Laminated Ceramic Sample Holder Grain Size Trade-off
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Solution Overview
Problem
Existing sample holders for semiconductor wafers face challenges in achieving both improved thermal uniformity and strength, as increasing ceramic grain size enhances thermal conductivity but reduces strength, while decreasing grain size improves strength but degrades thermal conductivity, and applying high-frequency waves can lead to ceramic layer breakdown.
Innovation Solution
A sample holder with a laminate structure comprising two ceramic substrates of different grain sizes, where the first substrate has a larger grain diameter for enhanced thermal conductivity and the second substrate with a smaller grain diameter for increased strength, along with a meandering flow path for efficient heat exchange, and an electrostatic chuck design using tungsten electrodes for secure sample holding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the average grain diameter of ceramic grains is increased to improve thermal conductivity, then thermal uniformity is improved, but strength is decreased
Solution Approach 1:
The patent divides the ceramic layer into multiple layers with different grain diameters. The lower layer (closer to heating element) has larger grain diameter for high thermal conductivity, while the upper layer (closer to sample) has smaller grain diameter for high strength. This segmentation allows each layer to optimize for its specific function without compromising the other.
Solution Approach 2:
Different regions of the ceramic structure are given different properties: the lower layer has large grains for thermal conduction where heat generation occurs, while the upper layer has small grains for mechanical strength where the sample contacts. This local differentiation of quality resolves the contradiction between thermal performance and structural integrity.
2Strength
If the average grain diameter of ceramic grains is decreased to increase strength, then strength is improved, but thermal conductivity is degraded
Solution Approach 1:
The ceramic structure is segmented into functional zones: the upper layer uses fine grains for strength at the sample interface, while the lower layer uses coarse grains for thermal conduction near the heating element. This spatial segmentation eliminates the need to compromise either property in a uniform structure.
Solution Approach 2:
The patent applies local quality by assigning different grain sizes to different spatial locations within the ceramic layer, matching the functional requirements of each region: strength-critical areas receive fine grains, while heat-transfer areas receive coarse grains.
3Productivity
If high frequency wave is applied to electrostatic chuck for wiring pattern processing, then processing capability is improved, but breakdown of ceramic layer may occur
Solution Approach 1:
The patent creates a composite ceramic structure with multiple layers of different grain sizes, which provides both the electrical properties needed for high-frequency operation and the mechanical strength to prevent breakdown. The multi-layer composite structure offers optimized electrical field distribution and higher breakdown voltage tolerance.
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 solution achieves improved thermal uniformity and strength, enabling efficient temperature adjustment and reliable sample holding with enhanced withstand voltage, while minimizing the risk of ceramic layer damage.
Implementation Method 1
a flow path which allows a cooling medium to flow therethrough is formed in an intermediate ceramic layer
Implementation Method 2
an electrostatic chuck formed of a plurality of ceramic layers
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3~4
AI summary
A sample holder of the present invention includes a base body formed of ceramic substrates laminated to each other and having an upper surface functioning as a sample holding surface. In this sample holder, the base body includes a first ceramic substrate including a flow path for a heating medium and a second ceramic substrate which is laminated at an upper side than the first ceramic substrate, which has an upper surface functioning as the sample holding surface, and which is formed of the same material as that of the first ceramic substrate, and the average grain diameter of ceramic grains forming the second ceramic substrate is smaller than that of ceramic grains forming the first ceramic substrate.