Method of making a dual DMOS device by ion implantation and diffusion

A diffused MOS (DMOS) device and method for making same are disclosed. The prior art DMOS device is improved upon by ion implanting a depletion extension LD to the drain. However, the introduction of the depletion extension LD introduces a manufacturing statistical variation in the characteristics of the resultant devices so produced. The problem of the effects of the variations in the length LD+L, and thus, variations in the resulting transconductance of the device, is solved by placing two of these devices in parallel. When one device has its LD relatively shorter, the companion device will also have its LD correspondingly longer. The method of producing the dual devices is by ion implanting a single conductivity region which forms the LD for both the left- and right-hand channels for the left- and right-hand DMOS structures. If the mask for the ion-implanted region is misaligned slightly to the right, then the effective LD for the right-hand channel is somewhat longer but the effective LD for the left-hand channel is correspondingly shorter, so that the net parallel transconductance for the two devices remains the same as the transconductance for a perfectly symmetric ion-implanted region.