Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Total dielectric isolation
Reexamination Certificate
1999-06-24
2001-06-19
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Total dielectric isolation
C438S423000, C438S766000
Reexamination Certificate
active
06248642
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to silicon wafer processing, and more particularly, to Separation by Implanted OXygen” (SIMOX) silicon wafer processing.
Ion implantation techniques are particularly useful in forming a class of buried layer devices known as silicon-on-insulator (SOI) devices. In these devices, a buried insulation layer is formed beneath a thin surface silicon film. These devices have a number of potential advantages over conventional silicon devices (e.g., higher speed performance, higher temperature performance and increased radiation hardness). The lesser volume of electrically active semiconductor material in SOI devices, as compared with bulk silicon devices, tends to reduce parasitic effects such as leakage capacitance, resistance, and radiation sensitivity. In addition, the isolation between adjacent devices eliminates parasitic problems such as latch-up.
In one known technique, known by the acronym SIMOX, a thin layer of a monocrystalline silicon substrate is separated from the bulk of the substrate by implanting oxygen ions into the substrate to form a buried dielectric layer. The SIMOX process provides a heterostructure in which a buried silicon dioxide layer serves as a highly effective insulator for surface layer electronic devices.
In the SIMOX process, oxygen ions are implanted into silicon, after which the material is annealed to form the buried silicon dioxide layer or BOX region. The annealing phase redistributes the oxygen ions such that the silicon/silicon dioxide boundaries become smoother and more abrupt, thus forming a sharp and well-defined BOX region.
One important criterion for SIMOX wafers is the defect density, which should be minimized in order to produce high quality wafers. Defect density can be defined in terms of the departure from perfect crystallinity in the silicon layer that is separated from the bulk substrate by the buried oxide layer. In general, as the oxygen ions are implanted into the wafer to produce the buried SiO
2
layer, atomic silicon is displaced. Additionally, excess silicon atoms from the growing BOX region can alter the crystal structure of the top silicon layer resulting in a variety of point and extended defects, such as threading dislocations and stacking faults, during the ion implantation and/or annealing processes. These defects degrade the quality and reliability of devices, e.g., transistors, that are subsequently formed in the upper silicon layer.
Hence, there exists a need for better SIMOX wafers having lower defect densities. Processes that can reduce the presence of interstitial silicon would satisfy a long felt need in the art.
SUMMARY OF THE INVENTION
The present invention provides a SIMOX wafer processing system that processes wafers in the presence of a background fluid for reducing the defect densities of the wafers. Although the invention is primarily shown and described as implanting oxygen ions into a bulk silicon wafer, it is understood that the system has other applications as well, such as implanting different types of ions into various materials and the formation of buried oxide (or other compounds) layers in materials in general.
In one aspect of the invention, a SIMOX wafer manufacturing system is disclosed including an ion source for providing an ion beam that is manipulated for optimal implantation of ions into one or more substrates, such as a series of silicon wafers secured on a wafer holder assembly. The system further includes a wafer holder assembly disposed in an implantation or vacuum chamber to which a vacuum pump is coupled for evacuating the chamber to a desired pressure. A fluid port, which is adapted for coupling to a fluid source, provides a passageway for fluid, such as water vapor, to enter the chamber. A fluid valve disposed between the fluid source and the fluid port allows the fluid to enter the chamber.
In a further aspect of the invention, the system further includes a controller for actively controlling the amount of fluid introduced into the chamber based upon one or more operating parameters in the chamber. In one embodiment, a monitoring device is coupled to a sensor located in the chamber for monitoring conditions in the chamber. The controller, which receives information from the sensor, effects desired operating conditions in the chamber by controlling the fluid valve, and thereby the fluid concentration, in the chamber.
In another aspect of the invention, methods for SIMOX wafer processing are disclosed. In one embodiment, silicon wafers are placed within the evacuated implantation chamber and subjected to an ion beam so as to form a buried silicon dioxide layer in the wafers. Before and/or during the implantation process, water vapor is introduced into the vacuum chamber via the fluid port to increase the background pressure in the chamber. Without being bound to a particular scientific explanation, it appears that the water vapor alters the surface chemistry of the wafer during the implantation process permitting displaced silicon atoms to rise to the wafer surface, and thereby, facilitating their removal from the wafer during subsequent processing (e.g., by sputtering or etching of the wafer surface). By decreasing the amount of interstitial silicon trapped in silicon device layer, the defect density of the processed wafers is reduced.
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Datta et al., “Effect of Varying Implant Energy and Dose on the SIMOX Microstructure”, Proceedings 1997 IEEE International SOI Conference, Oct. 1997, pp 42-43.*
G. Hinriches et al., “A New Process for Simultaneous Fabrications of a Buried and a Surface Oxide Layer” (Solid State Electronics) Vol. 39., No. 2, pp. 231-235 (1996).
Cordts Bernhard
Dolan Robert
Farley Marvin
Ryding Geoffrey
Chaudhuri Olik
Eaton Kurt
Engellenner Thomas J.
Ibis Technology Corporation
Mollaaghababa Reza
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