JPH1064965A - Method for measuring capacitance of sample using scanning capacitive microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method for two-dimensionally and efficiently measuring doping information of a sample through the use of a scanning capacitive microscope even if the sample us such that charge is partially trapped. SOLUTION: The probe of the scanning capacitive microscope is brought into contact with the surface of the semiconductor sample provided with an insulating film on the front surface and with an electrode on the rear surface so as to execute scanning (401). The tip of the prove is stopped at plural measuring points on the sample which are previously decided (402 and 403). At the respective stopped measuring points, bias voltage is applied between the electrode and the probe while it is changed in a previously decided and capacitance between the electrode and the probe is measured (404 and 405). The bias voltage dependence characteristic of capacitance at the plural measuring points of the sample is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the electrical characteristics of a semiconductor sample by using a scanning capacitance microscope (SCaM) or a scanning force microscope (SFM) and measuring the electrical characteristics of the semiconductor sample. And a method for obtaining a two-dimensional map of the electrical characteristics.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 7-32177 describes that a concentration distribution of implanted atoms of silicon subjected to ion implantation, that is, a doping profile is two-dimensionally measured by a scanning capacitance microscope. I have. Specifically, a bias voltage or an AC voltage is applied to the doped semiconductor sample, and the probe is moved two-dimensionally on the sample while measuring the capacitance between the probe and the sample. A method is described. In this method, the probe is vibrated, and the distance between the probe and the sample is controlled so that the vibration frequency and amplitude are constant, so that the distance between the probe and the sample is kept constant without bringing the probe into contact with the sample. The measurement is performed in the contact mode.

[0003]

When the capacitance between the probe and the sample is measured while scanning the surface of the sample with the probe, the bias voltage applied to the sample is generally kept constant. A method is used in which the measurement is carried out in a state of being held. This is because if the bias voltage is changed during the measurement, the force at which the probe is attracted to the sample surface changes due to the change in the bias voltage, so in the non-contact mode, it is necessary to control the distance between the probe and the sample. Because it becomes difficult. In addition, when the force that the probe is attracted to the sample surface changes, the distance between the two changes, and the capacitance also changes.Therefore, whether the change in the capacitance obtained by the measurement is due to the change in the space or the sample Must be separated by analysis to determine whether the change is due to a change in the doping amount. Therefore, there is a problem that signal processing becomes complicated.

On the other hand, the measurement method using a constant bias voltage as described above can measure the doping profile of a sample in the case of an ideal sample.
It is difficult to measure the doping profile when there is a region where charges are trapped on the sample surface, inside the sample, or at the interface within the sample. The reason is that the bias voltage dependence curve of the capacitance in the region where the charge is trapped depends on the presence or absence of the charge trap as shown in FIG.
This is for shifting in parallel to the bias voltage axis. For this reason, it is necessary to separate the change in capacitance due to charge trapping and the change in capacitance due to change in doping amount from the measurement results, but it is very difficult to separate them.

According to the present invention, there is provided a measuring method capable of two-dimensionally and efficiently measuring doping information of a sample using a scanning capacitance microscope, even for a sample in which charges are partially trapped. The purpose is to provide.

[0006]

In order to achieve the above object, according to the present invention, there is provided the following measuring method.

That is, a conductive probe is brought into contact with the surface of a semiconductor sample having an insulating film on the front surface and an electrode on the back surface,
While maintaining a constant force between the sample and the probe, the tip of the probe is relatively scanned up to one of a plurality of predetermined measurement points on the sample, and the Stopping the probe, applying a bias voltage to the electrode and the probe while changing the bias voltage within a predetermined range, and measuring the capacitance between the electrode and the probe during the application. By measuring the bias voltage dependence of the capacitance, while again maintaining a constant force between the sample and the probe,
The tip of the probe is scanned relative to the next measurement point out of a plurality of predetermined measurement points on the sample and stopped.
A bias voltage is applied between the electrode and the probe while changing the bias voltage within a predetermined range, and the measurement of the capacitance between the electrode and the probe is repeatedly performed, whereby the sample is obtained. This is a capacitance measuring method using a scanning capacitance microscope that measures the bias voltage dependence of capacitance at a plurality of predetermined measurement points.

[0008]

Embodiments of the present invention will be described with reference to the drawings.

First, the configuration of the scanning capacitance microscope used for the measurement in the present embodiment will be described with reference to FIG.

The sample 102 is a silicon 12 having a silicon oxide film 11 on the surface as shown in FIG. Silicon 1
The electrode film 13 is formed on the back surface side of the second electrode 2. Sample 1
02 is supported by the sample stage 103 as shown in FIG.
The sample stage 103 is provided with a piezo actuator 104 for driving the sample 102 in the XYZ directions. The scanner driving amplifier 401 is connected to the piezo actuator 104.

Further, as shown in FIG. 1, a cantilever 101 having a conductive probe 14 has a tip 102
It is arranged so that it may touch. This is because the measurement is performed in a contact mode in which the tip of the probe 14 contacts the surface of the sample 102. A semiconductor laser 201 and a two-division photodiode 203 are arranged above the cantilever 101 as shown in FIG. A laser power supply 202 is connected to the semiconductor laser 201. The signal processing device 204 is connected to the two-division photodiode 203. Further, a capacitance sensor 302 is connected to the cantilever 101. The output of the capacitance sensor 302 is input to the lock-in amplifier 303.

An AC / DC voltage supply source 301 is connected to the electrode film 13 of the sample 102. The AC / DC voltage supply source 301 is also connected to the capacitance sensor 302, and inputs a reference signal.

Laser power supply 202, signal processing device 20
4. The scanner driving amplifier 104, the AC / DC voltage supply source 301, and the lock-in amplifier 303
Control device 501 via D / D / A conversion board 503
It is connected to the. The control device 501 includes a CRT
502 is connected.

The control device 501 processes the measured signal while controlling the operation of each unit according to the procedure shown in the flowchart of FIG. 4 according to a program in a built-in storage device. Thereby, the capacitance of each predetermined point on the sample 102 is measured, a doping profile is created, and the CR
It is displayed on T502.

This will be described below with reference to the flowchart of FIG.

First, the control device 501 controls the semiconductor laser 2
In order to turn on 01, a control signal for instructing to supply a voltage to the laser power supply 201 is output. As a result, a voltage is supplied to the semiconductor laser 201 (see FIG. 5).
(B)), a laser beam is emitted. Semiconductor laser 201
Is emitted to the cantilever 101, and reflected light is received by the two-division photodiode 203.
The output signal of the two-division photodiode 203 is processed by the signal processing device 204 and the A / D / D / A conversion board 503
A / D converted by the controller and input to the control device 501. Thus, the amount of deflection of the cantilever 101 is detected by the optical lever method. The control device 501 controls the sample 102 so that the amount of deflection of the cantilever 101 is kept constant.
Forming a voltage signal for adjusting the height (Z direction) of the
The D / A is changed by the A / D / D / A conversion board 503 and output to the scanner driving amplifier 401. The scanner driving amplifier 401 amplifies the voltage signal to a predetermined magnification, and then applies the voltage signal to the piezo actuator 104 to displace the sample 102 in the Z direction. This allows
The force between the probe 14 of the cantilever 101 and the sample 102 is kept constant.

As described above, the probe 14 of the cantilever 101
The controller 501 causes the probe 14 of the cantilever 101 to scan to one position A among a plurality of predetermined measurement positions on the sample 102 while keeping the force between the sample and the sample 102 constant. . For this purpose, the control device 501 forms a voltage signal for scanning the sample 102 in the X and Y axis directions, performs D / A conversion by the A / D / D / A conversion board 503, and outputs the voltage to the scanner driving amplifier. Supply to 401. The amplifier 401 for driving the scanner amplifies this voltage signal to a predetermined magnification, and then applies it to the piezo actuator 104 (FIG. 5A). Thus, the tip of the probe 14 of the cantilever 101 reaches the position A on the sample 102. The controller 501 stops the tip of the probe 14 of the cantilever 101 at the position A by causing the scanner driving amplifier 401 to hold a voltage for scanning the X and Y axes of the piezo actuator 104 (FIG. 4). Step 401).

At time t1 when the predetermined position A is reached, the control device 501 outputs a control signal to the laser power source 202 to instruct the laser power supply 202 to stop supplying voltage. As a result, the semiconductor laser 201 is turned off (step 402). Further, the control device 501 causes the scanner driving amplifier 401 to supply the sample 10
The voltage for displacing 2 in the Z direction is held at the voltage at time t1 (step 403). Thus, the positional relationship between the cantilever 101 and the sample 102 in the Z direction is held.

Next, the controller 501 operates the AC / DC voltage supply 30 so as to output a bias voltage and an AC voltage.
Instruct 1 At this time, the control device 501 sets a minimum value V1 as a bias voltage value, and instructs it to linearly change this to a maximum value V2 during a predetermined time. The amplitude and frequency of the AC voltage are set to predetermined constant values. As a result, as shown in FIG.
A bias voltage that changes from the minimum value V1 to the maximum value V2 from t1 ′ to t1 ′ and an AC voltage having a constant frequency and amplitude are applied to the electrode film 13 on the back surface of the sample 102 (steps 404 and 405). . The minimum value V1 and the maximum value V2 are predetermined values so that the maximum value and the minimum value of C in the CV characteristic curve of the sample in FIG. 2 can be measured. However, V1 and V2 are C
The shift amount is taken into consideration so that the minimum value and the maximum value of C can be measured even when the -V characteristic shifts.

When a voltage is applied to the electrode film 13 on the back side of the sample 102, the sample 102 and the probe 14 are separated from each other by a MOS having the probe 14 as a gate electrode and the electrode film 13 as an ohmic electrode.
Make the structure. For example, when a negative voltage is applied to the electrode film 13, when the silicon 12 is p-type, a depletion layer 15 is generated in the silicon 12 immediately below the probe 14, and the capacitance between the probe 14 and the electrode film 13 is reduced. Decrease. The relationship between the capacitance and the applied voltage, that is, the CV characteristic depends on the thickness of the silicon oxide film 11 and the doping density of the silicon 12. Specifically, as the doping density increases, the difference between the maximum value and the minimum value of the capacitance, that is, the amount of change in the capacitance decreases. By utilizing the doping dependency of the CV characteristic,
The doping density at the measurement position of the sample 102 is obtained.

In steps 404 and 405, while the bias voltage and the AC voltage that change from the minimum value V1 to the maximum value V2 are applied to the electrode film 13 of the sample 102,
The capacitance sensor 302 detects the capacitance between the probe 104 and the electrode film 13. Lock-in amplifier 303
Detects the amplitude of a signal having the same frequency as the AC voltage applied to the sample 102 from the capacitance detected by the capacitance sensor 302 using a reference signal from the AC / DC voltage supply source 301. The output signal of the lock-in amplifier 303 indicates a dC / dV-V characteristic. The output signal of the lock-in amplifier 303 is A / D-converted by the A / D / D / A conversion board 503, taken into the control device 501, and stored in correspondence with the measurement position A on the sample 102.

At time t1 'when the bias voltage reaches the maximum value V2, the control device 501 sets the AC / DC voltage supply source 301 to a bias voltage value of zero (step 4).
06). Then, as shown in FIG. 5B, the laser power supply 202 is instructed to supply a voltage again, and the semiconductor laser 201 is turned on. In addition, the scanner driving amplifier 401
Release the hold of the direction position. Then, from the signal representing the deflection of the cantilever 101 obtained from the signal processing device 204, the amount by which the sample 102 is to be displaced in the Z direction is calculated and output to the scanner driving amplifier 401. As a result, feedback for keeping the amount of deflection of the cantilever 101 constant is restored, and the cantilever 101 and the sample 102 are restored.
Can be kept constant (step 4).
08) After that, returning to steps 401 to 408, the control device 501 moves the tip of the probe 14 to the next predetermined measurement position on the sample 102, holds the position of the probe 14, and sets the bias voltage. The routine for measuring the dC / dV-V characteristic is repeated while changing from the minimum value to the maximum value. As a result, dC / dV-V characteristic data at each of a plurality of measurement positions on the sample 102 is obtained.

After the measurement is completed, the control device 501 integrates the dC / dV-V characteristic data at each predetermined measurement position to obtain the CV characteristic (FIG. 2) at each measurement position. By calculating the difference between the maximum value and the minimum value of the obtained capacitance, the change amount of the capacitance is obtained. Control device 5
01 indicates the amount of change in capacitance at each measurement position and
By associating the above measurement positions with each other, a two-dimensional image representing the distribution of the amount of displacement of the capacitance on the sample 102 is created and displayed on the CRT 502. Note that the measurement position on the sample 102 is obtained from the scanning amount in the XY axis direction output to the scanner driving amplifier 401.

Since the amount of change in the capacitance depends on the doping density at the measurement position of the sample 102, the user can obtain a 102
The distribution of the above doping density can be known.

Further, the control device 501 determines whether the scanning amount in the XY-axis direction output to the
By associating the amount of displacement in the axial direction, the sample 102
A surface unevenness image is created and displayed on the CRT 502.

In the measuring method of the present embodiment, the sample 102
After stopping the probe 14 at each of the above points, as shown in FIG. 2, since the CV characteristics are measured while changing the bias voltage in a wide range, the amount of change in the obtained capacitance is obtained. Is
It is not affected by the shift of CV characteristics due to charge trapping, and depends only on the doping density of the sample 102. Therefore, even when there is a region where charges are trapped in the sample 102, the distribution of the doping density of the sample can be accurately detected without being affected by this.

In the measuring method according to the present embodiment, the semiconductor laser 2 is stopped while the probe is stopped at the measuring point on the sample.
01 is turned off. Thereby, the semiconductor laser 201
By irradiating the sample 102 with a part of the laser light, it is possible to avoid a change in measurement conditions such as generation of electric charge in the sample 102. Therefore, the amount of change in capacitance can be measured more accurately.

Further, in the measurement method of the present embodiment, since the measurement is performed in the contact mode in which the tip of the probe 14 of the cantilever 101 is brought into contact with the surface of the sample 102, even if the bias voltage is changed, The distance between the probe 14 and the sample 102 does not change unlike the contact mode. Therefore, there is no need to consider a change in capacitance due to a change in the distance between the probe 14 and the sample 102, and the doping density is detected by simple signal processing that simply integrates the output of the lock-in amplifier 303 as it is. be able to.
Moreover, in the present embodiment, at the same time, the sample surface shape can be obtained by SFM (scanning force microscope) in the constant force mode.

As described above, in the measuring method of the present embodiment, while the probe is being scanned in the contact mode, the sample is temporarily stopped at each point of the sample, and the bias voltage is changed at each point to obtain d.
By using the method of measuring the C / dV-V characteristic,
Even for a sample in which charges are partially trapped, the doping density distribution of the sample can be efficiently measured with high accuracy and simple signal processing.

In this embodiment, dC / dV-V
While the characteristics are being measured, the semiconductor laser 201 is turned off to prevent a change in the measurement conditions due to the irradiation of a part of the laser beam to the sample 102.
1 instead of turning off the semiconductor laser 20
It is also possible to use a method of blocking the laser light by means such as disposing it in the optical path between the sample 1 and the sample 102.

In the present embodiment, the CV characteristic is measured a plurality of times by changing the bias voltage a plurality of times from the minimum value to the maximum value at each measurement point on the sample. It is also possible to adopt a configuration in which an average value of the amounts is obtained. As a result, the amount of change in the capacitance can be obtained with higher accuracy. In this case, a boxcar circuit can be used to determine the average value.

The direction of changing the bias voltage is as follows.
Not only in the direction of changing from the minimum value to the maximum value, but also in the direction from the maximum value to the minimum value.

In this embodiment, the control device 501
Is obtained by integrating the measured dC / dV-V characteristic to obtain a CV characteristic, further obtaining an amount of change in capacitance from the CV characteristic, and using this distribution as a two-dimensional image as a CR.
Although displayed in T502, the physical quantity to be displayed is
Not only the change amount of the capacitance but also another physical amount such as a peak value of the dC / dV-V characteristic can be displayed. In this case, only the peak value can be measured without measuring the entire dC / dV-V characteristic at the time of measurement.

[0034]

As described above, according to the present invention,
It is possible to provide a measurement method capable of efficiently measuring two-dimensionally doping information of a sample in which charges are partially trapped by using a scanning capacitance microscope.

[Brief description of the drawings]

FIG. 1 shows an MO constituted by a probe 14 and a sample 102 in a capacitance measuring method using a scanning capacitance microscope according to the present invention.
Sectional drawing which shows S structure.

FIG. 2 is a graph showing that a bias voltage curve of capacitance of a sample shifts due to trapping of charge of the sample.

FIG. 3 is a block diagram showing a configuration of a scanning capacitance microscope used in the measurement method according to one embodiment of the present invention.

FIG. 4 is a flowchart showing a control procedure of a control device in the measurement method according to one embodiment of the present invention.

FIG. 5 shows a measurement method according to an embodiment of the present invention.
(A) a graph showing a scanning signal applied to the piezo actuator 104, (b) a graph showing a supply voltage to the semiconductor laser, and (c) a graph showing a bias voltage applied to the sample 102.

[Explanation of symbols]

11: silicon oxide film, 12: silicon, 13
... electrode film, 14 ... probe, 101 ... cantilever, 102 ... sample, 103 ... sample stage, 104
... Piezo actuator, 201 ... Semiconductor laser, 202 ... Power supply for laser, 203 ... Divided photodiode, 204 ... Signal processing device, 301 ...
・ AC / DC voltage supply source, 302: capacitance sensor, 303: lock-in amplifier, 401
・ Scanner driving amplifier, 501 ・ ・ ・ Control device, 5
02 ... CRT, 503 A / D / D / A conversion board.

Claims (9)

[Claims] 1. A method according to claim 1, wherein a conductive probe is brought into contact with the surface of the semiconductor sample having an insulating film on the front surface and an electrode on the back surface, and the force between the sample and the probe is kept constant. The tip of the probe is relatively scanned up to one of a plurality of predetermined measurement points on the sample, the probe is stopped on the measurement point, and a bias is applied between the electrode and the probe. By applying a voltage while changing the voltage within a predetermined range, and measuring the capacitance between the electrode and the probe during that time, the bias voltage dependence of the capacitance is measured, and the sample is again measured. While maintaining a constant force between the probe and the probe, the tip of the probe is scanned relative to the next measurement point out of a plurality of predetermined measurement points on the sample, and stopped. A bias voltage is applied between the electrode and the probe while changing the bias voltage within a predetermined range. Then, by repeatedly measuring the capacitance between the electrode and the probe, measuring the bias voltage dependence of the capacitance at a plurality of predetermined measurement points on the sample. Characteristic method of measuring capacitance using a scanning capacitance microscope. 2. The method according to claim 1, wherein a difference between a maximum value and a minimum value of the capacitance is obtained from the bias voltage dependence of the capacitance for each of the measurement points. A capacitance measuring method using a scanning capacitance microscope, wherein a two-dimensional image representing the distribution of the difference on the sample is created and displayed by associating the position with a position. 3. The method according to claim 1, wherein an AC voltage having a predetermined frequency is applied between the electrode and the probe together with the bias voltage in order to measure a bias voltage dependence characteristic of the capacitance. , By detecting the amount of change in the capacitance between the electrode and the probe in the same frequency component as the frequency, dC / dV (where C is the capacitance and V is the bias voltage A bias voltage dependence characteristic of the capacitance is measured and integrated to obtain a bias voltage dependence characteristic of the capacitance, thereby obtaining a capacitance measurement method using a scanning capacitance microscope. 4. The method according to claim 1, wherein a force applied to the probe is measured in order to maintain a constant force between the sample and the probe, and the sample is moved so that the force is constant. A method for measuring capacitance using a scanning capacitance microscope, wherein the capacitance is moved in a vertical direction relative to a probe. 5. A two-dimensional image representing the shape of the sample surface is created and displayed by associating the amount of vertical movement of the sample with the amount of scanning of the tip of the probe. A capacitance measuring method using a scanning capacitance microscope. 6. The method according to claim 4, wherein in order to measure a force applied to the probe, a probe with a cantilever is used as the probe, and the reflected light is detected by irradiating light to the cantilever. A method for measuring capacitance using a scanning capacitance microscope, wherein the amount of deflection of a cantilever is detected. 7. A scanning capacitance microscope according to claim 6, wherein irradiation of light to said cantilever is stopped while measuring capacitance between said electrode and said probe. How to measure capacitance. 8. A scanning capacitance microscope is brought into contact with an insulating film on the surface and a probe of a scanning capacitance microscope on the surface of a semiconductor sample provided with an electrode on the back surface, and the tip of the probe is brought into contact with a plurality of predetermined points on the sample. Stop at each of the measurement points, and apply a bias voltage between the electrode and the probe while changing the bias voltage within a predetermined range at each of the stopped measurement points. A bias voltage dependence characteristic of the capacitance at a plurality of measurement points of the sample by measuring the capacitance of the sample. A method for measuring capacitance using a scanning capacitance microscope. 9. A sample stage for mounting a sample, a conductive probe, scanning means for scanning the probe relatively to the sample, and a force between the probe and the sample. To detect
Force holding means for vertically moving the sample relative to the probe in order to keep the force constant, bias voltage applying means for applying a bias voltage between the probe and the sample, It has a capacitance measuring means for measuring the capacitance between the probe and the sample, and a control means, wherein the control means, the force holding means, between the sample and the probe While keeping the force constant, the scanning means relatively scans the tip of the probe to one of a plurality of predetermined measurement points on the sample, and moves the tip of the probe over the measurement point. To the stop, the bias voltage applying means, while applying a bias voltage between the electrode and the probe while changing it in a predetermined range, between the electrode and the probe between the By causing the capacitance measuring means to measure the capacitance, By repeatedly instructing the measurement of the bias voltage dependence characteristic of the capacitance, the scanning bias characteristic dependence of the capacitance is measured at a plurality of predetermined measurement points on the sample. Volume microscope.