Abstract:
A probe needle apparatus and method provides a drive guard having the same potential as a probe needle for reducing signal noise in low current measurements. The probe needle apparatus includes a central conductive core covered with alternating layers of dielectric and conductive materials, a first layer of dielectric material applied to maintain electrical access to the conductive central core while providing continuous isolation of the conductive central core elsewhere, and a conductive drive guard layer applied around the first layer of dielectric material in electrical isolation from the conductive central core.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 11/242,610, filed Oct. 3, 2005, now U.S. Pat. No. 7,271,607 which is a Continuation of U.S. patent application Ser. No. 10/809,051, filed Mar. 25, 2004, now U.S. Pat. No. 6,975,128, issued on Dec. 13, 2005, which claims benefit of U.S. Provisional Patent Application Ser. No. 60/458,467, filed Mar. 28, 2003, the contents of which are incorporated herein in its entirety by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to semiconductor test equipment, and more particularly, to a probe apparatus used in semiconductor test equipment for electrically probing devices on a semiconductor wafer. 
   BACKGROUND OF THE INVENTION 
   The semiconductor industry has a need to access many electronic devices on a semiconductor wafer. As the semiconductor industry grows and devices become more complex, many electrical devices, most commonly semiconductor devices, must be electrically tested, for example, for leakage currents and extremely low operating currents. These currents are often below 100 fA. In addition, the currents and device characteristics are often required to be evaluated over a wide temperature range to understand how temperature affects a device. Also, because of materials characteristics of dielectrics, it is often difficult to test characteristics of semiconductor devices in a wide operating temperature range. 
   To effectively measure at currents below 100 fA (Femto Ampere), a measurement signal must be isolated from external electrical interference, leakage currents through the dielectric material, parasitic capacitance, triboelectric noise, piezoelectric noise, and dielectric absorption, etc. 
   Accordingly, there is a need for improved semiconductor test equipment for electrically probing semiconductor devices at low currents over a wide temperature range. 
   SUMMARY OF THE INVENTION 
   To solve the above and the other problems, the present invention provides a probe needle apparatus and method including a driven guard having the same potential as a probe needle for reducing signal noise in low current measurements. The probe needle apparatus includes a central conductive probe needle covered with alternating layers of dielectric and conductive materials. 
   In one embodiment, the probe needle apparatus comprises a central conductive probe needle surrounded by a high temperature dielectric layer of material. A conductive layer is deposited around the dielectric layer to provide a driven guard. The initial layer of dielectric material provides a thin and continuous barrier to prevent the conductive driven guard from contacting electrically to the probe needle. In one embodiment, a subsequent protective layer is applied over the driven guard. 
   In one embodiment of the present invention, the probe needle can be a probe needle disclosed in U.S. Provisional Patent Application Ser. No. 60/392,394, filed Jun. 28, 2002, entitled “SHIELDED PROBE APPARATUS FOR PROBING SEMICONDUCTOR WAFER”. Also, in one embodiment, the probe needle is masked at the distal and proximate ends to allow continuity. The masked probe needle is then coated with a flexible high temperature dielectric, prior to being coated with a conductive layer, such as gold, for the driven guard. An optional top layer can be applied by a method, such as dipping and spinning, or depositing by other means to protect the outer conductive layer. 
   In one embodiment of the probe needle, an initial dielectric layer is applied by dipping and spinning. After thermally curing the dielectric layer, the conductive layer for the driven guard is applied. 
   Additionally in one embodiment of the present invention, the probe needle may be coated with an initial dielectric layer of SiO2. A thin conductive layer of the driven guard may be strengthened by over-plating. 
   These and other features of the present invention will become apparent to those skilled in the art from the following detailed description, wherein it is shown and described illustrative embodiments of the invention, including best modes contemplated for carrying out the invention. As it will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of one embodiment of a shielded probe apparatus in accordance with the principles of the present invention. 
       FIG. 2  is a masking technique for masking a shielded probe in accordance with the principles of the present invention. 
       FIG. 3  is a rotational technique for applying one or more conformal coatings on the shielded probe in accordance with the principles of the present invention. 
       FIG. 4  is a cross sectional view of another embodiment of a shielded probe apparatus in accordance with the principles of the present invention. 
       FIG. 5  is a perspective view of one embodiment of a probe apparatus having a co-axial shielded probe terminating with a co-axial signal cable at a terminating device, in accordance with the principles of the present invention. 
       FIG. 6  is a perspective view of one embodiment of a probe apparatus having a tri-axial shielded probe terminating with a tri-axial signal cable at a terminating device, in accordance with the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following description of a preferred embodiment, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
   For purposes of explanation, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, it will be evident to one of ordinary skill in the art that the present invention may be practiced without some of these specific details. 
   While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detailed preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated. 
   The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiments, wherein these innovative teachings are advantageously applied to the particular problems of a probe needle for measuring low currents with a wide operating temperature range in probing a semiconductor device. However, it should be understood that these embodiments are only examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in the plural and visa versa with no loss of generality. 
   The following terms are particularly described throughout the description: 
   Semiconductor Device Not Limitive 
   The present invention is particularly suitable for probing semiconductor devices, but the use of the present teachings is not limited to probing semiconductor devices. Other devices may be applied to the present invention teachings. Thus, while this specification speaks in terms of probing ‘semiconductor’ devices, this term should be interpreted broadly to include probing any suitable device. 
   Low Current Not Limitive 
   The present invention solves the problem of measuring currents below 100 fA, but the current range of the present teachings is not limited to below 100 fA. For example, the present invention may be applied to measure the currents at or above 100 fA in a semiconductor device. Thus, while this specification speaks in terms of ‘low currents’ or ‘measuring currents below 100 fA’, these terms should be interpreted broadly to include any current that flows through a semiconductor device which could be at or above 100 fA. In a grounded guard controlled impedance configuration the present invention also solves the problem of measuring high frequency signals at high temperatures. 
   Wide Temperature Not Limitive 
   The present invention solves the problem of measuring currents of a semiconductor device in a narrow or limited operating temperature range. The present teachings do not limit to a specific operating temperature range. The present application allows a tester to electrically probe semiconductor devices over a wide operating temperature range, not only at a low operating temperature but also a high operating temperature, e.g. an operating temperature up to 300 C and beyond. Thus, while this specification speaks in terms of ‘wide temperature range’ or ‘measuring currents in a wide operating temperature range’, these terms should be interpreted broadly to include any suitable operating or testing temperature range of a semiconductor device. 
   Probe Not Limitive 
   The present invention solves the problem of measuring currents of a semiconductor device using a co-axial or a tri-axial shielded probe. However, nothing in the teachings of the present invention limits application of the teachings of the present invention to a probe needle with more or less layers. Advantageous use of the teachings of the present invention may be had with a probe needle of any number of layers. 
   Signal Cable Not Limitive 
   The present invention solves the problem of measuring currents of a semiconductor device using a co-axial or a tri-axial signal cable. However, nothing in the teachings of the present invention limits application of the teachings of the present invention to a signal cable with more or less layers. Advantageous use of the teachings of the present invention may be had with a signal cable of any number of layers. 
   Metals Not Limitive 
   Throughout the discussion herein there will be examples provided that make reference to metals in regards to needle and driven guard. The present invention does not recognize any limitations in regards to what types of metals may be used in affecting the teachings of the present invention. One skilled in the art will recognize that any conductive material may be used with no loss of generality in implementing the teachings of the present invention. 
   Dielectric Not Limitive 
   Throughout the discussion herein there will be examples provided that make reference to dielectric. The present invention does not recognize any limitations in regards to what types of dielectric may be used in affecting the teachings of the present invention. One skilled in the art will recognize that any non-conductive, highly heat-resistant material may be used with no loss of generality in implementing the teachings of the present invention. 
   Exemplary Embodiment 
   As shown in  FIG. 1 , a shielded probe needle apparatus  100  includes a probe needle  101  covered with a dielectric layer  102 , a conductive driven guard layer  103 , and an optional protective coating layer  104 . The dielectric layer  102  and the optional protective coating layer  104  are preferably applied to the probe needle  101  using a physical/chemical vapor deposition (P/CVD) of high temperature polymer. 
   As also shown in  FIG. 1 , the connection or contact between the probe needle  101  side and the connector or signal cable  107  side is head on head. Alternatively, the connection or contact between the probe needle  101  side and the connector or signal cable  107  side is side-by-side as shown in  FIGS. 5 and 6 , which are disclosed in U.S. Utility patent application Ser. No. 10/383,079, filed Mar. 6, 2003, now U.S. Pat. No. 6,963,207, issued Nov. 8, 2005 subject matter of which are incorporated herewith by reference.  FIG. 2  illustrates a masking technique for making a probe needle  201 . As shown, making materials  202  and  203  are applied to the ends of the probe needle  201  to prevent the conductive driven guard layer  103 , such as the conductive driven guard layer  103  in  FIG. 1 , from depositing over the end of the dielectric creating a conductive path between the conductive guard layer  103  and the probe needle  201 . The masks are applied towards the ends of the probe needle necessary to provide required access and protection. 
   Alternate methods may be used to achieve at least similar masking functions to prevent electrical contact between the conductive driven guard layer  103  and the probe needle  201 , and to provide required access and protection to the probe needle. For example, in one exemplary method, the end of the conductive driven guard layer is removed by ablation or chemical etch to prevent the conductive driven guard layer, such as the conductive driven guard layer  103  in  FIG. 1 , from remaining on the dielectric creating a conductive path between the conductive guard layer and the probe needle  201 . The protective coating  104  is applied over the conductive driven guard layer to provide required access and protection. The mask is then removed or can be left behind as the protective layer. 
     FIG. 3  illustrates a rotational curing technique for coating the shielded probe with dielectric or the conductive guard layer. As shown, a plurality of probe needles  301  are mounted radially on an axially rotational rod  304  by devices, such as clamps  302 . A layer is uniformly applied to the probe needles by dipping or spraying and then spinning the probe needles. The masks at the ends of the probe needle also prevent the protective coating layer from touching the probe needle. Alternatively, the masking is not used and the layer is removed by mechanical or chemical means. Uniformly coated materials can be deposited and dried by a flow of thermally conditioned and humidity controlled gas. 
   Further, in another alternative technique, a mask is applied one end, e.g. a proximal end (the back end) of the probe needle. After a dielectric layer is applied over the probe needle, e.g. a P/CVD layer is deposited over the probe needle, another mask is applied to the other end, e.g. a distal end (the tip end) of the probe needle. Next, a conductive layer, such as gold, is sputtered over the dielectric layer. 
     FIG. 4  illustrates one embodiment of a probe needle apparatus  400  in a tri-axial configuration.  FIG. 1  illustrates one embodiment of the probe needle apparatus  100  in a coaxial configuration. As shown in  FIG. 4 , the probe apparatus  400  comprises a probe needle  401 , a base dielectric layer  402  covering the probe needle  401 , a conductive guard layer  403  covering the base dielectric layer  402  which is in turn covered by a second dielectric layer  404 , and a second conductive guard layer or an outer guard layer  405  covering the second dielectric layer  404 . A nonconductive protective layer  406  may be added for electrical and mechanical protection. 
   As briefly discussed above,  FIG. 5  shows an embodiment of a probe apparatus having a co-axial shielded probe terminating with a co-axial signal cable at a terminating device side by side. The following detailed descriptions have been disclosed in U.S. Utility patent application Ser. No. 10/383,079, filed Mar. 6, 2003, now U.S. Pat. No. 6,963,207, issued Nov. 8, 2005 subject matter of which are incorporated herewith by reference. In  FIG. 5 , a probe apparatus  100   a  includes a co-axial shielded probe  108   a  terminating with a co-axial signal cable  102  at a terminating device  132 . The shielded probe  108   a  includes a center conductive probe needle  146   a , a dielectric layer  148   a  surrounding the center conductive probe needle  146   a , a conductive guard layer  150   a  surrounding the conductive guard layer  150   a . The signal cable  102   a  includes a center signal conductor  154   a , a dielectric layer  156   a  surrounding the dielectric layer  156   a , and a non-conductive heat-shrinkable sleeve  160   a  surrounding the conductive dispersion/guard layer  158   a.    
   At a distal end  126   a , the shielded probe  108   a  extends from the dielectric block  130  toward the bond pad  110 . The sleeve  152   a  is removed when it is inserted into the dielectric block  130 . 
   As shown in  FIG. 5 , at the proximal end  128   a , the center conductive probe needle  146   a  of the shielded probe  108   a  is disposed side by side with and electrically connects to the center signal conductor  154   a  of the signal cable  102   a . The dielectric layer  148   a  of the shielded probe  108   a  is disposed side by side with and connects to the dielectric layer  156   a  of the signal cable  102   a . The conductive guard layer  150   a  of the shielded probe  108   a  is disposed side by side with and electrically connects to the conductive dispersion/guard layer  158   a  of the signal cable  102   a . The sleeve  152   a  of the shielded probe  108   a  is disposed side by side with and connects to the sleeve  160   a  of the signal cable  102   a.    
   As shown in  FIG. 5 , the terminating device  132  includes a shrink tube  162   a  for shrink-tubing the sleeve  152   a  of the shielded probe  108   a  and the sleeve  160   a  of the signal cable  102   a  together, for shrink-tubing the conductive guard layer  150   a  of the shielded probe  108   a  and the conductive dispersion/guard layer  158   a  of the signal cable  102   a  together, for shrink-tubing the dielectric layer  148   a  of the shielded probe  108   a  and the dielectric layer  156   a  of the signal cable  102   a  together, and for shrink-tubing the center conductive probe needle  146   a  of the shielded probe  108   a  and the center signal conductor  154   a  of the signal cable  102   a  together. The shrink tube  162   a  is covered by the strain relief  144   a.    
   An extension  164   a  of the shrink tube  162   a  is disposed at an end of the center conductive probe needle  146   a  and the center signal conductor  154   a , and is configured sufficiently wide enough to prevent electrical current from leaking from the center conductive probe needle  146   a  and the center signal conductor  154   a  to the strain relief  144   a . In addition, the center conductive probe needle  146   a  and the center signal conductor  154   a  may be soldered, brazed, welded, crimped, or snuggled therebetween at  166   a  to provide additional clearance between the center conductive probe needle  146   a  and the strain relief  144   a , and additional clearance between the center signal conductor  154   a  and the strain relief  144   a.    
   Similarly, as briefly discussed above,  FIG. 6  shows an embodiment of a probe apparatus  100   b  having a tri-axial shielded probe terminating with a tri-axial signal cable at a terminating device side by side. The following detailed descriptions have been disclosed in U.S. Utility patent application Ser. No. 10/383,079, filed Mar. 6, 2003, now U.S. Pat. No. 6,963,207, issued Nov. 8, 2005 subject matter of which are incorporated herewith by reference. In  FIG. 6 , the probe apparatus  100   b  includes a tri-axial shielded probe  108   b  terminating with a tri-axial signal cable  102   b  at the terminating device  132 . The tri-axial shielded probe  108   b  additionally includes a second dielectric layer  168  sandwiched between a conductive guard layer  150   b  and the sleeve  152   b . A guard layer  169  may be included between the second dielectric layer  168  and the sleeve  152   b . The signal cable  102  additionally includes a second dielectric layer  170  sandwiched between the conductive dispersion/guard layer  158   b  and the sleeve  160   b . A guard layer  171  may be included between the second dielectric layer  171  and the sleeve  160   b . Accordingly, as shown in  FIG. 6 , the shielded probe  108   b  includes a center conductive probe needle  146   b , a dielectric layer  148   b  surrounding the center conductive probe needle  146   b , the conductive guard layer  150   b  surrounding the dielectric layer  148   b , the second dielectric layer  168  surrounding the conductive guard layer  150   b , the guard layer  169  surrounding the second dielectric layer  168 , and the sleeve  152   b  surrounding the guard layer  169 . The signal cable  102   b  includes a center signal conductor  154   b , a dielectric layer  156   b  surrounding the center signal conductor  154   b , the conductive dispersion/guard layer  158   b  surrounding the dielectric layer  156   b , the second dielectric layer  170  surrounding the conductive dispersion/guard layer  158   b , the guard layer  171  surround the second dielectric layer  170 , and the sleeve  160   b  surrounding the guard layer  171 . 
   At a distal end  126   b , the shielded probe  108   b  extends from the dielectric block  130  toward the bond pad  110 . The sleeve  152   b  is removed when it is inserted into the dielectric block  130 . 
   As shown in  FIG. 6 , at the proximal end  128   b , the center conductive probe needle  146   b  of the shielded probe  108   b  is disposed side by side with and electrically connects to the center signal conductor  154   b  of the signal cable  102   b . The dielectric layer  148   b  of the shielded probe  108   b  is disposed side by side with and connects to the dielectric layer  156   b  of the signal cable  102   b . The conductive guard layer  150   b  of the shielded probe  108   b  is disposed side by side with and electrically connects to the conductive dispersion/guard layer  158   b  of the signal cable  102   b . The second dielectric layer  168  of the shielded probe  108   b  is disposed side by side with and connects to the second dielectric layer  170  of the signal cable  102   b . The guard layer  169  of the shielded probe  108   b  is disposed side by side with and electrically connects to the guard layer  171  of the signal cable  102   b . The sleeve  150   b  of the shielded probe  108   b  is disposed side by side with and connects to the sleeve  160   b  of the signal cable  102   b.    
   As shown in  FIG. 6 , the terminating device  132  includes a shrink tube  162   b  for shrink-tubing the sleeve  152   b  of the shielded probe  108   b  and the sleeve  160   b  of the signal cable  102   b  together, for shrink-tubing the second dielectric layer  168  of the shielded probe  108   b  and the second dielectric layer  170  of the signal cable  102   b  together, for shrink-tubing the conductive guard layer  150   b  of the shielded probe  108   b  and the conductive dispersion/guard layer  158   b  of the signal cable  102   b  together, for shrink-tubing the guard layer  169  of the shielded probe and the guard layer  171  of the signal cable  102   b , for shrink-tubing the dielectric layer  148   b  of the shielded probe  108   b  and the dielectric layer  156   b  of the signal cable  102   b  together, and for shrink-tubing the center conductive probe needle  146   b  of the shielded probe  108   b  and the center signal conductor  154   b  of the signal cable  102   b  together. The shrink tube  162   b  is covered by the strain relief  144   b.    
   An extension  164   b  of the shrink tube  162   b  is disposed at an end of the center conductive probe needle  146   b  and the center signal conductor  154   b , and is configured sufficiently wide enough to prevent electrical current from leaking from the center conductive probe needle  146   b  and the center signal conductor  154   b  to the strain relief  144   b . In addition, the center conductive probe needle  146   b  and the center signal conductor  154   b  may be soldered, brazed, welded, crimped, or snuggled therebetween at  166   b  to provide additional clearance between the center conductive probe needle  146   a  and the strain relief  144   b , and additional clearance between the center signal conductor  154   a  and the strain relief  144   b.    
   From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustration only and are not intended to limit the scope of the present invention. Those of ordinary skill in the art will recognize that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. References to details of particular embodiments are not intended to limit the scope of the invention.