Semiconductor wafer grinders
Many companies have developed several types of grinding machines used in the semiconductor industry for the production of silicon wafers and the production of integrated circuits. The vertical and horizontal spindle systems are used in conjunction with specially designed diamond grinding wheels that only cut at the edge of the grinding wheel, ensuring high grinding speeds and low heat generation. Machines are available for single-sided wafer grinding in IC production, for double-sided wafer grinding in silicon wafer production, and for grinding the edges of silicon wafers. Built into the motor, aerostatic air bearing spindles are available for high precision grinding applications.
Single side grinders are used in the semiconductor industry for thin wafers. Typical applications are SOI wafer thinning or chip manufacturing for IC cards and smart cards.
Many companies can offer several types of the single-sided cutter. This type of grinder can be equipped with 1 or 2 loading stations for automatic loading and unloading.
The latest advancement in grinding technology are double-sided grinders. Both sides of the wafer are ground at the same time. These machines are highly efficient in terms of flatness, roughness and throughput and can completely replace the lapping process - sometimes even the etching process. For advanced 450mm, 300mm and 200mm wafer production, wire cutting is becoming more and more popular due to lower cost compared to ID cutting technologies. In the production of silicon wafers with a diameter of 450 mm and 300 mm, wire cutting is already the leading technology. However, wire cutting creates wafers with a non-rotationally symmetrical surface, showing a wave structure and a cone. This geometry is difficult to remove.
Lapping requires a rather large amount of material to be removed and causes much greater damage to the crystals compared to grinding. One-sided sanding is also not an ideal technology for removing this wave structure as the insert must be clamped on one side. In this case, the geometry of the back side is "copied" to the ground side. Double-sided sanding combines several advantages. The free-floating insert has a rotationally symmetrical geometry with little crystal damage and a very flat and smooth surface. Double-sided sanding is a single plate operation, and after this process, all silicone plates will be the same thickness. Ground wafers can be transferred to polishing without sorting procedures. Thanks to this technology, it becomes much easier to fully trace tiles at all stages of production. Due to slight damage to the crystals, the following costly polishing procedure may be shortened.
In some grinders, the wafer is kept upright. Horizontal spindles are used. This design provides a very uniform flatness and roughness on both sides of the wafer. Gravity is not a factor that can affect geometry in this configuration. To obtain very high performance, the mounting of the wafer and the stiffness of the grinding wheel support are key issues. Some companies have developed a 300mm waffle machine that holds the tile upright by means of rollers. Traction is provided by separate rollers that touch the plate on both sides. Due to this design, flatness data of 5 µm can be obtained. The machine is fully automatic, incl. transport of tiles from the input cassette to the notch finder, to the grinding station, after the brushing, rinsing and spin-drying stage. The wafers are transferred dry and clean to the output cassette. In the meantime, this machine was further developed.
The result is new models for 200mm wafers and 300mm wafers, as well as for 450mm wafers. Both machines are fully enclosed now including robots. The main change is the modified wafer holder. The patented system holds the wafer by means of hydrostatic pressure washers on both sides in a special ring of the support plate. The plate traction is achieved simply by snapping a small nose into a cutout or flat surface of the silicon plate. In this way, the insert assembly is stress-free and a flatness data of 0.5 µm can be obtained. The accuracy of the GBIR wafer is achieved by adjusting the degree of inclination vertically and horizontally of the grinding wheel spindles. Improving the accuracy of GBIR and SBIR is achieved by changing the contact position of the grinding wheel with the insert while the insert oscillates vertically.
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