JP2020161557A - Gap control method and electrical characteristic measurement method - Google Patents

Abstract

To correctly measure a gap width between a probe electrode and a sample surface, thereby improving the measurement accuracy of the electrical characteristics of a sample.SOLUTION: A gap control method includes the steps of actually measuring a charging voltage ratio v (t)/V (t) of a voltage V (t) applied from a probe electrode to a sample by a pulsed photoconduction method and a charging voltage v (t) of the sample, obtaining an ideal curve of the charging voltage ratio v (t)/V (t) with respect to a gap width W obtained by considering the slope θ between the entire electrode and the sample surface, specifying the slope θ at which the actually measured value of the charging voltage ratio v (t)/V (t) and the ideal curve match, and obtaining a gap capacitance Cgap in consideration of the slope θ.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gap control method and an electrical characteristic measurement method, and measures the electrical characteristics of a semiconductor wafer, for example, the capacitance of a dielectric film formed on a semiconductor wafer, or the interface state between a dielectric film and a semiconductor in a non-destructive manner. The present invention relates to a gap control method and an electrical characteristic measurement method for precisely controlling the gap (space) between the probe electrode and the semiconductor wafer.

In a device that measures the capacitance of a sample by bringing an electrode close to the sample of a semiconductor wafer, the capacitance of the sample and the capacitance generated in the gap (space) between the probe electrode and the sample are arranged in series. .. Therefore, in order to correctly measure the capacitance of the sample, it is necessary to accurately control and grasp the capacitance of the gap.

The capacitance C _gap of the _gap is represented by Equation 1. Since the gap is filled with air, the dielectric constant ε ₀ and the electrode area S are known. Therefore, in order to correctly determine the capacitance of the gap, it is necessary to accurately measure the gap width W _gap between the electrode and the sample. Desired.

Patent Document 1 discloses an apparatus for nondestructively measuring electrical characteristics such as CV characteristics of a sample (semiconductor wafer). In order to measure the electrical characteristics, it is necessary to bring the measurement electrode close to the sample and measure the gap width between the measurement electrode and the sample surface correctly. As a means for that, measurement using the tunneling phenomenon of light is used. The method is adopted.

Explaining this light tunneling phenomenon, when laser light is reflected by a reflecting portion under geometrical optics total reflection conditions, the gap between the reflecting surface (electrode holding surface) and the sample surface is the wavelength of the laser light. When the size is less than the same, a part of the laser beam seeps out from the reflecting surface into the sample. This is called the tunneling phenomenon, and the intensity of the transmitted light that seeps into the sample side depends on the width of the gap.

Similarly, the intensity of the laser beam reflected by the reflecting surface of the reflecting portion also depends on the width of the gap. The relationship between the intensity of the reflected light and the gap can be obtained in advance by a calculation based on Maxwell's equation. By utilizing this relationship, the width of the gap can be obtained by measuring the intensity of the reflected light.

Further, Non-Patent Document 1 discloses a method for obtaining the interface state density in a non-destructive manner by a pulse photoconductivity method (PPCM), and there is a method for obtaining a gap width between an electrode and a sample from a measured value. Is stated.

FIG. 14 shows an equivalent circuit of a measuring device that implements the pulsed photoconduction method disclosed in Non-Patent Document 1. In the equivalent circuit of FIG. 14, a probe electrode (shown) is provided with a predetermined gap (capacity C _gap ) with respect to the upper surface (oxide film side) of the silicon wafer sample (oxide resistance R _ox and oxide film capacity C _ox ). Is installed, and a rectangular wavy pulse voltage is applied to the sample 12 from the pulse voltage application unit 11 from the probe electrode.
An optical fiber (not shown) is passed through the probe electrode so that the sample 12 can be irradiated with ultraviolet (UV) pulsed light at the same time as the pulse voltage is applied.

Further, on the lower surface side (silicon substrate side) of the sample 12, a coaxial cable (parasitic capacitance C _f ) 13 for picking up a transient signal response accompanying the movement of the photocarrier in the sample is provided, and in addition to the coaxial cable. The measuring unit 15 at the end is connected to an oscilloscope (not shown) via a preamplifier (internal resistance R _in ) 14.

Further, a charging resistor R _c is connected in parallel with the parasitic capacitance C _f , whereby the sample 12 can be charged.
Further, a load resistor _RL is connected to the measuring unit 15. At the time of measurement, the internal electric field of the sample 12 is relaxed and a measurable state is created by removing the charge resistance R _c from the measurement circuit and switching to the load resistance _RL at the same time.

The applied voltage is distributed to the gap (capacity C _gap ) between the probe electrode and the sample 12, the oxide film (oxide resistance R _ox and oxide film capacitance C _ox ), and the cable parasitic capacitance C _f . Since the applied voltage consumption in the gap portion changes according to the gap width, the electric field strength of the oxide film changes. Since the output signal depends on the electric field strength of the oxide film, it is necessary to keep the gap width constant.

In the measurement, in order to determine the parameters of the circuit equation of the measurement circuit, the silicon substrate is put into a strongly inverted state, and the oxide film capacity is treated as a fixed value.
Therefore, the measurement sequence is such that the oxide film of the sample 12 is first charged, then the pulsed light of ultraviolet rays is irradiated, and the transient signal response at that time is observed.

The graph of FIG. 15 shows the charging voltage v (t), the applied voltage V (t), and the optical signal ΔV (t _d ). After the rectangular wave pulse voltage is applied to the sample to complete charging of the oxide film capacity, the sample is irradiated with ultraviolet pulsed light and transient signal changes are observed. The ratio of the applied voltage V (t) to the charging voltage v (t) at that time is given by the following equation 2 from the equivalent circuit of FIG.

C _gap is the gap capacitance, C _oxid is the oxide film capacitance, and C _f is the stray capacitance of the cable in the measurement circuit. In this equation, _Oxide and C _f are known constants.
Using the gap width W _gap as a variable, create a theoretical curve of the charging pressure ratio v (t) / V (t) corresponding to it in advance, and compare this theoretical curve with the measured charging pressure ratio v (t) / V (t). The gap width can be obtained with.

In the measuring method disclosed in Non-Patent Document 1, the electric field strength to the oxide film is made constant based on the gap width obtained as described above, the excitation carrier density is calculated from the optical signal ΔV (t _d ), and the carrier density is calculated. The interface state density is calculated by extrapolating the carrier density when the applied voltage V (t) = 0 from the voltage dependence graph.

Japanese Patent No. 2802825

Masaaki Furuta, Kojiro Shimizu, Takahiro Maeta, Moriya Miyashita, Koji Izunome, and Hiroshi Kubota: Japanese Journal of Applied Physics, Vol.57,031301 (2018)

However, the gap control method between the electrode and the sample disclosed in Non-Patent Document 1 is accurate when the electrode is tilted with respect to the sample surface due to the waviness of the sample wafer or sample holder, the tilt of the electrode, or the like. There is a problem that the capacitance of a large gap cannot be obtained.
For precise measurement, it is required to minimize the inclination of the gap and the sample, or to correct the inclination in the calculation at the time of measurement and measure the gap width correctly. Especially in the pulsed photoconduction method, precise control of the gap is required in order to obtain an accurate interface state density.

The present invention has been made under the above-mentioned circumstances, and in the measurement of electrical characteristics in which probe electrodes are arranged with a predetermined gap width in a semiconductor sample on which a dielectric film is formed, the probe electrodes are used. It is an object of the present invention to provide a gap control method and an electrical characteristic measurement method capable of accurately measuring the gap width between the sample and the sample surface and thereby improving the measurement accuracy of the electrical characteristics of the sample.

凹凸と傾きを考慮しないギャップ幅をＷ_ｇａｐとし、空気の誘電率をε_０とし、φ／ｋの領域を更にｎ個に分割して最も突起が大きいところからの変位をＷ_ｃｎとし、ｎ個に分割された各領域の面積をＳ_１〜Ｓ_ｎとすると、前記傾きθを考慮したギャップ容量Ｃ_ｇａｐは、下記式により求められることに特徴を有する。

The gap control method according to the present invention, which has been made to solve the above problems, includes a step of arranging probe electrodes with a predetermined gap width in a semiconductor sample on which a dielectric film is formed, and a pulsed photoconduction method. The step of actually measuring the charging voltage ratio v (t) / V (t) of the voltage V (t) applied from the probe electrode to the sample and the charging voltage v (t) of the sample, and the entire electrode. The step of obtaining the ideal curve of the charging voltage ratio v (t) / V (t) with respect to the gap width W in consideration of the inclination θ between the sample surfaces, and the measured value of the charging voltage ratio v (t) / V (t). It includes a step of specifying a slope θ that matches the ideal curve and a step of _obtaining a gap capacitance C _gap in consideration of the slope θ, and the electrode diameter is Φ and the electrode tip surface is k pieces in the radial direction (k is). When the ratio of the region to the total surface area of the electrode is α _k , the gap width W _k considering the inclination θ between the entire electrode and the sample surface can be calculated by the following formula.

The gap width that does not consider unevenness and inclination is W _gap , the permittivity of air is ε ₀ , the region of φ / k is further divided into n, and the displacement from the largest protrusion is W _cn , n. the area of each divided region is When S ₁ to S _n, the gap capacitance C _gap considering the inclination θ is characterized in that obtained by the following equation.

In the step of arranging the probe electrodes with a predetermined gap width in the semiconductor sample on which the dielectric film is formed, a tubular insulating synthetic resin material is incorporated into the tip of the probe electrodes to provide the insulating properties. The step of adjusting the gap between the tube tip of the synthetic resin material and the electrode tip in advance, and holding the probe electrode swingably in the vertical direction, the tube tip of the insulating synthetic resin material comes into contact with the sample surface. It is desirable to provide a step of adjusting the gap.

Alternatively, in the step of arranging the probe electrodes with a predetermined gap width for the semiconductor sample on which the dielectric film is formed, the inclination is adjusted by attaching the probe electrodes to the gimbal mechanism that rotates around two independent axes. However, a capacitance displacement meter may be installed next to the probe electrode to measure the gap width.

According to such a method, the charging voltage ratio v (t) / V (t) is actually measured by the pulsed photoconduction method, and the charging voltage ratio v (t) / V (t) with respect to the gap width considering the inclination of the electrode is taken into consideration. ) Is obtained, and the inclination θ of the electrode is specified. As a result, the gap capacitance C _gap can be obtained in consideration of the inclination θ between the entire electrode and the sample surface, and the electrical characteristics of the sample can be measured with high accuracy based on the gap capacitance C _gap .

Further, the method for measuring electrical characteristics according to the present invention, which has been made to solve the above problems, is characterized in that the gap capacitance C _gap is obtained by the gap control method and the electrical characteristics are measured by the pulsed photoconduction method.

According to the present invention, in the electrical property measurement in which a probe electrode is arranged with a predetermined gap width in a semiconductor sample on which a dielectric film is formed, the gap width between the probe electrode and the sample surface is correctly measured. Thereby, it is possible to provide a gap control method and an electrical characteristic measurement method capable of improving the measurement accuracy of the electrical characteristics of the sample.

FIG. 1 is a plan view of an electrode tip for explaining a method of correcting an inclination in the charge voltage ratio method of the present invention. FIG. 2 is a cross-sectional view of the tip of the electrode for explaining the method of correcting the inclination in the charge voltage ratio method of the present invention. FIG. 3 is another cross-sectional view of the tip of the electrode for explaining the method of correcting the inclination in the charge voltage ratio method of the present invention. FIG. 4 is a cross-sectional view when the tip of the electrode is tilted. FIG. 5 is a cross-sectional view showing a structure in which a PTFE tube is provided at the tip of the probe electrode. FIG. 6 is a cross-sectional view showing a configuration in which a plurality of probe electrodes of FIG. 5 are arranged side by side. FIG. 7 is a perspective view showing a configuration in which a probe electrode is attached to a gimbal optical mount. FIG. 8 is a graph showing the results of Example 1 of the present invention. FIG. 9 is another graph showing the results of Example 1 of the present invention. FIG. 10 is a front view showing the apparatus configuration of the second embodiment of the present invention. FIG. 11 is a graph showing the results of Example 2 of the present invention. FIG. 12 is a side view for explaining the apparatus configuration of the third embodiment of the present invention. FIG. 13 is a graph showing the results of Example 3 of the present invention. FIG. 14 is an equivalent circuit of a measuring device that implements a conventional pulsed photoconduction method. FIG. 15 is a graph showing a charging waveform and an optical signal measured by the equivalent circuit of FIG.

Hereinafter, embodiments of the gap control method according to the present invention will be described with reference to the drawings.
The gap control method according to the present embodiment is an unevenness of the electrode surface that causes an error in the gap capacitance in the measurement of electrical characteristics in which the probe electrodes are arranged with a predetermined gap width in the semiconductor sample on which the dielectric film is formed. , And a method of correcting the inclination between the electrode surface and the sample surface.

FIG. 1 is a plane of the electrode tip showing a plurality of regions of a measuring electrode (hereinafter, also simply referred to as an electrode) to which the gap control method of the present invention is applied, when the electrode is divided at equal intervals along the radial direction thereof. It is a figure.
In FIG. 1, while the diameter (assumed as φ) of the electrode 1 is several mm, the period of the unevenness on the electrode surface is several μm, so that the period of the unevenness on the electrode surface is very large compared to the size of the electrode. Is small. Therefore, as shown in FIG. 1, the roughness of the entire electrode region can be known by measuring any one region of the region divided into k equal parts along the electrode diameter with a stylus type roughness measuring instrument. , The unevenness of the electrode surface of each of the regions 1, 2, ... K in FIG. 1 is approximated to be equal between the regions.

From the result of the roughness measurement, as shown in the cross-sectional view of the electrode tip in FIG. 2, the φ / k region is further divided into n pieces with reference to the most protruding point in the φ / k region. the displacement from the most where the projection is large _{W c2, W c3,} and · · · _{W cn,} the area of each region divided into n _{S 1, S 2, S 3} , and · · · _{S n.}
If the electrode is installed parallel to, as shown in FIG. 3 with respect to the sample surface, the gap capacitance C _k between the electrodes and the sample in the region of phi / k from the gap distance W _gap measured by the capacitance meter , Can be expressed by Equation 3.

The gap capacitance C _gap between the entire electrode and the sample surface is represented by Equation 4. α ₁ , α ₂ , α ₃ , ... α _k is the ratio of the area of the regions 1, 2, 3, ... k to the total surface area of the electrode.

Further, when there is an inclination θ between the surface of the electrode 1 and the surface of the sample 12 as shown in FIG. 4, the distance W ₂ between the electrode 1 and the surface of the sample 12 in each region 2, 3, ... K of the electrode, W ₃ , ..., W _k are represented by the formula 5, and the gap capacitance C _gap between the entire electrode 1 and the surface of the sample 12 is represented by the formula 6.

That is, if the inclination θ can be obtained, the gap capacitance C _gap considering the inclination θ between the entire probe electrode 1 and the surface of the sample 12 can be obtained by Equation 6, and the electrical characteristics of the sample are measured with high accuracy based on the gap capacitance C _gap. It becomes possible.

In the gap control method according to the present invention, the inclination θ between the entire probe electrode 1 and the sample surface is obtained as follows.
(1) After the rectangular wave pulse voltage is applied to the sample to complete charging the oxide film capacity, the sample is irradiated with an ultraviolet pulsed light and a transient signal change is observed. The charging voltage v (t) and the applied voltage V (t) at that time are measured, and an actual measurement plot of the charging voltage ratio v (t) / V (t) is obtained.

(2) Macro for calculating the charging voltage ratio (When the C _gap , C _box , and C _f values are set based on the equation (2), the v (t) / V (t) values at each gap width are calculated to obtain a theoretical curve. Using the program to be displayed), the theoretical curve of v (t) / V (t) with respect to the gap width is obtained.
In _obtaining this theoretical curve, since C _gap includes the slope θ as shown in equations (5) and (6), the θ value for _obtaining C _gap is appropriately assigned to obtain a curve that overlaps the actual measurement plot. Therefore, the inclination angle θ can be specified.

Further, in the present embodiment, in order to minimize the inclination between the probe electrode 1 and the sample 12, a probe electrode structure using an insulating synthetic resin material, for example, a PTFE (polytetrafluoroethylene) tube is adopted.
Since the material of the probe electrode 1 is metal, contact of the electrode 1 with the sample wafer 12 must be avoided due to concerns about metal contamination. In order to prevent metal contamination from the electrode 1 and reduce physical stress on the sample 12, the probe electrode structure as shown in FIG. 5 is adopted in this embodiment.

As shown in FIG. 5, a PTFE tube 4 (tubular PTFE material) is incorporated so as to be worn on the tip of the probe electrode 1. The gap between the tip of the PTFE tube 4 and the tip of the probe electrode 1 is adjusted in advance, and the tip of the PTFE tube 4 comes into light contact with the surface of the sample 12 to perform measurement in the adjusted gap state. Since the probe electrode 1 incorporating the PTFE tube 4 comes into contact with the sample surface, it needs to be automatically adjusted in the vertical direction according to the unevenness thereof. Therefore, as shown in the figure, the structure is such that the metal guide 6 to which the probe electrode 1 is attached can be swung in the vertical direction by the spring 7.

By this mechanism, as shown in FIG. 6, the gap mechanism can be made constant by following the unevenness of the sample 12. The reasons for selecting the PTFE material as the insulating synthetic resin material include high insulation, high heat resistance, and ease of processing.

Further, in the present invention, a gap width adjusting mechanism (referred to as a gimbal mechanism) using a gimbal optical mount may be adopted. By this mechanism, the probe electrode 1 can be adjusted so as to be parallel to the sample surface.
That is, as shown in FIG. 7, the probe electrode 1 is attached to the gimbal mechanism 21 to form an inclination adjusting mechanism. Further, in this case, it is desirable to measure the gap width between the probe electrode 1 and the sample 12 surface by attaching the capacitance displacement meter 9 next to the probe electrode 1.

As described above, according to the embodiment of the present invention, the charging voltage ratio v (t) / V (t) is actually measured by the pulsed photoconduction method, and the charging voltage ratio v with respect to the gap width in consideration of the inclination of the electrode. The ideal curve of (t) / V (t) was obtained, and the inclination θ of the electrode was specified. As a result, the gap capacitance C _gap can be obtained in consideration of the inclination θ between the entire electrode and the sample surface, and the electrical characteristics of the sample can be measured with high accuracy based on the gap capacitance C _gap .

The gap control method according to the present invention will be further described based on examples. In this example, the following experiment was performed based on the above embodiment.

(Example 1)
In Example 1, the inclination correction using the charge voltage ratio method was verified.
A sample in which an oxide film having a thickness of 82.9 nm was formed on a silicon wafer having a diameter of 300 mm was prepared. The cross section of the electrode used for the measurement was circular, the diameter was 3.15 mm, and a hollow with a diameter of 1 mm was formed in the center.

The graph of FIG. 8 shows the result of measuring the surface roughness of the electrode surface with a stylus type roughness measuring instrument. In the graph of FIG. 8, the horizontal axis is the moving distance (μm), and the vertical axis is the difference from the reference point (μm).
As shown in the graph of FIG. 8, the maximum height difference of the unevenness on the electrode surface was about 2.4 μm. Table 1 shows the calculation of the occupancy rate in the entire measurement area from the maximum height at intervals of 0.1 μm.

The distance from the reference in Table 1, _W C2, corresponds to · · · _{W Cn} in equation 3, _{S 1,} S 2 electrode area × occupancy in Equation 3 corresponds to · · · _{S n.}
When the electrode surface is divided into 10 equal parts in the radial direction, the occupancy rate of the region in the total electrode area is as shown in Table 2.

The occupancy rates in Table 2 correspond to α ₁ , α ₂ , ... α _k in Equation 4.
Then, according to the pulsed photoconduction method, a square wave pulse voltage was applied to the sample to complete charging the oxide film capacitance, and then the sample was irradiated with ultraviolet pulsed light to observe a transient signal change. When the actual measurement plot of the gap width and the charging voltage ratio v (t) / V (t) at that time is acquired, and the angle θ is given in the equations 2 and 6 so as to reduce the error from the actual measurement. The theoretical curve was calculated.

Specifically, when the macro (C _gap , C _oxide , C _f value) for calculating the charge voltage ratio of Equation 2 is set, the v (t) / V (t) value at each gap width is calculated, plotted, and a curve is drawn. By using a program that displays the theoretical curve), the θ value for _obtaining the C _gap was appropriately assigned, and the angle θ that overlaps with the measured plot was used as the temporary electrode inclination. The result is shown in the graph of FIG.
In the graph of FIG. 9, the horizontal axis is the gap width (μm), and the vertical axis is the charging voltage ratio (v (t) / V (t)). At this time, θ, which matches the measured plot, was 0.96 °.

Table 3 shows the error of the measured average value with respect to the theoretical curve considering the surface unevenness and inclination.

By giving θ = 0.96 °, as shown in Table 3, the theoretical curve could be calculated with an error of 5% or less in the range of 0.5 to 3.0 μm. Using the theoretical curve considering the surface unevenness and inclination, it was possible to obtain the corrected gap width from the charging voltage ratio measured at each point of the sample.

It is possible to measure the optical signal ΔV (td) with high accuracy by adjusting the electric field strength in the oxide film by the above procedure and performing the measurement by the pulsed photoconduction method.

(Example 2)
In Example 2, the PTFE tube (tubular PTFE material) probe structure was verified.
As an apparatus configuration, as shown in FIG. 10, a PTFE tube probe structure was applied to 10 probes to construct a mechanism for performing pulsed photoconduction measurement. The construction process is shown below.

(1) Connect the SMA adapter with ferrule (male) and the SMA adapter (female) attached to the optical fiber.
(2) Attach a PTFE tube to the tip of the ferrule portion of the SMA adapter with ferrule, and adjust the gap between the tip of the probe electrode (ferrule portion of the SMA adapter) and the tip of the PTFE tube.
(3) Attach the SMA adapter (female) to the metal guide using plastic screws. At this time, a mica plate for insulation between the metal guide and the SMA adapter and a spring for stabilizing the probe and adjusting the vertical position of the probe are incorporated.
(4) Repeat steps (1) to (3) above to attach 10 probes to the metal guide and arrange them in the radial direction of the wafer.
(5) Attach the metal guide to the forklift and fix it.

Regarding the above process (2), a mechanism capable of adjusting the gap between the tip of the probe electrode and the tip of the PTFE tube and measuring the gap is required. Therefore, a gap adjustment mechanism between the tip of the probe electrode and the tip of the PTFE tube was constructed. Specifically, the SMA adapter (female) was fixed to the stand with an arm, the stage (wafer chuck) was moved in the Z-axis direction, and the PTFE tube was pushed in to adjust the gap. After adjusting the gap, the stage was moved in the X-axis direction in the apparatus of FIG. 10, and the gap was measured by scanning the probe tip with a laser displacement meter.

The mechanism constructed above was constructed as a pulsed photoconductivity measurement system capable of acquiring a charging waveform and an optical signal, and pulsed photoconductivity measurement was performed. The sample wafer is a p-type silicon wafer on which a 10 nm-thick thermal oxide film is formed. The applied voltage was 6 V, and the delay time td from the voltage application to the pulsed light application was 1 msec.
As a result, as shown in FIGS. 11A to 11J, all probe Nos. 1-No. While observing the charging waveform for 10, the state of the gap was unified, and it was actually confirmed that the optical signal could be acquired with the adjusted probe.

(Example 3)
Further, in Example 3, the adjustment of the gap width in the pulsed photoconduction method measurement using the gimbal mechanism was verified.
As shown in FIG. 7, a probe electrode was attached to a gimbal optical mount (T-OMG-KT03U, manufactured by Zaber Technologies) to form a tilt adjusting mechanism. As a mounting method, an L-shaped jig using brass was prepared, and the probe electrode and the gimbal optical mount were connected. Further, as shown in FIG. 7, a capacitance displacement meter (MicroSense 4830 Nippon Laser Co., Ltd.) probe is attached next to the probe electrode to measure the gap width. As a mounting method, screwing was performed at a position about 50 μm higher in the Z-axis direction with respect to the probe electrode mounting position.
Specific methods for adjusting the gap width are shown in FIGS. 12 (a) to 12 (c).

(1) That is, as shown in FIG. 12 (a), a gap width of about 10 mm is opened between the probe electrode and the sample, and (θ, Φ) = (0,0) is pointed out by initializing the gimbal optical mount.
(2) Next, as shown in FIG. 12B, the gap width is manually adjusted to 1 μm with the capacitance displacement meter value.
(3) Finally, as shown in FIG. 12 (c), the drive is driven every ± 0.005 ° in the θ · φ axis direction so that the charging voltage value becomes maximum.

This mechanism was incorporated and the measurement was performed by the pulsed photoconduction method. The sample wafer is an N-type silicon wafer formed with a thermal oxide film having a thickness of 9.3 nm. The applied voltage is 6 V, t _d is 5 deg, and the gap width is 100 nm.
The measurement result is shown in FIG. FIG. 13A is a waveform before tilt adjustment, and FIG. 13B is a waveform after tilt adjustment. It was confirmed that the optical signal was greatly increased by adjusting the tilt by this mechanism.

As a result of the above examples, it was possible to accurately correct the waviness of the sample wafer and the sample holder, the inclination of the electrode, and the like in the gap control method between the electrode and the sample. As a result, it was confirmed that the measurement accuracy of the electric capacity measurement of the dielectric film formed on the semiconductor wafer and the interface state measurement of the dielectric pair film by the pulsed photoconduction method was significantly improved.

1 Probe electrode 4 PTFE tube 6 Metal guide 12 Sample 21 Gimbal mechanism

Claims (4)

The process of arranging the probe electrodes with a predetermined gap width for the semiconductor sample on which the dielectric film is formed, and
A step of actually measuring the charging voltage ratio v (t) / V (t) of the voltage V (t) applied from the probe electrode to the sample by the pulsed photoconduction method and the charging voltage v (t) of the sample. ,
The process of obtaining the ideal curve of the charging voltage ratio v (t) / V (t) with respect to the gap width W considering the inclination θ between the entire electrode and the sample surface, and
A step of specifying a slope θ at which the measured value of the charging voltage ratio v (t) / V (t) and the ideal curve match, and
A step of _obtaining a gap capacitance C _gap in consideration of the inclination θ is provided.
When the diameter of the electrode is Φ, the tip surface of the electrode is divided into k pieces in the radial direction (k is an integer of 2 or more), and the ratio of the region to the total surface area of the electrode is α _k , the distance between the entire electrode and the sample surface The gap width W _k considering the inclination θ is calculated by the following equation.

The gap width that does not consider unevenness and inclination is W _gap , the permittivity is ε ₀ , the region of φ / k is further divided into n pieces, and the displacement from the place with the largest protrusion is W _cn, and it is divided into n pieces. and the area of each region and S ₁ to S _n, the gap capacitance C _gap considering the inclination θ, the gap control method characterized in that it is determined by the following equation.

In the step of arranging the probe electrodes with a predetermined gap width for the semiconductor sample on which the dielectric film is formed,
A step of incorporating a tubular insulating synthetic resin material into the tip of the probe electrode and adjusting the gap between the tube tip and the electrode tip of the insulating synthetic resin material in advance.
The first aspect of claim 1, wherein the probe electrode is held swingably in the vertical direction, and the tip of the insulating synthetic resin material is brought into contact with the sample surface to adjust the gap. Gap control method. In the step of arranging the probe electrodes with a predetermined gap width for the semiconductor sample on which the dielectric film is formed,
The gap control according to claim 1, wherein the inclination is adjusted by attaching a probe electrode to the gimbal mechanism, and a capacitance displacement meter is provided next to the probe electrode to measure the gap width. Method. A method for measuring electrical characteristics, which comprises obtaining a gap capacitance C _gap by the gap control method according to any one of claims 1 to 3 and measuring electrical characteristics by a pulsed photoconduction method.

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