SU1494732A1 - Device for measuring contact difference of potentials - Google Patents

Description

(46) 07.01.91. Bul № 1

(21) 4265698/21

(22) 06/22/87 (72) Yu.P. Vorontsov (53) 621.317.3 (088.8)

(54). DEVICE FOR MEASURING CONTACT DIFFERENCE (57) This invention relates to electrical measurements, in particular, devices for measuring the distribution of electric potential on solid surfaces, and can be used to measure the contact potential difference between semiconductor wafers in the production of semiconductor devices. The purpose of the invention is to increase the functional reliability of the device by eliminating damage to the working surfaces of the measuring probe and the measuring plate - achieved by introducing

connected to a voltage transducer, optically connected to a moving element of the vibrator, and a vibrator control signal generator, the output of which is connected to the inductance coil of the vibrator. The in-control control signal generator contains a resonant amplifier tuned to a frequency that is a multiple of the mechanical resonance frequency of the vibrator, and together with the displacement-to-voltage converter forms a positive feedback. Thus, the device is a self-guided repetitive: high quality Q-channel, oscillations in which quickly fade out when the vibrator oscillation frequency changes, for example as a result of touching a plate with a probe, and do not occur until the cause of the frequency change is eliminated.

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with

The invention relates to electrical measuring equipment, in particular, to devices For measuring the distribution of electric potential across solid surfaces, and can be used to measure the contact potential difference of semiconductor wafers in the production of semiconductor devices.

The aim of the invention is to increase the functional reliability of the device by eliminating damage to the working surfaces of the measuring probe and the measuring plate.

The goal is achieved by the fact that in a device for measuring the conductivity of potentials, mainly semiconductor plates, containing an electromagnetic vibrator with an inductance coil, a measuring probe mounted on the movable element of the vibrator, a metal table for accommodating a measuring plate electrically connected to the measuring unit, serially connected transforms gel transfer to voltage optically coupled to a moving element

with

four

00

to

3

the vibrator control signal shaper, the output of which is connected to the inductance coil, the aforementioned shaping circuit contains a resonant power amplifier tuned to a frequency multiple of the vibrator mechanical resonance frequency.

The drawing shows schematically an example of the implementation of the proposed device for measuring contact potential difference.

The device contains an electromagnetic vibrator 1 with a coil 2 of inductance and a moving element (membrane) 3, on which the measuring probe A, located above the surface of the metal

5 to accommodate the measured photodiode on an optoelectronic pair LED phototransistor with mode elements providing the phototransistor in linear mode.

The shaper 9 of the control signals of the vibrator I is designed to amplify the positive feedback signal received at the input of the shaper 9 to generate a signal

6. Metal table 5 is electrically connected with measurement unit 7, and movable element 3 with probe A is optically connected with input of displacement transducer 8 into voltage connected in series with shaper 9 of control signals of vibrator 1, whose output is connected to coil inductance 2.

25

Shaper 9 control signals 30 control, whose frequency is equal to

Neither the vibrator I consists of a voltage amplifier 10 connected in series, a frequency divider 11, an integrator 12 and a resonant power amplifier 13.

Electromagnetic vibrator 1 is designed to transmit to the measuring probe A the harmonic oscillations excited in the coil 2 of the inductance by means of a control signal, 40 must be very high - on the order of

produced by shaper 9.

The measuring probe A serves to form a dynamic capacitor together with the measured semiconductor wafer 6. The end surface of the probe A is one of the plates of the specified dynamic capacitor. Structurally, the measuring probe A is made in the form of a cylindrical rod with a diameter O, A mm and a conductive material with a gilded or platinum coating 10 μm thick, which ensures a high stability of the surface potential of the probe A in time.

Metal table 5, designed to accommodate the measured guitar 6, is used to transfer information about the measured parameter to the input

block

7 of a measurement designed to clear out of this information useful signals carrying information about the magnitude and sign of the contact potential difference.

The displacement transducer 8 to voltage serves to convert the mechanical harmonic oscillations of the measuring probe 4 into a sinusoidal electrical signal, which is a positive feedback signal for the vibrator control signal generator 9 that allows them to close the ring and form a self efylo resonant system high quality factor. Converter 8 is an optical phototransmitter, made to the mechanical resonance frequency of vibrator I, and transmitting this signal to inductor 2 of vibrator 1. Circuit design of shaper 9 is due to the design of the vibrator used, but in any case the use of a resonant power amplifier is mandatory, and shaper gain 9

five

0

five

10. In this example, the design of the vibrator 1 ensures the operation of the measuring probe A at the doubled signal frequency, i.e. the probe attracts both with positive and negative signal values, which causes the use of the frequency divider 11 signal in the imaging unit 9. And at the signal frequency, the need for a frequency divider 1I is eliminated.

The device works as follows.

The investigated semiconductor Plate 6 is placed on a metal table 5. The device is started by supplying power to the nodes and blocks of the device. As a result, the measuring device U begins to oscillate at the frequency of the mechanical resonance of the vibrator 1. At the initial moment of time these oscillations occur in the result of passing through the coil 2 inductance current due to transients.

Since the mobile element 3 of the vibrator 1 is optically coupled to the displacement transducer 8 in voltage, a feedback signal is generated at the output of the latter, which is proportional to the amplitude of oscillations. This signal is fed to the shaper 9 of the control signal of the vibrator 1, where at nodes 10-13, the feedback signal is amplified, its frequency is divided into two, the waveform is converted and its power is subsequently amplified. The signal obtained at the output of the imaging unit 9 is fed to the inductor 2 inductance, a current flows through it, which induces harmonic oscillations of the measuring probe 4 at the frequency of the mechanical resonance of the vibrator 1.

this changes the capacitance of the capacitor

formed by the surfaces of the measuring probe A and the plate 6.: A variable signal caused by a change in the density of the surface charge and surface charge on the plate 6 through the metal table 5 enters the input of the measuring unit 7, where the constant component carrying the information about contact potential difference.

In case of accidental contacting of the measuring probe 4 and the semiconductor plate 6, there occurs a sharp decrease in the quality factor of the resonant system formed by the oscillating circuit of the vibrator 1, the transducer 8 moving to voltage and forming

control signal 9 of the vibrator I. This leads to a sharp decrease in the signal from the output of the driver 9 and, ultimately, to the breakdown of the oscillations. The resumption of oscillations hpo- occurs with the elimination of the cause that caused the accidental contact of the probe 4 with the plate 6.

Thus, the proposed device eliminates multiple oscillations of the probe when it is accidentally contacted with the plate, resulting in the elimination of mechanical damage to the probe and plate, leading to an increase in measurement error and a decrease in the percentage of yield of plates.

Claims (1)

Invention Formula A device for measuring contact potential difference, mainly semiconductor wafers, containing an electromagnetic vibrator with an inductance coil, a measuring probe mounted on a movable element of the vibrator, a metal table for accommodating a measuring plate, electrically connected to the measuring unit, characterized in that increase the functional reliability of the device by eliminating damage to the working surfaces of the measuring probe and the measuring plate; Flax coupled transducer to voltage, optically coupled to the vibrator moving element, and vibrator control signal generator, the output of which is connected to an inductance coil, the former comprising a resonant power amplifier tuned to a frequency multiple of the vibrator mechanical resonance frequency.