Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-10-12
2001-01-30
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298060, C204S298160, C204S298080, C204S298190, C204S298110
Reexamination Certificate
active
06179974
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods and apparatus for sputtering and in particular, but not exclusively, to sputtering material onto workpieces having high aspect ratio formations.
As is well known in the art, the sputtering process normally consists of causing energetic ions from a plasma to strike a target of the desired material, or a component part thereof, so that atoms from the target are ejected. In sputter deposition these ejected atoms are intended to be deposited on the surface of a workpiece. The initial direction of travel of the atoms is close to being cosine, however several apparently conflicting factors can determine how many atoms reach the workpiece and with what level of uniformity across the surface of the workpiece at what angular distribution and to what extent they penetrate into high aspect formations, occurs.
Thus, for example, given a uniform erosion of a large target (as is typically the case) a low chamber pressure will usually produce good uniformity, across a substantially planar surface. This is because of the relatively low working gas density reducing the number of scattering collisions. For those atoms which are ejected substantially normally to the target, there is a low probability of collision and hence a higher probability that they will reach the workpiece with the same angular distribution. Conversely, high pressures produce a higher number of collisions causing more of the sputtered atoms to be lost to the chamber walls. This tends to lead to a deposited layer that is thicker towards the centre than the outside of the workpiece. However at higher pressures, with the relatively high probability of collisions of sputtered material, there is a higher probability of sputtered material being ionized due to these collisions. Ionised sputtered material may then be attracted normally to the substrate surface by the application of a negative charge e.g. through the use of a bias R.F. or D.C. power supply or self biassing controlled by a variable impedance to ground potential. The need to have a good percentage of the ejected atoms ionised is particularly great, when there are high aspect ratio formations in the workpiece, because it is only those atoms which are travelling at or near perpendicularly to the opening of the mouth of the formation. As the aspect ratio increases e.g. as a recess diameter decreases and/or depth increases the direction of the arriving material needs to be more nearly perpendicular. This is to avoid the recess being closed off at its mouth by sputtered material arriving at non-normal angles and to ensure an adequate coverage of the base of recesses. Hence, an ionised high pressure sputter process will achieve improved base coverage in high aspect ratio recesses, but at the expense of bulk surface uniformity across the workpiece.
Additionally the Applicants have also determined that where, particularly, an internal or immersed R.F. coil is used lack of uniformity arises through non-symmetrical coupling at the feedthroughs to the R.F. coil. These effects increase significantly with chamber pressure. This invention achieves improved base coverage previously achieved by high pressure ionisation processes whilst simultaneously achieving good surface uniformity previously achieved by lower pressure processes without the non uniformities inherent in internal R.F. coil arrangements of the prior art.
SUMMARY OF THE INVENTION
From one aspect the invention consists in a method of sputtering from a target or targets to a negatively biassed workpiece on a support, the target and support being disposed in a vacuum chamber containing a plasma and having a R.F. coil for enhancing the ionisation of the sputter material, the method including: supplying power to the R.F. coil at a frequency in the range of 100 kHz to 2 MHz and at the same time inducing a D.C. magnetic field in the vicinity of the R.F. coil.
The D.C. magnetic field, which preferable extends normally through the R.F. coil, may be induced by a D.C. coil disposed between the target and the vicinity of the support. Preferably the D.C. coil is external to the vacuum chamber, but the R.F. coil may be internal. In certain circumstances the R.F. coil may constitute the D.C. coil.
The D.C. magnetic field may be induced by a pair of coils disposed between the target and the vicinity of the support, in which case the ratios of currents in the coil further from the support and the coil nearer to the support is about 1:3.
The chamber pressure may be between 10 and 40 mT and preferably is about 30 mT.
Conveniently the R.F. and D.C. coils are symmetrically disposed.
From another aspect the invention consists in sputtering apparatus including a vacuum chamber, means for forming a plasma in the chamber, a target or targets disposed in the chamber, a R.F. coil for enhancing the ionisation of the sputter material, a negatively biased support for a workpiece disposed in the chamber opposite the target, at least one external D.C. coil disposed between the target and the vicinity of the support for inducing a magnetic field in the vicinity of the R.F. coil, R.F. power supply means for supplying power to the R.F. coil in a frequency range of 100 kHz to 2 MHz and a D.C. power supply for supplying power to the D.C. coil.
A single coil may constitute the R.F. coil and the D.C. coil and the R.F. coil may lie within the chamber, in which case it may constitute a secondary target.
Ideally a single D.C. coil would enclose the volume between the target and the workpiece and in particular enclose the volume contained by the R.F. coil. However practical constraints may require the use of a number of D.C. coils to achieve an approximation to this ideal. To better achieve this approximation the D.C. coils may be driven at different current levels and in a particular arrangement the ratio of currents was 1:3. It may be necessary to limit current flow through the D.C. coils nearest the target to avoid magnetic interaction as the target is commonly attached to a magnetron device.
Although the invention has been defined above, it is to be understood it includes any inventive combination of the features set out above or in the following description.
REFERENCES:
patent: 3897325 (1975-07-01), Aoshima et al.
patent: 3962988 (1976-06-01), Murayama et al.
patent: 4013533 (1977-03-01), Cohen-Solal et al.
patent: 4046660 (1977-09-01), Fraser
patent: 4810935 (1989-03-01), Boswell
patent: 4880515 (1989-11-01), Yoshikawa et al.
patent: 5085755 (1992-02-01), Setoyama et al.
patent: 5178739 (1993-01-01), Barnes et al.
patent: 5180476 (1993-01-01), Ishibashi et al.
patent: 5431799 (1995-07-01), Mosely et al.
patent: 0 710 056 A1 (1996-05-01), None
patent: 0 818 556 A1 (1998-01-01), None
patent: 8-302464 (1996-11-01), None
patent: 9-256149 (1997-09-01), None
patent: 10-183344 (1998-07-01), None
patent: 10-204634 (1998-08-01), None
Chacko-Davis Daborah
Jones Volentine, LLC
Nguyen Nam
Trikon Holdings Ltd.
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