JP2567474B2 - Infrared sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a thermopile type infrared sensor having high detection sensitivity.

(Prior Art) As a conventional thermopile type infrared sensor, for example, there is one as shown in FIG. 6 and FIG.
o Other `` AN INFRARED SENSING ARRAY BASED ON INTE
GRATED SILICON THERMOPILES "TRANSDUCERS '87 p
p.227-230 (1987)).

In FIGS. 6 and 7, 21 is a p-type silicon substrate as a semiconductor substrate, 22 is an n-type epitaxial layer, and n
The cantilever 23 is formed by etching away the p-type silicon substrate portion and the surrounding three sides below the epitaxial layer 22. The thinned cantilever 23 having a large thermal resistance forms a heat separation region that is thermally separated from the substrate region (hereinafter, the substrate region is also denoted by the same reference numeral 21 as the p-type silicon substrate). A silicon oxide film 24 is formed on the surface of the n-type epitaxial layer 22 including the cantilever 23.

An infrared absorption layer 25 is formed at the tip of the cantilever 23, and a p-type diffusion layer resistance (p-type semiconductor resistance layer) 26 is formed from the infrared absorption layer 25 toward the substrate region 21 which is the fixed portion. The book is formed in parallel. The three p-type diffusion layer resistors 26 are connected in series by the Al wiring 27 via the contact holes to form the thermopile 30. Reference numeral 28 is an n ⁺ contact region for applying a bias potential to the n-type epitaxial layer 22.

Now, when infrared rays are incident on the infrared absorption layer 25 of the thermopile type infrared sensor having such a structure, this energy is converted into heat, the temperature of the tip side of the cantilever 23 rises, and the temperature of the substrate area 21 side is increased. There is a temperature difference between them. The cantilever structure has only one side connected to the substrate area 21
Since an N ₂ atmosphere or a vacuum can be made, the thermal resistance from the infrared absorption layer 25 at the tip of the cantilever 23 to the substrate region 21 can be increased, and the heat converted by the infrared absorption layer 25 can be used. The resulting temperature difference can be increased. This temperature difference causes electromotive force on both ends 27a and 27b of the thermopile 30.
V ₀ occurs. Assuming that the infrared sensor chip is now mounted in a vacuum state and that the heat generated at the tip side of the cantilever 23 flows only through the Si (silicon) cantilever 23, the incident energy P _{0 of the} infrared ray P ₀ On the other hand, the electromotive force V ₀ of the thermopile 30 is expressed as follows.

V ₀ = n · α _P · R ₀ · P ₀ (1) where n is the p-type diffusion layer resistance forming the thermopile 30.
The number of 26, α _P, is the Seebeck coefficient of the p-type diffusion layer resistance 26, and the Seebeck effect of the Al wiring 27 is sufficiently small and can be ignored. R ₀ is the thermal resistance from the tip of the cantilever 23 to the substrate region 21, where the thermal resistance of the Si cantilever 23 and the thermal resistance of the Al wiring 27 formed on the cantilever 23 are It becomes a parallel combined resistance and is expressed as follows.

R ₀ = L / (K _SI・ A _SI ＋ K _AL・ A _AL ) (2) where L is the length of the cantilever 23, K _SI and K _AL are respectively
The thermal conductivity of Si and Al, A _SI and A _AL are Si cantilever 23 and Al, respectively.
It is a cross-sectional area of the wiring 27.

Now, the cantilever 23 has a length L = 2 mm, a width 400 μm, and a thickness 10
Considering an infrared sensor of μm, the thermopile 30 is composed of 10 p-type diffusion layer resistors 26 (n = 10), K _SI
= 1.41 (W / cm · K) and K _AL = 2.36 (W / cm · K), the thermal resistance R ₀ has the following value from the above equation (2).

R ₀ = 0.2 / [1.41 x (400 x 10) x 10 ^-8 +2.36 x (1 x 20) x 10 ^-8 x 10] = 3.27 x 10 ³ (K / W) Therefore, for example, α _P = 1 mV Assuming / K, V ₀ = 32.7 mV for P ₀ = 1 mW incident.

Next, a method of manufacturing such a cantilever infrared sensor will be briefly described. First, the n-type epitaxial layer 22 is formed on the p-type silicon substrate 21 as in the bipolar process.
After 10 to 20 μm growth, p-type element isolation diffusion (not shown) is performed to reach the p-type silicon substrate 21 in a U-shape so as to surround the cantilever beam 23 from three sides. Next, the p-type diffusion layer resistor 26 which constitutes the thermopile 30 is formed, and then the n ⁺ contact region 28 is formed. Next, an etching resistant film such as a silicon nitride film is deposited on the back surface of the wafer. After etching the contact hole and forming the Al wiring 27, a window is opened in the etching resistant film on the back surface and the p-type silicon substrate 21 is biased from the back surface to KOH, E while biasing the n-type epitaxial layer 22 to a positive potential.
Etch with a strong alkaline anisotropic silicon etching solution such as DP (ethylenediamine / pyrocatechol aqueous solution) (electrochemical etching). When the etching progresses to reach the n-type epitaxial layer 22, the etching is stopped, but the p-type element isolation region formed in the U shape is continuously etched, and the cantilever structure as shown in FIG. 6 is completed.

(Problems to be Solved by the Invention) In the conventional infrared sensor, the heat separation structure is
Since the cantilever was formed, the infrared absorption layer was formed at the tip of the cantilever, and the thermopile was formed by the p-type diffusion layer resistance and Al wiring between the infrared absorption layer and the substrate area. , The thermal resistance of the cantilever portion of Si cannot be sufficiently increased, and it is difficult to increase the infrared detection sensitivity.

Therefore, an object of the present invention is to provide an infrared sensor capable of significantly increasing the thermal resistance of the heat separation structure portion and significantly increasing the infrared detection sensitivity.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, an infrared sensor according to the present invention is configured such that a substrate region of a semiconductor substrate is thermally separated from a space of the substrate region. One or more pairs of p-type semiconductor resistor portions and n-type semiconductor resistor portions, each of which is formed in a column shape between the formed infrared absorbing portion and are alternately arranged with a space therebetween in the width direction. The gist is that the thermopile is formed by bridging and connecting the p-type semiconductor resistance part and the n-type semiconductor resistance part alternately in series.

(Operation) According to the infrared sensor of the present invention, the thermopile is formed by alternately connecting one or more pairs of p-type semiconductor resistance portions and n-type semiconductor resistance portions in series.
The Seebeck effect of both the n-type semiconductor resistance part and the n-type semiconductor resistance part is utilized. Here, the thermoelectromotive force with respect to the temperature difference generated between the terminals of the thermopile is obtained in relation to the product of the sum of the Seebeck coefficients of the two types of resistance portions and the incident energy of infrared rays, etc. Compared with using only the Seebeck effect of the semiconductor resistance layer,
The conversion efficiency of the thermoelectromotive force with respect to the temperature difference generated between the terminals of the thermopile is significantly improved.

Moreover, in addition to increasing the sensitivity of the infrared sensor by connecting the resistance units in series, the thermopile is formed into a substrate region of the semiconductor substrate and an infrared absorption unit formed so as to separate heat from the substrate region with a space. And a pair of p-type semiconductor resistance portions and n-type semiconductor resistance portions, which are formed in a columnar shape and are alternately arranged in the width direction with a space therebetween. Because I did
The p-type semiconductor resistance part and the n-type semiconductor resistance part are thermally separated from each other with a space therebetween, and the thermal resistance generated between the terminals of the thermopile is set to a sufficiently large value. The temperature difference between the terminals becomes large, and as a result, higher sensitivity of the infrared sensor is realized.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 to 4 are views showing an embodiment of the present invention.

First, the structure of the infrared sensor will be described. In FIGS. 1 to 3, 1 is a p-type silicon substrate serving as a semiconductor substrate, 2 is an n-type epitaxial layer, and a part of the n-type epitaxial layer 2 and its lower part. Side p-type silicon substrate is removed by etching until the surface side,
A cantilever portion composed of a semiconductor resistance portion of a book and an infrared ray supported by the cantilever portion so as to be thermally separated from a substrate region (hereinafter, also referred to as a substrate region by the same reference numeral 1 as a p-type silicon substrate). The absorption section 20 is formed. Infrared absorber
A silicon oxide film 3 is formed on the surface of the n-type epitaxial layer 2 including portions such as 20.

Each of the beams in the cantilever portion is made of silicon oxide 3,
3a is formed by a p-type semiconductor resistor 4 and an n-type semiconductor resistor 5, and these p-type semiconductor resistor 4 and n-type semiconductor resistor 5 are alternately connected in series by a wiring layer 7 via a contact portion 6. The thermopile 10 consists of two pairs of thermocouples. The n-type semiconductor resistor 5 is formed by separating the beam-shaped portion of the n-type epitaxial layer 2 formed by etching using the p ⁺ element separation diffusion region 8.

In addition, the infrared absorption section 20 includes the p ⁺ element isolation diffusion region 8 and
It is formed by depositing an infrared absorption layer 11 of carbon black or the like on the island-shaped region of the n-type epitaxial layer 2 surrounded by the p ⁺ buried layer 9 via the silicon oxide film 3.

Next, an example of the manufacturing method will be described with reference to FIG. 4 to further describe the configuration thereof. In the following description, the item symbols (a) to (d) correspond to the items (a) to (d) in FIG. 4, respectively.

(A) A p-type silicon substrate 1 having a (100) plane is prepared, a p ⁺ buried layer 9 is formed on the main surface thereof, and then an n-type epitaxial layer 2 is formed.
Is grown, and ap ⁺ element isolation diffusion region 8 and a p-type diffusion region to be the p-type semiconductor resistor 4 are sequentially formed in the n-type epitaxial layer 2. Next, a cantilever portion composed of a semiconductor resistance beam surrounded by the silicon oxide films 3 and 3a constituting the thermopile 10 is manufactured as follows.

That is, the silicon nitride film 12 is formed as an oxidation resistant film on the silicon oxide film 3 formed on the surface of the n-type epitaxial layer 2 by LP.
It is deposited by CVD and then reactive ion etching (RI
A silicon oxide film 13 is deposited by CVD as a mask of E) to form a three-layer film.

(B) The above three-layer film is patterned into a required pattern, and Si is etched by RIE to form a vertical groove 14 <1.
Formed along the 10> direction.

(C) The inner surface of the groove 14 is etched with an alkaline anisotropic etching solution such as KOH. When etching is performed with an alkaline anisotropic etching solution, the etching proceeds until the diamond-shaped cross section surrounded by the (111) plane is reached, and the etching is stopped there. This is because the etching rate of the (111) plane is extremely slow. At this time, the width of the semiconductor resistance beam whose cross-sectional shape is an inverted triangle can be easily controlled by adjusting the etching depth of the groove 14.

(D) Oxidation treatment is performed until the constricted portion is completely formed into the silicon oxide film 3a, and p-type and n-type semiconductor resistors 4 and 5 composed of triangular pillar-shaped single-crystal silicon regions separated by the oxide film are formed on the upper side thereof. To do.

After that, the silicon nitride film 12 is removed, contact etching, n ⁺ or p ⁺ contact portion ion implantation (not shown) for taking ohmic contact with the n-type semiconductor resistor 5 and the p-type semiconductor resistor 4, wiring The layer 7 is formed. Finally,
By etching the silicon substrate 1 from the back side to the front side with an anisotropic anisotropic etching solution such as KOH using the silicon nitride film as a mask, an infrared sensor having a structure as shown in FIGS. 1 to 3 is obtained. obtain. Where p-type and n
Since the semiconductor resistors 4 and 5 of the shape are surrounded by the silicon oxide film 3a and the infrared absorption portion 20 is surrounded by the p ⁺ regions 8 and 9, neither of them is etched and the beam shape is changed. The cantilever composed of the semiconductor resistance part and the infrared absorbing part 20 supported by the cantilever are formed.

Next, the operation of the infrared sensor configured as described above will be described.

When infrared rays enter the infrared absorption section 20, the energy is converted into heat and the temperature rises, and a temperature difference occurs between the infrared ray absorption section 20 and the base region 1. Due to this temperature difference, both ends of the thermopile 10
An output electromotive force V ₀ is generated at 7a and 7b. At this time, the electromotive force
V ₀ is the thermal resistance of the cantilever, as shown in the equation (1).
It increases in proportion to R ₀ . Further, in this embodiment, the cantilever portion is composed of a plurality of semiconductor resistance beams, and the thermal resistance R ₀
Is set to an extremely large value, the electromotive force V ₀ is increased and the infrared detection sensitivity is significantly improved.

That is, the length L of the cantilever portion is 2 mm, and the thermopile 10
Consists of 10 pairs of semiconductor resistive beams, each beam having a width of 10
μm. Here, regarding the heat conduction by the silicon oxide films 3 and 3a, assuming that the heat conductivity of SiO ₂ is 0.014 (W / cm · K), that value is about two orders of magnitude smaller than that of Si. Furthermore, since the film thickness is as thin as about 1 μm, it can be ignored. Therefore, the thermal resistance R ₀ of the cantilever beam has the following value.

R ₀ = 0.2 / [1.41 × (10 × 5 · tan 54.74 ° × 1/2) × 10 ⁻⁸ × 20] = 2.02 × 10 ⁶ (K / W) Thus, the cantilever of this embodiment is used. The thermal resistance R _{0 of the} portion becomes extremely large as compared with the conventional one, and a very high heat conversion efficiency is obtained, and the infrared detection sensitivity is remarkably enhanced.

In FIG. 1, the thermopile 10 is composed of two pairs of thermocouples with four semiconductor resistance beams, but the thermopile output is increased by increasing the number of thermocouples to further increase the infrared detection sensitivity. Can be increased.

 Next, FIG. 5 shows another embodiment of the present invention.

In FIG. 5, the same or equivalent members and parts as those in FIG. 1 and the like are designated by the same reference numerals, and the duplicated description will be omitted.

In the infrared sensor of this embodiment, two sets of thermopiles 10a and 10b, which also serve as a heat separating structure, are formed between both sides of the infrared detecting section 20 and the substrate region 1 facing each other. 10a and 10b are electrically connected in series.

In this embodiment, the thermal resistance of the thermal isolation structure is halved and the number of thermocouples is doubled, so the sensitivity does not change, but the mechanical strength can be increased.

In addition to the above configuration, four sets of thermopiles can be formed between the four sides of the infrared detection unit 20 and the substrate region 1.

In addition, each of the above-described embodiments has a structure of a p-type silicon substrate-n-type epitaxial layer, so that other bipolar devices and the like can be integrated on the same substrate, and a smart sensor in which peripheral circuits are integrated. Can be easily realized.

[Effects of the Invention] As described above, according to the infrared sensor of the present invention, the thermopile is formed by alternately connecting in series one or more pairs of p-type semiconductor resistor portions and n-type semiconductor resistor portions. Therefore, both Seebeck effects of the p-type semiconductor resistance part and the n-type semiconductor resistance part are utilized. Here, the thermoelectromotive force with respect to the temperature difference generated between the terminals of the thermopile is obtained in relation to the product of the sum of the Seebeck coefficients of the two types of resistance portions and the incident energy of infrared rays, etc. The conversion efficiency of the thermoelectromotive force with respect to the temperature difference generated between the terminals of the thermopile is significantly improved, as compared with the case where only the Seebeck effect of the semiconductor resistance layer is used.

Moreover, in addition to the high sensitivity ratio of the infrared sensor due to the series connection of the resistance parts, the thermopile is formed into a substrate region of the semiconductor substrate and an infrared absorption part formed so as to separate heat from the substrate region with a space. And a pair of p-type semiconductor resistance portions and n-type semiconductor resistance portions, which are formed in a columnar shape and are alternately arranged in the width direction with a space therebetween. Because I did
The p-type semiconductor resistance part and the n-type semiconductor resistance part are thermally separated from each other with a space therebetween, and the thermal resistance generated between the terminals of the thermopile is set to a sufficiently large value. The temperature difference between the terminals becomes large, and as a result, an extremely excellent effect is achieved that the sensitivity of the infrared sensor is further increased.

[Brief description of drawings]

1 to 4 show an embodiment of an infrared sensor according to the present invention. FIG. 1 is a plan view, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 1 is a sectional view taken along line BB of FIG.
FIG. 4 is a process drawing showing an example of the manufacturing process, FIG. 5 is a plan view showing a second embodiment of the present invention, FIG. 6 is a longitudinal section of a conventional infrared sensor, and FIG. It is a figure. 1: p type silicon substrate (semiconductor substrate), 2: n type epitaxial layer, 4: p type semiconductor resistor, 5: n type semiconductor resistor, 10, 10a, 10b: thermopile, 20: infrared absorption part.

Claims (1)

(57) [Claims] 1. A substrate region of a semiconductor substrate and an infrared absorbing portion formed so as to be thermally separated from the substrate region with a space therebetween, each having a columnar shape and having a space therebetween in the width direction. And one or more pairs of p-type semiconductor resistance parts and n-type semiconductor resistance parts arranged alternately, and the p-type semiconductor resistance parts and n-type semiconductor resistance parts are alternately connected in series. An infrared sensor characterized by being formed into a thermopile.