Abstract:
A probe comprising a probe body having a body longitudinal axis and a shoulder, and a microstylet mechanically coupled to the shoulder, and a method of manufacturing the same. The microstylet extends from the shoulder and has a microstylet longitudinal axis coincident the body longitudinal axis with the microstylet having a cross section substantially smaller than a cross section of the probe body.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed, in general, to integrated circuit metrology and, more specifically, to a probe having a nanotube stylet and to a method of manufacturing and mounting same for use in integrated circuit metrology. 
     BACKGROUND OF THE INVENTION 
     A conventional stylus nanoprofilometer employing a probe stylet of quartz or diamond may be used to measure integrated circuit features down to approximately 100 nm line width. However, below 100 nm line width features, i.e., at about 80 nm, problems are encountered that are aggravated by the length and diameter of the probe stylet. A conventional quartz stylus has a Young&#39;s Modulus of Elasticity of approximately 70 gigapascals (GPa) [1 GPa=1×10 9  Pa]. As feature sizes continue to shrink, the l 3 /r 4  portion of the deflection equation degrades, forcing a major change in the Young&#39;s Modulus required of the material being used. 
     One promising material form that could substitute for quartz, yet has a higher Young&#39;s Modulus than quartz, is the carbon nanotube. Carbon nanotubes were discovered in 1986 as a discharge material byproduct from a carbon arc. They are actually sheets of graphite where opposing edges have become attached to each other creating a tube. They have exhibited extraordinary material properties including a Young&#39;s Modulus approaching a terapascal, i.e., 1 terapascal=1000 Gpa=1×10 12  Pa. However, no material is problem free, and in the case of carbon nanotubes, the problems are associated with orienting and manipulating them due to their extremely small size. While carbon nanotubes may range from approximately 5 nm to 100 nm in diameter and from about 500 nm to about 5000 nm in length or longer, by their very size, manipulating and orienting them becomes a problem. 
     Nanotube material is now commercially available having diameters of ranging from about 10 nm to about 80 nm. A diameter nominally smaller than the feature size is preferable for probe stylets. Slightly larger or smaller diameter nanotubes can also be used depending upon the semiconductor technology, i.e., feature sizes of 160 nm, 120 nm, or 100 nm, etc., being investigated. Carbon nanotubes are extremely hard to manipulate and therefore, to orient, to tolerances within less than about 10 degrees to 20 degrees of the angle desired. While some efforts have been made to use a carbon nanotube as a probe tip for atomic force microscopes, all nanotube-based probes have heretofore been manufactured by attaching a carbon nanotube to an existing probe body by fastening the nanotube tip with an adhesive to the probe body tip. The method, in some cases consists of projecting the nanotubes against a probe body tip and literally hoping that one sticks in the correct orientation. The problem with this procedure is clearly in orientation, reproducibility and cost. For integrated circuit metrology, this is totally unacceptable due to common features having sidewalls within 1 degree of normal. 
     Accordingly, what is needed in the art is an alternative probe having a microstylet suitable for measuring semiconductor features having on the order of 160 nm or less line widths, and a method of manufacturing the probe. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, the present invention provides a probe comprising a probe body having a body longitudinal axis and a shoulder, and a microstylet mechanically coupled to the shoulder, and a method of manufacturing the same. In a preferred embodiment, the microstylet extends from the shoulder and has a microstylet longitudinal axis coincident the body longitudinal axis with the microstylet having a cross section substantially smaller than a cross section of the probe body. 
     Therefore, the present invention incorporates the positive attributes of a material having a higher Young&#39;s Modulus and extremely small diameter, while dispensing with the problems of manipulating and attaching such a small particle to a probe body in an exact orientation. 
     The foregoing has outlined preferred features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying FIGUREs. It is emphasized that various features may not be drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
     FIG. 1A illustrates an elevation view of one embodiment of a tube preparatory to forming a probe body of a probe manufactured according to the principles of the present invention; 
     FIG. 1B illustrates the tube of FIG. 1A with one end sealed and an opposite end open; 
     FIG. 1C illustrates a suspension of microstylets in a menstruum in the tube of FIG. 1B; 
     FIG. 1D illustrates the tube of FIG. 1B, at least a portion of which was filled with the suspension as shown FIG. 1C, after evaporation of the menstruum; 
     FIG. 2 illustrates the tube of FIG. 1D preparatory to drawing; 
     FIG. 3 illustrates the resultant tube after drawing and just before tube collapse; 
     FIG. 4 illustrates the necked portion of FIG. 3 after collapse of the tube; 
     FIG. 5A illustrates an elevational view of the shank being subjected to a chemical etchant for a first etch; 
     FIG. 5B illustrates an elevational view of the shank after the first etch; 
     FIG. 5C illustrates an elevational view of the probe body being subjected to a chemical etchant for a second etch; and 
     FIG. 6 illustrates an elevational view of a completed probe manufactured according to the principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to FIG. 1A, illustrated is a sectional elevation view of one embodiment of a tube  100  preparatory to forming a probe body of a probe manufactured according to the principles of the present invention. In an advantageous embodiment, the tube  100  comprises a glass tube  110  having an inner wall  120  and a longitudinal axis  130 . However, other non-glass materials may also be used in place of the glass tube  110 . The glass tube  110  is prepared by sealing an end  111 , preferably by melting the glass. A melting point tube may work well, as will a pulled pipet or a small capillary tube. FIG. 1B illustrates the tube  110  of FIG. 1A with the end  111  sealed and an opposite end  112  open. The tube  100  is therefore suitable to hold a liquid with particulate matter, i.e., microstylets, in suspension. FIG. 1C illustrates a suspension  140  of microstylets  150  in a menstruum  160  in the tube  100  of FIG.  1 B. In a preferred embodiment, the microstylets  150  are carbon nanotubes. More specifically, the carbon nanotubes may be either single-walled carbon nanotubes or multi-walled carbon nanotubes. Alternatively, the microstylets  150  may be acerate microparticles  150  such as: carbon whiskers, metal needles, or diamond. Tungsten needles are among suitable metal needles available. 
     In a particularly advantageous embodiment, multi-walled carbon nanotubes are used as the acerate microstylets  150  because of their size and Young&#39;s Modulus. Base carbon nanotube material is now commercially available and multiwalled carbon nanotubes with a diameter of approximately 60 nm to 80 nm may work particularly well for the present invention. Slightly larger or smaller nanotubes may be used depending upon the semiconductor line widths, e.g., 160 nm, 120 nm, 100 nm, etc. It should be noted that commercially available, multi-walled, carbon nanotubes come in bundles that must be separated before used as set forth herein. 
     The suspension  140  is prepared by adding the commercial carbon nanotube bundles to the menstruum  160 . The menstruum  160  is selected from among liquids that: (a) evaporate quickly, (b) are extremely clean, and (c) will not damage the carbon nanotube structure itself. Suitable menstrua may include low carbon number alcohols, e.g., methyl alcohol, ethyl alcohol and isopropyl alcohol. The microstylets  150  are placed in suspension in the menstruum  160  so that separation into individual microstylets  150  can occur. Dilution of the menstruum  160  by volume will help to decrease the concentration of the mirostylets  150 . After preparing the suspension  140 , it is poured into the hollow glass tube  110  sealed at one end  111  as shown in FIG.  1 C. 
     Referring now to FIG. 1D, illustrated is the tube  110  of FIG. 1B, at least a portion  113  of which was filled with the suspension  140  as shown FIG. 1C, after evaporation of the menstruum  160 . The menstruum  160  chosen because of its highly volatile nature, evaporates quickly. As the menstruum  160  evaporates, the microstylets  150  which are not soluble in the menstruum  160  attach to the inner wall  120  of the glass tube  110 , leaving the condition illustrated in FIG.  1 D. Of course, each of the microstylets  150  will attach themselves randomly to some point on the inner wall  120 . 
     Referring now to FIG. 2, illustrated is the tube  100  of FIG. 1D preparatory to drawing of the tube as further described. The open end  112  of the tube  110  is secured to a fixed location  210 , preferably a bench or other substantially fixed object, and a free weight  220 , or other device that may exert a pulling force against tube  110 , such as a person&#39;s hand, is attached to the closed end  111 . Heat is applied to the portion  113  of the tube  110  wherein the microstylets  150  are attached to the inner wall  120 . Heat may be applied using a circular filament  230  located circumferentially about the tube  110  at the portion  113  having microstylets  150  therein. Using gravity to an advantage, the tube  110  is axially loaded with the free weight  220  applying a force F along the tube longitudinal axis  130  while heat is applied proximate the portion  113 . Heat is applied until the combination of heat and longitudinal force F causes the glass tube  110  to be drawn and necked at the portion  113 . The portion  113  proximate the circular filament  230  will decrease in diameter as the heat and force F are continuously applied until of the tube  110  collapses on itself in that portion  113 . One who is skilled in the art is familiar with the process of heating and drawing glass tubing into a capillary or pipette and the ultimate result of the radial collapse of the tube on itself. 
     Referring now to FIG. 3, illustrated is the resultant tube  110  after drawing and just before tube collapse. As the glass tube  110  of FIG. 2 is heated, the microstylets  150  attached to the inner wall  120  become embedded in the viscous, semifluid glass of the glass tube  110 . When heated and combined with the axial force F, the longitudinal axes of the microstylets  150  align with the pulling direction  240 , that also coincides with the longitudinal axis  130  of the glass tube  110 . It is important that this heating and drawing process not be continued to the point at which the tensile strength of the tube  110  in its semifluid state is exceeded. The objective is to narrow the tube  110  and to therefore align the microstylets  150  with the longitudinal axis  130  of the tube  110  without breaking the tube  110 . The tube  110  now comprises first and second tubular portions  310 ,  320  and a necked portion  330 . Microstylets  150  in the necked portion  330  are aligned with the longitudinal axis  130  of the tube  110 . The necked portion  330  is then purposely fractured at points  331  and  332 . 
     Referring now to FIG. 4, illustrated is the necked portion  330  of FIG. 3 after collapse of the tube  110 . In a preferred embodiment, the necked portion  330  comprises solid amorphous glass  410  on the order of 50,000 nm to 200,000 nm in diameter  420  wherein there are embedded microstylets  150  spaced apart along the longitudinal axis  130  as a function of the previously described pulling process. That is, the microstylets  150  become integrally bound to the glass  410 , in contrast to the prior art that has sought to adhesively bond nanotubes to a probe body. One of the microstylets  150  will form a microstylet that is substantially smaller in cross section than the necked portion  330  that will be used as a shank  330  for a microprobe to be completed in accordance with the principles of the present invention. A microprobe is defined as a probe that is revealed by or has its structure discernible only by microscopic examination. 
     For the purpose of this discussion, isotropy is the property of the material, e.g., glass, to etch at the same uniform rate in all axes when subjected to a chemical etchant. Referring now to FIG. 5A, illustrated is a sectional elevational view of the shank  330  being subjected to a chemical etchant  510  for a first etch. 
     As a basis for the etchant, a basic oxide etchant (BOE) is prepared that, may comprise in parts by volume for example: 
     615 parts ammonium fluoride (NH 4 F), 
     104 parts hydrofluoric acid (HF) (49%), and 
     62 parts deionized water (H 2 O). 
     In addition to the BOE, the chemical etchant  510  may further comprise hydrofluoric acid, distilled water and acetone in ratio concentrations to control the etch rate. A typical solution chemistry for the chemical etchant may comprise, for example: 
     5 parts BOE, 
     5 parts hydrofluoric acid (HF) (49%), 
     1 part distilled water (H 2 O), and 
     1 part acetone (CH 3 COCH 3 ). 
     Of course, various formulations may be employed with varying results; that is, the rate of etch may be controlled by the etchant formulation and concentration. The etchant detailed above is suitable for etching when the shank  330  is glass. In those embodiments where the shank  330  is comprised of a non-glass material, etching chemistries appropriate for those materials should be used. The above formulation has been successfully used to complete the first chemical etch of the shank  330 . In the case of this etchant, a typical fast radial etch rate of about 45 nm/sec and slow etch rate of about 1 nm/sec have been achieved. 
     When a portion  510  of the shank  330  is placed in the etchant solution  520 , a meniscus  521  forms about the shank  330 . The purpose of the first chemical etch is to create a region  511  that has a taper proportional to a height  522  of the meniscus  521 . As a function of the concentration of the etchant  520 , thicker etchant causes more extensive etching. Therefore, in area  513 , where the etchant  520  is thinner, less chemical action occurs, while in area  514 , where the etchant  520  is thicker, more etching action occurs, resulting in a morphology that is a right circular cone as indicated by surface  530 . 
     Referring now to FIG. 5B, illustrated is an elevational view of the shank  330  after the first etch. Thus, the result of the first chemical etch is a tapered cone  530  located about a central axis  130  wherein spaced apart microstylets  150  are located along the central axis  130 . A specific microstylet  540  within the apex  531  of the cone  530  now becomes the microstylet that will be exposed by a second etch. A main portion  550  of the shank  330 , not etched by the etchant  520 , may now be referred to as a probe body  550 . The transition from the probe body  550  to the cone  530  forms a shoulder  560 . 
     Referring now to FIG. 5C, illustrated is a sectional elevational view of the probe body  550  being subjected to a chemical etchant  510  for a second etch. Once the tapered conical shape  530  has been formed, a greater portion of the probe body  550  including the conical shape  530  is placed in the etchant  520 . As the etchant continues to etch the glass isotropically, material is removed from the probe body  550  and the conical shape  530  at areas  532  and  533 . As before, the etching results in a conical shape about the central axis  130 . Again, in area  533 , where the etchant  520  is thinner, less chemical action occurs, while in area  532 , where the etchant  520  is thicker, more etching action occurs. 
     Referring now to FIG. 6, illustrated is a sectional elevational view of a completed probe  600  manufactured according to the principles of the present invention. The probe body  550 , subjected to a thinner etch in area  533  has not etched as much as area  532  where the etchant  520  was thicker. This difference in etching rates has resulted in a morphology that is a tapering, right circular cylinder  610 . However, because the glass material of the conical shape  530  comprises less mass than the probe body  550 , the shoulder  560  (FIG. 5C) decreases in circumference as the etch proceeds reforming the shoulder  560 . The transition from the surface  610  to a new conical shape  630  demarks a transition from a conical slope of one portion  610  to a conical slope of a second portion  630 . This transition may be referred to as a fastigiate shoulder  660  in so much as the tapering, right circular cylinder  610  transitions to the right circular cone  630  which tapers to an apex  631 . The process of the second etch has exposed a portion of the specific microstylet formerly within the apex  531  of the cone  530  of FIG.  5 B. Thus, the microstylet  540 , a portion  641  of which is secured mechanically within the conical shape  630  and coincident with the longitudinal axis  130  is formed. This is in contrast to that of the prior art in which a microstylet would be adhesively attached to a shank with a poor chance of being co-aligned with the shank longitudinal axis. Such a microprobe may be used as a field emitter, a micromanipulator or a microinjector in a variety of tools, e.g., scanning electron microscope, stylus nanoprofilometer, etc., or in laboratory procedures. 
     Therefore, a microprobe has been described as the present invention incorporating a microstylet, in the form of a single- or multi-walled nanotube, directly into the probe body itself and thereby eliminating any gluing or attachment of the microstylet to a probe body. It also aligns the microstylet directionally with respect to the central axis of the glass tube being used as a shank or probe body. 
     Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.