Dual-Sensitivity Resist Stack for Multi-Depth Photomask Patterning
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Solution Overview
Problem
Conventional photomask and layer patterning methods require multiple lithography steps, leading to positional accuracy issues, increased process time, and costs, especially when using electron beam lithography, which can result in charging effects and impaired component quality.
Innovation Solution
A method involving a resist stack with two resist materials of different sensitivities, where one resist is exposed to a higher dose than the other in a single exposure step, allowing for the creation of structures with varying depths without the need for multiple exposure steps, thereby improving alignment accuracy and reducing process time and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple lithography steps are used for patterning, then structures with different depths can be produced, but positional accuracy deteriorates due to alignment deviations between steps
Solution Approach 1:
The patent divides a single resist layer into multiple regions with different exposure doses within one lithography step, creating patterned structures of different depths simultaneously. This segmentation of exposure doses within one step achieves multi-depth patterning without requiring multiple sequential lithography steps, thereby maintaining positional accuracy while reducing process complexity.
Solution Approach 2:
The patent introduces a new dimension of control by varying exposure doses across different spatial regions within a single lithography step. Instead of using multiple steps in the time dimension, the invention utilizes the spatial dimension of exposure dose variation to create structures of different depths simultaneously, resolving the contradiction between precision and complexity.
2Manufacturing precision
If multiple lithography steps are used, then different structure depths can be achieved, but process time increases
Solution Approach 1:
The patent combines multiple lithography operations into a single exposure step by applying different exposure doses to different regions of the resist layer simultaneously. This merging of what would traditionally require sequential steps into one parallel operation reduces process time while maintaining the capability to produce structures of different depths through dose variation.
Solution Approach 2:
The patent enables continuous pattern formation across the entire resist layer in one uninterrupted exposure step, with different regions receiving different doses simultaneously. This continuous action eliminates the idle time and repositioning required between multiple sequential lithography steps, reducing overall process time while achieving the same structural differentiation.
3Manufacturing precision
If electron beam lithography is used for multiple steps, then precise patterning is achieved, but charging effects occur in previously patterned layers
Solution Approach 1:
The patent applies preliminary action by exposing all regions of the resist layer simultaneously in one step, with different exposure doses assigned to different regions based on the desired final structure depths. This preliminary simultaneous exposure prevents the sequential charging effects that occur when electron beam lithography is applied multiple times, as the entire pattern is formed in a single pass before any charging can accumulate.
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 enables the production of photomasks and patterned layers with improved positional accuracy and reduced process time and costs, while avoiding charging effects and topography-related imaging issues, by using a single exposure step to create structures of different depths in a layer or layer stack.
Implementation Method 1
Both resists are exposed to an exposure dose in an exposure step in defined regions of the layer surface, wherein the exposure dose varies locally between a first and a second exposure dose
Data Source
AI summary
Methods for producing a photomask or layer or stack patterning include applying two resists to a layer, a layer stack, or a mask substrate (collectively “the layer”). Sensitivity of the first resist with respect to the exposure dose is greater than sensitivity of the second. Both resists are subjected to an exposure dose in defined regions of the layer surface, the dose varying locally between first and second doses. The first dose is chosen to expose the first resist but not the second. The second dose is chosen to expose the second resist. After a first development of the second and of the first resist the layer is etched at the uncovered locations for a first time. After complete removal of the second resist and a second development of the first resist, the layer is etched. As a result, it is possible to produce structures of different depths in the layer.