Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier – Avalanche diode
Reexamination Certificate
1999-09-14
2001-02-20
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
Avalanche diode
C257S551000, C257S603000, C257S605000
Reexamination Certificate
active
06191466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor devices and more particularly to a diode which prevents the flow of electrons into a peripheral element on a semiconductor substrate and which is superior, for example, in the slope (&Dgr;I/&Dgr;V) of forward bias current.
2. Description of the Background Art
Referring to
FIG. 34
, a conventional diode includes an n-type buried semiconductor layer with a high donor content (which may be referred to as an “n
+
buried layer ” hereinafter)
503
which is formed on a p-type semiconductor substrate (hereinafter, referred to as a “p substrate ”)
504
. An n-type semiconductor region as a cathode region (which may be referred to as an “n-type cathode region ” hereinafter)
501
is formed on n
+
buried layer
503
, and a p-type semiconductor region as an anode region (which may be referred to as a “p-type anode region ” hereinafter)
502
is formed in the vicinity of the n-type cathode region to be in contact with p substrate
504
. It is noted that diodes including the above described diode generally have a cylindrical p-type anode region which is formed on the side surface of the central n-type cathode region. Therefore, the two right and left p-type anode regions in
FIG. 34
constitute the longitudinal section of one cylindrical anode.
The operation principle of the above described diode will be described in the following. The energy band of a junction between p-type anode region
502
and n-type cathode region
501
is shown in FIG.
35
. In
FIG. 35
, a potential barrier Vo is caused at the boundary of the p-type anode region and the n-type cathode region, resulting in an energy difference eVo. The energy band chart is represented for an electron. Thus, the energy difference eVo has to be exceeded in order for electrons produced in the n-type cathode region to flow into the p-type anode region.
In the chart, Ec is energy at the bottom of a conduction band, Ev is energy at the top of a valence band, Efn is chemical potential (Fermi-energy) in the n-type cathode region, and Efp is chmical potential in the p-type anode region.
If voltage is externally applied to a diode in the energy state shown in
FIG. 35
, the energy band changes as shown in
FIG. 36
or
37
.
FIG. 36
shows a case in which positive voltage, relative to n-type cathode region
501
, is applied to p-type anode region
502
(forward bias), indicating that the potential barrier of a depletion layer decreases by an applied voltage V
A
from the level of
FIG. 35
to e(Vo-Va). It facilitates hole movement from p-type anode region
502
to n-type cathode region
501
and electron movement from n-type cathode region
501
to p-type anode region
502
. Thus, current flows from p-type anode region
502
to n-type cathode region
501
.
On the other hand,
FIG. 37
shows a case in which negative voltage, relative to n-type cathode region
501
, is applied to p-type anode region
502
(reverse bias), indicating that the potential barrier of a depletion layer increases by applied voltage V
A
from the level of
FIG. 35
to e(Vo+Va). It reduces the probability of hole movement from p-type anode region
502
to n-type cathode region
501
and electron movement from n-type cathode region
501
to p-type anode region
502
. Thus, the amount of flowing current is very small. Semiconductor devices of the above described type have been improved to have the reverse bias voltage higher than an actual used voltage and widely used as clamp diodes. In other words, the semiconductor devices are used as diodes for circuit protection in case reverse bias surge voltage, for example, which exceeds an actual used voltage is suddenly applied to cathodes.
In the semiconductor device having the above described structure, application of positive voltage, relative to n-type cathode region
501
, to p-type anode region
502
causes electrons to move from n-type cathode region
501
to p-type anode region
502
. Electrons also move from n-type cathode region
501
to p substrate
504
. Therefore, electrons flow from p substrate
504
to an element provided in the vicinity of the diode on the semiconductor substrate, contributing a malfunction of the peripheral element.
In order to solve this problem, a proposal was made to surround the entire side and bottom surfaces of an n-type cathode region by a p
+
buried semiconductor layer (Japanese Utility Model Laying-Open No. 2-146458). It was found out, however, that the problems as described below occur depending on application when a region which originally functions as an anode is made a p
+
region with a high acceptor content. The problems are: (a) when forward bias voltage is applied, the slope (&Dgr;I/&Dgr;V), that is, a current increase for a voltage increase is small in lower voltage, that is, the diode rectification does not occur steeply when positive voltage is applied; and (b) electrons do not move easily to the anode region and therefore the controllability of a diode by diode voltage becomes insufficient.
The following proposal was made as a semiconductor device which avoids the problems of (a) and (b) and prevents the flow of electrons into a peripheral element. In other words, two types of buried semiconductor layers, that is, p and n type buried semiconductor layers are provided between a substrate and a diode formation layer, and the resistance of a guiding region which extends upward from each of the two types of buried semiconductor layers is adjusted so as to form the reverse bias or equal potential relations between the n-type buried semiconductor layer and the p-type buried semiconductor layer (Japanese Patent Laying-Open No. 10-74958).
However, the above described structure cannot prevent the flow of electrons from the cathode through the guiding region to the semiconductor substrate, which bypasses the buried semiconductor layers. Further, adapting the above described structure makes it difficult to miniaturize semiconductor devices. Therefore, the above described structure is insufficient to prevent the flow of electrons into semiconductor substrates in the latest miniaturized and lower-voltage semiconductor devices.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a semiconductor device which is easily miniaturized and achieves various properties as a diode (such as the steep slope (&Dgr;I/&Dgr;V) at the time of forward bias voltage application) and also prevents the flow of electrons into a substrate.
The semiconductor device of the present invention includes a p-type buried semiconductor layer provided at a main surface of a semiconductor substrate, a cathode region formed of an n-type semiconductor layer provided on the p-type buried semiconductor layer, and an anode region formed of a p-type semiconductor layer formed to surround and be in contact with the side surface of the cathode region, the p-type buried semiconductor layer being higher than the anode region in acceptor content, and the p-type buried semiconductor layer being in contact with the bottom surfaces of the cathode region and the anode region.
According to the above described structure, the direct flow of electrons into the semiconductor substrate can be prevented by a conduction band of the buried semiconductor layer, which forms on a high potential barrier resulting from a high acceptor content (p
+
). Meanwhile, the acceptor content of the p-type anode region is lower than that of the buried semiconductor layer, and therefore the potential barrier of a conduction band in the p-type anode region is not high enough to be able to ignore the inflow of electrons. Thus, the slope (&Dgr;I/&Dgr;V) for lower voltage at the time of forward bias voltage application can be increased. In the semiconductor device of the present invention, therefore, the acceptor content of the anode region is set lower than that of the p-type buried semiconductor layer which is aimed at preventing the inflow of electrons. Thus, the proportion of electrons flowing tow
Terashima Tomohide
Yamamoto Fumitoshi
Yamashita Yasunori
Chaudhuri Olik
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Pham Hoai
LandOfFree
Semiconductor device containing a diode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor device containing a diode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device containing a diode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2570500