Critical dimension improvement of plasma enhanced chemical vapor deposition silicon nitride thin films in GaAs devices

Silicon nitride thin films are widely used in GaAs device fabrication. Plasma enhanced chemical vapor deposition is the most commonly used technique by which silicon nitride is deposited. Changing the process conditions may significantly change the layer physical properties and chemical composition. The device definition includes both deposition of the dielectric layer and its patterning, by etching the exposed SiN via a photoresist mask with sub-microns resolution. The current study examines the influence of the deposition and etching process conditions on the layer characteristics and the devices critical dimension (CD) control. Empirical formulae that correlate process parameters (temperature, gas flow ratio, pressure and RF power) with layer properties have been found and with very high precision yield the deposition rate, wet and dry etching rates and refractive index of the layer. Better understanding of the deposition and etching processes led to significant improvement in controlling the device CD.