Table of Contents
Obtaining silicon
Most Si goes to the steel industry with <10% going to making wafers. [Wiki: Si]
: what does Si ore look like?
Making ingots
Silicon must be highly purified for use in semiconductors. Its melted in high temp furnace with several variations on how to purify it based on whether cost or purity (quality) is a higher concern. Chemicals are added to give p or n doping.
: steal a picture from Wiki or something
Making raw wafers
A large saw slices ingots into thin slices known as wafers. They are then polished. While elemental Si is gray, the above wafer is blue due to doping and coating. Also, note the notch at the top to identify doping and crystal orientation. As this has only a single large notch it is p doped {111} See [Crystalgraphic orientation] for more info.
Designing the circuit
Programs like Cadence VLSI, Magic VLSI, and others are used to design a circuit and produce CAD files.
: put a magic screenshot
Printing the photomask
An ion beam etches a fused quartz photomask with a layer from the CAD files. A photomask is needed for each layer. This is typically only done once for every mask needed, but contact masks wear out and even sometimes non-contact masks [Indistinguishable from magic]. Above is labeled a Cypress CY7B1731B-A from Electronics Goldmine. It appears to be a metal layer from a RAM chip.
Printing the wafer
There are two different methods: contact and w/e the other one is called. In the contact method, the plate and wafer are pressed together. This results in low separation, meaning cleaner print. However, the ever so expensive photomask will wear out sooner. In the other method the photomask is above. One or more complete IC layers will be on the photomask. If necessary, a stepper will move the mask around to print as many repetitions as will fit on the wafer. Each time a layer is added, it must be aligned to previous layers. It seems layer misalignment is responsible for many failed wafers. Above shows some registration marks on the wafer to make aligning layers easier (DEC 57-19400-04, left chip).
Wafer testing
Some circuits can undergo basic testing.by using test pads when still in the wafer. This eliminates the following steps only to find the entire wafer was bad. If too many units are bad during initial testing, the whole process is typically aborted. Each bad IC is marked with a dot of black ink. Above is from the same wafer as in the next section.
: get a picture of a probe card (off of my phone…)
: add probe scrube marks
Dicing
Wafers are placed on a sticky mat, often blue, and then cut with diamond saws into individual dies. The saws are precisely positioned to be just into the plastic layer. The non-dotted (good) dies are then collected. See first photo for an example (unknown device, probably a power diode). Only the dotted (bad) dies remain. The second photo shows the side of the wafer where the depressions between dies ends just where the wafer ends. Also note the punch marks where good dies were ejected.
Alternatively, smaller research runs are sometimes scribed (thin surface cut) and then snapped. This is less accurate and safe but requires less equipment and setup. Second photo was scribed and notice how not everything is broken, chips slightly vary and size, and some are even broken from a bad snap.
Bonding and early packaging
The bare die is sometimes glued onto a carrier island to ease handling. It is then inserted into half a chip carrier (package) with leads. Using typically either wedge or ball bonding, wires are made between the pins and the die onto the bond pads.
Final packaging
The top is then sealed and the packaging is complete.
Final testing
Chips are tested for basic functionality. If they pass, they are ready to be boxed up and shipped.
Extended testing
Military, aerospace, and automotive parts are tested for reliability. A large part of this is testing that the device is within specifications over a large temperature range. It seems radiation hardened parts are typically not tested for acceptable radiation dose as this might damage the chip prematurely.
References
- Wiki: Si: http://en.wikipedia.org/wiki/Silicon
- Crystalgraphic orientation: http://en.wikipedia.org/wiki/Wafer_%28electronics%29#Wafer_flats_and_crystallographic_orientation_notches
- Indistinguishable from magic
