Chip making
Semiconductors are everywhere. In the dishwashers, microwaves and TVs in our homes. In our smartphones, PCs and tablets. In our workplaces and in the transportation we use – cars, trains, ships and planes. Driving the everyday devices we have come to take for granted over the past 40 years.
Their use has revolutionized how we live, work and play. Enabling us to understand, create and share information faster and more easily. We now assume that devices will get more powerful and ever smaller every year. But, despite this, how semiconductors are actually made remains a mystery to the general public. Here’s how it is done.
1. FROM SAND TO PURE SILICON
It all starts with one simple, common substance – sand. The silicon found in sand is in the form of silicon dioxide. To make chips, manufacturers need pure silicon so the first step in the process is to separate the silicon from the oxygen molecules.
The pure silicon needed to make silicon chips can have only one foreign atom for every billion silicon atoms. It must also be mono-crystalline form. The way that atoms are organized in this form of silicon is essential to some of the later processes.
2. WAFER BLANKS
The silicon is then extracted, or pulled, from liquid silicon in the form of long cylindrical ingots at roughly 1,400 degrees centigrade.
3. WAFERS ARE CUT
Wafers are cut from the ingots before being polished to produce a smooth surface. They’re then sent to chip manufacturers for processing. The following steps in wafer processing are then repeated many times to create the finished wafer containing chips.
4. COATING A WAFER
The wafer is put into a high temperature furnace and exposed to oxygen forming a layer of silicon dioxide on the surface. Then Chemical Vapor Deposition (CVD) is used to add a layer or film of nitride.
5. CREATING MASKS
Once the circuit layout of the chips has been designed, glass plates or masks are created which help copy the design onto the surface of the wafer. Several masks are used in sequence to add more and more complexity to the chips.
6. ADDING THE PATTERN
Now it’s time to begin creating the design on the surface of the wafer using the masks as a guide. Photolithography, a type of optical printing, is used. The wafer is first coated with photoresist that changes when exposed to ultraviolet (UV) light. The mask is placed above the wafer and precisely aligned with it. UV light shining above the mask reacts with the exposed parts of the photoresist creating a pattern. The wafer is covered with a developing solution to develop these patterns that are then etched leaving the parts not exposed to UV light intact. The surface now contains trenches that run across the surface.
DEPOSITION
Dielectric or insulating film is deposited in the trenches by one of a number of deposition technologies such as Chemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD) or Plasma-Enhanced ALD (PEALD). Gates are formed between the trenches creating part of the many millions of transistors that may be created on a single chip. Gates can be switched to allow charge carriers like electrons to flow or to prevent them.
Contacts are formed by each gate to create a source and drain. Ion implantation is used to implant special elements into the wafer for the source and drain. The charge carrier enters a gate channel at the source contact and exits at the drain contact.
CONNECT
Once the basic chip components have been created they need to be connected. The same processes of lithography, etching and deposition are used to form trenches filled with metal connections. These connections between components are created not just on one level but on many. The finished wafer will contain up to several thousand individual chips in a space of 200 to 300mm and some chips can hold billions of transistors.
7. WAFERS SEPERATED INTO INDIVIDUAL CHIPS
Once wafer processing has been completed, the finished wafers are transported to another plant for cutting, assembly & packaging. The individual wafers are cut into separate chips.
8. LEAD FRAMES
Chips are then placed in a lead frame forming a protective housing.
9. TESTING PACKING
Each chip is then tested before being packaged to be sent for placement on circuit boards.
SUMMARY
The equipment and processes used to create chips are very complex and draw on leading-edge research. But the objective is simple. To keep enabling us to understand, create and share more.
