Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1998-05-01
2002-04-02
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192130
Reexamination Certificate
active
06365009
ABSTRACT:
FIELD OF INDUSTRIAL UTILIZATION
The present invention relates to a method for manufacturing thin films, and in particular to a process of manufacturing thin films using the combined RF (Radio Frequency)-DC (Direct Current) magnetron sputtering method. In this invention, the supply of power is improved to prevent a tracking arc from being produced and to ensure the consistent manufacture of thin films.
BACKGROUND OF THE INVENTION
Sputtering is an indispensable technique for depositing films typical used in electronic device manufacturing processes, and is widely known as a dry process technique with a wide range of applications. Sputtering is a method in which a rare gas such as argon is introduced into a vacuum container. Direct current (DC) or radio frequency (RE) power is supplied to a cathode including a target to produce a glow discharge and thereby deposit a film. The former is referred to as DC sputtering, while the latter is referred to as RF sputtering.
FIG. 6
schematically depicts the potential distribution between the cathode and anode (ground potential) during discharge. Vp is the plasma time-averaged potential, and Vt is the cathode surface (that is, target surface) time-averaged potential. As shown in the figure, the resulting Vt of glow discharge is a negative potential with respect to the Vp. As a result of the difference in potential (Vp−Vt: referred to as self bias in the case of RF sputtering), positive ions such as those of accelerated argon collide with the surface of the target, which is attached to the cathode, and the target is sputtered. Sputtered particles from the target build up on a treatment piece (substrate) facing the target. When a mixed gas of a rare gas such as argon and a reactive gas such as O
2
or N
2
is introduced into the vacuum container at this time, the reaction product of the target material and this reactive gas builds up on the substrate.
The aforementioned sputtering includes magnetron sputtering, where magnets are placed behind the target to increase the plasma density around the target surface, resulting in more rapid film deposition. Magnetron sputtering includes RF magnetron sputtering using RF power, and DC magnetron sputtering using DC power. Both are widely used methods for depositing films during mass production.
There has been considerable progress in electronic devices recently, resulting in the need to develop techniques for improving thin film properties, including techniques for depositing films by magnetron sputtering. A factor which adversely affects the properties of thin films, when films are deposited by sputtering, is that the thin film is damaged by the impact of high energy particles on the substrate. The energy of these high energy particles is caused by differences in potential mainly arising on the front surface of the target. The difference in potential must be reduced to obtain high quality thin films. In the case of RF and DC magnetron sputtering, the Vt given in
FIG. 6
is determined by the container configuration, pressure, magnetic field intensity, and the conditions of the power supply.
Another method is combined RF-DC magnetron sputtering, where RF and DC power are simultaneously supplied to the target to cause sputtering. The Vt can be controlled by the voltage of the DC power source supplying the DC power during combined RF-DC magnetron sputtering. A high quality thin film can thus be manufactured because the difference in potential produced on the front surface of the target can be reduced by increasing Vt during combined RF-DC magnetron sputtering.
However, one problem with sputtering is that an abnormal discharge is produced on the target or on the surface of other parts inside the vacuum container. More specifically when an ITO transparent conductive film consisting of In (indium), Sn (tin), and O (oxygen) is formed on a substrate using an In and Sn oxide as a target by magnetron sputtering, or when a GeSbTe phase change type of recording film is deposited on a substrate using a Ge (germanium), Sb (antimony), and Te (tellurium) compound as the target (general composition: Ge
2
Sb
2
Te
5
), an abnormal discharge with rotating arcing is produced in portions on the target where the magnetic field perpendicular to the target surface is zero (that is, the portion where the target is mostly etched). Such an abnormal discharge is referred to as a “tracking arc” here. A tracking arc is not unusual even when using combined RF-DC magnetron sputtering which capable of manufacturing high quality thin films.
When a tracking arc is produced, the discharge impedance changes, and power cannot be supplied efficiently to the target. As a result, the film is formed at a lower rate, or films cannot be completely deposited. In some cases, a tracking arc results in the deposition of films with completely different properties.
A tracking arc also causes dust particles to be produced. When such dust particles adhere to the substrate, defects and product imperfections result.
A tracking arc is less readily produced when the magnetic field intensity at the target surface is weakened, when the film depositing pressure is lowered, and when the power supplied is reduced. However, a tracking arc cannot be completely suppressed by such methods. Such methods also cause production problems by lowering the film deposition rate.
An object of the present invention is to provide a thin film manufacturing method which suppresses a tracking arc and allows thin films to be consistently manufactured when such thin films are manufactured by combined RF-DC magnetron sputtering.
TECHNICAL ASPECTS OF THE INVENTION
Findings leading to the structure of the present invention as a means to achieving the aforementioned objectives will be discussed first.
The mechanism and causes of a tracking arc are not currently understood. The inventors conducted painstaking research to remedy the problem of a tracking arc in magnetron sputtering. As a result, they arrived at the following considerations on the mechanism and causes of a tracking arc.
It has been reported that in processes featuring the use of RF discharge, negatively charged clusters grow in the interface between the plasma and cathode sheath in the course of discharge. This is discussed, for example in the article by Shiratani et al in
J. Appl. Phys.
79(1), (January 1996), pp. 104-109. This is attributed to cohesion with positively ionized free particles as a result of collision between negatively ionized free particles and high energy electrons of the g-electrons released from the cathode. The clusters which increase as a result of particle cohesion are negatively charged because of the increase in the collision area with the electrons. The negatively charged clusters and positive ions cohere further, and the clusters grow. The growth of the negatively charged clusters are considered a cause of the aforementioned tracking arc.
In the case of magnetron sputtering, most g-electrons and sputter particles are released in a part where target erosion is deepest, and the g-electrons are trapped in the magnetic field produced by the magnets. Extremely large clusters thus continue to be negatively charged and grow over the part where target erosion is deepest. Once such cluster growth and “charging up” passes a certain level, an arc is produced between the cluster past the level first and the target. The target is ablated by this arcing, resulting in a plume (fuming). Pressure in the plume is high, and arcing persists through the concentration of discharged power. At this time, the plume acts as a current path, and the arc rotates in the part of deepest erosion because it behaves as a conductor through which flows the current moving in the magnetic field. The aforementioned tracking arc is an arc with such properties.
Because of the above, time is needed for cluster growth in the case of materials (such as ITO consisting of In and Sn oxides, or Ge
2
Sb
2
Te
5
, a compound of Ge, Sb, and Te) which have a high g-electron emission coefficient, are readily ablated, and tend to produce a p
Anelva Corporation
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
VerSteeg Steven H.
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