Hollow-anode glow discharge apparatus

Hollow-anode glow discharge apparatus in the form of two-electrode and three-electrode reactors provide, in various embodiments, improved uniformity, efficiency and low-pressure substrate surface processing. In one improved uniformity embodiment for ion-dominated processes, the apparatus of the invention includes a high-energy-density uniformizing grid having multiple, multi-sized and evenly-spaced holes. In one improved uniformity embodiment for chemically-dominated processes, the apparatus of the invention includes a high-energy-density uniformizing grid having multiple, evenly-spaced holes and a stepped or continuously-variable non-planar profile. In one improved low pressure embodiment for ion-dominated and/or chemically-dominated processes, the apparatus of the invention includes a high-energy-density grid having multiple, evenly-sized and spaced holes of widths large enough to overcome dark space effects. In one improved efficiency selected ion energy embodiment for ion-dominated and/or chemically-dominated processes, the apparatus of the invention includes a high-energy-density source that synergistically cooperates with an apertured grid to provide selected-energy ions at higher densities than heretofore possible. In any embodiment, both build-up on and removal from the substrate are possible.

FIELD OF THE INVENTION 
The instant invention is drawn to the field of substrate processing, and 
more particularly, to a novel glow-discharge substrate surface processing 
apparatus providing improved uniformity, efficiency and low-pressure 
operation. 
BACKGROUND OF THE INVENTION 
There are generally two types of single-substrate substrate surface 
processing apparatus. In one form thereof, a substrate surface processing 
medium, such as a plasma, is controllably produced by two electrodes in a 
diode configuration, and in another form thereof, the substrate surface 
processing medium is controllably produced by three electrodes in a triode 
or other three-electrode configuration. For such machines, one or more 
selected surface processing media are caused to interact with suitably 
prepared surfaces of semiconductor wafers or other materials to form 
intended microstructures thereon and/or to remove unwanted residues 
therefrom that remain from one or more prior substrate surface processing 
steps. The model "384" diode reactor, commercially available from the 
instant assignee, and the model Wafer Etch 606/616 Triode Reactor, 
commercially available from GCA Corporation, are among the diode and 
triode reactors known to those skilled in the art. For the diode reactors, 
the substrate surface processing medium, such as a plasma, is controllably 
produced between the two electrodes in the diode configuration, while in 
the triode reactors, the substrate surface processing media, such as 
plasmas, are controllably produced between the upper electrode and the 
grid electrode on the one hand and between the grid electrode and the 
lower electrode on the other hand. 
There are generally two types of substrate surface processing media 
controllably produced by the single-substrate substrate surface processing 
reactors in either the diode or triode configurations. For some types of 
substrate surface processing, such as for etching oxide or other materials 
on semiconductor wafers or other substrates, these reactors produce 
substrate surface processing media constituted principally by selected 
ions, while in other types of substrate surface processing, such as for 
chlorine etching of aluminum or other materials on semiconductor wafers or 
other substrates, these reactors produce substrate surface processing 
media constituted principally by certain selected chemical species. The 
former type of processing is known as "ion-dominated" processing while the 
latter type is known as "chemically-dominated" processing. Ion-dominated 
and chemically-dominated processing, in dependence on the specific 
microstructure being formed and on the phase of the overall fabrication 
process, may controllably effect either a build-up on (deposition, growth 
and the rest) or a removal from (etching and the rest) the surface of the 
substrate. 
The utility of the heretofore known reactors in either the triode or diode 
configurations for both ion-dominated and chemically-dominated processing 
has been limited in respect to the degree of uniformity of substrate 
surface processing able to be obtained. In the application to very large 
scale integration (VLSI), for example, where more integrated circuits are 
being fabricated on ever larger semiconductor wafers, the effective yield 
of manufactured devices depends on the degree of uniformity obtained by 
the substrate surface processing apparatus. As the radial size of the 
wafer is increased to provide greater yield of integrated circuit devices 
to be fabricated per substrate, the difficulty of obtaining uniformity 
over the entire wafer becomes correspondingly more severe. Since device 
yield is directly proportional to the degree of uniformity obtained, the 
art of machine design is advanced to the same degree that substrate 
surface processing uniformity may be improved. 
The utility of the heretofore known reactors in either the diode or triode 
electrode configurations has been further limited in respect to the 
pressures at which selected ion-dominated and chemically-dominated 
processing were able to be efficiently run on semiconductor wafers and 
other substrates. In the application to VLSI, where, for example, it is 
desirable to fabricate microstructures with ever smaller features, the 
fineness and scale of the detail able to be fabricated depends on the 
pressure in the reactors. As the pressures are reduced at which the 
selected ion-dominated and chemically-dominated processes are run, the 
fineness and scale of the microstructures able to be fabricated thereby 
are correspondingly increased. However, below a certain pressure, about 
seventy (70) mTorr for the reactors in the triode configuration and about 
eight hundred (800) mTorr for the reactors in the diode configuration, the 
efficiency of the heretofore known substrate surface processing apparatus 
became too low to provide practicable processing, which has "frozen" the 
fineness and scale of the microstructures that have heretofore been able 
to be fabricated at levels that are larger and coarser than what are 
otherwise desirable. Since the degree of fineness and scale of the 
microstructures able to be fabricated is inversely proportional to the 
pressure level in these reactors, the art of machine design is advanced to 
the same degree that lower pressure processing may be able to be 
efficiently obtained. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention discloses as its principal object a 
substrate surface processing apparatus, in either a diode or a triode or 
other multi-electrode configuration, providing improved uniformity, 
efficiency and low-pressure operation for ion-dominated and/or 
chemically-dominated processing for substrate build-up and/or removal. In 
accord with one embodiment thereof for improved-uniformity ion-dominated 
processing, the apparatus of the invention includes a reaction vessel; at 
least first and second spaced-apart electrodes mounted in the reaction 
vessel and defining a substrate surface processing medium forming region 
between the first and second spaced-apart electrodes; a substrate holder 
proximate one of the electrodes; gas injecting means for injecting 
substrate surface processing medium forming reactants into the reaction 
vessel; at least one source of electrical excitation; coupling means 
connected between the at least one source of electrical excitation and the 
at least first and second spaced-apart electrodes to ground one of the 
electrodes while powering the other of the electrodes in a manner to 
induce a hollow-anode glow discharge in said grounded one of the 
electrodes; said grounded one of said electrodes having at least first and 
second groups of holes thereinthrough in which said hollow-anode glow 
discharge occurs; the holes of the at least first and second groups of 
holes are of preselected different characteristics selected to provide 
substantial uniformity of substrate surface processing over the entire 
surface of the substrate. In the exemplary improved-uniformity 
ion-dominated processing embodiment, the preselected characteristics of 
the holes of the at least first and second groups of holes of the grounded 
electrode are selected to be differential sizing. 
In further accord therewith and in one exemplary embodiment for 
improved-uniformity chemically-dominated processing, the apparatus of the 
invention includes a reaction vessel; at least first and second 
spaced-apart electrodes mounted in the reaction vessel and defining a 
substrate surface processing medium forming region between the first and 
second spaced-apart electrodes; a substrate holder for holding a substrate 
proximate one of said electrodes; a gas injector for injecting reactants 
into the reaction vessel; a source of electrical excitation; coupling 
means connected between the source of electrical excitation and said at 
least first and second spaced-apart electrodes to ground one of said 
electrodes and to power the other of said electrodes to induce a 
hollow-anode glow discharge in said grounded one of said electrodes; said 
grounded one of said electrodes having at least one hole thereinthrough in 
which said hollow-anode glow discharge occurs; said grounded one of said 
at least first and second electrodes having a preselected non-planar 
profile that departs from planarity in a manner selected to provide 
substantial uniformity of substrate surface processing over the entire 
surface of the substrate. In the exemplary improved-uniformity 
chemically-dominated processing embodiment, the preselected non-planar 
profile is selected to be concave. Continuous non-planar profiles other 
than concave profiles and non-planar "stepped" profiles may be employed 
without departing from the inventive concept. 
In further accord therewith and in one embodiment for improved low-pressure 
processing for selected ion-dominated and/or chemically-dominated 
processing the apparatus of the invention includes a reaction vessel; at 
least first and second spaced-apart electrodes mounted in the reaction 
vessel and defining a substrate surface processing medium forming region 
between the first and second spaced-apart electrodes; a substrate holder 
for releasably holding a substrate proximate one of said first and second 
spaced-apart electrodes; a gas injector for injecting substrate surface 
processing reactants into the reaction vessel; a source of electrical 
excitation; coupling means connected between the source of electrical 
excitation and the first and second spaced-apart electrodes to ground one 
of said electrodes while powering the other of the electrodes to induce a 
hollow-anode glow discharge in said grounded one of said at least first 
and second electrodes; pressure control means for selectively establishing 
a preselected pressure in the reaction vessel selected to be below one 
hundred (100) mTorr; said one of said electrodes that is grounded having a 
plurality of holes thereinthrough in which said hollow-anode glow 
discharge occurs of preselected width selected to be larger than four and 
nine tenths (4.9) mm. In accord with the present invention, the size of 
the holes of the grounded grid electrode controls the manner that the 
hollow-anode glow discharge occurs therein and enables to provide 
substrate surface processing at lower pressures and to fabricate 
microstructures of correspondingly finer detail and scale than heretofore 
thought possible. 
In further accord therewith and in one embodiment for improved 
low-pressure, selected-energy ion-dominated and/or chemically-dominated 
processing, the apparatus of the invention includes a reaction vessel; a 
high energy source providing ions; first and second electrodes spaced 
apart from each other and the high-energy source and mounted in the 
reaction vessel defining a first substrate surface processing medium 
forming region between the high-energy source and one of the first and 
second spaced-apart electrodes and defining a second substrate surface 
processing medium forming region between said first and second 
spaced-apart electrodes; a holder for releasably holding a substrate 
proximate one of said first and second spaced-apart electrodes; a source 
of electrical excitation; coupling means connected between the source of 
electrical excitation and said first and second spaced-apart electrodes to 
ground one of said first and second electrodes, to power the other of said 
electrodes to induce a hollow-anode glow discharge in the grounded one of 
the first and second electrodes and to cause ions of selected energy to be 
moved to the substrate; the grounded one of the first and second 
electrodes having a plurality of holes thereinthrough in which the 
hollow-anode glow discharge occurs and through which the high-energy ions 
produced by the high-energy source in the first substrate surface 
processing medium forming region communicate with the second substrate 
surface processing medium forming region and synergistically enhance the 
hollow-anode glow discharge by providing a larger percentage of ions of 
the selected energy in the second substrate surface processing medium 
forming region than would otherwise be present therein at a given 
low-pressure operation point thereby providing improved efficiency 
selected energy processing at pressures lower than and densities higher 
than heretofore thought possible. The high energy source is a 
magnetically-enhanced source in the exemplary embodiment although RFI 
(Radio Frequency Induction) and ECR (Electron Cyclotron Resonance) or 
other high-energy sources may be employed without departing from the 
inventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1A, generally designated at 10 is a schematic diagram 
illustrating a typical diode reactor of the prior art. The reactor 10 
includes a reaction vessel 12 having two (2) electrodes 14 and 16 in 
spaced-apart relation. The upper electrode 14 is grounded and the bottom 
electrode 16, upon which a substrate to be processed, not shown, is 
releasably mounted, is coupled to a source of electrical excitation 18 
designated "RF" via a matching network that includes a variable capacitor 
marked "C.sub.1 " and an inductor marked "L" in series between the 
electrode 16 and the source of electrical excitation 18 and a variable 
capacitor marked "C.sub.2 " in parallel with the source of electrical 
excitation 18. 
A gas injection system 20 is coupled to the reaction vessel 12 for 
injecting reactants in gas phase thereinto, a temperature control system 
22 is coupled to the reaction vessel 12 for controlling the temperature of 
the vessel and the electrodes therewithin and a pressure control system 24 
is coupled to the reaction vessel 12 for controlling the pressure 
therewithin. 
The upper electrode 14, because it is grounded, looks to be at a lower 
potential than the powered electrode 16, whereby the upper electrode 14 is 
referred to as the "anode" and the lower, powered electrode 16 is referred 
to as the "cathode". A reactive ion etch (RIE) plasma schematically 
illustrated by ellipse 26 and marked "RIE" is controllably produced 
between the anode 14 and the cathode 16 in the reaction vessel 12 of the 
reactor 10 in well-known manner. 
Referring now to FIG. 1B, generally designated at 30 is a schematic diagram 
of a triode reactor of the type shown and described in commonly-assigned 
U.S. Pat. No. 5,013,400 to Kurasaki et al. that issued May 7, 1991, 
entitled DRY ETCH PROCESS FOR FORMING CHAMPAGNE PROFILES, AND DRY ETCH 
APATUS, incorporated herein by reference. The triode reactor 30 
includes a reaction vessel 32 into which an upper electrode 34, a grounded 
grid 36 and a lower electrode 38 are mounted in spaced-apart relation in a 
triode configuration. The upper electrode 34 and the bottom electrode 38 
are coupled to a source of electrical excitation 40 marked "RF" 
respectively via variable capacitors marked "C.sub.1 " and "C.sub.2 " 
along a circuit path that includes a series inductor marked "L" and a 
capacitor marked "C" in parallel to the source of electrical excitation 
40. 
A gas injection system 42 is coupled to the reaction vessel 32 to 
controllably inject selected reactants in gas phase thereinto, a 
temperature control system 44 is coupled to the reaction vessel 32 to 
control the temperature of the electrodes thereof as well as the 
temperature of the vessel 32 and a pressure control system 46 is coupled 
to the reaction vessel 32 to establish and maintain a selected operating 
pressure. In the preferred embodiment, the gas injection system 42 
includes a gas diffuser, not shown, positioned between the upper electrode 
34 and the grid 36, and the upper electrode 34 is provided with a 
plurality of holes thereinthrough, not shown, through which the injected 
gas flows into the reaction vessel 32. 
The temperature control system 44 in the preferred embodiment includes 
passageways, not shown, within the upper electrode 34 that allow the 
circulation of the a transport fluid, such as water, thereinthrough to 
control the temperature thereof. Bores, not shown, are preferably provided 
into the vessel 32 that receive resistive heating elements to control the 
temperature of the reaction vessel, and the lower electrode has apertured 
bores therein, not shown, to allow the circulation of a heat transport 
fluid, such as helium, thereinthrough to control the temperature of the 
bottom electrode 38. The lower electrode 38 also has apertures 
thereinthrough, not shown, to allow the circulation of a heat transport 
fluid, such as water, to control its temperature. 
The grid electrode 36 is electrically grounded, as illustrated. It is 
apertured uniformly by holes whose widths are not larger than four and 
nine-tenths (4.9) mm. The source of electrical excitation 40 is coupled to 
the upper electrode 34 and to the lower electrode 38 via the variable 
capacitors "C.sub.1 ", "C.sub.2 ", which enable to selectively form only a 
plasma 48 marked "Remote" between the upper electrode 34 and the grid 36, 
to form only a plasma 50 marked "RIE" between the grid 36 and the lower 
electrode 38 and to form plasmas between the upper electrode 34 and grid 
36 as well as between the grid 36 and the lower electrode 38. 
The pressure control system 46 in the preferred embodiment includes a 
pressure controller, not shown, that preferably receives feedback from a 
pressure manometer, not shown, positioned inside the reaction vessel 32. 
The controller responds to chamber set point pressure selected from a 
pressure range that includes fifty (50) mTorr to three-thousand (3,000) 
mTorr and to the pressure reading supplied by the manometer to 
controllably throttle an orifice valve, not shown, coupled between the 
reaction vessel 32 and a pump, not shown, to establish and maintain the 
corresponding set point pressure in the reaction vessel 32. Other pressure 
ranges, such as from one (1) Torr to ten thousand (10,000) mTorr, may, of 
course, be provided. 
In one operational mode of the triode reactor 30 of FIG. 1B, only the RIE 
plasma 50 may be provided by supplying all power to the bottom electrode 
38 but no power to the upper electrode 34, with the grid 36 grounded. The 
so-operated triode reactor 30 of FIG. 1B, and the diode reactor 10 of FIG. 
1A, that likewise produces a RIE plasma 26 between the electrodes 14 and 
16 thereof, have identical electrode and plasma configurations. However, 
when the same reaction is run in the diode reactor 10 and the triode 
reactor 30 operated as a diode reactor, it has been found that the diode 
reactor 10 and the triode reactor 30 configured as a diode reactor 
unexpectedly produce quite different process characteristics. For example, 
for an exemplary etch by means of the process of reacting C.sub.2 F.sub.6 
with S.sub.i O.sub.2 to provide silicon dioxide etching in both the diode 
reaction 10 and the triode reactor 30 operated as a diode of the FIGS. 1A, 
1B, the etch rate for the diode reactor 10 is measured to decrease as the 
pressure in the diode reactor decreases, while the triode reactor 30 
configured as a diode reactor maintains its etch rate at a comparatively 
high level notwithstanding that the pressure decreases. Below about one 
hundred (100) mTorr, the etch rate becomes only a few hundred angstroms 
per minute for the diode reactor 10, while at about the same one hundred 
(100) mTorr pressure in the triode reactor 30 configured as a diode 
reactor, the etch rate remains on the order of thousands of angstroms per 
minute, a factor of about twenty (20) better than that of the standard RIE 
etch in the diode reactor 10. 
In addition to the unexpected difference in pressure performance, it has 
been found that the uniformity exhibited for the same exemplary etch in 
the diode reactor 10 of FIG. 1A is different from the uniformity provided 
by the triode reactor 30 of FIG. 1B notwithstanding that the triode 
reactor 30 is configured and operated as a diode reactor. For the diode 
reactor 10 of FIG. 1A, the etch rate is high in regions at and near the 
center of the wafer while at the edge thereof the etch rate is low; for 
the triode reactor 30 of FIG. 1B operated as a diode reactor, the 
uniformity maintains itself across the wafer and does not show the same 
variation between the center and the edge thereof as the diode reactor 10 
of FIG. 1A does. 
The present invention is based in the recognition that these and other 
differences in etch rates and in uniformity are attributable to a 
hollow-anode glow discharge to be described that occurs in the voids 
themselves of the grid of the triode reactor 30 of FIG. 1B that dominates 
the RIE plasma and sustains the etch rate and provides the uniformity even 
at the low pressures where the otherwise identical RIE plasma in the diode 
reactor 10 of FIG. 1A distorts the uniformity of processing and/or 
extinguishes itself. This phenomenon, heretofore unrecognized, enables 
glow discharge apparatus to be constructed in accord with the present 
invention that provides improved uniformity, efficiency and low-pressure 
operation. 
Referring now to FIG. 2, generally designated at 60 is a pictorial diagram 
useful in explicating the principles of the present invention. Between a 
powered bottom electrode generally designated 62 and a grounded grid 
generally designated 64 of the triode reactor 30 (FIG. 1B) an electric 
field 66 marked "E" extends. Electrons schematically illustrated by 
circles 68 marked "e" that are present in the RIE plasma forming region 
defined between the electrodes 62, 64 are accelerated by the field 66 to 
the grid 64. Some of the electrons 68 collide with the inside walls 
defining at least one hole generally designated 70 through the grid 64, 
and for each such electron 68, plural electrons 72 schematically 
illustrated by circles marked "e" are generated by the process of 
secondary emission. The secondary electrons 72, in turn, are trapped in 
each of the at least one hole 70 and oscillate back and forth between the 
confronting inside walls defining the hole. 
The oscillating secondary electrons 72 collide with gas molecules present 
within the void of the at least one hole 70 producing ions thereby 
schematically illustrated by circles 74 marked "+" in great numbers. The 
secondary electron and ion generation processes avalanche, and breakdown 
occurs, whereby a hollow-anode glow discharge is produced in each of the 
voids of the at least one hole 70 that is characterized by an enhanced 
electron density along the axis of each of the at least one holes. 
In accord with the present invention, about the periphery of each of the at 
least one holes 70, a dark space sheath of no-glow schematically 
illustrated by dashed lines 76 is formed that has a potential marked 
"V.sub.DS.sbsb.1 ". The intensity of the glow discharge in each of the 
holes 70 is related to the hole size, and the spacial extent of the dark 
space sheath 76 is inversely related to the pressure in the corresponding 
hole 70. A dark space sheath of no-glow schematically illustrated by 
dashed line 80 having a potential marked "V.sub.DS.sbsb.2 " is formed 
about the powered electrode 62, which typically adopts a negative DC bias 
voltage. 
FIG. 3 in the FIGS. 3A-3D thereof illustrates the variation in saturated 
ion current plotted as the ordinate, with Z position in the reactor 
plotted as the abscissa, where the one and five tenths (1.5) abscissa 
value corresponds to the grid position in the reactor for an exemplary 
C.sub.2 F.sub.6 chemistry, and where the values of the ordinates were 
measured by a Z profilometer. As shown by a graph 82 in FIG. 3A, which 
represents ion current with position in Z for a "holeless" grid, the ion 
current peaks at less than one hundred fifty (150) microamperes for the 
region below the grid. The graphs 84, 86 and 88 respectively of the FIGS. 
3B, 3C and 3D, which severally correspond to grids have plural, 
uniformly-sized apertures therethrough of seven (7) mm, eleven (11) mm and 
seventeen (17) mm diameters, represent the way the saturation ion current 
varies as the size of the holes through the grid is changed. The ion 
current in each of the graphs 84, 86 and 88 peaks at the grid location at 
a maximum value that depends on the applied power (compare the several 
peaks at one hundred (100), two hundred (200) and three hundred (300) 
watts) for the exemplary C.sub.2 F.sub.6 chemistry. 
Referring now to FIG. 4, generally designated at 90 is a 
high-energy-density uniformizing grid for ion-dominated processing in 
accord with the present invention. The grid 90 in the preferred embodiment 
is mounted within the triode reactor 30 of FIG. 1B, although it could be 
mounted within the diode reactor 10 of FIG. 1A or in any other reactor 
configured either as a diode or a triode or other multi-electrode reactor 
without departing from the inventive concept. In whatever reactor in which 
it is mounted, the grid 90 is preferably grounded and the substrate 
supporting electrode is powered in order to induce a hollow-anode glow 
discharge in each of the holes thereof. 
The grid 90 has at least first and second groups of holes respectively 
designated generally at 92, 94 thereinthrough of preselected different 
characteristics, at which the high-energy-density hollow-anode glow 
discharge occurs. By changing the size of the holes the intensity of the 
high-energy-density hollow-anode glow discharge is changed (compare FIG. 
3), and the preselected different characteristics of the at least first 
and second groups of holes 92, 94 are selected to provide substantial 
uniformity of substrate surface processing over the entire surface of the 
substrate. In the preferred embodiment, the characteristic is selected to 
be differential aperture width respectively of the holes of the at least 
first and second groups 92, 94. The grid 90 having the illustrated 
concentrically arranged groups of differentially sized holes 92, 94 
provides substantial uniformity for the exemplary ion-dominated etch 
discussed in connection with the description of FIG. 1. Other arrangements 
of holes of different sizes and more than two groups of holes of different 
sizes may be employed without departing from the inventive concept. 
The hollow-anode glow discharge in each of the several holes of the grid 90 
proceeds downwardly towards the substrate from the grid, and it both drops 
in intensity and expands the closer it gets to the confronting surface of 
the substrate. To prevent the replication of the hole pattern on the 
substrate, it is preferred that the intrahole spacing between holes of the 
same size and the interhole spacing between holes of different sizes be 
selected to be that minimum dimension 98 marked "D" that ensures overlap 
of the several hollow-anode glow discharges of intragroup and intergroup 
holes at the surface of the substrate. In the exemplary embodiment, the 
dimension 98 is about two-tenths (0.2) mm although other hole spacings may 
be employed to prevent hole pattern replication in dependance on the 
particular ion-dominated process selected. While in the preferred 
embodiment the space between the holes of the same and different sizes is 
selected to be the same dimension in order to prevent duplicating the hole 
pattern on the wafer or other substrate, other hole spacing arrangements 
may be employed in accord with the instant invention so long as the 
pattern of the holes of the at least first and second groups of holes is 
not duplicated on the substrate. 
The thickness 104 marked "T" of the grid 90 need only be not too thin as to 
not support a hollow-anode glow discharge in the several holes while not 
too thick as to extinguish the same. For the exemplary embodiment 90, 
thicknesses from twelve hundredths (0.12) mm to six and three-tenths (6.3) 
mm have been found to be effective, although other thickness may be 
employed without departing from the inventive concept. Any suitable 
material, such as aluminum, that does not deform or melt may be selected 
for the material of the grid 90. 
Referring now to FIG. 5, generally designated at 110 is a graph useful in 
explaining the principles of construction of a high-energy-density 
uniformizing grid for an exemplary ion-dominated process in accord with 
the present invention. The exemplary ion-dominated process is etching of a 
semiconductor wafer by the chemistry C.sub.2 F.sub.6. The graph 110 plots 
an index of the particular substrate surface process selected as the 
ordinate, here "etch rate", with increasing hole size as the abscissa. 
The graph 110 is exemplary of one procedure that may be employed in 
constructing a high-energy-density uniformizing grid for ion-dominated 
processes in accord with the invention. For an intended pressure, 
different grids with different uniformly-sized holes are severally mounted 
in the triode reactor 30 of FIG. 1B and measurements are taken of the etch 
rate obtained for each grid of different uniformly-sized holes. In the 
graph 110, those etch rates are plotted as data points schematically 
illustrated by the solid boxes thereof. Lower pressure set-points shift 
the graph 110 to the right, and higher pressure set-points shift the graph 
110 to the left. To design a uniformizing grid, profilometer measurements 
are taken of the uniformity of etch rate across a substrate using a grid 
of one selected size hole, such as that at the midpoint of the graph 110. 
Departures from uniformity above and below the intended etch rate are 
compensated by referring to the graph 110 and selecting that hole size 
that gives the intended etch rate for those regions where the etch rate 
departs from uniformity. A grid with groups of holes of different sizes 
selected to provide uniformity is then constructed, profilometer 
measurements are taken, and the same process may be repeated until 
substantial uniformity is obtained. Graph 110 is exemplary only, and it 
will be appreciated that the high-energy-density uniformizing grid for 
ion-dominated processing of the invention may be designed for other 
ion-dominated processes by means of other control grids and design 
methodologies and by gathering other kinds of data about different 
dimensions and parameters and along different directions than that 
illustrated by the graph 110 without departing from the inventive concept. 
Referring now to FIG. 6, generally designated at 120 is a 
high-energy-density uniformizing grid for chemically-dominated processing 
in accord with the present invention. Like for the case of the 
high-energy-density uniformizing grid for ion-dominated processing 90 of 
the embodiment of FIG. 4, the grid 120 may be mounted in any suitable 
two-electrode or three-electrode or other multi-electrode reactor, the 
triode reactor of FIG. 1B being the presently preferred embodiment. Unlike 
for the case of the high-energy-density uniformizing grid for 
ion-dominated processing 90 of the exemplary embodiment of FIG. 4, where 
it is differential hole size that determines the relative intensity of the 
high-energy-density hollow-anode glow discharge, and that is selected to 
provide substantial uniformity of substrate surface processing over the 
entire surface of the substrate, the grid 120 of the exemplary embodiment 
of FIG. 6 for chemically-dominated processing has a preselected non-planar 
profile that departs from planarity in a manner selected to provide 
substantial uniformity of substrate surface processing over the entire 
surface of the substrate being processed for the selected 
chemically-dominated process. In accord with the present invention, the 
local intensity of the hollow-anode glow discharge is determined by the 
local spacing of the grid from the substrate to be processed which, by 
controllably changing the spacing, enables to provide substantial 
uniformity of substrate surface processing for any selected 
chemically-dominated processes. 
In the exemplary embodiment, the uniformizing grid 120 includes a member 
122, such as of aluminum, through which a plurality of equal-sized holes 
generally designated 124 are provided in uniformly spaced-apart relation. 
In the exemplary embodiment, the preselected non-planar profile of the 
grid 120 is selected to be continuously arcuate in two-dimensions with 
centrally-positioned holes spaced further from the substrate than 
peripherally-positioned holes. The thickness of the grid 120 should be not 
too thin that the uniformizing grid 120 would melt, nor too thick that the 
high-energy-density glow discharge would extinguish itself. Typical values 
of thicknesses range from twelve hundredths (0.12) mm to six and three 
tenths (6.3) mm, although other thicknesses may be employed without 
departing from the inventive concept. 
For any selected chemically-dominated process the non-planar profile is 
selected to provide substantial uniformity over the entire surface of the 
wafer for the chemically-dominated process selected. To determine the 
specific non-planar profile that corresponds to a particular 
chemically-dominated process selected, measurements of an index of the 
selected chemically-dominated process are made at points spaced about the 
entire surface of the substrate using a planar grid mounted a first 
predetermined distance from the substrate. The planar grid is then 
remounted in the reactor, but at a different predetermined distance from 
the substrate, and the index of the particular chemically-dominated 
process selected is measured at the same substrate points. The process of 
remounting the planar grid and measuring the index of the selected 
chemically-dominated process for the same set of substrate points is 
repeated a predetermined number of times. Each set of measurements of the 
index with location about the same points of the substrate is 
parametricized by the particular value of the spacing of the planar grid 
from the substrate for a substantially constant index; that spacing that 
gives the same index at each of the points is taken directly or by 
extrapolation from the measurements or by other calculating techniques. 
This spacing specifies the way the non-planar profile departs from 
planarity to provide substantial uniformity for the particular 
chemically-dominated process selected. Discrete (stepped) non-planar 
profiles and continuous non-planar profiles other than the concave grid 
120 of the exemplary embodiment may be employed without departing from the 
inventive concept. 
Referring now to FIG. 7, generally designated at 130 is a graph that plots 
electrode spacing in inches as the ordinate with location in millimeters 
from the edge of the wafer as the abscissa parametricized for different 
uniform etch rates at different pressures as illustrated by the curves 
132, 134, and 136 thereof. The graph 130 was experimentally obtained on a 
modified diode chamber with an electrostatic chuck, in which the grounded 
grid was hung from the upper electrode with a teflon baffle around the 
sides. The particular chemically-dominated process selected was an 
aluminum etch. 
The samples that were used were six (6) inch aluminum five-tenths percent 
(0.5%) Cu wafers that had been DUV (deep ultraviolet) baked at two-hundred 
(200) C.degree.. A three factor quadratic design with three (3) replicate 
points was used to produce an eighteen (18) run experiment. Held constant 
during the experiment were fifty (50) sccm C1, fifteen (15) sccm 
SiCl.sub.4, three-hundred (300)W, and ten (10) torr He backside pressure. 
The factors that were varied were pressure (60 mt-120 mt), electrode 
spacing (0.25"-1.25"), and grounded grid hole size (3/16"-5/8"). All the 
wafers were partially etched and profilometer measurements were taken at 
fourteen (14) points along the diameter of each wafer. The measurements 
were taken before etch, after etch, and after resist strip. From this data 
the aluminum (A1) etch rate and resist etch rate were calculated at each 
of the fourteen (14) points on each wafer. The responses that were 
measured were the average aluminum and resist etch rates across the wafer, 
and the etch rate uniformities. A detailed picture of uniformity was 
obtained by analyzing the experimental results using, as the responses, 
the etch rates at seven (7) points from the edge to the center of the 
wafer. Data from these plots were used to generate the curves 132, 134, 
136 of FIG. 7 to plot electrode spacing with wafer location for a given 
etch rate. The data points for each curve are marked on the contour plots 
to illustrate how the curves were created. The curves show what spacing is 
needed to produce a specific etch rate at a specific location on the 
wafer. The curves represent the shape of the grounded grid needed to 
produce a uniform etch rate across the wafer for the exemplary 
chemically-dominated process selected. Other chemically-dominated 
processing, other control grids and design methodologies and other ways of 
gathering data than that of the FIG. 7 may be employed without departing 
from the inventive concept. 
Referring now to FIG. 8, generally designated at 140 is a 
high-energy-density low-pressure grid in accord with the present 
invention. The grid 140 preferably is mounted within the triode reactor 30 
of FIG. 1B but it may be mounted in the diode reactor 10 of FIG. 1A or any 
other reactor configured as a diode or triode or other multi-electrode 
reactor without departing from the inventive concept. The grid 140 has a 
plurality of holes generally designated 142 thereinthrough of preselected 
width selected to be larger than four and nine tenths (4.9) millimeters 
and typically eleven (11) millimeters. As described above in connection 
with the description of FIG. 1, when the pressure in the reactors in 
either the diode or the triode configurations is reduced beyond a certain 
threshold, below about one hundred (100) mTorr for the triode reactor 30 
of FIG. 1B and below about eight hundred (800) mTorr for the diode reactor 
10 of FIG. 1A, processing efficiency either becomes impracticable or 
processing stops altogether, with the result that a limit was reached on 
the type, scale and fineness of microstructures capable of being 
fabricated by the heretofore known reactors configured either as diode or 
triode or other multielectrode reactors. In accord with the present 
invention, by means of providing the grid 140 with holes none of which 
have widths that are sized to be smaller than or equal to four and nine 
tenths (4.9) mm, and which typically are eleven (11) mm, the lower limit 
on the practicable pressures heretofore is overcome enabling the 
fabrication of microstructures of sizes and of degrees of fineness not 
heretofore thought possible. On the heretofore existing triode reactors, 
the aperture widths of the grid were all no bigger than four and 
nine-tenths (4.9) millimeters. The dark space in the holes of the grid, 
which, as described hereinabove, is a function of both the pressure and 
the applied radio frequency excitation, increases as the pressure 
decreases. For the hole sizes heretofore, the dark space in the holes 
effectively extinguished and/or distorted the hollow-anode glow discharge 
of the grounded grid at the minimum pressure levels heretofore, whereby 
the geometries of the microstructures that were able to be formed were 
"frozen" at magnitudes larger than desirable for present and future VLSI 
and other applications. 
In accord with the present invention, the holes are large enough that the 
hollow-anode glow discharge in the grid 140 maintains itself 
notwithstanding the size of the dark space in the voids of the grid at 
pressures below the minimum pressures heretofore, thereby enabling the 
triode reactor 30 of FIG. 1B with the grid 140 to provide substrate 
surface processing at pressures selected below the minimum pressures 
heretofore. The grid 140 in accord with the present invention enables in 
this manner to provide substrate surface processing at a range of 
pressures heretofore thought impossible, and thereby it enables to 
fabricate microstructures of a type, scale and fineness that were 
heretofore not thought possible. While aperture widths of eleven (11) 
millimeters are preferred for the exemplary embodiment of the grid 140, 
other aperture widths sized above the minimum width of four and nine 
tenths (4.9) mm yield a plasma and a corresponding increase in ion density 
that are at least an order of magnitude greater than that heretofore 
thought possible. 
Referring now to FIG. 9, generally designated at 150 is an embodiment of 
the invention for improved low-pressure selected-energy ion-dominated 
and/or chemically-dominated processing. Instead of the upper electrode 34 
of the triode reactor 30 of FIG. 1B, a high density source 152 is provided 
inside the reaction vessel in spaced apart relation to a grounded grid 
154, which in turn is in spaced-apart relation to a lower electrode 156. 
Between the high-density source 152 and the grid 154 a first substrate 
surface processing medium forming region generally designated 158 and 
marked "remote" is provided and, between the grid 154 and the lower 
electrode 156, a second substrate surface processing medium forming region 
generally designated 160 and marked "RIE" is provided. The high density 
source may be any suitable source such as a radio frequency induction 
(RFI) source, an electron cyclotron resonance (ECR) source, a 
magnetically-enhanced source, and among others, a helical resonator 
well-known to those skilled in the art. 
A first source of excitation 162 is coupled to the high-density source 152 
to energize the same. A gas injection system 164, a temperature control 
system 166 and a pressure control system 168, that correspond to the 
elements 42, 44 and 46 of FIG. 1B, are coupled to the reaction vessel and 
function in substantially the same manner as in the embodiment 30 of FIG. 
1B, and are not specifically described again herein for the sake of 
brevity of explanation. 
The high-energy-density source 152 boosts the efficiency of the 
hollow-anode glow discharge produced by the grounded grid 154; the 
high-energy ions produced by the high density source 152 in the first 
substrate surface processing medium forming region 158 communicate with 
the second substrate surface processing medium forming region 160 through 
the holes of the grid 154 and synergistically enhance the hollow-anode 
glow discharge in the grid 154 by providing a comparatively larger 
percentage of ions of selected energy in the second substrate surface 
processing region than would otherwise be present therein at a given 
low-pressure operation point. The ions of the high density source 152 
synergistically cooperate with the hollow-anode glow discharges of the 
grounded grid to provide a greater percentage of ions in the region 160, 
which ions may be selectively extracted by controllably biasing the lower 
electrode 156 by means of a controllable negative RF source 170. The 
controllable source 170 creates a negative potential whose magnitude may 
be varied to extract from the upper region 158 ions of a particular energy 
level. In polysilicon etching, for example, where it is desirable to use 
the minimum ion energy necessary to create anisotropic etching of the 
film, selection of minimum energy ions is desirable to prevent charge 
build-up and gate oxide damage, which minimum energy ions can readily be 
selected by varying the potential of the ion selector 170 to apply the 
corresponding negative potential on the lower electrode that attacks ions 
of the selected energy. Other applications of the embodiment 150 may, of 
course, be implemented without departing from the inventive concepts. 
While in the embodiments described herein the preferred biasing provides a 
hollow-anode glow discharge, where the grid is grounded, it should be 
understood that the grid may be powered, and a hollow-cathode glow 
discharge, such as for film removal, may also be provided without 
departing from the inventive concept. It should also be understood that 
the inventive apparatus of the several embodiments described herein, such 
as the grid embodiment 90 (FIG. 4) primarily for ion-dominated processes 
and the grid embodiment 120 (FIG. 6) primarily for chemically-dominated 
processes, may be combined, such as by providing the high-energy-density 
uniformizing grid 90 or 120 in the reactor 150 (FIG. 9), without departing 
from the inventive concept. 
Many modifications of the presently disclosed invention will be apparent to 
those skilled in the art having benefitted from the instant disclosure 
without departing from the inventive concept.