Patent Publication Number: US-6703258-B2

Title: Enhanced probe for gathering data from semiconductor devices

Description:
This application is a Divisional Ser. No. 09/703,107 filed on Oct. 31, 2000. 
    
    
     FIELD OF INVENTION 
     The present invention relates, in general, to probes that are used for gathering data with respect to semiconductor devices, and materials, and more particularly, to a novel probe for gathering data, including atomic force microscopy images of a semiconductor surface. 
     BACKGROUND OF THE INVENTION 
     In the past, the semiconductor industry has used scanning probe microscopy (SPM), such as atomic force microscopy (AFM), scanning capacitance microscopy (SCM), electrostatic/field force microscopy (EFM), scanning tunneling microscopy (STM), scanning thermal microscopy (SThM), to gather surface images and other types of data with respect to semiconductor devices. Specific types of data that can be gathered simultaneous with the gathering of surface images, more specifically topographical data, are thermal data, capacitance data, magnetic field data, electrical field data, and the like. One problem with prior AFM measurement apparatus and measuring techniques is the inability for the devices to provide simultaneous thermal images of a surface, capacitance data, electrical field data, and topographic data while maintaining optimal signal to noise ratio. 
     Typically, during the process of gathering surface image data, a scanning process is undertaken in which a probe tip is dragged across the surface of the semiconductor device in a rastering manner and the topography of the surface is measured by an optical signal which is reflected off of a mirror affixed to the probe. As another example, during the process of gathering thermal data, a scanning process is undertaken in which a probe tip includes a thermocouple. The thermocouple provides for thermal data to be collected by measuring the temperature of the surface as the probe is moved. During such processes in which data is gathered, amplification of the input signal is a requirement, and thus the inclusion of an amplifier within close proximity to the probe tip is required. More particularly, amplification of such things as the input current, voltage, electric field shifts, and the like, is required. 
     It is well known in the art to use such amplifiers to amplify the input signal. Generally, an amplifier is provided in conjunction with the probe, being formed as a separate integrated circuit, and spaced a distance, typically millimeters, away from the probe tip. This spacing of the amplifier remote from the probe tip provides for a decrease in signal to noise ratio, but does not overcome the detrimental noise level. In addition, typical probes as they are known today, require for a slow rastering of the probe across the surface. This provides for a very slow procedure for gathering data. 
     Thus, it is a purpose of the present invention to provide for an enhanced probe for gathering surface image data and additional informational data. More particularly, it is a purpose of the present invention to provide for an improved device and method of forming a conductive nano-probe that includes an amplifier incorporated into the probe tip or the amplifier as defining the probe tip. 
     It is a purpose of the present invention to provide for a conductive nano-probe that can simultaneously provide for the gathering of information data and a topographical image of a semiconductor surface. 
     It is yet still a further purpose of the present invention to provide for a probe that incorporates an amplifier for the purpose of amplifying an input signal so as to improve signal to noise ratio, and provide for enhanced gathering of data by the probe. 
     It is yet another purpose of the present invention to provide for an enhanced probe incorporating an amplifier to provide for the gathering of information in a timely manner. 
     It is still a further purpose of the present invention to provide for a method of fabricating a probe that provides for the fabrication of an amplifier within the probe or defining the probe. 
     SUMMARY OF THE INVENTION 
     The above problems and others are at least partially solved and the above purposes and others are realized in a probe tip that facilitates the gathering of data and a method of fabricating the probe tip. The probe includes an amplifier fabricated to define the probe tip. More particularly, the probe tip includes an amplifier formed as at least one of a metal oxide semiconductor (MOS) transistor, a bipolar amplifier, or a metal semiconductor field effect transistor (MESFET), thereby providing for the amplification of the input signal and increased signal to noise ratio during operation of the probe tip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings: 
     FIGS. 1-4 are greatly enlarged, simplified sectional views illustrating steps in the method of forming a first embodiment of an enhanced probe in accordance with the present invention; 
     FIG. 5 is a simplified orthogonal view illustrating an enhanced probe tip in accordance with the present invention; 
     FIGS. 6-8 are greatly enlarged, simplified sectional views illustrating steps in the method of forming a second embodiment of an enhanced probe in accordance with the present invention. 
     FIG. 9 is a greatly enlarged, simplified sectional view illustrating in further detail, an enhanced probe tip in accordance with the present invention; and 
     FIG. 10 is a greatly enlarged, simplified sectional view illustrating an enhanced probe tip in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, FIGS. 1-4 illustrate steps in a preferred method of forming an enhanced probe tip  10  according to the present invention. Probe tip  10  is capable of providing signals that facilitate simultaneous formation of thermal images, topographical images, and additional information such as capacitance, electrical field, magnetic field, and the like, of a semiconductor device or material (not shown). Probe  10  includes an amplifier  12  formed therein, and more particularly a metal oxide semiconductor (MOS) transistor, formed therein (as illustrated in FIG.  4 ), that provides for the receipt and amplification of a produced electrical signal representing information gathered from the semiconductor device. 
     Referring more particularly to FIG. 1, illustrated is a first step in the method of forming enhanced probe tip  10  of the present invention. As illustrated, there is provided a substrate  14 , typically formed of a P+ material, such as silicon, gallium arsenide, or any other similar type of material, suitable for forming a P+ substrate. Substrate  14  has grown on an uppermost surface  15  an optional layer  16 . Layer  16  is formed of one of an oxide or a nitride material, such as silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like. It should be understood that although layer  16  is illustrated in this particular embodiment, it is optional in the fabrication of an enhanced probe tip according to the present invention. 
     Next, an epitaxial layer (epi layer)  20  of a P type material is grown on a surface  18  of layer  16 . Epilayer  20  is formed of a material similar to substrate  14 , at a thickness of approximately 10-15 microns, having a P doping level of approximately 10 Ohm/cm. An oxide mask layer  22  is subsequently grown on an uppermost surface  24  of epilayer  20  according to standard silicon processing techniques. Oxide mask layer  22  will serve as a mask layer for the implant step (discussed presently) necessary to define probe tip  10 . 
     Referring now to FIG. 2, illustrated is the next step in the fabrication of enhanced probe tip  10 , according to this specific embodiment of the present invention. As illustrated, with oxide mask layer  22  in place, an N doped material is implanted so as to form N wells  24 . It will be understood that oxide mask layer  22  prevents the implanting of N doped material in specific areas and thus serves to aid in defining N doped wells  24 . Substrate  14 , optional layer  16 , P doped layer  20  and N doped wells  24  define stack  30 . 
     Referring now to FIG. 3, as illustrated, stack  30  is etched to define probe tip  10 . More particularly, stack  30 , including N doped wells  24 , P doped material  20 , optional layer  16 , and substrate  14  are etched to define probe tip  10 , including sidewalls  32 , and tip point  34 . 
     Referring now to FIG. 4, illustrated is enhanced probe tip  10  including metal contacts  36 . To form metal contacts  36 , a photoresist (not shown) is positioned prior to the deposition of a conductive metal, such as aluminum, gold, or any other similar conductive metal. Metal contacts  36  are formed adjacent sidewalls  32  and (as illustrated in FIG. 5) lead to a first coupling wire  38  and a second coupling wire  40 . Wires  38  and  40  can be any variety of coupling metal or alloy that are well known to those skilled in the art. 
     In this preferred embodiment, probe tip  10  includes a diamond shard  42  that is positioned proximate the defined MOS transistor, and more particularly adjacent tip point  34 . It should be understood that while diamond shard  42  is described with reference to this preferred embodiment, diamond shard  42  is optional and it is anticipated that a probe tip could be fabricated without the inclusion of diamond shard  42 . Diamond shard  42  is used because it is electrically isolating, thermally conducting and provides for a more robust tip point  34 . There should be no contamination or adhesive between diamond shard  42  and MOS transistor. 
     As illustrated in FIG. 5, probe tip  10 , including amplifier  12 , provides for the amplification of input signals and thus increased signal to noise ratio. 
     Referring now to FIGS. 6-8, illustrated is a second embodiment of an enhanced probe tip according to the present invention. In this particular embodiment, illustrated is an enhanced probe tip, generally referenced  50 , and the steps in the method of fabricating probe tip  50 . Referring specifically to FIG. 6, illustrated is a stack  52 , comprised of a substrate material  54 , and epi layers  56 ,  58  and  60 . Substrate material  54  is typically an N+ material, but it should be understood that a P+ material is anticipated by this disclosure. Substrate  54  is formed of silicon, gallium arsenide, or similar type material. Next, a plurality of epi layers  56 ,  58  and  60  are formed on an uppermost surface  55  of substrate  54 . Epi layers  56 ,  58  and  60  are generally formed of a suitable material in which epilayer  56  is N+ doped, layer  58  is P+ doped and layer  60  is N+ doped. Epi layers  56 ,  58  and  60  are generally formed by techniques such as chemical vapor deposition. 
     Referring now to FIG. 7, illustrated is probe tip  50  that has been formed by etching stack  52 , to define sidewalls  62 . Layers  56 ,  58  and  60  in combination will serve as a bipolar amplifier, generally referenced  64 . As illustrated, bipolar amplifier  64  is formed to define the actual probe tip  50 . 
     Referring now to FIG. 8, illustrated in simplified sectional view is enhanced probe  50  including bipolar amplifier  64 . Next, during the fabrication of enhanced probe  50 , a plurality of oxide insulating layers  66  are deposited on sidewalls  62  and substrate  54 . Oxide insulating layers  66  provide for isolation of epi layers  56 ,  58  and  60 , and thereby preventing the electrical shorting of bipolar amplifier  64 . A contact metal  68  is next formed for the base and a contact metal  70  is formed for the emitter portion of bipolar amplifier  64 . It should be understood that contact metal  68  extends beyond amplifier  64  and is then defined as described below. 
     Next, an etch is performed to etch away a portion of substrate  54 , thereby providing for formation of a contact metal  72  for the collector portion of bipolar amplifier  64 . Contact metals  68 ,  70  and  72  are typically formed of any conductive metal, such as aluminum, gold, or the like. Contact metal  68 ,  70  and  72  provide for electrical interface of probe tip  50  with the input source (not shown). As a final step in the fabrication of enhanced probe tip  50 , including bipolar amplifier  64 , bipolar amplifier  64  is further defined by using focused ion beam techniques for final shaping of metal contact  68 , thereby forming a tip point  74  to aid in the collection of data. 
     Referring now to FIG. 9, illustrated in simplified sectional view is an enlarged sectional view of an enhanced probe tip  80 , formed according to the present invention. Probe tip  80  is formed generally similar to probe tip  10  of FIGS. 1-5, and includes a MOS amplifier  82 , formed within tip  80 . In this particular embodiment, and in contrast to the embodiment illustrated in FIGS. 1-5, probe tip  80  during operation is reverse biased, source to drain, thereby providing for the manipulation of electrically charged organic matter. In addition, by reverse biasing probe tip  80 , a means for changing or modifying the electrical fields of a charged surface at submicron resolution is provided. 
     Referring now to FIG. 10, illustrated is a third embodiment of an enhanced probe tip according to the present invention. In this particular embodiment, illustrated is an enhanced probe tip, generally referenced  90 . Illustrated is probe tip  90 , where probe tip  90  is formed as a metal semiconductor field effect transistor (MESFET). Probe tip  90  is generally comprised of a substrate material  92 , onto which an optional nitride insulating layer  94  is formed. Substrate  90  is formed of silicon, gallium arsenide, or similar type material. Next, a second substrate layer  96  is formed having a channel layer  100  formed thereon an uppermost surface. There is formed about an exterior aspect of probe tip  90 , a source contact  98  and a drain contact  99 . A gate metal  102  forms the tip  104  of probe tip  90 . Tip  104 , is formed of gate metal  102 , thereby providing for the measuring of potential, or the measuring of voltages as a function of tip  104  position. 
     In yet another alternate embodiment, any of the previous disclosed-probe tips, including probe tips  10 ,  50  and  90 , as described with reference to FIGS. 1-10, can be treated, such as through dipping, coating, or the like, with a protein. Proteins which may be utilized include biotin or steptavidin, or any other similar protein material. This treating of the probe tip provides for the enhancement in the collection, manipulation, and imaging of organic matter. 
     Thus, an efficient method of manufacturing an enhanced probe tip device and the actual enhanced probe tip device have been disclosed. The enhanced probed tip device as disclosed, includes an amplifier formed within or formed as the actual probe tip. The amplifier is formed as a MOS transistor, a bipolar amplifier, or a metal semiconductor field effect transistor. As disclosed, dependent upon operation sought, the probe tip when including a MOS amplifier, can be forward biased to act as a standard transistor or reverse biased to serve to manipulate organic matter. Further, while specific examples and method of fabrication steps are utilized herein for purposes of explanation, those skilled in the art will understand that many varieties of materials, forms, and methods of fabrication may be utilized. 
     While we have shown and described specific embodiments of the present invention, further modifications and improvements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is not limited to the particular forms shown and we intend in the appended claims to cover all modifications that do not depart from the spirit and scope of this invention.