Low Density Polishing Pad With Closed Cell Pores
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Solution Overview
Problem
Current CMP pad technologies face challenges in achieving high porosity and low density with closed cell structures, as adding porogens can increase viscosity unmanageably, and controlling pore size and distribution is difficult with existing methods.
Innovation Solution
The development of low density polishing pads with a thermoset polyurethane material and a plurality of closed cell pores, where the pores are formed by expanding unexpanded or pre-expanded porogens during the molding process, achieving a density range of 0.4-0.55 g/cc and a total pore volume of 50-60% of the total volume, using a mixture of pre-polymer, chain extender, and microelements in a formation mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If porogens are added to create closed cell pores, then porosity is improved, but viscosity increases unmanageably
Solution Approach 1:
The patent changes the physical state and timing of porogen expansion by using heat-activatable porogens that remain in a compact state during mixing and molding, then expand to desired size during a post-molding heat treatment step. This parameter change in the porogen's expansion timing allows high porosity (50-90%) to be achieved without increasing mixture viscosity during manufacturing.
Solution Approach 2:
The patent performs preliminary selection of heat-activatable porogens that maintain stable, low-viscosity characteristics at processing temperatures, then activates their expansion after molding is complete. This preliminary preparation of the porogen system allows the mixture to be handled easily during manufacturing while still achieving high porosity through subsequent heat treatment.
2Quantity of substance
If porosity is increased to reduce density, then density is improved, but structural integrity and durability worsen
Solution Approach 1:
The patent employs closed-cell porous foam structure where pores are completely enclosed within the polyurethane matrix. This porous material design achieves low density (0.4-0.55 g/cc) while maintaining structural integrity because the closed cells prevent collapse and the uniform distribution provides mechanical strength throughout the polishing pad body.
Solution Approach 2:
The patent creates a composite material system combining polyurethane base material with dispersed closed-cell porous structures. This composite approach allows the dense polyurethane matrix to provide structural strength while the porous regions reduce overall density, achieving both durability and low density simultaneously.
3Manufacturing precision
If pore size and distribution are controlled, then manufacturing precision is improved, but process complexity worsens
Solution Approach 1:
The patent replaces complex mechanical or chemical control systems with a simple thermal activation mechanism. By using heat-activatable porogens that expand at predictable temperatures, the patent achieves precise pore size and distribution control through straightforward heat treatment processes, avoiding the need for sophisticated mixing equipment or multi-step chemical reactions.
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 fabrication of polishing pads with improved durability and consistent performance, addressing the issues of short lifespan and inconsistent performance of conventional low density pads, while maintaining manageable viscosity and controlled pore distribution.
Implementation Method 1
heating the mixture in the formation mold to provide a partially cured molded polishing body... the plurality of closed cell pores formed by expanding each of the plurality of microelements to a larger size during the heating
Implementation Method 2
providing a mixture of a pre-polymer and a chain extender or cross-linker... subsequent to removing the partially cured molded polishing body and support layer pairing from the formation mold, further curing the partially cured molded polishing body outside of the formation mold to provide a molded polishing body bonded to the support layer
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 2D~2F
AI summary
Low density polishing pads and methods of fabricating low density polishing pads are described. In an example, a polishing pad (222) for polishing a substrate includes a polishing body having a density approximately in the range of 0.4 - 0.55 g/cc. The polishing body includes a thermoset polyurethane material and a plurality of closed cell pores (218) dispersed in the thermoset polyurethane material. Each of the plurality of closed cell pores (218) has a shell composed of an acrylic co-polymer.