Wafers are thin discs that serve as the basis for the manufacture of microchips. The production of wafers involves several processing steps. In order to use silicon (Si) or silicon carbide (SiC) in the semiconductor industry, for example, it must be grown as a single crystal. The so-called ingots and boules are then machined into a blank disc. When cut into slices, these form the wafers, which are ground thin, polished and coated with an epitaxial layer to prepare them for the photolithography process. Using appropriate masks and light, circuit patterns are etched into the wafer. Finally, individual microchips can be cut from the wafer.

Significant growth potential

Don’t be afraid of (semiconductor) ceramics

Silicon carbide (SiC) is increasingly becoming the substrate of choice in semiconductor manufacturing. According to the Fraunhofer CSP in Halle (Saale), a semiconductor made from a compound of silicon and carbon offers a wide bandgap compared to a semiconductor made from pure silicon. This is a decisive factor for electrical conductivity and means that the semiconductor can be used under extreme conditions such as high temperatures, high voltages and high frequencies. For grinding operations, however, the substrate presents a challenge, as Michael Egeter notes: “We have already observed a certain degree of caution among grinders who have previously worked almost exclusively with metallic materials,” he reports. The machining behaviour of the grinding process on ceramics is completely different. Once this hurdle is overcome, the ever-expanding field of applications for technical ceramics and single-crystal semiconductor substrates will reveal itself as a huge potential for grinding technology.

Save time in the manufacturing process

Semiconductor manufacturing is a time-consuming process. As a result, the delivery of chips requires a correspondingly long lead time, which poses a challenge for many sectors of industry. Even the raw crystal, which is grown in a high-temperature furnace at around 2,400˚C, takes a good two weeks before it can be shaped into a semi-finished product. For this so-called ‘ingot/boule to puck’ step, the Hardinge Group – to which Kellenberger belongs – formed a development team comprising engineers and application engineers, supported by SiC industry experts and raw material suppliers. The team analysed the inefficiencies in existing SiC ingot processing. The findings were incorporated into the development of an automated all-in-one 5-axis machine capable of machining all currently relevant specifications and diameters of SiC ingots. With automated loading and unloading, the machine can reduce the machining time for an ingot/boule into a puck – a process that takes more than 24 hours using conventional methods – to two to three hours, according to Kellenberger.

An ultra-fine challenge for grinding tools

Eliminate individual process steps

Wafers are usually first ground and then polished to achieve the required high surface finish. The slurries used for polishing are mixtures of fine solid particles and a liquid. This polishing agent is expensive. “The longer a polishing process usually takes and the larger the wafer surface, the more appealing it becomes to minimise the polishing process as much as possible or eliminate it from the process altogether,” says the grinding expert. The greatest challenge in machining the hard wafer surfaces was developing the right bond for the sub-micron diamond grain (< 1 μm). This is precisely where Sileno sees Meister Abrasives’ strength: the ability to tailor the abrasive coating structure in detail for every application. By shortening or even eliminating polishing processes, the customer saves valuable time, reduces costs, requires less infrastructure and increases throughput.

Source | VDW
Photos | Kellenberger AG, Meister Abrasives