Plasma processing method

In a plasma etching apparatus, an inactive gas and a reactive gas are supplied from a gas spouting surface of a shower head, and are turned into plasma by means of RF discharge, so that a semiconductor wafer placed on a susceptor is etched by the plasma. The inactive gas is continuously supplied from inactive gas spouting holes formed all over the gas spouting surface. The reactive gas is supplied from reactive gas spouting holes, which are formed all over the gas spouting surface and divided into a plurality of groups, by repeatedly scanning the groups in a time-sharing manner.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for subjecting a 
target object, such as a semiconductor wafer or LCD substrate, to a 
process, using plasma generated by means of radio frequency (RF) 
discharge, and in particular to a method and apparatus for subjecting a 
target object having a large surface area to plasma etching or plasma 
deposition at a high planar uniformity and a high processing rate. 
In processes of manufacturing semiconductors, various kinds of plasma 
processes, such as etching, are performed on a target object, such as a 
semiconductor wafer, in a plasma atmosphere, while plasma is generated in 
a process chamber. In recent years, target objects of this kind have 
become higher in their diameter or surface area, such that, for example, 
semiconductor wafers have changed their size from 6 inches to 8 inches and 
further to 12 inches (300 mm), in order to decrease the processing cost 
per unit surface area of the target objects. 
In consideration of this demand, researches have been conducted on plasma 
processing apparatuses for processing a target object of a large surface 
area. It is thought that, as a type of generating plasma used in such 
processing apparatuses, the parallel plate type or the ICP (Inductively 
Coupled Plasma) type is promising. This is because, the other types of 
generating plasma, such as the ECR (Electron Cyclotron Resonance) type and 
the helicon wave type, are apt to produce a plurality of modes, thereby 
bringing about a difficulty in obtaining uniform plasma, when a plasma 
source becomes large in accordance with a target object. 
There is another problem caused due to a large magnet in these plasma 
processing apparatuses. In this case, where plasma is spread by means of 
diffusion due to gradient of a magnetic field without making a plasma 
source larger, electrons are accelerated at the peripheral region, thereby 
causing plasma properties to be different between the central region and 
the peripheral region. 
Further, if a wafer larger than an 8-inch (200 mm) wafer needs to be 
provided with process properties, such as processing rate, selectivity, 
and processed shape, which are equal to those obtained relative to the 
8-inch wafer, the flow rate of a process gas should be increased in 
proportion to an increase in the surface area of the target surface. In 
this case, where the height of a plasma space, i.e., the distance between 
upper and lower electrodes in the parallel plate type, is maintained to be 
equal to that of a conventional apparatus, the aspect ratio of the plasma 
space between its height and width becomes greater with an increase in the 
surface area of the target surface, thereby reducing its exhausting 
conductance. As a result, a high vacuum suitable for a plasma process is 
hardly obtained while causing a large predetermined amount of a processing 
gas to flow, in consideration of the performance of, e.g., a vacuum pump 
currently being used. For example, as compared with an 8-inch wafer, a 
300-mm (12-inch) wafer increases its surface area 2.24 times larger, and 
thus requires a 2.24 times greater amount of processing gas, thereby 
bringing about a difficulty in vacuum exhaustion. Further, exhaustion of a 
reactive gas differs between the central and peripheral regions of the 
target surface, and thus process properties, such as a processing rate, 
are not uniform between the central and peripheral regions of the target 
surface. 
It can be assumed that the exhausting conductance should be increased by 
expanding the distance between the electrodes so as to allow the vacuum 
exhaustion to be performed easily. In this case, however, if its 
dissociated gas state is to be the same as that in a conventional 
apparatus while preventing the plasma density from lowering, it is 
necessary to set the residence time of the gas in the plasma space to be 
also equal. As a result, the flowing amount of the gas has to be 
increased, thereby further bringing about a difficulty in vacuum 
exhaustion. 
BRIEF SUMMARY OF THE INVENTION 
The present invention has been made in light of the above described 
problems, and its object is to provide a plasma processing method and 
apparatus in which a target object having a large surface area can be 
subjected to a process at a high planar uniformity and a high rate, 
without increasing the exhausting performance of a vacuum pump currently 
being used. 
The present inventors have conducted researches on methods of supplying a 
reactive gas in a plasma processing apparatus, and found the following 
knowledge to reach the present invention. Namely, even if the whole amount 
of gas supplied per unit time is decreased, it is possible to maintain a 
high planar uniformity of a plasma process, by continuously supplying an 
inactive gas for initiating and uniformly keeping plasma toward a target 
surface to keep a high plasma density, while supplying a reactive gas in a 
time-sharing manner among the local areas of the target surface. 
According to a first aspect of the present invention, there is provided a 
plasma processing apparatus for processing a target object, using plasma, 
comprising: 
an airtight process chamber; 
a work table arranged in the process chamber for supporting the target 
object; 
an exhaust for exhausting and setting the process chamber at a vacuum; 
a shower head arranged in the process chamber and having a gas spouting 
surface facing the work table; 
an inactive gas supply for supplying an inactive gas into the process 
chamber, the inactive gas supply having inactive gas spouting holes formed 
substantially all over the gas spouting surface; 
a reactive gas supply for supplying a reactive gas into the process 
chamber, the reactive gas supply having reactive gas spouting holes formed 
substantially all over the gas spouting surface and divided into a 
plurality of groups, the reactive gas supply being arranged such that the 
groups of the reactive gas spouting holes are capable of supplying and 
stopping the reactive gas independently of each other; 
an electric field generator for generating an electric field in the process 
chamber, the electric field being used for turning the inactive gas and 
the reactive gas into plasma by means of RF discharge; and 
a control section for controlling the reactive gas supply such that the 
groups of the reactive gas spouting holes are repeatedly scanned in a 
time-sharing manner to supply the reactive gas. 
According to a second aspect of the present invention, there is provided a 
plasma processing apparatus for processing a semiconductor wafer having a 
diameter of 300 mm or more, using plasma, comprising: 
an airtight process chamber; 
a work table arranged in the process chamber for supporting the target 
object; 
an exhaust for exhausting and setting the process chamber at a vacuum; 
a shower head arranged in the process chamber and having a gas spouting 
surface facing the work table; 
a process gas supply for supplying a process gas into the process chamber, 
the process gas supply having process gas spouting holes formed 
substantially all over the gas spouting surface; and 
an electric field generator for generating an electric field in the process 
chamber, the electric field being used for turning the process gas into 
plasma by means of RF discharge, the electric field generator comprising 
first and second electrodes incorporated with the work table and the 
shower head, respectively, and an RF power supply connected to at least 
one of the first and second electrodes through a matching circuit, the RF 
power supply and the matching circuit being connected by a line having a 
characteristic impedance of less than 50 ohms. 
According to a third aspect of the present invention, there is provided a 
plasma processing method of processing a target object, using plasma, 
comprising the steps of: 
placing the target object on a work table arranged in a process chamber; 
supplying an inactive gas and a reactive gas into the process chamber from 
a gas spouting surface facing the work table, while exhausting the process 
chamber, such that the inactive gas is continuously supplied from inactive 
gas spouting holes formed substantially all over the gas spouting surface, 
and the reactive gas is supplied from reactive gas spouting holes, which 
are formed substantially all over the gas spouting surface and divided 
into a plurality of groups, by repeatedly scanning the groups in a 
time-sharing manner; 
turning the inactive gas and the reactive gas into plasma by means of RF 
discharge in the process chamber; and 
subjecting the target object to a process, using the plasma. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a structural view showing a plasma etching apparatus 2 
exemplifying a plasma processing apparatus according to an embodiment of 
the present invention. 
The plasma etching apparatus 2 has an airtight process chamber 4 having a 
cylindrical shape and made of, e.g., aluminum, whose inner surface is 
anodized. The process chamber 4 defines an airtight process field and is 
grounded. 
A susceptor 8 having a circular column shape is arranged via an insulating 
plate 6 made of, e.g., ceramics, on the bottom of the process field formed 
in the process chamber 4, for mounting a target object, such as a 
semiconductor wafer W. The susceptor 8 is made of, e.g, aluminum covered 
with the anodized surface. The diameter of susceptor 8 is set at, e.g, 
about 250 mm where the wafer W to be processed is 8 inches in size, while 
it is set at, e.g., about 410 mm where the wafer W is 300 mm in size. 
A coolant room 10 is formed in the susceptor 8. A coolant for temperature 
adjustment, such as liquid fruolocarbon, is introduced in the coolant room 
10 through a coolant supply pipe 12, so that the coolant is circulated in 
the coolant room 10. The cold of the coolant is transmitted from the 
coolant room 10 to the wafer W through the susceptor 8 to cool the wafer 
W. The heat-exchanged coolant is exhausted to the outside of the process 
field through a coolant exhaustion pipe 14. 
A gas passage 18 is formed in the insulating plate 6, the susceptor 8, and 
an electrostatic chuck 16 described later, for supplying a heat medium, 
such as He gas, to the backside of the wafer W to be processed. A heat 
transmission passage is ensured by the heat medium from the susceptor 8 to 
the wafer W, so that the wafer W is kept at a predetermined temperature by 
the coolant. 
The central portion of the top of the susceptor 8 is formed to be a 
projection of a circular plate shape, on which the electrostatic chuck 16 
having a diameter almost the same as that of the wafer W is disposed. The 
electrostatic chuck 16 has a conductive layer interposed between two 
polyimide films. When a DC (direct current) voltage, such as 1.5 kV, is 
applied to the conductive layer from a high DC power supply 20 located 
outside the process chamber 4, the wafer W placed on the electrostatic 
chuck 16 is attracted and held there by a Coulomb' force. Where the 
conductive layer is interposed between two layers of alumina ceramics, in 
place of the polyimide films, it is possible to prevent problems, such as 
malfunction of breakdown voltage, from being caused, and thereby to 
prolong its life. 
A focus ring 22 is arranged around the top of the susceptor 8 so as to 
surround the wafer W placed on the electrostatic chuck 16. The focus ring 
22 is made of an insulating material to shut out an electric field. Since 
no reactive ions are accelerated above the focus ring 22, the reactive 
ions generated by plasma are effectively radiated onto the wafer W inside 
the ring 22. 
An electric feeder rod 24 is connected to the susceptor 8 and penetrates 
the portion therebelow while keeping an insulated state. An RF (radio 
frequency) power supply 28, which outputs an RF power of, e.g., 13.56 MHz, 
is connected to the electric feeder rod 24 by a wiring line 29 through a 
matching circuit 26 including, e.g., a decoupling capacitor, so that a 
self bias can be applied to the susceptor 8 for attracting ions toward the 
wafer W. 
Where the semiconductor wafer W is 8 inches in size, the impedance of the 
susceptor 8 relative to an RF power is about several ohms, and thus the 
characteristic impedance of the line 29 between the RF power supply 28 and 
the matching circuit 26 is set at about 50 ohms. However, where the wafer 
W is 300 mm in size, the surface area of the susceptor 8 grows several 
times larger, and the impedance of the susceptor 8 is greatly decreased in 
accordance with the increase in the surface area. As a result, if the 
characteristic impedance of the line 29 between the RF power supply 28 and 
the matching circuit 26 is set at 50 ohms where the wafer W is 300 mm in 
size, power loss or the like are increased by the resistor component of a 
reactor in the matching circuit 26. 
For this reason, where the wafer W is 300 mm in size or a size larger than 
300 mm, the characteristic impedance of the line 29 between the RF power 
supply 28 and the matching circuit 26 is set to be less than 50 ohms, so 
that the power loss in the reactor is suppressed. For example, where the 
susceptor 8 is used for the wafer W of 300 mm in size, the output 
impedance of the RF power supply 28 and the characteristic impedance of 
the line 29 are set to be from about 20 ohms to about 30 ohms. 
A circular shower head 30 used as an upper electrode as well is supported 
by and fixed to the ceiling of the process chamber 4 through an insulating 
member 32. The shower head 30 has a bottom surface or gas spouting surface 
34, which faces the upper surface of the susceptor 8 in parallel with a 
distance of from 20 mm to 40 mm therebetween. A number of reactive gas 
spouting holes 36 and a number of inactive gas spouting holes 38 are 
formed on the gas spouting surface 34 facing the susceptor 8. 
The shower head 30 includes an electrode plate 40 having the gas spouting 
surface 34, and a head body 42 supporting the electrode plate 40. The 
electrode plate 40 is made of a conductive material, such as SiC or 
amorphous carbon, while the head body 42 is made of a conductive material, 
such as aluminum covered with the anodized surface. 
FIG. 2 is a plan view showing the gas spouting surface 34 of the shower 
head 30. As shown in FIG. 2, the inactive gas spouting holes 38 and the 
reactive gas spouting holes 36 are coaxially arranged in this embodiment. 
The inactive gas spouting holes 38 and the reactive gas spouting holes 36 
are alternately arranged in radial directions of the circular shower head 
30. In FIG. 2, the inactive gas spouting holes 38 are indicated with black 
dots while the reactive gas spouting holes 36 are indicated with white 
dots. 
More specifically, the reactive gas spouting holes 36 are divided into a 
plurality of groups coaxially arranged, e.g., four groups in the 
embodiment. The inactive gas spouting holes 38 are coaxially arranged 
between the coaxial groups of the reactive gas spouting holes 36. The 
groups of the reactive gas spouting holes 36 are identified as first 
(36A), second (36B), third (36C), and fourth (36D) groups from the central 
side as a matter of convenience. 
As shown in FIG. 3, the groups of the reactive gas spouting holes 36A to 
36D respectively communicate with reactive gas head grooves 44A to 44D, 
which are coaxially formed in the head body 42 and independent from each 
other, through passages 46. FIG. 3 is a cross-sectional plan view showing 
the shower head 30 cut along the reactive gas head grooves 44A to 44D. The 
head grooves 44A to 44D respectively and independently communicate with 
reactive gas supply lines 48A to 48D. The gas supply lines 48A to 48D are 
respectively provided with time-sharing open/close valves 50A to 50D, 
which are formed of high speed valves, and with mass-flow controllers 52A 
to 52D. 
The gas supply lines 48A to 48D are combined into one line 56, which is 
connected to a process gas source 58 storing a reactive gas, such as 
C.sub.4 F.sub.8 gas, and provided with an ordinarily open/close valve 54. 
As described later, the mass-flow controllers 52A to 52D and the 
time-sharing open/close valves 50A to 50D are controlled by a gas supply 
control section 60, such as a micro-computer. In particular, the 
time-sharing open/close valves 50A to 50D are independently controlled 
over their open/close operation, i.e, start and stop of gas supply, in a 
time-sharing manner. 
The inactive gas spouting holes 38 coaxially arranged as described above 
communicate with four inactive gas head grooves 62, which are coaxially 
formed in the head body 42, through passages 64. The four inactive gas 
head grooves 62 are connected to one inactive gas supply line 66 in 
common. The gas supply line 66 is divided into two lines 72A and 72B 
through an open/close valve 68 and a mass-flow controller 70. One of the 
lines 72A is connected to a gas source 76 storing an inactive gas, such as 
Ar gas, for initiating and uniformly keeping plasma, through an ordinarily 
open/close valve 74, while the other line 72B is connected to a gas source 
80 storing an inactive gas, such as N.sub.2 gas, for a purging operation, 
through an ordinarily open/close valve 80. The open/close valve 68 and 
mass-flow controller 70 are also controlled by the gas supply control 
section 60. 
Although the four inactive gas head grooves 62 are coaxially formed in this 
embodiment, another structure may be adopted to spout an inactive gas from 
the entirety of the gas spouting surface. For example, as shown in FIG. 4, 
an inactive gas head groove 62 formed of a circular thin bore may be used 
in place of the four inactive gas head grooves. Further, inactive gas head 
grooves may be arranged to radially extend from the center of the head 
body. 
A coolant room 82 is formed in the head body 42. A coolant for temperature 
adjustment, such as liquid flurocarbon is introduced in the coolant room 
82 through a coolant supply pipe (not shown), so that the coolant is 
circulated in the coolant room 82. The cold of the coolant is transmitted 
from the coolant room 82 to the electrode plate 40 to cool the electrode 
plate down to a predetermined temperature. The heatexchanged coolant is 
exhausted to the outside of the process field through a coolant exhaustion 
pipe (not shown). The electrode plate 40 is set at a temperature higher 
than that of the surface of the wafer W, such that radicals are directed 
to the wafer W and are not deposited on the surface of the electrode plate 
40. 
The shower head 30 having the above described structure is easily 
manufactured by dividing it into a plurality of blocks. 
An electric feeder rod 84 is connected to the head body 42. An RF power 
supply 88, which outputs an RF power of, e.g., 13.56 MHz, for generating 
plasma is connected to the electric feeder rod 84 by a wiring line 90 
through a matching circuit 86 including, e.g., a decoupling capacitor. 
Where the wafer W is 8 inches in size, the characteristic impedance of the 
line 90 between the RF power supply 88 and the matching circuit 86 is set 
at about 50 ohms, as on the susceptor side. However, the impedance on the 
upper electrode (head) side is decreased in accordance with an increase in 
the surface area of the wafer W. For this reason, where the wafer W is 300 
mm in size or a size larger than 300 mm, the characteristic impedance of 
the line 90 between the RF power supply 88 and the matching circuit 86 is 
set to be less than 50 ohms. For example, where the wafer W is 300 mm in 
size, the output impedance of the RF power supply 88 and the 
characteristic impedance of the line 90 are set to be from about 20 ohms 
to about 30 ohms. 
In other words, where the wafer W has a larger size and the impedance on 
the susceptor 8 side is decreased, the impedance of the line 90 on the 
head 30 side is set to be lower. By doing so, impedance matching is 
obtained between the susceptor and head sides, thereby suppressing power 
loss. 
An exhaustion pipe 92 communicating with vacuum exhausting means (not 
shown), such as a turbo molecular pump, is connected to a side wall of the 
process chamber 4. The process field in the process chamber 4 can be 
vacuum exhausted down to a predetermined decreased pressure by the 
exhausting means. 
A load lock chamber 96 is connected to a side wall of the process chamber 4 
through a gate valve, which can be hermetically opened and closed. The 
wafer W to be processed is transferred between the process chamber 4 and 
the load lock chamber 96 by a transfer means (not shown), such as a 
transfer arm, arranged in the load lock chamber 96. 
An explanation will be given in relation to an operation of the plasma 
etching apparatus 2 having the above described structure. It will be 
assumed that a silicon oxide film on a wafer having a silicon substrate is 
to be etched, using the plasma etching apparatus 2. 
At first, a wafer W to be processed is transferred by the transfer means 
from the load lock chamber 96 to the process chamber 4 and is mounted onto 
the electrostatic chuck 16, after the gate valve 94 is opened. The wafer W 
is attracted and held on the electrostatic chuck 16 by applying a power 
from the DC power supply 20. Then, the process chamber 4 is 
vacuum-exhausted by the exhausting means after the transfer means is 
retreated to the load lock chamber 96. 
Meanwhile, the ordinarily open/close valve 54 is opened and the 
time-sharing open/close valves 50A to 50D are opened and closed in a 
time-sharing manner, so that C.sub.4 F.sub.8 gas is supplied from the 
process gas source 58 while its flow rate is controlled by the mass-flow 
controllers 52A to 52D. Further, the open/close valves 68 and 74 are 
opened, so that Ar gas is supplied from the Ar gas source 76 while its 
flow rate is controlled by the mass-flow controller 70. 
The Ar gas for initiating and uniformly keeping plasma reaches the shower 
head 30 through the inactive gas supply line 66, and flows into the 
inactive gas head grooves 62 coaxially arranged. Then, the Ar gas is 
supplied into the processing space between head 30 and susceptor 8, 
through the passages 64 and the inactive gas spouting holes 38 arranged 
all over the gas spouting surface 34. 
On the other hand, the C.sub.4 F.sub.8 gas used as a reactive gas for 
etching flows into the reactive gas head grooves 44A to 44D through the 
respective reactive gas supply lines 48A to 48D. Then, the C.sub.4 F.sub.8 
gas is supplied into the processing space through the passages 46 and the 
groups of the reactive gas spouting holes 36A to 36D in a time-sharing 
manner. 
While the Ar gas and C.sub.4 F.sub.8 gas are supplied, the process chamber 
4 is exhausted, so that inside of the process chamber is kept at a 
predetermined pressure of, e.g, about 1 Pa. 
Under such conditions, an RF power for generating plasma is applied to the 
shower head 30 from the RF power supply 88 and an RF power for self-bias 
is applied to the susceptor 8 from the RF power supply. By doing so, the 
gases are turned into plasma by an electric field generated between the 
susceptor 8 and the shower head 30, so that a layer of, e.g., SiO.sub.2 on 
the wafer W is etched by the plasma. During etching, the susceptor 8 and 
the shower head 30 are cooled down to a predetermined temperature by a 
coolant flowing therein. 
The least amount of Ar gas for initiating and uniformly keeping plasma is 
continuously supplied into the process space from all the inactive gas 
spouting holes 38 during etching, so as to stably generate plasma all over 
the process space. In contrast, the reactive gas is supplied into the 
process space while the time sharing open/close valves 50A to 50D 
corresponding to the grooves, respectively, are opened and closed in a 
time-sharing manner by means of electric signals or pneumatic pressure 
under control of the gas supply control section 60. As a result, the 
amount of gas supplied per unit time is decreased, so that no problems 
arise where the exhausting performance is limited. 
In other words, the residence time of the gas per unit area in the process 
space in the case of processing a 300-mm (12-inch) wafer can be almost the 
same as that in the case of processing an 8-inch wafer, without changing 
the exhausting performance. It follows that planar uniformity of a plasma 
process can be high without a decrease in its processing rate. 
Manners of supplying the reactive gas will be explained in detail. 
FIGS. 5A and 5B are a timing chart showing operation of valves and a view 
showing the order of spouting a reactive gas, respectively, in a first 
pattern of gas spouting. As shown in FIG. 5A, the open/close valve 68 for 
the Ar gas is continuously opened during etching so that the Ar gas is 
continuously supplied from the entirety of the gas spouting surface. In 
contrast, the time-sharing open/close valves 50A to 50D are repeatedly 
opened and closed to supply the reactive gas in a time-sharing manner, 
such that, e.g., each valve is opened for a period of time T of 1 second 
at intervals of 3 seconds. In this case, as shown in FIG. 5B, the groups 
of reactive gas spouting holes 36A to 36 D are repeatedly scanned from the 
center to the periphery in the sequential order of the first group (36A), 
second group (36B), third group (36C) and fourth group (36D). 
Note that the numerals in FIG. 5 indicate the order of supplying the 
reactive gas. Since the inactive gas is continuously supplied overall, it 
is not indicated in FIG. 5B. In the following drawings, this indication 
manner will be also adopted. Intervals and flow rates of the time-sharing 
open/close valves of the respective groups are optimized in consideration 
of parameters, such as etching rate, etching selectivity, etched shaped, 
and process uniformity. 
FIGS. 6A and 6B are a timing chart showing operation of valves and a view 
showing the order of spouting a reactive gas, respectively, in a second 
pattern of gas spouting. 
In the second pattern, an operation reverse to that of the first pattern is 
carried out. Namely, in this case, the groups of reactive gas spouting 
holes 36A to 36D are repeatedly scanned from the periphery to the center 
in the sequential order of the fourth group (36D), third group (36C), 
second group (36B) and first group (36A). 
FIGS. 7A and 7B are a timing chart showing operation of valves and a view 
showing the order of spouting a reactive gas, respectively, in a third 
pattern of gas spouting. the reactive gas spouting holes may be divided 
into a plurality of groups other than four groups, so as to supply and 
stop the reactive gas in a time-sharing manner. 
Further, the present invention is not limited to a coaxial arrangement of 
the gas spouting holes as shown in this embodiment. Other arrangements may 
be adopted, as far as the reactive gas can be supplied in a time-sharing 
manner. 
FIG. 9 is a structural view showing a shower head having a gas spouting 
surface on which groups of gas spouting holes are linearly arranged. In 
FIG. 9, the inactive gas spouting holes 38 are indicated with black dots 
while the reactive gas spouting holes 36 are indicated with white dots. 
The gas spouting holes 36 and 38 are linearly arrayed in longitudinal 
directions in FIG. 9, and the reactive gas spouting holes 36 and the 
inactive gas spouting holes 38 are alternately arrayed in latitudinal 
directions. The reactive gas spouting holes are divided into eight groups 
(36A to 36H) in accordance with the longitudinal arrays in FIG. 9. The 
eight groups (36A to 36H) respectively communicate with reactive gas 
supply lines 48A to 48H respectively provided with time-sharing open/close 
valves 50A to 50H and mass-flow controllers 52A to 52H, which are 
respectively and independently controlled. 
In the third pattern,the reactive gas is supplied such that the coaxial 
groups of the reactive gas spouting holes are alternately selected, i.e., 
in a non-sequential order relative to the arrayed order of the groups. 
Namely, in this case, the groups of reactive gas spouting holes 36A to 36D 
are repeatedly scanned in the non-sequential order of the first group 
(36A), third group (36C), second group (36B) and fourth group (36D). 
FIGS. 8A and 8B are a timing chart showing operation of valves and a view 
showing the order of spouting a reactive gas, respectively, in a fourth 
pattern of gas spouting. 
In the fourth pattern, the reactive gas is supplied such that the inward 
scanning and the outward scanning of the coaxial groups of reactive gas 
spouting holes are concurrently performed. Namely, in this case, the 
groups of reactive gas spouting holes 36A to 36D are repeatedly scanned in 
the order of the first and fourth groups (36A and 36D), second and third 
groups (36B and 36C), third and second groups (36C and 36B), and fourth 
and first groups (36D and 36A). In other words, the reactive gas is 
supplied from the two groups of the reactive gas spouting holes at each 
time. 
As an example, the reactive gas spouting holes are divided into four groups 
in this embodiment. Instead, The time-sharing open/close valves 50A to 50H 
are controlled to open and close in a predetermined order and in a 
time-sharing manner, so that the reactive gas is supplied in units of a 
group and in a time-sharing manner. In this case, the least amount of the 
inactive gas for initiating and uniformly keeping plasma is also 
continuously supplied from the entirety of the gas spouting surface. 
FIGS. 10A and 10B are views showing different patterns of gas spouting, 
which are performed with the shower head shown in FIG. 9. In the pattern 
shown in FIG. 10A, a line 98 representing a selected and gas spouting 
state of each group of the reactive gas spouting holes 36 is horizontally 
moved in parallel from one end toward the center of the head. In the 
pattern shown in FIG. 10B, two lines 98 are horizontally moved in parallel 
from the center of the head toward right and left ends. 
Further, in the present invention, it is possible to design groups of 
reactive gas spouting holes to be selected in a time-sharing manner, as 
shown in FIGS. 11 to 13. In FIGS. 12 and 13, the numerals "1" to "4" 
indicate the order of spouting the reactive gas. 
In the embodiments shown in FIGS. 11 to 13, the number of reactive gas 
spouting holes selected at the same time to spout the gas is constant, 
i.e, the respective numbers of selected holes are the same. In this case, 
the least amount of the inactive gas for initiating and uniformly keeping 
plasma is also continuously supplied from the entirety of the gas spouting 
surface. 
In a shower head 30 shown in FIG. 11, a line 98 representing a selected and 
gas spouting state of each group of reactive gas spouting holes 36 is 
rotated about the center of a gas spouting surface 34, so that the groups 
of reactive gas spouting holes are selected in a time-sharing manner. 
In a shower head 30 shown in FIG. 12, a gas spouting surface 34 is 
essentially uniformly divided into a plurality of regions, such as four 
groups 99, in an angular direction. A number of reactive gas spouting 
holes belonging to each region 99 constitute one group. The groups are 
selected in a time-sharing manner. 
In a shower head 30 shown in FIG. 13, a gas pouting surface 34 is 
essentially uniformly divided into a plurality of regions 100 arrayed in a 
matrix format. In FIG. 13, a single region 100 is indicated with hatching. 
Each one of groups of reactive gas spouting holes to be selected in a 
time-sharing manner, such as four groups, has one spouting hole in every 
region 100. 
Note that in place of C.sub.4 F.sub.8 used as the reactive gas in the above 
described embodiments, other CF-based gas, such as CH.sub.4, CHF.sub.3, 
CH.sub.2 F.sub.2, CH.sub.3 F, C.sub.2 F.sub.6, C.sub.2 H.sub.2 F.sub.2, or 
C.sub.3 F.sub.3, may be used. CO and O.sub.2 may be included in the 
reactive gas. Further, the reactive gas may be diluted with an inactive 
gas, such as Ar gas. On the other hand, in place of Ar gas used as the 
inactive gas for initiating and uniformly keeping plasma, other inactive 
gas, such as He, Xe, or Kr gas, may be used. 
Further, in place of a plasma processing apparatus In of the parallel plate 
type explained in the above described embodiments, the present invention 
may be applied to a plasma processing apparatus of another type, such as 
ICP type, or ECR type. 
Furthermore, a plasma processing apparatus according to the present 
invention may be applied to a CVD, ashing, or sputtering apparatus other 
than an etching apparatus. As a target object to be processed other than a 
semiconductor wafer, an LCD substrate or the like is included. 
With a plasma processing method and apparatus, the following advantages are 
obtained. 
The least amount of an inactive gas for initiating and uniformly keeping 
plasma is continuously supplied during a process to make plasma density 
uniform, while a reactive gas is supplied in a time-sharing manner to scan 
the entirety of a gas spouting surface in a predetermined pattern, so that 
the gas flow rate per unit time is decreased as a whole. 
As a result, even where a target object has a large surface area, a high 
vacuum level and a gas residence time per unit surface area in a process 
space can be ensured sufficiently to perform a plasma process. It follows 
that a plasma process can be performed at a high planar uniformity and a 
high processing rate. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details and representative embodiments shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.