Abstract: Methods are described to fabricate, program, and sense a multilevel one-time-programmable memory cell including a steering element such as a diode and two, three, or more dielectric antifuses in series. The antifuses may be of different thicknesses, or may be formed of dielectric materials having different dielectric constants, or both. The antifuses and programming pulses are selected such that when the cell is programmed, the largest voltage drop in the memory cell is across only one of the antifuses, while the other antifuses allow some leakage current. In some embodiments, the antifuse with the largest voltage drop breaks down, while the other antifuses remain intact. In this way, the antifuses can be broken down individually, so a memory cell having two, three, or more antifuses may achieve any of three, four, or more unique data states.

Abstract: In a first aspect, a method for forming a non-volatile memory cell is provided. The method includes (1) forming a metal-insulator-metal (MIM) antifuse stack including (a) a first metal layer; (b) a silicon dioxide, oxynitride or silicon nitride antifuse layer formed above the first metal layer; and (c) a second metal layer formed above the antifuse layer. The method also includes (2) forming a contiguous p-i-n diode above the MIM stack, the contiguous p-i-n diode comprising deposited semiconductor material; (3) forming a layer of a silicide, silicide-germanide, or germanide in contact with the deposited semiconductor material; and (4) crystallizing the deposited semiconductor material in contact with the layer of silicide, silicide-germanide, or germanide. The memory cell comprises the contiguous p-i-n diode and the MIM stack. Other aspects are provided.

Abstract: The present invention provides for a low-temperature method to crystallize a silicon-germanium film. Metal-induced crystallization of a deposited silicon film can serve to reduce the temperature required to crystallize the film. Increasing germanium content in a silicon-germanium alloy further decreases crystallization temperature. By using metal-induced crystallization to crystallize a deposited silicon-germanium film, temperature can be reduced substantially. In preferred embodiments, for example in a monolithic three dimensional array of stacked memory levels, reduced temperature allows the use of aluminum metallization. In some embodiments, use of metal-induced crystallization in a vertically oriented silicon-germanium diode having conductive contacts at the top and bottom end is be particularly advantageous, as increased solubility of the metal catalyst in the contact material will reduce the risk of metal contamination of the diode.

Abstract: In deposited silicon, n-type dopants such as phosphorus and arsenic tend to seek the surface of the silicon, rising as the layer is deposited. When a second undoped or p-doped silicon layer is deposited on n-doped silicon with no n-type dopant provided, a first thickness of this second silicon layer nonetheless tends to include unwanted n-type dopant which has diffused up from lower levels. This surface-seeking behavior diminishes when germanium is alloyed with the silicon. In some devices, it may not be advantageous for the second layer to have significant germanium content. In the present invention, a first heavily n-doped semiconductor layer (preferably at least 10 at % germanium) is deposited, followed by a silicon-germanium capping layer with little or no n-type dopant, followed by a layer with little or no n-type dopant and less than 10 at % germanium. The germanium in the first layer and the capping layer minimizes diffusion of n-type dopant into the germanium-poor layer above.

Abstract: A method of making a nonvolatile memory device includes forming a first electrode, forming at least one nonvolatile memory cell including a diode and a metal oxide antifuse dielectric layer over the first electrode, and forming a second electrode over the at least one nonvolatile memory cell. In use, the diode acts as a read/write element of the nonvolatile memory cell by switching from a first resistivity state to a second resistivity state different from the first resistivity state in response to an applied bias.

Abstract: A method of making a nonvolatile memory device includes forming a first electrode, forming at least one nonvolatile memory cell comprising a silicon, germanium or silicon-germanium diode, doping the diode with at least one of nitrogen or carbon, and forming a second electrode over the at least one nonvolatile memory cell.

Abstract: Shrinking the dimensions of PMOS or NMOS thin film transistors is limited by dopant diffusion. In these devices an undoped or lightly doped channel region is interposed between heavily doped source and drain regions. When the device is built with very short gate length, source and drain dopants will diffuse into the channel, potentially shorting it and ruining the device. A suite of innovations is described which may be used in various combinations to minimize dopant diffusion during fabrication of a PMOS or NMOS polycrystalline thin film transistor, resulting in a highly scalable thin film transistor. This transistor is particularly suitable for use in a monolithic three dimensional array of stacked device levels.

Abstract: A nonvolatile memory device includes at least one memory cell which comprises a diode and a metal oxide antifuse dielectric layer, and a first electrode and a second electrode electrically contacting the at least one memory cell. In use, the diode acts as a read/write element of the memory cell by switching from a first resistivity state to a second resistivity state different from the first resistivity state in response to an applied bias.

Abstract: A method for annealing a diode formed of a silicon-germanium alloy that minimizes leakage current is disclosed. The method includes the steps of forming semiconductor pillars of an alloy of silicon and germanium; heating the pillars at a first temperature for at least 30 minutes, and then heating the pillars at a second temperature higher than the first temperature of the alloy for up to 120 seconds. The invention further includes a monolithic three dimensional memory array of a plurality of p-i-n diodes, the p-i-n diodes being formed of a silicon-germanium alloy that have been subjected to a two-stage heating process.

Abstract: A nonvolatile memory device includes at least one nonvolatile memory cell which comprises a silicon, germanium or silicon-germanium diode which is doped with at least one of carbon or nitrogen in a concentration greater than an unavoidable impurity level concentration.

Abstract: A semiconductor device comprising a bipolar transistor having a base region, an emitter region and a collector region, wherein the base region comprises polycrystalline semiconductor material formed by crystallizing silicon, germanium or silicon germanium in contact with a silicide, germanide or silicide germanide is described. The emitter region and collector region also may comprise polycrystalline semiconductor material formed by crystallizing silicon, germanium or silicon germanium in contact with a silicide, germanide or silicide germanide forming metal. The polycrystalline semiconductor material is preferably silicided polysilicon, which is formed in contact with C49 phase titanium silicide.

Abstract: A method is described for forming a semiconductor device comprising a bipolar transistor having a base region, an emitter region and a collector region, wherein the base region comprises polycrystalline semiconductor material formed by crystallizing silicon, germanium or silicon germanium in contact with a silicide, germanide or silicide germanide. The emitter region and collector region also may be formed from polycrystalline semiconductor material formed by crystallizing silicon, germanium or silicon germanium in contact with a silicide, germanide or silicide germanide forming metal. The polycrystalline semiconductor material is preferably silicided polysilicon, which is formed in contact with C49 phase titanium silicide.

Abstract: A method is described for forming a thin film transistor having its current-switching region in polycrystalline semiconductor material which has been crystallized in contact with titanium silicide, titanium silicide-germanide, or titanium germanide. The titanium silicide, titanium silicide-germanide, or titanium germanide is formed having feature size no more than 0.25 micron in the smallest dimension. The small feature size tends to inhibit the phase transformation from C49 to C54 phase titanium silicide. The C49 phase of titanium silicide has a very close lattice match to silicon, and thus provides a crystallization template for the silicon as it forms, allowing formation of large-grain, low-defect silicon. Titanium does not tend to migrate through the silicon during crystallization, limiting the danger of metal contamination. In preferred embodiments, the transistors thus formed may be, for example, field-effect transistors or bipolar junction transistors.

Abstract: A rewritable nonvolatile memory cell is disclosed comprising a steering element in series with a carbon nanotube fabric. The steering element is preferably a diode, but may also be a transistor. The carbon nanotube fabric reversibly changes resistivity when subjected to an appropriate electrical pulse. The different resistivity states of the carbon nanotube fabric can be sensed, and can correspond to distinct data states of the memory cell. A first memory level of such memory cells can be monolithically formed above a substrate, a second memory level monolithically formed above the first, and so on, forming a highly dense monolithic three dimensional memory array of stacked memory levels.

Abstract: A method to form a rewriteable nonvolatile memory cell is disclosed, the cell comprising a steering element in series with a carbon nanotube fabric. The steering element is preferably a diode, but may also be a transistor. The carbon nanotube fabric reversibly changes resistivity when subjected to an appropriate electrical pulse. The different resistivity states of the carbon nanotube fabric can be sensed, and can correspond to distinct data states of the memory cell. A first memory level of such memory cells can be monolithically formed above a substrate, a second memory level monolithically formed above the first, and so on, forming a highly dense monolithic three dimensional memory array of stacked memory levels.

Abstract: An upward-pointing p-i-n diode formed of deposited silicon, germanium, or silicon-germanium is disclosed. The diode has a bottom heavily doped p-type region, a middle intrinsic or lightly doped region, and a top heavily doped n-type region. The top heavily doped p-type region is doped with arsenic, and the semiconductor material of the diode is crystallized in contact with an appropriate silicide, germanide, or silicide-germanide. A large array of such upward-pointing diodes can be formed with excellent uniformity of current across the array when a voltage above the turn-on voltage of the diodes is applied. This diode is advantageously used in a monolithic three dimensional memory array.

Abstract: A method to create a low resistivity P+in-situ doped polysilicon film at low temperature from SiH4 and BCl3 with no anneal required. At conventional dopant concentrations using these source gases, as deposition temperature decreases below about 550 degrees C., deposition rate decreases and sheet resistance increases, making production of a high-quality film impossible. By flowing very high amounts of BCl3, however, such that the concentration of boron atoms in the resultant film is about 7×1020 or higher, the deposition rate and sheet resistance are improved, and a high-quality film is produced.

Abstract: The present invention relates to use of selective oxidation to oxidize silicon in the presence of tungsten and/or tungsten nitride in memory cells and memory arrays. This technique is especially useful in monolithic three dimensional memory arrays. In one aspect of the invention, the silicon of a diode-antifuse memory cell is selectively oxidized to repair etch damage and reduce leakage, while exposed tungsten of adjacent conductors and tungsten nitride of a barrier layer are not oxidized. In some embodiments, selective oxidation may be useful for gap fill. In another aspect of the invention, TFT arrays made up of charge storage memory cells comprising a polysilicon/tungsten nitride/tungsten gate can be subjected to selective oxidation to passivate the gate polysilicon and reduce leakage.

Abstract: In deposited silicon, n-type dopants such as phosphorus and arsenic tend to seek the surface of the silicon, rising as the layer is deposited. When a second undoped or p-doped silicon layer is deposited on n-doped silicon with no n-type dopant provided, a first thickness of this second silicon layer nonetheless tends to include unwanted n-type dopant which has diffused up from lower levels. This surface-seeking behavior diminishes when germanium is alloyed with the silicon. In some devices, it may not be advantageous for the second layer to have significant germanium content. In the present invention, a first heavily n-doped semiconductor layer (preferably at least 10 at % germanium) is deposited, followed by a silicon-germanium capping layer with little or no n-type dopant, followed by a layer with little or no n-type dopant and less than 10 at % germanium. The germanium in the first layer and the capping layer minimizes diffusion of n-type dopant into the germanium-poor layer above.

Abstract: A method is described for isotropic or nearly isotropic shallow doping of a non-planar surface exposed in a void. The results of ion implantation, a common doping method, are inherently planar. Some fabrication methods and devices may require doping a surface of a non-planar feature exposed in a void, such as a trench. The feature is doped by flowing a gas which will provide the dopant over the exposed surfaces, or by exposing the surfaces to a plasma including the dopant. The feature may be a patterned feature, including a top surface and a sidewall. In a preferred embodiment, a semiconductor feature having a top surface and a sidewall is exposed in a trench formed in a dielectric, and a gas providing a p-type or n-type dopant is flowed in the trench, providing a p-type or n-type dopant to the semiconductor.