The Universal Probe combined with the RM3000+ Test Unit is a unique system for general purpose use as well as for certain special applications.
Applications
- 4-Point Probe Measurement of wafer sheet resistance
- 4-Point Probe Measurement of epitaxial and diffused layer resistivity (where the layer is of the opposite conductivity type to the substrate, or the substrate is an insulator)
- 3-Point Spreading Resistance Measurement
Principle Features
- Highly repeatable needle contact conditions owing to controlled velocity of descent
- Individually adjustable needle loadings with direct indication of set load
- Kinematic needle guidance system employing precision ruby ball guides and polished tungsten carbide rods
- Solid tungsten carbide needles with precision radiused tips
- Accuracy of needle spacing +/- 0.01mm, no side play
- Needles may be readily replaced without fear of derangement or loss of accuracy
- Fully visible contact area
- Micrometer controlled slice displacement for determination of resistivity gradient or junctions on a beveled slice.
- Hinged steel cover to eliminate effects of light and electrical interference during measurement
General Construction
The probe guidance system is kinematic and thus free of all lateral play. The needles are positioned by upper and lower jeweled guides, each needle being constrained by a spring-loaded ruby ball at each guide. The needles slide through their guides with minimum friction, and exchanging new needles for old or broken ones is a simple, quick operation. Changing needles does not affect the characteristics of the unit – provided that replacement needles are the same diameter – spacing and co-linearity will be retained. Variation in needle diameter do not introduce play.
Velocity Control
This device controls the velocity of the needle descent and the rate of applying load and thus offers uniform contact conditions from one measurement to the next. An air dashpot has been employed, since it’s mechanism is vibration free and has a continuous motion. A spring is applied to the raising and lowering lever, tending to lower the needles. The dashpot is attached to the lever so that the lever is retarded by the piston.
Method of Operation
A cam shaft operated by a small lever projecting through the perspex cover sets the machine for either four probe operation (lever up) or three probe operation (lever down).
i) During four probe operation all four needles rise and fall normally. The velocity control should be set as desired.
ii) During three probe operation for spreading resistance measurements, the tension on the first probe should be reduced to zero and the lever pulled down. This lifts the first probe tension gauge finger so that it is inoperative. the central probe finger is raised slightly so that this probe contacts the specimen last. The velocity control knob should be set to give a probe descent rate of approximately 1mm per second.
The Universal Probe uses four user-replaceable probe tips that are mounted in the Guidance Unit. The Guidance Unit determines the probe tip spacing of either 1.0mm, 1.27mm, or 1.59mm. The individual tips can be user replaced or the entire Guidance Unit (which includes four tips) can be user replaced.
A complete four point probing system consists of the Universal Probe shown above, combined with the RM3000+ Test Unit
The Universal Probe is sometimes used to make the three point spreading resistance measurement. Click here for more information.
| SPECIFICATION – PROBE NEEDLES | |
| Material: | 0.5mm diameter tungsten carbide, 26mm long, 45 degree included angle, 25 micron tip radius (or larger up to 100 microns) |
| Spacings: | 1.00mm, 1.27mm, 1.59mm – tolerance +/- 0.01mm |
| Travel: | 4mm |
| Insulation resistance: | 2 x 105 megOhms at 500 volts |
| Load: | 0-100 grams applied by adjustable individual tension gauges |
| Specimen: | Slice only, 76mm diameter is normal maximum |
| Mounting table: | Ball bearing co-ordinate table with 0-25mm x 0.01mm micrometer screws (others available to order) carries a rotary table with 76mm diameter vacuum slice adaptor 14mm high |
| Packed for shipment: | 480mm x 320mm x 320mm high |
| Net weight: | 7 Kg |
| Gross weight: | 9 Kg |
The RM3000+ Test Unit is a specialty electronics instrument designed specifically for the four point probe measurement. It features high accuracy, an excellent range, and many features which simplify the four point probing measurement. The following are features of the RM3000+ Test Unit:
- The sheet resistance range of the RM3000+ Test Unit is from 1 milliohm-per-square (10^-3) to 10^8 ohms-per-square with 0.3% accuracy. The volume resistivity range is from 1 milliohm-cm (10^-3) up to 10^6 ohms-cm, however, that resistivity range refers to measuring a bulk material directly as opposed to measuring a thin film and converting to volume resistivity using the software. For example, a thin layer of copper (1.68 x 10^-6 ohm-cm) up to about 16 microns thick can be measured. The RM3000+ can determine the volume resistivity value if one enters the film thickness.
- The RM3000+ includes PC control software which can be used for measurement logging (storing data in CSV format) and can save measured values as sheet resistance or volume resistivity.
- The RM3000+ display reads-out the input current as well as either ohms-per-square (sheet resistance), ohms-cm (volume resistivity), or millivolts, without requiring the use of the included PC software. The volume resistivity readout requires entering thickness for a wafer or thin film, or tip spacing if measuring a bulk sample.
- The RM3000+ has onboard non-volatile memory so that up to 50 measurements can be stored internally and then downloaded and saved all at one time using the software. Alternately, each measurement can be saved to a PC as it is made using the included software.
- The RM3000+ has an auto-range button that can be used to automatically determine the optimum input current for a given material without using the trial and error method.
- The RM3000+ has forward (FWD) and reverse (REV) buttons to reverse the direction of current flow. A common way to determine if a measurement is valid is to reverse the direction of current flow and then check to see if the forward and reverse voltage readings correlate well, i.e., the values should be similar, but with the reverse current voltage being a negative value.
- The RM3000+ allows the input of a correction factor for samples that need to be corrected for size.
- The RM3000+ has a date and time stamp feature
Superior Current Source
- 10nA to 100mA (99.999mA) current source selectable in steps to 3 decimal place resolution
- Current set numeric keypad
- 4 default preset current programs (user programmable)
Superior Inbuilt DVM
- Input Impedance 1,000,000,000,000 ohms
- Input Bias current 4pA
- DVM 1300mV range and 130mV range
- 130mV accuracy
- 0.2% +/- 5uV resolution (10uV or 1uV) range
- 1300mV accuracy 0.2%+/-100uV resolution
- 100uV Ohms/Square
- Rapid Zeroing null function for DVM
Features
- 28 Key high quality Keypad
- 16×2 line LCD Display for simultaneous indication of Set Current and either Ohms/Sq or mV
- Auto-Ranging capability to determine the optimum input current based upon the material being measured.
- Intuitive operation
- Microprocessor controlled
- Reduced Footprint
- Robust Attractive ABS Case
- Accurately measures down to 10’s of milliohms/square without external meter
- 4mm socket facility to connect an external meter
- RS232/USB connectivity for control and for collecting data in CSV format
- Automatic compliance voltage limit protects your sample which reduces maximum voltage as higher currents are set 5-40V
- Warning messages when compliance limit is reached, or DVM input exceeded
- Self test facility
- Flash upgradeable software
- CE Marked
Downloads
![Universal Probe with RM3000+ Test Unit product brochure [188K PDF file]](/images/pdf.jpg){kind=small}
Four-Point-Probes is a division of Bridge Technology. To request further information please call Bridge Technology at (480) 219-9007 or send e-mail to Joshua Bridge at: sales@bridgetec.com
