Vacuum processing apparatus

A vacuum processing apparatus includes a process chamber capable of being evacuated and a gas quantity detector for outputting a gas quantity signal corresponding to a partial pressure of each kind of gas contained in the process chamber. The gas quantity detector has a detection sensitivity set in response to a sensitivity calibration signal externally supplied and generates the gas quantity signal at the set detection sensitivity. A controller receives the gas quantity signal output from the gas quantity detector and outputs the sensitivity calibration signal to the gas quantity detector so that a magnitude of the gas quantity signal for one reference gas selected from gasses contained in the process gas becomes near a target value. Vacuum processing techniques are provided for stably detecting the content of impurity gas by calibrating the sensitivity of the gas quantity detector.

BACKGROUND OF THE INVENTION 
a) Field of the Invention 
The present invention relates to a vacuum processing apparatus, and more 
particularly to a vacuum processing apparatus for processing a workpiece 
by introducing processing gas into a vacuum chamber. 
b) Description of the Related Art 
Impurity gas in a process chamber of a vacuum processing apparatus such as 
a vacuum sputtering apparatus has been detected heretofore with a mass 
analyzer mounted in the process chamber, through differential evacuation 
of the inside of a sensor of the mass analyzer. Alternatively, a mass 
analyzer is mounted on a cryopump for evacuating the inside of a process 
chamber to measure a partial pressure of impurity gas. Abnormal states 
such as leakage of the vacuum apparatus can be detected by measuring the 
amount of impurity gas. 
A mass analyzer typically uses an amplifier such as a secondary electron 
multiplier for amplifying small ion current. As the mass analyzer 
continues to measure gas partial pressure for a long time, the gain of the 
secondary electron multiplier lowers because of contaminant attached to 
the secondary electron multiplier or native oxide films or the like formed 
on the secondary electron multiplier, or the position of a peak detection 
signal of each mass may shift from a normal position on the mass number 
coordinate axis. 
Such a lowered gain of the secondary electron multiplier or a position 
shift of a peak detection signal makes difficult to correctly measure a 
partial pressure of impurity gas. 
The partial pressure of impurity gas fluctuates with time. A partial 
pressure measured with a mass analyzer is an instantaneous value. 
Therefore, even a momentary abnormal value of a gas partial pressure which 
does not substantially affect vacuum processing may be detected as an 
abnormal state of the vacuum processing apparatus. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide vacuum processing 
techniques allowing a stable measure of the content of impurity gas by 
calibrating the sensitivity of a gas content detector. 
It is another object of the present invention to provide vacuum processing 
techniques allowing to neglect a momentary abnormal value of an impurity 
gas content and to detect only an abnormal value which substantially 
affects vacuum processing. 
According to one aspect of the present invention, there is provided a 
vacuum processing apparatus comprising: a process chamber capable of being 
evacuated; gas introducing means for introducing process gas into said 
process chamber; a gas quantity detector for outputting a gas quantity 
signal corresponding to a partial pressure of each kind of gas contained 
in the process chamber, the gas quantity detector having a detection 
sensitivity set in response to a sensitivity calibration signal externally 
supplied and generating the gas quantity signal at the set detection 
sensitivity; and control means for receiving the gas quantity signal sent 
from the gas quantity detector and outputting the sensitivity calibration 
signal to the gas quantity detector so that a magnitude of the gas 
quantity signal for one reference gas selected from gasses contained in 
the process gas becomes near a target value. 
The sensitivity is calibrated so that the magnitude of the gas quantity 
signal for the reference gas becomes in an allowable range. A relative 
concentration of impurity gas in process gas can be measured by monitoring 
the magnitude of the gas quantity signal of impurity gas in the process 
chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic diagram showing the structure of a sputtering 
apparatus according to an embodiment of the invention. An airtight process 
chamber 1 is coupled via a main valve 2 to a cryopump 3 to evacuate the 
inside of the process chamber 1. A gas pipe 15 communicates with the 
inside of the process chamber 1 to introduce process gas into the process 
chamber 1. The inflow amount of the process gas is controlled by a flow 
control valve 16 connected to the gas pipe 15. 
A quadrupole mass analyzer 4 is coupled to the process chamber 1. The 
inside of the mass analyzer is subjected to differential evacuation by a 
turbo molecule pump 6. The turbo molecule pump 6 is first roughly 
evacuated by a roughing vacuum pump 7. The mass analyzer 4 is constituted 
of an ionizing unit for ionizing gas, a separation unit for separating 
ionized gas into respective masses, and a secondary electron multiplier to 
which gasses of respective masses separated by the separation unit are 
introduced. A gain of the secondary electron multiplier is variably 
controlled by a sensitivity control signal supplied from a mass analyzer 
controller 8. 
Another mass analyzer 5 is coupled to the cryopump 3 which analyzer 
measures partial pressures of various gasses in the cryopump 3. The mass 
analyzer 5 has the structure similar to the mass analyzer 4 and the gain 
of its secondary electron multiplier is also controlled by the mass 
analyzer controller 8. Signals corresponding to gas partial pressures 
measured with the mass analyzers 4 and 5 are supplied to the mass analyzer 
controller 8. 
A controller 13 for the sputtering apparatus adjusts a process gas flow by 
controlling the flow control valve 16, and sends various signals to be 
described later to the mass analyzer controller 8. 
A bar code reader 10 reads a bar code 12 attached to a wafer carrier 11 
which stores a plurality of wafers, the read bar code being supplied to 
the mass analyzer controller 8. 
A storage device 14 has a storage area corresponding to the bar code 
attached to each wafer carrier 11. The mass analyzer controller 8 stores 
gas partial pressure information received from the mass analyzers 4 and 5 
in the storage area corresponding to the bar code of the wafer carrier 11 
under process. The gas partial pressure information is also sent to a host 
computer 9 which performs concentrated management of the gas partial 
pressure information. 
FIG. 2 is a plan view showing the outline of the sputtering apparatus shown 
in FIG. 1. Two process chambers 1A and 1B are coupled via gate valves to a 
transport chamber 20. Also coupled via gate valves to the transport 
chamber 20 are a preliminary heating chamber 21, a cooling chamber 22, a 
load lock chamber 23, and an unload lock chamber 24. A robot arm 25 is 
installed in the transport chamber 20 to transport a process wafer to and 
from each chamber coupled to the transport chamber 20. 
In the process chambers 1A and 1B, films are deposited on the wafers by 
sputtering. In the preliminary heating chamber 21, the wafer is heated 
preliminarily before the film is deposited. In the cooling chamber 22, the 
wafer is cooled down near to the room temperature after the film is 
deposited. 
Wafer carriers 11A and 11B housing wafers to be processed are placed on a 
wafer carrier stand 28. The wafer carriers 11A and 11B have bar code 
labels 12A and 12B affixed thereto. The wafer carriers 11A and 11B to be 
processed are transported into the load lock chamber 23 by a robot arm 26, 
and during this transport the lot number is read with the bar code reader 
10. 
Each wafer transported into the load lock chamber 23 is transported into 
the preliminary heating chamber 21 and pre-heated. The pre-heated wafer is 
then transported into the process chamber 1A or 1B to deposit a film 
thereon by sputtering. After this sputtering, the wafer is transported 
into the cooling chamber 22 and cooled down near to a room temperature. 
The cooled wafer is housed in a wafer carrier in the unload lock chamber 
24. 
After all wafers of one lot are processed, the wafer carrier in the unload 
lock chamber 24 is picked up by a robot arm 27 and placed on the wafer 
carrier stand 28. Wafer carriers 11C and 11D carry wafers subjected to the 
sputtering process. 
Next, sputtering by the sputtering apparatus shown in FIGS. 1 and 2 will be 
described with referent to FIGS. 1 to 3. Ar is used as sputtering gas and 
one of the process chamber 1A and 1B shown in FIG. 2 is used in the 
following description by way of example. The description of preliminary 
heating, cooling, and other processes for wafers is omitted. 
FIG. 3 is a flow chart demonstrating the sputtering process of one lot. At 
step s1 a lot process starts. For example, one lot has fifty wafers to be 
processed. These fifty wafers are housed in one wafer carrier 11. The 
wafer carrier 11 has a bar code label 12 affixed thereto, the bar code 
label having a bar code representative of a lot identification number. 
As the lot process starts, the wafer carrier 11 is transported into the 
load lock chamber 23 (FIG. 2). At this time, the lot number of the lot to 
be processed is read with the bar code reader 10. The lot number read with 
the bar code reader 10 is supplied to the mass analyzer controller 8. The 
first wafer of the lot is placed in the process chamber 1. 
At step s2, the controller 13 manipulates the flow control valve 16 to 
introduce sputtering gas into the process chamber 1. The controller 13 
notifies the mass analyzer controller 8 of the wafer number of the first 
wafer in the process chamber 1. This wafer number is an identification 
number of each wafer of one lot. 
At step s3, plasma is generated in the process chamber to start film 
formation. The mass analyzers 4 and 5 generate ion currents proportional 
to respective gas partial pressures in the process chamber 1. The ion 
current value corresponding to each gas partial pressure is sent to the 
mass analyzer controller 8. 
FIG. 4 shows an example of the results of gas partial measurements by the 
mass analyzer 4 or 5. The abscissa represents a mass number of molecule or 
atom, and the ordinate represents an ion current value in an optional 
scale corresponding to a gas partial pressure. Peaks appearing at mass 
numbers 2, 18, 28, 32, and 44 correspond to H.sub.2, H.sub.2 O, N.sub.2, 
O.sub.2, and CO.sub.2, respectively. Large peaks corresponding to .sup.40 
Ar appear at mass numbers 20 and 40, and a small peak corresponding to 
.sup.36 Ar appears at a mass number 36. 
A concentration of impurity gas relative to process gas Ar can be measured 
from the ion current value for the impurity gas obtained when the ion 
current value for Ar takes a certain target value at the adjusted gain of 
the mass analyzer. However, the probability of an isotope .sup.40 Ar is 
dominant in Ar gas, and the ion current value for .sup.40 Ar is usually 
larger than the upper limit of the measurable range of the mass analyzer 4 
or 5. Therefore, it is difficult to adjust the sensitivity of the mass 
analyzer and to measure the concentration of the impurity gas based on 
.sup.40 Ar signal. 
In this embodiment, the gain of the secondary electron multiplier of the 
mass analyzer is adjusted so that the ion current value for .sup.36 Ar 
takes a certain target value. If the ion current value for a stable 
isotope contained at a small percentage in process gas having a plurality 
of atom isotopes is adjusted to take a certain target value, the ion 
current value for impurity gas can be measured. The probability of .sup.36 
Ar is far less than that of .sup.40 Ar in Ar gas, and the difference 
between the ion current values for .sup.36 Ar and for the impurity gas is 
not so large. Also, the ion current for .sup.36 Ar is stable. Therefore, 
the concentration of impurity gas can be easily measured. 
At step s4 shown in FIG. 3, the sensitivities of the mass analyzers 4 and 5 
are calibrated so that the ion current value for .sup.36 Ar takes a 
certain target value. This sensitivity calibration is executed by sending 
a sensitivity calibration signal from the mass analyzer controller 8 to 
the mass analyzers 4 and 5. In response to the received sensitivity 
calibration signal, the mass analyzers 4 and 5 increase or decrease the 
gains of the secondary electron multipliers. 
The mass analyzer controller 8 stores information corresponding to ion 
current values at predetermined mass numbers, i.e., information 
corresponding to partial pressures of impurity gasses, in the storage 
device 14 at a storage area designated by the wafer number and lot number 
under process. The information stored in the storage device is referred 
to, for example, for product inspection after a lot process. 
At step s5, plasma is extinguished to stop the film formation. At step s6, 
introducing the sputtering gas is stopped. Next, at step s7 the wafer 
deposited with a film is picked up from the process chamber 1 and a new 
wafer is placed in the process chamber 1. The controller 13 notifies the 
mass analyzer controller 8 of the wafer number of the new wafer. 
At step s8 the ion current value for .sup.36 Ar immediately before the 
sputtering gas is stopped being introduced, is compared with the target 
value. If the measured ion current is equal to the target value or it is 
in an allowable range, the process advances to step s9, whereas in the 
other case the process returns to step s2 to execute steps s2 to s7 for 
the new wafer. 
In the above manner, steps s2 to s8 are repeated until the ion current 
value for .sup.36 Ar becomes equal to the target value or in the allowable 
range. 
FIG. 5A shows an example of a change with time of the ion current value for 
.sup.36 Ar during the execution of steps s2 to s8. Times t.sub.11, 
t.sub.21, and t.sub.31 correspond to the introduction of sputtering gas 
(step s2 in FIG. 3), times t.sub.12, t.sub.22, and t.sub.32 correspond to 
the start of film formation (step s3), and times t.sub.13, t.sub.23, and 
t.sub.33 correspond to the ends of film formation (step s5) and sputtering 
gas introduction (step s6). 
During the periods from time t.sub.12 to time t.sub.13, from time t.sub.22 
to time t.sub.23, and from time t.sub.32 to time t.sub.33, the 
sensitivities of the mass analyzers 4 and 5 are calibrated. Therefore, 
during this sensitivity calibration, the ion current value for .sup.36 Ar 
gradually comes to the target value I.sub.o. At the time t.sub.33, the ion 
current value for .sup.36 Ar becomes nearly equal to the target value 
I.sub.o. At step s8 of FIG. 3 executed immediately after time t.sub.33, it 
is judged whether the sensitivity calibration is completed and the process 
advances to step s9. 
Once the ion current value for .sup.36 Ar is set in the allowable range of 
the target value, the sensitivities of the mass analyzers are maintained 
constant during one lot process. 
At step s9 shown in FIG. 3, sputtering gas is introduced into the process 
chamber 1 to generate plasma and start film formation. 
At step s10 the ion current values of impurity gasses are measured. The 
mass numbers of impurity gasses to be measured are set in advance in the 
mass analyzer controller 8. Since the ion current value for .sup.36 Ar is 
set near to the target value, the ion current value for impurity gas 
indicates an impurity gas partial pressure relative to the Ar gas partial 
pressure. 
At step s11, plasma is extinguished to terminate film formation and stop 
introducing the sputtering gas. 
At step s12 the wafer with a deposited film is picked up from the process 
chamber 1 and a new wafer is placed in the process chamber 1. The 
controller 13 notifies the mass analyzer controller 8 of the wafer number 
of the new wafer. During the exchange of wafers, a time average of partial 
pressures of impurity gasses measured at step s10 is calculated for each 
of impurity gasses. 
FIG. 6 shows a change with time of the ion current value of one impurity 
gas. The period from time u.sub.i1 to u.sub.i2 (i=1, 2, . . . ) 
corresponds to the period while a film is formed at steps s9 to s11, and 
the period from time u.sub.i2 to time u.sub.(i+1)1 corresponds to the 
period while wafers are exchanged and the gas partial pressure average is 
calculated at step s12. 
As sputter gas is introduced, for example, at time u.sub.11, the ion 
current value for impurity gas momentarily shows a sharp peak. This 
phenomenon has been confirmed empirically. The width of this peak just 
after the introduction of sputtering gas is about one second. FIG. 6 shows 
the peaks higher than an alarm level I.sub.AL. Thereafter, the gas partial 
pressure becomes stable while being slightly changed in a certain range. 
At step s12, during the period from time u.sub.11 to time u.sub.12, a time 
average of ion current value of each impurity gas is calculated to obtain 
an average I.sub.AV. 
At step s13 shown in FIG. 3 the average I.sub.AV is compared with the alarm 
level I.sub.AL. If the average I.sub.AV is higher than the alarm level 
I.sub.AL, the process advances to step s14 to give an alarm. If the 
average I.sub.AV is equal to or lower than the alarm level I.sub.AL, the 
flow advances to step s15. 
In a usual sputtering process, it is supposed that an increase of an 
impurity gas concentration in a very short time duration will not 
adversely affect the film quality. Since the time average of ion current 
is calculated and compared with the alarm level at step s12, an 
unnecessary alarm can be suppressed which otherwise is issued in response 
to a momentary increase of an impurity gas concentration immediately after 
process gas is introduced as described with FIG. 6. 
The width of the peak generated just after the introduction of process gas 
is empirically about one second. In order to absorb such a peak in the 
average calculation, it is preferable to set the ion current measurement 
period for each impurity gas at step s10, to 300 ms or shorter. 
At step s15 it is judged whether all wafers of one lot have been processed. 
If there is a wafer still not processed, steps s9 to s15 are executed for 
such a wafer. If all wafers of one lot have been processed, the process 
advances to step s16. 
At step s16, the wafer carrier housing fifty processed wafers is picked out 
from the unload lock chamber 24. 
In the above embodiment, the sensitivity calibration of the mass analyzer 
is performed while the first and following wafers of one lot are processed 
as illustrated in FIG. 5A. The sensitivity calibration may be performed 
prior to processing the first wafer and thereafter, the wafers may be 
processed. 
FIG. 5B shows a change with time in the ion current value for .sup.36 Ar 
wherein wafers are processed after the sensitivity of the mass analyzer is 
calibrated. Prior to film formation, sputtering gas is introduced at time 
v.sub.11 to perform sensitivity calibration. After the ion current value 
for .sup.36 Ar becomes equal to the target value I.sub.o, film formation 
is executed during the period from time v.sub.12 to time v.sub.13. The 
process after time v.sub.13 is similar to the process after time t.sub.33 
shown in FIG. 5A. 
If the sensitivity calibration of the mass analyzer is performed during the 
wafer processing as illustrated in FIG. 5A, measurement of an amount of 
impurity gas cannot be made until the peak of the ion current value for 
.sup.36 Ar becomes equal to the target value. In contrast, with the method 
of FIG. 5B, measurement of an amount of impurity gas can be performed 
starting from the first wafer. However, its throughput becomes lower than 
the method of FIG. 5A because the wafer processing cannot be performed 
until the sensitivity calibration is completed. 
As the mass analyzer continues to measure partial pressures of impurity 
gasses for a long time, a peak position of ion current of each mass may 
shift from a normal position. This peak position shift may result in an 
inability of measuring a correct amount of impurity gas. It is therefore 
preferable to correct the peak position shift at step s12 shown in FIG. 3. 
In the above embodiment, a film is formed by sputtering. This embodiment 
may be applied to other vacuum processes using process gas in a vacuum 
chamber, such as ion implantation, plasma etching, and plasma enhanced 
CVD. 
Also in the above embodiment, although an ion current value for .sup.36 Ar 
is used as a reference gas for sensitivity calibration of a mass analyzer, 
an ion current value for another gas contained in the process gas may be 
used as a reference gas. In this case, if an isotope contained at a 
maximum percentage in the reference gas among isotope atoms of each 
element constituting the reference gas is used as a reference gas, ion 
current for impurity gas becomes too small or ion current for reference 
gas becomes too large and the amount of impurity gas becomes difficult to 
measure. It is therefore preferable to use as the reference gas an isotope 
contained not at a maximum percentage in the reference gas among isotope 
atoms of each element constituting the reference gas. 
The present invention has been described in connection with the preferred 
embodiments. The invention is not limited only to the above embodiments. 
It is apparent that various modifications, improvements, combinations, and 
the like can be made by those skilled in the art.