Dimensional Measurement of Large-scale Quartz Glass Products

Differences from ordinary glass

Ordinary glass is made from sand called silica sand and contains various impurities. Quartz glass is made from refined or chemically synthesized crystals. Quartz glass is characterized by its very high light transmission properties because it contains few impurities. It can also withstand rapid temperature changes because it has high heat resistance and an extremely low coefficient of thermal expansion.

Type of quartz glass

Quartz glass can be broadly divided into fused silica glass and synthetic silica glass according to the manufacturing method.

Fused silica glass

Fused silica glass is manufactured by fusing crystal powder with an oxyhydrogen flame or electric furnace and then cooling. The crystals used for fused silica glass contain many metal impurities, but high transparency can be achieved by removing them through refining. Fused silica glass can be manufactured easily and at lower cost than synthetic silica glass.

Synthetic silica glass

Synthetic silica glass uses crystals containing few impurities as a raw material and is manufactured by chemical synthesis, such as hydrolysis of silane using hydrogen and oxygen. Synthetic silica glass has high light transmission properties over a wider wavelength band than fused silica glass. However, its manufacturing costs tend to be higher than fused silica glass because synthetic silica glass needs to be processed in clean environment.

Quartz glass applications

Quartz glass, which has high heat resistance and light transmission properties, is mainly used for electrical and electronic devices.
The high heat resistance of fused silica glass makes it suitable for parts that need to have high thermostability to retain their shapes, so it sees use in furnace tubes, boats, lamps, and other parts used in high-temperature processes such as heat treatment in semiconductor manufacturing. Fused silica glass is also used for vacuum depositors, vacuum chambers, and similar devices.
Synthetic silica glass has high homogeneity and light transmission properties, so it is used for optical parts, such as lenses and prisms mounted on exposure equipment used for semiconductor or liquid crystal manufacturing, photomasks for manufacturing of optical fibers, semiconductors, and liquid crystal displays, and other parts that need these characteristics. Synthetic silica glass also has high resistance to chemicals, including corrosion resistance, except for some solutions and gases such as hydrofluoric acid, phosphoric acid, alkalis, and alkali metal compounds. This makes it an indispensable material for parts used in semiconductor manufacturing processes that use chemicals.

Measurement point

For dimensional measurement of quartz boats, it is important to measure the flatness of the top and bottom plates and the perpendicularity of the plates to the pillars that connect them. Inappropriate flatness or perpendicularity may cause misalignment between the centers of the top and bottom plate, which also needs to be inspected by dimensional measurement. It is also important to measure the width of wafer holders. These are important inspection points not only during manufacturing but also during periodic maintenance because their accuracy directly leads to process reliability.

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Dimensional measurement of quartz boats and quartz tubes

Important dimensional measurement elements for quartz boats include the width of holders, flatness of top and bottom plates and their perpendicularity to the pillars. For quartz tubes that cover quartz boats, important measurement elements are the cylindricity and distance between the cylinder center and the gas tube center as well as their inner and outer diameters.
Process reliability is especially likely to be impacted when the inner and outer diameters, cylindricity, or distance between the cylinder center and the gas tube center of quartz tubes are out of tolerance, because the boats are prevented from containing the correct number of wafers or achieving a high level of vacuum.
Hand tools are not accurate enough for measurement, because dimensions of the parts of quartz boats and quarts tubes need to be accurate within tolerances of 0.1 mm (0.0039″). Measured values can vary from measurer to measurer and it is difficult to convert warpage and curvature to values as flatness. When using bridge CMMs, the number of operators that can perform measurement is limited and a lot of work is required to transport workpieces to a measuring room.

The WM Series enables easy dimensional measurement of quartz boats and quartz tubes by simply touching with the wireless probe. Unlike hand tools, measurement results do not vary, enabling quantitative measurement. It is possible for a single person to measure GD&T of quartz tubes, such as flatness, circularity, and cylindricity, as well as their inner and outer diameters and the distance between the cylinder center and the gas tube center. The measured elements can be converted to values, and the distance between virtual lines can also be visualized.
What’s more, the portability of the WM Series allows it to be brought into manufacturing and installation sites and immediately measure the dimensions. Workpieces can be measured in manufacturing lines, so they do not need to be removed and returned, eliminating the risk of deformation.
It can also automatically convert measurement results into inspection reports. Photographs can be included in inspection reports, making them easy to understand. The reports use the rich text format (RTF) is used, so they can be edited easily.

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