JP3672516B2 - Infrared sensor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an infrared sensor device and a manufacturing method thereof.
[0002]
[Prior art]
The conventional quantum infrared solid-state imaging device (infrared sensor device) has a major drawback in that it requires a cooling mechanism for low-temperature operation. On the other hand, in recent years, development of an uncooled infrared sensor that does not require a cooling mechanism has become active. In the non-cooling type infrared sensor, after the incident infrared ray having a wavelength of about 10 μ is converted into heat by the absorption structure, the temperature change of the heat sensitive part caused by the weak heat is converted into an electric signal by some thermoelectric conversion means, The infrared image information is obtained by reading the electrical signal.
[0003]
In this type of uncooled infrared sensor, an infrared sensor unit consisting of a thermosensitive part (infrared absorbing structure) that converts incident infrared light into heat and a thermoelectric conversion part that converts the heat into an electrical signal is thermally transferred from the surroundings. Separation and improvement of thermoelectric conversion efficiency are essential for improving infrared sensitivity. Therefore, one effective method is to suppress the diffusion of heat to the support substrate of the thermoelectric conversion part by etching the infrared sensor part formed on the silicon substrate so as to float from the silicon substrate by micromachining technology. (For example, Tomohiro Ishikawa, et al., Proc. SPIE Vol. 3698,
p.556, 1999).
[0004]
However, an input / output of an electric signal to the infrared sensor unit and a support structure for supporting the infrared sensor unit in a hollow state on the support substrate are necessary, and heat conduction by this support structure must be minimized. Therefore, in the example of the above document, a method is proposed in which a leg-like support structure made of a material having a low thermal conductivity is laid out to be thinner and longer as long as it can be designed. However, when the pixel size is miniaturized to about 40 μm × 40 μm, the support structure is also miniaturized, and the cross-sectional area is reduced to about several tens μm ² .
[0005]
[Problems to be solved by the invention]
Even if the cross-section of the support structure is made fine, the length cannot be shortened so much from the viewpoint of thermal separation. Therefore, the support strength is lowered and the element structure is deformed accordingly. For example, after the cavitation etching process around the infrared sensor part, the infrared sensor part sinks into the cavity formed in the support substrate due to the surface tension of pure water during drying, and “sinks” that contact the support substrate Phenomenon or “sticking” phenomenon occurs in which the infrared sensor unit and the support structure or the support structure and the support substrate are stuck due to thermal deformation of the support structure during drying. This impairs the thermal separation performance of the infrared sensor unit and causes a decrease in detection sensitivity. In addition, the reduction in the support strength facilitates the destruction of the infrared sensor unit due to external impact, causing a decrease in yield of the infrared sensor device and an increase in cost.
[0006]
An object of the present invention is to provide an infrared sensor device and a method for manufacturing the infrared sensor device that ensure thermal separation and hollow support of the infrared sensor unit.
[0007]
An infrared sensor device according to the present invention includes a semiconductor substrate, a frame body portion disposed on the semiconductor substrate so as to partition a plurality of pixel regions, and a matrix selection line embedded therein, and the frame body portion Infrared absorbing part that absorbs infrared rays and converts it into heat, and is formed in each pixel region partitioned by An infrared sensor unit having a thermoelectric conversion element for converting the heat generated into an electrical signal, and the support structure of the infrared sensor unit is provided between the infrared sensor unit and the frame body part with a gap on the semiconductor substrate. for coupling, the frame from the body portion is provided so as around along at least two sides of the infrared sensor unit over the infrared sensor portion, a first support beam comprising readout wiring of the infrared sensor unit At a space on the semiconductor substrate, between the first support beam and the infrared sensor unit, and to connecting the at least one between said first supporting beam and the frame portion And a second support beam provided.
[0008]
In the manufacturing method of the infrared sensor device according to the present invention, an element isolation insulating film having a depth reaching the semiconductor substrate is formed on the semiconductor layer formed by being separated from the semiconductor substrate by the insulating layer, thereby dividing the element formation region. Forming a pn junction diode to be a thermoelectric conversion element in the element formation region, forming a readout wiring connected to a terminal of the pn junction diode on the element isolation insulating film, and the element Forming a support member layer on the isolation insulating film; forming an interlayer insulating film covering the readout wiring and the supporting member layer and having a matrix selection line embedded therein; and absorbing infrared light on the interlayer insulating film And forming the frame body portion including the matrix selection line into a state of being fixed to the semiconductor substrate, and the infrared absorbing portion and the pn junction surrounded by the frame body portion The first support formed by an infrared sensor unit made of iodine, a first support beam unit including the readout wiring and connecting the infrared sensor unit and the frame body unit, and the support member layer And an etching process for processing a second support beam portion connecting between the beam portion and at least one of the infrared sensor portion and the frame body portion so as to float from the semiconductor substrate.
[0009]
According to the present invention, as a support structure for supporting the infrared sensor unit in a hollow state, in addition to the first support beam including the readout wiring, the first support beam is used as a frame including the infrared sensor unit and the matrix selection line. By providing the second support beam connected to at least one of the parts, it is possible to obtain sufficient support strength while suppressing heat conduction of the infrared sensor part as much as possible.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a layout of one pixel portion of an infrared sensor device according to an embodiment, and FIG. 2 shows a cross section taken along line II ′. In the infrared sensor device, pixels are two-dimensionally arranged. Apart from this pixel arrangement, active elements such as transistors used for signal processing, and passive elements such as diffused resistors and capacitors are simultaneously formed using a normal LSI process. Is done.
[0011]
As shown in FIGS. 1 and 2, in this apparatus, an infrared sensor unit 3 is formed on a single crystal silicon substrate (support substrate) 1 as a semiconductor substrate with a gap 2. Frame portions 4 and 5 in which row selection lines 41 and column selection lines 51 for performing pixel selection are embedded define pixel areas arranged in a matrix and are arranged in a state of being fixed to the silicon substrate 1. . In order to support the infrared sensor unit 3 in a hollow state, the first support beam 6 (6a, 6b) connecting the infrared sensor unit 3 and the frame parts 4 and 5 is also lifted from the substrate 1. It is formed. This support beam 6 incorporates a readout wiring 8 for connecting the signal terminal of the infrared sensor unit 3 to the matrix selection line.
[0012]
The first support beam 6 is elongated so as to travel along substantially three sides of the infrared sensor unit 3 in order to suppress heat conduction. And between the 1st support beam 6 and the infrared sensor part 3, and between the 1st support beam 6 and the frame parts 4 and 5 so that the support strength of this elongate 1st support beam may be reinforced. A second support beam 7 (7a-7d) is provided. The second support beam 7 has a lateral thickness (width) smaller than that of the first support beam 6 and does not include wiring, but, like the first support beam 6, the second support beam 7 floats from the substrate 1. Arranged. Therefore, heat conduction by the second support beam 7 is also suppressed.
[0013]
FIG. 3 is an enlarged perspective view showing a connecting portion between the first support beam 6 and the second support beam 7. The first support beam 6 is composed of an insulating layer made of a silicon oxide film in which a readout wiring 61 is built. In this embodiment, the second support beam 7 is composed of a single layer of silicon nitride film.
[0014]
Next, the manufacturing process of the infrared sensor device of this embodiment will be described with reference to FIGS. These drawings are cross-sectional views corresponding to the cross section of the almost right half in FIG. As shown in FIG. 4, a so-called SOI substrate is prepared, in which a buried silicon oxide film 101 having a thickness of 140 nm and a single crystal silicon layer 102 having a thickness of 400 nm are sequentially stacked on a single crystal silicon substrate 1 as a supporting substrate. As shown in FIG. 5, an element isolation insulating film 103 is buried in this SOI substrate with STI (Shallow Trench Isolation), and an element formation region 104 is defined in the silicon layer 102.
[0015]
Specifically, the resist is patterned, and the silicon layer in the element isolation region is etched by a technique such as RIE (Reactive Ion Etching), and then the resist is removed, and a silicon oxide film is formed in the element isolation region by CVD (Chemical). Embedding is performed using a technique such as Vapor Deposition, and planarization is performed using a technique such as CMP (Chemical Mechanical Polishing). A region where a support beam is formed later is an element isolation region.
[0016]
Next, as shown in FIG. 6, an n ⁺ -type diffusion layer and a p ⁺ -type diffusion layer are formed in each element formation region 104 to form a pn junction diode 31 as a thermoelectric conversion element. Specifically, a plurality of pn junction diodes are arrayed in an infrared sensor portion of one pixel, and these are connected in series later.
[0017]
Next, as shown in FIG. 7, a readout wiring 61 to be built in the first support beam 6 is formed. Specifically, a 200 nm polysilicon film 61a is deposited by the CVD method, and this is patterned using the RIE technique. Thereafter, a 100 nm oxide film is deposited by CVD, and etched back by RIE to form sidewalls 62 on the polysilicon film 61a. As shown in FIG. 1, the readout wiring 61 is connected between one end of the pn junction diode row of the infrared sensor unit 3 and the frame portion 4 in the row direction, and the other end of the pn junction diode row and the frame portion in the column direction. 5 is disposed.
[0018]
This process can be performed simultaneously with the formation of the gate of the transistor formed in the periphery. In the embodiment, polysilicon is used as the wiring. However, the present invention is not limited to this, and Al wiring can be used in consideration of the thermal conductivity and resistance required for the support structure. It is also possible to use Al wiring and polysilicon together.
[0019]
Subsequently, as shown in FIG. 7, a support member layer 70 for constituting the second support beam 7 is deposited. Specifically, as described with reference to FIG. 3, the support member layer 70 is a silicon nitride film, which is deposited by CVD. After the support member layer 70 is deposited, the terminal diffusion layer portion of the pn junction diode and the portion on the polysilicon film 61a are removed by etching using RIE. Then, Ti / TiN is deposited by sputtering to a thickness of 25 nm / 15 nm, and after RTA treatment at 700 ° C. for 30 seconds in a nitrogen atmosphere, Ti / TiN is removed with a mixed solution of sulfuric acid and hydrogen peroxide, and again RTA treatment is performed at 800 ° C. for 20 seconds in a nitrogen atmosphere. Thereby, a Ti silicide 61b is formed on the terminal diffusion layer region of the pn junction diode and the polysilicon film 61a.
[0020]
In this embodiment, Ti is used as the silicide material, but this is intended to reduce the sheet resistance of the pn junction diode and readout wiring, and may be other metals such as Co and Ni. In addition, this process can be performed simultaneously with the formation of silicide on the source / drain of the transistor in the peripheral circuit.
[0021]
Next, as shown in FIG. 8, a first interlayer insulating film 106 is formed by CVD. In the interlayer insulating film 106, a contact hole is formed by RIE or the like on the terminal layer of the pn junction diode at the contact portion between the readout wiring 61 and the Al wiring to be formed later, and a contact plug 107 is embedded. Specifically, the contact plug 107 is buried by depositing Ti / TiN / Ti as a barrier metal by sputtering and then depositing a tungsten film on the entire surface of the substrate by CVD and performing CMP. This process can be performed simultaneously with the contact formation on the source / drain of the transistor of the peripheral circuit.
[0022]
Thereafter, aluminum or an aluminum alloy is deposited by sputtering as the first metal wiring layer and patterned. Thereby, the row selection line 41 is formed simultaneously with the wiring 108 for connecting the pn junction diodes in each sensor unit. Although not visible in the cross section of the figure, an interlayer insulating film is further deposited and a column selection line is formed by the Al film.
[0023]
Thereafter, an interlayer insulating film 109 is deposited, and a silicon oxide film 32 a and a silicon nitride film 32 b are stacked as the infrared absorber layer 32. The infrared absorption layer 32 can also serve as a passivation for MOS transistors or the like in the peripheral circuit. The infrared sensor part which consists of an infrared absorption part and the thermoelectric detection element which detects the heat | fever generated by this is formed by the above. At this stage, the infrared sensor portion has not been patterned yet and is not separated from the support substrate.
[0024]
Next, as shown in FIG. 9, an etching opening 202 is formed to expose the single crystal silicon support substrate 1 in order to form a hollow structure around the infrared sensor unit 3. Specifically, the resist mask 201 is patterned by photolithography so as to cover the regions of the infrared sensor unit 3, the frame units 4 and 5, and the support beams 6 and 7 shown in FIG. 1, and reaches the substrate 1 by RIE. Opening 202 is formed. The second support beam 7 is preferably patterned to a width of 0.2 to 0.5 μm in a state where the support member layer 70 is also sandwiched between the insulating layers from above and below. The first support beam 6 is preliminarily patterned with a built-in readout wiring 61, but is patterned wider than the second support beam 7 with the readout wiring 61 embedded in an insulating layer in this process. The
[0025]
Next, the insulating layer is etched between the infrared sensor portion 3 and the frame portions 4 and 5 in FIG. 1, that is, in the region where the support beams 6 and 7 are disposed. That is, as shown in FIG. 10, the resist mask 203 is patterned so as to cover the infrared sensor unit 3 and the frame parts 4 and 5, and the silicon nitride film 32b, the silicon oxide film 32a around the infrared sensor unit 3 are formed. The interlayer insulating film 109 is etched by RIE. In the figure, etching is performed up to a part of the interlayer insulating film 106 below the wiring layer, but the etching amount can be selected within a range where the readout wiring 61 is not exposed.
[0026]
Next, as shown in FIG. 11, the surface of the single crystal silicon substrate 1 is etched by anisotropic etching through the opening 202 to form a gap 2 that separates the infrared sensor unit 3 and the substrate 1. As the etchant at this time, a chemical solution such as TMAH (Tetra-Methyl-Ammonium-Hydroxide) is desirable.
[0027]
Thereafter, in order to further reduce the thermal conductivity of the support beams 6 and 7, the insulating layer remaining under these beams is removed using an etchant having a high selectivity to aluminum, for example, a mixed solution of acetic acid and ammonium fluoride. To do. Since the portion of the second support beam 7 not including the wiring is as narrow as 0.2 to 0.5 μm, the remaining upper and lower insulating films 106 and 103 are completely removed by etching from the side surface. As shown in FIG. 12, the support beam 7 is formed only by the support member layer 70 having a line width of 0.2 to 0.5 μm and a thickness of 35 nm.
[0028]
Next, the drying process after wet etching is started. In the conventional support structure without the second support beam 7, the ratio of the infrared sensor part sinking due to the surface tension of pure water during drying and contact with the support substrate is about 30%, and the infrared ray due to thermal deformation of the support structure during drying. About 5% of sticking occurs between the sensor unit and the support structure, and between the support structure and the support substrate. On the other hand, in this embodiment, the second support beam 7 that does not contain wiring is provided between the first support beam 6 and the infrared sensor unit 3 and between the first support beam 6 and the frame parts 4 and 5. By connecting the gaps, sinking and sticking can be reliably suppressed.
[0029]
Next, another embodiment of the present invention will be described. Since the layout of the pixel portion of the infrared sensor device and the cross-sectional structure thereof are the same as those of the previous embodiment, detailed description thereof will be omitted. FIG. 13 shows an enlarged perspective view of the connecting portion of the first support beam 6 and the second support beam 7 in this embodiment, corresponding to FIG. 3 of the previous embodiment. The first support beam 6 is composed of an insulating layer made of a silicon oxide film in which the readout wiring 61 is built, as in the previous embodiment. The second support beam 7 is constituted by an insulating film laminated structure in which a silicon oxide film 132 is sandwiched between silicon nitride films 131 and 133, and its cross section is I-type.
[0030]
The manufacturing process of the infrared sensor device according to this embodiment is the same up to FIG. 6 of the previous embodiment. Thereafter, as shown in FIG. 14, a support member layer 130 for forming the second support beam 7 is deposited. Specifically, the support member layer 130 is an insulating film in which a silicon nitride film 131, a silicon oxide film 132, and a silicon nitride film 133 are sequentially stacked by CVD. The patterning of the support member layer 130 is performed when the silicon nitride film 131 and the silicon oxide film 132 are etched back on the sidewall insulating film of the polysilicon film, and the silicon nitride film 133 is on the terminal diffusion layer portion of the pn junction diode and the polysilicon film 61a. This is performed at the time of RIE.
[0031]
Then, Ti / TiN is deposited by sputtering to a thickness of 25 nm / 15 nm, and after RTA treatment at 700 ° C. for 30 seconds in a nitrogen atmosphere, Ti / TiN is removed with a mixed solution of sulfuric acid and hydrogen peroxide, and again RTA treatment is performed at 800 ° C. for 20 seconds in a nitrogen atmosphere. Thereby, a Ti silicide 61b is formed on the terminal diffusion layer region of the pn junction diode and the polysilicon film 61a.
In this embodiment, Ti is used as the silicide material, but this is intended to reduce the sheet resistance of the pn junction diode and readout wiring, and may be other metals such as Co and Ni. In addition, this process can be performed simultaneously with the formation of silicide on the source / drain of the transistor in the peripheral circuit.
[0032]
Thereafter, the steps up to FIG. 11 are the same as those in the previous embodiment. Thereafter, as shown in FIG. 15, in order to reduce the thermal conductivity of the support beams 6 and 7, the insulating layer remaining below them is made of an etchant having a high selectivity with aluminum, for example, acetic acid and ammonium fluoride. Remove with mixture. Since the portion of the second support beam 7 not including the wiring is as thin as 0.2 to 0.5 μm, the remaining upper and lower silicon oxide films 103 and 106 are etched from the side surfaces and completely removed. . Since the second support beam 7 has a structure in which the silicon oxide film 132 is sandwiched between the silicon nitride films 131 and 133, as shown in FIG. The support beam 7 can have an I-type cross-sectional structure with a recessed oxide film portion.
[0033]
Since the thermal conductivity of the silicon oxide film is about 1/10 that of the silicon nitride film, even if the cross-sectional area is made larger than that of the previous embodiment due to the laminated structure, the overall strength is not increased without increasing the thermal conductivity. In particular, the strength in the vertical direction can be increased.
[0034]
The present invention is not limited to the above embodiment. For example, in the embodiment, a pn junction diode is used as the thermoelectric conversion element. However, the present invention is not limited to this, and for example, a bolometer or the like can be used.
In the embodiment, the first support beam 6 including two readout lines per pixel is used as the second support beam 7 at the two corners of the first support beam 6 and the infrared sensor. Two sets of beams 7a and 7b that connect between the parts 3 and beams 7c and 7d that connect the other two corners to the frame parts 4 and 5 are used. Depending on the support structure, Only one of these sets may be used. For example, in the embodiment, the first support beam 6 is a long beam having three corners. However, if the structure has two corners, the second support beam 7 can be reduced. Or conversely, more second support beams may be used.
[0035]
【The invention's effect】
According to the present invention, as a support structure for supporting the infrared sensor unit in a hollow state, in addition to the first support beam including the readout wiring, the first support beam is connected to at least the infrared sensor unit and the frame body unit. By providing the second support beam connected to one side, it is possible to obtain sufficient support strength while suppressing heat conduction of the infrared sensor unit as much as possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a main part layout of an infrared sensor device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along the line II ′ of FIG.
FIG. 3 is an enlarged perspective view showing a structure of a connection portion between the first support beam and the second support beam according to the embodiment;
4 is a sectional view of the starting substrate in the manufacturing process of the embodiment. FIG.
FIG. 5 is a cross-sectional view showing an element isolation step of the same embodiment.
6 is a cross-sectional view showing a manufacturing process of the pn junction diode of the same embodiment; FIG.
7 is a cross-sectional view showing a formation step of the readout wiring and the support member layer in the embodiment. FIG.
FIG. 8 is a cross-sectional view showing a process of forming the metal wiring and the infrared absorbing portion according to the embodiment.
FIG. 9 is a cross-sectional view showing a step of forming a substrate etching opening according to the embodiment;
FIG. 10 is a cross-sectional view showing an insulating layer etching step of the support structure portion of the embodiment.
FIG. 11 is a cross-sectional view showing a silicon substrate etching step of the same embodiment;
FIG. 12 is a cross-sectional view showing an insulating film etching step for exposing the second support beam in the embodiment;
FIG. 13 is an enlarged perspective view showing a structure of a connecting portion between a first support beam and a second support beam of an infrared sensor device according to another embodiment.
14 is a cross-sectional view showing a step of forming the readout wiring and the support member layer according to the embodiment; FIG.
15 is a cross-sectional view showing an insulating film etching step for exposing a second support beam according to the embodiment; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Air gap, 3 ... Infrared sensor part, 4, 5 ... Frame part, 6 (6a, 6b) ... 1st support beam, 7 (7a-7d) ... 2nd support beam, 31 ... pn junction diode (thermoelectric conversion element), 32 ... infrared absorption part, 32a ... silicon oxide film, 32b ... silicon nitride film, 41, 51 ... matrix selection line, 61 ... readout wiring, 70 ... support member layer (silicon nitride film) , 71, 73 ... Silicon nitride film, 72 ... Silicon oxide film, 101 ... Silicon oxide film, 102 ... Silicon layer, 103 ... Element isolation insulating film, 104 ... Element formation region, 106, 109 ... Interlayer insulating film, 107 ... Contact plug, 108, 41 ... Al wiring, 201, 203 ... resist mask, 202 ... etching opening, 130 ... support member layer, 131, 133 ... silicon nitride film, 132 ... silicon Oxide film.

Claims (6)

A semiconductor substrate;
A frame body portion arranged on the semiconductor substrate so as to divide a plurality of pixel regions and having matrix selection lines embedded therein;
Infrared absorbing portions for absorbing infrared rays and converting them into heat, which are formed by supporting each of the pixel regions defined by the frame portions with a gap on the semiconductor substrate and supported by the frame portions, and the infrared rays An infrared sensor unit having a thermoelectric conversion element that converts heat generated in the absorption unit into an electrical signal;
The support structure of the infrared sensor unit is
In order to connect the infrared sensor part and the frame body part with a gap on the semiconductor substrate, the circuit extends from the frame part to the infrared sensor part along at least two sides of the infrared sensor part. A first support beam including a readout wiring of the infrared sensor unit,
At a space on the semiconductor substrate, between the first support beam and the infrared sensor unit, and to connecting the at least one between said first supporting beam and the frame portion An infrared sensor device comprising: a second support beam provided. The thermoelectric conversion element is a pn junction diode formed in a semiconductor layer, and the infrared absorption part is an insulating film including at least one of a silicon oxide film and a silicon nitride film formed on the pn junction diode part. The infrared sensor device according to claim 1, wherein the infrared sensor device is provided.  2. The infrared sensor device according to claim 1, wherein the lateral thickness of the first support beam is larger than that of the second support beam.  2. The infrared sensor device according to claim 1, wherein the second support beam is configured by at least one of a silicon nitride film and a silicon oxide film or a laminated structure thereof.  Forming an element isolation insulating film having a depth reaching the semiconductor substrate in a semiconductor layer formed by separating the semiconductor substrate from the insulating layer to partition the element formation region; and a thermoelectric conversion element in the element formation region; Forming a pn junction diode, forming a readout wiring connected to a terminal of the pn junction diode on the element isolation insulating film, and forming a support member layer on the element isolation insulating film A step of forming an interlayer insulating film with a matrix selection line embedded therein covering the readout wiring and the support member layer, a step of forming an infrared absorption part on the interlayer insulating film, and the matrix selection line An infrared sensor unit configured to process the frame body part including the infrared ray absorption part and the pn junction diode surrounded by the frame body part; A first support beam portion that includes a readout wiring and connects between the infrared sensor portion and the frame body portion, and the support member layer, the first support beam portion, the infrared sensor portion, and the frame. And an etching step for processing the second support beam portion that connects at least one of the body portions into a state of floating from the semiconductor substrate. The etching step includes forming a mask that covers the infrared sensor unit, the frame body unit, and the first and second support beam units, and forming an opening that reaches the semiconductor substrate from the infrared absorption unit; Forming a mask that covers the infrared sensor part and the frame part, and etching the interlayer insulating film on the first support beam part to a depth not reaching the readout wiring; Etching the surface of the semiconductor substrate to form a gap between the infrared sensor portion, the first and second support beam portions, and the semiconductor substrate; and the step above the second support beam portion. 6. The infrared ray according to claim 5, further comprising a step of etching the interlayer insulating layer and the underlying element isolation insulating film to form a second support beam only consisting of the support member layer. Method of manufacturing capacitors apparatus.

Images