Method for Obtaining Contact Holes With Almost Identical Slopes Through Oxide Layers Having Different Thicknesses and Compositions
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
In semiconductor processing it may be desired to open contact holes with identical slopes through oxide layers having different thicknesses and/or compositions. A common example is shown in Fig. 1. Because polysilicon and monocrystalline silicon are different materials, the native oxides which are formed over both types of silicon during a thermal oxidation step have different thicknesses and compositions, and therefore will behave differently; particularly, they will have different etch rates. Generally, these oxides are coated with a phosphosilicate glass (PSG) layer in a LPCVD (low pressure chemical vapor deposition) equipment, as depicted in Fig. 1. The genetic oxide over silicon is thicker but will be etched faster than the genetic oxide over polysilicon.