JPH1174545A - Manufacture of microbridge structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a contact strength of a transition metal oxide layer with a protective film interface, by inserting the step of forming a first protective film such as a silicon oxide film or the like between the step of forming the metal oxide layer and the step of processing photoresist. SOLUTION: Part of a titanium electrode 5 is exposed, a contact hole is formed, and then a vanadium oxide layer 6 is formed. Then, a silicon oxide film 7 is formed as a first protective film on the layer 6 by using a plasma chemical vapor growth method. Thereafter, photoresist is processed on the layer 6 formed with the film 7. Subsequently, the layer 6 is partly etched, and then a silicon nitride film 9 is formed as a second protective film on the overall surface. And, a through hole 10 is formed, a polysilicon layer 3 is partly exposed, and then the layer 3 is selectively removed. Thus, a microbridge structure is completed, and a diaphragm is thermally isolated from a board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a microbridge structure useful for sensors and actuators.

[0002]

2. Description of the Related Art Uncooled infrared sensors such as a pyroelectric infrared sensor, a bolometer infrared sensor, and a thermopile infrared sensor, a diaphragm gas sensor, and a piezoelectric actuator have a microbridge structure containing a transition metal oxide. . This microbridge structure is generally manufactured by applying micromachining technology using a silicon process, and the silicon oxide film and the silicon nitride film used in a normal silicon process are used as components of the microbridge structure. Can be considered.

In particular, the silicon nitride film has a higher resistance to an alkaline etching solution used in the step of etching and removing the sacrificial layer, has a larger Young's modulus, is more likely to suppress the deformation of the microbridge structure, and has parameters for forming the film. This is advantageous in that the film quality can be easily changed, and in the prior art, a silicon nitride film is used as a constituent material.

FIG. 3 is a plan view showing a microbridge structure of a conventional bolometer type infrared sensor. This example is an application example of a microbridge structure incorporating a transition metal oxide, and is a bolometer-type infrared sensor using vanadium oxide. This micro bridge structure is
2 and the diaphragm 13 and the diaphragm 1
When the infrared rays are absorbed by 3, the temperature of the bolometer layer 16 built in the diaphragm 13 rises, and the electric resistance changes. This change is due to the titanium electrode 15 and the aluminum wiring 1
4 to the signal processing circuit.

FIG. 2 is a diagram showing an example of a structure and a manufacturing method of a conventional bolometer type infrared sensor. First, a borophosphosilicate glass layer 1 is formed on a silicon substrate in order to flatten unevenness caused by a signal readout circuit or the like. Next, a silicon oxide film 2 is formed in order to prevent contamination such as gas released from the borophosphosilicate glass layer 1 in a subsequent step. Next, a polysilicon layer 3 as a sacrificial layer is formed. The layer 3 is etched away later. Next, a silicon nitride film 4 serving as a lower protective film having a microbridge structure is formed. Next, a titanium electrode 5 is formed by sputtering, photolithography, and plasma etching.

Next, a silicon nitride film 4 is formed again from above the titanium electrode 5, and a part of the titanium electrode 5 is exposed by photolithography and plasma etching to form a contact hole. Next, a vanadium oxide layer 6 is formed by reactive sputtering, and the vanadium oxide is adjusted to an optimum oxidation state by a hydrogen reduction treatment. Here, the state in which the electric resistance and the temperature coefficient are optimal is the desired oxidation state, and the composition is VO ₂ . FIG. 2A is a cross-sectional view of the microbridge structure having undergone the above steps.

Next, as shown in FIG. 2B, a photoresist is processed on the vanadium oxide layer 6, that is, a photoresist is applied, exposed, and developed. Next, as shown in FIG. 2C, the vanadium oxide layer 6 is formed by plasma etching.
Is partially etched, and then the photoresist 8 is removed.

Next, as shown in FIG. 2D, a silicon nitride film 9 is formed on the entire surface. At this time, since it is necessary to form the film at a low temperature so as not to deteriorate the vanadium oxide layer 6, plasma chemical vapor deposition is used for the film formation.

Next, as shown in FIG. 2E, after forming a through hole 10 and partially exposing the polysilicon layer 3, the polysilicon layer 3 is selectively removed with an alkaline etching solution. This completes the microbridge structure and thermally separates the diaphragm from the substrate.

[0010]

In the above-mentioned conventional example, the following two problems occur, and a bolometer type infrared sensor showing good characteristics could not be obtained.

The first problem is that transition metal oxides such as vanadium oxide have the property of adsorbing organic molecules,
A residual layer of a resist or an organic solvent used for cleaning is formed between the upper protective film and the adhesive layer between the metal oxide and the protective film interface. In particular,
After the resist layer 8 is removed in FIG. 2C, the sacrificial layer (polysilicon layer 3) is removed by etching because the residual layer of the resist or the organic solvent exists on the surface of the vanadium oxide layer 6 after the removal. Release layer 11 as shown in (f)
Will appear.

The second problem is that a silicon nitride film formed by plasma enhanced chemical vapor deposition releases hydrogen contained in the film during film formation by a plasma reducing action or during film formation / heat treatment after film formation. This means that the electrical resistance of the transition metal oxide in contact with the silicon nitride film changes. Specifically, the electric resistance of the vanadium oxide layer 6 is reduced by the formation of the silicon nitride film 9 in FIG.

That is, an object of the present invention is to provide a method for producing a microbridge structure which has excellent adhesion strength between a transition metal oxide layer and an interface of a protective film and has a stable electric resistance of the transition metal oxide.

[0014]

SUMMARY OF THE INVENTION The inventor of the present invention has proposed a method for forming a first metal oxide layer such as a silicon oxide film by plasma enhanced chemical vapor deposition between a step of forming a transition metal oxide layer such as a vanadium oxide layer and a photoresist processing step. It has been found that it is very effective to insert a step of forming a protective film, and the present invention has been completed.

That is, according to the present invention, in a method for manufacturing a microbridge structure including a transition metal oxide layer, a step of forming a transition metal oxide layer and forming a first protective film on the transition metal oxide layer Step, a step of patterning the transition metal oxide layer on which the first protective film is formed by using a photolithographic processing method, and after the patterning, forming a second protective film on the first protective film. A method of manufacturing a microbridge structure including a step of forming the same, and a method of manufacturing an infrared detector provided with the microbridge structure.

Preferably, the first protective film is a silicon oxide film formed by a plasma enhanced chemical vapor deposition method.
Preferably, the second protective film is a silicon nitride film, and further has a microbridge structure including a patterned transition metal oxide layer, and is formed on the transition metal oxide layer. A microbridge structure having a first protective film made of a silicon oxide film and a second protective film made of a silicon nitride film formed on the first protective film.

In the prior art, when the surface of the transition metal oxide layer comes into contact with a resist or an organic solvent, these organic molecules are bonded to the transition metal atoms and tend to remain even after a subsequent removal step. On the other hand, in the present invention, since the transferred metal oxide layer is in contact only with the first protective film, surface adsorption of organic molecules does not occur. In addition, since the transition metal oxide layer is not in contact with the silicon nitride film formed by the plasma enhanced chemical vapor deposition method, the influence of desorption of hydrogen which is not contained in the silicon nitride film and reduces the transition metal can be eliminated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of a method for manufacturing a bolometer type infrared sensor as a preferred embodiment of the present invention will be described below with reference to FIG. 1 together with specific data.

In FIG. 1A, first, a borophosphosilicate glass layer 1 is formed on a silicon substrate in order to flatten unevenness caused by a signal readout circuit or the like. Next, a silicon oxide film 2 is formed in order to prevent contamination such as gas released from the borophosphosilicate glass layer 1 in a subsequent step. Next, a polysilicon layer 3 as a sacrificial layer is formed. The layer 3 is etched away later. Next, a silicon nitride film 4 serving as a lower protective film having a microbridge structure is formed. Next, a titanium electrode 5 is formed by sputtering, photolithography, and plasma etching.

Next, a silicon nitride film 4 is formed again from above the titanium electrode 5, and a part of the titanium electrode 5 is exposed by photolithography and plasma etching to form a contact hole. Next, a vanadium oxide layer 6 is formed by reactive sputtering, and the vanadium oxide is adjusted to an optimum oxidation state by a hydrogen reduction treatment. Here, the state in which the electric resistance and the temperature coefficient are optimal is the desired oxidation state, and the composition is VO ₂ .

Next, a silicon oxide film 7 is formed as a first protective film on the vanadium oxide layer 6 by using a plasma chemical vapor deposition method. The thickness of the first protective film is not particularly limited, and may be appropriately determined as desired within a range in which the effects of the present invention can be obtained. FIG. 1A is a cross-sectional view of the microbridge structure having undergone the above steps.

Next, as shown in FIG. 1B, a photoresist process is performed on the vanadium oxide layer 6 on which the silicon oxide film 7 is formed, that is, photoresist coating, exposure, and development are performed. Next, as shown in FIG. 1C, after the vanadium oxide layer 6 is partially etched by plasma etching, the photoresist 8 is removed.

Next, as shown in FIG. 1D, a silicon nitride film 9 is formed on the entire surface. At this time, since it is necessary to form the film at a low temperature so as not to deteriorate the vanadium oxide layer 6, plasma chemical vapor deposition is used for the film formation.

Next, as shown in FIG. 1 (e), after forming a through hole 10 and partially exposing the polysilicon layer 3, the polysilicon layer 3 is selectively removed with an alkaline etching solution. This completes the microbridge structure and thermally separates the diaphragm from the substrate.

According to the above method, as a result of the present invention, FIG.
As shown in (e), peeling does not occur, and a good microbridge structure is obtained.

[0026]

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

<Example 1> A vanadium oxide film surface used as a bolometer material of a bolometer type infrared sensor,
The following comparative experiment was conducted on the easiness of the resist and the organic solvent for removing and cleaning the resist on the surface of the silicon oxide film.

In the experiment, three levels of samples having different resist coating conditions were prepared. Both are 1000mm on the substrate
Using a thick silicon substrate with a silicon oxide film, a 1300 ° thick vanadium oxide film was formed thereon by sputtering, and the composition was changed to VO ₂ by hydrogen reduction treatment.

Sample No. In No. 1, a resist was applied to the surface of the vanadium oxide layer, baked, removed with acetone, and washed. Sample No. 2 is 5 on vanadium oxide
A silicon oxide film having a thickness of 60 mm was formed, on which a resist was applied, baked and washed and removed with acetone. Sample No.
3 was an untreated sample for reference.

The carbon residue on the surfaces of these samples was examined by Auger electron spectroscopy. As a result, the sample NO. In No. 1, carbon was present not only in the composition ratio of 80% or more at the outermost surface, but also did not disappear even if the surface was shaved by sputtering for 10 minutes. On the other hand, the sample No. In No. 2, 40% of carbon was present on the outermost surface and disappeared by sputtering for 1 minute. Sample No. In No. 3, the outermost surface contained 20% of carbon and disappeared in about 20 seconds.

Next, the absolute intensities of Auger electrons were compared. NO. From the intensity of Auger electrons emitted from the carbon atoms on the outermost surface of each of the samples Nos. When the intensity of the outermost surface of Sample No. 3 was subtracted as the amount mixed during the movement of the sample, the results shown in Table 1 below were obtained. Do you get it.

[0032]

[Table 1] From these results, it was confirmed that the surface of the vanadium oxide layer has a property of hardly dissociating the adsorbed organic molecules, and that the formation of the silicon oxide film on the surface of the vanadium oxide layer can prevent the adsorption of the organic molecules.

<Embodiment 2> In the case where a silicon nitride film or a silicon oxide film is formed on a vanadium oxide layer, the reduction of the electric resistance value due to these protective film forming steps themselves is described.
The following experiment was conducted.

The bolometer resistance of the sample obtained through the steps shown in FIGS. 1 and 2 was measured. However, here, the vanadium oxide layer 6
By adding an oxidation-reduction treatment, the state was made to be susceptible to fluctuations in the oxidation state due to the protective film forming step. Each sample had a resistance value of 9 k to 15 kΩ measured with the vanadium oxide layer 6 exposed before forming the protective film.

The process of FIG. 2, ie, the vanadium oxide layer 6
In the step of forming the silicon nitride film 9 directly on top of
After the completion of the protective film forming step, the resistance was reduced to 1.2 k to 1.3 kΩ. On the other hand, in the step of FIG. 1, that is, the step of forming the silicon oxide film 7 on the vanadium oxide layer 6 and then forming the silicon nitride film 9, after the protection film forming step is completed, the resistance value is 5.1 k to 6. It decreased to about 0 kΩ.

In the case of FIG. 2 in which the silicon nitride film is formed directly on the vanadium oxide layer, the reason why the vanadium oxide is reduced and behaves like a metal is unknown. It is considered that the reduction effect is caused by the ammonia in the plasma or the reduction effect due to the release of hydrogen contained in the silicon nitride film during or after the formation of the silicon nitride film. In any case, it was confirmed that the reduction effect of the vanadium oxide layer due to the formation of the silicon nitride film was reduced by inserting the silicon oxide film.

The bolometer-type infrared sensor using vanadium oxide has been described above. However, the present invention relates to other uncooled infrared sensors such as a pyroelectric infrared sensor and a thermopile infrared sensor, and a diaphragm-type gas sensor and a piezoelectric actuator. It is effective for a microbridge structure containing a transition metal oxide.

[0038]

According to the present invention described above, it is possible to provide a method for producing a microbridge structure having excellent adhesion strength between the transition metal oxide layer and the protective film interface and having a stable electric resistance of the transition metal oxide. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure and a manufacturing method of a bolometer-type infrared sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure and a manufacturing method of a conventional bolometer-type infrared sensor.

FIG. 3 is a plan view showing a microbridge structure of a conventional bolometer-type infrared sensor.

[Explanation of symbols]

 Reference Signs List 1 borophosphosilicate glass layer 2 silicon oxide film 3 polysilicon layer 4 silicon nitride film 5 titanium electrode 6 vanadium oxide layer 7 silicon oxide film 8 photoresist 9 silicon nitride film 10 through hole 11 release layer 12 beam 13 diaphragm 14 aluminum wiring 15 Titanium electrode 16 Bolometer layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 41/08 H01L 41/08 Z 41/22 41/22 Z

Claims (5)

[Claims] 1. A method for manufacturing a microbridge structure including a transition metal oxide layer, wherein a step of forming a transition metal oxide layer, a step of forming a first protective film on the transition metal oxide layer, Patterning the transition metal oxide layer on which the first protective film is formed by using a photolithographic processing method, and forming a second protective film on the first protective film after the patterning A method for manufacturing a microbridge structure, comprising: 2. The method according to claim 1, wherein the first protective film is a silicon oxide film formed by a plasma enhanced chemical vapor deposition method. 3. The method according to claim 1, wherein the second protective film is a silicon nitride film. 4. A micro-bridge structure including a patterned transition metal oxide layer, wherein the first protective film comprises a silicon oxide film formed on the transition metal oxide layer; And a second protective film made of a silicon nitride film formed on the protective film. 5. A method for manufacturing an infrared detector having a microbridge structure containing a transition metal oxide layer,
A step of forming a transition metal oxide layer, a step of forming a first protective film on the transition metal oxide layer, and forming the first protective film on the transition metal oxide layer by photolithography. And a step of forming a second protective film on the first protective film after the patterning.