Fabrication method of spiral inductor on porous glass substrate

A fabrication method of RF chip inductor, fabricating on porous glass substrate to give low k, low loss and high Q inductor, comprising the following steps:

• a P-type silicon wafer is used as the substrate;
• an N-type silicon film is formed on the back side of the substrate by implanting;
• a porous silicon layer, formed by electrochemical etching in hydrogen fluoride (HF) solution to a high degree of porosity;
• a porous glass layer, thermally oxidizing at high temperature to convert said porous silicon layer into porous glass texture;
• a thin layer of electrically conductive metal film is deposited on the porous glass to be the plating electrode of copper plating;
• a first layer of photo-resist is spun on the front side of said silicon wafer;
• a mask process is adopted for patterning to said first layer photo-resist and formed openings for the under layer of a spiral inductor;
• a layer of copper is electroplated on the wafer surface complementary to said openings;
• the photo-resist is stripped away;
• the electrically conductive metal film is etched out in hydrogen peroxide;
• a cover layer of polyimide is spun on the surface and a second mask process is taken for patterning the cover polyimide to define the contact via;
• another electrically conductive metal film is deposited on said cover layer of polyimide and said contact via to be the plating electrode of copper plating;
• a second layer of photo-resist is spun on the front side of the silicon wafer;
• a mask process is adopted for patterning said photo-resist and form opening for the second layer of the spiral inductor;
• a second layer of copper is electroplated on the top to a thickness of the inductor strip;
• the photo-resist is stripped away;
• the electrically conductive metal film is etched out in hydrogen peroxide;
• a thin layer of gold is plated to the exposed copper surface by electro-less plating to protect the inductor surface.