Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-04-05
2001-12-04
Booth, Richard (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
C438S308000, C438S795000
Reexamination Certificate
active
06326219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a method for determining the wavelength and pulse length of radiant energy used to anneal amorphous semiconductor regions, or to activate doped semiconductor regions, disposed in contact with crystalline semiconductor substrates. The radiant energy can be generated by a laser, flash-lamp or other relatively intense radiant energy source. The method can also be used to perform activation annealing of doped source and drain regions of integrated transistor devices, for example.
2. Description of the Related Art
In the integrated electronic circuit fabrication industry, ion implantation is often used to introduce dopants of appropriate conductivity type (i.e.,—or p-type) into the source and drain regions of integrated transistors. The implantation of the dopant atoms breaks chemical bonds in the source and drain regions of the integrated transistors and, in some instances, can render such regions amorphous. To obtain proper electrical performance of the integrated transistors, the source and drain regions must be annealed to bring such regions to a relatively crystalline state aligned with the substrate and/or to ‘activate’ such regions by incorporating the dopant atoms into the semiconductor crystalline lattice. One technique for performing annealing uses relatively intense radiant energy from a laser or flash-lamp, for example, to melt and crystallize the amorphous regions, or to heat the doped region sufficiently for activation.
Currently, the wavelength, energy dose and pulse length used for radiant energy annealing are determined largely by trial and error, and little thought has heretofore been given to determining relatively effective wavelength and pulse length for the radiant energy without performing numerous experiments. It would be desirable to provide a method which can be used to derive a wavelength and pulse length appropriate for radiant energy annealing, without the need to perform numerous experiments.
In addition, previous methods typically use energy doses in excess of the dose necessary to anneal an integrated device. The excess energy can damage the integrated device by overheating its components or by diffusing dopants beyond safe boundaries to create leakage paths. It would therefore be desirable to provide a method that can minimize, or at least reduce, the amount of energy required to anneal a semiconductor region, relative to previous methods.
In addition, improvement in the determination of the wavelength and pulse length of the radiant energy used for annealing an integrated device and/or circuit would generally permit enhancement of the process margin, leading to relaxed constraints on the materials and process steps used in integrated device or circuit fabrication processes, as well as improvement in the yield of properly functioning integrated devices and circuits, relative to previous methods.
SUMMARY OF THE INVENTION
The invented methods achieve the above-stated objects of the invention, and overcome the above-stated disadvantages of previous methods. Generally stated, the invented methods include a step of determining the wavelength and/or pulse length of radiant energy used to anneal at least one relatively disordered semiconductor region situated in contact with a crystalline semiconductor substrate. As used herein, the term ‘disordered region’ can refer to an amorphous semiconductor region(s) that is to be annealed by melting and crystallizing such region so that is assumes a crystalline state that is crystallographically aligned with the semiconductor substrate. The term ‘disordered region’ can also refer to a doped or implanted semiconductor region(s) in contact with a crystalline semiconductor substrate, that is to be annealed by heating through exposure to radiant energy and subsequent cooling for crystallization, to incorporate the doped or implanted atoms into the crystalline lattice of the semiconductor region.
The invented methods are useful and can be used in electronic device integration processes which involve the implantation of dopant ions into the source and drain regions of the integrated transistor devices formed on a semiconductor substrate. Such implantation often disorders the source and drain regions to a depth dependent on the dosage, atomic weight of the dopant species, and the energy used to implant the dopant ions into the substrate. The invented methods are useful in melting and crystallizing the disordered semiconductor regions resulting from ion implantation, or to activate the source and drain regions after doping, to obtain proper electrical performance of the integrated devices.
The invented methods utilize radiant energy from a laser, flash-lamp or other device, for example, preferably with an energy or a wavelength and pulse-duration that is effective for annealing the disordered region. Since there will inevitably be variations in the energy and the temporal shape and spatial distribution of energy in each pulse, the determined wavelength and pulse length are deemed effective if they yield relatively wide process margins and use a relatively small amount of power to anneal a disordered region on the substrate.
In the performance of relatively specific embodiments of the invented methods, it is generally desirable to confine the dopant impurity to the region where it was implanted so that the junction between the disordered region and the substrate, remains shallow. Prolonged heating would promote diffusion of the impurity atoms into the substrate, and results in a much less desirable, deeper junction. In the case where the dopant is contained in a disordered region that is amorphous, it is highly desirable that after heating with radiant energy, the crystal growth begin at the amorphous region-crystalline substrate interface so the result is a single crystal aligned to the crystal axis of the substrate. In other words, it is desirable to produce a temperature profile by exposure to the radiant energy so that the crystalline substrate acts as a seed for crystallization of the disordered region upon cooling. If the material composing the amorphous region were to begin crystallization at some other point then a much less desirable polycrystalline junction would likely result.
In the invented methods, the wavelength of the radiant energy used for annealing the disordered semiconductor region(s) is determined based on at least one, and preferably all, of the following criteria:
(1) the radiant energy at the wavelength has an absorption length in the disordered region that is greater than or equal to one-third (⅓) of the thickness of such region;
(2) the radiant energy at the wavelength has an absorption length in the disordered region that is less than or equal to five times the thickness of the disordered region or one micron, whichever is larger;
(3) the radiant energy at the wavelength has an absorption length in the crystalline substrate that is at least twice the absorption length of the wavelength in the disordered region;
(4) the absorption of radiant energy at the wavelength in the field isolation region used to electrically isolate the disordered region, is less than half as much as that through a similar thickness of the disordered region;
(5) the radiant energy at the wavelength can be efficiently generated, can be uniformly distributed over a relatively extended area, and the energy content of a single pulse can be controlled with relative accuracy; and/or
(6) the radiant energy at the wavelength that is absorbed in the gate conductor layer and the underlying gate insulator layer is not substantially greater than the radiant energy absorbed in a similar thickness of the disordered region.
In general, the inventors have determined that the photon wavelength range for annealing radiant energy which satisfies the above-stated criteria for a disordered region composed of silicon in contact with a crystalline silicon substrate and electrically isolated by a silicon dioxide field isolation region, is from four-hundred-
Hawryluk Andrew M.
Markle David A.
Talwar Somit
Booth Richard
Jones Allston L.
Ultratech Stepper, Inc.
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