PECVD and CVD processes for WNx deposition

Details PECVD and CVD processes for WNx deposition PECVD and CVD processes for WNx deposition

1999-09-30

2003-10-21

Fahmy, Wael (Department: 2814)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S654000

Reexamination Certificate

active

06635570

ABSTRACT:

FIELD OF THE INVENTION
The present invention is in the area of methods and apparatus for processing wafers as a step in manufacturing integrated circuits (ICs), and relates in particular to chemical vapor deposition (CVD) processes for depositing tungsten and alloys and mixtures of tungsten with other elements such as, in particular, silicon and nitrogen, using NF
3
and in some cases, NH
3
as a gaseous source of nitrogen in the processes.
BACKGROUND OF THE INVENTION
Manufacturing of integrated circuits is historically a procedure of forming thin films and layers of various materials on wafers of base semiconductor material, and then selectively removing areas of the films to produce structures and circuitry. Doped silicon is a typical base wafer material, and in various process schemes, metal layers are formed on the doped silicon or on polysilicon or silicon oxide formed from the base material. It is well known in the art that there are many difficulties in forming thin metal films and in particular in forming such films on non-metallic base materials. Among these difficulties are problems of adhesion and problems related to diffusion and reaction of materials across material boundaries.
There are a number of well-developed technologies for deposition of materials in the ultra-thin layers required for IC fabrication schemes. The deposition techniques can be roughly classed as either physical vapor deposition (PVD) or Chemical Vapor Deposition (CVD) techniques. PVD processes include such processes as evaporation and re-condensation, wherein a material, typically a metal, is heated to a temperature at which the metal melts and vaporizes. The metal then condenses on surfaces generally in line-of sight of the evaporation, forming a film.
Another PVD process is the well-known sputtering process, wherein plasma of usually an inert gas is formed near a target material, and the target is biased to attract ions from the plasma to bombard the target. Atoms of the target material are dislodged by momentum transfer, and form an atomic flux of particles, which coalesce on surrounding surfaces generally in line-of-sight of the target surface eroded by the sputtering process.
PVD processes have distinct advantages for some processes, such as high rate of deposition, and relatively simple coating apparatus. There are drawbacks as well, notably an inherent inability to provide adequate step coverage. That is, on surfaces having concavities as a result of previous coating and etching steps, PVD processes are prone to shadowing effects resulting in local nonuniformity of coating thickness. This problem has grown in importance as device density has increased and device geometry has shrunk in size with multi-level interconnect schemes involving vias and trenches on microscopic scale.
CVD processes comprise deposition from gases injected into a chamber, wherein the gases or components of the gases are chemically decomposed and/or recombined by energy input. In typical CVD processes the substrate to be coated is heated, and gases introduced into a chamber holding the substrate react at or very near the substrate surface in a manner to deposit a film of material on the surface. For example, a film of metallic tungsten may be deposited on a heated substrate surface by flowing Tungsten hexafluoride to the surface in conjunction with a reducing gas such hydrogen. Resulting chemical reaction at a hot substrate surface reduces the tungsten hexafluoride, depositing a film of tungsten on the substrate, and producing HF gas.
It is well-known in the art that there are a wide variety of CVD processes known and available for semiconductor circuit processes, including deposition from organo-metallic materials and plasma-enhanced CVD, wherein energy is added to the process by exciting the gas above the deposition surface with a high-frequency discharge (plasma).
In the fabrication of an integrated circuit, transistors are developed on the surface of a doped silicon substrate. Once transistors are formed, to make a circuit, gates and drains have to be interconnected with electrically conductive tracks. This point in the overall IC fabrication process serves as perhaps the best example of a thin-film interface between a substrate material and an electrically conductive metal.
Over several years in the IC industry, a variety of materials have been tested for interconnecting tracks. Among these are aluminum, titanium. tungsten, and gold. Each has advantages and drawbacks, and different characteristics related to interaction with silicon, electrical conductivity, and electromigration, among others. Also, specific deposition processes have been developed suitable for specific materials. Aluminum, for example is typically deposited by the PVD process of sputtering, and there is currently no commercialized process for CVD deposition of aluminum as an interconnect material. A CVD process, on the other hand, can conveniently deposit tungsten.
There are a variety of known CVD processes employing variations of known chemistries to produce a variety of films of a single element, or a combination of two or more elements. Tungsten is deposited as a continuous (blanket) film on substrates for example to provide, after etching, both via plugs and interconnect tracks between devices implemented in doped silicon. Combinations of tungsten with other elements are deposited for other purposes, such as adhesion and barrier layers on gates of transistors implemented in silicon as an intermediate layer to improve adhesion and combat diffusion, for example, of silicon from the gates into the interconnect film. In these applications the films deposited directly on the gates prior to the interconnect material are called barrier layers.
One of the elements frequently combined with tungsten to provide specific desirable characteristics of a resulting film for adhesion and barrier purposes is Nitrogen to form tungsten nitride. The inventors are aware of conventional chemistry and processes for deposition of WN
x
(Tungsten Nitride). In some instances it is desirable to combine tungsten with other elements as well as Nitrogen. One such combination of interest and potential use in gate technology is Tungsten-Silicon-Nitride.
There are also elements competitive to tungsten for gate processes. One of these is Titanium, and materials of interest in combination with Titanium are Titanium Nitride (TiN) and Titanium Silicon Nitride (Ti
x
Si
y
N
z
).
The common element among the materials described above is Nitrogen, and perhaps the most common gas utilized as a source of Nitrogen in the CVD processes is ammonia (NH
3
). It is well known in the art that there are many problems with handling NH
3
and mixing NH
3
with other gaseous components for CVD processes. One such component is WF
6
which, when combined with NH
3
at room temperature produces an instantaneous and highly exothermic chemical reaction. Such a gas phase reaction is highly undesirable because it leads to serious complications in CVD reactor design and operation. Also an undesirable gas phase reaction leads to particulate formation, powdery deposits, and poor adhesion of films to the substrate. In addition to this, the instantaneous reaction between WF
6
and NH
3
leads to coating on the reactor (process chamber) walls. This coating contributes significantly to particles due to peeling, and hence reactors must be completely and periodically cleaned for operation in the actual production environment.
The processes with which the present patent application is concerned pertain to the art of depositing layers of materials typically less than 1 &mgr;m thick, which are used to manufacture semiconductor integrated circuits. These processes are generally termed thin film deposition. The teachings of this disclosure address improvements to the art of chemical vapor deposition (CVD) for thin films consisting generally of the two elements tungsten and nitrogen.
The films in the processes of interest are typically deposited on silicon wafers placed in reaction chambers that provide a highly

Affiliated with

Also associated with

Rating

PECVD and CVD processes for WNx deposition does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with PECVD and CVD processes for WNx deposition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PECVD and CVD processes for WNx deposition will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3136309