Sandisk 3d LLC

Matrix Semiconductor, Inc.

Shuo Gu

James Montague Cleeves

Sucheta Nallamothu

A method to laser anneal a silicon stack (or a silicon-rich alloy) including a heavily doped region buried beneath an undoped or lightly doped region is disclosed. By F selecting laser energy at a wavelength that tends to be transmitted by crystalline silicon and absorbed by amorphous silicon, crystallization progresses through the silicon layers in a manner that minimizes or prevents diffusion of dopants upward from the doped region to the undoped or lightly doped region. In preferred embodiments, the laser energy is pulsed, and a thermally conductive structure beneath the heavily doped layer dissipates heat, helping to control the anneal and limit dopant diffusion.

Laser anneal of vertically oriented semiconductor structures while maintaining a dopant profile

A method is disclosed to form a large-grain, lightly p-doped polysilicon film suitable for use as a channel region in thin film transistors. The film is preferably deposited lightly in situ doped with boron atoms by an LPCVD method at temperatures sufficiently low that the film is amorphous as deposited. After deposition, such a film contains an advantageous balance of boron, which promotes crystallization, and hydrogen, which retards crystallization. The film is then preferably crystallized by a low-temperature anneal at, for example, about 560 degrees for about twelve hours. Alternatively, crystallization may occur during an oxidation step performed, for example at about 825 degrees for about sixty seconds. The oxidation step forms a gate oxide for a thin film transistor device, for example a tunneling oxide for a SONOS memory thin film transistor device.

Large-grain p-doped polysilicon films for use in thin film transistors

A method to enhance grain size in polysilicon films while avoiding formation of hemispherical grains (HSG) is disclosed. The method begins by depositing a first amorphous silicon film, then depositing silicon nuclei, which will act as nucleation sites, on the amorphous film. After deposition of silicon nuclei, crystallization, and specifically HSG, is prevented by lowering temperature and/or raising pressure. Next a second amorphous silicon layer is deposited over the first layer and the nuclei. Finally an anneal is performed to induce crystallization from the embedded nuclei. Thus grains are formed from the silicon bulk, rather than from the surface, HSG is avoided, and a smooth polysilicon film with enhanced grain size is produced.

Method to form large grain size polysilicon films by nuclei-induced solid phase crystallization

Large grain size polysilicon films formed by nuclei-induced solid phase crystallization

A method to create a polysilicon layer with large grains and uniform grain density is described. A first amorphous silicon layer is formed. A crystallizing agent is selectively introduced in a substantially symmetric pattern, preferably symmetric in two dimensions, across an area of the first amorphous layer. The crystallizing agent may be, for example, silicon nuclei, germanium, or laser energy. A mask layer is formed on the amorphous silicon layer, and holes etched in the mask layer in a symmetric pattern to expose the amorphous layer to, for example, silicon nuclei or germanium) only in the holes. The mask layer is removed and a second amorphous layer formed on the first. If laser energy is used, no mask layer or second amorphous layer is generally used. The wafer is annealed to form a polysilicon layer with substantially no amorphous silicon remaining between the grains.

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Fremont, CA, United States of America

Shuo Gu