Silicon Wafer in Production: Type and Specification

By Assoc. Prof. Dr. Uda Hashim School of Microelectronic Engineering

Silicon Wafers: Basic unit • Silicon Wafers Basic processing unit •150, 200, 300 mm disk, 0.5 mm thick • Newest ones 300 mm (12 inches) • Typical process 25 - 1000 wafers/run • Each wafer: 100 - 1000's of microchips (die) • Wafer cost $10 - $100's • 200 mm wafer weight 0.040 Kg • Typical processing costs $1200/wafer (200 mm) • Typical processed wafer value $11,000(all products, modest yield) • Value/Mass of processed wafer $275,000/Kg

Conversion of Raw Sand into Metallurgical Grade Silicon

Comparison of Cz and Fz growing Methods

Comparison of Material Properties and requirements for VLSI

Current common Si Wafer Sizes •Since 1994 common sizes: • 200 mm (8 inch) state of art fabrication • 150 mm (6 inch) most 2nd level to front line fabs • 125 mm (5 inch) Bastard size (only a few facilities) • 100 mm (4 inch) Smallest production wafers: research • 75 mm (3 inch) Obsolete size: still used in research •(special order: more expensive than 4 inch) • 300 mm (12 inch) now in some production • Basically need to rebuild entire fab to change wafer size

General Wafer Specs • Orientation type – ,

• Crystal growth type – Cz – Fz (Float Zone)

• Substrate Type – – – – –

Si substrate Ge substrate GaAs InP SiGe

Si Wafer Types in Production • Reclaim (Dummy) wafer • Test wafer • Prime wafer – Si Wafer – SOI Wafer

Reclaimed Silicon Wafers •As larger diameter silicon wafers were being developed, pricing for the larger diameter wafers increased. In order to provide cost savings to customers, the wafer reclaim process was developed. •Reclaiming wafers is a process in which, the wafers are stripped of films, metals or other contaminants, cleaned and then polished to a customer’s specification. This allows customers to get three and four uses out of one wafer, instead of having to buy new wafers each time. •This service has become especially popular since the introduction of 300 mm wafers. Considering 300 mm wafers can cost anywhere from $600 each, many customers wanted to get the most usage as possible out of each wafer. •Different types of reclaim can be provided depending on the condition of the wafers. The customer specifies how clean and flat the wafers need to be after the reclaim process is finished. •The wafers can also be sorted into specific groups for resistivity, thickness, type and dopant or any specification that is of particular interest to you or your project.

Test Wafer •Test Silicon wafers are ideal for running equipment tests, research and development, experiments and many other applications. •We supply very high quality test grade wafers and sometimes there is very little difference between a test grade and prime grade wafer. •Test wafers are manufactured in all diameters. Furnace Grade •Furnace grade wafers have very tightly controlled electrical characteristics. Typically they are used for high temperature applications or thin film depositions. • Furnace grade wafers display very tightly controlled Oxygen content, resistivity, radial resistivity gradient (RRG) and carbon content. •The wafers are also doped very evenly. •All of these factors help films grow uniformly without slip lines or stress fractures. Lithography Grade •Lithography grade wafers are used for lithography or photolithography applications that require wafers to have very tightly controlled metrology. •Litho wafers have a very tight site flatness specification that provides little variation in thickness from site to site making for a very flat wafer.

Mechanical Grade – Mechanical grade wafers are usually 300 mm wafers. Although the specifications can be applied to any diameter wafer, the term “mechanical grade” most often refers to a 300 mm specification. – Mechanical grade wafers are also referred to as handling wafers. Mechanical grade specifications aren’t quite as stringent as most other wafer grades. Example of mechanical grade specifications. : • Diameter: 300 +/- 0.5 mm Type/Dopant: P/Boron Orientation: {100} +/- 1º Growth Method: Cz Resistivity: 1-100 Ω-cm Thickness: 750-800 µm Front Surface: Polished Back Surface: Polished Notch: SEMI Standard

Particle Grade Particle grade wafers typically refer to 300 mm wafers and have a minimal amount of contaminants, or particles. Particles are measured at various sizes, 0.09 µm, 0.12 µm, 0.16 µm, 0.20 and 0.30 are common specifications. The number of particles at a certain size is limited to a predetermined number, 10, 20, 50, etc. The specification is written: ≤50@≥0.12 µm. This means there are less than or equal to 50 particles greater than 0.12 µm in size on the entire wafer. Considering one human hair is approximately 1 µm thick, these particles are very small and cannot be seen with the naked eye. The smallest particle that can be seen with the naked eye is 0.5 µm. Particle Grade wafers are considered to be very clean. Depending on the user’s application, there are a couple of specifications that can be considered particle grade. Here are a couple of particle grade specification. Diameter: 300 +/- 0.5 mm Type/Dopant: P/Boron Orientation: {100} +/- 1º Growth Method: Cz Resistivity: 1-30 Ω-cm Radial Resistivity Gradient (RRG):