REFRACTORY METAL SILICON DEVICE TECHNOLOGY

Films 2000-5000 Å thick of Mo or W deposited over thin films of thermally grown SiO2 are shown to be effective high temperature diffusion masks against both phosphorous and boron. These metal films may be precisely patterned and their diffusion masking properties can be used to define the source and drain regions of MOSFETs. In this manner, self-registered MOSFETs can be fabricated with a portion of the diffusion masking metal film acting as the gate electrode. Using P or B doped deposited glasses as diffusion sources, n or p channel enhancement mode MOSFETs were made by diffusion through the exposed thin SiO2 film into p and n type Si to form source and drain junctions. Contact was subsequently made by etching holes through the oxide layers to the source and drain regions and to the refractory metal gate electrode buried within the oxide layers. These devices exhibit channel mobilities between 200 and 300 cm2/V-sec at gate voltages about 10 V above threshold. The stability of MOS structures processed in a similar manner has been measured. After being stressed at ±6 × 105 V/cm and 250°C for 15 hr, these devices exhibited shifts in their CV characteristics less than 200 mV. © 1968.