Ceramic-Metal Hydrostatic Pad for Wafer Nanotopography Control
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Solution Overview
Problem
Conventional double-side grinding apparatuses for semiconductor wafers face challenges in reducing nanotopography due to thermal expansion of hydrostatic pad members, leading to uneven surface finish and potential circuit disconnection issues, as the metal materials used expand and deform during grinding, causing irregular pressure distribution and heat conduction issues.
Innovation Solution
The use of hydrostatic pad members made from ceramic materials with low thermal expansion coefficients, face-bonded to metal base members, which helps in minimizing thermal expansion and maintaining flatness by preventing excessive temperature rise and enhancing rigidity, thereby reducing nanotopography and ensuring precise surface grinding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metal hydrostatic pad members are used to support the wafer, then the apparatus can effectively conduct heat away from the wafer, but the pad members thermally expand during grinding, causing deformation and nanotopography
Solution Approach 1:
The patent employs a composite structure consisting of a ceramic hydrostatic pad member (low thermal expansion) bonded to a metal base member (high thermal conductivity). This composite design allows the ceramic component to maintain dimensional stability and surface flatness during thermal cycles, while the metal base provides efficient heat dissipation pathways, thereby resolving the contradiction between heat dissipation and surface precision
Solution Approach 2:
The patent changes the material parameter (thermal expansion coefficient) of the hydrostatic pad member from metal to ceramic material. This parameter change reduces thermal expansion during grinding, maintaining surface flatness and nanotopography control, while the metal base member compensates for heat dissipation requirements through its high thermal conductivity
2Stress or pressure
If pockets are formed in the hydrostatic pad member to adjust static pressure, then pressure distribution can be optimized, but thermal expansion still causes deformation of the pad member surface
Solution Approach 1:
The ceramic-metal composite structure addresses this contradiction by using the ceramic component to maintain dimensional stability under thermal loads, ensuring that the pocket-formed pressure distribution patterns remain accurate, while the metal base provides thermal management to prevent overall pad member deformation
3Manufacturing precision
If the hydrostatic pad member is placed at very short distance from the wafer, then hydrostatic support is effective, but heat generated during grinding cannot be released efficiently
Solution Approach 1:
The composite structure resolves this spatial contradiction by separating the hydrostatic support function (ceramic pad member at close distance to wafer) from the heat dissipation function (metal base member providing thermal pathways). The ceramic maintains the necessary proximity for effective hydrostatic support while the metal base extends thermal conduction pathways for heat release
4Temperature
If fluid is supplied to the back surface of the hydrostatic pad member to release heat, then heat release effect is enhanced, but the pad member still thermally expands due to grinding heat
Solution Approach 1:
The patent uses the ceramic-metal composite to address this contradiction: the ceramic hydrostatic pad member resists thermal expansion and maintains surface geometry even during fluid cooling, while the metal base member provides primary heat conduction pathways. The fluid supplied to the back surface efficiently removes heat through the metal base without causing significant thermal expansion of the precision-critical ceramic pad surface
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 effectively reduces nanotopography on wafer surfaces by controlling thermal expansion and maintaining surface flatness, achieving a PV value of 14 nm or less, compared to 20 nm with traditional methods, while preventing metallic contamination and improving abrasion resistance.
Implementation Method 1
hydrostatic supporting units to apply static pressure to the wafer through a fluid
Implementation Method 2
the hydrostatic pad members in practice thermally expand due to the heat generated during the grinding
Implementation Method 3
the wafer is sandwiched by fluid layers, and is supported without any physical contact with other components
Implementation Method 4
Grindstones that are rotating are then pressed against the wafer, and the wafer is also rotated while being held by a holder
Data Source
AI summary
A double-side grinding apparatus is designed to be capable of minimizing thermal expansion of hydrostatic pad members and reducing nanotopography in performing wafer grinding. The double-side grinding apparatus is a double-side grinding apparatus for wafers that can simultaneously grind either surface of a wafer to be ground by pressing a grindstone against either surface of the wafer to be ground while hydrostatically supporting either surface of the wafer to be ground in a noncontact manner. Each hydrostatic supporting unit is formed with a hydrostatic pad member facing the wafer to be ground, and a base member placed on the back surface of the hydrostatic pad member. The hydrostatic pad member is made of a ceramic member, and the base member is made of a metal member.