Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-11-05
2002-07-02
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200
Reexamination Certificate
active
06414328
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the process of ion implantation, and particularly to an apparatus and method for implanting ions of different elements into metal, quartz, and semiconductor wafers ranging in diameter from 76 mm to 450 mm in the fabrication of very large scale integrated circuits. The apparatus and method of the present invention provides for the very high efficiency large scale manufacture of various types of semiconductor devices such as solar cells and integrated circuits and for the surface modification of metal and dielectric wafer surfaces.
2. Description of the Related Art
Ion implantation plays an essential role in the synthesis of thin films, the epitaxial growth of thin films, and the manufacturing of semiconductor devices. Ion implantation makes it possible to synthesize high quality thin films, to grow high quality thin films, and to manufacture semiconductor devices with a very high degree of precision and accuracy, and with high yields. Ion implantation equipment typically consists of an ion implanter and an end station or target unit that houses the articles to be processed. Ion implantation is achieved either by beam scanning of the target, which involves the electrostatic or magnetic movement of the beam across the target, or mechanical scanning of the target, which involves moving the target through the beam.
Mechanical scanning of the target through the beam results in a more uniform implanting of the target than does beam scanning across the target; therefore, mechanical scanning is the preferred technique. The implantation ions of the ion beam are mass-selected using a magnet housed in the ion implanter. Mass selection of the implanted ions enables the implantation of specific ionic species. For example, C
+
ions are mass-selected from the other ionic species present in the ionized source gas used to obtain C
+
ions for implantation into the target element.
The present invention is a method and an apparatus for automatically handling wafers having different configurations, such as silicon wafers, silicon dioxide wafers, metal wafers, other dielectric wafers and other semiconductor wafers. These wafers are commonly referred to as substrates.
Ion beam processing of substrates having diameters larger than 150-200 mm is cumbersome, inefficient, and expensive. There are a number of problems associated with the ion beam processing of substrates, particularly silicon substrates, using conventional ion beam processing equipment. For example, the quality of thin films synthesized using either ion beam deposition or ion beam epitaxy is considerably better when the synthesis occurs at temperatures higher than room temperature. On the other hand, the manufacture of semiconductor devices and integrated circuits require ion beams having values in the range of hundreds of microamperes to a few milliamperes.
Ion implantation is used in semiconductor device manufacturing to introduce dopants into a semiconductor substrate; for example, a silicon substrate, to alter the conductivity of portions of the semiconductor substrate. Ion beams having those magnitudes of currents require accelerating voltages in the range of 200-300 keV. However, at such high magnitudes of ion beam current and accelerating voltage, heating of the silicon substrate, which is extremely undesirable, is unavoidable and inevitable.
The present invention utilizes a spiral graphite heater to heat the silicon substrates during the ion beam deposition or the ion beam growth of thin films and a cooling means to remove heat generated during the ion beam fabrication of integrated circuits. Presently, the primary commercial use of ion implantation is in the manufacture of large scale integrated circuits (LSIC) chips. Implanting conductivity modifying chemical impurities into semiconductor wafers is a significant part of the process for manufacturing semiconductor devices such as large scale integrated circuit chips.
The density of integrated circuits and their speed of operation are very dependent upon tight control of the profile of doped regions in a wafer, that is, regions to which substantial concentrations of conductivity modifying impurities have been added. The tight control of wafer doping is best achieved using ion implantation techniques and equipment. Ion implantation doping methods result in improved very large scale integration (VLSI) by making more efficient use of the wafer area, shortening interconnects between devices, producing smaller geometries, and reducing noise.
Ion implantation is the doping process of choice because of the kinds of doping profiles, concentrations, and lateral geometries required on a VLSIC wafer. Only ion implantation is capable of providing the uniformity of doping that is critical in the fabrication of smaller geometry devices. Furthermore, doping uniformity across the wafer and repeatability from wafer to wafer, which is achievable with ion implantation, dramatically improves fabrication yields of high density devices.
Silicon ingots of diameters up to 300 mm are now available; however, most conventional ion implantation equipment is designed to accommodate substrates, that are cut from an ingot, of substantially smaller diameter (150 mm or less). The processing of substrates with diameters in excess of 150 mm by conventional ion implantation equipment requires costly modifications of the equipment.
The mechanical scanning cylindrical carousel apparatus can accommodate substrates with diameters in excess of 150 mm; however, the carousel apparatus has a low capacity being able to accommodate no more than 50 substrates with diameters of 300 mm, which results in a low throughput. The widely used spinning disc apparatus requires substrates with diameters in excess of 250 mm to have the same capacity as the cylindrical carousel apparatus; however, the spinning disc apparatus is not able to accommodate substrates with such a large diameter. In addition, scanning errors arise as a result of the radial translation of the discs (substrates) through the ion beam which results in dose nonuniformity in the radial direction.
The ion implantation apparatus of the present invention readily accommodates substrates with diameters in excess of 150 mm; therefore, a high degree of integration in the fabrication of integrated circuits is possible which results in a reduction in the cost of fabricating the integrated circuits. The present invention is capable of accommodating a large number of substrates with diameters in excess of 150 mm resulting in a method and apparatus with a high throughput and an excellent yield. The prior art does not describe any method or apparatus with the capabilities of the present invention.
U.S. Pat. No. 4,975,586 issued on Dec. 4, 1990 to Andrew M. Ray describes the end station of an ion implantation apparatus that includes a rotatable wafer support. The wafer being processed is rotated during and between implants; therefore, the wafers are implanted at variable implant angles. The wafer support is mounted on a first housing which is supported for rotation by a hub assembly extending through the wall of the end station vacuum chamber and is driven by a stepper motor through a drive belt and sheave system.
Rotation of the support about its own axis is provided by a stepper motor mounted on the rotating housing and connected to the wafer support by means of a drive system within the housing such that the two drive systems are operable independently of each other. The ion implantation apparatus of the Ray patent has a low throughput and a low capacity because the processing chamber can only accommodate a single wafer.
U.S. Pat. No. 4,948,979 issued on Aug. 14, 1990 to Yasao Munakata et al. describes a vacuum device that consists of a vacuum working chamber, a vacuum prechamber, and a communicating member that connects the vacuum working chamber and the vacuum prechamber. The communicating member is an independent member that is inserted between both vacuum chambers when needed.
Lee John R.
Litman Richard C.
Quash Anthony
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