Plasma Etching Selectivity Control for CD Loading
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Solution Overview
Problem
In semiconductor device manufacturing, the coexistence of high-density and low-density regions on a semiconductor wafer leads to Critical Dimension (CD) loading issues due to differences in photoresist mask dimensions, causing variations in groove or hole dimensions during plasma etching.
Innovation Solution
A plasma etching method that uses a photoresist as a mask with two distinct processing conditions: a first condition with high selectivity for initial etching and a second condition with lower selectivity for further etching, without removing scum from the photoresist, to maintain consistent dimensions across high-density and low-density regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single etching process is used, then the manufacturing process is simple, but CD loading occurs due to dimensional variations in low-density and high-density regions
Solution Approach 1:
The etching process is divided into two distinct stages: a first etching process with high selectivity (using gas mixture of CF4, CH4, and H2) to etch the base film while preserving the photoresist mask dimensions, and a second etching process with lower selectivity (using gas mixture of CF4 and O2) to complete the etching. This segmentation allows each process to be optimized for its specific function, preventing CD loading while maintaining overall process control.
Solution Approach 2:
The patent changes multiple parameters between the two etching processes: gas composition (from CF4/CH4/H2 to CF4/O2), selectivity (from high to lower), and power conditions. These parameter changes enable the first process to protect the photoresist mask from dimensional changes while the second process completes the etching, thereby suppressing CD loading effects.
2Ease of manufacture
If the photoresist mask is used without scum removal, then the process is simpler, but dimensional variations occur between high-density and low-density regions
Solution Approach 1:
By changing the selectivity parameter in the first etching process (using high selectivity with CF4/CH4/H2 gas mixture), the patent enables etching of the base film while the photoresist mask with scum remains dimensionally stable. The high selectivity protects the mask from excessive etching that would cause dimensional variations, allowing scum to be retained without compromising precision.
Solution Approach 2:
The first etching process with high selectivity acts as a preliminary step that prepares the base film for subsequent etching while preserving the photoresist mask structure. This preliminary action with controlled selectivity prevents mask dimensional changes before the second etching process begins.
3Reliability
If high selectivity is used throughout etching, then the photoresist mask is well protected, but the etching efficiency decreases
Solution Approach 1:
The etching process is segmented into two phases: the first phase uses high selectivity (CF4/CH4/H2 mixture) to protect the photoresist mask and establish precise dimensions, while the second phase uses lower selectivity (CF4/O2 mixture) to increase etching efficiency and complete the process. This segmentation allows each phase to be optimized for its primary function.
Solution Approach 2:
The patent employs periodic action by alternating between two etching conditions with different selectivities. The first periodic stage uses high selectivity for mask protection, then transitions to the second stage with lower selectivity for efficient completion, creating a rhythmic process that balances protection and efficiency.
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 reduces CD loading by ensuring consistent groove and hole dimensions across the wafer, improving etching precision and reducing dimensional variations.
Implementation Method 1
etching the base film by a plasma, under a first processing condition in which a selectivity of the base film to the photoresist is set to a first selectivity
Data Source
AI summary
There is provided a plasma etching method for etching a base film by a plasma using a photoresist as a mask. The method includes etching the base film by the plasma, under a first processing condition in which a selectivity of the photoresist to the base film is set to a first selectivity, while using as a mask the photoresist formed in a predetermined pattern by exposure and development and a scum remaining in the photoresist, without performing a process of removing the scum; and switching, during the etching of the base film, the first processing condition to a second processing condition in which the selectivity of the photoresist to the base film is set to a second selectivity lower than the first selectivity and further etching the base film by a plasma while using the photoresist as a mask under the second processing condition.