JP2005183419A - Processing method of silicon substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form trenches having different depths in a silicon substrate by crystal surface anisotropic etching employing alkali etching liquid without forming a photosensitive material on an underlying film having a level difference and without increasing the number of photolithographic steps. <P>SOLUTION: An etching mask layer 3 is formed on a silicon substrate 1 substantially having no level difference (a), and after a photosensitive material 5 is formed on the etching mask layer 3 (b), a photosensitive material 5 having a three-dimensional structure is formed on the etching mask layer 3 through exposure using a transmissivity regulation mask (c), three-dimensional profile of the photosensitive material 5 is then transferred to an etching mask layer 7 by dry etching (d), and trenches having different depths are formed in the silicon substrate 1 using the etching mask layer 7 as a mask by crystal surface anisotropic etching employing alkali etching liquid ((e) and (f)). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a silicon substrate processing method in which grooves having different depths are formed in a silicon substrate by crystal plane anisotropic etching using an alkaline etching solution. In the claims and the specification of the present application, the groove formed in the silicon substrate includes a through hole. Such a silicon substrate processing method is used for fine processing of a silicon substrate such as a semiconductor sensor such as a semiconductor pressure sensor, a semiconductor acceleration sensor, and a semiconductor angular velocity sensor, and a recording print head for an ink jet printer using silicon.

  As an etching method for a silicon substrate, there is crystal plane anisotropic etching using an alkaline etchant. Since the etching rate of single crystal silicon differs depending on the crystal plane orientation with respect to the alkaline etching solution, for example, the (100) silicon substrate has a significantly lower etching rate of the (111) plane than the (100) plane. A smooth surface of (111) is obtained. Using such characteristics, a three-dimensional structure such as a semiconductor sensor or a recording print head for an inkjet printer is processed into a silicon substrate.

FIG. 2 is a process cross-sectional view for explaining a conventional silicon substrate processing method. This conventional example shows a method for processing an inkjet printer head.
(1) A thermal oxide film 23 is formed on the silicon substrate 21 (see (a)).
(2) The thermal oxide film 23 is patterned into a shape corresponding to the ink flow path by photolithography and hydrofluoric acid etching (see (b)).
(3) The silicon substrate 21 is etched to a predetermined depth with an alkaline etchant to form the ink flow path 25 (see (c)).
(4) A thermal oxide film 27 is formed on the surface of the ink flow path 25 by thermal oxidation (see (d)).
(5) An opening is formed at a position corresponding to the ink discharge port of the thermal oxide film 27 by photolithography and hydrofluoric acid etching (see (e)).
(6) Etching is performed until the discharge port 29 is formed through the alkali etching solution. Thereby, the ink flow path 25 and the ejection port 29 having different depths are formed in the silicon substrate 21 (see (f)).

  In the silicon substrate processing method as described above, the ink flow path 25 is already formed in the silicon substrate 21 in the step (5) described with reference to FIG. The depth of the ink flow path 25 is about 100 μm (micrometer) to 200 μm. A photoresist for forming an opening in a predetermined region of the thermal oxide film 27 in the silicon substrate 21 having such a deep step. It is very difficult to apply (a representative example of a photosensitive material) uniformly. In particular, since the photoresist is extremely thin at the step portion of the silicon substrate 21, a portion corresponding to the step portion of the thermal oxide film 27 is slightly etched during the hydrofluoric acid etching, and the step portion of the silicon substrate 21 is etched during the subsequent silicon etching. There was a problem that the desired shape could not be obtained due to etching.

Further, on the bottom surface of the ink flow path 25, the thickness of the photoresist is increased, and the pattern exposure is performed at a distance of about 100 μm to 200 μm, so that the pattern accuracy is poor, and the shape of the resulting discharge port 29 is obtained. There was a problem that accuracy deteriorated.
Such a problem is not only when the inkjet printer head is manufactured, but also when the silicon substrate is etched to a depth of several hundred μm by crystal plane anisotropic etching, such as when an element such as a semiconductor sensor is manufactured on a silicon substrate. The same problem occurs.
Further, in the conventional silicon processing method, since the patterning step is performed on the silicon substrate whose strength has been reduced by the already formed grooves, the silicon substrate may be damaged in the patterning step.

  In order to solve such a problem, in a silicon substrate processing step in which grooves, through holes, diaphragms, etc. are formed in a silicon substrate by crystal plane anisotropic etching using an alkaline etching solution, there are portions having different thicknesses as etching masks. During the etching of the silicon substrate using the oxide film, the thin portion of the oxide film is sequentially erased by etching, and the silicon substrate underlying the disappeared oxide film is subsequently etched, so that a plurality of silicon substrates are etched. Has been disclosed (see, for example, Patent Document 1).

In Patent Document 1, as a method of forming an oxide film having a portion having a different thickness on a silicon substrate, (1) a method of performing thermal oxidation of the silicon substrate and patterning of the thermal oxide film a plurality of times, and (2) a silicon substrate. A method of forming an oxide film on the oxide film and performing pattern processing on the oxide film including one or more half-etching processes; and (3) applying a positive photoresist on the oxide film, and then applying the positive photoresist. A method is disclosed in which different pattern formation is performed a plurality of times, and selective etching including half etching is performed on the oxide film for each pattern formation.
JP 2001-230241 A Japanese Patent Laid-Open No. 9-80740

However, even in the method disclosed in Patent Document 1, in the above methods (1) and (2), when forming a photoresist in the photolithography process, an oxide film serving as a base film is about 0.2 to 0.3 μm. There is a possibility of causing the same problem as that of the prior art described with reference to FIG.
Furthermore, when forming oxide films having portions with different thicknesses, the number of steps for forming a thermal oxide film, which is a mask pattern, is increased in order to process the target shape, or at least twice or more with respect to the mask pattern. There is a problem that a photoengraving process is necessary, and the manufacturing process is increased due to such an increase in the process, resulting in an increase in process time and a complicated manufacturing process.

  Accordingly, the present invention provides a method for processing a silicon substrate in which grooves having different depths are formed in a silicon substrate by crystal plane anisotropic etching using an alkaline etchant, and a photosensitive material is formed on a base film on which a step is formed. It is an object to form grooves having different depths in a silicon substrate without increasing the number of photolithography processes.

The present invention is a method for processing a silicon substrate in which grooves having different depths are formed in a silicon substrate by crystal plane anisotropic etching using an alkaline etchant, and includes the following steps (A) to (D).
(A) a step of forming an etching mask layer on a silicon substrate on which no step is substantially formed;
(B) a step of forming a photosensitive material having a three-dimensional structure on the etching mask layer by exposure using a transmittance adjusting mask after forming the photosensitive material on the etching mask layer;
(C) a process of transferring the three-dimensional shape of the photosensitive material to the etching mask layer by dry etching technology;
(D) A step of forming grooves having different depths in the silicon substrate by crystal plane anisotropic etching using an alkali etching solution, using the etching mask layer as a mask.

  Here, the silicon substrate on which no step is substantially formed means that a step that does not form a step on the surface of the etching mask layer formed on the silicon substrate may be formed on the silicon substrate. Further, the silicon substrate here may have a step formed in a region different from a region where grooves having different depths are formed.

  A transmittance control mask (TCM: Transmission Controlled Mask) is a device in which a difference in transmittance (light transmittance) is provided in a single exposure mask so as to give a difference in exposure amount to an object to be exposed. is there. For example, Patent Document 2 discloses a transmittance adjustment mask.

In the present invention, examples of the etching mask layer include those having an etching rate smaller than that of the silicon substrate with respect to an alkaline etching solution, such as an oxide film.
Further, in the step (C), anisotropic etching may be performed under the condition that the etching rates of the photosensitive material and the etching mask layer are the same.

In the method for processing a silicon substrate according to the present invention, an etching mask layer is formed on a silicon substrate on which no step is substantially formed (step (A)), so that no step is formed on the surface of the etching mask layer. . Furthermore, after forming a photosensitive material on the etching mask layer, a photosensitive material having a three-dimensional structure is formed on the etching mask layer by exposure using a transmittance adjusting mask (step (B)), once. A photosensitive material having a three-dimensional structure can be formed by the photoengraving process of (1), and a groove formed on the silicon substrate by transferring the three-dimensional shape of the photosensitive material to the etching mask layer (step (C)). An etching mask layer having a three-dimensional structure corresponding to the shape can be formed. Then, by performing crystal plane anisotropic etching using an alkaline etchant on the silicon substrate using the etching mask layer as a mask, the thin portions of the etching mask layer are sequentially erased by etching, and the disappeared etching By subsequently etching the silicon substrate underlying the mask layer, a structure having a plurality of depths can be formed in the silicon substrate.
As described above, according to the method for processing a silicon substrate of the present invention, the depth of the silicon substrate can be reduced without forming a photosensitive material on the base film on which the step is formed and without increasing the number of photolithography processes. Thus, it is possible to improve the processing shape accuracy of the three-dimensional structure formed on the silicon substrate without complicating the manufacturing process.

  In the present invention, if an etching mask layer having an etching rate smaller than that of the silicon substrate, such as an oxide film, is used with respect to the alkaline etching solution, the etching layer is formed with respect to the depth of the groove formed in the silicon substrate. Since the film thickness can be reduced, the film thickness of the entire etching mask layer formed on the silicon substrate can be reduced.

  Furthermore, in the step (C), if anisotropic etching is performed under the condition that the etching rates of the photosensitive material and the etching mask layer are the same, the three-dimensional shape formed in the photosensitive material is directly used as the etching mask layer. Since it can be transferred, the design becomes easy.

  FIG. 1 is a process sectional view for explaining one embodiment. This embodiment is a processing example of an ink jet printer head, in which an ink flow path and an ink discharge port are formed on a silicon substrate. This embodiment will be described with reference to FIG.

(1) A thermal oxide film (etching mask layer) 3 having a film thickness of 0.5 μm is formed on the surface of a silicon substrate 1 having a crystal plane orientation of (100) and having a thickness of 200 μm. Here, since no step is formed on the surface of the silicon substrate 1, no step is formed on the surface of the thermal oxide film 3 (see (a)).

(2) A positive photoresist (photosensitive material) 5 is applied to a thickness of 0.5 μm on the thermal oxide film 3 by spin coating, and then the photoresist 5 is pre-baked. Here, since no step is formed on the surface of the thermal oxide film 3, no step is formed on the surface of the pre-baked photoresist 5 (see (b)).

(3) The transmittance of the transmittance adjustment mask (not shown) is 100% for the region 7 corresponding to the ink ejection port, 60% for the region 9 corresponding to the ink flow path, and 0% for the other regions. As an unexposed area, the photoresist 5 is exposed at a time with a light amount that dissolves by 0.5 μm at an exposure amount of 100% during the development process, and thereafter the development process is performed to pattern the photoresist 5. As a result, the remaining film of the photoresist 5 becomes 0 μm in the region 7 corresponding to the ink discharge port, 0.2 μm in the region 9 corresponding to the ink flow path, and 0.5 μm in the other regions, and the photoresist 5 has a depth. It becomes a three-dimensional structure with different grooves. Thereafter, the photoresist 5 is post-baked (see (c)).

(4) Dry etching is performed under the condition that the etching rate of the photoresist 5 and the thermal oxide film 3 is 1: 1. As a result, the three-dimensional shape of the photoresist 5 is transferred to the thermal oxide film 3 as it is, and the remaining film of the thermal oxide film 3 is 0 μm in the region 7 corresponding to the ink discharge port and 0 in the region 9 corresponding to the ink flow path. 0.2 μm and 0.5 μm in other regions, and the thermal oxide film 3 has a three-dimensional structure having grooves with different depths (see (d)).

(5) Crystal plane anisotropic etching of the silicon substrate 1 is performed with an alkaline etchant. In the present embodiment, for example, a KOH aqueous solution (KOH concentration 25 wt%, 80 degrees Celsius) was used as the alkaline etching solution. Under this condition, the etching rate of the silicon substrate 1 is 1.0 μm / min, and the etching rate of the thermal oxide film 3 is 0.002 μm / min. In this example, etching of the silicon substrate 1 with a KOH aqueous solution was performed for 200 minutes.
At 100 minutes after the start of etching, the thermal oxide film 3 disappears by etching in the region 9 corresponding to the ink flow path, and the underlying silicon substrate 1 is exposed. Further, in the region 9 corresponding to the ink flow path, the silicon substrate is selectively removed by 100 μm (see (e)).
By subsequent etching for 100 minutes, the discharge port 11 penetrates in the region 7 corresponding to the ink discharge port of the silicon substrate 1 having a thickness of 200 μm. Further, the silicon substrate 1 is selectively removed by 100 μm in the region 9 corresponding to the ink flow path, and the ink flow path 13 is completed (see (f)).

  According to this embodiment, in the step (5) described with reference to FIGS. 1 (e) and 1 (f), the discharge port 11 and the ink flow path 13 of the ink jet printer head are separated by one crystal plane anisotropy. Since the patterning process is not performed on a silicon substrate with reduced strength unlike the case where grooves are separately formed, the patterning process is not performed at all. Sometimes, the strength of the silicon substrate is not reduced due to the grooves, and there is no possibility of causing problems such as breakage.

Further, since the photoengraving process is performed on the smooth surface on the thermal oxide film 3 without including any photoengraving process on the step as in the prior art, the photo resist 5 and the etching mask layer are provided. The pattern processing accuracy of the thermal oxide film 3 is very good, and the processing shape accuracy of the silicon substrate 1 can be improved.
Further, in the exposure step for the photoresist 5 in the above step (3), the discharge port 11 and the ink flow path formed in the silicon substrate 1 using a transmittance adjustment mask capable of arbitrarily changing the exposure amount for each region. The three-dimensional photoresist 5 corresponding to the groove 13 having different depths can be formed by one photolithography process, and the manufacturing process can be simplified.

  Although the embodiments of the present invention have been described above, the materials, dimensions, shapes, arrangements, and the like are examples, and the present invention is not limited thereto, and is within the scope of the present invention described in the claims. Various changes can be made.

  For example, in the above embodiment, the present invention is applied to the processing of an ink jet printer head, but the processing method of the silicon substrate of the present invention is not limited to this, a semiconductor sensor having a flexible part such as a diaphragm, etc. The present invention can be applied to the processing of a three-dimensional structure having grooves with different depths on a silicon substrate.

  In the above embodiment, the thermal oxide film 3 as an etching mask layer is formed on the silicon substrate 1. However, the present invention is not limited to this, and the etching mask layer is formed by, for example, CVD (Chemical Vapor Deposition). ) May be another film such as a CVD oxide film formed by the method.

  In the above embodiment, dry etching is performed under the condition that the etching rate of the photoresist 5 as the photosensitive material and the thermal oxide film 3 as the etching mask layer is 1: 1 so that the three-dimensional shape of the photoresist 5 is obtained. However, the present invention is not limited to this, and the three-dimensional shape of the photosensitive material is formed by dry etching under conditions where the etching rates of the photosensitive material and the etching mask layer are different. You may make it transcribe | transfer to an etching mask layer.

It is process sectional drawing for demonstrating one Example. It is process sectional drawing for demonstrating the processing method of the conventional silicon substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 3 Thermal oxide film 5 Photoresist 7 Area | region corresponding to an ink discharge port 9 Area | region corresponding to an ink flow path 11 Discharge port 13 Ink flow path

Claims (4)

A silicon substrate processing method for forming grooves having different depths in a silicon substrate by crystal plane anisotropic etching using an alkaline etchant, comprising the following steps (A) to (D): Processing method.
(A) a step of forming an etching mask layer on a silicon substrate on which no step is substantially formed;
(B) After forming a photosensitive material on the etching mask layer, forming a photosensitive material having a three-dimensional structure on the etching mask layer by exposure using a transmittance adjustment mask;
(C) transferring the three-dimensional shape of the photosensitive material to the etching mask layer by a dry etching technique;
(D) A step of forming grooves having different depths in the silicon substrate by crystal plane anisotropic etching using an alkali etching solution, using the etching mask layer as a mask.   The method for processing a silicon substrate according to claim 1, wherein the etching mask layer has an etching rate smaller than that of the silicon substrate with respect to an alkaline etching solution.   The method for processing a silicon substrate according to claim 1, wherein the etching mask layer is an oxide film.   4. The method for processing a silicon substrate according to claim 1, wherein in the step (C), anisotropic etching is performed under the condition that etching rates of the photosensitive material and the etching mask layer are the same.

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