Structures using chemo-mechanical polishing and chemically-selective endpoint detection

A structure on a silicon substrate created by using a selective etching process, the selective etching process comprising:

• receiving the silicon substrate with a first layer composed of a first material, wherein the first layer includes voids created by a first etching operation;
• forming a second layer composed of a second material over the first layer, so that the second layer fills in portions of the voids in the first layer created by the first etching operation;
• and
• performing a chemo-mechanical polishing operation on the second layer down to the first layer so that only remaining portions of the second layer within the voids created by the first etching operation remain;
• forming a third layer composed of a third material over the first layer and the second layer;
• and
• performing a second etching operation using a selective etchant to remove the remaining portions of the second layer so that voids are created between the first layer and the third layer;
• wherein the first material comprises Si;
• wherein the second material comprises Si—Ge or Si—Ge—C;
• wherein the selective etchant comprises TMAH or HNA and
• wherein an etch rate of the selective etchant through the second material is faster than an etch rate of the selective etchant through the first material and the third material, so that the second etching operation etches through the remaining portion of the second layer without significantly etching the first layer and the third layer.