Thermal membrane sensor and method for the production thereof

• US 6,825,057 B1
• Filed: 10/25/1999
• Issued: 11/30/2004
• Est. Priority Date: 11/25/1997
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Frey, Wilhelm, Heyers, Klaus
• Primary Examiner(s): Fourson, George
• Assistant Examiner(s): Toledo, F L.
• Application Number:
  US09/355,373
• Time in Patent Office: 1,863 Days
• Field of Search: 438/54, 438/411, 438/421, 438/466, 438/705, 438/931, 438/977, 438/FOR.330, 438/FOR.485, 438/960, 257/467, 257/522
• US Class Current: 438/54
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01K 7/028 using microstructures, e.g. made of silicon

Abstract

A process for manufacturing a membrane sensor over a silicon substrate, preferably a thermal membrane sensor. A thin layer of silicon carbide or silicon nitride is deposited over an area of porous silicon formed in the surface of the substrate, and then openings that extend as far as the layer of porous silicon are formed in the silicon carbide or silicon nitride layer via a dry etching process. Next, semiconductor structures and conductor path structures are implanted into the upper surface of the membrane layer via lithographic steps, and then the sacrificial layer of porous silicon is removed using a suitable solvent such as ammonia. Thus an empty space that thermally isolates the sensor membrane from the substrate is created beneath the membrane layer.

Claims

1. A process for manufacturing an exposed membrane over a silicon substrate, comprising the steps of:

creating an etching mask on a main surface of the substrate that leaves an area of the silicon substrate where the membrane is to be created exposed;

electrochemically etching the exposed area of the silicon substrate to a preselected depth to form a layer of porous silicon within the exposed area;

removing the etching mask;

after performing the step of electrochemically etching, depositing on the layer of porous silicon within the exposed area a membrane layer composed of at least one of silicon carbide and silicon nitride;

creating openings inward from an upper surface of the membrane layer in preassigned areas of the membrane layer;

selectively creating circuit structures on the upper surface of the membrane layer, the selective creating step including the step of implanting the circuit structures into the upper surface of the membrane layer, wherein the selectively creating step includes creating conductor paths made of aluminum for the circuit structures into the upper surface of the membrane layer; and

removing the layer of porous silicon below the membrane layer by sacrificial layer etching.

2. The process according to claim 1, wherein the exposed membrane is manufactured for a thermal membrane sensor.

3. The process according to claim 1, wherein the electrochemical etching step includes an electrochemical anodizing process in a hydrofluoric acid electrolyte.

5. The process according to claim 1, wherein the membrane layer is deposited via a reactive sputter deposition.

6. The process according to claim 1, wherein the openings in the membrane layer are created via a dry etching process.

7. The process according to claim 6, wherein the dry etching process is carried out via a plasma etching.

8. The process according to claim 1, wherein the circuit structures include semiconductor elements.

9. The process according to claim 1, wherein the sacrificial layer etching is carried out using at least one of ammonia, KOH and tetramethylammonium hydroxide.

10. The process according to claim 1, further comprising the step of applying a protective layer over the entire upper surface of the membrane layer.

11. The process according to claim 10, wherein the protective layer is composed of at least one of silicon carbide and silicon nitride.

12. A thermal membrane sensor manufactured in accordance with the process of claim 1.

13. The thermal membrane sensor according to claim 12, wherein the circuit structures have a thermopile made of two different substances having a Seebeck effect.

14. The thermal membrane sensor according to claim 12, wherein the thermal membrane sensor is a radiation sensor having an additional absorber layer over a protective layer covering an entire surface.

15. The thermal membrane sensor according to claim 14, wherein the additional absorber layer is composed of at least one of black gold and black silicon.

4. A process for manufacturing an exposed membrane over a silicon substrate, comprising the steps of:

creating an etching mask on a main surface of the substrate that leaves an area of the silicon substrate where the membrane is to be created exposed;

electrochemically etching the exposed area of the silicon substrate to a preselected depth to form a layer of porous silicon within the exposed area;

removing the etching mask;

depositing a membrane layer composed of at least one of silicon carbide and silicon nitride;

creating openings inward from an upper surface of the membrane layer in preassigned areas of the membrane layer;

selectively creating circuit structures on the upper surface of the membrane layer, the selective creating step including the step of implanting the circuit structures into the upper surface of the membrane layer, wherein the selectively creating step includes creating conductor paths made of aluminum for the circuit structures into the upper surface of the membrane layer; and

removing the layer of porous silicon below the membrane layer by sacrificial layer etching wherein the depositing step includes at least one of a low-temperature LPCVD process and a low-temperature PECVD process.