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SEMI G78-0699 © SE MI 1999 19 A1- 1 .18.7 T ip s for gr aph ma king : • Add gridlines across the X-axis to separate wafers. • Print all graphs (X and Y, different lots , different probers) w ith the same scale in X and Y…

SEMI G78-0699 © SEMI 1999 18

A1-1.15 Step 13 — Calculate

Normaliz ed (by lot) Die Offset (11) = Average Die Offset (3) - Average Lot Offset

(9) [Accuracy]

loti setj wafk diel

loti setj wafk diel loti setj wafk diel

xoff

yn yoff

LOTX

LOTY

,, ,

,, , ,, ,

=−

(11)

A1-1.15.1 Discussion of Normalized (by lot) Die Offset

A1-1.15.1.1 This step is useful if you need to compare the variation between several different lots. It is not

completely necessary for the next step, since subtracting a constant from a string of numbers does not change the 3σ

variation, only the center point.

A1-1.16 Step 14 — Calculate

TTLX or TTLY = 3σ of Normalized (by lot) Die Offset (11) [Repeatability]

A1-1.16.1 Discussion fo TTLX or TTLY

A1-1.16.1.1 This is the value for determini ng (with 3σ confidence) whether your probe marks will always fall

within your desired spec. They are the hatch-marked lines.

A1-1.17 Step 15 — This normalized die offset includes Die-to-Die, Wafer-to-Wafer, and Setup-to-Setup offsets

thus a 3σ variation of this offset will be called Total Prober

Variation (TTLX and TTLY).

A1-1.17.1 Calculate Total Prober Error Range (3

LOTX + TTLX, LOTX - TTLX = Total Prober X-Error Range (3σ)

LOTY + TTLY, LOTY - TTLY = Total Prober Y-Error Range (3σ)

A1-1.17.2 Suggested Graphs:

X-Offset Y-Offset

LOTX + TTLX LOTY + TTLY

LOTX LOTY

LOTX - TTLX LOTY - TTLY

Average Die X-Offset (3) Average Die Y-Offset (3)

A1-1.17.2.1

It is recommended to create on e graph illustrating the prober accuracy in X and one graph for Y.

A1-1.18 Discussion of Graphs (one exa mple for X [Figure X] and one for Y [Figure Y])

A1-1.18.1 Average Lot X-Offset is the va lue from Step 10. This number shows where the probe mark distribution

is centered (the accuracy of the prober).

A1-1.18.2 Average Lot X-Offset +3σ is t he result from step 10 + the result from step 14

A1-1.18.3 Average Lot X-Offset -3σ is th e result from step 10 – the result from step 14

A1-1.18.4 These two lines show the ± 3σ range of your distribution. This describes the repeatability of the prober.

NOTE: There will always be explainable and unexplainable accuracy and repeatability errors on a prober. If these two lines fall

within your desired specification, you will probably not have any problems. The example graph for X-offset illustrates a well-

behaved, or “passing” prober. The example graph for Y-offset, on the other hand, is representative of a prober which failed to

meet the desired accuracy specification.

A1-1.18.5 The upper and lower desired specification limits have been added to the graphs.

A1-1.18.6 The final piece of data added t o the graph is the Average Die Offset. This, as stated in Step 1, is very

good at illustrating any trends throughout the lot.

SEMI G78-0699 © SEMI 199919

A1-1.18.7 Tips for graph making:

• Add gridlines across the X-axis to separate wafers.

• Print all graphs (X and Y, different lots, different probers) with the same scale in X and Y.

• Add a legend to your graphs, so that they will be readable by your “audience” as well as yourself.

Avg Lot X-Offset

Avg Lot X-Offset +3s

Avg Lot X-Offset -3s

Lower Spec Limit

Upper Spec Limit

Avg Die X-Offset

Figure 7

X-Offset

SEMI G78-0699 © SEMI 1999 20

Avg Lot Y-Offset

Avg Lot Y-Offset +3s

Avg Lot Y-Offset -3s

Lower Spec Limit

Upper Spec Limit

Average Die Y-Offset

Figure 8

Y-Offset

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