Method of fabricating a semiconductor device using laser annealing

A semiconductor device, comprising:

• a string of transistors disposed along a channel hole, the string of transistors being vertically stacked over a substrate along a vertical direction perpendicular to a surface of the substrate, the string of transistors including:
• a gate dielectric layer formed over an inner surface of the channel hole;
• a channel layer including polysilicon having a first refractive index formed over an inner surface of the gate dielectric layer, the channel layer having an upper surface that is parallel to the surface of the substrate, the first refractive index being larger than a second refractive index of the gate dielectric layer;
• and
• an insulating layer over an inner surface of the channel layer, the first refractive index being larger than a third refractive index of the insulating layer, wherein
• an average crystal size of polysilicon in a top portion of the channel layer is larger than an average crystal size of polysilicon in a bottom portion of the channel layer,
• wherein a distribution of crystal sizes in the top portion of the channel layer is more uniform than a distribution of crystal sizes in the bottom portion of the channel layer.

A memory system, comprising:

• a controller that is connected to a semiconductor device, and
• the semiconductor device including:
• a string of transistors disposed along a channel hole, the string of transistors being vertically stacked over a substrate of the semiconductor device along a vertical direction perpendicular to a surface of the substrate, the string of transistors including:
• a gate dielectric layer formed over an inner surface of the channel hole;
• a channel layer including polysilicon having a first refractive index formed over an inner surface of the gate dielectric layer, the channel layer having an upper surface that is parallel to the surface of the substrate, the first refractive index being larger than a second refractive index of the gate dielectric layer;
• and
• an insulating layer over an inner surface of the channel layer, the first refractive index being larger than a third refractive index of the insulating layer, wherein
• an average crystal size of polysilicon in a top portion of the channel layer is larger than an average crystal size of polysilicon in a bottom portion of the channel layer,
• wherein a distribution of crystal sizes in the top portion of the channel layer is more uniform than a distribution of crystal sizes in the bottom portion of the channel layer.