Method of etching a layer including polysilicon

• Main Authors: SHWARTZMAN,STANLEY, LEAHY, MICHAEL FRANCIS
• Format: Patent
• Language: English; French; German
• Published: 27.09.1989
• Subjects: BASIC ELECTRIC ELEMENTS; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; SEMICONDUCTOR DEVICES

The present invention relates to a method of forming gate lines of a polycrystalline silicon, polysilicon, which may have a layer of a metal silicide thereon. The gate lines (22 min ) are formed over islands (16) of silicon on an insulating substrate (12). The islands are first covered with a layer of silicon oxide. A polysilicon layer is coated over the silicon oxide layer on the silicon island and on the adjacent surface of the substrate. Resist masking strips are formed over the area of the polysilicon layer which are to form the gate lines. The exposed area of the polysilicon layer is first plasma etched in a gaseous mixture of nitrogen, chlorine and chloroform. The chlorine etches the polysilicon to form the gate lines (22 min ) and the chloroform forms a protective coating of a polymer over the side walls of the formed gate lines. The device is then subjected to a second plasma etch in a gaseous mixture of helium, chlorine and carbon dioxide. The chlorine etches away any polysilicon stringers (26) which may extend between the gate lines along the side walls of the silicon island. The carbon dioxide provides oxygen to maintain the silicon oxide layer on the islands and carbon to maintain the polymer. Thus, any stringers which could short out the gate lines are removed without undercutting the gate lines and without removing the silicon oxide layer.