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SEMI G78-0699 © SE MI 1999 16 A1-1 .7 Step 5 — Calculate Normalize d (b y wafer) Die Offset (6) = A verage Die Offset (3) - Average Waf er Offset (5) loti setj w afk diel loti setj w afk diel loti setj wafk loti setj waf…

SEMI G78-0699 © SEMI 199915

A1-1.4 Step 2 — Calculate

Normalized (by die) Pad Offset (4) = (2) - Average Die Offset (3)

loti setj wafk diel padm

loti setj wafk diel padm loti setj wafk diel

loti setj wafk diel padm loti setj wafk diel padm loti setj wafk diel

xnorm

off

ynorm yoff yoff

,, ,,

,, , , ,, ,

,, , , ,, ,, ,, ,

=−

(4)

A1-1.4.1 Discussion of Normalized (by die) Pad Offset

A1-1.4.1.1 This step helps to quantify how much error is caused by the prober vs. the probe card. The probe card

usually does NOT impact average offset of a die, just the variability within a die. In this equation, we subtract the

average die offset (presumed prober error) from each pad in that die. This data is then used for the next step.

A1-1.5 Step 3 — Calculate

P-P-X or P -P-Y = 3σ of Normalized (by die) Pad Offset (4).

A1-1.5.1 All the normalized pad offsets in the same lot (no matter on which die, on which wafer the pad resides)

are treated on an equal basis. In our example, a total of 2592 pads are sampled in a lot. All 1296 x-direction and

1296 y-direction pads of Normalized (by die) Pad Offset will be used to calculate a 3σ variation which is called

Pad-to-Pad variation

(P-P-X and P-P-Y).

A1-1.5.2 Discussion of P-P-X or P-P-Y (Pad-to-Pad Variation in the X-direction or Pad-to-Pad-Variation in the Y-

direction)

A1-1.5.2.1 These values describe how mu ch variability there is within all the pads in the lot. This value is

frequently attributed to probe tip variation in X, Y, and Z. Although probe tips do change and wear over time, their

unloaded position usually does not change dramatically within one lot. This value does not help tremendously in

describing prober accuracy nor should it be used for any sort of probecard metrology. However, be sure to perform

a mental reality check to verify that it is somewhere near (within an order of magnitude of) your probe card X/Y

probe needle position specification.

A1-1.6

Step 4 — Calculate

Average W afer Offset (5) = average of Average Die Offset (3).

loti setj wafk loti setj wafk diel

xoff xoff

yoff yoff

,, ,, ,

(5)

A1-1.6.1 Discussion of Average Wafer O ffset

A1-1.6.1.1 This equation will result in nine values for Average Wafer Offset-X and nine for Average Wafer Offset-

Y. These numbers could also be graphed to look for trends from wafer to wafer (this is not included on the example

graphs). If there is a consistent trend in one direction possible causes are:

• wafer loading error

• cumulative stepping error, and

• temperature stability errors

SEMI G78-0699 © SEMI 1999 16

A1-1.7 Step 5 — Calculate

Normalize d (by wafer) Die Offset (6) = Average Die Offset (3) - Average Wafer Offset

(5)

loti setj wafk diel

loti setj wafk diel loti setj wafk

loti setj wafk diel loti setj wafk diel loti setj wafk

xnorm

off

ynorm yoff yoff

,, ,

,, , ,,

,, , ,, , ,,

=−

(6)

A1-1.7.1 Discussion of Normalized (by wafer) Die Offset

A1-1.7.1.1 This normalization step is a pr ecursor to calculating a 3σ variation value. To calculate the true Die-to-

Die variation, any wafer-to-wafer induced error is subtracted out from the by-die-data. This data is used in the next

step.

A1-1.8 Step 6 — Calculate

D-D-X or D-D-Y = 3σ of Normalized (by wafer) Die Offset (6)

A1-1.8.1 These normalized die offsets a re again treated on the equal basis. A 3σ value is calculated and becomes

our Die-to-Die Variation

(D-D-X, D-D-Y).

A1-1.8.2 Discussion of D-D-X or D-D-Y (Die-to-Die 3

variation in the X-direction, Die-to-Die 3

variation in

the Y-direction)

A1-1.8.2.1 This equation will result in the 3σ variation of the average die offsets from Die-to-Die in both X- and

Y-directions. If this number is very large, there should be concern about the repeatability of the prober.

A1-1.9 Step 7 — Calculate

Average Setup Offset (7)

loti setj loti setj wafk

xoff xoff

yoff yoff

,,,

(7)

A1-1.9.1 Discussion of Average Setup Offset

A1-1.9.1.1 These equations will produce six values, three for Average- (by Setup) Offset-in-the-X-direction and

three for Average- (by Setup) Offset-in-the-Y-direction. These values describe the average offset of all of the die

“tested” with a particular setup.

A1-1.10

Step 8 — Calculate a

Normali zed (by setup) Wafer Offset (8) = Average Wafer Offset (5) - Average

Setup Offset (7).

loti setj wafk

loti setj wafk loti setj

loti setj wafk loti setj wafk loti setj

xnorm

off

ynorm yoff yoff

,, ,

,, ,, ,

=−

(8)

A1-1.10.1 Discussion of Normalized (by setup) Wafer Offset

A1-1.10.1.1 A normalizing step to help calculate the true wafer-to-wafer variation.

A1-1.11 Step 9 — Calculate

W-W-X or W-W-Y = 3σ of Normalized (by setup) Wafer Offset (8).

A1-1.11.1 A 3σ variation will be calculat ed based on the normalized wafer offset and will be cited as the Wafer-to-

Wafer variation (W-W-X, W-W-Y).

A1-1.11.2 Discusssion of W-W-X or W-W -Y (Wafer-to-Wafer variation in the X-direction, Wafer-to-Wafer

variation in the Y-direction)

A1-1.11.2.1 This equation will produce a v alue for the 3σ variation from Wafer-to-Wafer in the X and Y

directions. If this number were large, it would tend to indicate that the prober does not behave repeatably from

wafer-to-wafer. Possible causes are:

• loading problems

• temperature stability issues, and

• wafer rotation issues

A1-1.12 Step 10 — Calculate

Average Lot Offset (9) = average of Average Setup Offset (7).

LOTX xoff

LOTY yoff

loti setj

(9)

A1-1.12.1 Discussion of Average Lot Offset (LOTX or LOTY)

A1-1.12.1.1 This will be one of the values added to the graph. This is simply the average of all of the average die

offsets in the X-direction and all of the average die offsets in the Y-direction. If one needed to pick a single number

in X and Y to describe the accuracy of the prober – this is the one. This can be very misleading though – what this

number really tells you is what value the distribution is centered around. Refer to the graph to get a visual sense of

this data.

A1-1.13

Step 11 — Calculate

Normaliz ed (by lot) Setup Offset (10) = Average Setup Offset (7) - Average Lot

Offset (9)

loti setj

loti setj loti setj

xnorm

xoff

ynorm yoff

LOTX

LOTY

=−

(10)

A1-1.13.1 Discussion of Normalized (by lot) Setup Offset

A1-1.13.1.1 This is another normalization step used to calculate the true setup-to-setup error in X and Y.

A1-1.14 Step 12 — Calculate

S-S-X or S-S-Y = 3σ of Normalized (by lot) Setup Offset (10).

A1-1.14.1 A 3σ variation will be calculat ed based on the normalized setup offset and will be cited as the Setup-to-

Setup variation (S-S-X, S-S-Y).

A1-1.14.2 Discussion of S-S-X or S-S-Y (Setup-to-Setup variability in the X-direction, Setup-to-Setup variability in

the Y-direction)

A1-1.14.2.1 These two values describe how much variability there is between setups.