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Wafer Preparation Presentation Transcript
1.Wafer Preparation
2.Requirement of raw materials Silicon: specifications Optically flat substrate - disk type Thickness = 1 – 2 + 0.005 mm Diameter = 300 + 0.5 mm Free from defects Resistivity – as per design Type – n, n+, p, p+ - as per design Orientation – (111), (100) – as per design
3.How to get the raw material?
4.Silicon:Ingot and wafers
5.Steps in wafer preparation
6.Shaping Operations: Purpose, Steps, (1)End Removal: Q.C. ~ ?,O2, C, Bulk Defects (2)Diameter grinding ~ + 0.5 mm (3) Wafer Flat or Notch marking
7.Marking Crystal Orientation X- rays are used to precisely orient the ingot Mounting on block
8.Identification of Wafers: ~ Purpose, ~ Process steps
9.# Ingot Cutting:
(a) Saw
(b) Wire *Cutting action by abrasive slurry *Saw: ~ I.D. and O.D. ~ Stress on crystal, ~ High production time, ~ Low cutting damage, ~ Less material lost, *Wire: ~ Multiple wafers simultaneously, ~ Small production time # Chemical cleaning to remove slurry, (q423)
10.Wafer Finishing: Purpose: to make them stronger and flatter to achieve desired surface finish Process Steps: Wafer lapping and edge contour Etching Polishing Cleaning Wafer evaluation Packaging
11.Polishing the wafer Mirrored, super-flat surface Done in automated machines
12.Chem Mech Polish (CMP) Slurry – Colloidal solution of 100 Angstrom dia silica (SiO2) particles in aqueous NaOH Chemical Process – NaOH oxidises Silicon Mechanical Process – Silica particles abrade the SiO2 away from the silicon surface.
13.Cleaning after polishing
14.Quality Measures Physical dimensions Flatness Microroughness Oxygen content Crystal defects Particles Bulk resistivity
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