Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-12-01
2001-11-20
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
With measuring or testing
C438S514000, C438S530000, C250S492210
Reexamination Certificate
active
06319734
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method for establishing conditions of differential injection for manufacturing a semiconductor device.
(b) Description of the Related Art
In order to reduce a short channel effect in a deep sub-quarter micron MOSFET, extremely shallow source/drain regions having a junction depth below 50 nm is required. Low energy injection is one method of realizing such a shallow junction. However, the low injection energy reduces the amount of beam current to lower the productivity.
A differential injection method is employed as an ion injection method which has overcome the above problem. Before describing the differential injection method, an ordinary drift injection method will be described for comparison.
In a drift injecting apparatus shown in
FIG. 1
, an extraction electrode
10
extracts beams from an ion source
12
and injects the beams into a wafer
16
through a beam line
14
. The productivity is poor when the low energy injection is employed by the drift injecting apparatus.
In an ion injection apparatus employing the differential injection method shown in
FIG. 2
, the extraction electrode
10
extracts beams from the ion source
12
at an energy higher than the injection energy to the wafer. The extracted beams pass through the beam line
14
and are injected to the wafer
16
immediately after the speed of the beams is reduced to that corresponding to the desired injection energy by a speed-reducing electrode
18
immediately before the injection.
A beam current having a large energy is obtained in the differential injecting apparatus to elevate the productivity because the energy supplied to the ions by the extraction electrode
10
can be made higher.
However, the differential injection is accompanied with a problem of energy contamination (refer to J. Freeman et al., IIT Conference Proceedings, 357(1992)). Since the ion beams pAss within the beam line, the ion beams interact with atoms and molecules of residual gases in the beam line. The interaction called “charge exchange” proceeds as follows.
A
+
(higher speed ion)+B
0
(lower speed atom)→A
0
(higher speed atom)+B
+
(lower speed ion)
As a result of the interaction, a higher speed ion A
+
is converted into a neutralized ion A
0
. The neutralized ion reaches to the wafer at an energy different from desired injection energy without being affected by an s electric field of the speed-reducing electrode. That is, it may occur that the speed of the neutralized ions is not reduced by the speed-reducing electrode and the ions are injected at the initial speed of extraction from the extraction electrode. Thus, the ions are deeply injected and the depth of the junction is made deeper.
Such neutralized ion injection is called “energy contamination” and the injected ions are called “contaminated ions”. The energy contamination occurring in the differential injection causes deterioration or variations in the characteristics of the device.
The amount of the energy contamination is generally expressed as a ratio (%) between (the amount of dosage when the energy contamination exist) and (the amount of dosage when no energy contamination exist). In order to suppress the deterioration, the amount of the energy contamination should be in the range providing allowable deterioration of the device characteristics The permitted range is, for example, prescribed in the load map of SIA (Semiconductor Industry Association).
Accordingly after obtaining the permitted range of the amount of the energy contamination prescribed in the SIA load map, the device characteristics within the range can be obtained by either {circle around (1)} increasing the degree of vacuum of the beam line in the ion injection apparatus or {circle around (2)} reducing the distance in the beam line, to make the amount of the energy contamination at or below the permitted value.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a method for establishing conditions for manufacturing a semiconductor device having characteristics in the permitted range by evaluating influences of energy contamination to the characteristics.
The present invention provides, in a method for establishing conditions of making an index representing characteristics of a MOSFET in a permitted range by adjusting a degree of vacuum of and/or a distance of a beam line in an ion injection apparatus based on a condition in order to form source/drain regions of the MOSFET by means of differentially injecting ions into a wafer, the improvement including the steps of: making a curve indicating an amount of energy contamination with respect to a junction depth, and determining, as said condition, a permitted amount of energy contamination with respect to a desired junction depth.
In accordance with the present invention, the MQSFET having the characteristics within the permitted range can be obtained, when the source/drain regions of the MOSFET are formed by employing a differential injection apparatus, by preparing the curve indicating the amount of the permitted energy contamination, determining the permitted value of the energy contamination by referring to the curve, and establishing the degree of vacuum of and/or the distance of the beam line in the ion injection apparatus.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.
REFERENCES:
patent: 5969366 (1999-10-01), England et al.
T. Yasunaga, S. Matsuda, S. Shishiguchi, and S. Saito, “Effect of Energy Reduction in Sub-keV Boron Implantation Ultra-Shallow Formation,” 1998 International Conference on Ion Implantation Technology Proceedings, vol. 1, pp. 18-21, Jun. 1998.*
M. Halling and W. Krull, “Quantitative Measurements of Energy Contamination in ULE2 Deceleration,” 1998 International Conference on Ion Implantation Technology Proceedings, vol. 1, pp. 586-589, Jun. 1998.*
J. Freeman et al IIT Conference Proceedings; 1992 p. 357.
Bowers Charles
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
NEC Corporation
Smoot Stephen W.
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