Integrated Circuits - Scalable Consumer Technology

An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. The typical chip size these days is about 1 square centimeter A typical IC contains millions of interconnected devices.

The entire purpose of the integrated circuit is to precisely control the flow of electricity through various PN junctions and similar devices. To achieve this precision requires again, carefully control fabrication processes.

Among the most advanced integrated circuits are the microprocessors, which drive everything from computers to cellular phones to digital microwave ovens. Digital memory chips are another family of integrated circuits that are crucially important. Semiconductor ICs are fabricated in a layer process which includes these key process steps:

• Imaging
• Deposition
• Etching

While we don't want to get bogged down in the details of this processing, we do want to come away with a general understanding of how this process has been optimized to produce ever cheaper consumer electronics. Also, there must be quality control at every step of this process so that the final packaged produce works as designed. In the early days of IC fabrication the error rate was relatively large but no so anymore. If your country can manage to produce cheap labor that you can manufacture these components for the rest of the world, and that has EXACTLY happened,

Imaging also known as Photolithography:

• Make a photomask - this is basically a schematic roadmap of how the circuit board components need to be laid out, etc. This pattern needs to be transfered from the photomask to the substrate (usually crystalline silcone in the form of a thin wafer). This transfer process is called photolithography and is broadly similar to regular lithorgraphy where a metal plate containing some figure is pressed onto paper.

• Detail in the fabrication process is limited by the resolution of the photomask. Circuits have become smaller due to significant advancements in photomask construction and the subsequent transfer.

• Next a layer of conductive metal (usually a few nanometers thick) is deposited onto the substrate. This is usually done by evaporation methods (not efficient) or by using a sputtering machine. No, a sputtering machine is not your roomate, rather sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. This process is also called ion implementation.

• The sputtered atoms, those ejected into the gas phase, are not in their thermodynamic equilibrium state. Therefore, they tend to condense back into the solid phase upon colliding with any surface in the sputtering chamber. This results in deposition of the sputtered material on all surfaces inside the chamber. This allows for tight control of the sputtering process and the laying down of material at exactly the right place.

• A layer of photoresist -- a chemical that hardens when exposed to light (often ultraviolet) -- is applied on top of the metal layer. The photoresist is selectively "hardened" by illuminating it in specific places.

• A transparent plate with patterns printed on it, called a photomask or shadowmask, is used together with an illumination source to shine light on specific parts of the photoresist to create specific kinds of IC boards. Once the mask is made, thousands can be produced fast.

The last part of this process is known as etching. In brief, the circuit board is now bathed in pure water and acid to remove various bits of metal so as to make clean interfaces between metal and substrate. This is the most environmentally toxic part of the overall fabrication process due to the discharge of this water mix, usually in an adjacent wet land or stream. This was the problem in the former Hynex plant in Eugene located in the Eugene Wetlands (in west Eugene).

This entire manufacturing process is well described in this 10 minute video and watching it may help you parse the tortured text that you just tried to read.



If you walk around where some physics and chemistry labs are located you might see devices that look like below:

These are vacuum deposition chambers (try stuffing your roomate in one) that are used to study the properties of materials and to make new synthetic materials via the ion deposition processes discussed above. This takes a lot of energy, by the way.