Quartz Glass Sintering Defect Reduction
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Solution Overview
Problem
Existing methods for producing synthetic quartz glass often result in semifinished products with unforeseeable bubble inclusions or dislocations, known as striae or bubble nests, which impair the quality and usability of the final product, especially in semiconductor manufacturing.
Innovation Solution
A method involving zonewise sintering of a porous SiO2 soot body in a melt mold, followed by strict separation of sintering and shaping processes, where the sintered quartz glass body is shaped at increased temperatures without substantial cooling, ensuring complete filling of the mold volume and minimizing gas inclusions, with a two-phase shaping process adjusting viscosity and temperature to prevent defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If simultaneous sintering and shaping is performed in a graphite mold, then process time is reduced, but fusion defects such as bubble nests and dislocations occur
Solution Approach 1:
The patent divides the manufacturing process into two separate stages: first sintering the soot body to form a green body, then shaping it in a second step. This segmentation prevents the fusion defects that occur when both operations are performed simultaneously, while still maintaining high productivity through the use of a graphite mold that facilitates efficient heat transfer and processing.
Solution Approach 2:
The patent performs sintering as a preliminary action before shaping. By completing the sintering process first to form a stable green body, the subsequent shaping operation can proceed without causing fusion defects. This preliminary action ensures the structural integrity needed for high-quality final products.
2Ease of operation
If high temperature is used during shaping, then viscosity reduction and flowability improve, but gas inclusions and defects increase
Solution Approach 1:
The patent removes gas inclusions and performs dehydration treatment before the shaping operation. This preliminary preparation of the soot body ensures that when high temperature is applied during shaping for improved flowability, there are fewer gas inclusions to form defects, thus achieving both good operability and high product quality.
3Manufacturing precision
If chlorine treatment is applied to reduce hydroxyl groups, then optical transmission improves, but process complexity increases
Solution Approach 1:
The patent combines the chlorine treatment step with the sintering process by introducing chlorine gas into the sintering atmosphere. This merging of operations allows hydroxyl group reduction to occur during the existing sintering phase rather than requiring a separate treatment step, thereby improving optical transmission without significantly increasing process complexity.
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 significantly reduces the occurrence of fusion defects, such as dislocations and bubble nests, resulting in high-quality semifinished quartz glass products with improved etch resistance and reproducibility, suitable for semiconductor and optical components.
Implementation Method 1
zonewise sintering of a porous SiO2 soot body in a melt mold at a sintering temperature and during a sintering period with formation of a completely sintered transparent quartz glass body
Implementation Method 2
the soot body which has been dried or pretreated in another way is introduced for this purpose into an evacuable vitrification furnace and is sintered therein with formation of a transparent quartz glass body
Implementation Method 3
shaping the sintered quartz glass body by softening in the melt mold with formation of a viscous quartz glass mass
Implementation Method 4
the sintered quartz glass body is shaped at increased temperatures without substantial cooling, ensuring complete filling of the mold volume
Data Source
Figure 1~3(d)
Figure 2(a)~2(e)
AI summary
Method for producing a semifinished product from synthetic quartz glass Methods for producing a semifinished product from synthetic quartz glass by plastic deformation of a softened SiO2 mass in a melt mold are known. Starting from this, to avoid fusion defects as much as possible and to obtain semifinished products of quartz glass in a reproducibly high quality, a method is suggested that comprises the following steps: (a) providing a porous SiO2 soot body, (b) zonewise sintering of the SiO2 soot body in the melt mold at a sintering temperature and during a sintering period with formation of a completely sintered transparent quartz glass body, and directly thereafter (c) shaping the sintered quartz glass body by softening in the melt mold with formation of a viscous quartz glass mass which fills the volume of the melt mold entirely or partly, and (d) cooling the quartz glass mass and removing the mass from the melt mold with formation of the semifinished product.