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Method for Obtaining Contact Holes With Almost Identical Slopes Through Oxide Layers Having Different Thicknesses and Compositions

IP.com Disclosure Number: IPCOM000043598D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Auda, B: AUTHOR

Abstract

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.

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Method for Obtaining Contact Holes With Almost Identical Slopes Through Oxide Layers Having Different Thicknesses and Compositions

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. When contact holes are to be etched through a photoresist mask, as shown in Fig. 2, continuing the etching of the oxide to reach polysilicon surface in hole A will result in poor dimensional control of the slope of oxide in hole B. The following two-step process may be used in a Reinberg-type plasma reactor, such as the one described in U.S.

Patent 375,733. The ratio between C3F8 and CF4 controls the equilibrium between the etching and polymerization of the photoresist and therefore the slope of the holes. The addition of oxygen increases the etch rate and limits polymerization...