JP2771277B2 - Infrared sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an infrared sensor, in particular, a thermal infrared sensor capable of operating at room temperature.

2. Description of the Related Art Thermopiles and bolometers have been known as thermal infrared sensors operating at room temperature (for example, Japanese Patent Application Laid-Open No. Sho 59-95428).

FIGS. 9 and 10 show an example of the thermopile and the bolometer. Each of these sensors is thinned by etching the substrate 10 serving as a light receiving unit from the back surface, and is configured such that when infrared rays are absorbed by the absorbing film 12, the temperature of the thin film substrate 10a rises. The temperature rise is detected and output from the electrodes 18 and 18 as a thermoelectromotive force of the thermoelectric materials 14 and 16 in the thermopile shown in FIG. 9 and as a change in the resistance value of the resistor 20 in the bolometer shown in FIG. The magnitude of the output depends on the temperature change at the time of light reception determined by the thermal insulation structure such as the thin film substrate 10a and the temperature coefficient of the temperature sensor, that is, the Seebeck coefficient of the materials 14 and 16 in the thermopile, and the resistance 20 of the resistor 20 in the bolometer. It is determined by the temperature coefficient of resistance.

[Problems to be Solved by the Invention] However, the conventional infrared sensor has the following problems.

: Since the substrate 10 of the light receiving section is etched from the back surface, an alignment error easily occurs on both surfaces of the substrate. For this reason, there is a problem in that the position of the central part of the thin film substrate 10a where the temperature rise at the time of light reception is the largest and the temperature sensink part are displaced, resulting in a decrease in sensitivity and a variation in sensitivity. This problem cannot be ignored as the size of the sensor is reduced.

: In a bolometer as shown in FIG. 10, a resistor 20 functioning as a temperature sensing unit is used to increase sensitivity.
Needs a certain length. Therefore, since the resistance value changes in the form of averaging the temperature distribution for the length of the resistor 20, it is possible to efficiently detect the temperature change at one point in the center of the thin film substrate 10a where the temperature rise at the time of light reception is the largest. There was a problem that it was not possible.

On the other hand, in a thermopile as shown in FIG. 9, it is possible to efficiently detect a temperature change at the time of light reception by placing a hot junction 22 at one point in the center of the thin film substrate 10a. Since the Seebeck coefficient is two to three digits smaller than the resistance temperature coefficient of the bolometer, it is difficult to accurately detect a minute temperature change during light reception.

In some cases, multiple thermocouples are connected in series to increase the output.However, in this case, the number of thermocouple materials connecting the hot junction and the cold junction increases, resulting in poor thermal insulation and a rise in temperature during light reception. There was a problem that it could not be obtained efficiently.

: In a thermopile and a bolometer, there is also a problem that the measured value is easily affected by noise because the impedance of the sensor portion is large.

[Object of the Invention] The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a high-sensitivity infrared sensor that operates at room temperature.

Means for Solving the Problems To achieve the above object, an infrared sensor according to the present invention has a symmetrical shape formed on a semiconductor substrate and an etching-resistant material and provided on a main surface of the semiconductor substrate. An insulating membrane having, at least two openings provided so as to reach the semiconductor substrate through the membrane and maintain the symmetry of the membrane, and a semiconductor substrate below the membrane via the opening. A thermal insulation chamber formed by etching away a part thereof, a diode provided at a center of symmetry on the membrane, and an infrared absorbing film provided in a light receiving region on the membrane. The temperature change at the center of symmetry of the membrane is detected using the diode.

[Operation] Next, the operation of the present invention will be described.

When infrared light enters the infrared sensor of the present invention, the infrared light is absorbed by the infrared absorption line provided on the light receiving region of the membrane. At this time, due to the thermal insulation of the symmetric membrane, a temperature rise occurs at the top of the symmetric center.

This temperature rise is measured by a diode provided at the center of symmetry of the membrane, and the reception of infrared light is detected.

FIG. 8 shows the current-voltage characteristics of the diode provided at the center of symmetry using temperature as a parameter.
As is clear from the figure, this diode can output a temperature change at the center position of the membrane as an electric signal.

Thus, in the present invention, the insulating membrane is formed in a symmetrical shape. The symmetry of the membrane is to efficiently raise the temperature at the time of light reception and to clarify the position where the temperature rises most, that is, the center position of the symmetry.

In the present invention, since a diode capable of detecting the temperature at one point is used as the temperature detection method, this diode is installed at the symmetric center position of the membrane where the temperature change at the time of light reception is the largest, so that this center is obtained. A temperature change at a position can be detected efficiently.

In particular, by combining the infrared sensor of the present invention with a lens system and bringing a diode to the focal position of the lens system, the detection sensitivity of infrared light can be significantly improved.

Further, in the present invention, by providing a heat insulating chamber below the membrane, the received heat is prevented from being transmitted to the substrate in the vertical direction and escaped. Thereby, the heat absorption efficiency of the infrared absorbing film can be further improved, and the detection accuracy of infrared light by the diode can be improved.

In particular, in the present invention, as described in claim (5), the infrared absorbing film includes an upper layer made of an infrared absorbing material;
It is preferable to form a multilayer film including a lower layer portion made of a material having good thermal conductivity and reflecting infrared rays. As a result, the infrared light that has entered the infrared absorbing film and transmitted without being absorbed by the upper layer is reflected by the lower layer and is absorbed again by the upper layer. As a result, it is possible to further increase the infrared absorption efficiency and to increase the infrared detection accuracy.

In particular, such an infrared absorbing film is preferably provided over a large area including the diode. Thus, the heat absorbed in a large area can be collected in the diode via the lower layer having good thermal conductivity, and the accuracy of infrared detection can be further improved.

Further, as described above, in the present invention, a diode is used as the temperature detecting unit. The temperature characteristic of this diode is about the same as the temperature resistance coefficient of the bolometer, and is two to three orders of magnitude larger than the Seebeck coefficient of a thermopile. For this reason, a minute temperature change at the time of light reception can be reliably detected, and from this point, the infrared temperature detection accuracy can be improved.

Further, since the diode has a small impedance, it is less susceptible to noise than the thermopile or the bolometer, and can perform highly accurate infrared detection.

In particular, as for the diode, it is preferable to connect a total of four semiconductor leads, two on each side of the PN junction, as described in claim (4). Here, the formation of the four leads is for allowing a constant current to flow to the diode through two of the four leads and for directly detecting the junction voltage of the diode by the remaining two leads. Alternatively, the current flowing through the remaining two diodes is adjusted so that the junction voltage of the diode detected by the two leads is constant, and the current value is detected.

As a result, a change in junction voltage of the diode at the time of light reception can be directly detected, so that infrared light can be detected without being affected by the temperature characteristics of the lead itself.

A major feature of the present invention is that an infrared sensor can be manufactured by processing one surface of a semiconductor substrate. As a result, the alignment accuracy between the diode functioning as a temperature sensor and the membrane is remarkably improved, and the decrease in sensitivity and the variation in sensitivity due to the alignment error can be significantly reduced.

In particular, according to the present invention, even when the size of the infrared sensor is miniaturized, the diode and the membrane can be aligned with sufficiently high accuracy. It can be performed with high accuracy.

In particular, by using silicon nitride as the material of the membrane and forming the diode from doped polycrystalline silicon, the infrared sensor of the present invention can be manufactured by a normal LSI process, and it is possible to reduce the size and cost. And the signal processing circuit can be easily integrated.

[Effects of the Invention] As described above, according to the present invention, since the infrared sensor can be formed by processing the surface of the semiconductor substrate on one side, the alignment accuracy between the diode functioning as a temperature sensor and the membrane can be improved. Since the positioning accuracy can be remarkably increased, and particularly, even when the size of the sensor is miniaturized, the positioning accuracy does not decrease, there is an effect that a stable and highly sensitive infrared sensor can be obtained.

Further, according to the present invention, based on the temperature change at the center of symmetry of the membrane where the temperature change at the time of receiving infrared rays is the largest, it is possible to detect ultraviolet rays with extremely high accuracy. Since a small diode is used, there is an effect that infrared light can be detected without being affected by noise.

Embodiment Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

First Embodiment Next, a first preferred embodiment of the infrared sensor according to the present invention will be described sequentially along the manufacturing process. FIG. 1 shows this infrared sensor. FIG. 1A is an explanatory plan view of an essential part thereof, and FIG. 1B is an explanatory side sectional view of the essential part thereof.

First, the infrared sensor of the embodiment uses silicon having the (100) plane as a main surface as the semiconductor substrate 30. And
A silicon nitride film is formed as a membrane 40 over the entire main surface of the silicon substrate 30 to a thickness of 200 nm by low-pressure CVD.

Next, a diode 50 is provided on the surface of the membrane 40 as a temperature detection sensor. In the embodiment, the diode 50 is formed by doping boron and arsenic into polycrystalline silicon having a thickness of 200 nm to form P-type and N-type semiconductor leads 52 and 54, respectively, and by a PN junction at the boundary. Is done.

Next, a silicon nitride film is formed as a protective film 60 on the entire surface including the diode 50. In this embodiment, a silicon nitride film is formed to a thickness of 200 nm by low pressure CVD. At this time, heat conduction in the film thickness direction is not hindered because the cross-sectional area is large and the film thickness is extremely thin at 200 nm.

Next, at predetermined positions in the light receiving region, at least two etching solution injection openings 70 that penetrate the protective film 60 and the membrane 40 and reach the silicon substrate 30 are provided. In the embodiment, as shown in FIG. 1A, two openings 70, 70 are formed substantially symmetrically with the diode 50 interposed therebetween.

At this time, the membrane 4 left by the openings 70, 70
The shape of 0 needs to be formed to be a line-symmetric or point-symmetric plane-symmetric shape. In addition, the diode 50
Need to be provided on the axis of symmetry or on the point of symmetry of the membrane 40 formed in such a symmetrical shape.

Then, an alkaline solution, for example, an etching solution composed of an aqueous solution of potassium hydroxide is injected into the openings 70, 70, and anisotropic etching is performed to form a heat insulating chamber 80. In the embodiment, the region where the silicon substrate 39 is etched is
This is limited by forming a sacrificial phase made of polycrystalline silicon having a thickness of 70 nm between the silicon substrate 30 and the membrane 40 in advance. This sacrificial film is formed later by providing polycrystalline silicon in a region where substrate etching is performed.

Finally, gold black is vapor-deposited on the light-receiving region where the diode 50 is drawn to form the infrared absorbing film 90.

As described above, according to the present invention, since the ultraviolet sensor can be manufactured by processing the main surface of the silicon substrate 30 on one side, alignment between the diode 50 functioning as a temperature sensor and the membrane 40 can be performed easily and accurately. Can be. Therefore, even when the size of the infrared sensor is miniaturized, the diode 50 can be accurately positioned at the center of symmetry of the membrane 40, and stable and highly sensitive infrared detection accuracy can always be obtained.

In particular, in this embodiment, since the LSI process technology and the microfabrication technology with silicon are used, a small-sized, low-cost infrared sensor having stable detection accuracy can be realized.

Next, the operation of the infrared sensor according to the present embodiment will be described.

First, when the infrared sensor irradiates the infrared sensor of the embodiment, the infrared light is absorbed by the infrared absorbing film 90. When infrared rays are absorbed in this manner, a temperature rise occurs at the apex of the center of symmetry due to the thermal insulation of the membrane 40 having a symmetric shape.

In particular, in the present invention, since the heat insulating chamber 80 for preventing heat transfer to the substrate 30 is provided on the back surface side of the membrane 40, the temperature can be efficiently increased at the time of light reception.

The temperature rise at the center of the membrane is output as an electric signal by the diode 50 having the temperature characteristic shown in FIG. 8, and the reception of infrared light is detected.

In particular, the diode 50 used as a temperature sensor can detect the temperature at the center of symmetry of the membrane 40 at a single point, and its temperature coefficient is almost the same as the temperature coefficient of the bolometer. It can be performed with sensitivity.

Further, since the impedance of the diode 50 is extremely small, the diode 50 is hardly affected by noise, and from this point, infrared rays can be stably detected without being affected by surrounding conditions.

The magnitude and speed of the temperature rise at the time of receiving infrared rays depend on the shape of the membrane 40 left by the opening 70. For this reason, in the case of a bridge type membrane 40 as shown in FIG. 1, a thinner and longer bridge can obtain a more efficient temperature rise.

Second Embodiment FIG. 2 shows a preferred second embodiment according to the present invention. Members corresponding to those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The characteristic feature of this embodiment is that the P-type and N-type semiconductor leads 52 and 54 are formed on both sides of the diode 50 so as to branch into two.

This makes it possible to detect only the temperature characteristic of the diode 50 irrespective of the temperature characteristic of the P-type or N-type semiconductor lead itself.

That is, for example, the leads 52a and 54a are selected from the two P-type semiconductor leads 52a and 52b and the N-type semiconductor leads 54a and 54b, and a forward constant current is passed through them. Then, by reading the voltage change between the remaining two semiconductor leads 52b and 54b, the change in the junction voltage of the diode 50 is directly detected without being affected by the temperature characteristics of the P-type and N-type semiconductor leads themselves. be able to.

In particular, the infrared sensor of this embodiment is effective when the diode 50 is formed using a material having a high resistance value.

Third Embodiment FIG. 3 shows a third preferred embodiment of the infrared sensor according to the present invention. The members corresponding to those of the above embodiments are denoted by the same reference numerals, and description thereof will be omitted.

This embodiment is characterized in that the infrared absorbing film 90 is composed of an upper layer portion 92 made of an infrared absorbing material and a lower layer portion made of a material having good thermal conductivity and reflecting infrared rays as shown in FIG.
94, and the multilayer film is formed as shown in FIG.
As shown in FIG. 5, a large area including the diode 50 is covered.

In the embodiment, gold black was used for the upper layer portion 92, and aluminum formed by vapor deposition was used for the lower layer portion 94.

With the above configuration, according to the present embodiment, the heat absorption rate of the infrared absorbing film 90 can be improved in each step. That is, the infrared light transmitted without being absorbed by the upper layer portion 92 is reflected by the surface of the lower layer portion 94, passes through the upper layer portion 92 again, and is absorbed. For this reason, the heat absorption of the infrared absorbing film 90 is remarkably improved as compared with the case where the infrared absorbing film 90 is constituted only by the upper layer portion 92. When using absorbent material,
The same effect can be obtained with a half of the film thickness.

In addition, according to the present embodiment, since the infrared absorbing film 90 is formed over a wide area including the diode 50, a large light receiving area can be obtained, and heat absorbed in the wide area is collected in the diode 50. be able to.

That is, the incident infrared light is absorbed by the upper layer portion 92 made of the infrared absorbing material and converted into heat, and the heat reaches the diode 50 mainly through the lower layer portion 94 having good thermal conductivity. Therefore, when the infrared absorbing film 90 having a large area is provided, the heat absorbed in the large area is efficiently transmitted to the diode 50, and more heat is supplied to the diode 50.

As described above, according to the present embodiment, it is possible to more efficiently detect infrared rays by efficiently absorbing infrared rays and collecting them in the diode 50.

In particular, by using the infrared absorbing film 90 as in the present embodiment, even when the temperature sensing area is small as in the diode 50, infrared detection can be performed with high accuracy.

Fourth Embodiment FIG. 4 shows a fourth preferred embodiment of the present invention. The members corresponding to those of the above embodiments are denoted by the same reference numerals, and description thereof will be omitted.

The feature of this embodiment lies in that it is configured to have all the features of the first to third embodiments. That is, in the present embodiment, the diode 50 and the opening 70 are connected to the second
The infrared absorbing film 90 is formed in the same manner as in the third embodiment, and the infrared absorbing film 90 is formed in the same manner as in the third embodiment.

With the above configuration, incident infrared light can be detected at high speed and with high sensitivity.

Fifth Embodiment FIG. 5 shows a fifth preferred embodiment of the infrared sensor according to the present invention. FIG. 5A is an explanatory view of the planar structure, and FIG. FIG. In addition,
The same reference numerals are given to members corresponding to the respective embodiments, and the description thereof will be omitted.

The feature of this embodiment is that it is formed so as to have all the features of the first to third embodiments. That is, the diode 50 is formed in the same manner as in the second embodiment, and its semiconductor leads 52a, 52b, 54a, 54b are connected to the corresponding AL electrode 56.

Further, the infrared absorbing film 90 of this embodiment is formed in the same manner as in the third embodiment, and a heat collecting aluminum 62 is provided between the absorbing film 90 and the protective film 60.

With the above configuration, according to the infrared sensor of the present embodiment, the membrane is compared with the sensor of the fourth embodiment.
Since the strength of 40 is superior, the production yield can be increased. In addition, since the heat capacity of the membrane 40 is small, infrared rays can be detected at high speed. That is, the detection speed is higher as the thermal time constant of the sensor is smaller, and the thermal time constant is proportional to the heat capacity. In the membrane of the embodiment, since a large number of openings are provided, the heat capacity of the membrane is reduced, and the temperature is rapidly changed.

FIG. 6 shows the output characteristics of this embodiment. In the figure, the horizontal axis represents the difference between the surface temperature of the object to be measured and room temperature, and the vertical axis represents the output of the sensor of the embodiment. In the measurement, at room temperature T _RT = 25 ° C., the semiconductor leads 52a and 54a
The other semiconductor leads 52b, 54b
The voltage change output from was measured. From this data,
It will be understood that highly sensitive sensing is possible.

Sixth Embodiment FIG. 7 shows a sixth preferred embodiment of the present invention.

The feature of this embodiment is that the infrared sensor is integrated with a signal processing circuit and is formed as a so-called integrated infrared sensor.

FIG. 7 is an external view of the infrared sensor according to the present embodiment. In the present embodiment, the silicon substrate 30
The infrared sensor 100 of the present invention described in the first to fifth embodiments is formed at a predetermined position on the main surface of the semiconductor substrate 30. Further, an integrated circuit for amplifying the output from the infrared sensor 100 and performing signal processing is formed on the silicon substrate 30. Circuit 200, sensor 100 and integrated circuit
A plurality of electrodes 210 for connecting to a lead and connecting to the outside are provided.

In particular, in this embodiment, the lower substrate 30 is provided in the integrated circuit 200.
By incorporating the diode 50 which has not been etched and detecting its temperature characteristic, it becomes possible to correct changes in the output from the infrared sensor 100 and the characteristic of the amplification amplifier due to the substrate temperature.

Thus, it will be understood that the present embodiment is extremely suitable when the infrared sensor 100 is integrated with the integrated circuit 200 and is manufactured as a so-called integrated sensor.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention.

For example, in the above embodiment, the case where the membrane 40 is formed using a silicon nitride film has been described.
The present invention can be formed using a multilayer film including at least a silicon nitride film, or any other various materials as long as the material has etching resistance.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a preferred first embodiment of an infrared sensor according to the present invention, wherein FIG. 1 (A) is an explanatory plan view thereof, FIG. 1 (B) is a schematic explanatory sectional side view thereof, FIG. FIG. 3 is an explanatory view showing a preferred second embodiment of the present invention, FIG. 3 is an explanatory view showing a preferred third embodiment of the present invention, and FIG. FIG. (B) is a cross-sectional explanatory view of the infrared absorbing film, FIG. 4 is an explanatory view of a preferred fourth embodiment of the present invention, FIG. 5 is an explanatory view of a preferred fifth embodiment of the present invention, 6A is an explanatory view of the planar structure, FIG. 6B is an explanatory view of the cross-sectional structure, FIG. 6 is an output characteristic diagram of the sensor of the fifth embodiment, and FIG. 7 is an infrared ray of the present invention. FIG. 8 is an explanatory view showing a case where a sensor is integrated on a substrate together with a signal processing circuit. FIG. 9 and 10 are explanatory diagrams of a thermopile and a bolometer conventionally used as an infrared sensor. 30 ... semiconductor substrate, 40 ... membrane, 50 ... diode, 60 ... protective film, 70 ... opening, 80 ... thermal insulation chamber, 90 ... infrared absorption film, 92 ... upper layer, 94 ... ... Lower layer, 100 ... Infrared sensor.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01J 1/02 G01J 5/02 G01J 5/20

Claims (6)

(57) [Claims] A semiconductor substrate formed of an etching-resistant material and provided on a main surface of the semiconductor substrate, the insulating membrane having a symmetric shape, the membrane reaching the semiconductor substrate through the membrane; At least two provided to maintain the symmetry of
A plurality of openings, a heat insulating chamber formed by etching and removing a part of the semiconductor substrate below the membrane through the opening, a diode provided at a symmetric center position on the membrane, An infrared sensor comprising: an infrared absorbing film provided in a light receiving region; and detecting the infrared light reception as a temperature change at a symmetric center position of the membrane using the diode. 2. The infrared sensor according to claim 1, wherein the membrane is formed of a silicon nitride film or a multilayer film including at least a silicon nitride film. 3. The infrared sensor according to claim 1, wherein said diode is formed by doping polycrystalline silicon. 4. The semiconductor device according to claim 1, wherein a total of four semiconductor leads are connected to each of two sides of the PN junction of the diode, and a diode is connected from the four semiconductor leads. An infrared sensor which outputs a detection signal of the infrared ray. 5. The infrared absorbing film according to claim 1, wherein the infrared absorbing film comprises an upper layer made of an infrared absorbing material and a lower layer made of a material having good heat conductivity and reflecting infrared rays. An infrared sensor comprising a multilayer film including the diode, wherein the infrared absorbing film is formed in a wide area including the diode. 6. The semiconductor device according to claim 1, wherein a predetermined signal processing circuit, a plurality of electrodes for input and output of the signal processing circuit and a diode are provided on the main surface of the semiconductor substrate. And a plurality of leads for connecting the diode and the signal processing circuit.