To make our interconnections we need a layer of silicon dioxide to act as an insulator between  our n and p type materials and the aluminium we are going to deposit on the slice, as in the drawing below:

Integrated Circuits

Testing & Breaking

The aluminium is represented here by the solid black layer. Already the connections to the components can be seen, but were we to leave it like this all the components would be connected to each other and the IC would be useless.

In much the same way as we make a printed circuit board we can now etch away the parts of the aluminium we do not need and in this way create tracks that direct the current. The finished work will look something like this:

If we wished to have crossover sections then we can either do so by an n+ region which we would have to diffuse at the same time as the others, or we could add a layer of silicon dioxide to the above and use that to cross. Either way it needs careful consideration as we may introduce stray capacitance that will affect the workings.

We could now backlap the wafer, which means grinding it down from the non-circuit side to make the substrate thinner. This leads to smaller profiles of the finished IC.

Remember that we have made dozens of these on a single wafer cut from a boule. Now we need a method of testing them.