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Abstract

In the manufacture of a large-area electronic device (e.g. an active-matrix liquid-crystal display or other flat panel display), a TFT of improved lifetime stability results from the inclusion of a field-relief region (22) which is of lower doping concentration than the drain region (12) and which is formed in an area (2) of lateral separation between the channel region (21) and the drain region (22). An energy beam (40), e.g. from an excimer laser, is used to provide the field-relief region (22), by laterally diffusing the doping concentration of the drain region (12) along an area (2) of the semiconductor film (20) significantly larger than the thickness of the semiconductor film (20). The method is simple and easily controllable, an advantageous doping profile (FIG. 3b) is obtained along the field-relief region (22) by this lateral diffusion. The laterally-diffused low-doping profile near the channel region (21)increases progressively along the current path to the drain region (12) so avoiding the creation of areas of high field in the separation area (2). Near the drain region the laterally-diffused doping concentration approaches in magnitude the high doping concentration of the drain region (12), so reducing the increase in drain series resistance resulting from the inclusion of the field-relief region (22). The lateral diffusion length is generally an order of magnitude larger than the depths of the drain and field-relief regions (12,22), because the thickness of the thin film(s) limits the vertical diffusion.

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