Characterization of MOSFETs formed by gate masked ion implantation technique

Ion implanted MOSFETs formed with the gate as source-drain mask were described at the 1966 I EDM. These devices exhibited low Miller capacitance and freedom from critical mask alignment. Hewever, the devices were unstable because ions were implanted into unpassivated silicon. In addition, the characteristics were fixed because heavy ion concentrations were required for contact formation. MOSFETs formed by a combination of diffusion and ion implantation have recently been investigated. They retain the major attributes of the previously described device, but have greater stability and flexibility of characteristics. An offset-gate diffused device is first formed by standard techniques. The drain p-region is then extended to the edge of the gate by Boron implantation through the oxide-passivated area connecting the gate and diffused drain. The metallic gate acts as a mask to prevent ion doping of the modulated channel region. Device stability is achieved by implanting the ions through a passivated oxide layer. With diffused contact areas, the implanted doping concentration can be varied to allow formation of devices which simulate the Insulated Gate Tetrode. A light implantation produces high drain to source breakdown and low frequency response while heavy implantation produces low breakdown and high frequency response. The device fabrication procedure will be described. Noise, frequency response, and drain to sourer breakdown voltage will be evaluated at various implantation doping levels. Results will be compared with conventional devices.