Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1999-01-21
2001-05-29
Bueker, Richard (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C118S7230FE
Reexamination Certificate
active
06238512
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plasma generation apparatus for generating a negative ion plasma using low-electron-energy plasma.
2. Description of the Related Art
In recent years there has been extensive use of plasmas in processes for manufacturing various semiconductor devices, liquid crystal displays, and solar cells, etc.
A dry etching process that employs plasma is used for example when subjecting thin films formed on the surfaces of substrates to dry etching. A specific example of such a dry etching process is seen, for instance, in the process of etching a silicon oxide film formed on a silicon semiconductor substrate using the action of active species or ions generated in a plasma.
Film forming processes that use plasmas are also employed in forming requisite thin films on the surfaces of substrates. A specific example of such a film forming process is seen, for instance in the plasma CVD (chemical vapor deposition) process for forming requisite thin films on the surfaces of substrates using a plasma-based vapor-phase reaction. A specific example of such a plasma CVD process would be a process for forming an inter-layer insulating film on a silicon semiconductor substrate.
In other words, in recent years, wiring interconnections have come to be implemented in multiple layers in conjunction with the higher integration of semiconductor devices. As a consequence, it has become necessary to provide insulating films between the wiring layers (inter-layer insulating films). CVD processes can be used in forming these inter-layer films. One such CVD process is the thermal CVD process, which is a process that uses heat as the necessary energy for activating the reaction. Specifically, reactive gas introduced into a process reaction chamber is made to react by the application of heat, thereby forming an inter-layer film.
This thermal CVD process requires a comparatively high temperature, however, which often results in problems in the devices. Recently, therefore, processes have come into use which employ a plasma as the activation energy. An example of a plasma used in such cams is a plasma generated through glow discharges.
Plasma CVD processes are also used in forming requisite thin films on substrates in solar cells.
In the dry etching processes that are typical of plasma processes, however, it is being demanded
(1) that the plasma can be generated uniformly at high density in order to cope with larger substrate areas and improved apparatus throughput,
(2) that process precision and selectivity can be improved in order to cope with electronic device structure miniaturization and multi-layer implementation, and
(3) that uniform plasma can be generated in order to reduce charge-up damage.
In order to answer to these demands, in recent years, various kinds of plasma generation apparatuses (plasma sources) art being developed. Examples of such high-density plasma generation apparatuses are the ECR (electron-cyclotron-resonance) type plasma generation apparatus, the inductively-coupled plasma generation apparatus (ICP generator), the micro-surface wave plasma generation apps, the helicon wave plasma generation apparatus, and the magnetron high-frequency discharge plasma generation apparatus.
Adequate plasma density can be achieved with these apparatuses. When it comes to plasma uniformity, however, as things stand now, adequate uniformity cannot be achieved when &phgr; is in the 300 mm range.
In these apparatuses, moreover, it is demanded that the plasma electron temperature be kept low in order to suppress excessive dissociation in the process gas.
Nevertheless, high-density plasma generation apparatuses are now being developed for dry etching silicon oxide films. There are serious problems to overcome in these apparatuses, however, namely the accumulation of electrical charges on the substrate surface and the reduction in etching selectivity resulting from excessive dissociation in the gas.
In the etching processes that employ current high-density plasma generation apparatuses, the following problems are being faced.
(1) When forming contact holes by etching a fine silicon oxide film, selectivity for the substrate silicon declines.
(2) When etching gate polysilicon electrodes, abnormal side etching develops due to electric charge accumulation.
(3) Gate oxide film insulation damage occurs.
It is believed that these phenomena occur because of the presence of many high-energy electrons in the plasma generated by low-pressure high-density plasma generation apparatuses. In other words, it is believed that these problems are produced because of the high temperatures of the plasma electrons. That is, when the plasma electron temperature is high, dissociation reactions proceed excessively in the plasma. Consequently, the radical species (CFx radicals, etc.) that are determinative of selectivity become few, or the sheath potential produced at the substrate sure (difference between mean potential in plasma space and substrate surface potential) becomes high. As a result, it is thought, charge accumulation becomes large due to the sheath potential distribution caused by substrate irregularities and the plasma density distribution, whereupon the phenomena noted above arc produced. By sheath potential here is meant the potential at the substrate surface relative to the mean potential in plasma space.
In view of the foregoing, there is a need to develop a method for keeping the electron temperature low in process plasmas. Two methods of achieving this are currently being considered, namely a pulse modulation plasma method and a grid control method.
By pulse modulation plasma method here is meant a method for generating plasmas having low electron temperature by intermittently supplying electric power for plasma generation to a plasma generation electrode. That is, by repeatedly executing and terminating power supply, plasma exhibiting low electron temperature is generated In other words, this is a method for generating a plasma of low electron temperature by subjecting the plasma generation power to a pulse modulation. The pulse signals used in this case are signals having a small pulse width of several tens of micrometers or so.
By employing this method, the electron temperature can be lowered while maintaining the plasma density to some degree. In more specific terms, the speed of plasma density decline when the power supply is terminated is slower than the speed of electron temperature decline. Thus, by repeatedly executing and terminating the power supply, the electron temperature can be lowered while maintaining some degree of plasma density.
This method can be applied to any of the high-density plasma generation apparatuses noted earlier. When that is done, however, the pulse modulation frequency at which optimum electron temperature is obtained differs from apparatus to apparatus. This is due to the differences in rise time and decay time in plasma density and electron temperature between the different apparatuses.
By grid control method is meant a method wherewith a plasma of low electron temperature is generated in a plasma diffusion region by using a grid to divide the region inside the vacuum vessel between a plasma generation region and a plasma diffusion region.
FIG. 17
is a diagram representing the configuration of a conventional plasma generation apparatus wherein the grid control method is adopted as the method of reducing electron temperature. This figure diagrams a representative case wherein the grid control method is applied to a magnetron high-frequency discharge plasma generation apparatus. In the figure, an example configuration is diagrammed for a substrate surface processing apparatus having such a plasma generation apparatus. In the figure, moreover, in the interest of diagrammatic clarity, hatching is used to indicate cross-sections only for some configurational elements.
In the apparatus diagrammed in the figure, a flat plate-shaped grid
42
is placed so that it lies perpendicular to the center axis Z of a vac
Iizuka Satoru
Li Yunlong
Sato Noriyoshi
Bueker Richard
Fieler Erin
Hitachi Kokusai Electric Inc.
Oliff & Berridg,e PLC
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