How to Clean Metal Off Wafers After EUV Chipmaking

This patent describes a specialized system and cleaning fluid used to precisely remove tiny metal bits from silicon wafers after they've been patterned using extreme ultraviolet light for making advanced computer chips.

What it covers

This patent describes a system and method for cleaning semiconductor wafers after they've been processed using Extreme Ultraviolet (EUV) lithography. The system includes a chamber to coat a wafer with a "metal-containing photoresist material" (Claim 1). After patterning, "first nozzles" apply a "cleaning fluid" specifically designed to remove "metal contaminants" that come from this photoresist (Claim 1). The cleaning fluid contains a solvent with specific "Hansen solubility parameters" (delta D between 13-25, delta P between 3-25, delta H between 4-30) and an acid or base with a defined "acid dissociation constant" (Claim 2). "Second nozzles" then apply a "purging fluid" to further help remove these contaminants (Claim 1). The system can also spin the wafer (Claim 3) and spray fluids onto its backside or edges (Claims 6-9). For example, after an EUV exposure step, a wafer might have trace amounts of tin (Sn) from the photoresist, which this system's specialized cleaning fluid and process would remove to ensure the chip's quality.

What it doesn't cover

• —Cleaning processes that do not use a metal-containing photoresist material in the EUV lithography step.
• —Cleaning fluids that do not meet the specified Hansen solubility parameters (delta D, P, H ranges).
• —Cleaning fluids that do not contain an acid with a pKa between -11 and 4, or a base with a pKa between 9 and 40.
• —Systems that do not include both distinct cleaning fluid nozzles and distinct purging fluid nozzles.
• —The use of non-EUV lithography processes for patterning the photoresist.

The clever bit

The novelty lies in precisely defining the chemical properties of the cleaning solvent using "Hansen solubility parameters" (delta D, P, H) in combination with a specific acid or base strength (acid dissociation constant). This allows for highly selective and efficient removal of specific metal contaminants, which is crucial for the extremely demanding purity requirements of EUV lithography.

Why it matters

As computer chips get smaller, the features printed on them become incredibly tiny, requiring advanced techniques like Extreme Ultraviolet (EUV) lithography. This process often uses photoresists that contain metals, which can leave behind minute metal contaminants. These contaminants can ruin the delicate chip structures, leading to defects. This patent addresses a critical step in manufacturing advanced semiconductors, ensuring the purity and performance of next-generation microprocessors and memory chips.

Real-world examples

• 1.Advanced semiconductor fabrication plants
• 2.EUV lithography process lines
• 3.Manufacturing of leading-edge CPUs
• 4.Production of high-density memory chips