Shielded probe apparatus for probing semiconductor wafer

A shielded probe apparatus is provided with a shielded probe and a tri-axial cable that are electrically connected within a shielded chassis. The shielded probe apparatus is capable of electrically testing a semiconductor device at a sub 100 fA operating current and an operating temperature up to 300 C.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor test equipment, and more particularly, to a shielded probe 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. To effectively measure at currents below 100 fA, 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.

At present, semiconductor test equipment has been designed to try to prevent the above described interference or noise, etc. at a test equipment side, by driving a guard layer of a tri-axial cable at the same potential as a center signal conductor of the tri-axial cable. The outer shield of the tri-axial cable is grounded to the test equipment. It is desired that external electrical interference, leakage currents through the dielectric material, parasitic capacitance, triboelectric noise, piezoelectric noise, and dielectric absorption are significantly reduced or eliminated.

Also, because of the materials characteristics of dielectrics, it is often difficult to test characteristics of semiconductor devices in a wide operating temperature range.

Accordingly, there is a need for improved semiconductor test equipment for electrically probing semiconductor devices at low currents and over a wide temperature range.

SUMMARY OF THE INVENTION

To solve the above and the other problems, the present invention provides a shielded probe apparatus connected to semiconductor test equipment wherein the shielded probe apparatus includes a shielded probe and a tri-axial cable. The shielded probe includes a probe pin typically a metal wire made of electrochemically etched tungsten or the like. The probe pin is shielded and configured to electrically connect to the tri-axial cable for electrically probing semiconductor devices at low currents and over a wide operating temperature range.

In one embodiment, the shielded probe apparatus is capable of electrically testing a semiconductor device at a sub 100 fA operating current and an operating temperature up to 300 C.

In one embodiment, the tri-axial cable is connected to the shielded probe within a shielded chassis. The shielded probe includes a probe pin surrounded by a dielectric layer, an electrically conductive guard layer, and an optional protective dielectric layer. The tri-axial cable includes a center signal conductor surrounded by a dielectric layer, a conductive coating to reduce triboelectric effects, a conductive guard layer, a second dielectric layer, a conductive shield layer, and a protective cover. The tri-axial cable is connected to the shielded probe by electrically connecting the center signal conductor to the probe pin, such as by using high temperature to solder/braze or crimp the probe pin on the center signal conductor and in a preferred embodiment, shrink-tube, crimp, or clamp the tri-axial cable and the shielded probe to electrically connect the guard layer of the tri-axial cable to the conductive guard layer of the shielded probe. It will be appreciated that other suitable means of electrically connecting the center signal conductor and the probe pin and electrically connecting the guard layer of the tri-axial cable and the conductive guard layer of the shielded probe can be used without departing the scope of the principles of the invention.

Accordingly, the dielectric layer, the conductive guard layer, and the optional second dielectric layer of the shielded probe significantly reduce external electrical interference and allow the probe pin to test and measure small currents, such as below 100 fA. Also, the shielded probe is allowed to test the characteristics of the semiconductor devices not only in a low operating temperature but also in a high operating temperature, i.e. a wide operating temperature range by using flexible dielectric materials compatible with high temperatures. In addition, the connection between the guard layer of the tri-axial cable and the conductive guard layer of the shielded probe and the connection between the center signal conductor and the probe pin help prevent leakage currents through the dielectric materials, parasitic capacitance, piezoelectric noise, and dielectric absorption. Further, the conductive coating between the dielectric layer and the guard layer of the tri-axial cable significantly reduces and/or eliminates triboelectric noise.

These and other features and advantages 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description.

The present invention utilizes the center signal conductor, guard layer, and ground of a tri-axial cable provided by semiconductor test equipment or tester to electrically isolate a probe pin enabling the low current measurements, for example, sub 100 fA measurements. The present invention also allows the tester to electrically probe 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.

FIG. 1illustrates a cross-sectional view of a typical tri-axial cable100with a center signal conductor102surrounded by a first dielectric layer104. The first dielectric layer104is surrounded by a guard layer106. The guard layer106is electrically conductive and is surrounded by a second dielectric layer108. A conductive coating or dispersion layer107is sandwiched between the first dielectric layer104and the guard layer106. The tri-axial cable100also includes a shield layer110and a protective dielectric cover layer111to isolate the tri-axial cable from external interference or other environmental hazard.

It will be appreciated that the term “surrounded” used herein and hereinafter is not limited to describe one layer being surrounded by another layer in its entirety. In some embodiments, one layer may be partially surrounded by another layer, whereas in other embodiments, one layer may be entirely surrounded by another layer.

FIGS. 2A and 2Billustrate a shielded probe112which includes a probe pin114. The configuration of the probe pin114can be varied, a couple of which are disclosed in a pending utility patent application Ser. No. 09/730,130, filed on Dec. 4, 2000, which is a Continuation-In-Part (CIP) patent application of Ser. No. 09/021,631, filed on Feb. 10, 1998, which are incorporated herewith by references.

The probe pin114is surrounded by a first dielectric layer116preferably made of a thin, flexible high temperature dielectric material, such as poly (tetrafluoro-p-xylylene), a class of polymers known as parylene. The first dielectric layer116is preferably coated on the probe pin by a physical or chemical-vapor deposit (PVD or CVD) method. It will be appreciated that other suitable flexible high temperature dielectric materials, such as epoxies, or other suitable coating methods can be used within the scope of the present invention.

The probe pin114with the dielectric layer116is preferably sputter-coated with an electrically conductive guard layer118. The conductive guard layer118is preferably made of gold. It will be appreciated that other suitable conductive coating materials and coating methods can be used without departing from the scope of the present invention.

A second dielectric layer122may be provided outside of the conductive guard layer118. The second dielectric layer122is an optional protective coating which provides protection layer for the conductive guard layer118. The second dielectric layer122is preferably made of a thin, flexible high temperature dielectric material, such as polyamide. It will be appreciated that other suitable flexible high temperature dielectric materials can be used within the scope of the present invention.

As shown inFIG. 3, a shielded probe apparatus124, in accordance with the principles of the present invention, includes an electrically shielded chassis126and a ceramic assembly128for electrically probing semiconductor devices (not shown). A tri-axial cable130of semiconductor test equipment is inserted into the shielded chassis126at one end132and connected to the shielded probe112at the other end134.

As shown inFIG. 4A, the tri-axial cable130includes a center signal conductor136on which testing signals are carried from the test equipment to the shielded probe112. The center signal conductor136is surrounded by a first dielectric layer138preferably made of high temperature PTFE (Teflon). The first dielectric layer138is surrounded by an electrically conductive coating or dispersion layer140. The conductive coating or dispersion layer140is sandwiched between the first dielectric layer138and an electrically conductive guard layer142to reduce triboelectric effects. In a testing operation, the guard layer142is driven at the same potential as the center signal conductor136such that the capacitance between the guard layer142and the center signal conductor136is eliminated. Accordingly, the parasitic capacitance is eliminated, and current leakage is prevented.

An optional second dielectric layer144may be provided outside of the guard layer142. A shield146and a protective dielectric cover (not shown) are provided outside of the guard layer142and/or the optional second dielectric layer144to isolate the tri-axial cable130from external interference.

As shown inFIG. 3, the tri-axial cable130is inserted into the chassis126where the shield146and the protective dielectric cover (not shown) of the tri-axial cable130are stripped away and electrically connected to the ground.FIG. 4Billustrates a cross-sectional view of the cable130along line4B—4B inFIG. 3. The optional second dielectric layer144may extend to the shielded probe112or terminate at the chassis' sidewalls.

FIG. 4Cillustrates a cross-sectional view (along line4C—4C inFIG. 3) where the tri-axial cable130is connected to the shielded probe112.FIG. 5illustrates a side cross-sectional view of one embodiment of the tri-axial cable130connected to the shielded probe112of the shielded probe apparatus124. The tri-axial cable130is attached to the shielded probe112, preferably by using high temperature to solder/braze or crimp the probe pin114on the center signal conductor136, and shrink-tube, crimp, or clamp the tri-axial cable130and the shielded probe112into a shrink tube layer148to electrically connect the probe pin114to the center signal conductor136. A second shrink tube layer149electrically connects the guard layer142of the tri-axial cable130to the conductive guard layer118of the shielded probe112. It will be appreciated that other suitable means of electrically connecting the center signal conductor and the probe pin and electrically connecting the guard layer of the tri-axial cable and the conductive guard layer of the shielded probe can be used without departing the scope of the principles of the invention.

In one embodiment, the optional second dielectric layer144of the tri-axial cable130and/or the optional second dielectric layer122of the shielded probe may be shrink-tubed by folding back and over (not shown) the tri-axial cable130and the shielded probe112, respectively, so as to help retain the physical connection between the shielded probe112and the tri-axial cable130.

Further referring toFIG. 3, a probing end of the shielded probe112is inserted into a hole and a slot of the high temperature ceramic assembly128or other suitable high temperature-resistant material, as described in the pending utility patent application Ser. No. 09/730,130, filed on Dec. 4, 2000, which is a Continuation-In-Part (CIP) patent application of Ser. No. 09/021,631, filed on Feb. 10, 1998, which are incorporated herewith by references.

Further in one embodiment, the probe pin114is made of electrochemically etched tungsten or other suitable materials. The diameter of the probe pin114is preferably in a range of 0.1 mm to 0.25 mm. It will be appreciated that the materials, diameter, and configuration of the probe pin114can be varied without departing from the principles of the present invention.

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.