Registration Mark Formation in Sidewall Image Transfer
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Solution Overview
Problem
The challenge in semiconductor fabrication is creating effective registration marks during sidewall image transfer processes, where the need for high-density material designs at minimum pitch limits the availability of structures that can generate good contrast and quality signals, especially outside of minimum design size.
Innovation Solution
A method involving the formation of mandrels with spacers over a hard mask on a semiconductor layer, where selected mandrels are protected while others are removed, allowing for the creation of sub-lithographic structures and registration marks through a series of etching steps, enabling the formation of lithographic-sized registration marks alongside sub-lithographic structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sidewall image transfer process is used to achieve high-density material designs at minimum pitch, then sub-lithographic structures are formed, but the availability of structures that can generate good contrast and quality signals for registration marks is limited
Solution Approach 1:
The patent segments the mandrel structures into two categories: sacrificial mandrels that are removed to form sub-lithographic structures, and retained mandrels that serve as registration mark bases. This segmentation allows different portions of the same initial structure to serve different functions - one set for high-density patterning and another set for registration mark formation with sufficient size for good signal quality
Solution Approach 2:
The retained mandrels serve multiple functions: they act as bases for registration marks, provide alignment references, and maintain structural integrity during the etching process. This multi-functionality resolves the contradiction by allowing the same structure to contribute to both high-density patterning and registration mark quality
2Measurement precision
If registration marks are created with conventional methods, then good contrast and quality signals are achieved, but the marks cannot be formed outside of minimum design size due to pitch constraints
Solution Approach 1:
The registration mark structures are prepared in advance during the mandrel formation stage, before the actual sub-lithographic patterning occurs. By pre-forming retained mandrels with sufficient area for good signal detection, the patent ensures that alignment precision requirements are met without being constrained by the minimum pitch rules that apply to functional structures
3Quantity of substance
If all mandrels are removed to achieve maximum material density, then sub-lithographic structures are formed, but no structures remain to serve as registration marks
Solution Approach 1:
The patent applies different treatments to different locations of mandrels: some mandrels are completely removed to achieve maximum material density in active regions, while specific mandrels are retained in registration mark regions to provide structures for alignment and overlay marks. This local differentiation resolves the contradiction between achieving maximum density and maintaining manufacturability of registration marks
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 allows for the creation of registration marks with improved optical contrast and increased design options, enhancing alignment and overlay precision, and enabling more efficient semiconductor structure formation beyond traditional lithographic limits.
Implementation Method 1
a spacer material is deposited over the mandrels
Implementation Method 2
a spacer material is deposited over the mandrels
Implementation Method 3
the remaining sidewall spacer is used as a hard mask (HM) to etch the layer(s) below, for example, with a directional reactive ion etch (RIE)
Data Source
AI summary
Methods of forming a registration mark may include forming a plurality of mandrels over a hard mask over a semiconductor layer, each mandrel including a spacer adjacent thereto. At least one mandrel is selected and a mask is formed over the at least one selected mandrel. The plurality of mandrels are removed leaving the spacers, the mask preventing removal of the at least one selected mandrel. The mask is removed. A first etching patterns the sub-lithographic structures and the registration mark into the hard mask using the spacers as a pattern and the at least one selected mandrel and adjacent spacer for the registration mark. A second etching forms the sub-lithographic structures in the semiconductor layer using the patterned hard mask and to form the registration mark in the semiconductor layer using the at least one selected mandrel and the patterned hard mask.