Seagate

I attended work experience at Seagate Springtown in Derry from 1st-4th September 2014. Whilst there I had the opportunity to speak with employees and graduates, on placement, about their educational background to give myself a clearer view as to what I should expect if I choose to go to university and what courses that interest me are like at a further level of education. Some of the processes and facilities showed to us were photolithography, vacuuming, CMP, product analysis and the server room. Along with that we also had talks from senior employees, in relation to the courses they had studied and their uses within their current job, about physics, maths and statistics. We were also fortunate to get the opportunity to talk with graduates from Queens University Belfast on placement at Seagate about life at Queens and the subjects they were studying being physics and chemical engineering which was very helpful. Here are some of the things I found particularly interesting during our work experience.

C hemical M echanical P lanarization

The wafers made in the factory must be made free from impurities which is why CMP is carried out. The chemical used is slurry which forms an oxide layer when it comes into contact with the wafer. The slurry also contains tiny abrasive particles, of alumina and silica, which rubbed along with a pad are able to remove any oxide layer and remove the impurities.

Along with removal of oxide layers this process is used to create a flat, level surface on the wafer which is why key parameters must be met:

The downward pressure needs to be kept low as with a high pressure it causes non-uniformity in the wafer from the centre as the slurry cannot reach the centre of the wafer. Therefore a low pressure is used which allows an even spread of the slurry throughout the wafer but also leads to less abrasion occurring on the wafer and therefore longer processing times.

In the clean room (FAB 1)with a pad used in the CMP process

Back pressure is applied through the carrier of the CMP. Higher back pressure will result in an increase in centre removal on the wafer. Lowering back pressure results in an increase in edge removal.

A constant slurry flow must be maintained always as too little slurry will result in the centre of the wafer being starved resulting in a slow centre process while too much slurry can result in aqua-planing where-by there is a constant layer of slurry on the wafer and removal is inhibited.

One of the most important parameters is conditioning of the wafer as after a period of time it can undergo glazing whereby impurities make their way to the surface of the wafer causing non uniformity so it is conditioned with slurry and a diamond pad.

Photolithography

This is a printing process done onto the wafer on a microscopic level using light of either Krypton/Fluoride laser wavelength = 248 nm or Argon/Fluoride laser wavelength = 193 nm to transfer a pattern onto a photoresist polymer film. Then it is able to etch, mill, electroplate or curl these patterns into 3D structures.

Conditioning arm. 4” Diamond disk.

Excess resist is delivered to the substrateWafer surface is wetted with excess resist

Excess resist is removed from substrate surface

Solvent evaporation

^Applying a pattern onto the photoresist

<The process whereby the photoresist must first be added to the wafer

Vacuuming

Product analysis