Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-12-30
2004-05-04
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S217000, C438S276000, C438S530000
Reexamination Certificate
active
06730568
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for fabricating a semiconductor device and, more particularly, to a method for fabricating a semiconductor device with an ultra-shallow epi-channel of which the channel length is 100 nm or less.
DESCRIPTION OF THE PRIOR ART
Generally, in transistors such as MOSFETs or MISFETs, the surface area of a semiconductive substrate, which is disposed below a gate electrode and a gate dielectic layer, functions to allow the currents to flow due to the electric field applied to source/drain in a state that a voltage beyond the triggering is applied to the gate electrode. Therefore, this area is called “channel”.
In addition, characteristics of these transistors are determined by the dopant concentration of the channel. Accurate doping of the channel is very important since the general properties such as threshold voltage (V
T
) and drain currents (I
d
) of a transistor are determined by the dopant concentration.
As a doping method of the channel, channel ion implantation (or threshold voltage adjusting ion implantation) using ion implantation method are widely used. The channel structures that can be formed using the above ion implantation method include a flat channel having a constant concentration within a channel in depth, the buried channel formed the channel at a specific depth away from the surface, the retrograde channel having a low surface concentration and whose concentration within the channel increases rapidly in a depth direction, etc.
Among the above channels, the retrograde channel is widely used in a high performance microprocessor of which the channel length is 0.2 m or less. The retrograde channel is formed using heavy ion implantation of In, As, Sb, etc. Since the retrograde channel has high surface mobility due to the low surface dopant concentration, it has been applied to high performance devices with high driving current characteristics.
However, with decreasing the channel length, the required channel depth must be shallower. Also, the ion implantation techniques have limitations when implementing on the formation of retrograde channel of which the channel depth becomes 50 nm or less.
In order to meet these demands, there has been proposed the epi-channel structure in which an epitaxial layer is formed on a channel doping layer.
FIG. 1A
is a cross-sectional diagram of a semiconductor device with a conventional epi-channel structure.
Referring to
FIG. 1A
, a gate dielectric layer
12
and a gate electrode
13
are formed on a semiconductive substrate
11
, and the epi-channel consisting of an epitaxial layer
14
and a channel doping layer
15
is formed on the semiconductive substrate
11
disposed below the gate dielectric layer
12
. A high-concentration source/drain extension (SDE) region
16
and a source/drain region
17
are formed on both sides of the epi-channel.
However, since it is difficult to control dopant loss and diffusion of the channel doping layer
15
due to the process of forming the epitaxial layer and the following thermal process, there is a problem to implement the improved on/off current characteristic required for the high performance device with the epi-channel structure.
In order to solve this problem, there has been proposed a method for implementing a delta doped epi-channel by forming a dual epitaxial layer consisting of a doped epitaxial layer doped in a step shape and an undoped epitaxial layer, as shown in FIG.
1
B.
FIG. 1B
shows the change of a doping profile according to the transient enhanced diffusion (TED) or the thermal budget, followed by the forming of the delta doped epi-channel. Referring to
FIG. 1B
, since the step-like delta doping profile of the epi-channel below the gate dielectric layer (Gox) does not maintain an ideal delta doping profile (P
1
) due to the TED or the thermal budget, there occurs the broadening (P
2
) of the doping profile.
Accordingly, in case where the delta doped epi-channel is formed using the dual epitaxial layer consisting of the doped epitaxial layer and the undoped epitaxial layer, since a low concentration epitaxial layer of 1×10
19
atoms/cm
3
or less cannot be deposited, the diffusion (D) of dopants due to the TED or the thermal budget is too excessive, so that there is a limitation when implementing the delta doped epi-channel of which the channel depth is 30 nm or less.
In order to improve these problems, there is proposed a method in which after forming a delta doped n-channel doping layer having a precisely controlled concentration by ultra low energy boron ion implantation, laser thermal annealing (LTA) process is instantaneously performed to prevent the diffusion of the delta doped n-channel doping layer (referring to FIGS.
2
A and
2
B).
FIGS. 2A and 2B
are cross-sectional diagrams showing the method for fabricating a semiconductor device with an epi-channel formed by ultra low energy ion implantation and by laser thermal annealing (LTA) process.
As shown in
FIG. 2A
, a field oxide layer
22
with shallow trench isolation (STI) structure is formed on a semiconductive substrate
21
, and P-type dopants are ion-implanted into the semiconductive substrate
21
to thereby form P-type well
23
. Sequentially, boron ions are implanted under ultra low energy (1 keV) to form a delta doped channel doping layer
24
.
Then, the laser thermal annealing (LTA) process of 0.36 J/cm
2
to 0.44 J/cm
2
is directly performed without any pre-amorphization for amorphizing a surface of the semiconductor substrate
21
. As can be seen in
FIG. 2B
, the laser thermal annealing process suppress the re-distribution of boron within the channel doping layer
24
, as well as changing the channel doping layer
24
into chemically stable channel doping layer
24
A.
As shown in
FIG. 2B
, an epitaxial layer
25
is selectively grown on the channel doping layer
24
A at a temperature of 600 to 800 to thereby form the super steep retrograde (SSR) epi-channel structure.
Meanwhile, the TED of the delta doped channel doping layer can be prevented by using rapid thermal annealing (RTA) process as well as the laser thermal annealing process.
FIG.
3
A and
FIG. 3B
are the graphs showing the doping profiles of SSR epi-channel formed by selectively epitaxial growth on boron doped specimens of 1 KeV ion implanted or 5 KeV ion implanted, respectively.
As can be seen from
FIGS. 3A and 3B
, in the doping profiles of SSR epi-channel formed using the ultra low energy ion implantation, as the ion implantation energy becomes lower, a distribution range of delta doping becomes narrower. Since this delta doping which is narrowly distributed as shown in
FIG. 3A
can remarkably reduce the junction capacitance of device and the junction leakage current, it is an essential technique in manufacturing the low-power and high-efficiency semiconductor device.
However, the ultra low energy ion implantation has disadvantages that the available energy is limited, since it is difficult to extract enough ion beam currents at such ultra low energy range, as well as the manufacturing time is taken longer.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method for fabricating a semiconductor device with epi-channel structure, which is adapted to overcome an available energy limitation and to improve the productivity by providing the method of SSR epi Channel doping by boron-fluoride compound ion implantation without using ultra low energy ion implantation.
In addition, it is another object of the present invention to provide a method for fabricating the semiconductive device with epi-channel structure adapted to prevent the crystal defects caused by the epitaxial growth on ion bombarded and fluorinated channel doping layer.
In an aspect of the present invention, there is provided a method for forming the epi-channel of a semiconductor device, which comprises the steps of: a) forming a channel doping layer below the surface of a semiconductive substrate by implanting boron-fluoride compound ions containing boron; b) perfor
Hynix / Semiconductor Inc.
Jacobson & Holman PLLC
Picardat Kevin M.
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