JPH0562964A - Silicon substrate processing method - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to improve the processed shape accuracy when processing a silicon substrate by anisotropic etching using an alkaline solution. According to the present invention, a SiO ₂ film having portions having different thicknesses is used as an etching mask in a processing step of forming a groove, a through hole, a diaphragm, etc. in a silicon substrate by anisotropic etching using an alkaline solution, During the etching of the silicon substrate, the thinner portion of the SiO ₂ film was sequentially eliminated by etching, and the disappeared S
It is characterized in that a structure having a plurality of depths is formed in a silicon substrate by subsequently etching underlying silicon on the iO ₂ film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a silicon substrate by etching using an alkaline solution, and in particular, forming a groove, a through hole, a diaphragm, etc. on the silicon substrate,
The present invention relates to an etching method for producing a fluid control element such as a micropump or an inkjet printer head, a pressure sensor, or the like.

[0002]

2. Description of the Related Art In etching a silicon substrate with an alkaline solution, the etching rate varies depending on the crystal plane orientation.
So-called anisotropic etching becomes possible, for example (1
(00) Silicon substrate has (111) to (100) plane
Since the etching rate of the surface is extremely low, a smooth surface of (100) and (111) is obtained by etching. Therefore, various devices utilizing this characteristic have been devised. Then, in order to give these elements higher functions, it is required to process them into more complicated shapes.
As a conventional processing example, FIG. 6 shows a processing step diagram of an inkjet printer head. Silicon substrate 61
A thermal oxide film 62 is formed on the surface (FIG. 6A), and the thermal oxide film 62 is patterned into a shape corresponding to the ink flow path 65 by photolithography and hydrofluoric acid etching (FIG. 6A).
(B), the silicon substrate 61 is etched to a predetermined depth with an alkaline solution to form an ink flow path 65 (see FIG. 6).
(C)), a thermal oxide film 63 is formed on the entire surface by thermal oxidation (FIG. 6D), and the thermal oxide film 63 is similarly patterned into a shape corresponding to the ink ejection port 64 (FIG. 6).
(E)) Etching is performed until the discharge port 64 is formed by the alkaline liquid (FIG. 6 (f)).

[0003]

However, the above-mentioned prior art has the following problems. In the step (e) of FIG. 6, the ink channel 65 has already been formed in the silicon substrate 61, and the depth thereof is about 100 to 200 μm. It is very difficult to apply the resist uniformly, and especially since the thickness of the photoresist film is extremely thin at the convex portions 66, the underlying thermal oxide film is slightly etched during hydrofluoric acid etching, and during subsequent silicon etching. There is a problem that the upper portion of the ink flow path 65 is etched and a desired shape cannot be obtained. On the contrary, in the concave portion 67, the thickness of the photoresist film becomes extremely thick and the pattern exposure is performed with a distance of about 100 to 200 μm, so that the pattern accuracy is very poor and the resulting ejection port 64 is obtained. The shape precision of was also very poor. Such a problem is not limited to the example described here, and silicon is subjected to alkali anisotropic etching for several tens of times.
This is a problem that occurs when an element such as a pressure sensor is manufactured by etching to a depth of 0 micron. Therefore,
The present invention solves such a problem, and an object thereof is to improve the shape accuracy when processing a silicon substrate by anisotropic etching using an alkaline etching solution.

[0004]

A method of processing a silicon substrate of the present invention is a method of processing a silicon substrate in which a groove, a through hole, a diaphragm or the like is formed in the silicon substrate by anisotropic etching using an alkaline etching solution. , SiO ₂ having portions with different thickness as an etching mask
Using a film, during the etching of the silicon substrate, the Si
A structure having a plurality of depths is formed on a silicon substrate by sequentially removing portions of the O ₂ film having a smaller thickness by etching, and subsequently etching the underlying silicon of the removed SiO ₂ film. To do. Further, as a method of forming the SiO ₂ film having the portions having different thicknesses, thermal oxidation of the silicon substrate and patterning of the thermal oxide film are repeated a plurality of times, or S is formed on the silicon substrate.
forming an iO ₂ film and subjecting the SiO ₂ film to patterning including half-etching once or a plurality of times; or
A positive photoresist is applied on the SiO ₂ film, different patterns are formed on the positive photoresist a plurality of times, and selective etching including half etching is performed on the SiO ₂ film for each pattern formation. It is characterized by performing.

[0005]

EXAMPLE 1 Example 1 will be described in detail below based on the first example of the present invention. FIG. 1 shows a process drawing of the silicon substrate of the present invention. The present embodiment is an example of processing an inkjet printer head, in which an ink flow path 15 and an ink ejection port 14 are formed on a silicon substrate 11. A silicon substrate 11 having a crystal plane orientation of (100) and a thickness of 200 μm is subjected to 5 in an oxygen atmosphere containing water vapor.
It was heated to 1000 degrees Celsius for 0 minutes to form a 0.4-micron thermal oxide film 12 (FIG. 1A). The thermal oxide film 12 is patterned into a shape corresponding to the ink flow path 15 by photolithography and hydrofluoric acid etching (see FIG. 1).
(B)). Subsequently, the silicon substrate 11 is again heated in an oxygen atmosphere containing water vapor to perform thermal oxidation. The processing conditions are 900 ° C. and 50 minutes, and the portion corresponding to the ink flow path 15 is heated to 0.2 μm. The oxide film 13 is formed.
At this time, the thickness of the portion that had been 0.4 micron before the treatment also increased to 0.5 micron at the same time (Fig. 1).
(C)). Next, the thermal oxide film 13 is patterned into a shape corresponding to the ink ejection port 14 by photolithography and hydrofluoric acid etching (FIG. 1D). Next, silicon is etched with an alkaline solution. In this embodiment, as an alkaline solution, a KOH aqueous solution (KOH concentration 25
% By weight, 80 degrees Celsius) was used. Under the above conditions, the etching rate of silicon is 1.0 micron / minute,
The etching rate of the thermal oxide film is 0.002 micron / minute. Silicon substrate 11 made of the KOH aqueous solution
Was etched for 200 minutes. By the etching for 200 minutes, the ejection port 14 penetrates the silicon substrate 11 having a thickness of 200 μm. However, 100 minutes after the start of etching, the thermal oxide film 13 having a thickness of 0.2 μm corresponding to the ink flow path 15 is etched. Disappears and the underlying silicon substrate is exposed (FIG. 1 (e)), but this portion is etched by 100 microns in the subsequent 100 minutes of etching (FIG. 1 (f)). That is, FIG.
In the processes of (e) and FIG. 1 (f), the ejection ports 14 and the ink flow paths 15 of the inkjet printer head are collectively formed. Since this step does not include photolithography on a deep step as in the prior art, the patterning accuracy of the thermal oxide film that is the etching mask is very good, and therefore the etching shape of the silicon substrate is also as desired.

(Second Embodiment) A second embodiment of the present invention will be described below. FIG. 2 is a process drawing of the silicon substrate of the present invention. This embodiment is also an example of processing an inkjet printer head. A 200-micron-thick silicon substrate 21 having a crystal plane orientation of (100) was heated to 1000 ° C. for 70 minutes in an oxygen atmosphere containing water vapor to form a 0.5-micron thermal oxide film 22 (FIG. 2).
(A)). Next, a photoresist pattern having a shape corresponding to the ink flow path 25 is formed on the thermal oxide film 22 by photolithography, and the thermal oxide film 22 is half-etched to 0.3 μm by using a hydrofluoric acid-based etching solution. Etching is performed (FIG. 2B). Next, the thermal oxide film 23
A photoresist pattern having a shape corresponding to the ejection port 24 is formed thereon by photolithography, and the thermal oxide film 23 is etched using a hydrofluoric acid-based etching solution (FIG. 2).
(C)). The subsequent etching process of silicon with alkali is performed in the same manner as in the first embodiment to form the ejection port 24 and the ink flow path 25. In the present embodiment as well, as in the case of the first embodiment, since photolithography on a deep step unlike the conventional case is not performed, the desired etching shape of the silicon substrate is obtained without defects.

(Third Embodiment) The third embodiment of the present invention will be described in detail below. FIG. 3 shows a process drawing of the silicon substrate of the present invention. This example is an example of processing a micropump, and FIG. 4 shows a top view and a cross-sectional view of the micropump manufactured in this example. In FIG. 4, the structure of the micropump includes a silicon substrate 41 processed by the method for processing a silicon substrate of the present invention and two glass plates 42.
And 43, the structure is sandwiched between the suction side pipe 411 and the discharge side pipe 412. The operating principle is that the pressure in the pressure chamber 410 is changed by applying a voltage to the piezoelectric element 44 attached to the diaphragm 45 formed in the central portion of the silicon substrate 41 and causing the piezoelectric element 44 to bend. By displacing the suction side valve film 46 and the discharge side valve film 48 that are spatially continuous with the suction side valve 47 and the discharge valve 49, the fluid is pumped from the suction side pipe 411 to the discharge side pipe 412. is there. In FIG. 4B, the pressure chamber 410 and the space above the suction side valve membrane 46 and the space below the discharge side valve membrane 48 are continuous. next,
The process steps of the silicon substrate shown in FIG. 3 will be described. Polish both sides of (100) silicon wafer,
After the silicon substrate 31 having a thickness of 280 μm is formed, the silicon substrate 31 is subjected to heat treatment at 1100 ° C. for 4 hours in an oxygen atmosphere containing water vapor, and both sides of the silicon substrate 31 are made of SiO ₂ having a thickness of 1 μm. Membranes 34 and 3
5 is formed (FIG. 3A). Next, the silicon substrate 31
On the SiO ₂ film 34 formed on the one surface 32 of
Intake-side valve film 313, diaphragm 317, discharge-side valve film 3
Resist pattern 3 consisting of patterns corresponding to 15 etc.
6 is formed, and on the SiO ₂ film 35 formed on the other surface 33 of the silicon substrate 31, the suction side valve film 313, the suction valve 314, the diaphragm 317, the discharge side valve film 315, the discharge valve 316, etc. are formed. A resist pattern 37 composed of a pattern is formed, and the SiO ₂ film 34 is formed by a buffered hydrofluoric acid solution.
And 35 are half-etched. The etching amount was 0.92 μm, and etching was performed so as to leave the SiO ₂ films 38 and 39 of 0.08 μm. (Fig. 3
(C)). Next, on the SiO ₂ film 39 on the other surface 33, a through hole (not shown) that connects the through hole 318 and the pressure chamber 319 formed in the intake valve 314 with the space above the intake valve film 313. A resist pattern 310 having a pattern corresponding to is formed, a resist is applied to the entire surface on one surface 32 side (FIG. 3D), and the SiO ₂ film 39 is similarly etched with a buffer hydrofluoric acid solution. (Fig. 3
(E)).

Next, etching of silicon with an alkaline solution is performed. As in the first and second examples, etching was performed using a KOH aqueous solution having a concentration of 25% by weight and a temperature of 80 degrees Celsius. After 40 minutes from the start of etching, when a recess 312 having a depth of 40 μm and serving as a through hole 318 is formed, the thickness of the SiO ₂ films 38 and 39 is 0.08 μm before alkali etching. The existing portion disappears by etching, the underlying silicon of the SiO ₂ films 38 and 39 is exposed (FIG. 3 (f)), and the underlying silicon is continuously etched.
When the etching is performed for a minute, the concave portion 312 becomes a through hole 318, and the suction side valve film 313, the suction valve 314, the diaphragm 317, the discharge side valve film 315, the discharge valve 316, etc. are formed (FIG. 3 (g)).

In this embodiment as well, as in the first and second embodiments, since photolithography on a deep step like in the prior art is not performed, when the intake valve, the discharge valve, etc. are formed by etching. Since the mask pattern of the etching resistant material of can be accurately formed, in terms of the performance of the micro pump,
In particular, the shape of the intake valve, the discharge valve, etc., which requires shape accuracy, is accurately formed, and a micropump with good performance can be obtained.

(Fourth Embodiment) A fourth embodiment of the present invention will be described in detail below. Similar to the third embodiment of the present invention, this embodiment is a processing example of a micro pump, but in particular,
The method is characterized by a method of forming SiO ₂ films having different thicknesses that serve as etching masks. FIG. 5 shows a process drawing of the silicon substrate of the present invention. Similar to the third embodiment, 1-micron-thick SiO ₂ films 54 and 55 are formed on a 280-micron-thick silicon substrate 51 whose both surfaces are polished.
Positive type photoresists 56 and 57 are applied on the iO ₂ films 54 and 55 (FIG. 5A). Details of the coating conditions for the resist film are as follows. First, a resist solution having a viscosity of 50 cp is dropped on the SiO ₂ film 54 and 2500 rpm.
Spin coat at 100 degrees Celsius and pre-bake 1
This is performed for 0 minutes to form a resist film 56. Next, SiO ₂
Similarly, a resist is spin-coated on the film 55, and the temperature is 10 degrees Celsius.
Prebaking is performed at 0 ° C. for 30 minutes to form the resist film 57. At this time, the resist film 56 is prebaked for 40 minutes in total.

Next, the resist film 57 is subjected to pattern exposure and development corresponding to a through hole (not shown) that connects the through hole 520 and the pressure chamber 521 to the space above the suction side valve film 515, and the resist pattern 58 is formed. To form (Fig. 5
(B)), but no post bake is performed. The reason is that another pattern formation (exposure, development) is performed on the resist films 56 and 57 later. Then, the SiO ₂ film 55 is selectively etched with a hydrofluoric acid-based etching solution. 0.9 in the second hydrofluoric acid etching performed later
Since the etching is performed to 2 μm, the etching amount here may be 0.08 μm or more. In this embodiment, the etching amount is 0.1 μm, and the SiO ₂ film 59 of 0.9 μm is left (FIG. 5). (C)). Since the resist films 56 and 57 used as the etching mask for the hydrofluoric acid etching have not been subjected to baking (post-baking) at high temperature, the residual film portion does not peel off because it maintains the photosensitivity. Pattern processing by pattern exposure and development is performed. The resist film 56 is subjected to pattern exposure corresponding to the suction side valve film 515, the diaphragm 519, and the discharge side valve film 517, and the resist film 57 is subjected to the suction side valve film 515 and the suction valve 5.
16, pattern exposure corresponding to the diaphragm 519, the discharge side valve film 517, the discharge valve 518 and the like is performed, and then the resist films 56 and 57 are simultaneously developed to form resist patterns 510 and 511 (FIG. 5D). ..

Next, the second selective etching of the SiO ₂ film is performed with a hydrofluoric acid-based etching solution, and the etching amount is 0.92 μm as described above. At this time, the through hole 520 of the SiO ₂ film 55 and the pressure chamber 521
A portion corresponding to a through hole (not shown) connecting the suction side valve membrane 515 and the space above the suction side valve membrane 515 is completely etched, and the remaining etching portion has a remaining SiO ₂ film thickness of 0. It becomes 08 microns (Fig. 5 (e)). Figure 5
At the stage of (e), the SiO ₂ films 512 and 513 are respectively formed of Si of FIG. 3 (e) in the third embodiment of the present invention.
It has the same shape as the O ₂ films 38 and 39. Then, etching of silicon with an alkaline solution is performed. Since the subsequent steps are exactly the same as in the case of the third embodiment,
The description is omitted. The feature of the present invention is that the resist film is not applied once on the front and back surfaces of the silicon substrate,
This is to perform patterning of the SiO ₂ film a plurality of times.
In this embodiment, the pattern processing of the resist film is performed once on one surface (52 in FIG. 5) and twice on the other surface (53 in FIG. 5) depending on the structure of the micropump to be processed. Although performed, as described above, the positive resist film not subjected to the post-baking maintains the photosensitivity, so that the number of pattern processing is not limited to the number of pattern processing in this embodiment, and it is possible to process a plurality of times. The present invention can also be applied to processing and producing elements having a complicated shape other than the micropumps of the examples.

[0013]

As described above, according to the present invention, in the step of forming a groove, a through hole, a diaphragm or the like in a silicon substrate by alkali anisotropic etching, SiO ₂ having a portion having a different thickness as an etching mask. By using the film, it is possible to form various elements having high shape accuracy.

[Brief description of drawings]

1A to 1F are process diagrams of a silicon substrate according to the present invention.

2A to 2D are process diagrams of a silicon substrate according to the present invention.

3A to 3G are process diagrams of a silicon substrate according to the present invention.

FIG. 4A is a top view of the micropump according to the present invention. (B) is sectional drawing of the micro pump in this invention.

5A to 5G are process diagrams of a silicon substrate according to the present invention.

6A to 6F are process diagrams of a conventional silicon substrate.

[Explanation of symbols]

11, 21, 31, 41, 51, 61 Silicon substrate 12, 13, 22, 23, 34, 35 Thermal oxide film 38, 39, 54, 55, 59 Thermal oxide film 512, 513, 62, 63 Thermal oxide film 14 , 24, 64 Ink ejection port 15, 25, 65 Ink flow channel 32, 52 One side of silicon substrate 33, 53 The other side of silicon substrate 56, 57 Resist film 36, 37, 310, 58, 510 Resist pattern 511 Resist pattern 312,514 Recessed portion 313,46,515 Suction side valve membrane 314,47,516 Suction valve 315,48,517 Discharge side valve membrane 316,49,518 Discharge valve 317,45,519 Diaphragm 318,413,414,520 Penetration Hole 319,410,521 Pressure chamber 411 Suction side pipe 412 Discharge side pipe 42,43 Glass plate 44 Piezoelectric element 66 Convex portion 67 Recessed portion

Claims (4)

[Claims] 1. In a process of processing a silicon substrate in which a groove, a through hole, a diaphragm and the like are formed in the silicon substrate by anisotropic etching using an alkaline etching solution, SiO having a portion having a different thickness as an etching mask.
_Two films are used, and during the etching of the silicon substrate, the S
A structure having a plurality of depths is formed on a silicon substrate by sequentially removing the thinner part of the iO ₂ film by etching, and subsequently etching the underlying silicon of the SiO ₂ film. Method for processing silicon substrate. 2. The silicon substrate according to claim 1, wherein the thermal oxidation of the silicon substrate and the pattern processing of the thermal oxide film are repeated a plurality of times to form a SiO ₂ film having portions having different thicknesses. Processing method. 3. A SiO ₂ film is formed on a silicon substrate,
_2. The silicon substrate according to claim 1, wherein the SiO ₂ film is subjected to pattern processing including half etching once or a plurality of times to form a SiO ₂ film having portions with different thicknesses. Processing method. 4. A positive photoresist is applied on the SiO ₂ film, different patterns are formed on the positive photoresist a plurality of times, and half etching is performed on the SiO ₂ film after each pattern formation. 4. The method of processing a silicon substrate according to claim 3, wherein selective etching including is performed.