film as an etching mask or an etching stop layer, wherein the stress of the silicon nitride film is 3 × 10 ⁹ dyn / cm ² or less. And also
Secondly, after forming a sacrificial layer silicon oxide film and a patterned polycrystalline silicon film on the substrate, the silicon oxide film is etched using the silicon nitride film formed under the silicon oxide film as an etching stop layer. In the process, the stress of the silicon nitride film is 3 × 10 ⁹ dyn /
cm ² or less is the etching step according to the first aspect, and the third is the etching step characterized in that the silicon oxide film serving as the sacrificial layer is formed by a sputtering method. Is the etching process according to the first or second aspect, wherein the silicon nitride film is formed by a low pressure chemical vapor deposition method, and the fifth is a substrate covered with the silicon nitride film to be an etching stop layer. A fixed lower electrode, a movable electrode plate, one of which is fixed and supported through a gap, a switch movable electrode through an insulating film, a switch fixed electrode, and a drive unit, and the drive unit moves the movable electrode plate. Deflection, the tip of the switch movable electrode is lowered, contact the switch fixed electrode and the switch movable electrode and the switch fixed electrode become conductive, Drive means and a electrostatic force generated by applying a voltage between the fixed lower electrode and the movable electrode plate, the stress of the silicon nitride film, 3 × 10 ⁹ dyn /
The electrostatic microswitch according to the fifth aspect is characterized in that it is not more than cm ² , and the sixth is the electrostatic microswitch according to the fifth aspect, characterized in that the substrate is a silicon substrate on which a silicon oxide film is formed. The seventh is the fixed lower electrode,
The movable electrode plate, the movable electrode for the switch and the fixed electrode for the switch are made of polycrystalline silicon, and the void is formed by the silicon oxide film. After forming the movable electrode plate and the electrode for the switch, the silicon nitride film is used as an etching stop layer. The electrostatic microswitch according to the fifth aspect is characterized in that it is formed by etching away silicon oxide.

When the electrostatic microswitch structure having the above structure is formed by the process having the above characteristics, the silicon nitride film serves as a sacrificial layer etching stop layer and undergoes thermal expansion during film formation or heat treatment. There is no need to consider temperature stimuli such as. In addition, since it can withstand physical stimuli such as temperature changes during or after etching and during cleaning, there is no risk of cracking or peeling, and an electrostatic microswitch with a resistant silicon nitride film The etching step and the electrostatic microswitch obtained by using the etching step can be obtained.

[0011]

The details of the present invention will be explained based on the following examples and figures, but the present invention is not limited thereto.

Example 1 FIG. 1 shows a sectional view of an example (Example 1) that best shows the characteristics of the film structure of the polycrystalline silicon structure of the present invention. In the figure, 11 is a silicon substrate, 12 is a silicon nitride film, 13
Represents a polycrystalline silicon structure.

FIG. 2 shows a manufacturing process of the cantilever of Example 1. Normally, a silicon nitride film 22 is formed to a thickness of 150 nm on a silicon substrate 21 that does not have good adhesion to a silicon nitride film by low pressure chemical vapor deposition (FIG. 2A).
As film forming conditions, a mixed gas of SiH ₂ Cl ₂ and NH ₃ was used as a reaction gas, and the film was formed by changing the gas flow rate ratio. On top of this, a silicon oxide film 23 to be a sacrificial layer is formed with a film thickness of 2 μm.
Then, it is formed by sputtering and patterned by photolithography (FIG. 2B).

A polycrystal silicon film 24 is formed on this by a low pressure chemical vapor deposition method to a film thickness of 2 μm and patterned by photolithography (FIG. 2C). Finally, 5
After soaking in 0% hydrofluoric acid for 15 minutes to remove the sacrificial layer, it was soaked in pure water for 3 minutes and washed with running water. The silicon nitride film 22 was formed by the low pressure chemical vapor deposition method, the substrate temperature was 850 ° C., a mixed gas of SiH ₂ Cl ₂ and NH ₃ was used as a reaction gas, and the flow rate was 20 ccm / 0 to 60 ccm.

The film produced was a laser micro-displacement measuring instrument (made by IONIC SYSTEMS, trade name stress gauge auto cal.
The stress was measured with model no.30114). Figure 3 (a),
The relationship between the flow rate ratio and the stress of the silicon nitride film actually manufactured is shown in (b). It can be seen that the stress increases as the NH ₃ flow rate ratio increases. Using these films, the polycrystalline silicon cantilever of Example 1 was manufactured. Table 1
The state of the nitride film on the cantilever after fabrication is shown together.

[0016]

[Table 1] In the table, (C) is compression and (T) is Tension.
Means In addition, ◯ means that no cracks are present, × means that cracks or peeling occur on the entire surface,
△ represents a cracked part.

The stress of the silicon nitride film is 1 × 10 ⁹ dyn
/ Cm ² and a film of 3 × 10 ⁹ dyn / cm ² cause cracks or peeling of the silicon nitride film even after washing with running water, even on a silicon substrate with poor adhesion. It never happened. However, 4 × 10 ⁹ dyn /
The cantilever cannot be produced with good reproducibility in the sample prepared in cm ² because cracks or peeling occurred during removal of the sacrificial layer with hydrogen fluoride or during washing with running water. In addition, the stress of the silicon nitride film is 8 × 10 ⁹ dyn
In the case of / cm ² , all the samples collapsed during the sacrifice layer etching.

From the above, in consideration of heat resistance, hydrofluoric acid resistance, strength against mechanical stimulation, etc., the nitriding layer having a film stress of 3 × 10 ⁹ dyn / cm ² or less is formed in the sacrificial layer etching stop layer. It turns out that silicon is suitable. As described above, by using the silicon nitride film according to the present invention, it becomes possible to fabricate a polycrystalline silicon structure with good reproducibility.

Although silicon is used as the substrate here,
Any material may be used as long as it can form the above silicon nitride film. Further, as a method for manufacturing the silicon oxide film to be the sacrifice layer, any method can be used as long as the film thickness can be controlled.

Furthermore, when a silicon oxide film containing impurities such as a phosphoric acid type silicon oxide film or a boric acid type silicon oxide film is used, it becomes more soluble in hydrofluoric acid, and the time for etching the sacrificial layer is shortened. It becomes possible.

As for the method for producing the silicon nitride film, there is no particular limitation on the method for producing it as long as the film thickness can be controlled and the stress can be controlled by the substrate temperature, the kind and flow rate of the reaction gas. However, in consideration of flatness and hydrofluoric acid resistance, a film formed by a low pressure chemical vapor deposition method is preferable. Of course, the manufacturing method of the polycrystalline silicon structure is not limited as long as the film thickness can be controlled.

Example 2 FIGS. 4 and 5 are sectional views of a cantilever in Example 2,
A manufacturing process diagram is shown. 41 is a silicon substrate, 42 is a silicon oxide film, 43 is a silicon nitride film, 44 and 4
Reference numeral 5 represents a polycrystalline silicon structure.

The manufacturing process of this structure will be described with reference to FIG. First, a silicon oxide film 52 as an insulating film is formed on the silicon substrate 51 by thermal oxidation to a film thickness of 1 μm. A silicon nitride film 53 is deposited thereon to a film thickness of 300 nm by low pressure chemical vapor deposition. Since the influence of stress becomes more remarkable as the film thickness increases, it is usually difficult to obtain a film thickness of 300 nm. As the film forming condition, the substrate temperature is 8
At 50 ° C., the reaction gas was a mixed gas of SiH ₂ Cl ₂ and NH ₃ , and the flow rate ratio was changed to form a structure.

This silicon nitride film is patterned by photolithography. Further, the silicon oxide film is patterned using the patterned silicon nitride film as a mask (FIG. 5A). Polycrystalline silicon 54 is laminated thereon by low pressure chemical vapor deposition and patterned (FIG. 5B). Thereafter, as in the case of Example 1, a silicon oxide film 55 serving as a sacrificial layer is formed on this to a film thickness of 2 μm and patterned (FIG. 5C).

Further, a polycrystalline silicon structure 56 is formed (FIG. 5D), and the sacrificial layer 55 is removed (FIG. 5).
(E)). When this structure was formed by using a thick film with the same stress as in Example 1, the same stress of 1 × 1 was obtained.
In the case of 0 ⁹ dyn / cm ² and 3 × 10 ⁹ dyn / cm ^2, a cantilever was formed with good reproducibility, but 4 × 1
When it was more than 0 ⁹ dyn / cm ² , it was broken by cracking or peeling. From the above, it has become possible to produce a polycrystalline silicon structure with good reproducibility by using the silicon nitride film according to the present invention even with a silicon nitride film having a film thickness of 300 nm.

The produced cantilever can be used as an actuator using electrostatic force by applying a voltage between the substrate and the doped polycrystalline silicon. In addition to the insulating film formed on the substrate, a silicon oxide film may be used as long as the film can be controlled in thickness and can serve as an insulating film, but thermal oxidation is considered in consideration of good flatness and uniformity. A silicon film is preferred.

(Application Example) FIGS. 6 and 7 show a plan view and a sectional view of an electrostatic actuator manufactured by using a sacrifice layer etching technique. 61 and 62 are fixed electrodes, and the movable electrode of 63 is fixed by contact holes 64 and 64 ', which are configured to move using beams 65 and 65' as springs. When a voltage is applied between the fixed electrodes 61 and 62 and the movable electrode 63, an electrostatic attractive force is exerted, which causes the movable electrode 63 to move in parallel (FIG. 6).

As a manufacturing method, first, a silicon substrate 71
A silicon oxide film 72 is formed thereon as an insulating film to a film thickness of 1 μm. A silicon nitride film 73 of the present invention is formed thereon as a sacrifice layer etching stop layer by low pressure chemical vapor deposition. The film forming conditions are a substrate temperature of 850 ° C. and a flow rate of SiH.
20 sccm / 10 scc using ₂ Cl ₂ and NH ₃
m, and the stress was a tensile stress of 3 × 10 ⁹ dyn / cm ² . Next, the polycrystalline silicon 74 is formed to a film thickness of 300 n.
A film is formed on m and patterned.

This polycrystalline silicon is subjected to a conductive treatment by using a raw material containing a doping material as a reaction gas or by ion implantation after film formation. Next, a silicon oxide film 75 is formed as a sacrifice layer to a film thickness of 2 μm and patterned. Then, a polycrystalline silicon structure 7 on which a fixed electrode and a movable electrode are subjected to a conductive treatment is formed.
6 is formed (FIG. 7).

Finally, the sacrificial layer is removed with hydrofluoric acid to obtain an electrostatic actuator. The yield is improved by using the nitride film of the present invention. In addition to this, in the step of using a silicon oxide film as a sacrifice layer and a silicon nitride film as an etching stop layer in a micromotor, a micropump, etc., a structure can be formed with good yield by using the silicon nitride film of the present invention. Is possible.

(Application Example) FIG. 8 is a perspective view of the electrostatic micro switch, and FIG. 9 is a sectional view taken along the line AA ′ of FIG. When a voltage is applied between the fixed lower electrode 83 and the movable electrode plate 84 ', the movable electrode plate 84' bends due to electrostatic attraction. As a result, the fixed electrode 85 for switch and the movable electrode 86 for switch are brought into contact with each other, and 85 'and 86' are brought into conduction, and the switch O
The state becomes N.

The conventional electrostatic micro switch is formed by anisotropically etching single crystal silicon. Further, a p + epitaxial layer is used as the fixed lower electrode, a silicon oxide film is used as the movable electrode plate, and a metal thin film is used as the switch electrode. Therefore, the substrate is limited to silicon, and there is almost no freedom of shape. Further, since the lower side of the electrode plate becomes the lower electrode on the entire surface, even if a voltage is applied to the switch electrode, it is bent. Further, there is a problem in the resistance of the metal thin film used for the switch electrode to the single crystal silicon etchant.

A method of manufacturing this electrostatic switch will be described below. First, the silicon nitride film 82 of the present invention having a film thickness of 15 is formed on the silicon substrate 81 as a sacrifice layer etching stop layer.
The film is formed to 0 nm. The film forming conditions are a substrate temperature of 850 ° C. and a flow rate of SiH ₂ Cl ₂ / NH ₃ = 20 sccm / 5 scc.
m, and the stress was a tensile stress of 1 × 10 ⁹ dyn / cm ² . Next, as lower electrodes, polycrystalline silicon 83, 84, 8
5'and 86 'are formed to a film thickness of 300 nm.

A sacrifice layer silicon oxide film is formed and patterned to a film thickness of 1.5 μm thereon. Next, the movable electrode 8
4'and polycrystalline silicon to be the fixed electrode 85 for switches are formed to a film thickness of 1.5 .mu.m, and a second silicon nitride film 87 is formed and patterned on the movable electrode 84 '. The film forming conditions are the same as those for the first silicon nitride film, and the stress is a tensile stress of 1 × 10 ⁹ dyn / cm ² . Since this silicon nitride film 87 is also exposed to hydrofluoric acid, it is preferably the silicon nitride film of the present invention.

Further, a switch electrode 86 of polycrystalline silicon is formed on the silicon nitride film 87. Finally,
The sacrificial layer was removed with hydrofluoric acid, and an electrostatic microswitch was made of polycrystalline silicon. This is because the position and the shape of the fixed lower electrode can be freely designed to avoid the problem that the movable electrode plate is attracted to the substrate by applying a voltage to the switch electrode when it is formed using single crystal silicon. It can be avoided by

Since the switch electrode material is silicon, the durability is also improved. With the configuration of the present invention using the silicon nitride film of the present invention, it is possible to manufacture an electrostatic switch with high yield. Further, instead of forming the fixed lower electrode as the driving electrode, the substrate may be doped and used as the electrode.

[0037]

As described above, according to the etching process of the present invention, as the sacrificial layer etching stop layer necessary for forming the polycrystalline silicon structure, (1) thermal treatment such as heat treatment or polycrystalline silicon film forming temperature is performed. It is possible to obtain a silicon nitride film that is strong against stimuli, (2) has sufficient resistance to etching with hydrofluoric acid, and (3) has strong resistance to mechanical stimuli such as washing with running water.

As a result, the nitride film is not cracked or peeled off, and the polycrystalline silicon structure can be manufactured with good reproducibility. Further, the positions of the electrodes can be freely set, and it is possible to manufacture an electrostatic microswitch having a degree of freedom in shape.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a cantilever of Example 1.

2A to 2D are schematic views showing a manufacturing process of the cantilever of Example 1.

FIG. 3 is a diagram showing a relationship between a stress of a silicon nitride film and a gas flow rate during film formation.

FIG. 4 is a schematic cross-sectional view showing a cantilever of Example 2.

FIG. 5 is a schematic diagram showing a manufacturing process of a cantilever of Example 2.

FIG. 6 is a schematic plan view showing an electrostatic actuator of an application example of the present invention.

FIG. 7 is a schematic cross-sectional view showing an electrostatic actuator of an application example of the present invention.

FIG. 8 is a schematic perspective view showing an electrostatic micro switch of the present invention.

FIG. 9 is a schematic cross-sectional view showing an electrostatic microswitch of the present invention.

FIG. 10 is a schematic perspective view showing a conventional electrostatic micro switch.

[Explanation of symbols]

11, 21, 41, 51, 71, 81 Silicon substrate 12, 22, 43, 53, 73, 82, 87 Silicon nitride film 13, 24, 44, 45, 54, 56, 74, 76 Polycrystalline silicon structure 23 , 55, (75) Silicon oxide sacrificial layer film 42, 52, 72 Silicon oxide insulating layer film 61, 62 Comb-shaped fixed electrode 63 Comb-shaped movable electrode 64, 64 'Contact hole 65, 65' Beam (75) Void 83 Fixed lower electrode 84 ', 102 movable electrode plate electrode 85,103 switch fixed electrode 86,102 switch movable electrode 84,85', 86 'lower electrode 104 silicon oxide film 105 silicon epitaxial film 106 p + single crystal silicon

Claims (7)

[Claims] 1. In an etching process using a silicon nitride film as an etching mask or an etching stop layer, the stress (σ) of the silicon nitride film is given by: | σ | ≦ 3 × 10 ⁹ dyn / cm ² . An etching process characterized by the above. 2. A silicon oxide film to be a sacrificial layer and a patterned polycrystalline silicon film are formed on a substrate, and then the silicon oxide film is etched using the silicon nitride film formed below the silicon oxide film as an etching stop layer. In the step, an etching step characterized in that the stress (σ) of the silicon nitride film is: | σ | ≦ 3 × 10 ⁹ dyn / cm ² . 3. The etching process according to claim 2, wherein the silicon oxide film serving as the sacrificial layer is formed by a sputtering method. 4. The etching process according to claim 1, wherein the silicon nitride film is formed by a low pressure chemical vapor deposition method. 5. A movable electrode plate, one of which is fixed and supported with a fixed lower electrode via a gap, on a substrate covered with a silicon nitride film serving as an etching stop layer, and the movable electrode plate and a second insulating film. The movable electrode for the switch, the fixed electrode for the switch and the driving means, the movable electrode plate is bent by the driving means, the tip of the movable electrode for the switch is lowered, and the movable electrode for the switch and the switch are brought into contact with the fixed electrode for the switch. Is a static electricity generated by applying a voltage between the movable electrode plate and the fixed lower electrode, and the stress of the silicon nitride film ( σ) is the following: | σ | ≦ 3 × 10 ⁹ dyn / cm ² Electrostatic microswitch. 6. The electrostatic micro switch according to claim 5, wherein the substrate is a silicon substrate on which a silicon oxide film is formed. 7. The lower fixed electrode, the movable electrode plate, the movable electrode for a switch and the fixed electrode for a switch are made of polycrystalline silicon, and the void is formed of a silicon oxide film, and the movable electrode plate and the switch are formed. After forming the electrodes,
The electrostatic micro switch according to claim 5, wherein the silicon nitride film is formed by etching and removing the silicon oxide film by using the silicon nitride film as an etching stop layer.