How do they make silicon wafers and microchips ?
You may not realize it but we’re surrounded by arguably the greatest most revolutionary invention of the last 50 years. It’s in TVs, stereos, watches, cars, phones, traffic lights and pretty much every appliance in your kitchen. In fact these days if a device uses electricity, it probably uses one the tiny gizmo in question is of course the silicon chip. Making these extraordinary miniature electronic brains is one of the most complex manufacturing tasks ever attempted. So how do they do it ? Texas, USA home to big stuff …big cows, big boots, big hats, big moustaches but Texas is also the birthplace of a miniaturised miracle: the silicon chip and here in Sherman, 20 miles north of Dallas is the MC fabrication facility. In this strange futuristic-looking plant, they produce silicon wafers which are the basis for all modern micro chips. Silicon has special properties because it’s what’s called a semiconductor… that means that depending on how its treated, silicon can either conduct or block the flow of electricity. It’s this property that makes it ideal for supporting the millions of tiny transistors necessary for a modern computer chip but because these transistors are so incredibly small the silicon based on which they rest needs to be absolutely flawless. It took decades to perfect the process of producing silicon with a perfect mono crystalline structure. They begin with raw polysilicon or poly and heat it to over 2,500 degrees Fahrenheit inside a special sealed furnace which has been purged with argon gas to eliminate any air. The resulting lake of molten silicon is then spun in a crucible and a silicon seed crystal roughly the size and shape of a pencil is lowered into it while spinning in the opposite direction as the molten polysilicon is allowed to cool the seed crystal is slowly withdrawn at around one and a half millimeters a minute. The result is a single silicon crystal weighing around 440 pounds and with a diameter of around 200 millimeters. The crystal is so strong its entire weight can be supported by a single thread just three millimeters across but it is brittle and it must now be cut down to size without shattering. After testing with chemicals and x-rays to check its purity and molecular orientation it’s fed to a silicon salami slicer. This 10-ton wire saw uses a fast-moving web of ultra thin wire to produce wafers of silicon that are just two thirds of a millimeter thick and 99.999 percent pure. Once cut there are microscopic marks left on the wafer surface so it’s time for a buffing using a process called lapping after a twirl in this high-powered polisher. They are still not smooth enough so they’re given yet another buff using a chemical process the result is wafers of silicon with a surface roughness of less than one millionth of a millimeter buffed machine they’re finally ready for etching with this circuit design coming up. How do they eliminate the biggest enemy of manufacturing in a microscopic environment: the common dust particle? Find out next on “How do they do it” !
Packing millions of transistors on to these tiny silicon wafers is the job of chip manufacturers like texas instruments. Back in 1958, the inventor of the integrated circuit jack kilby managed to squeeze a single transistor onto his design. These days the latest generation uses almost a billion and according to Moore’s law that number doubles every two years. Of course the more they try and pack into the design, the smaller each transistor needs to get. There are over a quarter billion transistors in this design. Someone has to shrink them down to this. Working at this microscopic scale exposes the chipmaker’s to a major problem when a transistor is only one ten thousandth of a millimeter across the smallest particle of dust is enough to cause an electronic train wreck so before staff members like Dane Bailey set to work in the fab it’s on with the bunny soup for our general product that we make here at DSP typically takes on the order of about 1,500 individual processing steps from start to finish with an area of just under 190 4,000 square feet the fab is a class 1 clean room thanks to 12,000 tons of air conditioning equipment the air is 1000 times cleaner than a hospital operating room there’s actually less than 100 particles per square foot of air. One particle landing on a critical area can kill a chip. To give you an idea how clean this room is, walking alone produces five million particles every minute so to avoid contamination from the inadvertently dusty staff front opening unified pods or foods transport packets of wafers through the intricate process of component construction the key problem is miniaturizing the complex designs and imprinting them onto the wafers it’s done through a process known as photolithography. First the wafer is coated with photosensitive chemicals which harden when exposed to UV light. In sealed dark groans light is shone through an image of the design then through a miniaturizing lens and onto the coated wafer when the chemical is washed off the design remains just like a developed photographic image but in order to pack all the components onto the wafer they are built up layer by layer like floors in a miniature skyscraper. To complete the job the folks cycle the wafers up to 40 times repeating the photo etching process for each new layer. Some layers are cooked, some blasted with ionized plasma, some bathed in metals. Each different type of treatment changes the properties for that layer and slowly forms part of the jigsaw making up the chips design. The finished sheets of silicon wafer carry up to 1,000 individual micro chips and billions and billions of circuit elements all that remains is to slice and dice and the journey from sand to circuit board is complete. What was once a worthless pile of sand can now change hands for more than nearly seven hundred dollars an ounce and calculate pi to 1000 decimal places in the blink of an eye. Metaphysical poet William Blake reckoned he could see the world in a grain of sand but if he were to look again today he would surely be more amazed to discover a billion tiny transistors.