Method of Depositing Doped Refractory Metal Silicides Using DC Magnetron/Rf Diode Mode Co-Sputtering Techniques

The U.S. application for patent entitled "Method of Depositing Refractory Metal Silicides Using RF Diode Co-Sputtering Technique" by R. S. Nowicki, filed Nov. 6, 1980, Ser. No. 204,412, now abandoned.

This invention relates in the broadest sense to one of the steps in the process of manufacturing integrated circuits (IC's), and is particularly related to the deposition of refractory metal silicides on oxide or silicon substrates.

The advantages of refractory metal silicides for interconnections and gate electrodes in the manufacture of IC's is known and discussed thoroughly in an article entitled "Refractory Silicides For Integrated Cicuits" by S. P. Murarka in the Journal of Vacuum Science Technology, Volume 17, No. 4 (1980) pp 775-792. One method of depositing thin films of molybdenum disilicide (MoSi.sub.2) on oxide or silicon substrates by an RF diode co-sputtering technique and its advantages over a DC magnetron single target technique is discussed in the Technical Report No. 80.02 of the Perkin-Elmer Plasma Products Division by R. S. Nowicki and J. F. Moulder, which is a print of a paper submitted to the Journal of the Electrochemical Society in May of 1980 and was the subject of a talk at the Society meeting in March of 1980. The disclosure in the talk before the Electrochemical Society in March of 1980 was the first public disclosure of this invention.

In the article by Nowicki et al, it was shown that a film deposited by the co-sputtering technique retained its integrity i.e, did not crack or peel during subsequent heat treatment. The two targets used in the co-sputtering technique were refractory metal and silicon and the reason for using the RF technique rather than the DC technique is due to the difficulty of sputtering pure silicon by the DC technique. This difficulty is well known to those skilled in the art.

In the related application, the method of depositing thin films of molybdenum disilicide (MoSi.sub.2) on oxide or silicon substrates by an RF diode co-sputtering technique was disclosed and claimed.

This invention is an improvement over the RF diode method of the related application. In this invention, where a two target co-sputtering technique is utilized, one of the targets, preferably the silicon target, is doped, i.e., purposely mixed with small concentrations of elements such as phosphorus, boron, arsenic or antimony. The doping of the silicon allows the use of the DC magnetron method since doped silicon is more conductive. This has the additional advantage of increasing the deposition speed since DC magnetron sputtering is faster and more efficient than RF diode sputtering and offers the advantage of producing a doped thin film on the substrate, thus eliminating a doping step in the later process of integrated circuit manufacturing. Another advantage is that the dopant may relieve the stress of the deposited film, thus still further alleviating film degradation in later fabrication steps.

Another aspect of this invention uses the co-sputtering technique in both the RF diode and the DC magnetron modes, thus taking advantage of both modes and involving a pure silicon target, or a doped silicon target, or a pure silicon target, and a doped refractory metal target, so that both may be co-sputtered to provide a doped silicide thin film deposition.

The sole FIGURE is a simplified schematic illustration of a sputtering system useful in the practice of this invention in either the RF diode or DC magnetron mode or in the combined RF diode and DC magnetron mode.

The drawing illustrates a simplified version of a sputtering system for the purposes of the disclosure of this invention. In this version, the sputtering system 10 comprises a vacuum chamber 12 in which are placed a plurality of wafers 14, or other workpieces, preferably on a rotating table or pallet 16 facing at least two flat coplanar water cooled target electrodes 20 and 22 with their respective target surfaces 24 and 26. These surfaces 24 and 26 contain, or are provided with, the material which is to be sputtered on the wafers 14 and are subjected to a voltage differential between the target and the electrodes and the wafers to support a glow discharge, usually in the presence of argon, as a gaseous environment in the vacuum chamber which is at near vacuum, conventionally 5.times.10.sup.-7 Torr.

In this embodiment, the electrodes can be subjected to a high voltage, either at DC or at radio frequency (RF=13.56 Mhz), from suitable sources or power supplies sufficient to sputter a dielectric, such as pure silicon, onto the wafers, or to sputter a doped dielectric (conductor) and a refractory metal (conductor) and whether DC or RF voltages are applied, at different voltage levels to the two electrodes, is determined by the two different materials being sputtered. If the material on one of the targets surfaces is a dielectric, an RF voltage is applied to that target while the other target may have either RF or DC type voltages applied thereto as desired. However, if material on one of the targets is a conductor, such as doped silicon, and the other target surface is a refractory metal, doped or undoped, the voltage applied to the target electrodes will be a DC voltage in the presence of a magnetic field, i.e, the DC magnetron mode from, for example, removable or replaceable magnets 30. The use of the DC magnetron technique is preferable because the speed of deposition is faster than the RF diode mode.

Not shown is a rotatable shutter located between the target electrodes and the rotating pallet with openings that are positionable under the active targets for the deposition of the material therefrom onto the wafers that are closest to the target at the time.

In the practice of this invention, the following tabulation will show the type of voltage to be applied to the electrodes for co-deposition depending upon the material used:

In the practice of the foregoing, if doped silicon is used, the typical dopant is arsenic, although other dopants such as phosphorous or antimony may be used, depending upon the device design or configuration. Typically the refractory metal is molybdenum, doped or undoped, although other refractory metals can be used.

The film deposited will be a doped MoSi.sub.2 or a doped combination of Mo and Si which will form molybdenum silicide (MoSi.sub.2) during a later heating step.

The foregoing method can be practiced with or without a bias voltage supplied to the substrate. It has been found that with a biased substrate -25 to 50 V DC, the heat treated film resistivity is about 20% less than the resistivity of the heat treated film under substrate non-biased conditions, i.e, 87 micro-ohm-centimeter (biased) versus 110 micro-ohm-centimeter resistances (non biased) for the MoSi.sub.2 composition.