The 1.5 µm process refers to the manufacturing technology that came into use at leading semiconductor manufacturers from 1982 onward. At this node, several manufacturing methods changed at the same time because the previous techniques were reaching their physical limits.
For patterning, plasma dry etching replaced wet chemical etching. Wet etching acts equally in all directions and therefore undercuts the photoresist; at 1.5 µm, the resulting error could no longer be neglected. Plasma processes, by contrast, can be controlled so that they etch predominantly vertically into the layer.
In lithography, wafer steppers replaced full-field projection systems. Instead of exposing the entire wafer at once, they expose it field by field through reduction optics. The mask therefore carries the structure enlarged by a factor of five or ten, making mask fabrication easier, while each field can be individually focused and aligned.
For doping, ion implantation replaced furnace diffusion. It allows dose and depth to be adjusted independently and operates at low temperatures, preventing previously completed structures from becoming blurred by further diffusion. At the same time, the transition to CMOS began: the power dissipation of pure NMOS circuits increased so strongly with integration density that heat removal became the limiting factor.
Processors manufactured in 1.5 µm (selection):
- Intel 80286 (1982), 134,000 transistors
- Intel 80386 (1985, market introduction)
- Motorola 68020 (1984)