Phase Shift Mask Blank Etching Mask Film Thickness Control
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Solution Overview
Problem
The miniaturization of semiconductor devices poses challenges in achieving high-accuracy pattern formation due to the loading effect during mask fabrication, particularly at the DRAM half-pitch of 45 nm and beyond, where pattern density differences lead to variations in etching rates, affecting the precision of pattern transfer.
Innovation Solution
A phase shift mask blank is designed with a substrate, a phase shift film, a light-shielding film, and an etching mask film, where the etching mask film is formed to have a lower etching rate than the phase shift film, ensuring that the thickness of the etching mask film is set thin enough to prevent the loading effect, thereby improving pattern processing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If immersion exposure with NA>1 is used to form fine patterns, then resolution is improved, but CD accuracy deteriorates due to loading effect
Solution Approach 1:
The mask structure is segmented into multiple functional layers: a phase shift film (halftone layer) and a separate etching mask film. This segmentation allows the etching mask film to be optimized specifically for preventing loading effect during etching, while the phase shift film handles the resolution enhancement function. The etching mask film acts as an additional protective layer that maintains pattern dimensions during the etching process.
Solution Approach 2:
The mask employs a composite structure combining different materials with complementary properties: the phase shift film (e.g., MoSiN, WSiN) provides optical phase shift for resolution enhancement, while the etching mask film (e.g., SiN, SiON, SiO2) provides etching resistance to prevent loading effect. This composite material approach allows each layer to be optimized for its specific function without compromise.
2Length of moving object
If pattern miniaturization is advanced to achieve finer patterns, then device performance is improved, but loading effect increases causing reduction in pattern size accuracy
Solution Approach 1:
The etching mask film is formed preliminarily on the phase shift film before the etching process begins. This preliminary action ensures that the pattern dimensions are established and protected before etching commences, preventing the loading effect from altering the intended pattern size during the etching process. The etching mask film serves as a dimensional reference that maintains accuracy throughout manufacturing.
3Productivity
If etching rate of etching mask film is increased to improve manufacturing efficiency, then productivity is improved, but pattern processing accuracy deteriorates
Solution Approach 1:
The etching selectivity ratio between the phase shift film and etching mask film is carefully controlled as a key parameter. By adjusting the thickness of the etching mask film and controlling the etching rates, the process ensures that the etching mask film etches slower than the phase shift film. This parameter control allows optimization of both productivity and accuracy: the etching mask film provides sufficient protection during etching while allowing the phase shift film to be etched at the required rate for pattern formation.
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 configuration allows for the precise formation of fine patterns with reduced loading effect influence, enhancing the accuracy of mask fabrication and pattern transfer in semiconductor devices.
Implementation Method 1
A phase shift mask is a photomask that can improve the resolution of a transfer pattern using interference of light caused by a phase shifter
Implementation Method 2
The immersion exposure is an exposure method that can improve the resolution by filling a liquid between a wafer and a lowermost lens of an exposure apparatus so that the numerical aperture is increased by the refractive index of the liquid
Data Source
AI summary
Disclosed is a phase shift mask blank (11) that can prevent the occurrence of a loading effect. The phase shift mask blank (11) includes a phase shift film (5) containing silicon, a light-shielding film (2) made of a material resistant to etching of the phase shift film (5), and an etching mask film (3) made of an inorganic material resistant to etching of the light-shielding film (2), which are formed in this order on a substrate (1) transparent to exposure light. Assuming that the thickness of the phase shift film (5) is t1, the etching rate of the phase shift film (5) by dry etching with an etchant using the etching mask film (3) and the light-shielding film (2) as a mask is v1, the thickness of the etching mask film (3) is t2, and the etching rate of the etching mask film (3) by dry etching with the above etchant is v2, (t1/v1)≦(t2/v2) is satisfied.