lvts - macro-inspection using flatbed scanner concept

Macro inspection concept

based flatbed scanner

Vladislav Kaplan, September 2010

Currently numerous companies providing fully automated wafer inspection

systems used in the semiconductor fabrication process. All of the systems

are stand alone and have no possibility to be integrated in existed modules,

thus creating additional operation step. Existed technologies of macro

inspection are extremely difficult to integrate into existing toolsets, mostly

due to the optical lenses requirement for focal distance with minimal

distortion. Also requirements for high throughput are directly linked to one-

shot approach.

Most advanced systems of one shot technology developed by KLA and

Nanda. Anyway nobody could overcome layout issues and stand alone non

integrated technology is the main on the market.

Current approach

My proposition includes creation of the one-scan technology based on

CCS/CCD array, similar to the devices used in flatbed scanners. Taking into

the account that layout requirement for such technology significantly lower

as well as integration and modification cost for 200mm,300mm or even

450mm technologies, giving us prospective of accommodation of such

macro inspection devices in existed modules.

Proposition

In order to confirm the possibility to build prototype for macro inspection tool

following activities completed:

1. Automatic macro inspection program based Labview for macro defect

detection. Input of the program is and picture format file, scanned from

actual wafer surface.

Proposition

Task - Creation prototype of the SW to extract defective areas

Basic requirements :

A. Scanned wafer picture in any image format.

Automatic program for macro inspection based scanned image

Edge fields

Automatically found golden fields Defected fields

Processed imageScanned image

Compare and find Abs Difference

Flatbed Scanner picture

Extract Grey level per Intensity plane

Automatically Extract Field valid

fields based on minimal image

variation

Perform Grey Level Correlation Matching

Get a difference map with certain thresholds


Algorithm Flow

Do Hor Scan and define lowest frequency

(Xsize)

Do Ver Scan and define lowest frequency

(Ysize)


Extracted pattern Xsize*Ysize pixel

stored for reference, perform the operation

to find golden patterns based on minimal variation

and build averaged golden pattern.


Perform correlation matching of

calculated golden pattern with

wafer image Xcente and Ycenter

for every resembled field.


Compare Xsize*Ysize area with center at

Xcenter and Ycenter with Reference image

and get difference map ( different threshold

levels define sensitivity, for example 30

gives black-zero pixel for any difference

less than 30, red gives 30+Scale*1, green

30+Scale*2, etc….


Examples – see different Inspection options



Results – see different Inspection options

Defects Detection?



Focus Spots?



Stepper shifts?



Summary

Creation of device capable to incorporated even basic CCS/CCD array element

giving way to create new type of macro inspection metrology which is capable to be:

1. Cheap

2. Integrated

3. Having extra High throughput

lvts - macro-inspection using flatbed scanner concept

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