Continuous mesh three dimensional non-volatile storage with vertical select devices
View Patent ↗A three-dimensional array adapted for memory elements that reversibly change a level of electrical conductance in response to a voltage difference being applied across them. Memory elements are formed across a plurality of planes positioned different distances above a semiconductor substrate. Bit lines to which the memory elements of all planes are connected are oriented vertically from the substrate and through the plurality of planes.
1. A method of fabricating non-volatile storage, comprising:
adding one or more devices and signal lines on top of a substrate;
adding a select layer above the one or more devices and signal lines, the adding the select layer includes adding select lines and adding vertically oriented select devices above and not in the substrate; and
adding a monolithic three dimensional array above the select layer, the monolithic three dimensional array includes word lines, vertically oriented bit lines and memory elements forming a continuous mesh;
the vertically oriented select devices are connected to the vertically oriented bit lines, the select lines and global bit lines.
2. The method of claim 1 , wherein the adding select lines comprises:
depositing a lower oxide layer;
depositing gate material on top of the lower oxide layer;
depositing an upper oxide layer on top of the gate material; and
etching trenches in the lower oxide layer, the gate material and the upper oxide layer.
3. The method of claim 2 , wherein the adding vertically oriented select devices comprises:
depositing thermal oxide material;
depositing a sidewall spacer;
etching the trenches;
filling the trenches with p-polysilicon;
performing a n+ source implant to create a n+ region at the top of the polysilicon; and
performing a thermal anneal to create a n+ region at the bottom of the polysilicon.
4. The method of claim 3 , further comprising:
adding a n+ polysilicon layer prior to depositing the lower oxide layer, the thermal anneal activates a junction between the p-polysilicon and the n+ polysilicon layer such that the p-polysilicon has its bottom end doped with n+ to form the drains of vertically oriented select devices due to diffusion of an n+ implant from the n+ polysilicon layer.
5. The method of claim 1 , wherein the adding vertically oriented select devices comprises:
adding a n+ polysilicon layer;
etching trenches on both sides of signal lines and below locations to be occupied by vertically oriented bit lines;
filling the trenches with p-polysilicon;
performing a n+ source implant to create a n+ region at the top of the polysilicon; and
performing a thermal anneal to create a n+ region at the bottom of the polysilicon, the vertically oriented bit lines are added above the polysilicon after performing the thermal anneal.
6. The method of claim 1 , wherein the adding vertically oriented select devices comprises:
etching trenches on both sides of signal lines and below locations to be occupied by vertically oriented bit lines;
filling the trenches with a first type of polysilicon;
creating a second type of polysilicon region at the top of the first type of polysilicon; and
creating a second type of region at the bottom of the first type of polysilicon, the vertically oriented bit lines are added above the polysilicon after creating the second type of region at the bottom of the polysilicon.