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SEMI E79-0304 © SEMI 1999, 2004 21 • Nominal parameters are more representative of the physical systems bei ng studied. • Nominal parameters are more representative of the desired system perform ance. • It is not pr acti…

SEMI E79-0304 © SEMI 1999, 2004 20

Pre-AlignLoad

Set & Align

Load Box

Reticle Handler

Pre-Align Chuck

x (# wafers per reticle)

Exposure Stage

1.1 ExposeTransfer Transfer

Pre-AlignLoad

Figure R1-1

Example Resource Utilization Sequence

Step

Align Level Expose

x (# exposures)

Blade

Align

x (# exposures)

x (# images-1)

Step Level Expose

Figure R1-2

Example of Equipment Sub-Sequence

R1-2.10.3 The operations indicated by dashed boxes

represent the beginning phase of the main equipment

sequence. If the stepper is capable of processing wafers

of the same reticle indefinitely, then the beginning

phase is not included in theoretical production time. If,

however, there is a hardware and/or software limit to

the number of wafers that may be run consecutively,

then the beginning phase shall be counted in theoretical

production time.

R1-3 Modeling Theoretical Durations for

Operational Elements

R1-3.1 Once a theoretical equipment sequence is

defined, the next step is to measure and/or model

theoretical durations for each operational element in the

sequence. As a rule, it is preferable to acknowledge in

the model an elemental speed loss that can never be

recovered in lieu of inadvertently overlooking another

loss that could be reduced or eliminated.

R1-3.2 Legitimate Observations — Each theoretical

element duration should always be less than or equal to

any legitimate observation for that element, where a

legitimate observation is a traceable instance of an

operational element that does not result in a loss of

quality. The time for any legitimate observation that is

less than the existing theoretical element duration

should become the new theoretical element duration.

For legitimate instances of the same operational

element on different instances of identically configured

equipment, the best time observed among all equipment

of that type should be used as the theoretical element

duration.

R1-3.3 Basis for Theoretical Element Durations —

Theoretical element durations may be based on time

studies, nominal parameters, and/or parametric

modeling.

R1-3.3.1 Time Studies  Most mechanical operational

elements that have fixed execution times, like transport

and load lock operations, can be accurately determined

by time studies using either stopwatches, equipment

data acquisition systems, timing systems built into the

equipment, or stand-alone data acquisition systems that

use sensors to detect equipment events and/or state

changes.

R1-3.3.1.1 When it is difficult to directly measure

individual elements, collections of elements may be

observed and timed instead. On systems where a

number of consecutive identical elements occur too fast

to be measured individually, a set of elements should be

timed, and the time should be divided by the number of

elements in the set. For even more complicated

situations, element times may be derived algebraically

from observations of several linearly independent sets

of operational elements.

R1-3.3.2 Nominal Parameters — There are instances

where it is desirable to use nominal parameters to

represent theoretical conditions rather than using direct

observations, such as when:

SEMI E79-0304 © SEMI 1999, 2004 21

• Nominal parameters are more representative of the

physical systems being studied.

• Nominal parameters are more representative of the

desired system performance.

• It is not practical to obtain reliable data.

R1-3.3.3 Parametric Models — For cases where the

time for an operational element may have a range of

values that are dependent on recipe specifications,

theoretical time is best represented by a parametric

model. Parametric models for representing

semiconductor operations may be based on

mathematical formulas, e.g., implant time versus beam

current, and/or “lookup” tables, e.g., best observed etch

time vs. etch end point.

R1-3.3.3.1 For the photolithography example, one of

the recipe parameters is the exposure energy (EE).

Given the ideal or theoretical lamp intensity (LI) of the

stepper, the theoretical duration per exposure (THT

)

for the recipe may be calculated as THT

= EE / LI .

SEMI E79-0304 © SEMI 1999, 2004 22

RELATED INFORMATION 2

RAPID CHARACTERIZATION OF INTRINSIC EQUIPMENT EFFICIENCY

(IEE) AND THE PRODUCTIVITY EFFICIENCY PLANE

NOTICE: This related information is not an official part of SEMI E79. This related information was approved for

publication by vote of the responsible committee on December 15, 1999.

R2-1 Rapid Characterization of Intrinsic

Equipment Efficiency

R2-1.1 IEE may be rapidly characterized as follows

using a limited number of production experiments.

R2-1.2 Step 1: Design Production Experiments —

Select a limited number of scenarios to execute as

equipment experiments. It may be of interest to

characterize IEE according to either operating modes,

processing diversity, or a combination of operating

modes and process diversity.

R2-1.2.1 Determine the value-added in-process

theoretical production time per unit (VTHT) – (time per

unit) for all recipes involved. This information is

required for determining IEE. See Table A2-1.

R2-1.2.2 For assessment of operating modes,

experiments should examine only a single typical recipe

that is likely to be used most frequently. Each

experiment should examine a separate operating mode,

where examples of various equipment operational

modes may be as follows:

One wafer at a time mode (production monitor

wafer).

One batch is run, then the tool stops.

Two batches are run, then the tool stops.

Three batches are run, then the tool stops.

Continuous (cascade) mode. A larger number of

batches is run, then the tool stops.

R2-1.2.3 For assessment of process diversity, select a

limited number of representative recipes that will be

processed by a tool. This population should include at

least one recipe representing the minimum expected

processing duration and one representing the maximum.

R2-1.2.4 Each experiment should be designed and

executed to eliminate rate efficiency losses to the

greatest extent possible. It is further assumed that

quality efficiency losses are zero. Under this

approximation, (VA-OEE) = (OEE)

× (IEE).

R2-1.3 Step 2: Execute Process Experiments —

Perform process experiments recording all relevant

input variables including the configuration of lots and

wafers, and recipes. For each experiment, record the

elapsed production time using convenient means, e.g.,

stopwatch or existing data acquisition system.

R2-1.4 Step 3: Calculate Results — Calculate IEE and

throughput for each experiment. IEE may be used to

measure the effect of non-value-added overhead time

during equipment processing. Approximately:

Intrinsic Equipment Efficiency (IEE)

= (Value-Added In-Process Theoretical Time)

/(Non-Value-Added Overhead Time

+ Value-Added In-Process Theoretical Time)

R2-1.4.1 Hence, non-value-added overhead time for

each experiment may be calculated as:

Non-Value-Added Overhead Time

= [(Production Time)

- ( Value-Added In-Process Theoretical Time)]

R2-1.4.2 It should be the focus of efforts by the

equipment supplier and the end-user to reduce or

eliminate non-value-added overhead time through

improved equipment design, including scheduling

software, as well as hardware components (carrier and

wafer handling systems, valves, pumps, heaters,

coolers, etc.).

R2-1.4.3 Results may be shown in either tabular form

or plotted graphically on a Productivity Effectiveness

Plane. See Section R2-2.