1959: Invention of the "Planar" Manufacturing Process

Jean Hoerni develops the planar process to solve reliability problems of the mesa transistor, thereby revolutionizing semiconductor manufacturing.

 

 

 

Seeking a solution to reliability issues with the mesa transistor (1958 Milestone), Fairchild physicist Jean Hoerni recalled an idea he had recorded in December 1957 - a new process in which the oxide layer is left in place on the silicon wafer to protect the sensitive p-n junctions underneath. Focused on getting its first devices into production, the company did not pursue the approach at that time. Due to concerns about possible contaminants, conventional wisdom required removing this layer after completion of oxide masking, thus exposing the junctions. Hoerni viewed the oxide instead as a possible solution - his "planar" approach, named after the flat topography of the finished device, would protect these junctions. After writing a patent disclosure in January 1959, he demonstrated a working planar transistor that March. The oxide layer was indeed found to protect the junctions, as Hoerni had predicted.

Planar devices also proved to have better electrical characteristics - particularly far lower leakage currents, which is critical in computer logic design. And they permitted fabrication of all the components of an integrated circuit from one side of a wafer (1960 Milestone). Fairchild introduced the 2N1613 planar transistor commercially in April 1960 and licensed rights to the process across the industry. The billion-transistor integrated circuits of today rely on Hoerni's breakthrough idea. One historian has called it "the most important innovation in the history of the semiconductor industry."

While planar technology enabled silicon transistors to meet the stringent demands of the aerospace industry, semiconductor vendors continued to encounter new failure mechanisms with every major technology advance. Significant issues in the 1960s included "purple plague" on gold bonding wires, electromigration of aluminum interconnect lines, and MOS transistor stability. (1964 Milestone)