Layered Phase Shift Mask Blank for High Optical Density
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Solution Overview
Problem
In semiconductor manufacturing, phase shift masks with halftone-type phase shift masks face challenges in achieving high optical density in the light shielding zone, leading to exposure light leakage and decreased CD accuracy of fine patterns due to complex illumination systems and the limitations of existing materials like chromium-based light shielding films.
Innovation Solution
A mask blank with a layered structure of a phase shift film and a light shielding film, where the phase shift film is made of silicon and the light shielding film has a lower layer of chromium-based material and an upper layer of metal silicide-based material, achieving an optical density of 3.5 or more with specific atomic content and refractive index ratios to enhance light shielding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a chromium-based light shielding film is used in the outer peripheral region, then the optical density can be increased to some extent, but it is difficult to ensure the required optical density of 3 or more (transmittance of 0.1% or less)
Solution Approach 1:
The patent applies composite materials by combining a chromium-based light shielding film with a molybdenum-based light shielding film in a layered structure. The chromium-based film provides a base optical density, while the molybdenum-based film enhances the optical density to achieve the required value of 3 or more. This composite approach allows each material to contribute its strengths, with chromium providing good adhesion and molybdenum providing superior light shielding performance.
Solution Approach 2:
The light shielding film is segmented into multiple layers with distinct functions. The chromium-based layer serves as the base layer for adhesion, while the molybdenum-based layer is added as a separate functional layer specifically for enhancing optical density. This segmentation allows independent optimization of each layer's thickness and composition to achieve the desired overall performance.
2Illumination intensity
If the light shielding film thickness is increased to improve optical density, then light shielding performance improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the material parameter from using only chromium-based material to using a combination of chromium-based and molybdenum-based materials. This parameter change allows achieving the required optical density with a more efficient layered structure, where the molybdenum-based film has higher light shielding efficiency per unit thickness, thereby reducing the total film thickness needed while meeting the optical density requirement.
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
The solution provides high CD accuracy for fine patterns on the resist film and suppresses pattern collapse during cleaning, ensuring high accuracy in semiconductor device manufacturing even under complex illumination systems.
Implementation Method 1
the light shielding film has a structure in which a lower layer and an upper layer are formed as layers from the side of the transparent substrate... achieving an optical density of 3.5 or more
Implementation Method 2
The phase shift film has a function of transmitting light at an intensity which does not substantially contribute to exposure and causing the light having been transmitted through the phase shift film to have a predetermined phase difference
Data Source
AI summary
This mask blank has a structure wherein a phase shift film and a light shielding film are sequentially formed as layers in this order on a transparent substrate. The optical density of the layered structure composed of the phase shift film and the light shielding film with respect to exposure light, which is an ArF excimer laser, is 3.5 or more; and the light shielding film has a structure wherein a lower layer and an upper layer are formed as layers sequentially from the transparent substrate side. The lower layer is formed from a material wherein the total content of chromium, oxygen, nitrogen and carbon is 90 atomic % or more; and the upper layer is formed from a material wherein the total content of metals and silicon is 80 atomic % or more. The extinction coefficient kU of the upper layer for the exposure light is higher than the extinction coefficient kL of the lower layer for the exposure light.