JP2005024342A - Thermal infrared imaging element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal infrared photographing element having improved detection sensitivity of infrared rays, and to provide a method for manufacturing the thermal infrared imaging element. <P>SOLUTION: The thermal infrared imaging element comprises a first substrate 2, where an address line 1 for selecting a pixel is formed; a heat-sensitive section 3 that is formed separately on the first substrate 2 and converts incident infrared rays to heat; at least a pair of support legs 4 for separating the heat-sensitive section 3 from the substrate 2 for support; and a microprism array (second substrate) 6, where a plurality of V-shaped grooves 5 for guiding infrared rays to the heat-sensitive section 3 while being arranged opposite to the first substrate 2 are formed with a pixel pitch. A microprism made of a V-shaped groove is formed on the second substrate 6, the projecting section of the first substrate 2 mates with the V-shaped groove in a self-alignment manner, so that the alignment between the heat-sensitive section 3 and the microprism can be made precisely, infrared rays entering the microprism can be guided to the heat-sensitive section 3 without any leakage, and sensitivity for detecting infrared rays can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal infrared imaging device including a heat sensitive part that converts infrared rays into heat.
[0002]
[Prior art]
In recent years, a vanadium oxide bolometer type using a micromachining technology and a BST (Barium-Strontium-Titanium) pyroelectric sensor have been commercialized as thermal infrared image sensors that do not require a cooling device. These products have a heat sensitive part that absorbs infrared rays and raises the temperature, support legs for thermally separating the heat sensitive part from the silicon substrate, horizontal address lines for selecting pixels, and vertical signal lines. It consists of and.
[0003]
In principle, this type of thermal infrared image sensor absorbs infrared rays radiated from a subject with a heat-sensitive portion, and at that time, detects a temperature rise of the heat-sensitive portion by a resistance change, a capacitance change, or the like. For this reason, the support leg that supports the heat-sensitive portion has a structure in which the cross-sectional area is reduced and the length is increased in order to enhance the heat insulating effect. The support leg is mainly composed of a silicon oxide film or a silicon nitride film and a wiring for transmitting an electric signal, but its thermal resistance value is about one digit larger than the thermal resistance of air. Therefore, in order to reduce heat conduction by air, the image sensor is mounted in a vacuum package.
[0004]
In order to convert infrared rays incident from the outside into heat, it is necessary to increase the light receiving area as much as possible. For this reason, a technique has been proposed in which a structure such as an umbrella is formed so as to cover the support legs and address lines, the light receiving area is increased, the substantial aperture ratio is increased, and the temperature rise due to incident infrared rays is increased (Patent Document 1). reference).
[0005]
However, when the thermal resistance of the support legs is the same, adding a structure such as an umbrella increases the heat capacity, so the thermal time constant defined by the product of the heat capacity and the heat resistance increases, and high-speed response is achieved. It has become a problem that afterimages are deteriorated.
[0006]
In order to solve such problems, a microlens that is also used in a visible light image sensor is arranged to improve the substantial aperture ratio and increase the sensitivity without increasing the thermal time constant. (See Patent Documents 2, 3, and 4).
[0007]
In particular, Patent Document 2 discloses that by using a microlens as a seal for vacuum, it is not necessary to mount an image sensor in a vacuum package.
[0008]
[Patent Document 1]
JP-A-10-209418 [Patent Document 2]
JP 7-318416 A [Patent Document 3]
JP-A-9-113352 [Patent Document 4]
Japanese Patent Laid-Open No. 2002-280532
[Problems to be solved by the invention]
In the infrared image sensor described in Patent Document 2 and the like, it is considered effective to align the optical axis of the microlens and the heat sensitive portion and to make the microlens thin because the heat sensitive portion needs to effectively absorb a small amount of light. .
[0010]
However, since special pattern alignment is required at the time of bonding, it is difficult to reduce the alignment accuracy to 1 μm or less. Also, since it is difficult to bond in vacuum after thinning, it must be bonded without thinning, and the yield of infrared rays in the heat sensitive part does not improve sufficiently, and sufficient sensitivity is obtained. There wasn't.
[0011]
On the other hand, Patent Document 4 discloses a technique for condensing light with a V-grooved microlens using a visible light image sensor. In this document, since the shape of the lower electrode serving as the light shielding plate is formed in a rectangular shape, it is described that the condensing efficiency is better when the microlens is rectangular rather than circular.
[0012]
In the visible light image sensor of Patent Document 4, since the material used as the microlens is directly laminated on the element chip, the deepest part of the V groove and the thinnest part from the underlying silicon oxide film layer or silicon nitride film layer are formed. The thickness can be almost zero, and the transmittance of the microlens can be increased.
[0013]
However, when the technique disclosed in Patent Document 4 is applied to a thermal infrared image sensor, Patent Document 4 does not sufficiently consider thermal separation between the microlens and the heat-sensitive part.
[0014]
The present invention has been made in view of these points, and an object of the present invention is to provide a thermal infrared imaging device capable of improving infrared detection sensitivity and a method for manufacturing the same.
[0015]
[Means for Solving the Problems]
In order to solve the above-described problem, the present invention provides a first substrate having an address line for selecting a pixel and a convex portion formed at a pixel pitch, and spaced apart on the first substrate. A heat-sensitive part arranged to convert incident infrared light into heat, at least one support leg for supporting the heat-sensitive part spaced apart from the first substrate, and disposed opposite to the first substrate, And a second substrate having a microprism array in which a plurality of microprisms each having an inclined surface that is refracted and condensed on the heat-sensitive portion is formed at a pixel pitch, and the concave portion is engaged with the groove. Be joined.
[0016]
The second substrate is formed of at least one material of germanium, silicon, zinc sulfide, and chalcogenide glass.
[0017]
Further, the present invention provides an address line for selecting a pixel, a plurality of convex portions formed at a pixel pitch, a thermal portion that is disposed between the convex portions and converts incident infrared rays into heat, and the thermal portion is spaced apart from each other. A plurality of grooves having an inclined surface for refracting incident infrared rays and condensing the incident infrared rays to the heat-sensitive part, at the same interval as the heat-sensitive part. A thermal infrared imaging device comprising a second substrate having a microprism array, wherein the groove of the second substrate is engaged with the convex portion of the first substrate. The groove and the convex portion are bonded in a vacuum, and the surface of the second substrate opposite to the surface facing the first substrate is polished.
[0018]
The convex portion and the groove are bonded by an anodic bonding method or a surface activated bonding method.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a thermal infrared imaging device and a manufacturing method thereof according to the present invention will be specifically described with reference to the drawings.
[0020]
FIG. 1 is a sectional view showing an example of a sectional structure of a thermal infrared imaging device according to the present invention, and shows a sectional structure of one imaging device. The size of one element is about 40 μm square, and the image sensor shown in FIG. 1 is two-dimensionally arranged to constitute a thermal infrared image sensor.
[0021]
1 includes a first substrate 2 on which an address line 1 for selecting a pixel is formed, and a thermosensitive portion that is formed on the first substrate 2 so as to be separated and converts incident infrared rays into heat. 3, at least one support leg 4 that supports the heat-sensitive part 3 at a distance from the first substrate 2, and a V-shaped groove 5 that is disposed opposite to the first substrate 2 and guides infrared rays to the heat-sensitive part 3. And a plurality of microprism arrays (second substrates) 6 formed at a pitch.
[0022]
The first substrate 2 is formed by etching the silicon substrate 7. Protrusions 8 are formed at a pixel pitch, and address lines 1 are formed inside the protrusions 8. The convex portion 8 of the first substrate 2 is engaged with and joined to the V-shaped groove of the second substrate 6.
[0023]
A hollow portion 9 is provided between the heat sensitive portion 3 and the first substrate 2, and a hollow portion 10 is also provided between the heat sensitive portion 3 and the second substrate 6. The groove 11 between the support leg 4 and the heat sensitive part 3, the groove 12 between the support leg 4 and the first substrate 2, and the hollow parts 9 and 10 are maintained in a vacuum state of 1 Pa or less.
[0024]
The heat sensitive unit 3 includes an infrared absorption layer (not shown) that absorbs incident infrared rays, and a sensor (not shown) that converts a temperature increase due to the absorbed infrared rays into an electrical signal. The support leg 4 has a small cross-sectional area and a long length in order to minimize the escape of heat from the heat-sensitive part 3.
[0025]
The second substrate 6 is formed of a material that transmits infrared rays of 8 to 12 μm, such as germanium, silicon, zinc sulfide, and chalcogenide glass, and has a plurality of V-shaped grooves formed in a two-dimensional direction at a pixel pitch. These V-shaped grooves function as microprisms 6 that refract incident infrared rays and collect them on the heat-sensitive portion 3, and the convex portions 8 of the first substrate 2 are joined to the V-shaped grooves.
[0026]
Thus, in this embodiment, the convex part 8 of the 1st board | substrate 2 is made to mesh with the V-shaped groove | channel of the 2nd board | substrate 6 in the self-alignment, and the 1st and 2nd board | substrates 2 and 6 of FIG. Positioning can be performed with high accuracy.
[0027]
The first and second substrates 2 and 6 are bonded by degassing after bonding, such as an anodic bonding method in a vacuum or a surface activated bonding method in which surfaces are activated by ion irradiation. Therefore, it is desirable that the processing temperature is 400 ° C. or less.
[0028]
By the above method, the vacuum degree of the hollow part between the 2nd board | substrate 6 and the heat sensitive part 3 will be 1 Pa or less, and an effective aperture ratio will also be 90%. As a result, according to the experiment by the present inventor, the thermal time constant determined by the product of the heat capacity of the heat sensitive part 3 and the thermal resistance of the support leg 4 is made the same as in the past, so that no afterimage is observed when shooting at 60 frames / second. In this state, the aperture ratio, which was only 50% in the past, improved by about 80%, and the sensitivity improved by about 80%.
[0029]
2 to 16 are process diagrams illustrating the manufacturing process of the first substrate 2. First, as shown in FIG. 2, an SOI (Silicon On Insulator) substrate 21 is prepared. In the SOI substrate 21, a silicon oxide film 23 called a buried oxide film layer having a thickness of 0.2 μm is disposed on a single crystal silicon substrate 22 having a thickness of 0.7 mm, and a single-layer film having a thickness of 0.2 μm is disposed on the upper surface thereof. A crystalline p-type silicon thin film layer 24 is sequentially laminated.
[0030]
Next, as shown in FIG. 3, a silicon oxide film 23 is embedded in the SOI substrate 21 to form an element isolation region 25. Next, as shown in FIG. 4, with the NMOS transistor formation portion 26 covered with a resist mask 27, phosphorus ions are implanted into the PMOS transistor formation portion 28 to form an n-type region.
[0031]
Next, as shown in FIG. 5, a gate oxide film 29 is formed by thermal oxidation at the formation locations 26 and 28 of the NMOS and PMOS transistors and the formation location of the support legs 4, and a polycrystal is formed on the upper surface of the gate oxide film. A gate electrode 30 is formed of silicon.
[0032]
Next, as shown in FIG. 6, the portions other than the formation portion 26 of the NMOS transistor are covered with a resist mask 31, and phosphorus ions are implanted to form source and drain regions 32 and 33 of the NMOS transistor, as shown in FIG. Then, the portions other than the PMOS transistor formation portion 28 are covered with a resist mask 34, and boron ions are implanted to form the source and drain regions 35 and 36 of the PMOS transistor.
[0033]
Next, as shown in FIG. 8, an n ⁺ region 37 of a pn junction diode constituting a part of the heat sensitive portion 3 is formed by implanting arsenic ions, and as shown in FIG. 9, the p ⁺ region 38 is formed by boron ions. It is formed by injecting.
[0034]
Next, as shown in FIG. 10, after an interlayer film 39 is formed on the upper surface of the substrate, a contact 40 is formed of tungsten or the like for electrode wiring of transistors and diodes.
[0035]
Next, as shown in FIG. 11, after an aluminum wiring layer 41 is formed on the upper surface of the contact, an interlayer film 42 is formed on the upper surface of the substrate. Next, as shown in FIG. 12, a contact 43 connected to the wiring layer 41 is formed in the interlayer film 42, and a second aluminum wiring layer 44 is formed on the upper surface of the contact 43 as shown in FIG. An interlayer film 45 is formed on the upper surface.
[0036]
Thus, the NMOS and PMOS transistors are combined to form a signal amplification circuit and an output circuit that amplifies a signal generated according to the temperature of the diode by causing a constant current to flow in the two-dimensional selection circuit and the diode addressed thereby. .
[0037]
Next, as shown in FIG. 14, in order to thermally separate the two-dimensionally arranged sensor from the surrounding substrate, the single crystal silicon substrate 22 is reached by RIE (Reactive Ion Etching) or the like. A vertical etching hole 46 is formed.
[0038]
Next, as shown in FIG. 15, the recesses 47 are formed by uniformly etching the portions where the heat sensitive portion 3 and the support legs 4 are formed from the surface by about 1 μm.
[0039]
Next, as shown in FIG. 16, a cavity 48 is formed in the single crystal silicon substrate 22 with TMAH (Tetramethyl ammonium hydroxide) or the like through the etching hole 46.
[0040]
Through the above steps, the first substrate 2 of FIG. 1 is formed. Note that the NMOS transistor 49 and the PMOS transistor 50 in FIG. 16 show the peripheral circuit 51 made of CMOS formed at the end of the first substrate 2 as shown in FIG. Amplification of the electrical signal output from the unit is performed.
[0041]
FIG. 18 is an enlarged view of a part of the second substrate 6 disposed to face the heat sensitive part 3. As shown in the drawing, the end of the V-shaped groove 5 is arranged so as to face the end of the heat-sensitive part 3 in the vertical direction. As a result, the infrared light refracted by the V-shaped groove 5 enters the heat-sensitive portion 3.
[0042]
19 to 23 are process diagrams showing the manufacturing process of the second substrate 6. First, as shown in FIG. 19, a germanium substrate 61 having a thickness of 200 μm is prepared. Next, as shown in FIG. 20, while rotating the V-groove blade 62, micro prisms of the V-groove 5 having a depth of 2 μm, a width of 10 μm, and a pitch of 40 μm are sequentially formed in a two-dimensional direction. That is, the V-shaped groove 5 is formed by cutting to form the second substrate 6 (microprism).
[0043]
Next, as shown in FIG. 21, the completed second substrate 6 is turned upside down and activated by irradiating the V-groove slope with argon ions in a vacuum.
[0044]
Similarly, the surface of the first substrate 2 manufactured by the manufacturing method of FIGS. 2 to 16 is also irradiated with argon ions in a vacuum, and the microprism array 6 is self-aligned at room temperature as shown in FIG. Let them join and leave in vacuum for about 2 hours.
[0045]
Next, as shown in FIG. 23, the second substrate 6 of the thermal infrared imaging device taken out from the vacuum vessel is thinned to about 20 μm by CMP (chemical mechanical polishing), and the thermal infrared imaging device is completed.
[0046]
As described above, in the present embodiment, the microprism formed of the V-shaped groove is formed on the second substrate 6, and the concave portion of the first substrate 2 is engaged with the V-shaped groove in a self-aligning manner. 3 and the microprism can be accurately aligned, and the infrared light incident on the microprism can be guided to the heat sensitive part 3 without omission and the sensitivity of infrared detection is improved.
[0047]
In the above-described embodiment, the example in which the microprism including the V-shaped groove 4 is formed on the first substrate 2 has been described. However, the shape of the groove is not necessarily V-shaped. The convex portion 8 of the first substrate 2 is meshed with the groove so as to perform alignment in a self-aligning manner, and has an inclined surface for refracting incident infrared rays and guiding it to the heat-sensitive portion 3. Good.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, since the convex portion of the first substrate is engaged with and joined to the groove of the second substrate, the thermal sensitive portion and the micro prism are accurately aligned. And the infrared detection sensitivity of the heat sensitive part is improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a sectional structure of a thermal infrared imaging device according to the present invention.
FIG. 2 is a process diagram illustrating a manufacturing process of the first substrate 2;
FIG. 3 is a process diagram following FIG. 2;
FIG. 4 is a process diagram following FIG. 3;
FIG. 5 is a process diagram following FIG. 4;
6 is a process drawing following FIG. 5. FIG.
FIG. 7 is a process diagram following FIG. 6;
FIG. 8 is a process diagram following FIG. 7;
FIG. 9 is a process diagram following FIG. 8;
FIG. 10 is a process diagram following FIG. 9;
FIG. 11 is a process drawing following FIG. 10;
FIG. 12 is a process drawing following FIG. 11;
FIG. 13 is a process drawing following FIG. 12;
FIG. 14 is a process drawing following FIG. 13;
FIG. 15 is a process drawing following FIG. 14;
FIG. 16 is a process drawing following FIG. 15;
FIG. 17 is a diagram showing a peripheral circuit formed at an end portion of the first substrate.
FIG. 18 is an enlarged view showing a part of a second substrate disposed opposite to a heat sensitive part.
FIG. 19 is a process diagram showing a manufacturing process of the second substrate.
FIG. 20 is a process drawing following FIG. 19;
FIG. 21 is a process drawing following FIG. 20;
FIG. 22 is a process drawing following FIG. 21;
FIG. 23 is a process drawing following FIG. 22;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Address line 2 1st board | substrate 3 Thermosensitive part 4 Support leg 5 V-shaped groove 6 Micro prism array (2nd board | substrate)
7 Silicon substrate 8 Convex portions 9 and 10 Hollow portions 11 and 12 Groove portions 21 SOI substrate 22 Single crystal silicon substrate 23 Silicon oxide film 24 Single crystal p-type silicon thin film layer 25 Element isolation region 29 Gate oxide film 30 Gate electrodes 39 and 42 Interlayer Films 41 and 44 Wiring layer 43 Contact 47 Recess

Claims (8)

A first substrate having a plurality of convex portions formed at a pixel pitch;
A heat-sensitive portion that is disposed between the convex portions of the first substrate and spaced from the first substrate, and converts incident infrared rays into heat;
At least one support leg for supporting the heat sensitive part away from the first substrate;
A second substrate having a microprism array, which is arranged opposite to the first substrate, and in which a plurality of microprisms each having an inclined surface that refracts incident infrared rays and condenses them on the heat-sensitive portion is formed at a pixel pitch. With
Each of the convex portions is engaged with each of the grooves, and the thermal infrared imaging device. The thermal infrared imaging element according to claim 1, wherein the groove is processed into a V shape. 3. The thermal infrared imaging element according to claim 1, wherein an address line for selecting a pixel is formed on the convex portion. The gap between adjacent grooves of the second substrate is flat, and an end of the groove is flush with an end of the heat-sensitive part. Thermal infrared imaging device. The hollow part formed between the heat-sensitive part and the first substrate and the hollow part formed between the heat-sensitive part and the second substrate are set to a predetermined atmospheric pressure or lower. The thermal infrared imaging device according to any one of claims 1 to 4. An address line for selecting a pixel, a plurality of convex portions formed at a pixel pitch, a heat sensitive portion arranged between the convex portions to convert incident infrared rays into heat, and at least one supporting the heat sensitive portion apart from each other A first substrate having a book support leg;
And a second substrate having a microprism array in which a plurality of grooves having inclined surfaces for refracting incident infrared rays and condensing them on the heat-sensitive portion are formed at the same intervals as the heat-sensitive portion. A manufacturing method,
In a state where the groove of the second substrate is engaged with the convex portion of the first substrate, the groove and the convex portion are bonded in a vacuum,
A method of manufacturing a thermal infrared imaging device, comprising polishing a surface of the second substrate opposite to a surface facing the first substrate. Before joining the convex portion and the groove, the inclined surface of the groove is activated with an inert gas and the periphery of the convex portion of the first substrate is activated with an inert gas. The manufacturing method of the thermal type infrared imaging element of Claim 6. The method for manufacturing a thermal infrared imaging device according to claim 6 or 7, wherein the groove of the second substrate is formed by cutting.

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