Patterned UV Cure for Stress-Tunable Wafer Bow Compensation
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Solution Overview
Problem
Semiconductor manufacturing processes, particularly in 3D-NAND fabrication, face challenges with significant wafer warpage due to thick, high stress carbon-based hard masks and metallization lines, leading to front side lithographic overlay mismatch and wafer bow beyond chucking limits.
Innovation Solution
An apparatus and method for selective UV exposure using a patterned window with UV-transparent and UV-non-transparent regions to locally modulate stress on a stress-tunable film on a semiconductor substrate, allowing for controlled stress shifts and reduced wafer warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thick, high stress carbon-based hard masks and metallization lines are used in 3D-NAND fabrication, then manufacturing capability and device performance are improved, but wafer warpage increases significantly causing overlay mismatch and chucking limit violations
Solution Approach 1:
A stress-tunable film is deposited on the backside of the wafer before lithography operations. This film is then selectively exposed to UV light through a patterned window to induce compressive stress that counteracts the tensile stress from frontside metallization and hard masks, preventing wafer warpage and maintaining overlay accuracy throughout subsequent processing steps.
Solution Approach 2:
The stress-tunable film is selectively exposed to UV light only in specific regions through a patterned window, creating localized stress modulation. This allows different regions of the wafer to have different stress states, enabling precise compensation for localized warpage while maintaining the overall structural integrity required for high-density 3D-NAND fabrication.
2Productivity
If multi-stacked films with thick hard masks are deposited, then device density and performance are improved, but wafer bow exceeds electrostatic chuck holding capability
Solution Approach 1:
The stress-tunable film is prepared and patterned with UV exposure before the wafer undergoes multi-stacked film deposition. This preliminary stress induction creates a counterbalancing effect that prevents the wafer bow from exceeding electrostatic chuck holding capability during subsequent high-density fabrication processes.
Solution Approach 2:
The stress state of the stress-tunable film is changed by selective UV exposure, transforming it from an unstressed or tensile state to a compressive state. This parameter change in stress enables the film to counteract the warpage induced by multi-stacked films and thick hard masks, maintaining wafer flatness within chucking limits.
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 selective UV exposure method effectively mitigates asymmetric bowing in semiconductor substrates by inducing stress shifts in the stress-tunable film, thereby reducing wafer warpage and improving lithographic overlay accuracy.
Implementation Method 1
selectively exposing one or more first regions of the stress-tunable film to UV light using the window that is patterned so as to locally modulate stress on the stress-tunable film
Data Source
AI summary
UV light may be directed through a patterned window to cause selective UV exposure of certain areas of a substrate. A stress-tunable film deposited on the substrate may undergo localized stress changes from selective UV exposure. Localized stress changes in the stress-tunable film may mitigate wafer bowing in the substrate. The patterned window may be designed with UV-transparent regions and UV-non-transparent regions to facilitate targeted UV exposure of the stress-tunable film. In some implementations, the patterned window may include a metal coating, a ceramic cover, or a metal cover for selective UV exposure. In some implementations, the patterned window may further include transition regions that permit partial transmission of UV light to limit stress changes in corresponding areas of the stress-tunable film.