Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-10-04
2002-07-30
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S336000, C257S344000, C257S345000, C257S409000, C257S549000, C257S550000
Reexamination Certificate
active
06426535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device suited for small-sized elements and a manufacturing method of the same. The present invention relates to, in particular, a semiconductor device capable of preventing impurity concentration from varying in the neighborhood of a pn junction surface and a manufacturing method of the same.
2. Description of the Related Art
It is conventionally necessary to form a pn junction for most of semiconductor devices. In case of an n-channel MIS field effect transistor (metal insulator semiconductor field effect transistor), for example, an n-type source region and an n-type drain region are formed at the surface of a p-type semiconductor substrate. Thus, the pn junctions are formed between the substrate, and the source region and the drain region, respectively. In case of an npn-type bipolar transistor, an n-type emitter region is formed to come in contact with a p-type base region, the p-type base region is formed to come in contact with an n-type collector region. Thus, the pn junctions are formed between the emitter region and the base region and between the base region and the collector region, respectively.
In a semiconductor device having such pn junctions, if the impurity concentration of an n-type region is set higher than that of a p-type region, a pn junction is normally formed by the following method. First, p-type impurities (boron, indium or the like) are injected into a predetermined region of a substrate. N-type impurities (arsenic, phosphorous, antimony or the like) having a concentration higher than that of the p-type impurities are injected only into a region to form an n-type region by means of ion implantation or thermal diffusion. If n-type impurities are injected by means of ion implantation, heat treatment is conducted to activate the impurities. As a result, a pn junction in which the impurity concentration of the n-type region is higher than that of the p-type region, can be formed.
In case of forming an n-channel MIS type FET, in particular, a pn junction is normally formed by the following method. First, p-type impurities are injected into a semiconductor substrate. A gate insulating film is formed on the surface of the semiconductor substrate and a gate electrode is formed on the gate insulating film. Using the gate electrode as a mask, n-type impurities are injected into the surface of the semiconductor substrate by ion implantation. Thereafter, to activate the impurities, heat treatment is conducted. As a result, an n-type source region and an n-type drain region are formed in the region in which the n-type impurities are injected. Obviously, in either case, it is necessary to conduct heat treatment after injecting impurities so as to thermally diffuse or activate the impurities.
If a pn junction is formed by the above-stated method, however, or if a pn junction (n
+
/p junction) consisting of a p-type region into which boron as p-type impurities is injected and an n-type region having a higher impurity concentration than that of the p-type region, in particular, the spatial distribution of boron is changed by heat treatment. This disadvantageously results in the deterioration of the characteristics of semiconductor elements. This phenomenon does not cause a serious problem to a conventional large-sized semiconductor element. As for recent small-sized semiconductor elements or an MIS-type FET, in particular, it is, however, well known that the variation of the spatial boron distribution has considerably adverse effect on semiconductor element characteristics (D. K. Sadana et al.,: “Enhanced Short Channel Effects in NMOSFETs due to Boron Redistribution Induced by Arsenic Source and Drain Implant”, IEDM Technical Digest, IEEE, 1992, pp. 849-852).
That is to say, if a pn junction consisting of a p-type region into which boron is injected and an n-type region having a higher impurity concentration than that of the p-type region is formed, boron is absorbed into the n
+
region during heat treatment. Due to this, boron concentration is reduced in the vicinity of the boundary line of the n
+
/p junction in the p-type region. If this phenomenon appears in an n-channel MIS-type FET, boron concentration between the source and drain regions is reduced. The reduction of boron concentration is more conspicuous if the distance between the source and drain regions, i.e., a channel length is shorter. Thus, a short channel effect, i.e., the phenomenon that the shorter the channel, the lower the threshold of the FET, is higher, making it difficult to form elements having very small (short channel) dimensions. This phenomenon is particularly serious if an MIS type FET having a channel length of 0.1 &mgr;m or less is formed.
Considering the above, there is proposed a method of manufacturing a field effect transistor to form a source region and a drain region by means of Halo injection or pocket injection (Japanese Patent Application Laid-Open Nos. Hei 6-244196, 8-330587 and 9-181307).
FIGS. 1A and 1B
are cross-sectional views showing the structure of a conventional semiconductor device.
As shown in
FIGS. 1A and 1B
, an element separation insulating film
26
is formed at the surface of a semiconductor substrate
21
. Boron is injected into regions defined by the element separation insulating film
26
and a p-type element region is formed. Also, a gate insulating film
25
and a gate electrode
24
on the gate insulating film
25
are formed. First n-type regions
23
a
for putting a channel region below the gate electrode
24
between themselves are formed at the surface of the element region.
Furthermore, a boron injection region
22
a
or
22
b
into which boron ions are implanted is formed at a channel region side contacting with the n-type region
23
a
in the element region. A sidewall insulating film
27
is formed on the sidewall of the gate electrode
24
. N-type impurity ions are implanted into regions which are not covered with the sidewall insulating film
27
and the second n-type region
23
b
deeper than the n-type region
23
a
is formed. Thus, a source-drain region
23
consisting of the n-type regions
23
a
and
23
b
is formed.
In the conventional semiconductor device constituted as stated above, the boron injection region
22
a
or
22
b
is formed by ion implantation so as to protrude the region toward the channel region side of the n-type region
23
a
and
23
b.
The boron injection region
22
a
or
22
b
is formed by, for example, oblique ion implantation for implanting ions into the element region from the oblique direction with respect to a direction perpendicular to the surface of the substrate
21
.
FIG. 2
is a graph showing the distribution of impurity concentration at the surface of the semiconductor substrate shown in
FIG. 1A
, while the vertical axis indicates impurity concentration and the horizontal axis indicates the position of the semiconductor substrate. In
FIG. 2
, a broken line
36
indicates the concentration of p-type impurities injected into the surface of the semiconductor substrate
21
, a dashed line
34
indicates the concentration of n-type impurities at the surface of the semiconductor substrate
21
. A solid line
35
indicates the concentration of p-type impurities at the surface of the semiconductor substrate
21
after heat treatment.
As shown in
FIG. 1A
, in the conventional semiconductor device, the boron injection region
22
a
is formed so as to protrude the region
22
a
toward the channel region side of the n-type region
23
a
or
23
b.
Therefore, the neighborhood of the boundary line of the n
+
/p junction in the p-type region has a higher boron concentration than the remaining portions in the p-type region. Owing to this, boron isabsorbed into the highly doped n
+
region by heat treatment and boron concentration of the neighborhood of the boundary line of the n
+
/p junction in the p-type region is reduced. Further, boron concentration is increased in the neighborhood
Kumashiro Shigetaka
Takeuchi Kiyoshi
Hutchins, Wheeler & Dittmar
Jackson, Jr. Jerome
NEC Corporation
Ortiz Edgardo
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