Silicon controlled rectifier structure with guard ring...

Details Silicon controlled rectifier structure with guard ring... Silicon controlled rectifier structure with guard ring...

2002-06-25

2004-09-14

Loke, Steven (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S162000, C257S167000, C257S173000, C257S175000

Reexamination Certificate

active

06791146

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a structure of silicon-controlled rectifier (SCR) in a CMOS (complementary metal oxide semiconductor) device, and more particularly to bridging modified lateral silicon controlled rectifier of first conductivity type (PMSCR) with guard ring controlled circuit for electrostatic discharge (ESD) protection.
2. Description of the Prior Art
SCRs (Silicon controlled rectifier) are knows as thyristors. The SCRs are used extensively in power device application because of the capability to switch from a very high impedance state to a very low impedance state. For the same reason a properly designed SCR can also be a very efficient electrostatic discharge (ESD) protection circuit.
Referring to
FIG. 1
, the PMSCR structure (bridging modified lateral silicon controlled rectifier of first conductivity type)
110
with guard ring is formed within a substrate
100
. The PMSCR structure
110
with guard ring having a first lightly doped well region
112
of a second conductivity type such as N type, and a second lightly doped well region
114
of the first conductivity type such as P type. A N+ region
118
is formed in the first lightly doped well region
112
, and is electrically coupled to the anode
150
, and a P+ region
124
is formed in the second lightly doped well region
114
, and is electrically coupled to the cathode
160
. A P+ region
120
is formed in the first lightly doped well region
112
, and is electrically coupled to the anode
150
. A N+ region
122
is formed in the second lightly doped well region
114
, and is electrically coupled to the cathode
160
. An N+ region
126
is formed in the first lightly doped well region
112
, and is electrically coupled to the anode
150
. A P+ region
128
is formed in the first lightly doped well region
112
and the second lightly doped well region
114
such that the P+ region
128
overlaps a junction
116
between the first lightly doped well region
112
and second lightly doped well region
114
. A field insulator region
130
is formed in the first lightly doped well region
112
, and is formed between N+ region
118
and P+ region
120
. In addition, another field insulator region
132
is formed in the first lightly doped well region
112
, and is formed between the P+ region
120
and N+ region
126
. Then, a field insulator region
134
is formed in the first lightly doped well region
112
, and is formed between the N+ region
126
and P+ region
128
. A field insulator region
136
is formed in the second lightly doped well region
114
, and is formed between the P+ region
128
and N+ region
122
. Next, a field insulator region
138
is formed in the second lightly doped well region
114
, and is formed between the N+ region
122
and P+ region
124
.
In the PMSCR structure, an additional N+ region
126
is used as a guard ring to collect the electrons that from the cathode
160
to the anode
150
, such that when the trigger voltage is applied to the PMSCR structure
110
, the guard ring can prevent damage from voltage latch-up during normal operation. Therefore, the power-zapping immunity of the PMSCR structure can be improved. Nevertheless, in the PMSCR structure
110
, the worse ESD performance since the N guard ring will collect the electrons when SCR triggers.
Referring to
FIG. 2
is a schematic representation showing a PMSCR
210
with an additional N well guard ring structure
214
. The PMSCR with N well guard ring structure
210
is formed within the substrate
200
. The PMSCR with N well guard ring structure
210
having a first lightly doped well region
212
of the second conductivity type such as N type, a second lightly doped well region
214
of the second conductivity type, and a third lightly doped well region
216
of first conductivity type, wherein the second lightly doped well region is used as a guard ring to collect the electrons. An N+ region
224
is formed in the first lightly doped well region
212
, and is electrically coupled to the anode
260
. A P+ region
226
is formed in the first lightly doped well region
216
, and is electrically coupled to the anode
260
. A N+ region
228
is formed in the third lightly doped well region
216
, and is electrically coupled to the cathode
280
. A P+ region
230
is formed in the third lightly doped well region
216
, and is electrically coupled to the cathode
280
. A N+ region
232
instead of P+ region
128
of the PMSCR with N guard ring
110
(as shown in
FIG. 1
) is formed in the second lightly doped well region
214
, and is coupled to a high voltage node
270
. An P+ region
234
instead of the N+ region
126
of the PMSCR with N ring structure
110
is formed between the substrate
200
and the first lightly doped well region
212
, such that the P+ region
234
overlaps a first junction
218
between the substrate
200
and the first lightly doped well region
212
.
Then, a field insulator region
250
is formed in the first lightly doped well region
212
, and is formed between the N+ region
224
and the P+ region
226
. A field insulator region
252
is formed in the first lightly doped well region
212
, and is formed between the P+ region
226
and P+ region
234
. A field insulator region
254
is formed between the substrate
200
and the second lightly doped well region
214
, such that the field insulator region
254
overlaps a second junction
220
between the substrate
200
and the second lightly doped well region
214
. A field insulator region
256
is formed in the second lightly doped well region
214
and the third lightly doped well region
216
, such that the field insulator region
256
overlaps a third junction
222
between the second lightly doped well region
214
and the third lightly doped well region
216
. A field insulator region
258
is formed in the third lightly doped well region
216
. As the PMSCR with the N guard ring structure
110
, the N well guard ring
214
is used to collect the electrons from the cathode
280
toward the anode
260
. Even though the power-zapping immunity is improved when SCR triggers, nevertheless the N well guard ring
214
may attach to the same or another high voltage to collect electrons such that the ESD performance will be degraded.
For PMSCR with guard ring
110
(as shown in
FIG. 1
) or
210
(as shown in FIG.
2
), when the voltage of the anode
150
or
260
rises to the breakdown voltage of the junction between N-well
112
or
212
and P+
128
or
234
, lots of electron-hole pairs will be generated in this junction. Electrons are attracted by the high potential of the anode
150
or
260
, and holes by the low potential of the cathode
160
or
280
. When electrons flow into the anode, the parasitic PNP BJT will turn on and inject holes into P-well
114
or
216
. When holes flow into the cathode, the parasitic NPN BJT will turn on and inject electrons in to N-well
112
or
212
. Thus, these two BJT turn on each other and a positive feedback starts. It causes PMSCR snapback and enters the low-impedance holding region. This holding region can bypass ESD current effectively during ESD event. The power zapping issue, however, will occur if it enters the holding region during normal operation. As a result, N+
126
or N-well
214
guard ring can collect electrons to prevent them from flowing into the anode to turn on the parasitic PNP BJT, and then prevent PMSCR from entering the holding region and causing the power-zapping issue. During ESD event, however, the ESD robustness of PMSCR will be worse since it cannot enter the holding region easily.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a structure with a controlled N guard ring/controlled N well guard ring that is controlled by a control circuit such that the high/low impedance depends on an ESD (electrostatic discharge) even

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