CMOS-based semiconductor device on micro-hotplate and method of fabrication
It is disclosed herein a semiconductor device and a method of manufacturing the semiconductor device. The semiconductor device is made using partly CMOS or CMOS based processing steps, and it includes a semiconductor substrate, a dielectric region over the semiconductor substrate, a heater within the dielectric region and a patterned layer of noble metal above the dielectric region. The method includes the deposition of a photoresist material over the dielectric region, and patterning the photo-resist material to form a patterned region over the dielectric region. The steps of depositing the photo-resist material and patterning the photo-resist material may be performed in sequence using similar photolithography and etching steps to those used in a CMOS process. The resulting semiconductor device is then subjected to further processing steps which ensure that a dielectric membrane and a metal structure within the membrane are formed in the patterned region over the dielectric region.
1. A method of manufacturing a microhotplate comprising a semiconductor substrate, a dielectric region over the semiconductor substrate, a resistive heater within the dielectric region, the method comprising:
forming the semiconductor substrate, the dielectric region and the resistive heater using complementary metal oxide semiconductor (CMOS) compatible processing steps;
depositing a photo-resist material over the dielectric region using the CMOS compatible processing steps;
patterning the photo-resist material to form a patterned region over the dielectric region using the CMOS compatible processing steps;
etching at least a portion of the semiconductor substrate to form a dielectric membrane, wherein the steps of depositing the photo-resist material, patterning the photo-resist material and etching the portion of the semiconductor substrate are performed in sequence; and
wherein, after the etching of the semiconductor substrate, the method further comprises, depositing a metal structure in the patterned region over the dielectric region using a further process, wherein the further process is not a CMOS compatible process.
2. A method according to claim 1 , wherein the steps of forming the semiconductor substrate, the dielectric region and the resistive heater, and the steps of depositing and patterning the photoresist material are performed within the CMOS compatible processing steps.
3. A method according claim 1 , wherein said further process comprises at least one of depositing the metal structure by applying a sputtering or evaporation technique or depositing the metal structure both in the patterned region and on top of the photo-resist material.
4. A method according to claim 3 , wherein said further process comprises removing the photo-resist material and the part of the metal structure on top of the photoresist material so that the metal structure formed in the patterned region is retained over the dielectric region, and optionally the photo-resist material and the part of the metal structure on top of the photo-resist material are removed using a chemical solution or a chemical solvent, and/or the photo-resist material and the part of the metal structure on top of the photo-resist material are removed using a lift-off technique.
5. A method according to claim 1 , wherein the step of patterning the photo-resist material comprises at least one of applying a mask to define the patterned region over the dielectric layer or using a photolithography technique within the CMOS compatible processing steps to define the patterned region over the dielectric region.
6. A method according to claim 1 , wherein the step of etching the semiconductor substrate comprises applying a mask adjacent the semiconductor substrate to define the portion of the semiconductor substrate to be etched.
7. A method according to claim 1 , wherein the step of etching the semiconductor substrate comprises one of:
applying a Deep Reactive Ion Etching (DRIE) technique; or
applying a wet etching technique, preferably using potassium hydroxide (KOH) or tetramethyl ammonium hydroxide (TMAH).
8. A method according to claim 1 , wherein the resistive heater comprises a material selected from a group comprising tungsten, titanium, aluminum, polysilicon and single crystal silicon, and/or
further comprising forming a first barrier layer adjacent the resistive heater within the dielectric region.
9. A method according to claim 1 , wherein, after the etching of the substrate and prior to depositing the metal structures, the method further comprises depositing a second diffusion barrier or adhesive layer on top of the photoresist region and in the patterned region over the dielectric region, optionally wherein the second diffusion barrier or adhesive layer comprises one or more material selected from a group comprising titanium, nickel and chromium.
10. A method according to claim 1 , further comprising patterning the metal structure into one or more shapes selected from a group comprising:
(1) interdigitated electrodes
(2) electrodes arranged in shapes of concentric rings
(3) spiral shaped electrodes, and
(4) only two electrodes next to one another.
11. A method according to claim 1 , further comprising at least one of:
patterning the metal structure into a series of dots or holes; or
depositing a gas sensitive layer on the metal structure, and optionally wherein the gas sensitive layer comprises a pure or doped metal oxide material selected from a group comprising tin oxide, tungsten oxide and zinc oxide.
12. A method according to claim 11 , wherein the gas sensitive layer comprises a material selected from a group comprising polymers, nanowires, nanorods, nanoparticles and nano-plates.
13. A method according to claim 11 , wherein the gas sensitive layer is a porous layer and/or a nanostructured layer.
14. A method according to claim 11 , wherein the gas sensitive layer at least one of is deposited using a technique selected from a group comprising screen printing, sputtering, chemical vapour deposition (CVD) ink-jet and drop coating, or has a drop or conformal shape.
15. A method according to claim 1 , wherein the microhotplate is formed from a bulk silicon wafer or a silicon-on-insulator (SOI) wafer.
16. A method according to claim 1 , further comprising at least one of:
forming a passivation layer on the dielectric region using the CMOS compatible processing steps, the metal structure being deposited on the passivation layer, wherein optionally the passivation layer comprises a material comprising silicon dioxide or silicon nitride;
forming a temperature sensor within the dielectric region using the CMOS compatible processing steps, wherein optionally the temperature sensor is selected from a group comprising a diode temperature sensor, and a single crystal silicon, polysilicon or metal resistive temperature sensor;
forming a heat spreading plate within the dielectric region using the CMOS compatible processing steps, and optionally the heat spreading plate comprises a material selected from a group comprising single crystal silicon, polysilicon and a metal; or
integrating CMOS circuitry on the same chip as the microhotplate using the CMOS compatible processing steps, and optionally further comprising integrating a temperature sensor outside the dielectric membrane and within the same chip.
17. A method according to claim 1 , wherein at least one of the microhotplate has a circular or rectangular shape, the dielectric membrane has a circular or rectangular shape, or the metal structure comprises gold or platinum.
18. A microhotplate comprising:
a semiconductor substrate having an etched portion;
a dielectric region over the semiconductor substrate;
a resistive heater formed within the dielectric region; and
a patterned metal layer formed over the dielectric region,
wherein the semiconductor substrate, the dielectric region, the resistive heater, the etched portion in the substrate and the patterned metal layer are formed using the method according to claim 1 .