Explain fabrication process steps for micro-heater. State its advantages over conventional macro- sized heater
A micro-heater was fabricated based on the simulation results. Figure 4 shows the fabrication process used to manufacture the micro-heater. The micro-heater was 2.4 × 2.6 mm, and the size of the membrane was 1.2 × 1.4 mm. In order to fabricate the micro-heater using poly-Si as the heating element, a low stress silicon nitride film 1 μm in thickness was deposited on the silicon wafer (100) using the low pressure chemical vapor deposition (LPCVD) process.
The poly-Si thin film 2000 Å thick was then deposited on the nitride film also using the LPCVD process. In order to control the resistance of the poly-Si, phosphorous doping was applied using the ion implantation process. The sheet resistance of the poly-Si film was approximately 200 Ohm/square measured with a 4-point probe. The power compensated design was fabricated by etching areas of the poly-Si using the reactive ion etching (RIE) process.
The Pt for the electrical contact was deposited at a thickness of 2,000 Å using the sputtering process. In order to prevent oxidation of the poly-Si during heating, an SiO2 passivation layer was deposited with a thickness of 2,000 Å using plasma enhanced chemical vapor deposition (PECVD), followed by partial etching using the buffered oxide etchant (BOE). The membrane was fabricated by anisotropic etching of the Si substrate using the deep RIE process.