Non-plasma halogenated gas flow prevent metal residues

Details Non-plasma halogenated gas flow prevent metal residues Non-plasma halogenated gas flow prevent metal residues

2000-01-04

2001-01-16

Bueker, Richard (Department: 1763)

Coating apparatus

Program, cyclic, or time control

Having prerecorded program medium

C118S695000, C118S696000, C118S719000, C156S345420

Reexamination Certificate

active

06174373

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to metal deposition on semiconductor substrates in semiconductor processing systems, and in particular to the elimination of residue remaining after the etching of the metal.
One of the steps in the formation of a semiconductor chip is the creation of metal interconnections between devices on a semiconductor wafer. Typically, this is done by first depositing a layer of metal, such as tungsten, across the wafer. In one process, tungsten is deposited in a chemical vapor deposition (CVD) chamber by reacting WF
6
containing the tungsten and H
2
or Silane at elevated temperatures over a wafer sitting on a resistive heater (alternately, other methods may be used to heat the wafer, such as lamps). The process temperature is typically 475° C. Subsequently, the tungsten is etched away except for areas in which metal interconnections are desired. This may be done in the same chamber or by moving the wafer to a separate chamber.
It has been discovered that under certain processing conditions, when the wafer is later etched, tungsten residue remains on the wafer, which can form shorts in the interconnects. Although the process is not completely understood, it is believed that tungsten may preferentially grow in certain spots on the wafer (These spots may be areas where residue has formed as a result of previous processing steps). The preferentially growing tungsten may be in a different phase than other areas of the metal tungsten layer. Because the tungsten is in a different phase, these areas may then etch away at a different rate, leaving the undesirable tungsten residue in areas where there should be no interconnect after the etch step.
One approach to eliminate the residue is to clean the chamber in which the metal layer is deposited after every wafer is processed. This is typically done by removing the wafer, and then igniting a plasma composed of NF
3
, followed by a hydrogen plasma, with a subsequent argon gas purge. After this cleaning step, the next wafer can be inserted into the chamber for depositing of the tungsten layer without significant residue being present after etchback. A drawback of this plasma clean approach is that it requires a significant amount of time between each wafer being processed. One approach would be to do the plasma less often. But it has been discovered, for example, that a plasma clean after every 25 wafers is not sufficient since residue formation still occurs.
Accordingly, it would be desirable to have an improved process for eliminating residue formation after tungsten deposition and etchback which does not significantly impact wafer throughput.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and process for limiting residue remaining after the etching of metal in a semiconductor manufacturing process by exposing a wafer to a halogen-containing gas without a plasma in a processing chamber. The wafer may be exposed to the remnants of a halogen-containing gas remaining in the chamber from before the wafer was loaded into the chamber, or halogen-containing gas may be injected onto the wafer before deposition of a metal layer. The exposure can occur in the same chamber as the metal deposition, or a different chamber. The wafer can remain in the chamber or be moved to another chamber for etching after exposure and deposition.
In one embodiment, the halogen-containing gas is NF
3
and is injected into the chamber between wafer processing steps, although other gases, such as C
2
F
6
, CF
4
, ClF
3
, or Cl
2
may be used. Preferably, the halogen-containing gas is injected for less than 30 seconds and at a rate of between 10-2000 sccm (more preferably between 10-150 sccm) with a pressure between 50 milliTorr (mT) and 90 Torr (T) (more preferably, between 50 mT and 10 T), but the halogen-containing gas may be injected for up to 150 seconds. A longer injection period would be appropriate with a batch reactor, for example. In general, it is desired that the injection period be short, relative to the total clean time.
In another embodiment, a halogen-containing gas is injected onto the wafer after the wafer has been loaded into the chamber. The halogen-containing gas is WF
6
, and serves as a fluorine source that prevents metal residue after a subsequent deposition and etch step.
In yet another embodiment, a plasma chamber cleaning operation is performed after a number of deposition steps. The plasma is formed from a halogen-containing gas, for example, NF
3
. The plasma is maintained to “overetch” the chamber, that is, the plasma is maintained beyond the time required to clean unwanted residue from the chamber. It is believed that the plasma provides a source of fluorine during the overetch step, and that the fluorine is adsorbed onto the walls of the chamber. The walls of the chamber subsequently provide fluorine to passivate the surface of wafers during metal depositions.
For a further understanding of the nature and advantages of the invention, reference should be made to the ensuing description taken in conjunction with the accompanying drawings.


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