Книги2 / 1993 P._Lloyd,__C._C._McAndrew,__M._J._McLennan,__S._N

258

K. Nishi et al.: Technology CAD at OKI

Other criteria include a fast turn-around-time (TAT) and a

maintainability

of

the system.

In order to meet these

criteria, UNISAS is organized

as

shown in Fig.!.

UNISAS

can

be

divided into three parts: l)Gener-

al-purpose

simulator

group,

2)Special simulator group,

and

3) Graphical utilities.

simulation.

In order to achieve a

flexibility

for

simulation

purposes, OPUS and ODESA themselves

have capabilities

to simulate

in lD to 3D

spaces. An applicability

to versatile

devices is not

semiconductors and

even wiring capacitances.

Special simulator group now consists of VELMOT for stress-

oriented oxidation simulation, PIPS for Monte

Carlo

ion

implanta-

tion

simulation,

and MONTES for Monte Carlo

device

simulation.

They

are

linked

with OPUS and

ODE SA.

Right

now, they are

more

in research-oriented applications including

modeling,

but

also

help

to

achieve

more

accurate

simulation

of

device

characteris-

tic.

We note that other than these in-house simulators, a li-

thography

simulator

and

a device

simulator

based

on a

hydrodynam-

ic model are

also used

for R&D.

Results files of these simulators have the

same

unified

format and can

be

visualized by an in-house graphic system VDIOS.

All

the

simulators

have the

same

input

language

called

endures a full or a

simplified

description of

process

conditions

and applied voltage

conditions.

This language

is easy

to learn,

grammar.

This constitutes one of the easinesses for maintain-

ability because we need only one UNICOL compiler.

This also

practicalnesses

of

linkage between

simulators as

described in

the next section.

2.2 Linkage of the

simulators

Care should be taken to link general-purpose simulators.

Process and

device simulations are

used to study (1) the ef-

fects

of process conditions and (2) the effects

of device

parame-

ters

like dimensions

and oxide thickness. For

the

first

purpose,

sufficient, even

though dopant profiles by process

simulations

are preferred in

order to correlate the simulation

results with

processes are independently simulated by OPUS and

can be

merged

to form one CMOS device for the device simulation.

This

lessens

For a linkage between ODESA and

OCAP, the

first

choice

was

to have a table look-up

model. For

a

hand-free

linkage of

ODESA

and OCAP, analytical models may not be appropriate because

of

difficulties in automatic

parameter

extraction.

The

number

of

through

error

evaluation

of

currents and circuit delay

time

(tpd).

In addition to current/voltage table data, junction

capacitance is

also linked

by

tables simulated by ODE SA.

Other

structure for

device

simulation.

Thus, what are needed for engineers to run unified simula-

tions from

process to circuit

are

only the

upper-level

operation

to control

each

simulation,

in

addition to

process

flow, bias

K. Nishi et &1.: Technology CAD at OKI

267

distribution after

LOCOS(a)

and

cooling

down

to

room

temperature(b).

The

stress after cooling

down

is

much

larger

than that of right after LOCOS due to thermal mismatch

between

oxide and nitride.

We

have found

that

these

stress values

depend

on the

cooling temperature. These

kind of analyses are possible

only by

viscoelastic modeling.

Another interesting application

of viscoelastic modeling is

temperature

cycles with a parameter of different heating (cool-

ing) rate.

Different hysteresis curves were simulated for the

with

experiments, suggesting that viscoelastic modeling

can

be

used

to stress

migration of a aluminum interconnect.

VELMOT

can run

with an output file of OPUS. Thus,

it is

easy

to do

oxidation

simulation and stress calculation

with

a

surface roughness

model.

Impact ionization is also included in

the lucky-electron

model

with a soft-threshold energy.

Fig.1S

calculated

and carriers generate at the region where carriers

surpass the

electric field maximum point.

squares

indicates

the results

by drift

diffusion model, and

circles

indicates

the results by

MONTES.

For longer channel-

indicates the effectiveness

of the

Montes. However, the results

by a drift-diffusion model are

smaller

than experiments with