Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-06-25
2001-08-28
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
Reexamination Certificate
active
06281512
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an ion implantation system, and more particularly, to an ion implantation system in which the concentration of injected ions is uniform within the target.
2. Description of the Related Art
Ion implantation is a technique for implanting atomic ions into a target by imparting enough energy to the ions for them to penetrate the surface of a target, such as a silicon wafer.
Typical ion implantation systems in a semiconductor device manufacturing line are capable of regulating the concentration of an ion impurity in the range of 10
14
~10
18
atoms/cm
3
. This is an improvement over previous methods such as ion concentration regulation through diffusion. Ion implantation systems are widely used, particularly as the level of integration of semiconductor devices increases, due to their ability to inject the ion impurities to a precise depth.
In general, conventional ion implantation systems comprise a number of components, including an ion source, an ion mass analyzer, and an ion accelerator. At each of these components, power of various levels is applied. Ions generated from an ion source containing source gas are accelerated due to the applied power. The accelerated ions are injected into a wafer placed on the end station.
The voltage levels applied to respective components of the ion implantation system greatly affect the operation of the system. The voltage levels are varied based on factors such as the characteristics of the extraction, the acceleration, and the analysis. The voltage level used is an important factor in determining the dose (i.e., the applied concentration) of the ions to the wafer.
In the conventional ion implantation system, an equal level of high is direct voltage is applied to the ion extractor and the ion accelerator. These components extract and accelerate ions before injection into the target whether they are being used in a pre-acceleration system where extracted ions are accelerated before being mass-analyzed, or in a post-acceleration system, where extracted ions are accelerated after mass-analysis.
A more detailed description of the above described ion implantation systems will now be undertaken with reference to
FIGS. 1
a
-
3
.
FIG. 1
a
is a schematic diagram illustrating a “post-acceleration” ion implantation system
100
. Ions are supplied from an ion supply source
10
having impurities in a gas or solid form, and extracted by an ion-extractor
12
, to which a high voltage is applied. The extracted ion beam
16
includes ions of different masses, which then enter a mass analyzer
14
. Mass analyzer
14
selects ions having a specific mass.
The selected ions enter ion accelerator
18
where they are accelerated to a predetermined energy. The accelerated ion beam
16
is injected into wafer
24
mounted on end station
22
.
Ion extractor
12
, mass analyzer
14
, and ion accelerator
18
are shown in more detail in
FIG. 1
b
. Ion extractor
12
is connected to a variable DC power source
26
, mass analyzer
14
is connected to a power source
28
, and ion accelerator
18
is connected to variable DC power source
30
. Power sources
26
,
28
, and
30
supply power based on the weight of the ions and the desired ion implantation process. A specific power value set at any one of power sources
26
,
28
, and
30
corresponds to specific values at the other two power sources.
In the conventional ion implantation system
100
, DC power is applied to ion extractor
12
and ion accelerator
18
. A concentration distribution of ions injected into wafer
24
versus the depth of the ions in wafer
24
is shown in FIG.
3
. For example, when boron ions (B+) are implanted in the wafer with an acceleration energy of 130 keV, the highest values of the concentration dose (1.9E+17 atoms/cm
3
) occur a certain depth into the wafer (4.0E−7 m). Ion implantation system
100
works well when it is being used to inject the highest concentration of impurities at a specific depth.
An ion implantation system
200
using the conventional “pre-acceleration method” is shown in
FIGS. 2
a
and
2
b
. System
200
is similar to system
100
, the primary difference being that the ion accelerator
18
is placed before the mass analyzer
14
. In particular, DC power sources
26
and
30
are connected to an ion extractor
12
and an ion accelerator
18
. A detailed description of implantation system
200
is omitted because of its similarity to implantation system
100
.
The ion implantation process using the pre-acceleration ion implantation system
200
exhibits process characteristics similar to those of post-acceleration ion implantation system
100
. That is, the graph of
FIG. 3
applies to ion implantation system
200
as well as ion implantation system
100
.
Conventional attempts to implant a uniform concentration of impurities at a specified depth range often did not produce satisfactory results because, as shown in
FIG. 3
, the peak ion concentration occurs in a very narrow positional range in the wafer. To achieve uniform concentration at a specified depth range the implantation process was typically performed repeatedly with the acceleration energy varied in each process.
As described above, the conventional ion implantation process for implanting a specific dose throughout a certain range of depths required varying the acceleration energy values used in the implantation process and repeating the ion implantation process, resulting in wasted process time and decreased productivity.
SUMMARY OF THE INVENTION
The present invention provides an ion implantation system that injects a uniform ion dose to a constant depth of an implanted target by applying both DC (direct current) and AC (alternating current).
More specifically, one aspect of the present invention is directed to an ion implantation system comprising an ion extractor extracting ions from an ion supply based on application of power from one of a variable direct current power source, and a first direct current power source and a first alternating current power source; a mass analyzer receiving the extracted ions and separating the extracted ions based on weight; and an ion accelerator accelerating ions received from the mass analyzer by applying power to the ions from a second direct current power source and a second alternating current power source.
A second aspect of the present invention is directed to an ion implantation system including an ion extractor extracting ions from an ion supply based on application of power from a direct current power source and an alternating current power source; a mass analyzer receiving the extracted ions and separating the extracted ions based on weight; and an ion accelerator for accelerating ions received from the mass analyzer by applying power to the ions from a variable direct current power source.
A third aspect of the present invention is directed to an ion implantation system including an ion extractor extracting ions from an ion supply using power from one of a variable direct current power source, and a first direct current power source and a first alternating current power source; an ion accelerator accelerating ions received from the ion extractor by applying power to the received ions from a second direct current power source and a second alternating current power source; and a mass analyzer receiving the accelerated ions and separating the extracted ions based on weight.
A fourth aspect of the present invention is directed to an ion implantation system including an ion extractor extracting ions from an ion supply using power from a direct current power source and an alternating current power source; an ion accelerator accelerating ions received from the ion extractor by applying power to the received ions from a variable direct current power source; and a mass analyzer receiving the accelerated ions and separating the extracted ions based on weight.
REFERENCES:
patent: 6130436 (2000-10-01), Renau et al.
Jones Volentine PLLC
Nguyen Kiet T.
Samsung Electronics Co,. Ltd.
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