JP3254787B2 - Manufacturing method of infrared sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared sensor and a method for manufacturing an infrared sensor, and more particularly, to a small and highly sensitive infrared sensor.
The present invention also relates to an infrared sensor having good productivity and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, an infrared sensor has been used as a non-contact thermometer for detecting an object or measuring temperature in a special environment. For example, it is a blast furnace temperature measurement, a fire alarm, or an automatic flusher for a men's toilet. Recently, highly sensitive infrared sensors using silicon micromachining technology have been energetically researched and developed. In each case, a heat separation structure having a small heat capacity and a large heat resistance is formed by using silicon micromachining technology, and the heat separation structure is provided with an infrared absorber, and the heat separation structure is formed by absorbing incident infrared light. This is a method in which the temperature rise of the section is detected by a thermopile or the like.

FIG. 8 shows an example of an infrared sensor using a silicon bulk micromachining technique. (For details, see Transducers '87, (1987) PMSarro, H. Yashiro, A.
WvHerwaarden and S. Middlehoek, An Infrared Sensin
g Array Based on Integrated Silicon Thermopiles,
See pages 227-230. The outline of the configuration and the manufacturing method is as follows.
Then, an n-type epitaxial layer 102 is formed, and a cantilever beam 103 is formed by electrochemical etching from the back surface. As a result, the cantilever beam 103 has a heat separation structure, a light absorbing agent 104 is provided on the upper surface to serve as an infrared light receiving unit, and a thermopile 105 for detecting a temperature rise is formed.

Next, an example of an infrared sensor using a silicon surface micromachining technique is shown in FIG. (
For more information, see Technical Digest of the 9th Senser Sympo
sium (1990) M. Suzuki et al, An infrared Detecter Usi
See ng Poly-silicon p-n Junction Diode, p.71-74. The outline of the configuration and the manufacturing method is as follows.
Si3 N4 202, 203 via SiO2 209
And a layer of SiO2 204 are formed, and a cavity 205 is formed by alkali anisotropic etching from the surface of the P-type substrate 201.
The portion covering 05 is a diaphragm 206.
Then, a light absorbing agent 207 is provided on the upper surface of the diaphragm 206 to serve as an infrared light receiving portion, and a Pn junction 208 of polysilicon for detecting a temperature rise of the infrared light receiving portion is formed in the diaphragm 206.

However, the increase in sensitivity of the infrared sensor shown in FIG. 8 or 9 depends on how a heat separation structure having a small heat capacity and a large thermal resistance is formed in the infrared light receiving portion. Therefore, even if the size of the light absorbing agent is unnecessarily increased, it cannot be said that it is still sufficiently efficient. As a countermeasure against this, a method has been proposed in which incident infrared light is condensed and guided to an infrared light receiving unit. This method is rudimentary but extremely effective from the viewpoint of its detection performance.

Several methods have been proposed for collecting incident infrared light and guiding it to an infrared light receiving section. For example, as an example of attaching a sensor element to a condenser lens,
An example is disclosed in Japanese Patent Application Laid-Open No. 49-103688. As shown in FIG. 10, a condenser lens 303 for infrared rays is fixed on the upper surface of a so-called can package including a case 301 and an external lead terminal 302, and a sensor element 304 is attached to the bottom surface of the condenser lens 303. I have.

In addition, Japanese Patent Application Laid-Open No. 62-261,025 discloses a method of retrofitting a condenser lens to a can package having a sensor element.
As shown in FIG. 11, the sensor element 405 is supported by the header 401 in a can package including the header 401, the case 402, the filter 403, and the like.
Is provided, and a condenser lens 404 is placed on the case 402 of the can package.

[0008]

However, such a conventional infrared sensor is expensive due to the use of an infrared condensing lens formed of an infrared transmitting material, and has a structure in which it is individually mounted on a can package. Therefore, there is a problem that the external size becomes large. For this reason, it is not suitable for application to medical systems represented by microsurgery, for example, or for mounting on a TOB (chip-on-board), and the price is inevitably high due to poor productivity. Accordingly, the present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method of manufacturing an infrared sensor which is formed in a small size without using an expensive infrared condenser lens. And

[0009]

Means for Solving the Problems] Therefore, in the present invention,
A space is formed between the infrared filter constituent member and the semiconductor substrate which are overlapped with each other, an infrared detection unit is disposed in the space, and a reflecting mirror is formed on a surface of the semiconductor substrate which defines the space. red configured infrared incident from an infrared filter to reflect condensing toward the infrared detector
An outside line sensor is to be formed .

Therefore, a method of manufacturing an infrared sensor according to the present invention comprises a first step of sequentially forming an oxide film, a sacrificial layer, and a Si3 N4 film layer vertically sandwiching an infrared sensor element on one main surface of a semiconductor substrate. An opening is formed in the Si3 N4 film layer with the infrared sensor element portion laterally interposed therebetween, and a portion of the sacrifice layer and an oxide film thereunder that overlaps the sacrifice layer is removed by etching to form an infrared detection portion. A second step of forming a concave surface on the semiconductor substrate by isotropic etching from the opening, a fourth step of forming a reflecting mirror on the concave surface, and an infrared Fifth bonding of the filter component onto the semiconductor substrate
Process.

[0011]

According to the present invention, infrared detection is performed on a single semiconductor substrate.
A projection and a reflector are formed.

That is, a step of forming an infrared detecting portion on a semiconductor substrate, followed by a step of forming a concave surface on the substrate by isotropic etching and a step of forming a reflecting mirror on the substrate,
Since the infrared detecting section and the reflecting mirror are formed on one semiconductor substrate, the infrared detecting section and the reflecting mirror are formed in a particularly small size.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Destination
First, a reference example will be described before the embodiment. Figure 1 shows the first
It is a conceptual diagram which shows the whole structure of the reference example of FIG. In the infrared sensor 500, the semiconductor substrate 503 and the semiconductor substrate 505
A cavity 506 is formed between
The infrared sensor element 501 is located inside the semiconductor substrate 50.
A reflection mirror 504 is formed on the surface forming the fifth cavity 506. An infrared filter 502 is formed on the semiconductor substrate 503, and the infrared sensor element 50
1 is formed and supported on the semiconductor substrate 503. Here, for simplicity, the infrared light receiving section is represented by an infrared sensor element, and only the infrared sensor element 501 is shown in the figure, and the supporting structure thereof is omitted. The semiconductor substrate 503 is a component of the infrared filter of the present invention. Semiconductor substrate 50
3 and 505 are joined by anodic bonding, and electric wiring to the infrared sensor element 501 is simultaneously performed by solder bumps at the time of anodic bonding.

Next, a method of manufacturing the infrared sensor will be described. FIG. 2 shows a process of manufacturing a semiconductor substrate 503 which forms an infrared filter and supports an infrared receiving section including an infrared sensor element. Here, the infrared light receiving section and the infrared filter are formed on the same substrate by using the surface micromachining technology and the bulk micromachining technology. First, in step (a) of FIG. 2, one main surface of the silicon P-type
An oxide film (SiO2) 602 is formed by a method such as VD, and a polysilicon sacrificial layer 603 having a predetermined area is formed on the upper surface of the oxide film 602 by CVD or the like, and an n-type epitaxial layer 604 is formed on the back surface of the P-type substrate 601. Form.

In the step (b), the oxide film 60 is formed.
2 and polysilicon sacrificial layer 603, Si3 N4
After the film layer 605 is formed by CVD, an infrared sensor element 501 composed of a polysilicon diode is formed thereon by polysilicon deposition, photolithography and etching. Further, the whole is covered with a Si3 N4 film layer 607 by CVD. As a result, the infrared sensor element 501 is placed on the polysilicon sacrificial layer 603 near the approximate center thereof,
5,607.

In the next step (c), an opening 608 that reaches the polysilicon sacrificial layer 603 is formed by dry etching, and the polysilicon sacrificial layer 603 is sacrificed etched using a mixed acid of hydrofluoric acid and nitric acid. Further, the oxide film 602 below the polysilicon sacrificial layer is removed with hydrofluoric acid. As a result, a thermal isolation structure is obtained in which the infrared sensor element 501 is supported by the Si3 N4 film layers 605 and 607 extending from the periphery except for the opening 608.

Thereafter, in step (d), the P-type substrate 601 is formed.
To the n-type epitaxial layer 6 through the opening 608 while applying a bias to the n-type epitaxial layer 604.
Electrochemical etching using an alkali solution such as hydrazine is performed up to the interface with the substrate 04 to form a cavity 506 and an infrared filter 502 including an n-type epitaxial layer. Then, a light absorbing agent 612 is formed on the Si3 N4 film layer sandwiching the infrared sensor element 501 of the heat separation structure, and an infrared light receiving unit 611 as an infrared detecting unit is formed.

With respect to the infrared filter, the silicon substrate is an excellent infrared transmitting material having a transmission wavelength range of 1.2 to 15 μm, but because of its large refractive index, the reflection of incident infrared light at the air-silicon substrate interface. Large loss. That is, in the case of vertical incidence of infrared light, the loss represented by reflection loss = ((nsi−na) / (nsi + na)) ² is actually as high as 30%. Where, nsi: refractive index of silicon in the infrared region na: refractive index of air in the infrared region

In this case, the thickness of the infrared filter 502 formed by electrochemical etching is represented by the following formula: dsi = (λ / 2 nsi) · L where nsi: refractive index of silicon dsi: infrared filter By setting the thickness λ: the wavelength of the used infrared light L: an integer, the reflection loss of the incident infrared light on the surface of the silicon substrate can be reduced. For example, when trying to detect a human, infrared light having a wavelength of 10 μm is used, and dsi = (λ / 2nsi) · L (L = 1, 2, 3,...) = 0.73, 1.46, 2.19, 2.92 3.64,... (Μm).

Next, FIG. 3 shows a manufacturing procedure of the semiconductor substrate 505 having the reflecting mirror 504. First, in step (e), an oxide film 702 is formed on the silicon substrate 701 by thermal oxidation or CVD except for the portion corresponding to the cavity hole diameter, and the silicon substrate 701 and the oxide film 702 are covered thereon with Si3 N4. The film layer 703 is similarly formed by CVD. Then, an opening 704 is formed in the Si3 N4 film layer 703 by dry etching.

In the next step (f), isotropic etching is performed from the opening 704 with a mixed acid of hydrofluoric acid and nitric acid to form a concave surface 705 and then a Si 3 N 4 film 703.
Is removed with hot phosphoric acid or the like. Then, in the step (g), the reflecting mirror 504 is formed on the concave surface 705 by electrolytic plating such as gold, and then the oxide film 702 is removed with hydrofluoric acid.

As described above, it is formed by the steps shown in FIG.
FIG. 3 shows a semiconductor substrate 503 having an infrared receiving portion 611;
1. The infrared sensor 501 shown in FIG. 1 is formed by bonding the semiconductor substrate 505 having the reflecting mirror 504 formed in the steps shown in FIG.

In the present embodiment constructed as described above, the incident light X is filtered only by infrared rays by the infrared filter 502, directly reaches the light absorbing agent 612 of the infrared ray receiving section 611, and is reflected and collected by the reflecting mirror 504. Then, the light is guided to the infrared light receiving unit 611. This allows
The temperature of the infrared light receiving section 611, which is a heat separating structure, is increased, and this temperature rise is detected by the infrared sensor element 501 of a polysilicon diode, and an electric signal corresponding to the detected amount is output to detect infrared light. Is done.

Therefore, only the target infrared light is detected with high sensitivity without being disturbed by light other than the infrared light. The infrared sensor element 501 is completely shielded from the outside air, is less susceptible to wind and heat convection, and thus has low noise and stable characteristics, so that accurate measurement can be performed as an infrared sensor. . Similarly, since the infrared sensor element 501 is surrounded by the infrared filter 502, the semiconductor substrates 503 and 505, and serves as a protected infrared receiver, damage during the mounting process can be avoided.
The yield can be improved. In addition, according to this configuration, optical components such as the infrared filter 502 and the reflecting mirror 504 can be pre-assembled in a batch process, so that production can be performed efficiently and at low cost.

Since the substrates 503 and 505 are both silicon substrates, when using the anodic bonding method, one of the substrates is made of bare silicon, and Pyrex glass is sputtered on the bonding portion of the other substrate. What is necessary is just to join after forming a film. In addition to the above, in particular, when Pyrex glass is used as the material of the substrate on which the reflecting mirror is formed, bare silicon may be used as the substrate on which the infrared receiving section is formed. further,
In the case of bonding by anodic bonding in a vacuum, the cavity 506 formed by the semiconductor substrate forming the infrared receiving section 611 and the semiconductor substrate forming the reflecting mirror can be easily made substantially vacuum. As a result, not only stable characteristics with little noise can be obtained, but also the thermal resistance of the heat separation structure of the infrared light receiving section 611 where the infrared sensor element 501 is arranged is increased, and particularly high sensitivity is obtained.

The bonding of the substrates 503 and 505 can be performed by using an adhesive or soldering in addition to anodic bonding. Further, although a silicon substrate was used as a substrate material, a glass substrate or a metal substrate can be used in addition to the above, and the concave surface of the reflecting mirror portion is not limited to isotropic etching, but can be formed by ultrasonic processing. You may.

FIG. 4 shows a second reference example . here,
In the infrared sensor shown in FIG. 1, an optical element 801 made of an anti-reflection film or an interference filter is coated on an infrared filter 502 portion. The coating is easily realized by vapor deposition or the like. Although the silicon substrate constituting the infrared filter 502 is an excellent infrared region optical material, it has a large refractive index as described above, and therefore has a large reflection loss of the incident light X, thereby reducing the reflection loss. Is done.

FIG. 5 shows a third reference example . This is obtained by forming a piezo diffusion resistor 901 in the infrared filter 502 in the infrared sensor shown in FIG. The resistance value of the piezo diffusion resistor 901 changes according to the stress of the infrared filter 502 caused by the pressure in the cavity 506. Thus, by detecting the change in the resistance value, it functions as a pressure sensor for detecting the degree of vacuum or leakage in the cavity 506, and can be used for failure diagnosis and correction of an output signal, thereby further improving measurement accuracy. be able to.

FIGS. 6 and 7 show, as an embodiment of the present invention, a manufacturing method in which an infrared receiving section and a reflecting mirror are formed in one semiconductor substrate. First, step (a)
In one embodiment, thermal oxidation or C
An oxide film 1002 is formed by VD, and a polysilicon sacrificial layer 1003 is formed on the upper surface by CVD or the like. Next, in step (b), the oxide film 1002
And polysilicon sacrificial layer 1003, Si3 N4
After the film layer 1005 is formed by CVD, an infrared sensor element 1101 of a polysilicon diode is formed thereon in the same manner as in the first embodiment, and the whole is covered with a Si3 N4 film layer 1006 by CVD.

Thereafter, in the step (c), an opening 1008 reaching the polysilicon sacrificial layer 1003 is formed by dry etching so that the Si 3 N 4 film layers 1005 and 1005 are formed.
Then, the polysilicon sacrificial layer 1003 is sacrificed etched using a mixed acid of hydrofluoric acid and nitric acid, and the oxide film 1002 below the sacrificial polysilicon layer is removed by hydrofluoric acid.

Then, in the step (d), isotropic etching is performed from the opening 1008 using a mixed acid of hydrofluoric acid and nitric acid to form the cavity 11 having the concave surface 1105.
02 is formed. Finally, in step (e), the concave surface 11
A reflecting mirror 1104 is formed on the substrate 05 by electrolytic plating of gold or the like. The light absorbing agent 10 is provided on the infrared sensor element 1101 supported by the Si3 N4 film layers 1005 and 1006.
07 to form an infrared receiving section 1200. The infrared receiving section 1200 has a heat separation structure as described above.

Thereafter, although not particularly shown, an infrared filter is superimposed on the infrared light receiving portion side of the semiconductor substrate provided with the infrared light receiving portion and the reflecting mirror as described above, and the same as in FIG. The infrared sensor is completed.

According to this embodiment, since the infrared light receiving portion having the infrared sensor element and the reflecting mirror are formed on one substrate, the infrared light receiving portion is formed more compact and a simple infrared filter is provided on the semiconductor substrate. , Which has the advantage of reducing the number of manufacturing steps as a whole.
In the above step (d), when forming the concave surface 1105 by isotropic etching, if the eaves 1009 are formed due to under-etching, a photolithography and etching step may be further added.

In the above-described embodiment, the temperature rise of the infrared light receiving portion having the thermal isolation structure is detected by the infrared sensor element constituted by the polysilicon diode.
The invention is not limited to this, and any other detection method may be used. In addition, the thermal isolation structure of the infrared ray receiving section is also a bridge formed by a Si3N4 film layer extending from the surroundings into the space.
Other types of thermal isolation structures are possible. Also,
The light absorbing agent formed in the infrared receiving portion is also provided or omitted as necessary.

[0035]

As described above, the infrared sensor of the present invention
The manufacturing method of, on one main surface of the semiconductor substrate, an oxide film,
Si3 sandwiching the sacrificial layer and the infrared sensor element up and down
A first step of forming an N4 film layer and a red
An opening is formed by sandwiching the outside line sensor element in the horizontal direction
Together with the sacrificial layer and the sacrificial layer under the oxide film.
To form infrared detectors
Second step, semi-conductive by isotropic etching from opening
A third step of forming a concave surface on the body substrate and a reflecting mirror on the concave surface
Forming a fourth step, and covering the infrared detector with an infrared ray
A fifth step of joining the filter component to the semiconductor substrate;
In the space between the infrared filter component and the semiconductor substrate,
In addition to the detector, the semiconductor substrate has a reflector.
Thus, a high-sensitivity infrared sensor is obtained in which the infrared light incident from the infrared filter is reflected and collected by the reflecting mirror toward the infrared detection unit. In addition, since it is not necessary to use an expensive condenser lens for infrared rays, it is realized at low cost.

Further particularly, following the step of forming the infrared detection unit on a semiconductor substrate, since as by isotropic etching to form a concave surface to form a reflector, one is an infrared receiver and reflector since is formed on a substrate, especially
In addition to being formed in a small size, it is only necessary to cover an infrared filter on this, which has the effect of reducing the number of manufacturing steps as a whole.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first reference example of the present invention.

FIG. 2 is a diagram illustrating a process of manufacturing a semiconductor substrate on which an infrared filter and an infrared light receiving section are formed.

FIG. 3 is a diagram showing a manufacturing process of a semiconductor substrate on which a reflecting mirror is formed.

FIG. 4 is a cross-sectional view showing a second reference example .

FIG. 5 is a sectional view showing a third reference example .

FIG. 6 is a view showing a process of manufacturing a semiconductor substrate forming an infrared ray receiving section and a reflecting mirror according to the present invention .

FIG. 7 is a view showing a process of manufacturing a semiconductor substrate forming an infrared ray receiving section and a reflecting mirror according to the present invention .

FIG. 8 is a diagram showing a conventional example of an infrared sensor.

FIG. 9 is a diagram showing another conventional example of an infrared sensor.

FIG. 10 is a diagram showing a conventional example of an infrared sensor having a condenser lens.

FIG. 11 is a diagram showing another conventional example of an infrared sensor having a condenser lens.

[Explanation of symbols]

 101 P-type substrate 102 n-type epitaxial layer 103 cantilever beam 104 light absorbing agent 105 thermopile 201 P-type substrate 202, 203 Si3 N4 204, 209 SiO2 205 cavity 206 diaphragm 207 light absorbing agent 207 208 polysilicon Pn junction 301, 402 case 302 external lead terminal 303,404 Condensing lens 304,405 Sensor element 401 Header 403 Filter 500 Infrared sensor 501 Infrared sensor element 502 Infrared filter 503,505 Semiconductor substrate 504 Reflecting mirror 506 Cavity 601 Silicon P type substrate 602 Oxide film 603 Polysilicon sacrificial layer 604n Type epitaxial layer 605, 607 Si3N4 film layer 608 Opening 611 Infrared light receiving part 612 Absorbent 701 Silicon Substrate 702 Oxide film 703 Si3N4 film layer 704 Opening 705 Concave surface 801 Optical element 901 Piezo diffusion resistance 1001 Semiconductor substrate 1002 Oxide film 1003 Polysilicon sacrificial layer 1005, 1006 Si3N4 film layer 1007 Absorbent 1008 Opening 1100 Infrared ray sensor 1100 Cavity 1104 Reflecting mirror 1105 Concave surface 1200 Infrared receiver

Claims (1)

(57) [Claims] An oxide film is formed on one main surface of a semiconductor substrate.
Si3 sandwiching the sacrificial layer and the infrared sensor element up and down
A first step of forming an N4 film layer, and placing the infrared sensor element portion laterally on the Si3 N4 film layer.
The opening is formed sandwiching the sacrifice layer and the sacrifice layer.
And a portion of the oxide film thereunder that overlaps the sacrificial layer.
Second Step of Forming Infrared Detector by Etching Removal
And the semiconductor substrate isotropically etched from the opening.
A third step of forming a concave surface, and a fourth step of forming a reflecting mirror on the concave, the infrared filter components to cover the infrared detecting part before
And the fifth step of bonding on the semiconductor substrate.
A method for manufacturing an infrared sensor.