STRUCTURE AND FABRICATION METHOD OF A HIGH PERFORMANCE MEMS THERMOPILE IR DETECTOR

• US 20150137304A1
• Filed: 01/21/2013
• Published: 05/21/2015
• Est. Priority Date: 08/23/2012
• Status: Active Grant

• Current Assignee: Zhongke Future of Chip Microelectronics Technology Chengdu Company Limited
• Original Assignee: Jiangsu R&D Center For Internet Of Things
• Inventors: Mao, Haiyang, Ou, Wen
• Granted Patent: US 9,117,949 B2
• Time in Patent Office: Days
• US Class Current: 257/467
• CPC Class Codes: G01J 5/022 Monolithic
• CPC Class Codes: G01J 5/12 using thermoelectric elements, e.g. thermocouples
• CPC Class Codes: H01L 27/1443 with at least one potential jump or surface barrier
• CPC Class Codes: H01L 27/1446 in a repetitive configuration
• CPC Class Codes: H01L 31/028 including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/0352 characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H10N 10/17 characterised by the structure or configuration of the cell or thermocouple forming the device

Abstract

The invention involves structure and fabrication method of a high performance IR detector. The structure comprises a substrate; a releasing barrier band on the substrate; a thermal isolation chamber constructed by the releasing barrier band; a black silicon-based IR absorber located right above the thermal isolation chamber and the black silicon-based IR absorber is set on the releasing barrier band; a number of thermocouples are set around the lateral sides of the black silicon-based IR absorber. The thermopiles around the black silicon-based IR absorber are electrically connected in series. The cold junctions of the thermopile are connected to the substrate through the first thermal-conductive-electrical-isolated structures as well as the heat conductor under the first thermal-conductive-electrical-isolated structures. The hot junctions of the thermopile are in contact with the IR absorber through the second thermal-conductive-electrical-isolated structures, and the second thermal-conductive-electrical-isolated structures are located above the releasing barrier band. The structure of such detector is simple, and it is easy to implement and can also be monolithicly integrated. Such detector has high responsivity and detection rate, and is CMOS-compatible, thus can be used widely in a safe and reliable manner.

Claims

1. A high performance MEMS thermopile IR detector, comprising:

a substrate, wherein;

a releasing barrier band formed on the substrate;

a thermal isolation chamber formed in the releasing barrier band;

a black silicon-based IR absorber disposed above the thermal isolation chamber;

the black silicon-based IR absorber set on the releasing barrier band;

a number of thermocouples set around lateral sides of the black silicon-based IR absorber;

the thermocouples around the black silicon-based IR absorber are electrically connected in series to form a thermopile;

metallic electrodes are set beside the thermopile to output electrical signals;

one-side terminals of the thermopile adjacent to the IR absorber form the hot junctions and the other-side terminals far away from the IR absorber form the cold junctions;

the cold junctions of the thermopile are connected to the substrate through the first thermal-conductive-electrical-isolated structures as well as the heat conductor under the first thermal-conductive-electrical-isolated structures;

the heat conductor is located outside the thermal isolation chamber but between the releasing barrier band and the substrate;

the first thermal-conductive-electrical-isolated structures are embedded in the releasing barrier band;

the hot junctions of the thermopile are in contact with the IR absorber through the second thermal-conductive-electrical-isolated structures; and

the second thermal-conductive-electrical-isolated structures are located above the releasing barrier band.

2. The high performance MEMS thermopile IR detector according to claim 1, wherein:

the black silicon-based IR absorber comprises black silicon structures formed from black silicon material through reactive ion etching and releasing channels that run through the black silicon-based IR absorber; and

the releasing channels and the thermal isolation chamber are connected with each other.

3. The high performance MEMS thermopile IR detector according to claim 1, wherein:

the thermopile comprises P-type thermocouple strips and the N-type thermocouple strips corresponding to the P-type thermocouple strips;

the N-type thermopile strips and P-type thermocouple strips are isolated from each other by means of the barrier isolation layer;

the P-type thermocouple strips and N-type thermocouple strips are electrically connected through the first connecting lines at the terminals that form hot junctions; and

at the terminals that form cold junctions, the P-type thermocouple strips are electrically connected to N-type thermocouple strips and N-type thermocouple strips in adjacent thermocouples are electrically connected through the second connecting lines, such that thermocouples are electrically connected with each other for forming a thermopile.

4. The high performance MEMS thermopile IR detector according to claim 1, wherein:

material for both the first thermal-conductive-electrical-isolated structures and the second thermal-conductive-electrical-isolated structures includes Si₃N₄.

5. The high performance MEMS thermopile IR detector according to claim 1, wherein:

metallic electrodes are set beside the serially connected thermocouples around the lateral sides of the black silicon-based IR absorber.

6. The high performance MEMS thermopile IR detector according to claim 3, wherein:

the N-type thermocouple strips are under the P-type thermocouple strips,

the N-type thermopile strips are above the releasing barrier band,

the cold junctions of the N-type thermocouple strips contact with the first thermal-conductive-electrical-isolated structures and then connect with heat conductor through the first thermal-conductive-electrical-isolated structures;

the hot junctions of the N-type thermocouple strips are bridging one-side terminals of the second thermal-conductive-electrical-isolated structures, and

the other-side terminals of the second thermal-conductive-electrical-isolated structures are in contact with the black silicon-based IR absorber.

7. The fabrication method for a high performance MEMS thermopile IR detector, comprising:

(a) providing a substrate and setting a substrate protective layer on the surface of the substrate;

(b) etching the substrate protective layer selectively, so as to form substrate contacting windows above the substrate, wherein the substrate contacting windows run through the substrate protective layer;

(c) depositing a layer of heat conductor over the substrate contacting windows, and depositing a mask layer for the heat conductor, wherein the heat-conductor mask layer covers the substrate protective layer and fills in the substrate contacting windows;

(d) etching the heat-conductor mask layer selectively so as to form heat-conductor etching windows, wherein the heat-conductor etching windows run through the heat-conductor mask layer along the inner sides of the substrate contacting windows, and using the heat-conductor etching windows to etch the heat conductor till reaching the substrate protective layer to form heat-conductor through-holes;

(e) depositing a supporting layer on the heat-conductor mask layer, making the supporting layer fill in the heat-conductor through-holes and heat-conductor etching windows and also cover the heat-conductor mask layer so as to form a releasing barrier band structure and the supporting membrane above the substrate;

(f) etching the supporting layer selectively so as to form thermal-conductive-electrical-isolated openings within the supporting layer, wherein the thermal-conductive-electrical-isolated openings run through the supporting layer and locate at the lateral side of the releasing barrier band structure, and depositing a thermal-conductive-electrical-isolated layer over the supporting layer, wherein the thermal-conductive-electrical-isolated layer fills in the thermal-conductive-electrical-isolated openings and covers the supporting layer;

(g) etching the thermal-conductive-electrical-isolated layer so as to form the first thermal-conductive-electrical-isolated blocks and the second thermal-conductive-electrical-isolated blocks at the position of the above mentioned supporting layer, wherein the first thermal-conductive-electrical-isolated blocks are within the supporting layer and the second thermal-conductive-electrical-isolated blocks are over the supporting layer;

(h) setting the first thermocouple strips and the second thermocouple strips between the first thermal-conductive-electrical-isolated blocks and the second thermal-conductive-electrical-isolated blocks close to them, wherein the implantation types for the first thermocouple strips and the second thermocouple strips are different, the first thermocouple strips and the second thermocouple strips are isolated from each other by the barrier isolating layer, the terminals at one side of the first thermocouple strips are in contact with the first thermal-conductive-electrical-isolated blocks and the other-side terminals are in contact with the second thermal-conductive-electrical-isolated blocks;

(i) setting a thermocouple protective layer over the second thermocouple strips, wherein the region covered by the thermocouple protective layer comprises the second thermocouple strips and the first thermal-conductive-electrical-isolated blocks;

the black silicon material is formed within the region constructed by the second thermal-conductive-electrical-isolated blocks; and

the black silicon material is in contact with the second thermal-conductive-electrical-isolated blocks;

(j) etching the thermocouple protective layer selectively, so as to form electrical-connection through-holes for purpose of connecting the first thermocouple strips and the second thermocouple strips;

(k) sputtering a metal layer on the substrate with produced electrical-connection through-holes, wherein the metal layer is filled in the electrical-connection through-holes;

masking and etching the metal layer selectively and making the first thermocouple strips be electrically connected to the second thermocouple strips at one terminals of the second thermal-conductive-electrical-isolated blocks through the first connecting lines;

making the second thermocouple strips be electrically connected to the first thermocouple strips of the adjacent thermocouple through the second connecting lines;

forming the first electrical connectors at the lateral sides of the first thermal-conductive-electrical-isolated structures;

(l) depositing a passivation layer on the surface of substrate, on which the first connecting lines, the second connecting lines and the first electrical connectors have been produced, wherein the passivation layer covers the black silicon material, the thermocouple protective layer, the first connecting lines, the second connecting lines as well as the first electrical connectors;

(m) etching the passivation layer selectively, so as to form black silicon etching windows on the passivation layer over the black silicon material;

etching the black silicon material with help of the black silicon etching windows, till reaching heat conductor right under the black silicon etching windows to form releasing openings;

(n) releasing the heat conductor right under the black silicon material using the releasing barrier band structure as an etching stop, thus to obtain a thermal isolation chamber;

(o) using the passivation layer as the sidewall material for the black silicon material with rough surface; and

applying RIE on the black silicon material so as to form the black silicon-based IR absorber and, at the same time, to form the second electrical connector.

8. The fabrication method according to claim 7, wherein:

in the steps (m) and (n), coating the inner walls of the releasing openings with a releasing barrier layer for protecting the black silicon material.

9. The fabrication method according to claim 7, wherein:

in the step (h), the first thermocouple strips are N-type implanted and the second thermocouple strips are P-type implanted.

10. The fabrication method according to claim 7, wherein:

in the step (k), the material of the metal layer includes Al.