Bulk Silicon Polishing With Cyclic Slurry and Water Control
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Solution Overview
Problem
Traditional chemical mechanical polishing (CMP) processes for bulk silicon substrates often result in uneven polishing and damage to thin silicon layers due to irregularities, leading to over-polishing and device damage.
Innovation Solution
A method involving cyclic alternation between a silicon-reactive slurry and deionized water during mechanical polishing, where the silicon slurry reacts with bulk silicon to remove material, and deionized water interrupts this reaction to prevent over-polishing of thin layers, allowing precise control of silicon removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional CMP processes are used on bulk silicon substrates, then polishing can be performed, but uneven polishing and damage to thin silicon layers occur due to irregularities
Solution Approach 1:
The patent applies periodic action by cyclically alternating between applying silicon-reactive slurry and rinsing with deionized water during the polishing process. This periodic alternation allows the chemical reaction to occur in controlled intervals, preventing continuous aggressive removal that causes uneven polishing and damage to thin layers, thereby achieving both productivity and manufacturing precision.
Solution Approach 2:
The patent changes the chemical parameters of the polishing environment by alternating between reactive slurry (containing HF and other chemicals) and deionized water. This parameter change controls the chemical-mechanical interaction, allowing precise adjustment of material removal rates to achieve uniform polishing without damaging thin silicon layers.
2Productivity
If continuous slurry application is used during polishing, then material removal is continuous, but over-polishing of thin silicon layers occurs causing device damage
Solution Approach 1:
The patent implements periodic action by interrupting the continuous slurry application with periodic rinsing cycles using deionized water. This creates a pulsed chemical-mechanical polishing process where material removal occurs during slurry application, and the reaction is interrupted during rinsing, preventing over-polishing and protecting device integrity while maintaining overall productivity.
Solution Approach 2:
The patent maintains continuity of useful action by alternating between productive slurry application phases and protective rinsing phases. The useful action of material removal continues through repeated cycles, while the rinsing intervals prevent cumulative damage, ensuring both productivity and reliability are achieved.
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 precise control of silicon removal, avoiding damage to thin layers and ensuring uniform polishing, thus improving the backside processing of semiconductor devices without the need for scarce and expensive silicon on insulator (SoI) materials.
Implementation Method 1
a reaction between the bulk silicon and the slurry takes place allowing the polishing head to remove the bulk silicon
Implementation Method 2
The deionized water interrupts this reaction and helps prevent overpolishing of thin silicon layers
Data Source
AI summary
Methods for polishing bulk silicon are disclosed. In one aspect, mechanical polishing is facilitated by cyclically alternating between a silicon reactive slurry and deionized water while a mechanical polishing head operates on a surface. In exemplary aspects, the polishing head is polishing a bulk silicon carrier wafer to expose a backside of a radio frequency (RF) complementary metal oxide semiconductor (CMOS) switch, although other semiconductors may also benefit from exemplary aspects of the present disclosure. While the silicon slurry is present, a reaction between the bulk silicon and the slurry takes place allowing the polishing head to remove the bulk silicon. The deionized water interrupts this reaction and helps prevent overpolishing which might otherwise damage the device.