Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1998-03-26
2001-06-12
Warden, Sr., Robert J. (Department: 1744)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C118S7230AN, C118S7230MA
Reexamination Certificate
active
06245190
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing system and a plasma processing method, and in particular, it relates to a a plasma processing system and a method therefor which are suitable for forming fine patterns in the process of semiconductor manufacture.
RELATED ART
Various types of conventional plasma processing equipment have been used in the fine pattern processing in the semiconductor manufacture. In particular, the parallel plate type plasma processing equipment, which is known for its advantages of a relatively simple structure and uniformity of plasma, is widely used.
A conventional parallel plate type plasma processing system applies a high frequency power across a pair of parallel plate electrodes which are disposed oppositely in the upper part and the bottom part in a processing chamber, and processes a wafer using a plasma produced therein. For example, when processing a wafer by etching, so-called reactive ion etching (RIE) method is used. According to this RIE method, etching gas is introduced into the processing chamber, in which the etching gas is dissociated into ions and radicals (excited active species) by plasma to cause these ions and radicals to act on the surface of the wafer.
Also, the ion energy modulation (IEM) method is used in the parallel plate type plasma processing system. This IEM method which is disclosed in JP-A 7-297175 applies a different frequency power to each of the pair of electrodes in the upper and the bottom portions. A frequency of power to be applied to the electrode on the side where a plasma is produced is set at several tens MHZ or more, and a frequency of power to be applied to the electrode on the bias side on which a sample wafer is placed is set at several MHz or less. As a result, since a plasma density and a self bias of the sample, i.e., ion energy can be controlled independently, controllability of plasma and etching process is improved.
On the other hand, a magnetically enhanced RIE (MERIE) method which applies a magnetic field of approximately 30-90 gauss in a direction parallel to the upper and bottom parallel plate electrodes is also used in the parallel plate type plasma processing system. According to this MERIE method, an improved etching rate better than the RIE method is obtained due to the magnetic effect. Further, a magnetron RIE (M-RIE) plasma processing system as disclosed in JP-A 2-312231 is also used. According to this M-RIE method, a strong magnetic field in excess of 100 gauss is formed between the upper and the bottom electrodes in a direction parallel to the surfaces of the electrodes. Then, by interaction between this magnetic field and the electrical field generated between the upper and the bottom electrodes, electrons move in a cycloid motion in a manner to twine around a line of magnetic force. As a result, a frequency of collision between electrons and gas increases, thereby ensuring a high plasma density to be obtained.
Problems to be Solved by the Invention
Now, with an increasing demand for a larger-scale integration of semiconductor devices, it is required for the plasma processing system further to improve its fine pattern process capability and processing rate as well as selectivity. For example, in etching of a contact hole or via hole, it is required that a large aspect hole, i.e., a narrow and deep hole, can be etched vertically and at a higher rate. In addition, only a hole portion must be etched selectively and precisely. Also, such etching characteristics must be ensured to be highly reproducible and controllable. Still further, with an increasing diameter of wafers, it is required that uniformity of such etching rate and selectivity is ensured over the whole area of a large-sized wafer.
In order to satisfy such requirements, efforts to lower the process pressure and to increase plasma density are proceeding. If process pressure is lowered to several Pa, a frequency of collision between ions/radicals and molecules will decrease, thereby improving directivity of ions and radicals, and consequently, improvement in fine pattern processability can be expected. Further, since densities of ions and radicals which proceed etching can be increased by increasing plasma density, etching rate can be improved. However, a dissociate state of etching gas in such a plasma at a low pressure and with a high density acts, in most cases, disadvantageously against the selectivity, thereby preventing the selectivity from being ensured. Therefore, in order to satisfy the requirements to improve the fine pattern processibility, process rate and selectivity at the same time, it is necessary to optimize overall process conditions by controlling the dissociation state of etching gas which governs the process. It is also necessary to be able to control the plasma density and the dissociation state of the gas uniformly across the overall plasma and over the whole area of the wafer. This is because that if plasma density in a reactor chamber has any locally higher density region, there result in distributions in the density of ions and radicals as well as in the dissociation state of etching gas, thereby preventing the uniformity from being ensured. Further, in order to be able to cope with various etching conditions, it is necessary to set its optimum process conditions to have a wider process margin. Still further, in order to be able to construct a process in a short time, it is preferable for any main process parameters to be controlled independently as much as possible.
The above-mentioned prior arts are associated with the following problems to be solved in order to satisfy the imposed requirements described above.
The prior art parallel plate type plasma processing system can produce plasma stably without decreasing its plasma density at a low pressure of several Pa by increasing its frequency. However, by simply lowering the pressure, as high energy ions increase, the wafer will be damaged.
The above-mentioned IEM method is directed to solving this problem by controlling the plasma density and ion energy independently from each other. However, this IEM method does not have a means to control the dissociation state of etching gas directly. Therefore, the dissociation state of the gas will have to be controlled indirectly by appropriately controlling various process conditions, such as pressures in the reactor chamber, flow rate of etching gas, high frequency source power, bias power and the like. However, since these process parameters are interrelated in a very complicated manner from each other, it is not easy to construct any appropriate process therefor.
Still further, there is such a problem associated with the parallel plate type plasma processing system that the plasma density therein tends to have a distribution due to a distribution in the intensity of electrical fields. In the parallel plate type plasma processing system, it is necessary, in order to produce plasma stably, to have a wider area for a grounded portion than the plasma producing electrode in the reactor chamber. Thereby, there occurs uneven distribution in electrical fields within the reactor chamber, more specifically there occurs an intense electrical field at edge portions of the electrodes and in the peripheral portion of the wafer, thereby causing the plasma density to be distributed unevenly. In particular, when the diameter of the electrodes becomes large-sized with an increasing diameter of wafers, this problem becomes more significant, thereby it becomes more difficult to ensure the uniformity requirement.
On the other hand, with respect to the above-mentioned M-RIE method, there is a problem of drift due to the magnetic field. In order to increase the plasma density by magnetron effect, a strong magnetic field of at least 100 gauss or more is required. However, in such a strong magnetic field, there occurs a drift (E×B drift) due to interaction between the magnetic field and the electrical field formed across the electrodes, thereby causing a large uneven distribution in the plasm
Fukumoto Hideshi
Kaji Tetsunori
Koizumi Makoto
Masuda Toshio
Mitani Katsuhiko
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Olsen Kaj K.
Warden, Sr. Robert J.
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