Lithography Overviews

Subtractive vs. Additive Process
Positive vs. Negative Tone Photoresists >

Photoresist is used as a mask to transfer/pattern films of metals, dielectrics and many other materials. After removing or adding a layer, the photoresist mask is removed and fabrication of the device continues.

Subtractive (Etch): Single Resist Layer

The resist mask can be used to perform a subtractive wet or dry (plasma, RIE) etch.

• Highly selective
• Non-directional (isotropic)
• Low cost
(Plasma or RIE, DRIE which are anisotropic)
• More anisotropic
• Chemical and physical in nature
• HAR possible
Using S1800 Series (Dow)
• Positive (g-Line)
• Aqueous Processing
• Excellent etch resistance
• Easily removed
Using SPR 955 CM, UV 26, UV110, S1800 Series (Dow)
• Positive (g-Line)
• Aqueous Processing
• Easily removed

Additive: Single Resist Layer

Pattern Transfer — Subtraction

Ma-N 1400, MA-N 400 Series - Negative - (MRT)
• Simple processing
• Low cost
• Films from 0.5- 7 microns
SPR-220 Series (Dow)
• Positive (broadband)
• Aqueous Processing
• Easily removed
• Au, Cu plating without cracking
• 10+microns

KMPR 1000 Series (MCC)
• Negative
• Aqueous Processing
• Solvent removable

Additive: Bi-Layer (Lift-Off)

Microstructures can be fabricated by depositing materials such as metals (evaporation, sputtering).

Bi-layer Lift-Off Resist:

Although a single layer of photoresist can be used as an additive mask, much greater control of the undercut profile is obtained with a bi-layer lift-off structure. This uses a bottom lift-off film (e.g. LOR) with a top imaging resist. An example of bi-layer stack is a S1800 (Dow) resist over LOR (MCC). The choice of the specific LOR bottom layer depends on the desired deposited film thickness and the developer used for the top imaging resist

S1800, SPR 220, SPR 3600 Series (Dow) imaging resist on top of LOR (A, B or SF depending on film thickness to be deposited)
• Superb process control
• Aqueous processing
• Thick (>5 micron) metal deposition
• Excellent adhesion
• Sub micron structures

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