Plasma processing is widely used in the semiconductor industry for the fabrication of semiconductor devices. Both deposition and etching processes and have been extensively developed that utilize a plasma to create activated atoms and molecules. Plasma processing offers several advantages to more conventional deposition and etching techniques. For example, plasma deposition or growth processes are typically carried out at lower process temperatures than corresponding thermal reaction deposition or growth processes. The relatively low process temperatures allow the high reliability fabrication of semiconductor devices that are sensitive to excess thermal processing, such as shallow junction devices and the like. In particular, conventional thermal oxidation processes are typically carried out at temperatures that are high enough to establish a high reaction rate between oxygen and the substrate being oxidized. Often, the thermal oxidation temperature is high enough to cause unwanted diffusion of dopants in the substrate.
To avoid the high temperatures associated with thermal oxidation, plasma oxidation processes have been developed. Plasma oxidation processes are typically carried out at temperatures below about 600° C. In comparison, a convention thermal oxidation process used to form, for example, silicon dioxide is typically carried out at temperatures in excess of 900° C. By using a plasma oxidation process, diffusion of dopants in the substrate is greatly reduced, which enables the formation of the shallow junctions necessary for high-speed devices.
As the need to fabricate smaller memory devices grows, vertically structured memory cells have been developed to enable higher packing densities. The vertically structured memory devices incorporate memory cells disposed at numerous levels above a substrate. In one such device, each level includes a plurality of spaced-apart first conductors extending in one direction, which are vertically separated from a plurality of parallel spaced-apart second conductors in a second direction, for example, extending perpendicular to the first conductors. Memory cells are disposed between the first conductors and the second conductors.
The memory cells of a vertically structured array are programmed by rupturing an antifuse located in each cell. One particular kind of antifuse is fabricated by forming an oxide layer between two semiconductor layers. For proper functioning of the memory array, the antifuses need to be precisely fabricated to insure that they respond alike to an applied rupture current. Because p/n diodes are typically used in close proximity to the antifuses, excessive oxidation temperatures are undesirable.
In addition to antifuses, thermal oxidation is commonly used to form a gate oxide layer in metal-oxide-semiconductor (MOS) transistors. The gate oxide layer must be of high quality and of precise thickness to insure proper operation of the transistor.
One particular problem of plasma oxidation relates to the difficulty of controlling the oxidation process to the exacting requirements needed for critical oxide formation. The fabrication of critical oxide layers, such as antifuses, gate oxide layers and the like requires precise thickness control and precise thickness uniformity. Accordingly, improved plasma processing techniques are necessary to enable the fabrication of critical oxide layers using plasma oxidation.