Memory cell comprising a semiconductor junction diode crystallized adjacent to a silicide
View Patent ↗A memory cell is formed of a semiconductor junction diode in series with an antifuse. The cell is programmed by rupture of the antifuse. The semiconductor junction diode comprises silicon, the silicon crystallized in contact with a silicide. The suicide apparently provides a template for crystallization, improving crystallinity and conductivity of the diode, and reducing the programming voltage required to program the cell. It is advantageous to reduce a dielectric layer (such as an oxide, nitride, or oxynitride) intervening between the silicon and the silicon-forming metal during the step of forming the silicide.
1. A method for forming a first memory level of memory cells in a memory array, the method comprising:
forming a plurality of first conductors at a first height above a substrate in a first pattern and etch step;
forming a plurality of semiconductor pillars above the first conductors in a second pattern and etch step;
crystallizing the plurality of first semiconductor pillars, wherein each of the first semiconductor pillars is in contact with a silicide at the time it is crystallized;
forming a plurality of second conductors above the first semiconductor pillars in a third pattern and etch step; and
forming a plurality of dielectric rupture antifuses between the first and second conductors, each antifuse in series with a first semiconductor pillar of the plurality of first semiconductor pillars, and each antifuse in contact with one of the conductors,
wherein the first, second, and third pattern and etch steps are all separate.
2. The method of claim 1 further comprising removing the silicide before formation of the plurality of second conductors.
3. The method of claim 1 wherein the silicide is selected from a group consisting of titanium silicide, cobalt silicide, chromium silicide, tantalum silicide, platinum silicide, nickel silicide, niobium silicide, and palladium silicide.
4. The method of claim 1 further comprising forming the silicide, wherein the step of forming the silicide comprises:
forming an oxide, nitride, or oxynitride adjacent to a silicon layer;
depositing a silicide-forming metal in contact wit the oxide, nitride, or oxynitride, wherein the oxide, nitride, or oxynitride is disposed between the silicon layer and the silicide-forming metal; and
annealing to form the silicide and substantially entirely reduce the oxide, nitride, or oxynitride where the oxide, nitride, or oxynitride is adjacent to the silicon layer.
5. The method of claim 4 wherein the silicon layer is a portion of a semiconductor pillar of the first plurality of semiconductor pillars.
6. The method of claim 1 wherein the first memory level is one of a plurality of stacked memory levels formed in a monolithic three dimensional memory array.