Page 52 - Semiconductor Manufacturing Handbook

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Source: SEMICONDUCTOR MANUFACTURING HANDBOOK

CHAPTER 5

FUNDAMENTALS OF SILICIDE
FORMATION ON Si

L. P. Ren
Global Nanosystems, Inc.
Los Angeles, California

King N.Tu
University of California at Los Angeles
Los Angeles, California

5.1 INTRODUCTION

5.1.1 Why Is Silicide Essential in Very Large Scale Integration
of Circuits on Si
As microelectronics device dimensions scale down to the deep submicron level, reduction of parasitic
resistance is a key issue for high-speed operations of ICs. Silicide is a metal-Si compound and has
been used as electric contact to Si at the gate and source and drain regions for reducing both the sheet
resistance of the gate and source/drain regions and the contact resistance to them.
In the past the overall circuit performance has depended primarily on device properties. To enhance
the circuit and system speed, the primary effort had been on improving the device speed. However, dur-
ing the last decade the parasitic series resistance, capacitance, and inductance associated with inter-
connections and contacts have begun to influence circuit performance and will be one of the primary
factors in the evolution of deep submicron very large scale integration (VLSI) technology. For the sub-
micron feature size the impact of parasitic components adversely affects circuit and system perfor-
mance. RC time delay, IR voltage drop, power consumption, and crosstalk noise due to these parasitics
are becoming significant. Even with very fast devices the overall performance of a large circuit can be
seriously affected by the limitations of interconnections and contacts. Thus application of silicides to
modern microelectronics has become essential as the conventional metallization scheme yields intol-
erably high contact resistance.
For a certain conductor to be used to form multiplayer interconnections, several requirements that
are imposed by fabrication technology and circuit performance must be met. The main requirements
include good conductivity, reliability, and manufacturability. In a multiplayer interconnection struc-
ture, the layers incorporated early in the process sequence might be subjected to several fabrication
steps, to which layers incorporated later might not. Based on this, the most desired properties of the
silicide for integrated circuits are: low resistivity, ease of formation of thin films, ability to withstand
chemicals and high temperatures throughout processing, good adhesion to other layers and surface
smoothness, stability of electrical contacts to other layers, ability to contact shallow junctions, good
device characteristics, resistance to electromigration, and ability to be defined into fine patterns. 1

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