Optics: measuring and testing – Of light reflection
Reexamination Certificate
2002-06-07
2004-11-30
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Of light reflection
Reexamination Certificate
active
06825933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to low dose ion implantation monitoring. More particularly, this invention relates to a computer-implemented reflectance system and method for associating absolute values of reflectance changes over the entire measured spectra to doses of ions implanted in a semiconductor wafer for high resolution ion implantation monitoring in a non-destructive, efficient, accurate, and repeatable manner.
2. Description of the Related Art
In the semiconductor manufacturing industry, certain materials are often doped with impurities to change their properties such as electrical or physical properties during different stages of the semiconductor manufacturing process. These materials may include silicon, germanium, or gallium arsenide. The impurities, i.e., dopants or doping agents, such as B, P, Ga, Ge, F, Si, B11, BF2, Sb, In, As, and H, can be diffused or implanted into the materials. The diffusion process is useful for large-scale applications. The ion beam implantation is presently being utilized in small-scale electrostatic processes.
For different purposes, implant doses may vary from about 10
10
ions/cm
2
to about 10
18
ions/cm
2
. During an ion implantation process, ions of a doping agent enter a semiconductor material and collide with atoms of the material, causing displacements of the atoms. As a result, the material is damaged or modified in regions implanted, i.e., doped, with the ions. A common practice in the art to remove some of the damage to the crystalline structure is by thermally annealing the material, although part of the material may become amorphous rather than crystalline with a sufficiently high dose.
As is well known in the art, because of the small dimensions and narrow dose tolerances of the devices being created, it is critically important to accurately monitor and/or characterize the ion implant doses. The monitored result or characterization can also be used, for example, to evaluate, analyze, and characterize the electrical and/or physical properties of the semiconductor device and/or material for purposes such as flaw testing.
There are several known methods for monitoring ion implant doses, including sheet resistance based methods and thermal wave based methods. The sheet resistance based methods include, for example, single implant sheet resistance method and double implant sheet resistance method.
The single implant sheet resistance method uses a 4-point probe to measure the sheet resistance of specially prepared and treated silicon test wafers after implantation and activation. Most technologies do not rely on this method for low dose monitoring because of the fundamental difficulties in measuring reproducible sheet resistances in the regime of 100,000 ohm/sq. or more.
The double implant sheet resistance method measures the change in 4-point probe sheet resistance of a previously implanted and activated silicon test wafer that is subsequently damaged from a low dose (second) ion implantation. This method suffers from considerable process complexity that causes major wafer-to-wafer reproducibility problems.
The sheet resistance based methods are well known in the art and thus are not further described herein for brevity. For an exemplary teaching on the sheet resistance based methods, readers are referred to “Advances in Sheet Resistance Measurements for Ion Implant Monitoring” by W. A. Keenan et al., Solid State Tech., June 1985, pp. 143-148.
The thermal wave based methods are currently being used in the semiconductor manufacturing process. By analyzing thermal waves generated in an implanted silicon wafer, this type of methods provides a rather non-destructive way of monitoring ion implants in the wafer. The thermal wave methods are based on the effect that damage to the silicon crystal lattice that takes place during ion implantation increases the thermal wave signal above that of the non-implanted silicon wafer. Exemplary teachings on thermal wave systems and methods can be found in the following U.S. patents: U.S. Pat. No. 4,513,384, titled “THIN FILM THICKNESS MEASUREMENTS AND DEPTH PROFILING UTILIZING A THERMAL WAVE DETECTION SYSTEM” and U.S. Pat. No. 4,750,822, titled “METHOD AND APPARATUS FOR OPTICALLY DETECTING SURFACE STATES IN MATERIALS,” both of which are issued to Rosencwaig and assigned to Therma-Wave, Inc. of Fremont, Calif., U.S.A.; U.S. Pat. Nos. 4,854,710, 4,952,063, and 5,042,952, titled “METHOD AND APPARATUS FOR EVALUATING SURFACE AND SUBSURFACE FEATURES IN A SEMICONDUCTOR” and U.S. Pat. No. 5,074,669, titled “METHOD AND APPARATUS FOR EVALUATING ION IMPLANT DOSAGE LEVELS IN SEMICONDUCTORS,” all of which are issued to Opsal et al. and assigned to Therma-Wave, Inc. of Fremont, Calif., U.S.A.
The thermal wave based optical systems and methods utilize laser-induced modulation of the optical reflectance. As such, a thermal wave signal is a modulated reflectance signal. Values of the thermal wave signal thus vary depending upon the type of the doping agent (dopant) used. For example, the thermal wave signal values range from 200 to 10,000 for boron (B) ions and from 500 to 100,000 for heavier ions such as phosphorus (P) and arsenic (As) ions. The thermal wave signal and dose for P and As ion implants have a somewhat one to one correlation at low dose ranges of 1E10 to 3E14 ions/cm
2
. The thermal wave signal correlates well with dose and threshold voltage at low dose ranges of 1E11 to 1E12 ions/cm
2
.
It is important to note, although the thermal wave signal depends primarily on implant dose, it can be influenced, to a smaller degree, by other implant parameters such as beam energy, beam current and wafer temperature. According to “Materials and Process Characterization of Ion Implantation” edited by Michael I. Current and C. B. Yarling and published by Ion Beam Press, Autstin, Tex., USA, 1997, pp. 8-12, which is hereby incorporated by reference, the thermal wave sensitivity varies for different penetration depths of ions in silicon. It is also sensitive to channeling and various scanning effects.
Additionally, as discussed heretofore, thermally annealing the wafer may remove some of the undesirable damage to the crystalline structure. This annealing process has the potential to also remove some of the desirable modification thereof, i.e., regions of the crystalline structure modified (patterned) with ion implants, thereby causing an undesirable annealing effect. This undesirable annealing effect may potentially be a problem in thermal wave based systems as semiconductor technologies continue to scale because of the 100% intensity modulated laser beam commonly utilized in these systems. That is, some of the intended modification to the crystalline structure may be undesirably removed by the localized heating of the material, rendering the non-destructiveness of these thermal wave based systems questionable.
The concern of undesirable annealing effect generally applies to dose measurement monitoring systems where wafer temperature is increased during the measuring and/or monitoring process. For example, in U.S. Pat. No. 6,268,916, titled “SYSTEM FOR NON-DESTRUCTIVE MEASUREMENT OF SAMPLES,” issued to Lee et al., and assigned to Kla-Tencor Corporation of San Jose, Calif., U.S.A., Lee et al. disclosed how to use heat dissipation characteristics of a semiconductor wafer to measure physical properties thereof. The surface temperature of an area of the semiconductor wafer is increased by heat, which is generated by a pump beam produced by an infrared laser. When the wafer has been doped with a dopant, the heat dissipation characteristics of the wafer at the surface area are dependent upon the dose and the implant profile in the damaged layers in the wafer. The heat dissipation characteristics, in turn, determine the change in the temperature of the wafer surface and the change in the complex index of refraction of the surface. The ellipsometer system disclosed by Lee et al. provides a probe beam for interrogating such changes.
Other non-destructive optical sys
Forouhi Abdul Rahim
Roberts Jeff
Lumen Intellectual Property Services Inc.
N&K Technology, Inc.
Stafira Michael P.
LandOfFree
Computer-implemented reflectance system and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Computer-implemented reflectance system and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Computer-implemented reflectance system and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3275982