Metal Lift-Off

About

The Metal Lift-Off Process generally refers to the process of exposing a pattern into photoresist (or different material), depositing a thin film such as a metal or dielectric over the entire substrate area, and then removing or washing away the photoresist and excess metal leaving behind metal only in the designated patterned substrate area.

This process has commonly been done through a wet chemical process, but Takatori has developed a faster, more cost-effective, more environmentally-friendly alternative – Dry Metal Liftoff.

Traditional Metal Lift-Off

There are several methods currently used in Metal Lift-Off processes: toluene soak, negative/image reversal resist and the bi-layer method. These methods, however, produce chemical waste that requires proper disposal, often result in low yield, and offer challenges to reclaiming the often valuable waste metal.

Three Issues With Metal Lift-Off

Retention

This is a top issue for metal lift-off processes. If this happens, unwanted parts of the metal layer remain on the wafer. This can be created by different scenarios: The resist below the parts that should have been lifted off did not dissolve properly or the metal has adhered too effectively to areas it should not have, preventing lift-off.

Ears

Once the metal is deposited, covering the sidewalls of the resist, "ears" can form. They are made of the metal along the sidewall standing upwards from the surface. These “ears” can fall over the surface creating unnecessary forms on the substrate. The “ears” can also cause unwanted connections.

Redeposition

In some cases, metal particles will reattach to the surface in various locations during the lift-off process. Once the wafer is dry, these metal particles are quite difficult to remove.

Takatori’s Dry Metal Lift-Off Solution

The Dry Metal Lift-Off Process offers an efficient, high-yield process for removing unwanted metals. The process is simple. First, the substrate is laminated with an adhesive film compatible with metal required to be removed from the wafer surface. High-quality lamination is critical as wrinkles and bubbles are areas of improper adhesion. Once the film is laminated smoothly to the wafer, the adhesive film is gently peeled from the substrate at up to a 180° angle, taking with it the unwanted metal. A flash etch bath may be required to further remove particles.

1. The wafer with excess gold on the active surface, is placed onto the removal chuck.

2. Adhesive tape is laminated onto the surface of the wafer, adhering to the gold layer.

3. The tape is pulled back, removing excess gold.

4. Removal is complete. Excess gold is adhered to the tape, ready for reclaim.

Key Benefits

Dry metal lift off is faster than wet chemical processes. The AMR-2300 will process up to 40 wafers per hour (150mm).

Usage and disposal costs of chemicals are substantially reduced (and possibly eliminated).

Reduce usage and, thus, the dirty, unhealthy process of cleaning and maintaining chemical process machines.

Gold (Au) recovery is easier and less expensive (solid vs liquid)

Safe and easy operation (just press “Start” switch)

Monitors the Au on the tape. One roll of disposable adhesive holds approximately $3,000 ~$5,000 worth of gold.

Well-proven, high-production, low-maintenance machine.

Efficiency

The Dry Metal-Lift Off Process includes patented equipment developed by Takatori Corporation that is widely used in the semiconductor industry with a worldwide install base. It allows a more efficient way to recover precious metals, reduce chemical waste and addresses several concerns with solvent or chemical-based metal lift-off processes. It is another example of how Takatori and GTI work together with our customers to improve the speed, capability and efficiency of their fab.

AMR-2200G

DISCOVER

Contact Andre Kirkland

Semiconductor Sales Representative
GTI Technologies, Inc.