A suspended absorber layer thermoelectric device and method of fabrication

Abstract

The present application relates to a kind of suspended absorption layer thermoelectric device and its manufacturing method.The first aspect of the present application provides a kind of manufacturing method of suspended absorption layer thermoelectric device, comprising the following steps: providing semiconductor substrate, semiconductor substrate has front and back surface;Form first layer of thermocouple, first insulating layer, second layer of thermocouple, second insulating layer in order from bottom to top on the front surface of semiconductor substrate;Then make contact hole, fill contact hole to form lead layer;After that, form sacrificial layer, the part surface of sacrificial layer covers second insulating layer, and make lead layer bare;The surface of sacrificial layer and bare lead layer and second insulating layer surface cover light-absorbing layer, carry out patterning;Release part of sacrificial layer to make light-absorbing layer suspended, and etching is carried out to semiconductor substrate back surface and forms back cavity.The present application solves the problem that suspended thermoelectric device is not easy to process and the structure mechanical stability after processing is poor in prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor devices, and in particular to a suspended absorber thermopile device and a method for fabricating the same. BACKGROUND

[0002] At present, infrared detectors are widely used in civil and military fields, and thermopile infrared detectors are one of the earliest developed infrared detectors. Due to the advantages of normal temperature operation, wide response band, low manufacturing cost, etc., the thermopile infrared detector has developed rapidly and is widely used. In the preparation process of the thermopile infrared detector, making the manufacturing process compatible with the integrated circuit process is the main method to form a large-scale detection array, improve the detection response rate, and reduce the process manufacturing cost.

[0003] In terms of reducing the manufacturing cost of the thermopile, combining it with the CMOS process is the main technical route, and in order to make the device have higher performance, the sensor output should be as large as possible. The voltage output of the thermopile is directly related to the light absorption area, and satisfies the following relationship:

[0004] ΔU = NT diff (α A -α B ) = NT diff α AB .

[0005] Among them,

[0006] In the above formula, ΔU is the output voltage of the thermopile; α A and α B are the Seebeck coefficients of the two materials constituting the thermocouple; T diff is the temperature difference between the cold and hot ends of the thermopile, which is determined by the input heat power φ, the light absorption coefficient η, and the light absorption area A. From the formula, it can be seen that when the structural thermal conductivity G th is constant, the larger the light absorption area, the greater the temperature difference between the cold and hot ends, and the greater the output voltage of the thermopile device, in other words, the better the performance of the thermopile device. In this case, the suspended absorber layer can achieve a large light absorption area and a low structural thermal conductivity. However, usually due to the large area (>1×10 4 μm 2 ) of the suspended absorber layer, the suspended film is extremely difficult to manufacture, and the mechanical stability is poor, the structure is easy to collapse, resulting in insufficient yield and insufficient long-term stability after the structure is realized. SUMMARY

[0007] The main purpose of the present application is to provide a suspended absorption layer thermoelectric device and a manufacturing method thereof, which solves the problems of poor processing and poor mechanical stability of the structure after processing of the suspended thermoelectric device in the prior art.

[0008] In order to achieve the above purpose, the present application provides the following technical solutions.

[0009] The first aspect of the present application provides a manufacturing method of a suspended absorption layer thermoelectric device, comprising the following steps:

[0010] A semiconductor substrate is provided, which has a front surface and a back surface;

[0011] A support layer, a first layer of thermocouple, a first insulating layer, a second layer of thermocouple, and a second insulating layer are sequentially formed from bottom to top on the front surface of the semiconductor substrate;

[0012] Then, a contact hole is made, and the contact hole is filled to form a lead layer of the first layer of thermocouple, a lead layer of the second layer of thermocouple, and a lead layer for connecting the hot end between the first layer of thermocouple and the second layer of thermocouple;

[0013] Then, a sacrificial layer is formed, which covers part of the surface of the second insulating layer and exposes the lead layer for connecting the hot end between the first layer of thermocouple and the second layer of thermocouple;

[0014] An optical absorption layer is coated on the surface of the sacrificial layer, the exposed lead layer for connecting the hot end between the first layer of thermocouple and the second layer of thermocouple, and the surface of the second insulating layer, and is patterned;

[0015] The back surface of the semiconductor substrate is etched to form a back cavity, and then part of the sacrificial layer is released to suspend the optical absorption layer.

[0016] The second aspect of the present application provides a suspended absorption layer thermoelectric device, comprising a semiconductor substrate, which has a front surface and a back surface;

[0017] A support layer, a first layer of thermocouple, a first insulating layer, a second layer of thermocouple, a second insulating layer, a sacrificial layer, and an optical absorption layer are sequentially stacked from bottom to top on the front surface of the semiconductor substrate;

[0018] And a lead layer electrically connected to the first layer of thermocouple and the second layer of thermocouple, respectively, and a lead layer for connecting the hot end between the first layer of thermocouple and the second layer of thermocouple;

[0019] The sacrificial layer only covers part of the central area of the second insulating layer; part of the optical absorption layer is supported and covers the surface of the sacrificial layer and the surface of the lead layer for connecting the hot end between the first layer of thermocouple and the second layer of thermocouple, and the remaining part is suspended.

[0020] Compared with the prior art, the present application achieves the following technical effects.

[0021] In one aspect, the light-absorbing layer is suspended by forming a large-area sacrificial layer as a support and then releasing part of the sacrificial layer, and the size of the sacrificial layer that is finally retained can be controlled by adjusting the release conditions, so that the light-absorbing layer is provided with controllable support strength, and the final device has good mechanical performance stability.

[0022] In another aspect, the method has good compatibility with CMOS processes, and can reduce the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0023] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are intended to further aid the full and complete understanding of the present disclosure, and are not to be considered limiting of the present disclosure.

[0024] Figure 1 A top view of a suspended light-absorbing layer thermoelectric device according to the present disclosure;

[0025] Figure 2 A cross-sectional view of one group of thermocouple pairs in the X-X' direction; Figure 1

[0026] A cross-sectional view of one group of thermocouple pairs in the X-X' direction; Figures 3-10 A cross-sectional view of one group of thermocouple pairs in the X-X' direction; DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present disclosure. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid obscuring the concept of the present disclosure.

[0028] In the drawings, various structural diagrams according to embodiments of the present disclosure are shown. These diagrams are not drawn to scale, in which certain details are exaggerated for the purpose of clarity and can omit certain details. The shapes of various regions, layers, and their relative sizes and positional relationships shown in the drawings are merely exemplary, and in actuality can deviate due to manufacturing tolerances or technical limitations, and regions / layers having different shapes, sizes, and relative positions can be additionally designed by those skilled in the art as needed.

[0029] In the context of the present disclosure, when a layer / element is referred to as being located "on" another layer / element, the layer / element can be directly located on the other layer / element, or an intervening layer / element can be present therebetween. In addition, if a layer / element is located "on" another layer / element in one orientation, the layer / element can be located "under" the other layer / element when the orientation is reversed.

[0030] As described in the background, the prior art process for making a suspended absorber thermoelectric device is difficult and cannot guarantee the stability of the suspended structure, resulting in a low yield. Therefore, the present application provides a suspended absorber thermoelectric device with the following structure.

[0031] The top view of the thermoelectric device of the present application is shown in Figure 1 The figure shows four groups of thermocouple pairs 10 (but the present application does not limit the number of thermocouple pairs in the device, which can be more or less than four groups), which are connected in series by leads 7b. As can be seen from the figure, the light absorbing layer 9 and the sacrificial layer 8a partially overlap in the vertical direction, and this overlapping part can strongly support the light absorbing layer, making it stably suspended; the position of the back hollow structure (i.e. back cavity 1a) is shown by the dashed box in the figure. Taking the X-X' direction cross-sectional structure of one of the thermocouple pairs as an example, the stacking morphology of the device is introduced.

[0032] As shown in Figure 2 , it includes a semiconductor substrate 1, which has a front surface and a back surface. On the front surface of the semiconductor substrate 1, from bottom to top, are stacked a support layer (shown in the figure as a stack of silicon oxide layer 201, silicon nitride layer 202 and silicon oxide layer 203), first layer of thermocouples 3, first insulating layer 4, second layer of thermocouples 5, second insulating layer 6, sacrificial layer 8a and light absorbing layer 9; and leads 7b electrically connected to the first and second layers of thermocouples 3 and 5, respectively, and leads 7a connecting the first and second layers of thermocouples. Among them, the sacrificial layer 8a only covers part of the central area of the second insulating layer 6. Part of the light absorbing layer 9 is supported on the surface of the sacrificial layer 8a and the surface of the lead 7a, and the remaining part is suspended.

[0033] For the stacked device of the present application, the semiconductor substrate 1 can be any substrate known to those skilled in the art for carrying the constituent elements of a semiconductor integrated circuit, such as silicon-on-insulator (SOI), bulk silicon, germanium, germanium silicon, gallium arsenide or germanium-on-insulator, etc.; or a semiconductor substrate that has already been formed into other structures. The support layer mainly serves as an insulator and a support, and can be a single layer or a multi-layer stack, such as a single layer or a multi-layer combination stack of silicon oxide or silicon oxynitride, usually an ONO stack (i.e. the silicon oxide layer, silicon nitride layer and silicon oxide layer are stacked in turn), which can achieve a high critical electric field and a low defect density, and has good isolation properties. The deposition means for stacking the support layer includes but is not limited to LPCVD, RTCVD or PECVD.

[0034] The first layer thermocouple 3 and the second layer thermocouple 5 form a thermocouple pair, and the materials of the two can be one of N-type polysilicon or N-type monocrystalline silicon material, and the other can be P-type polysilicon or metal aluminum. For example, it can be a polysilicon / metal AL thermocouple pair or a monocrystalline silicon / polysilicon thermocouple pair or a monocrystalline silicon / metal AL thermocouple pair, etc.

[0035] The first insulating layer 4 and the second insulating layer 6 mainly play an insulating role, and can use silicon oxide, nitride oxide or other high-k dielectric materials, etc.

[0036] The sacrificial layer 8a needs to select a material that is easy to remove and has a large etching selectivity ratio with other layers, and at the same time needs to consider good support force. The present application can use polymers (including but not limited to PI, PMMA, etc.), amorphous silicon, silicon oxide or polysilicon as the sacrificial layer.

[0037] The light-absorbing layer 9 can be determined according to the light-absorbing requirements of the device (such as light-absorbing wavelength intensity and other factors), and a typical light-absorbing material is silicon nitride.

[0038] In order to improve the structural stability of the suspended light-absorbing layer 9, the following structural features are preferably used: the suspended light-absorbing layer is relatively thin, and the remaining light-absorbing layer below has support and is relatively thick, so that the center of gravity of the light-absorbing layer is located at the position with support, thereby the structure is more stable. More preferably, the structure is as shown in Figure 2 The surface height of the sacrificial layer 8a is higher than the surface height of the lead 7a, and / or in each thermocouple pair stack structure, the upper surface of the support layer 2 is connected to at least one side of the first insulating layer 4 and the second insulating layer 6 in a stepped shape, and the light-absorbing layer 9 is supported on the side of the stepped shape.

[0039] There are many methods for manufacturing a device with the above structure, and the present application provides one preferred method, which is as follows.

[0040] Step S1: forming a support layer 2 from bottom to top on the front surface of the semiconductor substrate 1, as shown in Figure 3 for example, an ONO stack structure (i.e., the silicon oxide layer 201, the silicon nitride layer 202 and the silicon oxide layer 203 in the figure are stacked in turn) is taken as an example. The deposition means for stacking the support layer 2 includes but is not limited to LPCVD, RTCVD or PECVD.

[0041] Continue step S2, form a first layer thermocouple 3, as shown in Figure 4As shown, the formation process is typically completed in steps, including large-area deposition or sputtering of thermocouple material, optional ion implantation (doping is required when silicon is used), and patterning. If ion implantation is performed, annealing activation is also required; if the second thermocouple layer also uses doped silicon, the annealing can be combined. The doping type depends on the thermocouple type (p-type or n-type), and the doping method can be in-situ synchronous doping or out-of-situ doping, etc. Patterning is used to form thermocouples with a predetermined number, shape, and positional distribution; the pattern shape can be stripes or circles, etc.

[0042] Continue with step S3 to form the first insulating layer 4, as follows: Figure 4 As shown. The deposition method can employ oxidation, LPCVD, RTCVP, or PECVD, etc. To form the stepped sidewalls described above, the first insulating layer needs to be patterned so that it is located on the central surface of the support layer, i.e., the edge surface of the support layer is exposed.

[0043] Continue with step S4 to form the second thermocouple 5, as follows. Figure 4 As shown. If the second thermocouple 5 needs to be doped, it can be annealed simultaneously with the first thermocouple 3 after doping. The preferred annealing conditions are: temperature 950–1150℃, time 15–120s. Patterning is then performed after annealing. Similarly, to form the stepped sidewalls described above, the size of the second thermocouple 5 needs to be controlled to be smaller than the size of the first thermocouple.

[0044] Continuing with step S5, a second insulating layer 6 is formed to cover the second thermocouple 5, as shown below. Figure 4 As shown. Figure 1 As shown, the side naturally forms a stepped shape.

[0045] In step S6, contact hole 7 is fabricated, resulting in the following: Figure 5 The structure shown.

[0046] Step S7: Fill the contact hole 7 to form leads 7b and 7a (where 7a is the hot-end connection line of the contact hole of the two thermocouples), resulting in the following... Figure 6 As shown. This step is usually done in stages, first with large-area sputtering or deposition, then patterning. The filler material can be metals such as aluminum, titanium, and tungsten, or other materials with good electrical conductivity.

[0047] Step S8, cover the sacrificial layer 8, which is covered only by the patterning process. Figure 1 Partial surface of the structure shown, such as Figure 7As shown, this can leave more space on the other side to fill the light-absorbing layer 9, thereby obtaining stable support. The height of the sacrificial layer 8 can be flush with or higher than the lead 7a, preferably higher than the lead 7a, so that the thickness of the sacrificial layer 8 can have more gradient changes. The forming method of the sacrificial layer 8 depends on the material, for example, when a high polymer material is used, it is usually first spin-coated and then cured. For example, PMMA, PI, etc., the curing temperature can be 120-350 degrees, and the time can be 15-60 minutes. When amorphous silicon, silicon oxide or polycrystalline silicon is used, methods such as LPCVD, RTCVP or PECVD can be used.

[0048] Step S8, covering the light-absorbing layer 9, as shown in Figure 8 For example, silicon nitride is first deposited on a large area (preferably grown by low-temperature CVD process, growth temperature below 350°C), so that it covers all surfaces, and the thickness can be 500nm-1μm. After chemical mechanical polishing (CMP) planarization, silicon nitride is deposited again, and the thickness can be 100nm-1μm. Then, patterning is performed to separate the pixel units and expose the PAD layer (not shown in the cross-sectional view).

[0049] Step S9, using dry BOSCH process or wet process (TMAH or KOH solution) to make the back hollow back cavity 1a, as shown in Figure 9 Specifically, a hard mask layer can be first formed on the back, then combined with photolithography and etching to form the back cavity 1a, and finally the hard mask layer is removed.

[0050] Step S10, releasing part of the sacrificial layer 8 to make the light-absorbing layer 9 suspended, as shown in Figure 10 The release means depends on the material of the sacrificial layer. For polymer materials such as PMMA, PI, etc., O2 plasma is usually used for controlled release of the front polymer. Remote plasma can be used for release, the radio frequency power can be 200mW-2000mW, the gas pressure can be 0.1T-1.5T, the O2 flow rate can be 200-2000sccm, and N2H2 or N2 can be loaded as a supporting gas. After release, part of the polymer can be left as a support column for the suspended SIN light-absorbing layer. For a silicon oxide layer as a sacrificial layer, VHF gas is used for controlled release. If α-Si or polycrystalline Si is used as a sacrificial layer, XeF2 gas is used for controlled release. The size of the remaining sacrificial layer can be controlled by the degree of etching.

[0051] In theory, the order of steps S9 and S10 can be exchanged, but since the light-absorbing layer is suspended first and then etched to form the back cavity, it is easy to cause damage to the suspended structure of the light-absorbing layer, so it is preferred to etch the back cavity first.

[0052] The above describes embodiments of the present disclosure. However, these embodiments are merely for illustrative purposes, and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Those skilled in the art can make various substitutions and modifications without departing from the scope of the present disclosure, and all such substitutions and modifications shall fall within the scope of the present disclosure.

Claims

1. A method for fabricating a suspended absorber layer thermopile device, characterized in that, Includes the following steps: A semiconductor substrate is provided, the semiconductor substrate having a front side and a back side; A support layer, a first thermocouple layer, a first insulating layer, a second thermocouple layer, and a second insulating layer are formed sequentially from bottom to top on the front side of the semiconductor substrate. Then, contact holes are made and filled to form the lead layer of the first thermocouple, the lead layer of the second thermocouple, and the lead layer for the hot junction connection between the first thermocouple and the second thermocouple. A sacrificial layer is then formed, which covers a portion of the surface of the second insulating layer and exposes the lead layer connecting the hot ends of the first and second thermocouples. A light-absorbing layer is covered on the surface of the sacrificial layer and the surface of the lead layer and the second insulating layer that connect the hot ends of the exposed first and second thermocouples, and then patterned. The back side of the semiconductor substrate is etched to form a back cavity; then a portion of the sacrificial layer is released to suspend the light-absorbing layer. In each thermocouple stack structure, the upper surface of the support layer is connected to at least one side of the first and second insulating layers to form a stepped shape, and the light-absorbing layer is supported on the side of the stepped shape.

2. The manufacturing method according to claim 1, characterized in that, The sacrificial layer is a polymer material, and a portion of the sacrificial layer is released using a plasma method. The sacrificial layer is amorphous silicon or silicon oxide, and a portion of the sacrificial layer is released using vapor phase etching.

3. The manufacturing method according to claim 2, characterized in that, The polymer material is PI or PMMA.

4. The manufacturing method according to claim 1, characterized in that, After the back cavity is formed, a portion of the sacrificial layer is released to suspend the light-absorbing layer.

5. The manufacturing method according to claim 1, characterized in that, In the first and second thermocouple layers, one is made of N-type polycrystalline silicon or N-type monocrystalline silicon, and the other is made of P-type polycrystalline silicon, P-type monocrystalline silicon, or aluminum.

6. The manufacturing method according to claim 5, characterized in that, The doping of the first and second thermocouple layers is completed by ion implantation and annealing. The annealing conditions are: temperature 950~1150℃, time 15~120s.

7. A suspended absorber layer thermopile device, characterized in that, Includes a semiconductor substrate, said semiconductor substrate having a front side and a back side; A support layer, a first thermocouple layer, a first insulating layer, a second thermocouple layer, a second insulating layer, a sacrificial layer, and a light-absorbing layer are stacked sequentially from bottom to top on the front side of the semiconductor substrate. And lead layers that are electrically connected to the first layer thermocouple and the second layer thermocouple respectively, and lead layers that are hot-end connected between the first layer thermocouple and the second layer thermocouple; The sacrificial layer covers only a portion of the central region of the second insulating layer; a portion of the light-absorbing layer supports and covers the surface of the sacrificial layer and the surface of the lead layer connecting the hot ends of the first and second thermocouples, while the remaining portion is suspended. In each thermocouple stack structure, the upper surface of the support layer is connected to at least one side of the first and second insulating layers to form a stepped shape, and the light-absorbing layer is supported on the side of the stepped shape.

8. The suspended absorber layer thermopile device according to claim 7, characterized in that, The support layer includes at least one of a silicon oxide layer and a silicon nitride layer; And / or, In the first and second layer thermocouples, one is made of N-type polycrystalline silicon or N-type monocrystalline silicon material, and the other is made of P-type polycrystalline silicon or P-type monocrystalline silicon or metallic aluminum. And / or, The sacrificial layer is made of polymer, amorphous silicon, silicon oxide, or polycrystalline silicon. And / or, The light-absorbing layer is made of silicon nitride.

9. The suspended absorber layer thermopile device according to claim 8, characterized in that, The support layer is composed of a silicon oxide layer, a silicon nitride layer, and a silicon oxide layer stacked together.

10. The suspended absorber layer thermopile device according to claim 7, characterized in that, The surface height of the sacrificial layer is higher than the surface height of the lead layer connecting the hot ends of the first thermocouple and the second thermocouple.

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