JPH05302182A - Production of comb-shaped actuator - Google Patents

Abstract

PURPOSE:To control the interelectrode gap to the mum order by forming the combined comb-shaped movable electrode and fixed electrode from a substrate. CONSTITUTION:A silicon substrate 1 coated with an Al mask 4 or a silver oxide-film mask is dry-etched with a mixture of gaseous SF6 and O2 and worked. Consequently, the recesses 51 and 52 having a vertical side wall and a throughhole 53 are formed, and a comb-shaped actuator consisting of a movable part having optional shape and size and a fixed part is obtained. Further, a silicon oxide film as an etching stop layer is embedded in the substrate to attain higher-precision working.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a comb-tooth type actuator in which one silicon substrate is processed to be manufactured in a state where comb-shaped fixed electrodes and movable electrodes are combined.

[0002]

2. Description of the Related Art For example, a comb-tooth type actuator used for driving a mirror for scanning light is a comb-tooth type movable electrode formed integrally with a mirror 22 of a movable portion 21 as shown in FIG.
23 is a gap between the comb-teeth type fixed electrodes 25 of the fixing portion 24, and an enlarged view A
The fixed portion 24 supporting the movable portion 21 by the support portion 26 is attached on the glass substrate 27. Then, both electrodes 23 having the surface coated with an insulating film,
The movable part 21 is moved by the electrostatic force generated by applying a voltage between 25, and the mirror 22 is rotated. In such an actuator, the movable electrode 23 and the fixed electrode 25 are required to be close to each other with a gap of about 5 μm. Therefore, it is difficult to combine the separately processed movable part 21 and fixed part 24 so that the movable electrode 23 and the fixed electrode 25 mesh without deformation, and if possible, they are separated from one substrate by a gap of the order of μm. It is desirable to process in a combined state. For that purpose, it is possible to make it from a silicon substrate capable of fine processing.

A conventional method of manufacturing a silicon substrate in which both are processed and a comb-teeth type actuator of a predetermined size is assembled is as shown in FIG. 3 (a). The silicon oxide film 2 and the silicon nitride film 3 are deposited on both surfaces of the so as to expose the processed portion,
As shown in (b), first, the silicon substrate 1 is etched from the shallow digging side with an alkaline solution to form recesses, and then, as shown in FIG. It is intended to form a concave portion and a through hole by etching to form the mirror portion 22, the movable electrode 23 and the fixed electrode 25. Alternatively, as shown in FIGS. 4 (a), (b), and (c),
First, the deep digging side is processed in the same manner as described above, and then the shallow digging side is processed to manufacture a comb-tooth actuator.

[0004]

In the method of processing a silicon substrate by wet etching as described above, since a hydrofluoric acid-based solution is used as the etching solution, the etching proceeds isotropically and the rounded shape shown in the figure is formed. It can only be processed into a tight shape. This is unsuitable as a method for manufacturing a comb-tooth actuator in which the fixed electrode 25 and the movable electrode 23 are desired to be combined as close to each other as possible. Therefore, in order to form a vertical side wall, if processing is performed using an alkaline solution that utilizes the fact that the etching rate differs for each plane orientation of the single crystal silicon substrate, accurate processing can be performed according to the plane orientation. Since the shape depends on the plane orientation, it is difficult to form a comb-teeth type actuator having an arbitrary size and an arbitrary shape. Further, since the plane orientation of the silicon substrate is limited, there is a drawback that the limiting conditions are increased in design.

Furthermore, in wet etching, since the thickness of the mask is limited, deep etching cannot be performed, and it is necessary to protect the surface opposite to the side to be processed.
It is also difficult to provide protection against etching operations for deep processing. Therefore, wet etching has a drawback that it cannot be used for manufacturing comb-teeth type actuators that require deep processing.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a method for manufacturing a comb-teeth type actuator capable of processing a silicon substrate and simultaneously forming a fixed portion and a movable portion having predetermined dimensions with high accuracy. To provide.

[0007]

In order to achieve the above object, the present invention provides a comb-tooth type movable electrode and a comb-tooth type electrode which are combined through a narrow space by processing both surfaces of one silicon substrate. In the manufacturing method of the comb-teeth type actuator, which produces a movable part and a fixed part each having a fixed electrode of
The processing is performed by dry etching using a mixed gas of sulfur hexafluoride and oxygen. And even if the mask during dry etching consists of aluminum thin films on both sides,
Alternatively, it may be made of a silicon oxide film. It is also effective that only the mask used for processing the gap between the movable electrode and the fixed electrode is made of a silicon oxide film. Further, using a silicon substrate having two portions that are overlapped with each other with an etching stop layer made of a silicon oxide film, after forming a recess reaching both sides of the etching stop layer, the silicon of the etching stop layer remaining between the recesses is formed. It is also effective to remove the oxide film. The two portions stacked via the etching stop layer may both be made of single crystal silicon, and one may be made of single crystal silicon.
The other may be made of polycrystalline silicon.

In addition, when there is a difference in the opening area of the recess formed by dry etching from one surface of the silicon base, the portion where the recess having a large opening area is formed is not covered with the silicon base. Dividing into multiple etching areas by a mask with a narrow width that does not remain by side etching, or forming a recess with a large opening area and a recess with a small opening area in separate dry etching steps, and in each step It is effective to cover the part that is not processed by a mask.

[0009]

The reaction mechanism of the dry etching using the fitting gas of SF ₆ and O ₂ is described in Japanese Patent Application Laid-Open No. 2-298049 filed by the present applicant.
As described in JP-A-275626, the following can be considered. First, the respective reaction gases of SF ₆ and O ₂ are dissociated in plasma to generate F radicals and O radicals. Next, O radicals in the plasma react with Si atoms in the wet etching of the processed portion, and SiO 2 is produced as an intermediate product. This intermediate product, SiO, reacts with the F radical to produce SiF ₄ . Since this SiF ₄ has a very low boiling point, it naturally becomes a gas and is discharged to the outside of the reaction chamber. Silicon is processed by this reaction mechanism. At that time, since no reaction product remains, fine processing becomes possible. Then, the side wall of the formed recess is temporarily oxidized by O radicals and the like remaining in the plasma, and etching proceeds while the side wall of the recess is protected by the temporary oxide at this time. Since this state is maintained until a recess or through hole having a predetermined shape is formed in the silicon substrate, the side wall of the recess or through hole is perpendicular to the main surface of the silicon substrate.

Further, in such dry etching using a mixed gas of SF ₆ + O ₂ , the selection ratio between silicon and silicon oxide film is 100 or more. Therefore, reaching the silicon oxide film of the etching stop layer embedded in the silicon substrate of the recess formed by etching is detected by, for example, monitoring the emission spectrum intensity of plasma, and the point is used as a reference. By further overetching, it is possible to form a recess having a vertical sidewall of a predetermined size.

[0011]

Embodiments Some embodiments of the present invention will be described below with reference to the drawings. In the embodiment shown in FIGS. 1 (a) to 1 (c), first, a thin film made of aluminum having a thickness of about 1 μm is formed on both surfaces of a silicon substrate 1 having a thickness of about 300 μm. A mask pattern of the Al thin film 4 is formed on the Si substrate by using an etching solution such as phosphoric nitric acid so that the processed portion is exposed (FIG. 1 (a)). Next, etching is performed on each side by using a parallel plate type dry etching apparatus of an anodic coupling type as shown in FIG. This device is described in Japanese Patent Application Laid-Open No. 2-280324, which is a patent application of the applicant of the present invention. The lower electrode also serves as a stage in the reaction chamber 31.
32 and the upper electrode 33 are opposed to each other with a distance in the range of 5 to 100 mm. Exhaust pipes 35, which are distributed around the bottom plate 34 of the reaction chamber, are open toward the center of the lower electrode 32 in parallel with the bottom plate. Matching tuner 36 for upper electrode 33
A high frequency power supply 37 is connected via. A gap 40 between the top 38 of the reaction chamber 31 and the connecting body 39 of the upper electrode 33 serves as an inlet for the reaction gas 41. The lower electrode stage 32 in the reaction chamber 31 of such an anodic coupled parallel plate type dry etching apparatus.
The Si substrate 1 on which the Al mask pattern 4 as shown in FIG. 1 (a) is formed is placed thereon, and SF ₆ and O ₂ are placed in the reaction chamber 31.
The reaction gas 41 mixed at a ratio of 3 was introduced from the inlet 40, the pressure inside the reaction chamber 31 was maintained at about 50 Pa, and the pressure of about 1 W / cm ² was maintained between the lower electrode 32 and the opposed upper electrode 33. Apply high frequency power to expose exposed silicon and plasma 42
By causing a physicochemical reaction with the radicals and reaction gas ions remaining in the substrate, Si is removed from the processed portion of the substrate 1.
And the bottom portion 11 having a thickness of 1 μm is left on the Si substrate 1, and the recesses 51 and 52 having a predetermined size and vertical side walls are formed.
Are formed (FIG. 1 (b)). In the range mixing ratio of 0-60% of O ₂ in the mixed gas of SF ₆ and O _2, the pressure in the reaction chamber in the range of 5～150Pa, also RF power 0.3~2.0W
/ Cm ² can be selected. Next, the silicon substrate 1 is turned upside down so that the recesses 51 and 52 are located below.
On top, the Si substrate is processed in the same manner to form a through hole 53 having a predetermined size and a vertical sidewall (FIG. 1 (c)). As a result, the movable electrode 23 has a thickness of 10 μm and a width of 130 μm, a thickness of 20 μm, and a height.
It is possible to simultaneously form a plurality of comb-teeth type actuators having a movable part and a fixed part in which the fixed electrode 25 of 300 μm is combined with a gap of 10 μm. The movable mirror portion 22 is formed so as to face the concave portion 51.

In the above embodiment, the deep recess is first formed to form the recesses 51 and 52, and then the shallow recess is performed to form the through hole 53.
However, on the contrary, shallow digging may be performed first. The shallow excavation process with a depth of about 10 μm is performed by reactive ion etching using a dry etching system of the cathode coupling type.
It can also be processed by the (RIE) method. The fact that the processing order can be changed or the processing method can be changed is the same in each of the following embodiments.

In the embodiment shown in FIGS. 6 (a) to 6 (c), the mask pattern on the two surfaces is formed of the silicon oxide film 2 by an etching solution such as hydrofluoric acid, and the mask pattern on the other surface is Al.
It is formed of the film 4 (FIG. 6 (a)). Thus, the recesses 51 and 52 through holes 53 are processed in the same manner as the embodiment described with reference to FIG. 1 to form a comb-tooth type actuator having the movable electrode 23 and the fixed electrode 25 (FIGS. 6B and 6C). When the silicon oxide film 2 is used as a mask, the side etching amount is halved as compared with the Al mask. Therefore, as in this embodiment, the movable electrode 23 and the fixed electrode are
It is advantageous to use it as a mask for shallow excavation forming narrow and long through holes 53 between 25. Also, the mirror unit 22
When a semiconductor element is to be integrated with, an Al mask cannot be used, and therefore it is advantageous to use an insulating silicon oxide film. However, since the silicon oxide film 2 has a smaller selection ratio to Si in dry etching using a mixed gas of SF ₆ and O ₂ than Al, it is used in processing deep recesses or through holes in thick substrates. Although it cannot be used as a double-sided mask, it can be used as a double-sided mask when processing a silicon substrate having a thickness of about 200 μm or less.

FIGS. 7A to 7C show an embodiment using a silicon oxide film as an etching stop layer. In this case, the silicon layer 6 having a thickness of 1 μm is laminated on the silicon substrate 1 with the silicon oxide film 2 interposed therebetween. Such a substrate can be easily manufactured by bringing two single-crystal silicon plates into close contact with each other through an oxide film, heating and bonding them together, and then grinding them to a predetermined thickness if necessary. .. In this case, provide aluminum masks 4 on both sides
(Fig. (A)), deep digging as in the above embodiment (Fig. 7 (b))
When the shallow etching process (FIG. 7C) is performed, the selectivity in dry etching between silicon and the silicon oxide film is 100 or more, and etching from any surface stops at the silicon oxide film 2. Therefore, if the silicon oxide film 2 is thereafter removed by over-etching or the like, a comb-teeth type actuator having a fixed portion and a movable portion having a predetermined size and shape can be formed. Also in this embodiment, the thickness of the silicon substrate 1 is
When the thickness is 200 μm or more, it is also effective to form a mask on the shallow side for processing the silicon layer 6 with a silicon oxide film. If the thickness is 200 μm or less, the masks on both sides may be replaced with silicon oxide films.

In the embodiment shown in FIGS. 8A to 8C, a substrate having an etching stop layer of a silicon oxide film, for example, a silicon oxide film is formed on one surface of a silicon substrate 1 having a thickness of 300 μm. , And a polycrystalline silicon layer 7 having a thickness of 10 μm is laminated thereon. After that, aluminum film masks 4 are formed on both sides (FIG. 8A), and dry etching is carried out in the same manner as in the above-mentioned embodiment. As a result, a predetermined size and shape are obtained as in FIG. 7C. Recesses 51, 52,
Through holes 53 can be formed (FIGS. 8 (b) and 8 (c)).

When the comb-teeth type actuator is further downsized, the etching rate may be different at the portions having different areas to be etched during dry etching. That is, the etching rate of a portion having a large etched area may be higher than that of other portions. The effect is great, and uniform deep digging may be difficult. Therefore, in the embodiment shown in FIGS. 9A to 9D, the processed portion 8 having a large etching area for leaving the mirror portion is
The mask 4 is densely formed in advance so that the etching area is divided into a large number of narrow portions (FIG. 9A). Next, deep digging is performed under the same conditions as in the embodiment described with reference to FIG.
(FIG. 9 (b)). At this time, the portion 8 in which the etching area is finely divided in advance is processed faster than other portions, but since the mask pattern is dense, the narrow partition wall 9 does not remain, and the concave portion 51 having the predetermined size and the vertical side wall is formed. Formed (FIG. 9 (c)).
Then, in the subsequent shallow digging, the same shape as that in FIG. 7C is obtained (FIG. 9D). Further, when the etching stop layer of the silicon oxide film 2 is provided as shown in the figure, even if the etching rate partially varies due to the different areas to be etched,
This silicon oxide film has an advantage that it is sufficiently absorbed and a vertical recess having a predetermined size can be formed.

In the embodiment shown in FIGS. 10 (a) to 10 (e), the pattern of the Al mask 4 firstly provided on the deep digging side is not provided on the portion 8 having a large area to be etched (FIG. 10 (a)). ). Then, when deep digging is performed as in each of the embodiments, a large recess 51 is formed only in the portion 8 (FIG. 10 (b)). Next, the pattern of the Al mask 4 is formed also on other portions, and the inside of the recess is also formed.
A comb is formed by covering with an Al thin film 4 (Fig. 10 (c)), performing deep digging again to form a recess 52 (Fig. 10 (d)), and further forming a through hole 53 by shallow digging from the opposite surface. Obtain a toothed actuator (Fig. 10 (e)).

In the above-described embodiments shown in FIGS. 8, 9 and 10, it is needless to say that the Al mask 4 may be replaced with the single-sided or double-sided silicon oxide film mask 2 as described above.

[0019]

According to the present invention, by processing by dry etching using a mixed gas of SF ₆ and O ₂ ,
Since the reaction product does not remain and a recess or through hole with a vertical side wall can be formed, a comb-type actuator combining a movable electrode and a fixed electrode with a narrow gap is combined from one silicon substrate. The comb-teeth type actuator can be miniaturized according to the production demands of the sensor and the micromachine because it can be produced in an arbitrary size and shape in the state and there is a margin in the design. Further, by using a silicon oxide film as an etching stop layer, higher precision processing can be expected. In addition, since a large number of actuators can be uniformly formed simultaneously from a large-diameter silicon wafer, cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 shows a silicon substrate processing step according to an embodiment of the present invention.
Sectional views shown in order of (a) to (c)

FIG. 2 is a perspective view showing an outline of a comb-teeth type actuator.

FIG. 3 is a sectional view showing a conventional silicon substrate processing step in the order of (a) to (c).

FIG. 4 shows another conventional silicon substrate processing step (a) to (c).
Sectional view shown in order

FIG. 5 is a sectional view of a dry etching apparatus used in an embodiment of the present invention.

FIG. 6 shows a silicon substrate processing step of another embodiment of the present invention.
Sectional views shown in order of (a) to (c)

FIG. 7 shows a silicon substrate processing step of another embodiment of the present invention.
Sectional views shown in order of (a) to (c)

FIG. 8 shows a silicon substrate processing step of another embodiment of the present invention.
Sectional views shown in order of (a) to (c)

FIG. 9 shows a silicon substrate processing step according to another embodiment of the present invention.
Sectional views shown in order of (a) to (d)

FIG. 10 is a sectional view showing a silicon substrate processing step of another embodiment of the present invention in the order of (a) to (e).

[Explanation of symbols]

 1 Silicon Substrate 2 Silicon Oxide Film 21 Movable Part 22 Mirror Part 23 Movable Electrode 24 Fixed Part 25 Fixed Electrode 4 Aluminum Thin Film 51 Recessed 52 Recessed 53 Through Hole 6 Single Crystal Silicon Layer 7 Polycrystalline Silicon Layer

Claims (9)

[Claims] 1. A comb-tooth type for producing a movable part and a fixed part, each of which has a comb-tooth type movable electrode and a comb-tooth type fixed electrode, which are combined at a narrow interval by processing from both sides of one silicon substrate. A method for manufacturing a comb-teeth type actuator, wherein the manufacturing is performed by dry etching using a mixed gas of sulfur hexafluoride and oxygen. 2. The method for manufacturing a comb-tooth type actuator according to claim 1, wherein the masks on both surfaces during the dry etching are made of an aluminum thin film. 3. The method for manufacturing a comb-tooth type actuator according to claim 1, wherein the masks on both surfaces during the dry etching are made of a silicon oxide film. 4. A method of manufacturing a comb-tooth type actuator according to claim 1, wherein only a mask used for forming a gap between the movable electrode and the fixed electrode is made of a silicon oxide film. 5. A silicon substrate having two parts which are overlapped with each other with an etching stop layer made of a silicon oxide film is used, and after forming a recess reaching both sides of the etching stop layer, the etching stop remaining between the recesses is formed. The silicon oxide film of the layer is removed.
5. A method for manufacturing a comb-tooth type actuator according to any one of 1. 6. The method for manufacturing a comb-tooth type actuator according to claim 5, wherein both of the two portions overlapped with each other with the etching stop layer formed of single crystal silicon. 7. The method of manufacturing a comb-tooth type actuator according to claim 5, wherein one of the two portions stacked with the intermediate layer interposed therebetween is made of single crystal silicon and the other is made of polycrystalline silicon. 8. When the opening areas of the recesses formed by processing one surface of the silicon base by dry etching are different, the part where the recesses having a large opening area are formed is covered with the silicon base. 8. The method for manufacturing a comb-tooth type actuator according to claim 1, wherein the mask is divided into a plurality of etching regions by a mask having a narrow width that does not remain by side etching. 9. When there is a difference in the opening area of a recess formed by dry etching from one surface, a recess having a large opening area and a recess having a small opening area are formed in different dry etching steps. The method for manufacturing a comb-tooth actuator according to any one of claims 1 to 7, wherein a portion not to be processed in each step is covered with a mask.