Photomask Cleaning via Infrared Desorption
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Solution Overview
Problem
The semiconductor industry faces challenges in maintaining the cleanliness and operational longevity of photomasks due to the formation of crystals caused by ammonia and sulphate residues, which lead to defects in microelectronic components, and existing cleaning processes are costly and inefficient.
Innovation Solution
A method involving infrared radiation and vacuum pumping to selectively desorb ammonia and sulphate residues from photomasks before applying a protective film, ensuring a clean surface for the film installation and reducing the frequency of cleaning operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cleaning processes are used to remove ammonia and sulphate residues, then the photomask surface is cleaned, but the process is costly and inefficient, and crystals still form under the protective film
Solution Approach 1:
The patent replaces conventional mechanical/chemical cleaning processes with infrared radiation heating. The infrared heater heats the photomask to a controlled temperature (below 200°C) to accelerate the desorption of ammonia and sulphate residues without requiring complex chemical cleaning steps, thereby reducing process complexity while maintaining cleaning effectiveness.
Solution Approach 2:
The patent changes the temperature parameter by applying controlled infrared heating to the photomask. By raising the temperature to a specific range (below 200°C), the desorption rate of ammonia and sulphate residues increases significantly, enabling more effective cleaning without the need for costly and complex conventional cleaning processes.
2Reliability
If the photomask is kept clean to prevent crystal formation, then defect rate decreases, but the frequency and cost of cleaning operations increase
Solution Approach 1:
The patent applies infrared heating immediately after the protective film is deposited on the photomask. This preliminary action accelerates the desorption of ammonia and sulphate residues before they can combine to form crystals under the film, preventing defect formation rather than requiring repeated cleaning operations.
Solution Approach 2:
The patent establishes a continuous process where infrared heating is applied as an integral step in the photomask manufacturing sequence, immediately following film deposition. This continuous action ensures residues are consistently removed without interruption, preventing crystal formation and eliminating the need for frequent separate cleaning operations.
3Length of moving object
If high energy exposure is used to create smaller patterns, then component size decreases, but crystal formation under the film increases due to recombination of gases
Solution Approach 1:
The patent applies infrared heating to accelerate the desorption of ammonia and sulphate residues before high-energy exposure occurs. By removing these residues in advance, the patent prevents their recombination into crystals that would otherwise be generated by the high-energy exposure process, thereby eliminating harmful effects while maintaining the ability to create small components.
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 method effectively extends the usable life of photomasks by reducing the formation of crystals and associated defects, while minimizing costs and maintaining the photomask's integrity, ensuring improved production efficiency and reduced sulphate content.
Implementation Method 1
the photomask is subjected to infrared radiation, the wavelength of which is adjusted between short wavelengths acting in depth and long wavelengths acting on the surface
Implementation Method 2
This method effectively extends the usable life of photomasks by reducing the formation of crystals and associated defects
Implementation Method 3
the infrared radiation is stopped by leaving the enclosure under low pressure
Data Source
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AI summary
The photomask manufacturing process includes at least one photomask cleaning step and at least one step of applying a protective film to the photomask at the end of manufacturing. The process according to the invention further includes at least one step of removing ammonia and sulfate residues between the cleaning step and the film application step. This step comprises the following operations: - the photomask is placed in a sealed chamber, a low pressure is established in the sealed chamber by pumping out the gases it contains, - the photomask is subjected to infrared radiation, - the infrared radiation is stopped, - the temperature of the photomask is verified to be at most 50°C, - atmospheric pressure is restored in the chamber, and - the photomask is removed from the chamber.The device for implementing the method according to the invention comprises a sealed enclosure containing at least one photomask, a pumping unit for installing and maintaining the vacuum inside the enclosure, a system for holding at least one photomask, placed inside the sealed enclosure, infrared radiation means and a gas injection system.