Coil for sputter deposition

Details Coil for sputter deposition Coil for sputter deposition

1999-10-08

2001-11-13

McDonald, Rodney G. (Department: 1753)

Chemistry: electrical and wave energy

Processes and products

Coating, forming or etching by sputtering

C204S192120, C204S192170, C204S298060

Reexamination Certificate

active

06315872

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to metal film deposition and more particularly to an improved coil for reducing defect generation during metal film deposition within a high density plasma deposition chamber.
BACKGROUND OF THE INVENTION
Metal films are used widely within semiconductor integrated circuits to make contact to and between semiconductor devices (i.e., metal interconnects). Because of the high densities required for modern integrated circuits, the lateral dimensions of interconnects, as well as the lateral dimensions between interconnects, have shrunk to such a level that a single defect can destroy an entire wafer die by shorting a junction region or open-circuiting a gate electrode of an essential semiconductor device. Defect reduction within interconnect metal films, therefore, is an ever-present goal of the semiconductor industry that increases in importance with each generation of higher density integrated circuits.
Interconnect metal films typically are deposited via physical vapor deposition and more recently via high density plasma (HDP) deposition, within a plasma chamber. In both processes, a target of to-be-deposited material (e.g., the metal comprising the interconnect) is sputtered through energetic ion bombardment that dislodges atoms from the target. The dislodged atoms travel to a substrate disposed below the target and form a metal film thereon. The metal film is patterned to form the interconnect.
For HDP deposition, in addition to the target, a coil is provided between the target and the substrate. The coil's primary role is to increase the plasma density, i.e., ionization fraction, and thereby create conditions to ionize target atoms sputtered from the target. Ionized target particles will, under the influence of an electric field applied between the target and the substrate, strike the substrate substantially perpendicular to the target face and substantially perpendicular to any feature base present on the substrate (e.g., allowing for improved filling of vias and other surface features). Where the coil is located internally of the chamber, the coil itself is sputtered, and dislodged coil atoms travel to the substrate disposed below the coil and deposit thereon. Sputtered coil atoms predominantly coat the substrate near its edges and, where the target atoms create a center thick film on the wafer, enhance the overall thickness uniformity of the material layer formed on the substrate. The material properties of an HDP coil therefore play an important role in overall deposited film quality.
As described in parent applications, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997 and U.S. Ser. No. 09/272,974, filed Mar. 18, 1999, both aluminum target manufacturers and copper target manufacturers conventionally focus on the purity of sputtering targets to reduce defect densities or to otherwise affect deposition of high quality metal films. Similar emphasis is placed on the purity of coils employed in HDP deposition chambers (e.g., HDP deposition chambers typically employ a target and a coil having similar purity levels). However, despite high purity levels for both targets and coils, the defect densities of conventional HDP deposited metal films remain high.
Accordingly, a need exists for a coil for use within an HDP deposition chamber that produces metal films having reduced defect densities.
SUMMARY OF THE INVENTION
The present inventors have discovered that in addition to target purity, other factors are of significant importance to defect reduction as recognized and described in parent applications, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997 and U.S. Ser. No. 09/272,974, filed Mar. 18, 1999. These other factors must be considered to reduce defect densities during plasma deposition as the purity of the target alone does not assure adequate metal film quality and high device yield.
Specifically, it has been found that in addition to target material purity, the following target material parameters have a direct affect on defect generation during sputter deposition of metal films: dielectric inclusion content (e.g., target material oxides, nitrides, etc.), porosity (e.g., non-conductive voids due to gas trapping during target formation), grain size, surface roughness and hardness. With respect to aluminum targets, control of dielectric inclusions is of primary importance for controlling aluminum film quality. Reducing the concentration of dielectric inclusions such as Al
2
O
3
within an aluminum target can decrease certain as-deposited or “in-film” defect densities (e.g., splat densities) by up to five fold. With respect to copper targets, increasing the hardness of a copper target is as much a factor in defect reduction as reduced dielectric inclusion concentration. Namely, a certain hardness range for the copper target is required to provide the copper target with sufficient mechanical/electrical strength to prevent localized mechanical breakdown, and thus ejection of a relatively large, greater than a few microns piece of target material, during plasma processing.
For HDP deposition processes, the present inventors have discovered that defect reduction results when a coil (e.g., aluminum or copper) has material parameters similar to the above described target material parameters (e.g., reduced dielectric inclusion concentration, sufficient hardness, etc.). Also, it has been found that thermal cycling can cause the coil to move sufficiently to disconnect it from the terminal or feedthrough through which it connects to its power supply or to short circuit the coil through contact with another chamber structure such as a shield that supports the coil. Thus, to prevent a coil from electrically disconnecting or short circuiting following repeated depositions (e.g., due to repeated expansion and contraction caused by thermal cycling), the thermal creep rate and mechanical strength of the coil must be considered. As used herein, thermal creep rate refers to the time rate at which a material changes shape due to prolonged stress or exposure to elevated temperatures.
To control the thermal creep rate and strength of a copper coil, the coil's grain size preferably is reduced. For example, a copper coil's grain size preferably is limited to below 50 microns, and most preferably to below 25 microns. The smaller the grain size, the lower the thermal creep rate and the greater the strength of the copper coil. The preferred thermal creep rate, strength and grain size are achieved by limiting the copper coil's purity level to a level of less than 99.9999%, preferably within the range from 99.995% to 99.9999% (e.g., less pure than previously believed necessary). This overall purity level range is maintained while the concentration levels of impurities that adversely affect a copper coil's thermal creep rate and strength are reduced (e.g., antimony, arsenic, bismuth, hydrogen, oxygen, sulfur, etc.). An aluminum coil's thermal creep rate and strength primarily are controlled by alloying (as is known in the art).
By thus controlling the dielectric inclusion content, porosity, grain size, surface roughness, thermal creep rate and strength of a coil, defect generation during HDP deposition may be decreased while the risk of the coil becoming electrically disconnected or short circuited during processing is reduced.
Other objects, features and advantages of the present invention, as well as the structure of various embodiments of the invention, will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.


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