From vehicles, cellular phones and defense systems to gaming consoles, refrigerators and coffeemakers, the ever expanding incorporation of microelectronics has dramatically magnified the demand for semiconductor chips at the heart of every digital device. As a result, there is an acute shortage of such chips, even though more than one trillion of them are manufactured worldwide each year.
Overcoming the chip shortage is easier said than done, as only a limited number of companies manufacture them in volumes large enough to fulfill the growing demand. While there used to be dozens of high-volume chipmakers in existence, the increasing sophistication of chips and the expense of building multi-billion-dollar facilities filled with multi-million-dollar equipment has led to industry consolidation to the point where there are now only six or seven major chipmakers.
Manufacture of a typical semiconductor chip starts with a round, 300 mm in diameter, 0.775 mm-thick silicon disc or wafer. Depending on the size of the finished chips, perhaps 600 may be created on a single wafer. Chip circuitry is unbelievably small and complex; a single chip can contain billions of transistors. Some circuit features are only two nanometers wide. In comparison, the width of a human hair is 100,000 nanometers. Accordingly, many chipmaking processes occur on the atomic level, and one of the biggest issues in semiconductor manufacturing is cleanliness.
Robots move wafers in the chipmaking process through a series of vacuum chambers, where they are subject to multiple treatments— including photolithography, physical and chemical vapor deposition (PVD and CVD), etching, chemical doping and cleaning. During processing, the chips may receive 175 layers or more of conducting, semiconducting and insulating material. Each application chamber is dedicated to a specific function and processes one wafer at a time. Some wafers go through hundreds of processes before completion, all of which can take between two and three months.
As chipmaking companies ramp up production, they look to their suppliers to quickly produce much needed components for new chipmaking systems. Among these key components are vacuum processing chambers.
There is a huge demand for vacuum processing chambers for building new chipmaking machines, as well as to replace chambers that wear out from handling the caustic gases used in the chipmaking process. Of the thousands of chambers produced yearly, most are machined from aluminum or stainless-steel billets.
During manufacturing, the majority of material is machined from the raw billet. Large chambers, for example, may start with 12,000 lbs (5,443 kg) of material and weigh only 1,000 lbs (454 kg) or less when completed. To quickly remove these massive amounts of material and produce high-precision finished chambers, the shops supplying them rely on advanced manufacturing technology that includes rugged, horizontal machining centers (HMCs), machines with full five-axis cutting capability and palletized automation.
As semiconductor chips become smaller and more complex, the equipment used to make them grows larger. Bigger vacuum chambers translate into longer machining times, and depending on chamber complexity, those times can run into the hundreds of hours. This is why many companies that supply chambers opt for HMCs, such as Mazak’s HCN 6800 or its HCN 8800, outfitted with substantial tool storage capacity—in some cases, as many as 300 tools. And for continuous production, these manufacturers incorporate multiple machines into automated palletized systems such as Mazak’s PALLETECH.
Some vacuum chambers can require more than 45 hours of in-the-cut time, and when the machining centers are outfitted with large capacity tool storage, worn tools are immediately replaced to get the machine back in the cut as quickly as possible. When incorporated into a Mazak PALLETECH automated pallet-changing system, shops can achieve unmanned operation while gaining the flexibility to adjust for changes in chamber production levels and designs.
Many vacuum chambers have an all-too familiar sealing face groove feature. The large monolithic shape of the chamber poses quite a challenge to machine this feature, especially with a conventional turning center. To overcome this challenge, Mazak’s MAZATROL SmoothG and SmoothAi controls allow a machining center to “turn” those face grooves with the milling spindle using the Mazak Orbiturn function.
For vacuum chamber joining, many manufacturers have opted for friction stir welding (FSW) instead of conventional welding methods. Mazak MegaStir, for instance, provides the FSW tools that allow these manufacturers to not only join surfaces without conventional weld beads, but to also do so on a Mazak five-axis HYBRID Multi-Tasking Machine that lets them finish cut the joined surfaces without having to remove the part.
Commonly considered a forging process, FSW is well suited for joining alloys with low melting points, including aluminum, copper and brass, as well as handling high-temperature welding in steels and nickel-based alloys. Producers of chambers and chamber components have discovered that FSW increases the total lifecycle of a chamber because there is no weld bead to degrade over time.
In an effort to meet the burgeoning demand for vacuum chambers, many manufacturers are also turning to full five-axis machine technology. With such capability, shops can machine all of a chamber’s features in one setup, which greatly reduces the need for handling. Such machines include Mazak’s INTEGREX i-800 with tilting B-axis and turning capability, its VARIAXIS i-800 NEOs with tilt/rotary tables and Mazak VORTEX machines with tilting spindles.
Wafers for chip production are round, as are the process chambers, and chamber features are engineered to handle those shapes. Without combined five-axis and turning capabilities, a chamber may have to be machined on four or more different pieces of equipment. In those instances, roughing occurs on two different machines, then other machines are employed to achieve desired feature diameters.
Unfortunately, every move of a chamber consumes time, and every refixturing creates opportunities for positioning errors and unwanted changes in the relationship between part features. The INTEGREX machines provide multi-tasking capability—milling, as well as the turning functions of a vertical turning lathe—and thereby minimize time-consuming, multiple-machine changeovers that limit production volumes.
In addition to application flexibility, process stability is essential. The chambers process chips under ultra-high vacuum. Welded components at those vacuum levels will leak no matter how good the welds are. Castings generally are too porous, and silicon in a sand casting can be a contaminant in the processing environment. Machining from solid billets of material ensures a reliable product.
Along with significant amounts of material removal, chambers also require circuitous 100"-long , 0.180"-diameter (2,540 x 4.6-mm) O-ring grooves. The O-rings seal the chambers from normal atmospheric pressure, and chamber lids and seals must have true, flat and smooth mating surfaces. Rigidity and stability of the machining system is critical. If a machine is not trammed correctly and it wobbles, has runout or is not balanced, the surface finish that results will not provide sufficient vacuum integrity.
A stable machine tool also permits use of more aggressive machining parameters that can boost throughput. The value of improving cycle times is clear on large, complex parts. One shop made a chamber it called “the monolith.” It was 12' long, 4.5' wide (3.7 x 1.37 m) and 18" (457 mm) thick and machined from a single aluminum billet. Machining the chamber to specification required removal of 70% of the billet’s weight. A strong, rigid machine tool’s ability to remove that much material quickly contributes to faster construction of chipmaking machines and eventually boosts output of semiconductor chips.
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