Semiconductor device having at least one field oxide area and CMOS vertically modulated wells (VMW) with a buried implanted layer for lateral isolation having a first portion below a well, a second portion forming another, adjacent well, and a vertical po

CMOS vertically modulated wells have a structure with a buried implanted layer for lateral isolation (BILLI). This structure includes a field oxide area, a first retrograde well of a first conductivity type, a second retrograde well of a second conductivity type adjacent the first well, and a BILLI layer below the first well and connected to the second well by a vertical portion. This structure has a distribution in depth underneath the field oxide which kills lateral beta while preventing damage near the surface under the field oxide.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to simplification of a manufacturing process 
for complementary semiconductor devices, which are becoming increasingly 
miniaturized and increasingly complex, to a high component-density 
semiconductor device having enhanced resistance to CMOS latch-up, and to 
well formation (single, twin, triple). 
2. Description of the Related Art 
The importance of CMOS technology in the VLSI field has grown, as a result 
of requirements for a high noise margin and low power consumption. 
However, as miniaturization has increased, serious problems have arisen 
with regard to preventing stray thyristor operation which causes the CMOS 
latch-up phenomenon to occur between mutually adjacent portions of an 
n-channel MOSFET and p-channel MOSFET, and with regard to maintaining a 
sufficient level of withstanding voltage between mutually adjacent 
elements. 
Various forms of device configuration and manufacturing process have been 
proposed for overcoming these problems. These proposals include the use of 
a configuration containing wells, formation of a buried high concentration 
layer, and formation of a self-aligned channel stop at the edge of a well 
region. 
Summaries of these various structures and methods have been presented, for 
example, in U.S. Pat. No. 5,160,996 at column 1 line 34 et seq. Additional 
disclosure of this technology appears in the article entitled "MeV 
implantation technology: Next-generation manufacturing with 
current-generation equipment" by Borland and Koelsch in the December 1993 
issue of Solid State Technology. 
SUMMARY OF THE INVENTION 
The present invention solves the following problems: 
1) single, twin and triple well CMOS process simplification: 
a) total number of steps 
b) 2-3 mask levels 
c) manufacturing time and cost reduction 
d) clustering well, isolation and channel implants, and V.sub.t implants 
e) clustering through a masking layer 
2) clustered implant to reduce wafer handling, particles, process 
simplification 
3) Improved CMOS latch-up, SER, .alpha.-particle, GOI, and ESD 
4) improved bulk wafer by optimum denuding techniques 
5) elimination of Epi for 
a) CMOS 
b) SOI wafer bonding 
c) CCD 
6) reduction/elimination of oxygen related implant defects 
The foregoing problems are solved in the following manner 
1) clustered implants up to six into one step 
2) BILLI structure formation for latch-up and single, twin and triple well 
3) Hydrogen and/or nitrogen denudation for improved Cz wafer and epi 
elimination 
The novel features of the invention include the following: 
1) clustered implants 
2) reduction in masks and process for twin and triple well 
3) epi replacement for CMOS, SOI, CCD etc. 
4) latch-up free 
5) hydrogen passivation 
6) oxygen-denuded-zone free 
7) defect free 
8) implant-related-defect free 
The features of the present invention may be summarized as follows: 
1) CMOS semiconductor device manufacturing process simplification and cost 
reduction for NMOS and PMOS transistor fabrication: 
a) single n or p well formation on p- or n-substrates. 
b) twin/double n & p well formation on p- or n-substrates. 
c) triple well formation, surface n & p well plus buried n or p well on p- 
or n-substrate. 
d) Vt implant through a masking layer. 
e) clustered implants; deep retro-well implant/channel stop implant/Vt 
implant. 
deep retro p or n-well implant/channel stop implant. 
channel stop implant/Vt implant 
deep retro p or n-well implant/channel stop implant/Vt implant. 
deep retro p or n-well implant/channel stop implant/deep retro n or p-well 
implant/channel stop implant. 
p or n-well channel stop implant/Vt implant/n or p-well channel stop 
implant/Vt implant. 
deep retro p or n-well implant/channel stop implant/Vt implant/deep retro n 
or p-well implant/channel stop implant/Vt implant. 
f) clustered implants through a masking layer; deep retro-well 
implant/channel stop implant/Vt implant. 
deep retro p or n-well implant/channel stop implant. 
channel stop implant/Vt implant 
deep retro p or n-well implant/channel stop implant/Vt implant. 
deep retro p or n-well implant/channel stop implant/deep retro n or p-well 
implant/channel stop implant. 
p or n-well channel stop implant/Vt implant/n or p-well channel stop 
implant/Vt implant. 
deep retro p or n-well implant/channel stop implant/Vt implant/deep retro n 
or p-well implant/channel stop implant/Vt implant. 
g) elimination of 1 to 4 masking layers. 
h) elimination of up to 4 medium current implants and the associated 
implanters. 
i) improved high energy implanter utilization. 
j) improved high energy implanter productivity by 25%. 
k) cost savings of $25 to $149 per 200 mm wafer. 
l) reduction in masking layer thickness for high energy ion implantation. 
2) Improved CMOS latch-up resistance and device scaling/shrink. 
a) reduction in lateral current gain/lateral beta (B.sub.L). 
b) reduction in vertical lcurrent gain/vertical beta (B.sub.V). 
c) reduction in well resistances (R.sub.W). 
d) reduction in substrate resistance (R.sub.S). 
e) improved n+ to p+ spacing. 
3) Hydrogen and/or nitrogen denudation for improved Cz silicon wafer 
surface properties. 
a) improved device performance 
gate oxide integrity 
oxide QBD 
junction leakage 
device yield 
b) improved oxygen out diffusion 
c) lower surface oxygen 
d) lower surface defect level 
e) equivalent to epi wafer surface quality 
f) improved resistance to surface native oxide 
g) improved wafer surface roughness 
h) pre-process intrinsic gettering for high energy implant device 
processing 
4) BILLI structure plus improved denudation=epi replacement 
a) CMOS technology 
b) CCD technology

Referring to the drawings, and first to FIG. 1 thereof, FIG. 1 shows a low 
cost MeV structure in accordance with the invention at the stage in its 
manufacture at which PMOS devices can be formed in a retrograde n-well and 
NMOS devices in a retrograde p-well. Although at this stage in its 
manufacture neither the PMOS devices nor the NMOS devices have been 
formed, in FIG. 1 PMOS devices are shown, in order to indicate where they 
will be formed in steps subsequent to said stage. Isolation areas 5 
separate adjacent PMOS devices which can be implanted into a retrograde 
n-well formed in a p-type substrate 10. Adjacent to the series of PMOS 
devices in an n-well retrograde p-wells have been formed, into which a 
series of NMOS devices will be implanted in subsequent steps of 
manufacture. The retrograde n-well includes an upper layer 6 wherein 
phosphorus ions have been implanted so as to form phosphorus (n) impurity 
atoms with a density that is produced by 5E12cm-2! and a lower layer 7 
wherein phosphorus ions have been implanted so as to form phosphorus (n) 
impurity atoms with a density that is produced by 3E13cm-2. The retrograde 
p-well includes an upper layer 8 wherein boron ions have been implanted so 
as to form boron (p) impurity atoms with a density that is produced by 
5E12cm-2! and a lower layer 9 wherein boron ions have been implanted so as 
to form boron (p) impurity atoms with a density that is produced by 
3E13cm-2. The term "upper layer" signifies the layer which is nearer the 
active surface of the substrate 10 and is 0.5 .mu.m deep. The term "lower 
layer" signifies the layer which is farther from the active surface of the 
substrate 10 and is 1.2 .mu.m deep. These are retrograde wells because the 
impurity-atom density is higher at the lower part of the well than at the 
upper part of the well. 
The BILLI structure is formed by continuance of the boron layers from the 
depths at which they are formed beneath a thick masking layer, for 
example: comprising at least 2 .mu.m of photoresist to the depths at which 
they are formed in the absence of the thick masking layer. The latter 
depths are under the retrograde n-well, deeper than both the upper layer 6 
and the lower layer 7, and the layers at these depths are designated 
"buried". The boron layers at these depths thus form a "buried implanted 
layer for lateral isolation" or "BILLI" structure, since they surround the 
n-well around the sides and the bottom. This BILLI structure provides best 
latch-up resistance for miminum n+ to p+ spacing even over epi-wafers. 
When combined with optimum denudation, this BILLI structure on bulk Cz 
wafers can lead to epi replacement. 
FIG. 3, in conjunction with FIG. 1, shows a method of forming the BILLI 
structure in accordance with the invention. This method of the invention 
not only has the advantage of resulting in the formation of the novel 
BILLI structure of the invention, but also results in both process 
simplification and cost reducton for single, twin and triple well 
formation. A preferred embodiment of the method of the invention 
comprehends the following steps. First, isolation areas 12 are formed (or, 
alternatively, active areas are formed) in the substrate 10. Then a mask 
11, such as a photoresist mask having a thickness of more than 2.0 .mu.m 
is placed on the surface as shown to block the phosphorus ions of maximum 
energy, and a clustered series of four to six implants are carried out. 
The clustered series of four to six implants may be carried out as follows: 
First, boron ions are directed onto the upper surface of the substrate 10 
with an energy of 2.00 MeV, thereby forming the lower layer 9 of p-type 
material (deep retrograde p-well). Second, without removing the substrate 
10 from the vacuum chamber in which it was irradiated with boron ions, the 
parameters of the ion accelerator are changed, and boron ions are directed 
onto the upper surface of the substrate 10 with an energy of 1.25 MeV, 
thereby forming the upper layer 8 of p-type material (channel stop implant 
or shallow retrograde p-well). As an optional third step, without removing 
the substrate 10 from the vacuum chamber in which it was irradiated with 
boron ions, the parameters of the ion accelerator are changed, and boron 
ions are directed onto the upper surface of the substrate 10 with an 
energy of 750 keV, thereby forming a shallow, thin threshhold voltage 
layer V.sub.t at the surface of the retrograde p-well 8,9. Fourth, without 
removing the substrate 10 from the vacuum chamber in which it was 
irradiated with boron ions, the parameters of the ion accelerator are 
changed, and phosphorus ions are directed onto the upper surface of the 
substrate 10 with an energy of 1 MeV, thereby forming the lower layer 7 of 
n-type material (deep retrograde n-well). Fifth, without removing the 
substrate 10 from the vacuum chamber in which it was irradiated with boron 
ions and phosphorus ions, the parameters of the ion accelerator are 
changed, and phosphorus ions are directed onto the upper surface of the 
substrate 10 with an energy of 450 keV, thereby forming the upper layer 6 
of n-type material (channel stop implant or shallow retrograde n-well). As 
an optional sixth step, without removing the substrate 10 from the vacuum 
chamber in which it was irradiated with boron ions and phosphorus ions, 
the parameters of the ion accelerator are changed, and phosphorus ions are 
directed onto the upper surface of the substrate 10 with an energy of 60 
keV, thereby forming a shallow, thin threshhold voltage layer V.sub.t at 
the surface of the retrograde n-well 6,7. Alternatively, the sixth step 
may comprise directing boron ions onto the upper surface of the substrate 
10 with an energy of 30 keV so as to form this threshhold voltage layer. 
The method of FIG. 3 may be modified by omitting the two optional steps 
and, in lieu thereof, carrying out a medium current blanket Vt implant 
after the M1 step and before the M2 step. Alternatively, the sixth step 
may be omitted and, in lieu thereof, a medium current blanket Vt implant 
may be carried out after the M1 step and before the M2 step. 
The method of FIG. 3 may also be modified to enable certain existing 
installations to take advantage of the principles of the present invention 
in forming a BILLI structure. In such a modification the second step of 
the method of FIG. 3 is omitted, and, after the remaining steps have been 
carried out, the mask 11 is removed and a mask (such as a photoresist mask 
having a thickness of more than 2.0 micrometers) is placed on the surface 
as shown in FIG. 2 to block the boron ions of subsequent additional steps, 
and then boron ions are directed onto the upper surface of the substrate 
10 in a sequence of implants with energies of 750 keV, 300 keV and 20 keV. 
More specifically, the method of the embodiment of the invention shown in 
FIG. 2 comprehends the following steps. First, isolation areas 12 are 
formed (or, alternatively, active areas are formed) in the substrate 10. 
Then a mask 11, such as a photoresist mask having a thickness of more than 
2.0 .mu.m is placed on the surface as shown to block the phosphorus ions 
of maximum energy, and a clustered series of three or four implants are 
carried out. 
The clustered series of three or four implants may be carried out as 
follows: First, boron ions are directed onto the upper surface of the 
substrate 10 with an energy of 2.00 MeV, thereby forming a p-type buried 
implanted layer for lateral isolation. Second, without removing the 
substrate 10 from the vacuum chamber in which it was irradiated with boron 
ions, the parameters of the ion accelerator are changed, and phosphorus 
ions are directed onto the upper surface of the substrate 10 with an 
energy of 1 MeV, thereby forming the lower layer 7 of n-type material 
(deep retrograde n-well). Third, without removing the substrate 10 from 
the vacuum chamber in which it was irradiated with boron ions and 
phosphorus ions, the parameters of the ion accelerator are changed, and 
phosphorus ions are directed onto the upper surface of the substrate 10 
with an energy of 450 keV, thereby forming the upper layer 6 of n-type 
material (channel stop implant or shallow retrograde n-well). As an 
optional fourth step, without removing the substrate 10 from the vacuum 
chamber in which it was irradiated with boron ions and phosphorus ions, 
the parameters of the ion accelerator are changed, and phosphorus ions are 
directed onto the upper surface of the substrate 10 with an energy of 60 
keV, thereby forming a shallow, thin threshhold voltage layer V.sub.t at 
the surface of the retrograde n-well 6,7. Alternatively, the fourth step 
may comprise directing boron ions onto the upper surface of the substrate 
10 with an energy of 30 keV so as to form this threshhold voltage layer. 
After carrying out the foregoing steps, the mask 11 is removed and a mask 
(such as a photoresist mask having a thickness of more than 2.0 
micrometers) is placed on the surface as shown in FIG. 2 to block the 
boron ions of subsequent additional steps, and then a second clustered 
series of one or two implants are carried out. 
The second clustered series of one or two implants may be carried out as 
follows: First, boron ions are directed onto the upper surface of the 
substrate 10 with an energy of 750 keV, thereby forming the lower layer 9 
of p-type material (deep retrograde p-well). Second, without removing the 
substrate 10 from the vacuum chamber in which it was irradiated with boron 
ions, the parameters of the ion accelerator are changed, and boron ions 
are directed onto the upper surface of the substrate 10 with an energy of 
300 keV, thereby forming the upper layer 8 of p-type material (channel 
stop implant or shallow retrograde p-well). As an optional third step, 
without removing the substrate 10 from the vacuum chamber in which it was 
irradiated with boron ions, the parameters of the ion accelerator are 
changed, and boron ions are directed onto the upper surface of the 
substrate 10 with an energy of 20 keV, thereby forming a shallow, thin 
threshhold voltage layer V.sub.t at the surface of the retrograde p-well 
8,9. 
The method of FIGS. 3 and 2 may be still further modified to enable certain 
other existing installations using diffused well techniques to take 
advantage of the principles of the present invention in forming a BILLI 
structure. An example of such a modification is shown in FIG. 5. 
More specifically, the method of the embodiment of the invention shown in 
FIG. 5 comprehends the following steps. First, a surface of a substrate 21 
is passivated by applying thereto a silicon oxide layer 22. Next, a first 
mask 23, such as a photoresist mask, is applied to portions of the surface 
layer 22 as shown. Then phosphorus ions are implanted into the substrate 
21 through the silicon oxide layer 22, so as to form an n-well. The 
resulting article is heated in an oxygen atmosphere, and the presence of 
the phosphorus dopant causes the thickness of the silicon oxide layer 22 
to increase in the region occupied by the phosphorus dopant. Next, boron 
ions are implanted at 100 keV, so as to form a p-well in regions not 
protected by the shielding action of the thick silicon oxide portions. 
After this formation of the p and n wells, the silicon oxide layer 21 of 
varying thickness is removed, and replaced by a silicon oxide layer 24 of 
uniform thickness but having a stepped shape. Next, a second mask 25 and a 
third mask 26 are applied and the substrate 21 is irradiated with boron 
ions so as to form p+ regions 27 (i.e, p-type regions of high 
concentration) as indicated. Next, the mask 26 is removed and the article 
is heated in an oxygen atmosphere so as to form the field oxide regions 
28. Next, a fourth mask 29 is applied so as to shield the p-well regions, 
and a BILLI layer 30 is formed by implanting boron ions of relatively high 
energy. For example, boron ions may be directed onto the upper surface of 
the substrate with an energy of 2.00 MeV, thereby forming a p-type buried 
implanted layer for lateral isolation. If desired, a fifth mask 31 may be 
applied as shown and Vt implants 32 may be formed by implanting boron ions 
at relatively low energy. 
As shown in FIG. 8, if the steps carried out in the method of FIG. 3 are 
applied to an n-type substrate, a BILLI triple well structure is formed. 
Alternatively, a BILLI triple well structure may be formed by the 
clustered implantation indicated in FIG. 9, wherein the implantation steps 
are carried out on a p-type substrate in the following sequence. 
First, phosphorus ions are directed onto the upper surface of the substrate 
110 with an energy of 2.5 MeV, thereby forming the lower layer 109 of 
n-type material. Second, without removing the substrate 110 from the 
vacuum chamber in which it was irradiated with phosphorus ions, the 
parameters of the ion accelerator are changed, and phosphorus ions are 
directed onto the upper surface of the substrate 110 with an energy of 
2.25 MeV, thereby forming the upper layer 108 of n-type material. As an 
optional third step, without removing the substrate 10 from the vacuum 
chamber in which it was irradiated with phosphorus ions, the parameters of 
the ion accelerator are changed, and phosphorus ions are directed onto the 
upper surface of the substrate 110 with an energy of 2.0 MeV, thereby 
forming a shallow, thin threshhold voltage layer V.sub.t at the surface of 
the retrograde n-well 108,109. Fourth, without removing the substrate 110 
from the vacuum chamber in which it was irradiated with phosphorus ions, 
the parameters of the ion accelerator are changed, and boron ions are 
directed onto the upper surface of the substrate 110 with an energy of 500 
keV, thereby forming the lower layer 107 of p-type material. Fifth, 
without removing the substrate 110 from the vacuum chamber in which it was 
irradiated with phosphorus ions and boron ions, the parameters of the ion 
accelerator are changed, and boron ions are directed onto the upper 
surface of the substrate 110 with an energy of 250 keV, thereby forming 
the upper layer 106 of p-type material. As an optional sixth step, without 
removing the substrate 110 from the vacuum chamber in which it was 
irradiated with phosphorus ions and boron ions, the parameters of the ion 
accelerator are changed, and boron ions are directed onto the upper 
surface of the substrate 110 with an energy of 30 keV, thereby forming a 
shallow, thin threshhold voltage layer V.sub.t at the surface of the 
retrograde p-well 106,107. 
Alternatively, a BILLI triple well structure may be formed by the clustered 
implantation indicated in FIG. 7, wherein the bottom ("buried") n-layer is 
formed prior to the clustered implant steps by a separate implantation of 
2.5 MeV phosphorus ions at a current of 3 to 5 E13 through a separate 
mask, designated "M2" in FIG. 7. The remaining, clustered implantation 
steps are carried out through a separate mask, designated "M3" in FIG. 7, 
in the following sequence. 
First, boron ions are directed onto the upper surface of the substrate 110 
with an energy of 2.0 MeV and a dose of 0.5 to 1 E13, thereby forming the 
lower layer 107 of p-type material in the p-wells. Second, without 
removing the substrate 110 from the vacuum chamber in which it was 
irradiated with boron ions, the parameters of the ion accelerator are 
changed, and boron ions are directed onto the upper surface of the 
substrate 110 with an energy of 1.25 MeV, thereby forming the upper layer 
106 of p-type material in the p-wells. As an optional third step, without 
removing the substrate 110 from the vacuum chamber in which it was 
irradiated with boron ions, the parameters of the ion accelerator are 
changed, and boron ions are directed onto the upper surface of the 
substrate 110 with an energy of 750 keV, thereby forming a shallow, thin 
threshhold voltage layer V.sub.t at the surface of the retrograde p-well 
106,107. Fourth, without removing the substrate 110 from the vacuum 
chamber in which it was irradiated with boron ions, the parameters of the 
ion accelerator are changed, and phosphorus ions are directed onto the 
upper surface of the substrate 110 with an energy of 1.0 MeV, thereby 
forming the lower layer 109 of n-type material. Fifth, without removing 
the substrate 110 from the vacuum chamber in which it was irradiated with 
boron ions and phosphorus ions, the parameters of the ion accelerator are 
changed, and phosphorus ions are directed onto the upper surface of the 
substrate 110 with an energy of 450 keV, thereby forming the upper layer 
108 of n-type material. As an optional sixth step, without removing the 
substrate 110 from the vacuum chamber in which it was irradiated with 
boron ions and phosphorus ions, the parameters of the ion accelerator are 
changed, and boron ions are directed onto the upper surface of the 
substrate 110 with an energy of 30 keV, thereby forming a shallow, thin 
threshhold voltage layer V.sub.t at the surface of the retrograde n-well 
106,107. Alternatively, the sixth step may comprise directing phosphorus 
ions onto the upper surface of the substrate 110 with an energy of 60 keV 
so as to form this threshhold voltage layer. 
If the steps carried out in the method of either FIG. 9 or FIG. 7 are 
applied to an n-type substrate, a BILLI twin-well structure is formed. 
In the foregoing description of clustered implantation, the sequence of 
clustered implantions are carried out by the same ion accelerator. 
However, if many ion accelerators are available at the same installation, 
the sequence of clustered implantations may be carried out by separate ion 
accelerators without departing from the spirit and scope of the invention; 
it is only necessary to ensure that the same mask is used throughout the 
sequence of clustered implantations. 
Also, in the foregoing description of clustered implantation, 
representative thicknesses of the masks are set forth, and representative 
energies of the ions being implanted are set forth. However, the invention 
is not limited to such thicknesses or energies, and the invention 
comprehends, in general, phosphorus-ion energies which are insufficient to 
pass through the mask involved, thus being blocked by the mask, and 
boron-ion energies which are sufficient to pass through the mask involved. 
Additional advantages of the invention are achieved if the implantation and 
masking steps hereinbefore set forth are carried out on a substrate the 
surface whereof has been subjected to hydrogen annealing. The resultant 
hydrogen denudation provides an improved Cz wafer and can eliminate epi. 
Using the BILLI structure in combination with hydrogen or nitrogen 
(optimum) denudation for epi replacement results in epi equivalent thin 
gate oxide quality, excellent junction leakage, improved resistance to RCA 
wet clean related surface micro-defect formation, improved surface 
smoothness and very low surface oxygen and defect levels. 
In the foregoing description the invention has been described in terms of 
boron ions and phosphorus ions. However, the invention includes the use of 
p-type dopants other than boron in lieu of boron ions, as well as the use 
of n-type dopants other than phosphorus in lieu of phosphorus ions. 
FIG. 4 shows the BILLI structure of the invention. A substrate 201 includes 
isolation layers 202 at a surface thereof and at least one p-well 203 and 
at least one n-well 204 adjacent thereto. The p-well 203 extends 
underneath the n-well 204 in a manner which provides a BILLI layer 205. In 
the portion of the p-well 203 lying underneath the n-well 204 at its 
deepest part, there are three concentration peaks, as may be seen from 
FIGS. 4 and 10. The deepest peak 206 lies at a depth of 2.9 microns and 
has a peak concentration of approximately 1E18 (10.sup.18) atoms per cubic 
centimeter. The middle peak 207 lies at a depth of 2.0 microns and has a 
peak concentration of approximately 2E17 atoms per cubic centimeter. The 
shallowest peak 208 lies at a depth of 1.4 microns and has a peak 
concentration of approximately 4E16 atoms per cubic centimeter. The 
deepest peak 206 is produced by implanting 2 MeV boron ions at a dose of 
3e13, the middle peak 207 is produced by implanting 1.25 MeV boron ions at 
a dose of 5e12, and the shallowest peak 208 is produced by implanting 750 
keV boron ions at a dose of 1e12. FIG. 11 shows the concentration 
distribution in depth produced by the 2 MeV boron implant alone, from 
which it can be seen that the contribution of this implant to the 
concentration in layers shallower than the peak concentration at 2.9 
microns is negligible. The same is true of the other boron implants. It 
may be noted that the silicon concentration is of the order of E15. If the 
peaks are too far apart, decoupling results and the advantage of the BILLI 
layer of the invention is not achieved. 
In the n-well 204, there are three concentration peaks, as may be seen from 
FIGS. 4 and 12. The deepest peak 209 lies at a depth of 1.3 microns and 
has a peak concentration of approximately 1E18 (10.sup.18) atoms per cubic 
centimeter. The middle peak 210 lies at a depth of 0.8 microns and has a 
peak concentration of approximately 2E17 atoms per cubic centimeter. The 
shallowest peak 211 lies at a depth of 0.1 microns and has a peak 
concentration of approximately 1E17 atoms per cubic centimeter. The 
deepest peak 209 is produced by implanting 1 MeV phosphorus ions at a dose 
of 3.0 E13 atoms per square centimeter, the middle peak 210 is produced by 
implanting 600 keV phosphorus ions at a dose of 5 E12 atoms per square 
centimeter, and the shallowest peak 211 is produced by implanting 60 keV 
phosphorus ions at a dose of 3 E12 atoms per square centimeter. It can be 
seen that the peak concentrations are comparable to those of the boron 
implantations, and so the concentration distribution in depth of the 
p-well 203 proper, lying adjacent the n-well, is comparable to that of the 
n-well 204. 
It is to be noted from FIG. 10 that, despite the high concentration at a 
depth of 3 microns, the concentration up to a depth of 1 micron is 
comparable to that of the silicon. 
FIG. 13 shows a prior-art proposal in which a MeV Retrograde Well is 
combined with a MeV blanket buried layer and a so-called "PAB" vertical 
MeV isolation implant. The formation of such a structure required four 
masks, and there are 62 process steps to gate. There are 8 implants. Epi 
replacement is achieved and the latchup prevention B.sub.V .times.B.sub.L 
is very good but the n+ to p+ spacing is limited due to the added mask. 
Photoresist thickness is more than 3.5 microns. The cost savings is $150. 
Two additional high-dose ion implantations are required; there is 
photoresist outgassing; defects are created in the article implanted; the 
use of high temperature anneals requires denuding. This proposal is 
disclosed in the Tsukamoto presentation cited at reference (1) of the 
aforementioned article by Borland and Koelsch. 
The aforementioned U.S. Pat. No. 5,160,996 to Odanaka shows a prior-art 
proposal in which the vertical high-concentration region is produced by a 
single implant through a mask the edge whereof coincides with an isolation 
area. The transition from the shallow implant under the mask to the deep 
implant under the opening, caused by the mask edge in conjunction with the 
effect of the field oxide, produces the desired vertical region for 
lateral isolation. However, as is shown by the concentration diagrams of 
the patents, the dose near the surface under the field oxide is high, and 
damage is caused to the article implanted. 
The BILLI structure and method of the present invention avoids the 
additional steps of the PAB technique, and avoids the article damage of 
the Odanaka technique, by the use of implantation energy sufficiently high 
to avoid high-dose implant near the surface regions. 
It will be noted that, in the BILLI structure of FIGS. 4, 10, 11 and 12, 
underneath the field oxide the boron concentration distribution in depth 
varies from a low but not negligible value directly under the field oxide 
to a maximum value at a depth of about 3 microns. Thus there is sufficient 
boron concentration to kill lateral beta, but the concentration near the 
surface is restrained so as to prevent damage to the semiconductor 
material. This vertical portion is created without the complexity of the 
PAB method and without the damaging effect of the Odanaka method. 
The superior results of the structure of the invention is shown by the 
measurements of lateral beta shown in FIGS. 14-15. 
The graphs of FIG. 16 show the reduction in latch-up produced by the BILLI 
structure as compared with other structures. The trigger current shown is 
that current required to initiate latch-up, and hence higher values for 
this trigger current indicate lower tendency for latch-up to occur. 
Suitable apparatus for making the product of the invention by means of the 
method of the invention is shown in FIGS. 17 and 18. FIG. 17 shows an ion 
implantation system. The process chamber and wafer handler modules of the 
system of FIG. 17 are shown in FIG. 18. Wafers to be implanted are loaded 
to the disk from a product cassette by means of a robot providing 
orientation and shuttle movement. The disk is mounted within a vacuum 
chamber which is sealed off from atmosphere after loading. A scan and tilt 
mechanism enables movement of the disk to be controlled from outside the 
vacuum chamber. An ion accelerator produces an ion beam which is injected 
into the vacuum chamber. The parameters of the accelerator, such as 
energy, beam current, and type of ion, can be varied without disturbing 
the vacuum in the vacuum chamber. The vacuum chamber is preferably of 
relatively large volume, such as about 1600 liters, in order to control 
the effects of photoresist outgassing and in order to permit the various 
motions of the disk. 
Suitable apparatus for making the product of the invention by means of the 
method of the invention is also shown in U.S. Pat. No. 4,745,287 to 
Turner, U.S. Pat. No. 4,980,556 to O'Connor et al., U.S. Pat. No. 
5,162,699 to Tokoro et al., U.S. Pat. No. 5,300,891 to Tokoro, U.S. Pat. 
No. 5,306,922 to O'Connor, and U.S. Pat. No. 5,486,702 to O'Connor et al. 
Having thus described the principles of the invention, together with 
several illustrative embodiments thereof, it is to be understood that, 
although specific terms are employed, they are used in a generic and 
descriptive sense, and not for purposes of limitation, the scope of the 
invention being set forth in the following claims.