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Doping Procedure for Polycide

IP.com Disclosure Number: IPCOM000048158D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Campbell, DR: AUTHOR [+4]

Abstract

In the future, very large scale integrated MOSFET (metal oxide semiconductor field effect transistor) devices will incorporate a low resistive composite conductor, called polycide. It will be used as a device gate or word line (and/or bit line) of a circuit, to achieve an RC delay improvement of more than an order of magnitude over that of conventional polysilicon gates, or word lines. A polycide conductor consists of an underlying Layer of polysilicon (called pad polysilicon), a middle layer of transition metal silicide (for example, WSi(2), MoSi(2) or TaSi(2)) and a top layer of polysilicon overlay (called cap polysilicon). Currently, the doping of the conductor composite is done at the pad polysilicon level by the open tube POCl(3) method.

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Doping Procedure for Polycide

In the future, very large scale integrated MOSFET (metal oxide semiconductor field effect transistor) devices will incorporate a low resistive composite conductor, called polycide. It will be used as a device gate or word line (and/or bit line) of a circuit, to achieve an RC delay improvement of more than an order of magnitude over that of conventional polysilicon gates, or word lines. A polycide conductor consists of an underlying Layer of polysilicon (called pad polysilicon), a middle layer of transition metal silicide (for example, WSi(2), MoSi(2) or TaSi(2)) and a top layer of polysilicon overlay (called cap polysilicon). Currently, the doping of the conductor composite is done at the pad polysilicon level by the open tube POCl(3) method. This method has a large tendency of introducing pinholes into the structure and into the underlying gate silicon dioxide. Therefore, deterioration of gate silicon dioxide integrity frequently results.

A through the top doping procedure circumvents this problem. Instead of carrying out the doping at the pad polysilicon level, doping is carried out after the cap polysilicon is in place, or even after the whole composite has been passivated by a thin Layer of insulator, such as chemical vapor deposited (CVD) Layer of SiO(2) or Si(3)N(4). The doping method can be ion implantation or conventional thermal diffusion. Ion implantation is preferred, as both the dopant species and doping level can be freely changed and closely controlled.

The following process is a detailed example of doping through the top by ion implantation: (1) The as formed polycide structure is coated with a

thin (20 to 100 nm) layer of low temperature (T(dep.)

less than 500 degrees C) CVD SiO(2).

(2) Pre-silicide homogenization anneal is then carried

out in an ambient of purified inert gas, at a temperature

to be set as close to the minimum silicide

formation temperature as possible and for a period of

time that is sufficient to induc...