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Why Do Silicon Wafers Have Flats or Notch?

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  • icon2 January 11, 2024
  • icon3 WaferPro
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Silicon wafers, the foundation of integrated circuits and semiconductor devices, come with an intriguing feature - a flattened edge or a tiny notch cut into the side. This small detail actually serves an important purpose for wafer handling and device fabrication. As a leading wafer manufacturer, we get asked frequently - why do silicon wafers have flats or notches? In this article, we'll explain the function of flats and notches and discuss some key differences.

*Looking for wafers with flats or a notch? We have a wide range of standard and custom silicon wafers available to order online via WaferPro - with precise SEMI standard flats, notches, and custom flats for your silicon needs.

The Role of Flats and Notches

Wafer Notch

A Wafer Notch Closeup

Silicon wafers are delicate and must be handled with precision during device manufacturing. Flats and notches provide a place for machines to safely grip the wafer without contacting the main surfaces. This protects the valuable wafer surface from any damage or contamination during processing.

There are two main types used in the semiconductor industry:

  • Flats - these are straight edges cut into the side of the round wafer
  • Notches - tiny V-shaped indents in the perimeter of the wafer

The machines that handle silicon wafers have end-effectors specifically designed to grip the flats or notches tightly for transportation and alignment in fabrication equipment. The grip area is kept very minimal to allow maximum surface area for building integrated circuitry.

Wafer Type Grip Mechanism Used
Flatted Wafer End-effector with flat edge grip
Notched Wafer End-effector with V-shaped grip

This allows automated and safe movement of wafers between process equipment in fab lines. Operators also may carefully handle wafers manually by the flats/notches when loading or unloading from cassette containers.

Why Have Flats and Notches?

Silicon Wafer Orientation Flats & Notch

A Diagram of Silicon Wafer Orientation Flats & Notch

The asymmetry of a flat or notch serves a vital alignment function for wafer fabrication. Without these, there would be virtually no way to reliably orient the wafer and map out die locations.

Alignment & Mapping

Silicon wafer crystals have atomic structures aligned to specific planes and directions - it matters greatly which way the wafer is turned!

Flats and notches are used to establish the orientation of these crystal planes and axes. With the asymmetry on the perimeter, engineers can precisely align to <110> or <100> crystal directions needed.

This orientation alignment ensures proper mapping from wafer to final chip devices. Masks and equipment target specific sites across the wafer surface to build structures and integrated circuits. Misalignment could make these devices useless!

Handling and Safety

As mentioned already, the shape of flats/notches allows safe handling by manufacturing equipment. Without these grip points, the tool would put uncontrolled forces and contact wafer surfaces.

Such contact risks contamination that ruins functionality. Grip locations at the perimeter avoid this contamination while better securing the wafer.

Furthermore, engineers generally avoid sharp corners and edges when handling fragile materials like silicon wafers. Flats and rounded notches mitigate cracks or breaking compared to handling by sharp edges.

The flats or notches maximize handling stability while clearing space for device fabrication.

SEMI Standards for Wafer Flats and Wafer Notch

As a high-volume wafer supplier, we closely follow industry specifications from SEMI for flats and notches. But what exactly sets these standards?

The SEMI M1 standard outlines requirements for silicon wafers up to 300mm diameter. This covers specifications for:

And more aspects critical for device manufacturing.

A 2 Inch Silicon Wafer With 1 Flat
A 2 Inch Silicon Wafer With 1 Flat

Here are the key SEMI standards for flats and notches on common wafer sizes:

Wafer Size Flat/Notch Type SEMI Standard Dimensions
50.8mm (2 Inch) 1 Flat 8.00 mm ± 1.65 mm
76.2mm (3 Inch) 2 Flats 11.18 mm ± 3.17 mm and 11.18 mm ± 1.52 mm
100 mm (4 Inch) 2 Flats 32.5 mm ± 2.5 mm and 18.0 mm ±2.0 mm
125 mm (5 Inch) 2 Flats 42.5 mm ± 2.5 mm
150 mm (6 Inch) 1 Flat 57.5 mm ± 2.5 mm
200 mm (8 Inch) 1 Notch 1.00 mm + 0.25 mm - 0.00 mm
300 mm (12 Inch) 1 Notch 1.00 mm + 0.25 mm - 0.00 mm

As you can see, standards evolve based on industry usage - flats commonly used for smaller sizes while notches allow tighter specifications for largest 300mm wafers.

Of course we can also supply custom flats/notches outside these specs per individual customer requirements.

Wafer Flats vs. Wafer Notch

Both flats and notches successfully serve the same role, so why have two types? There are some subtle differences...

Flats take up more space on the perimeter but offer a larger, straight grip surface. Notches are more compact yet provide a secure vertex grip point.

There are historical reasons based on industry evolution as well. Early on, flats provided an easy visual cue and grip access for wafer technicians. As automation increased, notches could be hidden inside end-effector jaws.

Mainly the type depends on equipment design and specs from vendors. Most fabrication tools now work easily with either flats or notches.

So semiconductor fabs adopt the standard that fits best rather than mix and match. Some plants use all flats, some all notches to simplify logistics.

As a leading wafer producer, we have capability to supply wafers with flats or notches as customers require for their fab lines.

The Takeaway

While a subtle feature, flats and notches enable handling, alignment, and safety for silicon wafer processing. The asymmetry allows foolproof orientation while providing equipment access to grip wafers without surface damage.

Next time you gaze at an integrated circuit, consider the critical role such a tiny flat or notch had in its fabrication!

Without flats or notches, the trillion-plus transistors on silicon would never have made it into your modern electronics in working order. Another reason why seemingly insignificant details matter greatly in semiconductor manufacturing!

Frequently Asked Questions

Q: Are flats and notches universal standards across all silicon wafer manufacturers?

A: There are industry standards, but some variation exists. Common flats or notches work for most equipment. As a leading manufacturer, we follow SEMI guidelines and can customize to customer fabs.

Q: Can a wafer have both a flat and a notch?

A: Technically yes, but generally not needed. Having an asymmetric flat or notch is enough for alignment, so a second would be redundant.

Q: Can flats or notches cause problems in device fabrication?

A: If flats/notches extend too far from the edge, the lost surface area could squeeze layout space. We optimize dimensions to maximize surface area.

Q: How are these flats or notches actually cut into the wafer?

A: We use precision diamond cutting tools. For notches, the wafer is held on a rotating chuck and brought into contact with the V-shaped cutting tool.

Q: Can wafers become damaged or contaminated during flat/notch creation?

A: Definitely a risk, but we employ specialized equipment, cleanroom controls, and stringent quality checks to avoid any issues.

Q: Beyond flats and notches, are there other wafer alignment methods?

A: Yes, there are other optical, laser, and RFID techniques. But mechanical flats/notches remain the most widespread and cost-effective approach.

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