JPH07176770A - Membrane structure and its manufacture and microdevice using membrane structure - Google Patents

Abstract

PURPOSE:To provide a micro device with improved characteristics and yield manufactured by a method for manufacturing a membrane structure by providing the method which can manufacture the membrane structure with an improved thickness accuracy with a high yield. CONSTITUTION:A process for forming a recessed part at a first substrate 101, a process for performing epitaxial growth of silicon 108 on one surface after forming a porous part 107 reaching a reverse side from a front on at least one part of a second substrate which is silicon, a process for joining the first substrate and the above second substrate by allowing the recessed part to oppose the epitaxial silicon layer 108, and a process for eliminating the porous part 107 after the joint are included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon membrane structure, a manufacturing method thereof, and a microdevice having the membrane structure manufactured by the manufacturing method.

[0002]

2. Description of the Related Art Conventionally, a technique for producing a membrane structure by selective etching of silicon has been proposed and used for producing a pressure sensor, a piezoresistive element and the like.

A conventional method for manufacturing a membrane structure will be briefly described below.

FIG. 7A shows an example in which a difference in etching rate due to impurity concentration is used. First, a high-concentration boron-doped layer (p ⁺ layer) 602 having a predetermined thickness is formed on one surface of a (100) silicon substrate 601 by an ion implantation method, and the other surface is made of a silicon nitride film, a silicon oxide film, or the like. A mask 603 is formed.

Then, silicon is etched in an etching solution such as a potassium hydroxide solution or an ethylenediaminepyrocatechol (EDP) solution. These solutions are
The etching rate depends on the impurity concentration, and the etching rate of the p ⁺ layer is several tenths lower than that of the n layer and the p layer. Therefore, when the heavily boron-doped layer 602 is reached, the etching is substantially stopped and a thin membrane structure of silicon is formed.

Further, FIG. 7B shows an example using an etch stop at the p / n junction surface. An n layer 605 having a predetermined thickness is formed on one surface of the (100) p-type silicon substrate 604 by an ion implantation method, an epitaxial growth method, or the like. A mask 603 made of a silicon nitride film, a silicon oxide film or the like is formed on the non-etched portion. The substrate is sealed so that the back surface (n layer side) of the substrate is not exposed to the etching solution, and silicon is etched in an etching solution such as potassium hydroxide or EDP solution. This time,
Etching is performed while applying a positive potential to the n-layer side and a negative potential to the electrode provided in the etching solution. When the p layer is removed by etching and reaches the n layer 605, an anode current flows and a silicon oxide film is formed on the surface of the n layer. The formation of the oxide film stops the etching and forms a thin membrane structure of silicon.

[0007]

However, the above-mentioned conventional manufacturing method has the following problems.

In the method of forming the high-concentration impurity-doped layer, since the impurity concentration has a concentration distribution in the thickness direction, the thickness of the obtained membrane varies and the thickness accuracy is not good.

In the method using the p / n junction, the passivation potential (oxidation on the silicon surface is caused by the subtle changes and variations in the temperature of the etching solution and the stirring state and the composition change of the etching solution due to the dissolution of silicon. Since the potential at which the film is formed changes and varies, it is difficult to control the potential and the manufacturing yield is not good.

Further, since a voltage has to be applied to the silicon n-layer, extra process steps such as an electrode forming and removing process increase, which causes an increase in cost and a decrease in yield.

[Object of the Invention] The present invention has been made to solve the above problems, and an object of the present invention is to provide a manufacturing method capable of manufacturing a membrane structure having excellent thickness accuracy with a good yield. To provide.

Another object of the present invention is to provide a microdevice manufactured by the method for manufacturing a membrane structure of the present invention.

[0013]

As a means for solving the above-mentioned problems, the present invention provides a step of forming a recess in a first substrate, and at least a part of a second substrate made of silicon, from front surface to back surface. After forming a porous portion reaching the surface of the first surface, epitaxially growing silicon on one surface, a step of facing the concave portion and the epitaxial silicon layer, and joining the first substrate and the second substrate; The method for producing a membrane structure according to claim 1, further comprising a step of removing a portion, a membrane structure produced by the method, and a microdevice having the membrane structure.

[0014]

According to the present invention, the difference in etching rate between the porous silicon portion and the non-porous silicon portion is as high as the power of 10 5. An extremely high membrane structure can be manufactured with high yield.

Further, according to the present invention, since the first substrate can be made of a material other than silicon, it is possible to form the membrane portion having extremely high film thickness accuracy on a material other than silicon. .

[Embodiment Example] A method for manufacturing a membrane structure of the present invention will be described below with reference to FIG.

As shown in FIG. 1A, the first substrate 101
A mask material 102 is formed on both sides of the film and patterned to form an opening 103 for etching.

Next, this substrate is etched to form a recess (FIG. 1B), the mask material 102 is removed, and the recess shown in FIG.
The state of (c) is obtained. Silicon, glass, metal, ceramics or the like is used as the first substrate. When the first substrate is silicon, a hydrofluoric nitric acid solution, a potassium hydroxide solution, a sodium hydroxide solution, an ethylenediaminepyrocatechol solution, a tetramethylammonium hydroxide solution, or the like can be used as the etching solution. At this time, a silicon oxide film, a silicon nitride film, or the like can be used as the mask material 102. When the first substrate is glass, a hydrofluoric acid solution can be used as the etching solution, and a hydrofluoric acid-resistant resist film, a silicon nitride film, or the like can be used as the mask material. In the case of metals and ceramics, the etching solution and mask material are selected according to the materials.

On the other hand, as shown in FIG. 1D, a mask material 105 is formed and patterned on both surfaces of a silicon substrate 104 which is a second substrate, and an opening portion 106 for anodization is formed.
To form. As the silicon substrate 104, a p-type or a low-resistance n-type substrate is used. As the mask material, a polyimide film having high resistance to hydrofluoric acid, a high resistance silicon thin film, or the like is used.

Next, this substrate is subjected to anodization in a hydrofluoric acid solution to form a porous silicon portion 107 as shown in FIG. 1 (e).

FIG. 3 shows a schematic diagram of an anodizing apparatus.
In the figure, 201 is a second substrate, 202 is a mask material, 203 is an electrode, and 204 is a hydrofluoric acid-based solution. As the electrode 203, a material that is not corroded by the hydrofluoric acid solution, such as gold or platinum, is used. Concentrated hydrofluoric acid (49% HF) is generally used as the hydrofluoric acid-based solution 204. Further, alcohol may be added as a surfactant for the purpose of efficiently removing bubbles generated from the surface of the substrate during anodization. The maximum current value for anodization is several hundred mA / cm ² , and the minimum value is not necessarily zero. This value is determined within a range that allows good quality epitaxial growth on the surface of porous silicon. A preferable range is 1 to 200 mA, and more preferably 5 to 100 mA.
mA.

Next, after removing the mask material 105, as shown in FIG.
As shown in (f), a silicon layer 108 is epitaxially grown on one surface of the silicon substrate 104. The epitaxial growth is performed by a general thermal CVD method, a low pressure CVD method, a plasma CVD method, a molecular beam epitaxial method, a sputtering method, or the like. The film thickness to be grown is the design value of the thickness of the membrane part.

Next, as shown in FIG. 1G, the concave portion of the first substrate and the epitaxial silicon layer 108 of the second substrate are opposed to each other, and the first substrate 101 and the second substrate 104 are bonded to each other. When the first substrate 101 is made of silicon, the substrates may be stacked directly or with a silicon oxide film interposed therebetween.
Direct bonding can be achieved by heating to a temperature of 0 to 1100 ° C. Alternatively, they may be joined via an adhesive or the like.

Next, as shown in FIG. 2H, the second substrate 104 is mechanically polished to have a desired thickness. When the thickness of the second substrate is equal to the design value, no particular polishing is necessary.

Next, as shown in FIG. 2 (i), the porous silicon portion 107 is removed by etching to form a membrane structure. The etching solution for the porous silicon portion 107 is hydrofluoric acid or
At least 1 of hydrofluoric acid, alcohol, and hydrogen peroxide
It is advisable to use a mixed solution in which the types are added. Such an etching solution can selectively etch porous silicon efficiently and uniformly without etching non-porous silicon.

In particular, by adding alcohol, the bubbles of the reaction product gas due to the etching can be instantly removed from the etching surface without stirring, and the porous silicon can be uniformly and efficiently etched.

Further, in particular, by adding hydrogen peroxide water, the oxidation of silicon can be accelerated and the reaction rate can be increased as compared with the case where no hydrogen peroxide is added, and the ratio of hydrogen peroxide water can be further changed. Thus, the reaction rate can be controlled.

The hydrofluoric acid concentration is preferably set in the range of 1 to 95%, more preferably 5 to 90%, and further preferably 5 to 80% with respect to the etching solution.

The hydrogen peroxide concentration is preferably 1 to 95%, more preferably 5 to 90%, based on the etching solution.
%, More preferably 10 to 80%, and set within a range where the effect of the hydrogen peroxide solution is exhibited.

The alcohol concentration is set to preferably 80% or less, more preferably 60% or less, still more preferably 40% or less with respect to the etching solution, and within the range in which the effect of the alcohol is exhibited.

The temperature is preferably set in the range of 0 to 100 ° C, more preferably 5 to 80 ° C, and further preferably 5 to 60 ° C.

As the alcohol used in the present invention, in addition to ethyl alcohol, isopropyl alcohol and the like which can be practically used in the manufacturing process and which can be expected to have the above-mentioned alcohol addition effect can be used.

In FIG. 1, the porous silicon portion is removed by etching after joining the first substrate and the second substrate. However, when the hydrofluoric acid resistance of the first substrate is poor, the porous silicon portion is removed. The first substrate and the second substrate may be joined after the portions are removed by etching.

Although the second substrate is partially made porous in FIG. 1, the entire surface of the second substrate may be made porous.

Further, as shown in FIG. 2J, the third substrate 109 may be bonded to the second substrate 104 to form cavities above and below the membrane portion. As the third substrate 109, silicon, glass, metal, ceramics or the like can be used.

As described above, according to the present invention, since the etching rates of the porous silicon portion and the non-porous silicon portion differ by as much as 10 5 power, the film thickness accuracy is extremely high only by immersing in the etching solution. A high membrane structure can be manufactured with high yield.

Further, according to the present invention, it is possible to form the membrane portion having extremely high film thickness accuracy on a material other than silicon.

[0038]

The present invention will be described in more detail with reference to the following examples.

(Example 1) Thickness of 500 μm, (100)
Oriented n-type silicon single crystal substrate (first substrate) at 90 ° C
Etching was performed in a 30% by weight potassium hydroxide solution heated to the above to form a recess having a thickness of 250 μm. At this time, the mask has a thickness of 1500 formed by the LPCVD method.
A Å silicon nitride film was used.

On the other hand, a high resistance epitaxial silicon layer was formed on both surfaces of a low resistance p-type silicon single crystal substrate (second substrate) having a thickness of 200 μm by a low pressure CVD method to a thickness of 5000 Å. The growth conditions were: used gas: SiH ₄ / H ₂ temperature: 850 ° C. pressure: 1 × 10 ^-2 Torr growth rate: 3.3 nm / sec.

Then, on the epitaxial silicon layer,
The resist is patterned by lithography technology,
The exposed area of the epitaxial silicon layer was etched by a reactive ion etching method to form a mask for anodization. At this time, the mask was formed at the same position on the front and back surfaces.

Next, this substrate was anodized in a 49% hydrofluoric acid solution under the condition of a current density of 100 mA / cm ² to form a porous silicon part.

Next, after removing the mask for anodization,
A single crystal silicon layer is formed on the surface of the substrate by the CVD method at 5.0.
μm epitaxially grown. The deposition conditions are as follows.

Gas used: SiH ₄ / H ₂ Temperature: 750 ° C. Pressure: 80 Torr Growth rate: 0.12 μm / min. Next, these two silicon substrates were superposed with the recess and the epitaxial silicon layer facing each other, and heated at 1000 ° C. in a nitrogen atmosphere to bond them.

Next, after mechanically polishing the surface of the substrate so that the thickness on the side of the second substrate becomes 10 μm, the bonded substrate is immersed in an etching solution to selectively select only the porous silicon portion. Removed. At this time, the composition of the etching solution is 49% hydrofluoric acid: 30% hydrogen peroxide: ethanol =
It was set to 5: 25: 6.

In this example, since the single crystal silicon portion was hardly etched and only the porous silicon portion was selectively etched, it was possible to manufacture a membrane structure having extremely good thickness accuracy.

(Example 2) Next, an example of a pressure sensor manufactured by the method for manufacturing a membrane structure of the present invention will be described.

FIG. 4A is a plan view of the pressure sensor of this embodiment, FIG. 4B is a sectional view taken along the line AA 'of FIG. 4A, and FIG. It is sectional drawing in the BB 'line of (a). In the figure, 301 is a first substrate, 302 is a second substrate made of silicon, 303 is a membrane portion of epitaxial silicon, and electrodes 304 are provided on the surface of the membrane portion 303 and the concave portion of the first substrate 301 so as to face each other. And 305 are formed, and the membrane part 3 is formed.
The pressure applied to 03 is detected by the capacitance change between electrodes 304 and 305. Reference numeral 306 is a lead electrode, and 307 is a lead electrode lead portion.

The method of manufacturing the pressure sensor of this embodiment will be briefly described below.

A high resistance n-type silicon single crystal substrate (first substrate 301) having a thickness of 200 μm and a (100) orientation was etched in a 30 wt% potassium hydroxide solution heated to 90 ° C. to form a recess having a thickness of 50 μm. . At this time, as the mask, a silicon nitride film with a thickness of 1500 Å formed by the LPCVD method was used.

Next, after patterning for electrode formation is performed to remove the silicon nitride film in the electrode formation portion, phosphorus (P) is injected and diffused to form the electrode 305 and the lead electrode 3.
06 was formed.

On the other hand, a high resistance epitaxial silicon layer is formed on both surfaces of a low resistance p-type silicon single crystal substrate (second substrate 302) having a thickness of 200 μm by a low pressure CVD method at a pressure of 5000Å.
Formed.

After that, the epitaxial silicon layer was partially removed by a lithography method and a reactive ion etching method to form a mask for anodization. At this time, the mask was formed at the same position on the front surface and the back surface.

Next, this substrate was immersed in a 49% hydrofluoric acid solution.
Anodization was performed under conditions of a current density of 30 mA / cm ² to form a porous silicon part.

Then, the mask for anodization was removed, and an epitaxial silicon layer was formed on the surface of the substrate under the same conditions as in Example 1 to a thickness of 5.0 μm.

Next, after forming a silicon thermal oxide film having a thickness of 1000 Å as an insulating layer on the epitaxial silicon layer, a gold film was formed by a sputtering method and etched into a predetermined shape to form an electrode 304.

Next, the first substrate 301 and the second substrate 302 were superposed with the concave portion and the epitaxial silicon layer facing each other, and heated at 1000 ° C. in a nitrogen atmosphere to bond them.

Next, this laminated substrate was treated with 49% hydrofluoric acid: 3
The pressure sensor of this example was manufactured by immersing it in a mixed solution of 0% hydrogen peroxide: ethanol = 5: 25: 3 and selectively removing only the porous silicon part.

In this embodiment, the electrode 304 is a metal electrode, and the electrode 305 and the lead electrode 306 are impurity diffusion electrodes, but the present invention is not limited to this, and the electrodes 304 and 305 and the lead electrode 306 are not limited to this. You may form by the method of.

Example 3 Next, an example of an optical element manufactured by the method for manufacturing a membrane structure of the present invention will be described.

FIG. 5 is a perspective view of the optical element of this embodiment. In the figure, 401 is a first substrate, 402 is a second substrate made of silicon, 403 is an epitaxial silicon membrane portion, and 404 is an electrode. . When a voltage of several tens of volts is applied between the electrode 404 and the silicon membrane portion 403 placed at intervals of several tens of μm, the silicon membrane portion 403 is bent by electrostatic force. By controlling the applied voltage, an optical element or the like having a variable focal length can be manufactured.

This is, for example, by forming a light reflecting film on the membrane portion to form a light reflecting mirror and bending it
An optical system whose focal length can be changed can be used.

The basic structure of the optical element of this example is the same as that of Example 2, and can be manufactured by the same method as in Example 2.

(Example 4) Next, an example of a micropump manufactured by the method for manufacturing a membrane structure of the present invention will be described.

FIG. 6A is a plan view of the micropump of this embodiment, and FIG. 6B is a sectional view taken along the line AA 'of FIG. 6A. In the figure, 501 is a first substrate, 502 is a second substrate made of silicon, 503 is an epitaxial silicon membrane part, 504 is a third substrate, 505 and 506 are electrodes, 507 is a lead electrode, 508 is a lead electrode lead part. , 509 is a fluid inlet, 510 is a fluid outlet,
511 is a fluid.

The fluid 511 is injected from the fluid injection port 509 and filled between the second substrate 502 and the third substrate 504. By controlling the voltage between the electrode 505 formed on the membrane portion 503 and the opposing electrode 506 and vertically vibrating the membrane portion 503, the fluid 511 can be ejected from the fluid ejection port 510.

The micropump of this embodiment can be used for transporting fluid in a microflow cell or the like, or for a head of an ink jet printer or the like.

The micropump of this embodiment is manufactured by the same manufacturing method as that of the first embodiment or the second embodiment.
It can be manufactured by forming a membrane structure composed of a bonded body of the first and second substrates 502 and then bonding the third substrate 504 having the fluid injection port 509 formed by etching. Glass, silicon, or the like can be used as the third substrate 504.

[0069]

As described above, according to the present invention, by utilizing the etching selectivity between porous silicon and non-porous silicon, it is possible to manufacture a membrane structure having extremely high film thickness accuracy with good yield. Is obtained.

Further, the method for manufacturing a membrane structure of the present invention can be widely applied to microdevices such as pressure sensors, optical elements and micropumps, and the yield can be similarly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for manufacturing a membrane structure of the present invention.

FIG. 2 is a diagram showing a method for manufacturing a membrane structure of the present invention.

FIG. 3 is a schematic diagram of an anodizing apparatus used in the present invention.

4A and 4B are views showing a structure of a pressure sensor according to an embodiment of the present invention, FIG. 4A is a plan view of the pressure sensor, and FIG.
4A is a sectional view taken along the line AA ′ in FIG.
Sectional drawing in the BB 'line of (a).

FIG. 5 is a perspective view of an optical element that is an embodiment of the present invention.

6A and 6B are views showing a structure of a micropump according to an embodiment of the present invention, FIG. 6A is a plan view of the micropump, and FIG. 6B is a sectional view taken along the line AA ′ of FIG. 6A.

FIG. 7 is a diagram showing a conventional method for manufacturing a membrane structure.

[Explanation of symbols]

101, 301, 401, 501 First substrate 102, 105, 202 Mask material 103, 106 Opening 104, 201, 302, 402, 502 Second substrate 203 Electrode 204 Hydrofluoric acid solution 107 Porous silicon part 108, 303, 403, 503 Epitaxial silicon layer 109, 504 Third substrate 304, 305, 404, 505, 506 Electrode 306, 507 Lead electrode 307, 508 Lead electrode extraction part 509 Fluid injection port 510 Fluid ejection port 511 Fluid

Claims (7)

[Claims] 1. An epitaxial silicon film of a first substrate having a concave portion and a second substrate bonded on the hollow portion of the concave portion, wherein the epitaxial silicon film has a porous portion on the film. A membrane structure characterized by being a thinned membrane portion removed. 2. A step of forming a recess in a first substrate, a step of forming a porous portion reaching from the front surface to the back surface on at least a part of the second substrate made of silicon, and then epitaxially growing silicon on one surface. And a step of bonding the first substrate and the second substrate to each other, the concave portion and the epitaxial silicon layer facing each other, and a step of removing the porous portion. A method for producing the described membrane structure. 3. The method for manufacturing a membrane structure according to claim 2, including a step of bonding a third substrate on the second substrate. 4. A microdevice having the membrane structure according to claim 1. 5. The microdevice according to claim 4, further comprising: the membrane portion; and means for measuring the amount of strain generated in the membrane portion by the pressure applied to the membrane portion. 6. The microdevice according to claim 4, further comprising means for causing the membrane section to bend and an optical system for varying the focal length by the deflection. 7. The microdevice according to claim 4, further comprising: a unit that causes a bend in the membrane unit; and a unit that sucks and / or discharges a fluid by the bend.