Semiconductor device and method of forming vertical structure

A method comprising:

• providing, over a substrate, a vertical structure having a source, a channel, and a drain;
• shrinking the source and the channel by oxidation;
• forming a metal layer over the drain of the vertical structure;
• and
• annealing the metal layer to form a silicide over the drain of the vertical structure;
• wherein shrinking the source and the channel comprises:
• forming a first oxide layer over the vertical structure,
• forming a nitride layer over the first oxide layer,
• forming a second oxide layer over the nitride layer,
• performing CMP on the first oxide layer and the second oxide layer and stopping at a portion of the nitride layer,
• etching the nitride layer and the first oxide layer to expose the drain,
• forming a spacer adjacent to the drain,
• etching the first oxide layer to expose the channel and the source,
• shrinking the source and the channel substantially without shrinking the drain covered by the spacer,
• removing the spacer, and
• removing oxidized portions of the source and the channel.