Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-04-19
2001-04-10
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S734000, C438S710000, C438S694000, C134S001000, C134S002000
Reexamination Certificate
active
06214720
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed generally to the formation of integrated circuits, and more specifically to a method of improving the rate of a plasma process.
BACKGROUND OF THE INVENTION
In the formation of integrated circuits (IC), thin films containing metal and metalloid elements are often deposited upon the surface of a semiconductor substrate or wafer. These thin films provide conductive and ohmic contacts in the circuits and between the various devices of an IC. For example, a thin film of a desired metal might be applied to the exposed surface of a contact or via hole on a semiconductor substrate, with the film passing through the insulating layers on the substrate to provide plugs of conductive material for the purpose of making interconnections across the insulating layers.
In processing semiconductor substrates or wafers to form an IC, sputter etching is a technique that is often used to remove a layer of unwanted material or an excess quantity of a material from the wafer surface. The process of sputter etching is generally known and takes advantage of the momentum of gas ions accelerated in an electric field. During sputtering, a gas is ionized and the gas ions are accelerated and collide with the surface of the material to be sputtered. During the collision, part of an ion's momentum is transferred to the surface of the material. The ionized particles of the charged gas plasma bombard the surface of the wafer and, if sufficient momentum is transferred, atoms and/or molecules are removed or etched from the surface.
In sputter etching, a gas is introduced into a processing chamber. The processing chamber may be metal, quartz or a dielectric other than quartz, and preferably is vacuum sealed. The wafer to be etched is supported on an electrical base or electrode within the reaction chamber so that the wafer develops an electrical potential or bias. A working gas is introduced into the vacuum chamber opposite the surface of the biased wafer, and energy is capacitively or inductively coupled to the gas through the processing chamber wall, such as by using an induction coil which surrounds the processing chamber. The energy from the induced field ionizes the gas particles so that they acquire a net charge that is of the opposite polarity to the potential of the wafer support and the wafer. The ionized particles of the gas collectively form what is referred to as a gas plasma or plasma cloud. Since the ionized particles of the plasma and the wafer are of opposite polarities, the ionized particles in the plasma are attracted to the wafer's surface, bombarding the surface of the wafer and dislodging material particles from the wafer to consequently etch the wafer surface.
For deposition processes, the sputter etching commonly occurs at wafer voltages of about 1000 volts (1 kilovolt). However, this relatively high voltage is inappropriate for microelectronic devices which are more susceptible to surface damage at these wafer charging voltages. As a result, lower wafer voltages, below 500 volts, are more desirable. Plasma etching that is accomplished using these lower wafer voltages and with a plasma generated independent from the bias on the wafer is referred to as a soft plasma etch.
The etch process occurs in a reaction chamber within which a low gas pressure is maintained. The gas, usually argon, is introduced and ionized via electron collision in an oscillating electromagnetic field (EMF). The accelerating voltage is supplied either by a separate radio frequency (RF) power supply, or in many cases may be the same power supply that provides for the ionization. Constant pressure is maintained by controlling the rates at which the sputtering gas is introduced into and is removed from the chamber.
The etch process is a first step in a variety of process sequences. One example is the fabrication of suicides where a contact surface is cleaned using sputter etch and a metal such as titanium (Ti) may be deposited over a metal oxide semiconductor structure to react with exposed silicon (Si), such as source and drain regions, to form metal silicides. Following the formation of the silicide regions, a selective acid etch has been used to remove unreacted metals without attacking the silicide. This removal is accomplished by completing the process to deposit the metal in the substrate, removing the substrate from the reactor, allowing the substrate to cool to room temperature and then etching the substrate with hydrogen peroxide, hydrogen peroxide containing a very small amount of ammonium hydroxide, or a mixture of hydrogen peroxide and sulfuric acid. This etch process removes any excess metallic Ti on the substrate as well as any substoichiometric titanium silicide (TiSi
x
) formed on the silicon dioxide. This method of forming silicides is disclosed in U.S. patent application Ser. No. 08/489,040 entitled METHOD FOR FORMING SILICIDES, filed Jun. 9, 1995 (inventor Arena) and assigned to Tokyo Electron Limited which is herein incorporated by reference in its entirety.
During the plasma etch process, SiO
2
is removed or etched from the surface of the material. The plasma further dissociates this SiO
2
. The by-products of the SiO
2
, which include silicon monoxide (SiO) and atomic oxygen (O), are liberated and released into the plasma. The effect of the increased concentration of oxygen in the plasma, however, is a reduction in the rate of a SiO
2
sputter process, such as a reduction in the sputter etch rate. A reduced sputter etch rate decreases the time efficiency, decreases wafer throughput and hence increases the cost of the entire process. Thus, a method is needed whereby sputter etch of SiO
2
and other dielectric materials may be accomplished without the undesirable concomitant decrease in the sputter rate or having to resort to an increase in the ion energy.
SUMMARY OF THE INVENTION
The invention is directed to a method of increasing the efficiency of a plasma process by reducing gaseous contaminants. The plasma process may include sputter etching, reactive ion etching, plasma chemical vapor deposition (CVD), ion milling, and reactive ion milling. In sputter etching of a substrate that liberates oxygen, nitrogen or other species of rate inhibiting by-product contaminants, the method maintains a low partial pressure of the gas in the reaction chamber. The low partial pressure may be maintained by a number of processes. One preferred process is by providing a plasma gas to the reaction chamber containing the substrate at a rate such that the steady state ratio of plasma gas to liberated oxygen, nitrogen or other contaminant gas species is at least 1. In a particularly preferred embodiment, the plasma gas has a mass greater than the oxygen, nitrogen or other gas species. Other methods of reducing contaminant gas partial pressure are by providing an in situ getter or by providing a reactive pump.
The invention is also directed to a process to sputter etch a substrate having a SiO
2
layer in a reaction chamber in which oxygen is produced during the etch process by providing argon to the substrate in the chamber at a rate so that the steady state ratio of argon to oxygen is at least 1.
The invention is additionally directed to a high throughput rate process for the formation of suicides and multilevel interconnect component layers of a substrate. One preferred process is by providing a plasma gas to the reaction chamber containing the substrate at a rate such that the steady state ratio of plasma gas to liberated oxygen, nitrogen or other contaminant gas species is at least 1. In a particularly preferred embodiment, the plasma gas has a mass greater than the oxygen, nitrogen or other gas species. Other methods of reducing contaminant gas partial pressure are by providing an in situ getter or by providing a reactive pump.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. The accompanying drawings, which are incorporated in and constitute a part of thi
Licata Thomas
Sill Edward L.
Anya Igwe U.
Smith Matthew
Tokyo Electron Limited
Wood Herron & Evans LLP
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