Measurements on pre-production wafers

at Udine

Presented by M. Cobalon behalf of the Udine groupPixel Week December 2001

Measured Wafers

• CiS • Tesla

- 4456-21- 4456-23- 4457-23- 4458-21

- A31-02- A31-07- A31-08- A31-12

Outline• Tiles and diodes with guard ring

– IV measurements– CV measurements– tile conformity

• SC’s and MC’s yield• Visual inspection

– ID marking correctness– visual inspection– mask alignment

IV measurements• This time, taken with 2-side chuck

• Temperature corrections applied

Diode position

n side

#17

#16

IV meas. on diode #17 (CiS)

IV meas. on diode #17 (Tesla)

Quality Control Parameters

• Tile conformity criteria:

– Vbd(tile)> Vop(diode)– Slope=I(tile @ Vop)/I(tile @ Vop-50)<2

• Vop=max(Vdep+50,150)

• Need to measure Vdep

Capacitance offset

CV results

CV results

- Measurements lie within 65 V < Vdep< 100 V

- Procedure specs demanded: 30 V < Vdep < 120 V

- For all wafers: Vdep <100 V Vop= max(Vdep+50,150) = 150 V

Determination of Vdep and Vop

• Cdep is between 1.7-4.2 (4.5-5.6) pF for CIS (Tesla)

• Determined as: Cdep=C(Vdep)-Coffset

Coffset of order of 0.2-0.7 pF (for positive polarity)

• lies within 2.1-3.3 kcm• conformity range is 2-5 kcm

Determination of Cdep and

Tile results (CiS)

• Results in agreement with CIS• 2 wafers with 2 good tiles• 2 wafers with 3 good tiles wafer 4456-21 with Slope (Tile 1) = 3.58

SC and MC yield (CiS)

• SC’s: 6 x 4= 24

• 5 are bad (Vbd<150)

• 79% are good

• MC’s: 4 x 4 = 16

• 1 is bad (Vbd<150)

• 94% are good

• Disagreement for 1 Wafer out of 4: Wafer A31-12 Slope(Tile 2): Our measure Tesla 2.08 1.85

Tile results (Tesla)

• SC’s: 6 x 4=24

• 1 is bad (Vbd<150)

• 96% are good

• MC’s: 4 x 4=16

• 4 are bad (Vbd<150)

• 75% are good

SC and MC yield (Tesla)

2- and 3-good-tile wafers:

– TILES: all 4 pads marked.– SC’s: only 1 of the 2 pads marked

(lower one).

– All markings are correct.

Scratch pad marking (CIS)

2 and 3 good tiles wafers

– TILES: only 2 out of 4 pads marked.– SC’s: only 1 of the 2 pads marked

(lower one).

– All markings are correct.

Scratch pad marking (Tesla)

Visual Inspection (CiS)• 4456-21n-side: Tile 2, small scratch (6 pixels)

#16, extended scratch (superficial)

• 4456-23n-side: Tile 1, one pixel defective Tile 2, “ “ Tile 3, three pixels defective #22, extended scratch (superficial) MC13, one pixel “larger”

Visual Inspection (Tesla)

• A31-02p-side: #17, small scratch

#12, small scratch

• A31-08n-side: #19, extended scratchp-side: bad end of the three top structures

Scratch

Mask alignment

vernier

Goal: Measure 2 mm misalignmentUse: “Nikon Optiphot 150” @ 200-500 X

Mask alignment (CiS)

•Good contrast•For vertical vernier, 4 vs 5 bars

Mask alignment (CiS)• Out of specifications:

Wafer 4457-23: n-side, left pad, 4th hor. right pad, 4th hor.

p-side, right pad, 4th hor.

Wafer 4456-23: n-side, right pad, 4th hor. p-side, right pad, 4th hor.

Wafer 4458-21: n-side, left pad, 4th hor. right pad, 4th hor. p-side, right pad, 4th hor.

• Quite bad contrast for all the vernier• All 3rd vernier are missing• All the 4th vernier are badly printed

Mask alignment (Tesla)

Mask alignment (Tesla)• Out of specifications:

Wafer A31-02: p-side, right pad, 1st vert.

Wafer A31-07: p-side, right pad, 1st vert.

Wafer A31-12: p-side, left pad, 4th vert.

Database

•The new wafers (both CiS and Tesla) have been already inserted in the database

• IV measurements will be added very soon

•For CV measurements, needs to understand better