Semiconductor devices and methods of fabrication
Some embodiments include a semiconductor device having a stack structure including a source comprising polysilicon, an etch stop of oxide on the source, a select gate source on the etch stop, a charge storage structure over the select gate source, and a select gate drain over the charge storage structure. The semiconductor device may further include an opening extending vertically into the stack structure to a level adjacent to the source. A channel comprising polysilicon may be formed on a side surface and a bottom surface of the opening. The channel may contact the source at a lower portion of the opening, and may be laterally separated from the charge storage structure by a tunnel oxide. A width of the channel adjacent to the select gate source is greater than a width of the channel adjacent to the select gate drain.
1. A method of forming a semiconductor device, comprising:
forming a stack structure comprising levels of conductor material and interleaved levels of dielectric material, wherein the levels of conductor material comprises a first select gate material comprising polysilicon, a control gate material comprising polysilicon over the first select gate material, and a second select gate material comprising polysilicon over the control gate material, wherein the polysilicon of the first select gate material and the polysilicon of the control gate material have different doping configurations;
forming an opening through the stack structure to vertically extend into the stack structure, the opening being defined by sidewalls of the levels of conductor material and the levels of dielectric material;
exposing the first select gate material, the control gate material, and the second select gate material to an etching solution through the opening to form recesses relative to sidewalls of adjacent dielectric levels, the recesses comprising a first recess of the first select gate material to a first depth, and a second recess of the control gate material to a second depth, wherein the first depth of the first recess is less than the second depth of the second recess; and
forming a charge storage structure in the second recess formed in the polysilicon of the control gate.
2. The method of claim 1 , wherein the etching solution used to form the recess comprises tetramethylammonium hydroxide (TMAH).
3. The method of claim 1 , wherein forming the stack structure comprises:
doping the first select gate with boron at a doping concentration of about 2E20 cm −3 during deposition of the first select gate;
doping the control gate with phosphorus at a doping concentration of about 1E21 cm −3 during Plasma Enhanced Chemical Vapor Deposition (PECVD) of the control gate; and
doping the second select gate with boron at a doping concentration of about 1E21 cm −3 .
4. The method of claim 1 , wherein the polysilicon of the second select gate remains unrecessed after exposure to the etching solution.
5. A method of forming a semiconductor device, comprising:
forming a stack structure comprising a first select gate material comprising polysilicon, a control gate material comprising polysilicon over the first select gate material, and a second select gate material comprising polysilicon over the control gate material, wherein the doping configurations of the first select gate, the control gate, and the second select gate are different;
forming an opening through the stack structure to vertically extend into the stack structure;
exposing the first select gate material, the control gate material, and the second select gate material to an etching solution through the opening to form a recess in at least the polysilicon of the control gate; and
forming a charge storage structure in the second recess formed in the polysilicon of the control gate,
wherein forming the stack structure comprises:
doping the first select gate with boron at a doping concentration of about 2E20 cm −3 during a deposition of the first select gate;
doping the control gate with phosphorus at a doping concentration of about 1E21 cm −3 during PECVD of the control gate; and
doping the second select gate with carbon at a doping concentration of about 1E16 cm −3 .
6. A method of forming a semiconductor device, comprising:
forming a stack structure comprising a first select gate material comprising polysilicon, a control gate material comprising polysilicon over the first select gate material, and a second select gate material comprising polysilicon over the control gate material, wherein the doping configurations of the first select gate, the control gate, and the second select gate are different;
forming an opening through the stack structure to vertically extend into the stack structure;
exposing the first select gate material, the control gate material, and the second select gate material to an etching solution through the opening to form a recess in at least the polysilicon of the control gate; and
forming a charge storage structure in the second recess formed in the polysilicon of the control gate,
wherein forming the stack structure comprises:
doping the first select gate with boron at a doping concentration of about 2E20 cm −3 during deposition of the first select gate;
doping the control gate with phosphorus at a doping concentration of about 1E21 cm −3 during PECVD of the control gate; and
doping the second select gate with about 1% to about 10% of N 2 .
7. A method of forming a semiconductor device, comprising:
forming a stack structure comprising a first select gate material comprising polysilicon, a control gate material comprising polysilicon over the first select gate material, and a second select gate material comprising polysilicon over the control gate material, wherein the doping configurations of the first select gate, the control gate, and the second select gate are different;
forming an opening through the stack structure to vertically extend into the stack structure;
exposing the first select gate material, the control gate material, and the second select gate material to an etching solution through the opening to form a recess in at least the polysilicon of the control gate; and
forming a charge storage structure in the second recess formed in the polysilicon of the control gate,
wherein forming the stack structure comprises:
doping the first select gate with boron at a doping concentration of about 2E20 cm −3 during deposition of the first select gate;
doping the control gate with phosphorus at a doping concentration of about 1E21 cm −3 during PECVD of the control gate; and
doping the second select gate with NH 3 .
8. A method of forming a semiconductor device, comprising:
forming a stack structure comprising a first select gate material comprising polysilicon, a control gate material comprising poi silicon over the first select gate material, and a second select gate material comprising polysilicon over the control gate material, wherein the doping configurations of the first select gate, the control gate, and the second select gate are different;
forming an opening through the stack structure to vertically extend into the stack structure;
exposing the first select gate material, the control gate material, and the second select gate material to an etching solution through the opening to form a recess in at least the polysilicon of the control gate; and
forming a charge storage structure in the second recess formed in the polysilicon of the control gate,
wherein forming the stack structure comprises:
doping the first select gate with boron at a doping concentration of about 2E20 cm −3 during deposition of the first select gate;
doping the control gate with phosphorus at a doping concentration of about 1E21 cm −3 during PECVD of the control gate; and
doping the second select gate with germanium at a doping concentration of about 2E20 cm −3 using an ion beam implant.