Method of making specular infrared mirrors for use in optical devices

A method of making mirrors on a silicon wafer in the manufacture of photonic devices, comprising:

• pre-heating the wafer for a duration between 30 and 180 seconds at temperature from 300 to 600° C. so as to eliminate adsorbed volatile contaminants;
• carrying out an SiO2 etch at a temperature from 300 to 600° C. to remove absorbed contaminants using an argon plasma;
• placing the wafer in ambient at a temperature equal to or less than about 25° C. so to cool a surface of the wafer and reduce the surface mobility of the impinging aluminum atoms during a subsequent aluminum deposition;
• carrying out a collimated titanium deposition at a temperature in the range −100° C.-100° C. so as to deposit a gettering layer for hydrogen, oxygen and nitrogen;
• carrying out an aluminum mirror deposition at a temperature in the range −100° C.-100° C. so as to minimise surface diffusion and grain growth in a deposition chamber;
• and
• removing the wafer from the deposition chamber at a temperature in the range −100° C.-100° C. so as to prevent excessive bulk oxidation.