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Selective Deposition of Palladium Contacts On CMOS Field-Effect Transistors

IP.com Disclosure Number: IPCOM000101966D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 4 page(s) / 144K

Publishing Venue

IBM

Related People

Akbar, S: AUTHOR [+2]

Abstract

This article describes a novel process for the metallization of CMOS field-effect transistor (CMOS-FET) terminals, which replaces existing processes which are more expensive and time consuming, i.e., those utilizing vacuum thermal evaporation (or sputter deposition) or metal blankets, followed by photolithographic pattern transfer and RIE etching to remove unwanted metal.

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Selective Deposition of Palladium Contacts On CMOS Field-Effect Transistors

       This article describes a novel process for the
metallization of CMOS field-effect transistor (CMOS-FET) terminals,
which replaces existing processes which are more expensive and time
consuming, i.e., those utilizing vacuum thermal evaporation (or
sputter deposition) or metal blankets, followed by photolithographic
pattern transfer and RIE etching to remove unwanted metal.

      A cross-section of a submicron CMOS field-effect transistor
(CMOS- FET) is shown in Fig. 1.  The initial steps in its fabrication
are accomplished by sidewall image transfer technology with
self-aligned polysilicon gates. Shown are palladium contacts 1, 2 and
3 on the source, gate, and drain regions, respectively, of the
structure.  An SiO2 sidewall 4 is identified around the polysilicon
gate region and the SiO2 isolation 5.  With the disclosed process,
the palladium contacts are deposited through a chemical exchange
reaction (1,2) with no metal deposition on either the SiO2 sidewalls
or isolation.

      The disclosed metallization process begins with a short etch in
7:1 buffered HF acid to remove any native silicon dioxide thin film
from the source, gate and drain silicon surfaces.  The wafer is then
dipped into an aqueous palladium chloride solution, which contains a
small amount of hydrochloric acid and certain complexing agents.  The
wafer is then rinsed in deionized water and dried.

      The silicon reacts with the palladium solution according to the
summary equation:
                     Si + 2 Pd2+ T Si4+ + 2 Pd.

      Since the exchange reaction takes place only where silicon is
exposed, the deposition is extremely selective, with no palladium
deposition on either the SiO2 sidewalls or isolation.

      Suitable complexing agents for palladium are glycine, salts of
lignin sulfonic acid and of ethylene diammine tetraacetic (EDTA).
The complexing agent is believed to prevent too rapid an exchange of
the silic...