Browse Prior Art Database

Reduced Oxidation of Nickel Silicide on Arsenic Doped Si Using Wet Cleaning

IP.com Disclosure Number: IPCOM000147440D
Publication Date: 2007-Mar-15
Document File: 3 page(s) / 108K

Publishing Venue

The IP.com Prior Art Database

Abstract

A novel process flow is presented for nickel silicide (NiSi) integration to form low resistance contacts to NiSi. It is shown that NiSi oxidizes rapidly when grown on arsenic (N+) doped silicon. A wet clean after silicide formation can remove the As which causes the fast oxidation thereby allowing the formation of low resistance contacts.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Reduced Oxidation of Nickel Silicide on Arsenic Doped Si Using Wet Cleaning

Abstract

A novel process flow is presented for nickel silicide (NiSi) integration to form low resistance contacts to NiSi.  It is shown that NiSi oxidizes rapidly when grown on arsenic (N+) doped silicon.  A wet clean after silicide formation can remove the As which causes the fast oxidation thereby allowing the formation of low resistance contacts. 

Introduction

Nickel silicide is being used for latest generation integrated circuits instead of cobalt silicide.  The critical advantages of NiSi are (1) better line width scaling for reduced gate lengths; and (2) lower silicon consumption.  However, problems with high contact resistance (Rc) can be observed. When using a standard contact etch recipe (same as for CoSi2), the contact chains on N+ active were found to be not functional, while contact chains on P+ were OK.  TEM analysis showed an oxide layer which had formed on top of the silicide preventing good contact resistance.

Unusual fast oxidation on As doped (N+) Si is a well known effect and has been documented in literature.[1] During silicidation the As is pushed out of the silicide lattice and accumulates at the surface and the interface.[2]  Figure 1 displays As profiles for NiSi grown on As doped Si (one Ni profile is included for reference).  As can be seen in the figure the As concentration is significantly lower in the NiSi film, it has been pushed to the surface and Si interface.  It is believed that the high As concentration on top of the silicide is the cause for rapid oxidation and therefore the open contacts.  Figure 2 shows TEM cross sections of the bottom of the contact and the NiSi film. 

Figure 1. Ni and As SIMS profile of NiSi grown on As doped Si.

(2)

 

(1)

 
  

Figure 2.  W contact–NiSi interface for (1) N+ Active and (2) P+ Active; showing thick oxide formation for N+ Active

Experiment and Discussion

A cleaning step has been inserted after silicide formation to remove the accumulated dopants.  This etch could use HF or SC1 chemistry, or any other chemistry which etches NiSi at a slow etch rate.  By removing the dopant from the ...