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SEMI P18-92 © SEMI 1992, 2004 1 SEMI P18-92 (Reapproved 1104) SPECIFICATION FO R OVERLAY CAPABILITIES OF WAFER STEPPERS This specificatio n was technically r eapproved by the Global Micropatterning Co mmittee and is the …

SEMI P17-92 © SEMI 1992, 1999 2

NOTICE: These standards do not purport to address

safety issues, if any, associated with their use. It is the

responsibility of the user of these standards to establish

appropriate safety and health practices and determine

the applicability of regulatory limitations prior to use.

SEMI makes no warranties or representations as to the

suitability of the standards set forth herein for any

particular application. The determination of the

suitability of the standard is solely the responsibility of

the user. Users are cautioned to refer to manufacturer's

instructions, product labels, product data sheets, and

other relevant literature respecting any materials

mentioned herein. These standards are subject to

change without notice.

The user's attention is called to the possibility that

compliance with this standard may require use of

copyrighted material or of an invention covered by

patent rights. By publication of this standard, SEMI

takes no position respecting the validity of any patent

rights or copyrights asserted in connection with any

item mentioned in this standard. Users of this standard

are expressly advised that determination of any such

patent rights or copyrights, and the risk of infringement

of such rights, are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI P18-92 © SEMI 1992, 2004 1

SEMI P18-92 (Reapproved 1104)

SPECIFICATION FOR OVERLAY CAPABILITIES OF WAFER

STEPPERS

This specification was technically reapproved by the Global Micropatterning Committee and is the direct

responsibility of the North American Microlithography Committee. Current edition approved by the North

American Regional Standards Committee on August 16, 2004. Initially available at www.semi.org

September 2004; to be published November 2004. Originally published in 1992.

1 Scope

1.1 Definitions for the overlay capabilities of wafer

steppers are established, consistent with the primary

application of wafer stepper (i.e., the manufacturing of

very large-scale integrated circuits). Also included are

definitions for associated parameters: registration,

exposure field, good fields, and alignment.

NOTICE: This standard does not purport to address

safety issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory or other limitations prior

to use.

2 Referenced Standards

2.1 Statistical methods shall be used in accordance

with the procedures in NBS Handbook #91

(Experimental Statistics, by M.G. Natrella) and ASTM

STD 15D (Manual on the presentation of data and

control chart analysis).

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

3 Terminology

3.1 Definitions

3.1.1 overlay — a vector quantity defined at every

point on the wafer. It is the difference,

, between the

vector position,

, of a substrate geometry, and the

vector position of the corresponding point, 2P

, in an

overlaying pattern, which may consist of photoresist:

= 1P

– 2P

3.1.2 interfield overlay (also referred to as field-to-

field overlay) — The center of the lens is chosen to be a

reference point. The overlay at the reference point in

each exposure field is the interfield overlay.

3.1.3 exposure field — the area of a wafer covered by a

single exposure.

3.1.4 intrafield overlay (also referred to as within-a-

field overlay) — the overlay within an exposure field,

relative to the overlay at the center of the lens reference

location.

NOTE 1: From these definitions, it follows that the overlay at

any point on the wafer is the vector sum of interfield and

intrafield overlays.

3.1.5 registration — a vector quantity defined at every

point on the wafer. It is the difference,

, between the

vector position, 1P

, of a substrate geometry, and vector

position of the corresponding point,

, in a reference

grid:

= 1P

- 0P

3.1.5.1 The reference grid must be clearly specified in

any specification of registration.

3.1.5.2 Interfield and intrafield registration are defined

in a manner similar to interfield and intrafield overlay.

3.1.5.3 Overlay may be computed from registration

measurements if the same reference standard is used on

all systems for determining registration.

3.1.6 alignment — the mechanical positioning of

reference points on the wafers (“alignment targets”) to

the corresponding points on the reticles. The measure of

alignment is the overlay at the position on the wafer

where the alignment targets are placed.

3.1.7 Registration and overlay vectors shall be

decomposed into orthogonal components, X and Y,

along the directions of the stepper stage motion.

3.1.8 good fields — exposure fields in which the

magnitude of the overlay at every point within the field

is less than a specified value, V, in both the X and Y

directions, exclusive of contributions to overlay from

the reticles and non-linear deformations of the wafers

during non-stepper processing.

NOTE 2: It should be recognized that contributions from

reticles are non-statistical in nature, and that a particular

reticle will make the same contributions to overlay and

registration in every exposure field in which it is imaged.

3.1.9 fraction of good field — the overlay capabilities

of wafer steppers shall be quantified in terms of the

fraction of good fields, F, out of the total number of

fields on the wafer:

umber of good fields

umber of total fields

Good fields may also be quantified as a percentage

(100 × F%).

3.1.10 Any specification of overlay must define the

applicable exposure field size and the stepping patterns

on the wafers over which the specification applies.

From Sections 3.1.8 and 3.1.9 it follows that the

specification of the overlay capability of wafer steppers

consists of at least two additional numbers, the overlay

value, V, and the fraction of good fields, F. It is

consistent to characterize stepper overlay capability for

multiple overlay values, V

, V

, ... with corresponding

multiple fractions of good fields, F

, F

...

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer's instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

By publication of this standard, Semiconductor

Equipment and Materials International (SEMI) takes no

position respecting the validity of any patent rights or

copyrights asserted in connection with any items

mentioned in this standard. Users of this standard are

expressly advised that determination of any such patent

rights or copyrights, and the risk of infringement of

such rights are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction of

the contents in whole or in part is forbidden without express written

consent of SEMI.