Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2002-04-25
2003-10-28
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S251000
Reexamination Certificate
active
06639230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-energy ion implanter for fabricating a semiconductor device. More particularly, the present invention relates to a high-energy ion implanter, which is capable of detecting abnormal operating conditions of a turbo pump that provides a predetermined vacuum in a stripper, to implant an impurity into a wafer to fabricate a semiconductor device. The present invention prevents yield loss and wafer defects caused by abnormal operating conditions of the turbo pump.
2. Description of the Related Art
Conventionally, a semiconductor device is fabricated by performing several sequential processes, such as photolithography, ion implanting and diffusion, and etching to a wafer. The ion implanting process, one process in the fabrication of a semiconductor device, implants impurities as an ion type into a wafer, thereby providing a semiconductor device with a predetermined electric characteristic.
To ionize an impurity in the ion implanting process, it is necessary to provide a vacuum having a predetermined level. Accordingly, an ion implanter should be equipped with a turbo pump to provide vacuum conditions.
The ion implanter for implanting an impurity as an ion type into a wafer may be typically referred to as a medium current, a high current, or a high-energy ion implanter, according to usages and process conditions. Regardless of the type of ion implanter, however, the relevant principles are similar.
In other words, when the implanting ion accelerates ionized dopants to a wafer surface, the accelerated ion is implanted into a wafer. In this case, dopant amounts and ion implanting depth are closely related to atomic size, ion speed and duration of time the wafer is exposed to an ion implanting beam.
A high-energy ion implanter equips a large acceleration tube to a medium current ion implanter or, additionally, to a high-current ion implanter. Therefore, the size of a high-energy ion implanter is larger than that of any other conventional ion implanter. Additionally, a beam path thereof is long.
Referring to
FIG. 1
, a conventional high-energy ion implanter includes an ion source
100
, a vaporizer cell
101
, an analyzer magnet
102
, a pre-accelerator
103
, a tendetron accelerator
315
, and a beam filter
108
.
In operation, the ion source
100
generates positive ions from boron fluoride (BF
3
) gas, and the vaporizer cell
101
converts the positive ions from the ion source
100
into a desired polarity by utilizing magnesium (Mg). The analyzer magnet
102
separates a desired ion (i.e., a negative ion) from the polarized ions in the vaporizer cell
101
. The pre-accelerator
103
applies a predetermined voltage to the separated ions (i.e., negative ions) from the analyzer magnet
102
and accelerates the separated ions by utilizing voltage differences.
The tendetron accelerator
315
includes a low-energy accelerator
104
, a stripper
105
, a high-energy accelerator
106
and a turbo pump
107
. The low-energy accelerator
104
draws the ions from the pre-accelerator
103
and accelerates the ions for smooth polarity conversion. The stripper
105
eliminates electrons from the ions accelerated from the low-energy accelerator
104
in vacuum conditions by a stripping gas (e.g., nitrogen) to generate positive ions. Next, the high-energy accelerator
106
accelerates the positive ions generated from the stripper
105
. The turbo pump
107
pumps the stripper
105
to provide vacuum conditions therein. The beam filter
108
filters the ion beam accelerated from the high-energy accelerator
106
of the tendetron accelerator
315
in an electrostatic state and implants the ion beam into a wafer transferred from a wafer transfer chamber
109
.
The above described conventional high-energy ion implanter generates positive ions from the gas ionized in the ion source
100
, wherein the ionized gas generated in the ion source
100
is sent to the vaporizer cell
101
. The vaporizer cell
101
changes the polarity of the ions by utilizing magnesium (Mg) and the analyzer magnet
102
separates desired negative ions. More specifically, after initially accelerating the ions in desired energy states (e.g., 100 keV) through the pre-accelerator
103
, the ions are accelerated again in the low-energy accelerator
104
of the tendetron accelerator.
The negative ions accelerated from the low-energy accelerator
104
are converted into positive ions, after the stripping gas (e.g., nitrogen) eliminates electrons in the vacuum conditions applied by the turbo pump
107
. More particularly, the converted ions are accelerated again through the high-energy accelerator
106
and beam ions, which are filtered through the beam filter
108
, are implanted into a wafer transferred from the wafer transfer chamber
109
.
To implant positive ions into a wafer, the turbo pump
107
provides vacuum conditions in the stripper
105
for extracting positive ions only and for eliminating negative ions, by the stripping gas, from the ions accelerated from the low-energy accelerator
104
. Referring to
FIG. 2
, another conventional high-energy ion implanter includes a turbo pump
107
including a circuit breaker
200
for supplying and interrupting power voltages applied from an outside source, a rotatable motor
201
for receiving the power voltages through the circuit breaker, a power transmission unit
205
for transmitting a rotational driving force from the motor
201
through a pulley
202
, a belt
203
, and a shaft
204
, an electric generator
206
for generating predetermined voltages by the driving force transmitted from the power transmission unit
205
, a central processing unit CPU
207
for driving the turbo pump
107
, and a monitor
208
for displaying procedures by the CPU
207
.
The rotational force from the motor
201
, however, is often not normally transmitted to the turbo pump
107
and the generator
206
due to unstable conditions caused by vibrations of the pulley
202
in the power transmission unit
205
, tension fluctuations of the belt
203
, a broken shaft
204
, or the like. Therefore, normal voltages, which are required to operate the pump smoothly and to provide desired vacuum conditions in the stripper
105
, are not applied to the turbo pump
107
from the generator
206
.
Accordingly, ions flowing in from the stripper
105
have inferior ion characteristics due to the abnormal vacuum conditions. Inferior ion characteristics are a cause of metal impurity generation and wafer defects while implanting the ions into a wafer.
Thus, when technical difficulties occur in the power transmission unit
205
, the generator
206
, or the turbo pump
107
, the circuit breaker
200
interrupts the supply of the power voltages to cease operation of the turbo pump
107
and the generator
206
. However, even though difficulties may occur in the turbo pump
107
, the motor
201
, the power transmission unit
205
, or the generator
206
, the conventional high-energy ion implanter may not be able to detect the abnormal operating conditions. Therefore, even though the generator
206
or the turbo pump
107
is not operating normally, the circuit breaker
200
does not perform the circuit interruption and continues to supply the AC power voltages to perform the ion implanting process.
As a result, the vacuum conditions in the stripper
105
are not normal due to abnormal operation of the turbo pump
107
. The abnormal vacuum conditions generate the phenomena of the inferior ion characteristics, and result in yield losses due to an unsuccessful ion implanting process and due to metal impurities.
SUMMARY OF THE INVENTION
A feature of a preferred embodiment of the present invention is to provide a high-energy ion implanter capable of detecting abnormal operating conditions of a turbo pump for providing vacuum conditions in a stripper, while the stripper converts accelerated and flowed-in ions, to interrupt a circuit breaker. Therefore, an ion implanting process is suspended to prevent an unsuccessful ion implanting pr
Kalivoda Christopher M.
Lee John R.
Lee & Sterba, P.C.
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