Quartz Product Baking for Copper Removal
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Solution Overview
Problem
Quartz products used in semiconductor manufacturing apparatuses are contaminated with copper, which penetrates into the material during machining and can lead to contamination of semiconductor substrates during heat treatment, affecting device yield due to inadequate surface-only cleaning methods.
Innovation Solution
A baking method for quartz products involving exposure to hydrogen chloride gas and a reactive gas, such as oxygen, within a controlled heating atmosphere to reduce copper concentration from the surface to 30 μm depth below 20 ppb, ensuring thorough removal of copper contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If quartz products are washed with hydrofluoric acid to remove copper from the surface, then surface copper contamination is reduced, but copper ions are coupled again to uncoupled sites of silicon atoms, leaving trace copper in the surface portion
Solution Approach 1:
The invention changes the chemical parameters of the washing solution by adding organic acids (oxalic acid, malonic acid, succinic acid, or maleic acid) to the hydrofluoric acid. This parameter change prevents copper ions from coupling with silicon atoms by altering the chemical environment, thereby eliminating the re-contamination issue while maintaining effective copper removal from the quartz product surface.
2Manufacturing precision
If conventional baking is performed at 1000°C for 2 hours in hydrogen chloride gas and oxygen gas, then surface copper atoms are reduced, but copper penetrates into the interior of the quartz product, creating higher copper concentration in the interior than at the surface
Solution Approach 1:
The invention performs preliminary washing with the improved washing solution (hydrofluoric acid plus organic acid) before baking. This preliminary action removes copper from the surface in a form that prevents subsequent penetration during baking, addressing the root cause before the thermal process occurs. The washing step prepares the quartz product by eliminating surface copper that would otherwise diffuse inward during high-temperature baking.
Solution Approach 2:
The invention uses a composite chemical solution combining inorganic acid (hydrofluoric acid) and organic acid (oxalic acid, malonic acid, succinic acid, or maleic acid). This composite approach leverages the complementary properties of both acid types: hydrofluoric acid etches and removes copper, while the organic acid complexes with copper ions to prevent their re-coupling with silicon and subsequent penetration during baking.
3Ease of operation
If quartz products undergo fine machining to create grooves or nails for wafer support, then wafer holding capability is improved, but copper contamination increases due to contact with machining tools and working atmosphere
Solution Approach 1:
The invention applies preliminary washing with the improved chemical solution immediately after machining operations. This preliminary action removes copper contamination introduced during machining of grooves and nails, ensuring that the fine structural features required for wafer holding do not become sources of copper contamination. The treatment is applied to the machined surfaces before assembly into the heat treatment apparatus.
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 method effectively reduces copper contamination in semiconductor substrates by controlling copper concentration in the quartz products, preventing degradation of semiconductor device yield and ensuring the purity of the quartz products approaches that of raw, uncontaminated material.
Implementation Method 1
supplying baking gases, including a hydrogen chloride gas and a gas for enhancing reactivity of the hydrogen chloride gas, into the reaction vessel, while heating the reaction vessel, for removing copper as a contaminant
Implementation Method 2
heating the reaction vessel, for removing copper as a contaminant incorporated during the manufacturing process of the quartz product
Data Source
AI summary
The present invention relates to control of copper contamination to semiconductor substrates upon operation of a heat treatment apparatus which is a semiconductor manufacturing apparatus and which is constructed with quartz products having been contaminated with copper when machined. The quartz product is placed in a heating atmosphere on the stage where it is not still used for a heat treatment for semiconductor substrates. Baking gases including a hydrogen chloride gas and a gas for enhancing activity of the hydrogen chloride gas, for example, an oxygen gas, are then supplied to the quartz product. Consequently, the copper concentration in the region from the surface to the 30 μm depth of the quartz product can be controlled below 20 ppb, preferably below 3 ppb. The baking process may be carried out before or after assembling the quartz product into the heat treatment apparatus.