Supercritical Drying of Semiconductor Substrates Preventing Particle Etching
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Solution Overview
Problem
Supercritical drying methods for semiconductor substrates face issues such as pattern collapse due to surface tension and potential etching of metal materials during the phase transition of carbon dioxide from a supercritical state to gas, leading to particle generation and deterioration of electric characteristics.
Innovation Solution
A method involving a supercritical drying system where a semiconductor substrate is treated with a supercritical fluid of carbon dioxide at a temperature above 75°C but below the critical temperature of the alcohol, allowing the alcohol to be dissolved and removed without re-adsorption, thereby reducing particle formation and minimizing etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If supercritical drying is performed by lowering pressure to transition CO2 from supercritical state to gas, then the alcohol is removed from the wafer surface, but the alcohol is cohered and re-adsorbed onto the wafer, generating particles
Solution Approach 1:
The wafer surface is pre-heated to 75°C or higher before introducing the supercritical CO2 fluid. This preliminary heating ensures that when pressure is reduced and CO2 transitions to gas, the alcohol remains in vapor state due to the elevated temperature, preventing condensation and particle formation on the wafer surface.
Solution Approach 2:
The patent changes the temperature parameter from conventional low-temperature drying to elevated temperature (75°C or higher) during supercritical drying. This parameter change fundamentally alters the behavior of alcohol during pressure reduction, keeping it in vapor state rather than allowing it to condense and form particles.
2Manufacturing precision
If supercritical drying is performed at low temperature, then particle generation is reduced, but metal materials on the semiconductor substrate may be etched, deteriorating electric characteristics
Solution Approach 1:
The patent raises the temperature parameter to 75°C or higher during supercritical drying, which simultaneously achieves two objectives: preventing alcohol condensation to reduce particle generation, and suppressing metal etching reactions that occur at lower temperatures. This parameter change resolves the contradiction between reducing particles and preventing metal damage.
3Reliability
If conventional drying with isopropyl alcohol is used, then the wafer can be dried, but pattern collapse occurs due to surface tension of the liquid during drying
Solution Approach 1:
The patent utilizes the phase transition of CO2 from supercritical state to gas state during pressure reduction. This phase transition occurs without liquid formation, eliminating surface tension effects that cause pattern collapse in conventional liquid-based drying methods, while still achieving effective drying.
Solution Approach 2:
The use of CO2 as an inert supercritical fluid creates a controlled environment that eliminates the harmful surface tension effects of conventional organic solvents like isopropyl alcohol, while the elevated temperature ensures alcohol vapor does not condense on the wafer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces particle generation on the substrate and prevents etching of metal films, maintaining the integrity and electrical characteristics of semiconductor devices.
Implementation Method 1
a wafer with its surface wet with IPA is brought into the state of being soaked in carbon dioxide in a supercritical state (supercritical CO2 fluid) so that the IPA on the wafer is dissolved into the supercritical CO2 fluid
Implementation Method 2
a pressure and a temperature inside the chamber are lowered to perform phase transition from the supercritical CO2 fluid to gas, which is then discharged to the outside of the chamber, to dry the wafer
Implementation Method 3
the IPA which is left inside the chamber while in the state of being dissolved in the supercritical CO2 fluid is cohered and re-adsorbed onto the wafer, resulting in generation of particles (dried trace)
Data Source
AI summary
According to one embodiment, a supercritical drying method for a semiconductor substrate includes introducing a semiconductor substrate formed with a metal film into a chamber, the surface of the substrate being wet with alcohol, supplying a supercritical fluid of carbon dioxide into the chamber, setting a temperature inside the chamber to a predetermined temperature, to replace the alcohol on the semiconductor substrate with the supercritical fluid, and discharging the supercritical fluid and the alcohol from the chamber while keeping the temperature inside the chamber at the predetermined temperature, to lower a pressure inside the chamber. The predetermined temperature is not lower than 75° C. but lower than a critical temperature of the alcohol.