PN Diode Lab - Albert Gural

Introduction

This lab involves the creation of a PN diode. The LED lab already involved the creation of a PN diode, however, the P-type mesas were etched with acid by first coating the layer with a permanent marker, then applying acid to etch away the unmasked material.

This lab will involve the use of industry standard photolithography.

Procedure and Results

: Obtain a piece of epitaxial silicon.

: Put the chips into a boat and dip in DI water, HF, DI water (x2) for an oxide etch.

: Place the chips in a field-oxide furnace.

: Oxygen should bubble through water at $1 ft^3/hr$ for 30 minutes at $1100^oC$.

$Cool chips on an aluminum block. Note the color, due to a $\approx 350nm$ thick oxide layer.$: Cool chips on an aluminum block. Note the color, due to a $\approx 350nm$ thick oxide layer.

: Place the chip in a centrifuge (with vacuum applied) and add a drop of photoresist.

: Turn on the centrifuge to get a very thin photoresist layer.

: Place the chips on a hot surface to allow the photoresist to harden.

: Chip with smooth layer of photoresist.

: Place the chip on a UV-expose machine (the mask should just have small dots).

: Make sure the chip is aligned adequately on the mask and apply the UV for 1.5 minutes.

: Develop the photoresist (un-exposed regions should dissolve away).

: Place the chips on boats and repeat the oxide etch (4 minutes in HF should be enough to remove the thick oxide layer).

: Remove the remaining photoresist with acetone, and the oxide holes should be visible.

: Place the chips in a boron furnace (note the white boron chips) to P-dope the exposed surfaces. Nitrogen should flow at $1 ft^3/hr$ for 30 minutes at $950^oC$.