Stacked Hard Mask Etching for Fine Pattern Precision
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Solution Overview
Problem
Current semiconductor manufacturing techniques face challenges in forming fine patterns narrower than the minimum resist pattern size due to resist instability, edge roughness, and deformation during reactive ion etching, especially at shorter wavelengths like 193 nm, which affects the formation of precise gate electrodes and bit lines.
Innovation Solution
A method involving a stacked hard mask structure where a resist pattern is used to etch and trim an upper hard mask, which is then used to etch a lower hard mask and the target film, ensuring precise pattern transfer and minimizing defects by removing the resist pattern before defining the target fine pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If resist pattern is used directly to etch the target film, then the process is simple, but the pattern width cannot be narrower than the minimum resist pattern size and edge roughness increases
Solution Approach 1:
The patent divides the etching process into multiple stages using a multi-layer hard mask structure. The resist pattern first forms a mask for etching the upper hard mask, then the upper hard mask serves as a mask for etching the lower hard mask, and finally the lower hard mask masks the target film etching. This segmentation allows each layer to be optimized for its specific function, enabling pattern widths narrower than the minimum resist pattern size while maintaining process control.
Solution Approach 2:
The patent introduces intermediate hard mask layers (upper and lower hard masks) between the resist pattern and the target film. These intermediate layers act as mediators that enable precise pattern transfer while protecting the target film from direct exposure to the resist pattern's limitations. The upper hard mask is etched using the resist pattern, then the resist is removed and the upper hard mask is trimmed, followed by using the upper hard mask to etch the lower hard mask, which finally masks the target film etching.
2Manufacturing precision
If resist pattern is trimmed by isotropic etching to narrow the pattern, then the pattern width decreases, but the resist film thickness becomes insufficient and the resist pattern falls
Solution Approach 1:
The patent performs preliminary trimming of the upper hard mask after the resist pattern has served its masking function. The upper hard mask is trimmed by etching to the target width after the resist pattern has been used to etch it, and the resist pattern is removed before the upper hard mask is trimmed. This preliminary action allows the resist pattern to maintain sufficient thickness for stability while achieving the desired narrow pattern width through subsequent hard mask trimming.
Solution Approach 2:
The patent uses the resist pattern as a temporary, disposable masking element that serves its purpose during the upper hard mask etching process, then is removed. The permanent pattern definition is achieved through the hard mask layers that remain after resist removal. This approach allows the resist to be optimized for easy removal while the hard masks provide the stable, precise final pattern.
3Manufacturing precision
If electron beam is used to reform the resist pattern surface, then different etch rates are achieved between vertical and horizontal directions, but the process complexity increases
Solution Approach 1:
The patent replaces complex electron beam surface reformation with a simpler chemical etching approach. Instead of using electron beam to create anisotropic etch rates through physical modification of the resist surface, the patent uses chemical etching processes with selective etch rates between different hard mask materials (silicon-rich silicon nitride, silicon oxynitride, silicon oxide) to achieve the desired pattern definition and dimensional control.
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 formation of fine patterns with improved yield and reduced pattern defects, maintaining pattern integrity and precision, even at small sizes like 50 nm or narrower, by using a poly-silicon upper hard mask and an inorganic lower hard mask with controlled etching processes.
Implementation Method 1
etching various films such as silicon films, silicon oxide films, and silicon nitride films by reactive ion etching (RIE) using a resist pattern formed by lithography
Implementation Method 2
reforming a surface layer of the resist pattern with an electron beam to set different etch rates between vertical and horizontal directions
Implementation Method 3
A light source of photolithography has changed from KrF excimer laser (wavelength 248 nm) to ArF excimer laser (wavelength 193 nm) to form finer resist patterns
Data Source
AI summary
A method for forming a pattern includes the steps of: (a) preparing a lower hard mask layer and an upper hard mask layer stacked on an etching target film; (b) forming a resist pattern above the upper hard mask layer; (c) etching the upper hard mask film by using the resist pattern as an etching mask to form an upper hard mask; (d) after the step (c), removing the resist pattern; (e) after the step (d), thinning the upper hard mask by etching; (f) etching the lower hard mask film by using the thinned upper hard mask as an etching mask to form a lower hard mask; and (g) etching the etching target film by using the upper hard mask and the lower hard mask as an etching mask. The method for forming a pattern can etch a fine pattern with good yield.