U.S. patent application number 09/898949 was filed with the patent office on 2003-01-09 for angled implant process.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Hook, Terence B..
Application Number | 20030008484 09/898949 |
Document ID | / |
Family ID | 25410274 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030008484 |
Kind Code |
A1 |
Hook, Terence B. |
January 9, 2003 |
ANGLED IMPLANT PROCESS
Abstract
Different symmetrical and asymmetrical devices are formed on the
same chip using non-critical block masks and angled implants. A
barrier is selectively formed adjacent one side of a structure and
this barrier blocks dopant implanted at an angle toward the
structure. Other structures have no barrier or have two barriers.
Source and drain engineering can be performed for LDD, halo, and
other desired implants.
Inventors: |
Hook, Terence B.; (Jericho,
VT) |
Correspondence
Address: |
James M. Leas
IBM Corporation, Mail 972E
1000 River Street
Essex Junction
VT
05452
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
25410274 |
Appl. No.: |
09/898949 |
Filed: |
July 3, 2001 |
Current U.S.
Class: |
438/524 ;
257/E21.345; 257/E21.427; 257/E21.437; 257/E21.618; 257/E21.619;
257/E29.268 |
Current CPC
Class: |
H01L 21/823412 20130101;
H01L 21/823418 20130101; H01L 29/66659 20130101; H01L 21/26586
20130101; H01L 29/66492 20130101; H01L 29/7835 20130101 |
Class at
Publication: |
438/524 |
International
Class: |
H01L 021/425 |
Claims
Thus, having described the invention, what is claimed is:
1. A method of fabricating a semiconductor device, comprising the
steps of a) providing a semiconductor substrate comprising a
surface; b) forming a first structure and a second structure on
said surface; c) selectively providing a first barrier adjacent a
first side of said first structure; and d) implanting a dopant at
an angle wherein said barrier shadows implanted dopant from a
portion of said first structure wherein no barrier shadows
implanted dopant from a corresponding portion of said second
structure.
2. The method as recited in claim 1, further comprising the step of
selectively providing a second barrier adjacent a second side of
said first structure, wherein in said implanting a dopant at an
angle step (d) said second barrier shadows implanted dopant from
said second side of said first structure.
3. The method as recited in claim 2, wherein no barrier shadows
implanted dopant from a corresponding portion of said second
structure.
4. The method as recited in claim 2, further comprising a barrier
shadowing implanted dopant from a second side of said second
structure.
5. The method as recited in claim 2, wherein in said implanting
step (d) said first structure is symmetric and said second
structure is symmetric, wherein said first structure comprises an
implant shadowed on two sides and said second structure receives
said implant on two sides.
6. The method as recited in claim 1, wherein said implanting step
(d) is for providing a halo implant, an extension implant, or an
LDD implant.
7. The method as recited in claim 1, wherein said implanting step
(d) comprises implanting at a first angle and then implanting at a
second angle different from said first angle.
8. The method as recited in claim 7, wherein said first angle is
approximately vertical to provide a portion of the implant to all
devices and said second angle is sufficient so a portion is blocked
by said first barrier.
9. The method as recited in claim 1, wherein in said implanting
step (d) said first structure comprises a thicker dielectric or a
longer channel or is used with a different applied voltage than
said second structure.
10. The method as recited in claim 1, wherein said first structure
that has said dopant blocked has a different threshold voltage than
said second structure receiving said dopant.
11. The method as recited in claim 1, wherein said first structure
comprises an FET.
12. The method as recited in claim 1, wherein providing step (c)
comprises providing said barrier of ion absorbing photoresist.
13. The method as recited in claim 12, wherein providing step (c)
comprises exposing said photoresist with a non-critical block
mask.
14. The method as recited in claim 1, further comprising the steps
of: e) removing the first barrier; f) forming a new barrier
adjacent a second side of said first structure; and g) implanting a
dopant at an angle wherein said new barrier shadows implanted
dopant from a portion of said first structure.
15. The method as recited in claim 14, wherein no barrier shadows
implanted dopant from a corresponding portion of said second
structure.
16. The method as recited in claim 14, further comprising the step
of selectively providing a barrier adjacent a second side of said
second structure, wherein in said implanting a dopant at an angle
step (g) said barrier shadows implanted dopant from said second
side of said second structure.
17. The method as recited in claim 14, wherein said implanting step
(d) is for providing an LDD implant, and said implanting step (g)
is for providing a halo implant.
18. The method as recited in claim 14, wherein said implanting step
(g) comprises implanting at a first angle and then implanting at a
second angle different from said first angle.
19. The method as recited in claim 18, wherein said first angle is
approximately vertical to provide a portion of the implant to all
devices and said second angle is sufficient so a portion is blocked
by said first barrier.
20. The method as recited in claim 14, wherein in said implanting
step (g) said first structure comprises a thicker dielectric or a
longer channel or is used with a different applied voltage than
said second structure.
Description
FIELD OF THE INVENTION
[0001] This invention relates to angled ion implants. More
particularly, it relates to a method of producing a symmetrical and
an asymmetrical semiconductor device using angled ion
implantation.
BACKGROUND OF THE INVENTION
[0002] Semiconductor devices, such as metal oxide semiconductor
field effect transistors (MOSFETs), produced with angled ion
implantation techniques are often constructed symmetrically. This
allows great flexibility in the layout of multiple devices as the
source and drain are interchangeable (and both sides of the gate
are consequently referred to simply as the "source/drain").
[0003] For some applications, this type of device symmetry is
highly desirable or essential. Devices produced by angled ion
implantation are generally made symmetric by rotating the
semiconductor device to allow the angled implant beam to implant
from all sides of the gate. This results in a series of symmetrical
implants and a symmetrical device.
[0004] High voltage devices have required a graded lightly doped
drain (LDD) implant while low voltage devices favor an abrupt
implant, such as an extension type implant, as is well known in the
art. Low voltage devices also often have a halo or a more heavily
doped halo than high voltage devices. Such high and low voltage
devices are frequently fabricated on the same chip. They generally
have different gate dielectric thicknesses, channel lengths, and
use separate masking steps and implants for the source/drain
design.
[0005] For other applications, performance can be improved if the
semiconductor device is constructed asymmetrically. For example,
for MOSFETs having an LDD region and a halo region, the LDD is
desirable exclusively on the drain side and the halo is desirable
exclusively on the source side of the gate.
[0006] The addition of an LDD region degrades device performance
because it increases series resistance and overlap capacitance.
Since the lightly doped LDD region is strictly required only on the
drain side of the device to mitigate hot carrier degradation, the
LDD on the source side of a symmetrical device adds series
resistance and capacitance with no additional benefit. Device
performance can be improved if the LDD implant could be blocked
from the source side thereby making an asymmetrical device.
Furthermore, where a particular device is never subjected to high
voltages, blocking the LDD implant from both sides may also be
advantageous.
[0007] However, a very accurately-aligned critical mask capable of
blocking the implant beam from the source side, but not blocking it
from the drain side, has been needed to provide the desired
asymmetrical device. To block the implant on one side, but not on
the other side of the gate requires aligning the critical mask to
within the width of the gate. This has required alignment tolerance
within one half the width of the gate. Obtaining such critical
alignment is an expensive and error-prone procedure.
[0008] Alternatively, the LDD implant may be produced through a
single ion implant beam which places the implant under one side of
the gate. Thus, the desired LDD is formed when the appropriate ion
implant beam is directed at an angle towards the drain side of the
gate. To produce many asymmetrical devices on the same
semiconductor substrate requires that all of the devices be
oriented in the same direction so that a single ion implant step
can produce all of the LDD regions desired on the same side of the
gate while avoiding implant on the opposite side.
[0009] It can be seen that controlled device asymmetry is possible
if all the devices are oriented in the same direction and the
opposite direction rotation is omitted. However, orienting all of
the devices in the same direction significantly limits layout
flexibility.
[0010] The same problem is encountered when constructing a halo
implant only on the source side of the device. If the halo implant
is placed on the drain side, it increases junction capacitance and
peak electric field. Achieving halo implants only on the source
side has heretofore required the same choice between an expensive
critical mask with alignment comparable to half the gate width or
an angle implant with uniform device orientation such that all of
the devices have the source on the same side.
[0011] Therefore, an improved process to provide implants is needed
and this solution is provided by the following invention.
SUMMARY OF THE INVENTION
[0012] It is therefore an object of the present invention to
selectively provide different implants on different devices or on
different sides of the same device on a semiconductor wafer.
[0013] It is a further object of the present invention to form both
symmetrical and asymmetrical semiconductor devices on a
semiconductor wafer.
[0014] It is a feature of the present invention to use a single
non-critical mask to selectively form barriers adjacent
semiconductor devices or adjacent one side of certain devices to
shadow ion implant beams.
[0015] It is an advantage of the present invention that the
location of ion implant can be controlled without adding critical
masks or reducing layout flexibility.
[0016] It is an advantage of the present invention to provide
asymmetrical devices without added critical masks or reducing
layout flexibility.
[0017] These and other objects, features, and advantages of the
invention are accomplished by a method for selectively blocking
angled ion implants on a semiconductor substrate. The method
includes providing a semiconductor substrate having a surface. A
first structure and a second structure are formed on the surface of
the substrate. A first barrier is selectively formed adjacent a
first side of the first structure. A dopant is implanted at an
angle, however the barrier shadows the dopant from a portion of the
first structure and no barrier shadows dopant from a corresponding
portion of the second structure.
[0018] The present invention also includes symmetrical and
asymmetrical semiconductor devices on the same wafer. Most
typically, this will include a field effect transistor, having an
LDD on the drain side of the gate, but not on the source side of
the gate, or having a halo on the source side of the gate, but not
on the drain side of the gate, or both; or a second set of devices
having no halo implant in the source/drain, or a set of devices
having no LDD implant in the source/drain.
[0019] Although the present invention may find application in
various types of ion implanted semiconductor devices, the invention
will be described here in connection with its application in MOSFET
technology in which the structures on the semiconductor surface are
the gates of MOSFETs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following detailed
description of the invention, as illustrated in the accompanying
drawings, in which:
[0021] FIGS. 1a-1c are top views of semiconductor devices being
implanted in accordance with the present invention.
[0022] FIGS. 2a-2c are cross-sectional views of the semiconductor
devices taken along the line 2-2 shown in FIGS. 1a-1c.
[0023] FIGS. 3a, 3c are cross-sectional views of the semiconductor
devices of FIGS. 1a, 1c and 2a, 2c after implant is complete.
[0024] FIGS. 3b, 3d, and 3e are cross-sectional views of other
semiconductor devices that can be made with the barrier and angle
implant of the present invention after the implant is complete.
[0025] FIGS. 4a-4c are cross-sectional views of semiconductor
devices made with a vertical LDD implant and an angled halo
implant.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0026] The present inventors recognized that providing a barrier
next to some devices but not others allowed both symmetrical and
asymmetrical devices to be formed at the same time without critical
masks and without changing the way a chip is laid out. They also
recognized that providing barriers on both sides of some devices
allowed four kinds of symmetrical devices to be formed at the same
time.
[0027] Commonly assigned U.S. Pat. No. 6,083,794 by Hook et al.,
teaches a barrier on one side of a gate to block angle implant from
that side, while implant angled toward the other side reaches the
other side of the gate, thereby forming an asymmetrical
semiconductor device. The present invention extends this idea to
provide different devices on a single chip without the need for any
more critical masks.
[0028] Semiconductor surface 10 has structures, such as gates 12a,
12b, 12c of field effect transistors 13a, 13b, 13c having sides 14
and 16 as shown in FIGS. 1a-1c and 2a2c. Additional transistors
(not shown) will usually be positioned in an array around
transistors 13a, 13b, 13c. In most implementations, the additional
transistors will be laid out in four mirror image orthogonal
orientations. Two or more of transistors 13a, 13b, 13c can be
formed on surface 10 of the same chip using the same non-critical
mask and the same angled implant, as further described herein
below. They are shown in separate figures for clarity but they can
all be on the same surface.
[0029] Four separate 90.degree. rotations provide angled ion
implant beams 24, 26, 30 and 32 as shown in FIGS. 1a-1c. Generally,
semiconductor surface 10 will be rotated 90.degree. between each
implant. Implants 30, 32 arriving from directions parallel to sides
14 and 16 of gates 12a, 12b, 12c add negligibly to the source/drain
doping but will not penetrate below corner 22 and corner 28, and
will not create LDD or halo structures. Implants 30, 32 may be
used, however, to form LDD or halo structures on other devices on
the same semiconductor surface 10 having an orientation at
90.degree. or 270.degree. to the devices shown in FIGS. 1a-c.
[0030] Three devices are compared in FIGS. 1a-c and in FIGS. 2a-c.
Symmetrical device 13a receiving all implants 24, 26, 30, 32 on
both sides 14, 16 is shown in FIGS. 1a, 2a. Barrier 18, of an ion
absorbing material, such as photoresist, having height h is
positioned distance d away from side 14 of gate 12b as shown in
FIG. 2b to provide asymmetrical device 13b having ion implant 26 on
side 16 but no ion implant 24 on side 14. Barrier 19 having height
h is positioned distance d away from side 16 as shown in FIG. 2c to
provide another symmetrical device 13c where implants 24, 26 are
all blocked from both sides 14, 16. The effects of ion implantation
in semiconductor surface 10 and the resulting semiconductor devices
produced by the present invention are shown in corresponding FIGS.
3a, 3c. FIGS. 3b, 3d, and 3e show other semiconductor devices that
can similarly be formed using the process of the present invention
or two such processes. The semiconductor devices all include
source/drain regions 54, 56 or drain region 36, source region 38,
and shallow trench isolation (STI) regions 40 and 42 surrounding
the device.
[0031] Without any barrier, when ion implant beams 24 and 26 are
directed to sides 14 and 16, respectively, the desired ion implants
will occur under right lower corner 22 and left lower corner 28 of
gate 12a of FET 13a as shown in FIG. 2a. These desired ion implants
produce LDD regions 44 and 60 in the source/drain regions 54, 56 of
gate 12a of FIG. 3a. Ion implant beams 30 and 32 have no effect
since they are not oriented in a proper direction to implant
underneath either corner 22 or corner 28.
[0032] Halo regions 46 and 58 are similarly implanted with angle
implant beams on both source/drain sides of gate 12a with no
barrier present as shown in FIG. 3a.
[0033] The halo implant is required only on the shorter
channel-length devices and it may be safely omitted on long-channel
devices. This is desirable as the device drain resistance may be
improved by eliminating the halo implant. By using the barriers and
angle implants of the present invention short symmetrical devices
with halo implant may be simultaneously created with long
symmetrical devices without halo implant.
[0034] For many short-channel devices threshold voltage is
determined primarily by the halo implant. Thus, by using the
barriers and angle implants of the present invention, short
symmetrical devices with different threshold voltages may be
simultaneously created.
[0035] Barrier 18 of height h shown in FIG. 2b casts a shadow from
upper corner 20 covering lower corner 22 of side 14 of gate 12b of
FET 13b, when ion implant beam 24 is directed at side 14 at an
angle 01 measured relative to semiconductor surface 10. The maximum
distance, d, that barrier 18 may be placed away from side 14 of
gate 12b and still protect lower corner 22 from ion implant beam 24
is illustrated by FIG. 2b. If barrier 18 is placed any farther to
the right, i.e. beyond maximum distance d, ion implant beam 24 will
not be fully blocked. Generally, barrier 18 may be placed at any
point between side 14 of gate 12b and maximum distance d. Barrier
18 may also extend on the upper surface of gate 12b between side 14
and side 16. Barrier 18 cannot be placed to the left of side 16
because in this position the barrier would block desired ion
implant beam 26 directed toward side 16 for providing desired ion
implant under left lower corner 28 of gate 12b. Thus, if gate 12b
has a length L, barrier 18 has an acceptable range of positions
equal to L+d.
[0036] If an additional implant at angle +must be provided with
barrier 18 in place to provide a dose along edge 14 then barrier 18
must be spaced from gate 12b to allow for that other implant. The
mask edge must then be located between h/tan .phi. and h/tan
.theta.1.
[0037] Barrier 18 will normally be placed somewhere near mid point
34 of this range of positions, as shown in FIG. 2b. The alignment
error in positioning barrier 18 at mid point 34 may be as large as
one half the sum of L plus d. The maximum distance d is given by
the relationship of h divided by the tangent of angle .theta.1. By
selecting angle .theta.1 and height h, the tolerance error for
positioning the mask may be adjusted. The shallower the angle
.theta.1 and the higher the height h of barrier 18, the greater the
maximum distance d and the greater the tolerance of the position
error in placing barrier 18.
[0038] Desired ion implant beam 26 produces LDD region 44 in drain
region 36 of gate 12b shown in FIG. 3b. There is no corresponding
LDD region underneath corner 22 because barrier 18 blocked ion
implant beam 24. Ion implant beams 30 and 32 were not oriented in
the proper direction to implant underneath either corner 22 or
corner 28. Barrier 18 will block only one of the four beams, ie.
ion implant beam 24, so it can remain on semiconductor surface 10
during all four rotations of the implant process. If desired, LDD
region 44 could be formed only under side 14, opposite to that
shown in FIG. 3b, by constructing barrier 18 on the left side, i.e.
on the drain side so that the shadow of barrier 18 would shield
corner 28 of gate 12b from ion implant beam 26, but would not
shield corner 22 of gate 12b from ion implant beam 24.
[0039] A halo region 46 found only on the source side and not on
the drain side is also shown in FIG. 3b. This makes the device
doubly asymmetric. Halo region 46 is formed by constructing a
barrier on the left side, i.e. on the drain side so that the shadow
of the barrier would shield corner 28 of gate 12b from halo ion
implant beam 26, but would not shield corner 22 from halo ion
implant beam 24.
[0040] If desired, halo region 46 could also be formed on the drain
side by constructing a barrier, or by using the same barrier that
was used to form LDD region 44, on the source side so that the
shadow of the barrier would shield corner 22 from halo ion implant
beam 24, but would not shield corner 28 from halo ion implant beam
26. In this way, both LDD region 44 and halo region 46 are on the
drain side of gate 12b. Likewise, both LDD region 44 and halo
region 46 can be formed on the source side of gate 12b by
constructing a barrier on the drain side of gate 12b. In addition,
if LDD region 44 is formed on the source side of gate 12b, halo
region 46 could be formed on the drain side of gate 12b by
constructing a barrier on the source side of gate 12b.
[0041] To form the doubly asymmetrical device described above where
halo region 46 is opposite LDD region 44, two masking steps are
needed to separately provide a barrier on one side of the gate for
the LDD implant and then a barrier on the other side for the halo
implant.
[0042] To provide a second symmetrical device, both sides 14 and 16
of gate 12c are shadowed at the same time as shown in FIG. 2c.
Similar to FIG. 2b, a first barrier 18 of height h casts a shadow
from its upper corner 20 which covers lower corner 22 on side 14
when ion implant beam 24 is directed at side 14 and has angle
.theta.1 measured relative to semiconductor surface 10. In
addition, barrier 19 of height h casts a shadow from its upper
corner 21 which covers lower corner 28 on side 16 when ion implant
beam 26 is directed at side 16 and has angle .theta.2 measured
relative to semiconductor surface 10. Typically, the angles
.theta.1 and .theta.2 of the ion implant beams are the same.
[0043] The same criteria described herein above for distance and
height with respect to one barrier, also apply for two barriers.
Generally, barriers 18, 19 are placed at any point between sides 14
and 16 of gate 12c and maximum distance d. Either one or both of
the barriers may be placed extending onto the upper surface of gate
12c at any point between side 14 and side 16. In the case of one of
the barriers placed on the upper surface of gate 12c, the barrier
may extend beyond a side of gate 12c. For example, when barrier 18
is formed at distance d away from side 14 as shown in FIG. 2c,
barrier 19 can be formed extending onto the upper surface of gate
12c and beyond side 14. Likewise, when barrier 19 is formed at
distance d away from side 16, then barrier 18 can be formed
extending onto the upper surface of gate 12c and beyond side 16.
This allows for an even greater tolerance of the position error in
placing the barriers. However, if a second implant is needed
adjacent a side of the gate with barrier 18 or 19 in place, then
overlap with the gate is not permitted.
[0044] Source/drain regions 54, 56 of gate 12c shown in FIG. 3c are
formed with vertical implants and have no LDD regions or halo
regions underneath either corner 22 or corner 28 due to the
presence of barrier 18 and barrier 19 blocking LDD and halo ion
implant beams. Ion implant beams 30 and 32 are not oriented in the
proper direction to implant underneath either corner 22 or corner
28. Because barrier 18 would block only one of the four beams (ion
implant beam 24) and barrier 19 would block another of the four
beams (ion implant beam 26), both barriers can remain on the
semiconductor surface during all four rotations of the implant
process.
[0045] Thus, two symmetrical devices can be formed on a chip with
one process. The first has LDD and halo, and the second has
neither. Other symmetrical and asymmetrical devices with LDD and
halo can be formed as well, as shown in FIGS. 3d and 3e. A
symmetrical device with no LDD and halo on both sides is formed on
the same chip as one or more of the other devices, as shown in FIG.
3d. An asymmetrical device with LDD on the drain side and halo on
both sides can also be formed, as shown in FIG. 3e.
[0046] The present invention is not limited to LDD and halo
implants. Various dopant doses and implant energies can be used
with barrier 18 and barrier 19 for providing source and drain
engineering. Separate angle implants and barriers can be provided
for each. Various symmetrical and asymmetrical devices can be
formed on the chip by providing barriers on one side, both sides or
no sides of particular devices.
[0047] Semiconductor devices having source/drain regions that
include symmetrical LDD regions 44 and 60 can also be formed using
spacers with vertical ion implant (not shown), as well known in the
art. The halo can still be provided with angle implant. A vertical
ion implant for the LDD is directed at an angle of about 90.degree.
with respect to semiconductor surface 10. Thus, the present
invention can combine vertical implants and angled implants to
provide different source and drain engineering structures.
[0048] Source/drain regions 54, 56 of gate 12a shown in FIG. 4a
include LDD implants from standard vertical implants before spacers
50, 52 are applied. Source/drain regions 54, 56 also include halo
regions 46 and 58 formed by the method of the present invention as
described with reference to FIGS. 1a and 2a. Halo regions 46 and 58
are formed underneath both corner 22 and corner 28 of gate 12a in
FIG. 4a by having no barriers present to block ion implant beams 24
and 26. Thus, a symmetrical semiconductor device is formed with LDD
and halo on both sides.
[0049] Source region 38 of gate 12b shown in FIG. 4b includes a
halo region 46 formed underneath corner 22. A barrier is formed on
drain side 36 to block ion implant beam 26 so a halo region is
prevented from forming in drain region 36. No barrier is formed on
the source side so ion implant beam 24 is able to implant
underneath corner 22. The method to form halo region 46 in source
region 38 is identical to that shown for the formation of LDD
region 44 with reference to FIGS. 1b and 2b, except barrier 18 is
on side 16 of gate 12b. Likewise, halo region 46 could be formed
underneath corner 28 in FIG. 4b by constructing a barrier on the
source side of gate 12b (as shown in FIGS. 1b and 2b) so that the
shadow of the barrier would shield corner 22 from ion implant beam
24, but would not shield corner 28 from ion implant beam 26. In
either case an asymmetrical semiconductor device is formed.
[0050] Source/drain regions 54, 56 of FIG. 4c show an absence of
halo regions. As described with reference to FIGS. 1c and 2c,
barrier 18 and barrier 19 are formed to block ion implant beams 24
and 26, respectively. In this way a symmetrical semiconductor
device is formed without halos while other devices on the chip are
formed without barriers and receive halo implants.
[0051] For all of the above cases the total halo or LDD dose may be
modulated by providing a portion of the dose at an angle near
90.degree.. Barrier 18 will not shadow this implant. The remainder
of the dose is provided at an angle at which barrier 18 is
effective to shadow the implant. Thus, devices with greater or
lesser doses of halo or LDD may be provided simultaneously with one
masking step and two or more implant steps.
[0052] A combination of any two or more of the various types of
semiconductor devices shown in FIGS. 3a-e or FIGS. 4a-c can be
formed by the method of the present invention. That is, a
non-critical masking step to provide a barrier adjacent a device is
used to selectively control the location of implants into the
various types of semiconductor devices being formed. The
symmetrical semiconductor devices shown in FIGS. 3a, 3c, and 3d and
the asymmetrical semiconductor devices shown in FIGS. 3b and 3e can
be formed on the same chip semiconductor surface by the method of
the present invention.
[0053] For other semiconductor devices at other orientations on the
same surface, the barrier (or barriers) will simply be positioned
relative to the other devices to shield the necessary side (or
sides). Of course, all of these barriers will be laid down with a
non-critical mask. For symmetrical devices with implants, no
barrier will be laid down; for asymmetrical devices, one barrier
will be laid down; and for devices where no implant is desired, two
barriers will be laid down to shadow both sides of the gate.
[0054] Typically, the construction of multiple semiconductor
devices includes numerous masking steps. The construction of
photoresist barriers 18 and 19 may often be incorporated into one
of these non-critical masking steps without requiring additional
process steps to implement this invention. Either photoresist or
hard mask can be used to form the barriers.
[0055] The invention is particularly well suited to making multiple
symmetrical and asymmetrical devices on a single substrate at
different orthogonal orientations using one or two non-critical
masking steps to selectively control the location of an ion
implant. The use of one non-critical masking step with angle
implants allows for at least three different devices (2
symmetrical, 1 asymmetrical) to be formed, whereas the use of two
non-critical masking steps with angle implants allows for at least
nine different devices (4 symmetrical, 5 asymmetrical) to be
formed. Thus, the present invention offers a greater flexibility in
providing symmetrical and asymmetrical devices on a single
substrate without requiring critical masks or restrictions in
device layout.
[0056] While the present invention has been particularly described,
in conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
* * * * *