Photomask Inspection

The defects on the mask are reflected on the wafer. As the complexity of the chip increases, the difficulty of detecting errors also increases. Defects are unwanted deviations in chips, which can impact yield and performance. They can crop up during the chip manufacturing process, including the production of a mask or photomask, sometimes called a reticle.

Alfa Chemistry is a technological leader in the field of photomasks, providing customers with cost-effective mask defect inspection services to capture statistical defects.

Our services are used in wafer manufacturing, photomask manufacturing, MEMS and LED manufacturing, and research institutions. Our services have the following significant advantages:

• Cost effective solution for statistical defects
• High quality objectives
• Flexible tool configurations available
• Bare mask and pellicle inspection

What Can Alfa Chemistry Inspect?

Hard Defects

A hard defect is any flaw affecting the photomask mask, other than contamination. One class of defects includes the presence of metallized coating where it should not be or unwanted clear areas (pin holes, clear breaks, clear extensions). Such defects may cause the circuit to fail to operate normally.

Inspection Methods:

• Microscope inspection: Use high magnification (50 to 200 times) to manually inspect the mask under the microscope.
• Automatic inspection: The automatic inspection tool is used with complex image processing routines to inspect the photomask for hard defects.

Soft Defects

Soft defects include dust, particles and residual photoresist.

The causes are as follows:

• Airborne particles deposited on the surface of the mask. (Particles in wet process; developing/etching/peeling/cleaning parts that are not completely removed in the process)
• Improper handling. Touching the surface of the mask or not wearing proper cleanroom clothing
• Improper cleanroom protocols.

Inspection Methods:

• Total light inspection: Check the mask for total contamination (visible to the naked eye) under high-intensity light.
• Microscope inspection: Use high magnification (50 to 200 times) to manually inspect the mask on the microscope.
• Automatic inspection: Automatic inspection tools are used with complex image processing routines to inspect the photomask for soft defects.

Cosmetic Defects

The existence of defects does not necessarily affect the function of the circuit, but the designer/end user may determine that this is unacceptable.

Cosmetic defects can include:

• Surface scratches
• Stains that don’t affect light transmission.
• Hard defects outside of the pattern area.
• Imperfections to the glass substrate.
• Defects on the non-metalized surface (glass side)