A method for manufacturing a thermopile sensor

Abstract

The present invention discloses a process for manufacturing a thermopile sensor, including forming a groove for making a cavity on the front side of a substrate by etching, and forming a hole at the bottom of the groove, the depth of the groove determines the depth of the sealed cavity, filling the groove with borophosphosilicate glass, and forming a special film layer on the surface of the borophosphosilicate glass, and then making a support layer on the flattened surface, forming a gap between the special film layer and the support layer and separating them by a high-temperature annealing process, and at the same time, high-temperature annealing makes the borophosphosilicate glass fluid, which is used to fill the hole at the bottom of the groove, so that the borophosphosilicate glass flows downward as a whole, thereby forming a sealed cavity with a certain depth under the support layer. Finally, the two thermocouple materials, the dielectric layer, the metal layer and the passivation layer are patterned on the support layer. Compared with the traditional sealed cavity manufacturing process, the cavity depth range formed by the technical solution of the present invention is wider, and the manufacturing process is simple, the cost is low, and the equipment capacity requirements are also low.

Description

Technical Field

[0001] The present invention relates to the field of thermopile sensors, and in particular to a method for manufacturing a thermopile sensor. Background Art

[0002] In the structure of some temperature-related semiconductor sensors, such as thermopile sensors, thermal flow sensors, etc., one end of the thermopile or thermistor needs to be placed on a suspended membrane. After packaging, the substrate under one end of the thermopile or thermistor does not contact the base of the package, but is suspended and in contact with air or vacuum to achieve the purpose of forming the hot end of the thermopile or reducing the interference of the external environment temperature on the thermistor. From the above, it can be seen that these temperature-related semiconductor MEMS sensors all need to use suspended or sealed cavity structures.

[0003] In the prior art, there are two main methods for forming suspended structures: wet release of the front structure and wet etching of the back. The front wet release or back etching process is based on the precise control of the etching time, which is closely related to the purity, concentration and temperature of the etching solution used. When processing in a semiconductor factory with a large number of batches, the uniformity of the devices in the wafer and the repeatability of the devices between wafers are more obvious. In particular, the back wet etching process has certain requirements on the thickness of the substrate and the size of the etching structure. For example, the thicker the wafer, the longer the etching time; at the same time, to achieve a fixed area of ​​suspended area, the thicker the wafer thickness, the larger the back etching window will be, resulting in an increase in chip design area and other cost-increasing problems.

[0004] In the prior art, there are mainly three methods for forming a sealed cavity:

[0005] (1) Silicon wafer bonding + CMP, the vacuum degree is good, but the process cost is high and the equipment capacity requirements are high.

[0006] (2) Porous silicon technology has good vacuum degree, but the cavity depth is limited by the thickness of porous silicon growth, and the porous silicon growth process capability is required to be high.

[0007] (3) Surface silicon corrosion + polysilicon filling. The vacuum degree is affected by the polysilicon filling equipment. There are special requirements for the selection of substrate crystal orientation. Dry and wet methods are used together, and the process is relatively complicated.

[0008] Therefore, technicians in this field are committed to developing a method for manufacturing a thermopile sensor, and the manufactured device has good uniformity within the slice and repeatability between slices, which is suitable for mass production. Summary of the invention

[0009] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to manufacture a sealed cavity in a thermopile sensor so that the manufacturing process is simple, the cost is low, and the equipment capacity requirement is also low.

[0010] To achieve the above object, the present invention provides a method for manufacturing a thermopile sensor, comprising the following steps:

[0011] providing a substrate;

[0012] Forming a first layer structure groove on the substrate by photolithography and etching;

[0013] Forming a plurality of second layer structure holes inside the first layer structure grooves by photolithography and etching;

[0014] Growing a borophosphosilicate glass oxide layer film inside and outside the first layer structure groove by plasma enhanced chemical vapor deposition;

[0015] Making a special thin film on the borophosphosilicate glass oxide layer film;

[0016] Removing the borophosphosilicate glass oxide layer film and the special film on the surface of the device;

[0017] Depositing a support layer on the surface of the device;

[0018] After the special film is separated from the support layer to form a gap, the fluidity of the borophosphosilicate glass oxide layer film at high temperature causes it to fill into the pores of the second layer structure, the gap under the support layer becomes larger, and a sealed cavity is formed under the support layer;

[0019] The first thermocouple and the second thermocouple, the dielectric layer, the metal layer and the passivation layer are prepared and patterned by deposition, photolithography and etching.

[0020] Furthermore, the process for making a special thin film on the borophosphosilicate glass oxide layer film is through a high-temperature furnace tube and / or chemical vapor deposition and / or spin coating.

[0021] Furthermore, the process method for removing the borophosphosilicate glass oxide layer film and the special film on the surface of the device is dry etching and / or chemical mechanical polishing.

[0022] Furthermore, the process method for depositing the support layer on the surface of the device is through low pressure chemical vapor deposition and / or plasma enhanced chemical vapor deposition.

[0023] Furthermore, the process method for separating the special film from the support layer to form a gap is through high temperature annealing.

[0024] Furthermore, before forming the first layer structure groove, a layer of silicon nitride is grown on the substrate.

[0025] Furthermore, the size of the pores in the second layer structure ranges from 0.5 μm to 1.5 μm.

[0026] Furthermore, the depth of the second layer structure hole is greater than the depth of the first layer structure groove.

[0027] Furthermore, when the second layer structure hole is formed by photolithography, if the depth of the first layer structure groove is greater than 5 μm, the photoresist is applied by spin coating, and if the depth of the groove is greater than 5 μm, the photoresist is applied by spray coating.

[0028] Furthermore, the growth thickness of the borophosphosilicate glass oxide layer film is smaller than the depth of the first layer structure groove.

[0029] Furthermore, the special film has a thickness ranging from 0.1 μm to 1 μm, and has the characteristics of forming a gap and separating from the supporting layer at high temperature.

[0030] Furthermore, the support layer is silicon oxide and / or silicon nitride, and the silicon oxide or silicon nitride is a single-layer or multi-layer film structure.

[0031] Furthermore, the temperature range of the high temperature annealing is 1200° C. to 1415° C., and the time of the high temperature annealing is greater than or equal to 2 hours.

[0032] Furthermore, the material of the first thermocouple is polysilicon, and the material of the second thermocouple is aluminum.

[0033] The method for manufacturing a thermopile sensor of the present invention comprises forming a groove for making a cavity on the front side of a substrate by etching, and forming a hole at the bottom of the groove, wherein the depth of the groove determines the depth of the sealed cavity, filling the groove with borophosphosilicate glass, and forming a special film layer on the surface of the borophosphosilicate glass, and then making a support layer on the flattened surface, forming a gap between the special film layer and the support layer and separating them by a high temperature annealing process, and at the same time, high temperature annealing makes the borophosphosilicate glass fluid, fills the hole at the bottom of the groove, and makes the borophosphosilicate glass flow downward as a whole, so that a sealed cavity with a certain depth is formed under the support layer. In the above process, the main function of the special film is to isolate the borophosphosilicate glass and the support layer. If the special film is not added between the borophosphosilicate glass and the support layer, the bonding between the borophosphosilicate glass and the support layer will cause the sealed cavity to be too small or fail. Finally, the two thermocouple materials, the dielectric layer, the metal layer and the passivation layer are patterned on the support layer. Compared with the process of making a sealed cavity with conventional porous silicon, the cavity depth range formed by the present invention is wider, and there is no need for excessive growth requirements and thickness requirements for the special film.

[0034] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 1 is a schematic diagram of the planar structure of a thermopile sensor according to a preferred embodiment of the present invention;

[0036] Figure 2 yes Figure 1 A schematic diagram of the cross-sectional structure of the sensor shown;

[0037] Figures 3 to 19 The cross-sectional structure schematic diagram of the manufacturing process of a thermopile sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0039] This embodiment relates to a manufacturing process of a thermopile sensor, and in particular to a manufacturing process of a sealed cavity. Figure 1 FIG. 1 is a schematic diagram of the planar structure of the thermopile sensor of this embodiment. Figure 1 In the plan view of the sensor structure shown, a sealed cavity and a thermocouple are included on the substrate. In order to better illustrate the structure of the temperature sensitive sensor, a cross-sectional structure diagram of the above sensor structure is shown as follows: Figure 2 As shown. Figure 1 As can be seen in the figure, the cold end of the thermocouple is formed on the silicon substrate, while the hot end of the thermocouple is formed on a substrate membrane with a certain thickness, and the membrane is suspended above the sealed cavity.

[0040] Those skilled in the art should realize that the above Figure 1 and Figure 2 The distribution diagram of the sensor structure shown is schematic. It should be understood that the positions of the internal units of the thermopile sensor structure can be arranged and adjusted as needed, which is within the scope of the protection claimed in the present invention. In addition, the number of thermocouple pairs, the shape and / or size of the sealed cavity involved in the present invention can also be adjusted as needed.

[0041] The manufacturing process of the thermopile sensor structure according to the embodiment of the present invention is further described below in conjunction with specific embodiments and drawings.

[0042] Figures 3 to 19It should be noted that these and other subsequent drawings are only for example, they are not drawn in proportion, and should not be used to limit the actual protection scope of the present invention.

[0043] like Figures 3 to 5 As shown, in this embodiment, the substrate 001 is silicon as an example, but the substrate material that can be used in this embodiment is obviously not limited to this, and those skilled in the art can make corresponding adjustments according to actual needs. Figure 4 and Figure 5 As shown, this step is to etch the substrate, and use photolithography and etching processes to form a first layer structure groove 003 for making a cavity in a specified area on the front side of the substrate, wherein the shape and / or depth of the first layer structure groove 003 can be adjusted according to actual needs. From the top view (not shown), the projection of the first layer structure groove 003 can be a polygon (including a rectangle) or a circle. Obviously, it can also be other shapes, which will not be repeated here. Before etching the first layer structure groove 003, a silicon nitride (SiN) protective layer 002 needs to be grown, such as Figure 3 As shown, the purpose of this layer is to protect the front side of the substrate and serve as a stop layer for subsequent processes.

[0044] like Figures 6 to 9 As shown, the second layer structure holes 004 with dense arrangement are formed inside the first layer structure groove 003 by using the photolithography process and the etching process. The key process of this step has the following characteristics: First, the typical value selection range of the size of the second layer structure hole 004 is 0.5μm to 1.5μm (too large or too small aperture is not conducive to the control of the subsequent process); Second, the depth of the second layer structure hole 004 should be greater than or equal to the depth of the first layer structure groove 003, so as to prepare for the subsequent formation of a sealed cavity with a certain depth. Those skilled in the art should recognize that the shape of the second layer structure hole 004 can be a strip, a circle, a square, and obviously can also be other shapes, which can be appropriately selected during the design according to the capability range of the photolithography equipment. At the same time, those skilled in the art should recognize that when the second layer structure hole 004 is photolithographic, the selected glue coating method needs to be adjusted accordingly according to the depth of the first layer structure groove 003. For example, if the depth of the first layer structure groove 003 is greater than 5μm, the traditional spin coating method cannot be used, and the spray coating method must be used instead to effectively and evenly coat the glue in the groove, which will not be repeated here.

[0045] like Figures 10 to 12As shown, a borophosphosilicate glass (BPSG) oxide layer film 005 is grown in the first structural groove 003 and on the surface of the device by plasma enhanced chemical vapor deposition (PECVD). The thickness of the borophosphosilicate glass oxide layer film 005 is determined according to the depth of the first structural groove 003 (generally, the growth thickness of the borophosphosilicate glass oxide layer film 005 is smaller than the depth of the first structural groove 003). At the same time, a thin special film 006 (whose typical thickness ranges from 0.1 μm to 1 μm) is grown on the borophosphosilicate glass oxide layer film 005. Then, the borophosphosilicate glass oxide layer film 005 and the special film 006 on the surface of the device are removed by dry etching or chemical mechanical polishing (CMP) (at this time, the protective layer 002 serves as a polishing stop layer of the CMP process), and finally a device as shown in FIG. Fig.12 structure. The first-layer structural groove 003 is filled with borophosphosilicate glass oxide film 005 and special film 006. The following points need to be explained here: First, there is no need to deliberately adjust the deposition conditions of the borophosphosilicate glass oxide film 005. The role of BPSG is not to fill the second-layer structural hole 004 at the bottom. Therefore, after deposition, the top of the second-layer structural hole 004 will be quickly sealed (BPSG deposited under conventional conditions of PECVD cannot effectively fill small-sized holes); second, the thickness of the special film 006 and the thickness of the borophosphosilicate glass oxide film 005 are selected. In this embodiment, the thickness of the special film 006 is selected to be 0.2μm, so the filling of the first-layer structural groove 003 is mainly achieved by BPSG. Those skilled in the art should realize that the thickness of the borophosphosilicate glass oxide film 005 and the special film 006 can be adjusted accordingly according to actual needs, such as according to factors such as production cost, production time and equipment capacity. Third, the special film 006 can be polyimide, which shrinks at high temperatures to achieve separation; similarly, the special film can also be hydrogen-implanted polysilicon, where hydrogen ions are implanted to form a bubble layer in the polysilicon, and the bubble layer will crack after high-temperature heat treatment to achieve separation. Those skilled in the art should realize that special films are not limited to the above two materials, as long as they meet the condition of "shrinking or splitting at high temperatures", the listed polyimide and hydrogen-implanted polysilicon are both commonly used materials and processes in semiconductor production and processing.

[0046] like Figure 13 to Figure 14As shown, a support layer 007 is deposited on the surface of the device layer after the CMP planarization process. The support layer can be silicon oxide SiO2 and / or silicon nitride SiN, or other insulating materials with a certain mechanical strength (the mechanical strength of the film can generally be reflected by its stress magnitude, such as the stress of silicon nitride SiN is generally required to be greater than 500 MPa). Those skilled in the art should recognize that excessive stress will lead to stress mismatch of the structure and cause structural damage, and too small stress will affect the structural strength of the film, so it is necessary to properly select the thickness and stress combination. Then, a high-temperature annealing process is performed. After the high-temperature annealing, the special film 006 and the borophosphosilicate glass oxide layer film 005 change at the same time, and a sealed cavity 008 with a certain depth is formed between the support layer 007 and the special film 006. The specific process is that the special film will shrink or crack during the high-temperature annealing process, thereby forming a whole gap under the support layer 007. At the same time, the high-temperature annealing will make BPSG have the ability to flow like a liquid to a certain extent, so at this time the borophosphosilicate glass oxide layer film 005 has an excellent hole filling ability. When the special film 006 is separated from the supporting layer (upper silicon nitride) 007 at high temperature to form a gap, the fluidity of BPSG at high temperature causes it to fill into the second layer structure hole 004, thereby enlarging the gap under the supporting layer 007 and forming a sealed cavity 008 with a certain depth (the depth of the sealed cavity is determined by the depth of the first layer structure groove 003). It is explained here that the high temperature annealing is performed at a temperature of about 1200°C or higher but lower than the melting point of Si at 1415°C for about 2 hours or longer. More preferably, the annealing is performed at a temperature of about 1200°C to 1300°C for about 5 hours.

[0047] like Figures 15 to 19As shown, two thermocouple materials, dielectric layer, metal layer and passivation layer are patterned by photolithography and etching processes, and a first thermocouple 009 and a second thermocouple 012 are formed on the support layer 007, respectively. A dielectric layer 010 and a connection hole 011 are formed between the first thermocouple 009 and the second thermocouple 012, and a passivation layer 013 is deposited on the second thermocouple 012. Those skilled in the art should recognize that the selection of the two thermocouple materials must have a large Seebeck coefficient difference between them. Low resistivity and low thermal conductivity can effectively improve the performance of the sensor. The following table shows a comparison table of Seebeck coefficients of several commonly used materials. In this embodiment, two materials that are easiest to make and relatively low in cost in a wafer foundry are selected as examples. The material of the first thermocouple 009 is polysilicon, and the material of the second thermocouple 012 is metal aluminum, which is also used as a metal lead and a metal pad. The dielectric material is also a key component of the thermopile sensor. First, it needs good mechanical strength to support the upper thermocouple material and passivation layer well, so it is necessary to consider the stress matching problem. Here, PECVD silicon oxide with adjustable stress is selected as the support layer. It should also be clearly pointed out that the shape, layout, line size, thickness and logarithm of the thermocouple involved in this embodiment do not limit the content of the present invention and can be adjusted according to different needs.

[0048]

[0049]

[0050] After metal patterning, the metal is usually alloyed using a 400°C furnace process. Finally, a passivation protective layer is deposited, and a metal PAD window is formed by photolithography and etching processes. It can be a single-layer or multi-layer structure, such as Fig.19 shown.

[0051] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for manufacturing a thermopile sensor, characterized in that: The following steps are involved: providing a substrate; Forming a first layer structure groove on the substrate by photolithography and etching; Forming a plurality of second layer structure holes inside the first layer structure grooves by photolithography and etching; Growing a borophosphosilicate glass oxide layer film inside and outside the first structural groove by deposition; Making a special thin film on the borophosphosilicate glass oxide layer film; Removing the borophosphosilicate glass oxide layer film and the special film on the surface of the device; Depositing a support layer on the surface of the device; Through high temperature annealing, the temperature range of the high temperature annealing is 1200°C to 1415°C, after the special film is separated from the support layer to form a gap, the fluidity of the borophosphosilicate glass oxide layer film at high temperature enables it to fill into the second layer structure pores, the gap under the support layer becomes larger, and a sealed cavity is formed under the support layer; The special film has the property of forming a gap between the special film and the supporting layer and separating at high temperature; The first thermocouple and the second thermocouple, the dielectric layer, the metal layer and the passivation layer are prepared and patterned by deposition, photolithography and etching.

2. The method for manufacturing a thermopile sensor according to claim 1, wherein: The deposition method in the step of growing a layer of borophosphosilicate glass oxide film inside and outside the first layer structure groove by deposition is plasma enhanced chemical vapor deposition.

3. The method for manufacturing a thermopile sensor according to claim 1, wherein: The process method for making the special film on the borophosphosilicate glass oxide layer film is to use a high-temperature furnace tube and / or chemical vapor deposition and / or spin coating.

4. The method for manufacturing a thermopile sensor according to claim 1, wherein: The process method for removing the borophosphosilicate glass oxide layer film and the special film on the surface of the device is dry etching and / or chemical mechanical grinding.

5. The method for manufacturing a thermopile sensor according to claim 1, wherein: The process method for depositing the support layer on the surface of the device is low pressure chemical vapor deposition and / or plasma enhanced chemical vapor deposition.

6. The method for manufacturing a thermopile sensor according to claim 1, wherein: The special film is polyimide or hydrogen-implanted polysilicon.

7. The method for manufacturing a thermopile sensor according to claim 1, wherein: Before forming the first layer structure groove, a layer of silicon nitride is grown on the substrate.

8. The method for manufacturing a thermopile sensor according to claim 1, wherein: The pores of the second layer structure have a pore size ranging from 0.5 μm to 1.5 μm.

9. The method for manufacturing a thermopile sensor according to claim 1, wherein: The depth of the second layer structure hole is greater than the depth of the first layer structure groove.

10. The method for manufacturing a thermopile sensor according to claim 1, wherein: When the second layer structure holes are formed by photolithography, if the depth of the first layer structure grooves is less than 5 μm, the photoresist is applied by spin coating; if the depth of the first layer structure grooves is greater than 5 μm, the photoresist is applied by spray coating.

11. The method for manufacturing a thermopile sensor according to claim 1, wherein: The growth thickness of the borophosphosilicate glass oxide layer film is smaller than the depth of the first layer structure groove.

12. The method for manufacturing a thermopile sensor according to claim 1, wherein: The thickness of the special film ranges from 0.1 μm to 1 μm.

13. The method for manufacturing a thermopile sensor according to claim 1, wherein: The support layer is silicon oxide and / or silicon nitride, and the silicon oxide or the silicon nitride is a single-layer or multi-layer film structure.

14. The method for manufacturing a thermopile sensor according to claim 1, wherein: The high temperature annealing time is greater than or equal to 2 hours.

15. The method for manufacturing a thermopile sensor according to claim 1, wherein: The material of the first thermocouple is polysilicon, and the material of the second thermocouple is aluminum.

Images