JP2002055040A - Physical quantity measurement device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To accurately measure the surface potential of, for example, a photoreceptor as a sample, by shortening the time until the start of physical quantity measurement. The distance between a probe and a surface of a sample is controlled by a distance control unit based on an output value of a distance measurement unit when the probe approaches and departs from the surface of the sample. , It is possible to perform the approach operation at high speed and without collision between the probe 2 and the surface of the sample 1, thereby shortening the time until the start of the physical quantity measurement, For example, for example, the surface potential of the photoconductor can be accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a physical quantity measuring device used for a scanning probe microscope, a scanning force microscope, a high-resolution surface electrometer, a shape measuring device, and the like.

[0002]

2. Description of the Related Art A first conventional example relating to a physical quantity measuring device (see Japanese Patent Application Laid-Open No. Hei 6-308180) will be described with reference to FIG. A cantilever 3 serving as a spring having a probe 2 (conductive needle) at the tip is provided at an upper position facing the sample 1.
The cantilever 3 has a base 4 at one end.
It is supported by and constitutes a cantilever. An adder 6 is connected to such a cantilever via an amplifier 5. In this case, the AC voltage at the frequency ω _ac and the frequency ω
_{When a} voltage on which an AC voltage of _ac / 2 and a DC bias voltage Vb are superimposed is applied to the adder 6, an electrostatic attractive force acts between the surface of the sample 1 and the probe 2, and the cantilever vibrates. I do. A mirror 7 is connected to the position of the cantilever 3 opposite to the probe 2, and this mirror 7 and a semiconductor laser (LD)
The laser beam is detected between the photodetector 8 and the photodetector (PD) 9 by the so-called optical lever principle. Thereby, PD9
The vibration state of the cantilever can be known from the detected light amount. Therefore, assuming now that the potential difference between the surface of the sample 1 and the probe 2 is V, the distance between the surface of the sample 1 and the tip of the probe 2 is Z, and the capacitance is C, the electrostatic attractive force F _es is

[0003]

(Equation 1)

[0004] When the surface potential of the sample 1 is Vs, V is

[0005]

(Equation 2)

[0006] Therefore, F _es is

[0007]

(Equation 3)

[0008] Here, _assuming that ω _ac is the resonance frequency ω _{o of the} cantilever, the electrostatic attractive force F _{es ωac} , which is a component of ω _ac of F _es , is

[0009]

(Equation 4)

And resonate. Therefore, the output v of the preamplifier 10 indicating the vibration of the cantilever caused by F _esωac is:

[0011]

(Equation 5)

## EQU1 ## Note that a is a proportional constant. Φ ₁ = φ (6) φ ₂ = (− π / 2) + φ (7) where φ is the phase difference between the phase of the force F _esωac and the resonance vibration caused by F _esωac. .

In this case, the first term in the equation (5) is the frequency ω
₀ represents the vibration caused by the first AC voltage, and the phase φ ₁
Is based on the phase of the applied first AC voltage.
The phase φ ₁ is determined from the first AC voltage to the lock-in amplifier 1
Reference signals given to the reference numerals 1 and 12 are used as a reference.
(5) the second term in the equation represents the vibration generated by the AC voltage of a frequency ω _0/2, the phase phi ₂ is based on the phase of the second alternating voltage applied. The phase φ ₂ is based on a reference signal supplied to the lock-in amplifiers 11 and 12 from the second AC voltage. The phases of the first AC voltage and the second AC voltage match. Further, the AC signal asin (ωt + ψ) is converted into the lock-in amplifiers 11 and 12 by the phase θ.
The output V at the time of phase detection and amplification by

[0014]

(Equation 6)

## EQU1 ## A is a proportional constant. Here, when equation (5) is applied to equation (8),

[0016]

(Equation 7)

## EQU1 ## Here, ω _ac is completely matched with the mechanical resonance frequency ω ₀ of the cantilever (ω _ac = ω ₀ ).
And φ = −π / 2. Substituting this into equation (9) gives

[0018]

(Equation 8)

## EQU1 ## If v is phase-detected and amplified by the lock-in amplifier 11 at the phase θ = θ ₁ = −π / 2, the output V ₁ of the lock-in amplifier 11 becomes the phase θ = θ in the equation (10).
₁ = −π / 2 is substituted. Also, the phase θ = θ
If the lock-in amplifier 12 detects and amplifies v at ₂ = −π, the output V ₂ of the lock-in amplifier 12 becomes (1
Equation (0) is obtained by substituting the phase θ = θ ₂ = −π. An integrator 13 is connected to the lock-in amplifier 11,
A comparator 14 and an integrator 15 are connected to the lock-in amplifier 12. Here, V ₁ and V ₂ are:

[0020]

(Equation 9)

Can be expressed as A ₁ and A ₂ are proportional constants.

As described above, the amplitudes of the first term and the second term in the parentheses in the equation (5) can be separated. Thus, by controlling the Vb so V ₁ is becomes 0, (∂C /
Regardless of ∂Z), the surface potential of the sample 1 can be measured from the value of Vb. Further, the apparatus of FIG. 6, such that a constant value of V _2, because controlling the Z-axis actuator 16, (image obtained from the actuator control voltage) Topozo's constant (∂C / ∂Z) It becomes an image. In this case, if the capacity of the insulating film of the sample 1 is sufficiently larger than the capacities of the tip of the probe 2 and the cantilever, the topo image shows the surface shape of the sample 1. Therefore, from this, the surface potential and the surface shape (physical quantity) of the sample 1 can be measured simultaneously.

Next, a second conventional example (observation of the surface potential of an organic thin film by a scanning Maxwell stress microscope, see IETF 92-3) will be described with reference to FIG. An AC voltage having a frequency ω and a DC bias voltage Vb are input to the adder 6, and a voltage obtained by superimposing these two voltages is applied to a conductive cantilever. This applied voltage causes an electrostatic attraction between the surface of the sample 1 and the tip of the probe 2, and the cantilever vibrates. Assuming that the potential difference between the probe 2 and the surface of the sample 1 is V, the electrostatic attractive force F _es is

[0024]

(Equation 10)

## EQU1 ## Here, assuming that the surface potential of the sample 1 is Vs, V is expressed as follows: V = Vb−Vs + _VA sinωt (14) Therefore, F _es is

[0026]

[Equation 11]

## EQU2 ## F _{esω which} is the ω component and 2ω component of F _es is

[0028]

(Equation 12)

The cantilever vibrates due to this _Fesω . Here, ω is a frequency equal to or lower than の of the mechanical resonance frequency of the cantilever. As a result, the output v of the preamplifier 10 indicating the vibration of the cantilever caused by F _esω is:

[0030]

(Equation 13)

## EQU1 ## Here, a is a proportional constant.

Here, V ₁ is obtained by phase-detecting and amplifying v by the lock-in amplifier 11 using the reference signal of the frequency ω, and V ₁ is obtained by the lock-in amplifier 12.
V ₂ is obtained by performing phase detection amplification using the reference signal of ω. These values of V ₁ and V ₂ are:

[0033]

[Equation 14]

Represented as A ₁ and A ₂ are proportional constants.

As described above, the amplitudes of the first term and the second term in the parentheses in the equation (17) can be separated. Thus, by controlling the Vb so V ₁ is becomes 0, (∂C
/ ∂Z), the surface potential of the sample 1 can be measured from the value of Vb.

In the apparatus shown in FIG. 7, the Z-axis actuator 16 is controlled so as to keep the value of V ₂ constant.
The top image (image obtained from the actuator control voltage) is an image in which (ΔC / ΔZ) is constant. In this case, if the capacity of the insulating film of the sample 1 is sufficiently larger than the capacities of the tip of the probe 2 and the cantilever, the topo image shows the surface shape of the sample 1. Therefore, from this, the surface potential and the surface shape of the sample 1 can be measured at the same time.

Next, a third conventional example will be described with reference to FIG. The apparatus shown in FIG. 8 is an example in which a personal computer 17 and a coarse actuator 16a are connected to the apparatus shown in FIG.
The distance between the probe 2 and the surface of the sample 1 before starting the measurement of the physical quantity is far greater than the distance at the time of scanning / actual measurement. A so-called approach operation to approach the distance at the time of measurement is required. In this case, since the output value of the lock-in amplifier 12 indicates the distance between the tip of the probe 2 and the surface of the sample 1, while monitoring the output value with the personal computer 17,
When the distance between the probe 2 and the surface of the sample 1 approaches a fixed value, the coarse movement actuator 16a is stopped to perform the approach operation. Then, the surface potential and the surface shape (physical quantity) of the sample 1 can be measured from the bending of the cantilever 3 due to the electrostatic attraction acting between the surface of the sample 1 and the probe 2 and the change in the vibration state. .

Next, a fourth conventional example (Tunnel current unit by surface micromachining, microscience and engineering, micromachining joint research material MP94-61, M
M94-61) will be described with reference to FIG. The probe 18 constituting the tunnel current unit and the support spring 1
9, the spring portion 20 of the electrostatic actuator is a movable portion, the other ground pad 21, the drive pad 22 of the electrostatic actuator, and the current detection pad 23 facing the probe 18 are fixed portions, It is fixed to a substrate (not shown) via an oxide film. Between the current detection pad 23 and the drive pad 22, a current-to-voltage converter (I
VC) 24, a computing unit 25, and an integrator (Ki / s) 26
And are connected.

In this case, the probe 18 is
9, via the ground pad 21 to the ground potential. On the other hand, a constant DC voltage with respect to the ground potential is applied to the current detection pad 23 by the tunnel bias. Now, in such a state, when the tip of the probe 18 approaches the current detection pad 23 in units of nanometers, a tunnel current flows between them. Current-voltage converter (IVC) 2
Numeral 4 converts the tunnel current into a voltage, and a calculator 25 calculates a deviation between the converted voltage value and the reference signal. The deviation value is calculated via an integrator (Ki / s) 26 by an electrostatic actuator. Is fed back to the drive pad 22.
When a voltage is applied to the drive pad 22 in this manner, an electrostatic attraction acts between the comb portion on the drive pad 22 side and the comb portion of the support spring 19, thereby causing the probe 18 of the movable portion to move. Displace. The displacement amount in this case corresponds to, for example, an amount by which the distance between the tip of the probe 18 and the current detection pad 23 changes due to disturbance or the like, and the distance between the two is kept constant.

Next, a fifth conventional example (OPTRONICS, 1992, N
o.9, p.97) will be described with reference to FIGS. As shown in FIG. 10, a cantilever 28 is provided at the center of the substrate 27, and an optical waveguide 29 is formed on the cantilever 28 along the direction in which it extends. Fixed portion 3 of substrate 27 sandwiching the gap at the tip of cantilever 28
On 0, an optical waveguide 31 having an end face 31a facing the end face 29a of the optical waveguide 29 is formed. In the substrate 27 having such a structure, the light propagating through the optical waveguide 29 is applied to the end face 2 located at the tip of the cantilever 28.
9a, the emitted light enters from an end face 31a facing the light, recombines, and propagates through the optical waveguide 31. In this case, as shown in FIG. 11A, when the cantilever 28 is not deformed, the optical waveguides 29 and 3 are not deformed.
Since there is no optical axis shift between the two, the amount of light to be propagated does not decrease. However, as shown in FIG.
When the cantilever 28 is deformed, an optical axis shift occurs, and the amount of light incident on the optical waveguide 31 decreases. Accordingly, since the amount of light propagated varies according to the amount of deformation (bending amount) of the cantilever 28, the amount of deformation of the cantilever 28 can be easily measured by detecting the amount of light on the optical waveguide 31 side. can do. Examples of this application include a pressure sensor, an acceleration sensor, and a flow sensor.

Next, a sixth conventional example (Japanese Journal o)
f Applied Physics, Vol. 28, No. 2, Feb., 1989, p. 287
Will be described with reference to FIG. A cantilever 33 is provided on the substrate 32. In the vicinity of the root of the cantilever 33, an optical waveguide 34 is provided orthogonal to the extending direction of the beam.
Are formed. On the fixed portion 35 of the substrate 32, an optical waveguide 36 is formed in a state parallel to the optical waveguide 34. In this case, the optical waveguide 34 is a signal detecting waveguide for detecting the amount of deformation of the cantilever 33, and the optical waveguide 36
Is a reference waveguide, and both branches into a Y-shape, merges, and is connected to the optical waveguide 37. In the substrate 32 having such a structure, the optical waveguide 34 is deformed in accordance with the deformation of the cantilever 33, whereby the refractive index changes and the phase of light propagating in the waveguide changes. The amount of deformation of the cantilever 33 can be measured by such a phase change.

Here, the principle of operation for detecting a signal based on such a phase change will be described using a Mach-Zehnder interferometer having a basic structure shown in FIGS. The deformation area corresponding to the cantilever beam 33 in FIG.
Corresponds to the region A (diaphragm portion of the fine structure).
The light whose phase has changed through the optical waveguide 34 on the deformable region A and the light whose phase does not change through the optical waveguide 36 on the fixed portion 35 join at the Y-shaped branch portion and are combined at the optical waveguide 37. When multiplex interference occurs, the light intensity of the light output from the optical waveguide 37 changes depending on the phase of both lights. in this case,
As shown in FIG. 14A, when both lights are in phase,
The zero-order mode is excited by the multiplexing, and the amount of light output from the optical waveguide 37 becomes maximum. FIG.
As shown in FIG. 4B, when both lights are out of phase, the first-order mode is excited, so that a light wave is radiated to the outside of the waveguide (in the case of a single mode waveguide). Is not output. By measuring the amount of light output from the optical waveguide 37 in this manner, the deformation amount of the region A, ie, the cantilever 33, can be measured.

Another example of detecting a signal based on a phase change will be described with reference to FIGS. As shown in FIG. 15, two optical waveguides 38 and 39 are provided on a substrate 32.
Are formed, and these optical waveguides 38 and 39 intersect with the optical waveguides 34 and 36 at the X-shaped branch portions. In this case, the width of the optical waveguide 39 is smaller than that of the optical waveguide 38. The reflection mirror 4 is provided on the end face of the substrate 32.
0 is provided. Such a structure functions as a mode divider. First, the light incident from the wide optical waveguide 38 on the left side is split 1: 1 at the branch portion, propagates in the optical waveguides 34 and 36, is reflected by the reflection mirror 40, and is again split at the branch portion. Come back to. At this time, if both lights are in phase as shown in FIG. 16A, the 0th mode is excited, and the light propagates toward the optical waveguide 38 having a wide width. If both lights are out of phase as shown in FIG. 16B, the first mode is excited, and the light propagates toward the optical waveguide 39 having a narrow width. As described above, whether or not the light is in phase is determined by the deformation amount of the cantilever 33 in the region A, that is, by measuring the amount of light returning to the optical waveguides 38 and 39 to measure the deformation amount of the cantilever 33. can do.

[0044]

In the first and second conventional examples (see FIGS. 6 and 7), the frequency ω _{ac of the} AC voltage is completely matched with the mechanical resonance frequency ω ₀ of the cantilever. . Therefore, as described in equation (10), φ = −π
/ 2, the phase θ =
At −π / 2, the phase θ = −π by the lock-in amplifier 12.
, The amplitudes of the first and second terms in parentheses in equation (5) can be separated and obtained as shown in equations (11) and (12).

However, the mechanical resonance frequency ω ₀ of the cantilever shifts little by little due to the influence of ambient temperature, humidity, air pressure, etc. during several measurements. On the other hand, since the frequency ω _{ac of the} AC voltage is stable, it does not change. For this reason, ω ₀ and ω _ac do not match with time. Further, near the resonance point of the cantilever, a change in the phase with respect to the deviation of the resonance frequency is very large, and the difference between φ and −π / 2 cannot be ignored due to a slight deviation of the resonance point. On the other hand, the phases at which the lock-in amplifiers 11 and 12 perform phase detection remain θ ₁ = −π / 2 and θ ₂ = −π adjusted at the beginning of the measurement.
Therefore, it is not possible to separate the first and second terms in parentheses in equation (5), as in equations (11) and (12).

For example, it is assumed that φ = −π / 2 + Δφ because ω ₀ = ω _ac is not satisfied. At this time,

[0047]

(Equation 15)

Is as follows. Here, the output V ₁ of the lock-in amplifier 11 when θ = θ ₁ = −π / 2, and θ = θ ₂ =
The output V ₂ of the lock-in amplifier 12 at −π is

[0049]

(Equation 16)

Is as follows. As can be seen from the equations (21) and (22), since Δφ ≠ 0, the first and second terms in parentheses in the equation (5) are not separated, and the signal V ₁ for measuring the surface potential is used. Contains the amplitude of the second term in parentheses in equation (5) for measuring the surface shape. Further, a signal for measuring the surface shape V ₂ in for measuring the surface potential (5)
The amplitude of the first term in parentheses in the formula is mixed. That is,
This means that the surface potential mixes and interferes with the measurement result of the surface shape, and the surface shape mixes and interferes with the measurement result of the surface potential. Thus, conventionally,
Since the resonance frequency ω _{0 of the} cantilever slightly fluctuates due to the influence of ambient temperature, humidity, and atmospheric pressure, the surface potential of the sample 1 and the measurement result of the surface shape interfere with each other, resulting in a non-negligible error. Appears.

Next, a third conventional apparatus (see FIG. 8)
Is obtained by adding a coarse actuator 16a and a personal computer 17 to the apparatus shown in FIG. 7, and the output of the lock-in amplifier 12 in this case is

[0052]

[Equation 17]

Is as follows. Here, if the capacity of the insulating film of the sample 1 is sufficiently larger than the tip of the probe 2 and the capacity of the cantilever, (∂C / ∂Z) is only the distance between the probe 2 and the surface of the sample 1. Dependent function, which allows V
_{From 2,} the distance between the tip of the probe 2 and the surface of the sample 1 can be measured. 8, the output of the lock-in amplifier 12 is monitored by the personal computer 17, and the probe 2 and the sample 1 are monitored.
When the distance to the surface approaches a fixed value, the coarse movement actuator 16a is stopped to perform the approach. On the other hand, the capacitance C between the tip of the probe 2 and the substrate of the sample 1 can be approximated to a parallel plate capacitor, and C = ε (S / Z) (23) Here, S is the area of the capacitor electrode, and ε is the dielectric constant of the dielectric between the electrodes. Thereby, (∂C / ∂
Z)

[0054]

(Equation 18)

Is as follows. From equation (25), V ₂ is inversely proportional to the square of Z.

On the other hand, in the development process of electrophotography, there is a demand to measure a surface potential distribution of a portion irradiated with a beam spot after writing on a photosensitive member sample with a laser beam. In this case, in the apparatus shown in FIG. 8, the sample 1 is charged by a charger in advance at a distance from the probe 2 and irradiated with a laser beam. Then, the sample 1 is moved below the probe 2, and the probe 2 and the sample 2 are moved. After approaching the surface, measurement of the surface potential distribution of the sample 1 is started. In this case, the photoreceptor sample is charged on the surface after electrification,
Even if no light is irradiated, the surface potential gradually decreases, which is a so-called dark decay characteristic. Although the speed of the dark decay varies depending on the conditions, in the case of a general photoconductor, the surface potential becomes about 80% of the initial value about 5 minutes after charging. For this reason, when measuring a photoconductor sample, it is preferable that the measurement be completed within about 5 minutes after charging. In fact, when measuring the surface potential of the photoreceptor with the apparatus of FIG.
It takes about 3 minutes. Such time is taken for the following reasons.

After the charging / exposure, the distance Z between the probe 2 and the surface of the sample when the sample 1 is moved directly below the probe 2 is several meters.
In contrast to m, Z at the time of measurement must be about 0.5 μm in order to obtain a sufficient resolution. Therefore,
In the approach step, Z is changed from several mm to 0.5 μm (1 μm) without collision between the tip of the probe 2 and the surface of the sample 1.
/ 100). During approach, the signal is detected the Z personal computer 17 is based on controlling the coarse actuator 16a is V _2, (2
5) As shown in the equation, it is inversely proportional to the square of Z. Therefore, at the time of approach, Z is reduced from several mm to 0.5 μm by about 1 /
Since it is 100, the value of V ₂ is about 10,000 times.
That is, V ₂ rapidly increases as Z decreases. Conversely, if the probe and the sample surface do not come close,
V ₂ will not have sufficient sensitivity to Z. If the apparatus of FIG. 8, negative feedback from the output of the V ₂ to the personal computer 17 is coarse actuator 16a, for performing the approach, when performing high-speed approaches, sufficient negative feedback to approach the value at Z measurement The probe 2 and the sample surface collide. For this reason, the approach must be performed slowly, and the approach takes time. As described above, the approach takes a long time, so that the dark decay of the photoconductor proceeds, and the error from the initial state to be measured increases.

As means for performing a high-speed approach, the distance ds between the probe 2 before the approach and the sample surface is used.
The measured beforehand from the output of the V _2, from the distance do between the predetermined probe tip at the time of measurement and the sample surface, the coarse actuator 16a calculates the distance ds-do should move during approach There is a method in which the personal computer moves the coarse actuator by that distance to approach the sample 1 and set the distance between the tip of the probe 2 and the sample surface to ds. However, also in this case, since V ₂ is inversely proportional to the square of the distance Z, if Z = ds (several mm) before the approach, V ₂ does not have sufficient sensitivity to the distance, and the probe 2 The distance between the tip of the sample and the sample surface cannot be measured accurately. Therefore, it is not possible to know the exact distance that the coarse movement actuator 16a should move, and the tip of the probe 2 collides with the sample surface during approach.

FIG. 17 shows an example in which the tunnel current unit of the fourth conventional example (see FIG. 9) is applied to surface potential measurement. The probe 18 has a support spring 19,
The output of the amplifier 41 is applied via the ground pad 21. The support spring 19 is deformed and vibrates due to electrostatic attraction acting between the surface potential of the sample 1 and the potential of the probe 2. The deformation and vibration are caused by the driving pad 2 constituting the electrostatic actuator.
It appears as a change in capacitance between the second comb electrode and the comb electrode of the support spring 19. By measuring the capacitance between the comb teeth with the capacitance meter 42, the deformation and vibration of the probe can be measured. However, when measuring a surface potential of 1 KV in electrophotography, the potential of the probe is equal to the surface potential of the sample 1 and is about 1 KV.
Therefore, the input terminal of the capacitance meter 42 connected to the ground pad 21 also has a high voltage of 1 KV. Therefore, the capacity meter 42
When the pressure exceeds the withstand voltage limit, the probe 18 is damaged or causes a large measurement error, so that the vibration of the probe 18 cannot be measured.

Next, in order to measure the surface potential of the photosensitive member, the measurement must be completed within a few minutes as described above. In order to realize this, it is necessary to perform the approach quickly and to shorten the actual measurement time. For that purpose, it is necessary to set the resonance frequency of the cantilever 3 in FIG. 6 to be high. In order to set the resonance frequency high, it is easiest to increase the spring constant of the cantilever 3, but when this is done, the interaction (electrostatic attraction) acting on the probe 2
, The bending of the cantilever 3 becomes smaller, and the sensitivity decreases. Therefore, as a method of increasing the resonance frequency and suppressing the increase in the spring constant, the entire size of the cantilever 3 may be reduced similarly (so-called shrink). Therefore, a micro cantilever 43 manufactured by a semiconductor processing process having dimensions as shown in FIG. 18 is used. That is, the length L of the cantilever 3 is 450 μm and the width Wa is 30
μm, thickness D = 2.2 μm, height H of the probe 2 = 13
μm.

On the other hand, the surface potential distribution V (x) with respect to the sample surface coordinate x when a laser beam having a spot diameter of 2 W is irradiated around the coordinate X = 0 is

[0062]

[Equation 19]

Can be approximated by In this case, a is a value determined by the photoreceptor material, aｃｍ0.01 cm, spot diameter 2W = 60 μm, exposure portion potential _VL = −100.
(V), when the non-exposed portion potential V _D = −1000 (V), the surface potential distribution is as shown in FIG. Now, as shown in FIG. 20, the probe 2 is at x = 0 (the position of V (0) = _VL ).
Assuming that the cantilever potential is V _cant = V _L by the potential measurement control system, the potential difference ΔV (x) between the sample surface and the cantilever at the coordinate x =
V (x) -V _L, and the relative x shows the curves of Figure 21.

The discharge starting voltage Vs (V) at 1 atmosphere in air and 20 ° C. is Vs = 2.44d + 65.3√d (28) with respect to the gap d (μm) of the electrode causing discharge. (Paschen's rule).

As shown in FIG. 20, when the cantilever 3 is arranged in parallel to the sample surface, the distance between them is 13.5 μm.
m. Here, if d = 13.5, the discharge starting voltage Vs at this time is about 273V. In FIG. 21, discharge occurs between the cantilever 3 and the sample surface in a portion where ΔV (x) exceeds Vs. That is, x
Discharge occurs at a portion> 60 to 70 μm, which disturbs the charge distribution on the surface of the sample, making measurement impossible. As a method for solving such a problem, a cantilever having a height H of 100 μm or more in FIG. 18 may be used. However, in the micro cantilever, the height H of the probe 2 is
It is very difficult to reduce the thickness to about 100 μm in the manufacturing process. If a large cantilever is used without using a micro cantilever, the height H can be reduced to about 100 μm, but the high frequency and the low spring constant cannot be simultaneously satisfied as described above.

Next, in the case of the fifth conventional example (see FIG. 10) and the sixth conventional example (see FIG. 12), the optical waveguides 29, 31, and
The basic operation principle of detecting the deformation amounts of the cantilever beams 28 and 33 from the light amount difference using the light amounts 34 and 36 is described. However, there is no example in which such optical waveguides 29, 31, 34, and 36 are applied to measurement of the surface potential of the photosensitive drum, measurement of the toner potential distribution, and the like.

[0067]

According to a first aspect of the present invention, there is provided a physical quantity measuring apparatus for measuring a physical quantity of a sample by bringing the probe close to the surface of the sample to be measured. A distance measuring means for measuring a distance between the probe and the sample is provided based on an output value of the distance measuring means when approaching and leaving the surface of the probe and the sample. Distance control means for controlling the distance from the surface is provided.

Therefore, based on the output value of the distance measuring means,
By controlling the distance between the probe and the surface of the sample using the distance control means, there is no need to control the distance between the probe and the surface of the sample with a coarse / fine actuator as in the past, Thus, the approach operation can be performed at a high speed without collision between the probe and the sample surface.

According to a second aspect of the present invention, in the physical quantity measuring apparatus according to the first aspect, the distance measuring means includes: a light source that emits light having a wavelength that does not have a spectral sensitivity of the sample; Optical measuring means comprising a combination with a light receiving element having

Therefore, the measurement of the surface potential and the like can be accurately performed without disturbing the state of the electrostatic latent image on the sample, for example, the photoconductor, without measuring errors.

[0071]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A reference example of the present invention will be described with reference to FIGS. The description of the same parts as those of the conventional technique (see FIG. 6) is omitted, and the same parts are denoted by the same reference numerals.

The physical quantity measuring device shown in FIG. 1 is provided with a probe voltage applying means 44. This probe voltage applying means 44
Includes a first alternating voltage Va ₁ cantilever 3 mechanical resonance frequency omega ₀ following frequency omega as a spring, the second AC voltage 1/2 of the frequency of the frequency omega of the first AC voltage Va ₁ A voltage on which Va ₂ is superimposed is applied to the probe 2. Hereinafter, the operation of the apparatus when the probe voltage applying means 44 is provided will be described.

The adder 6 includes a feedback DC voltage Vb and a first AC voltage Va ₁ having a frequency ω of 以下 or less, preferably １ ／ or less, of the mechanical resonance frequency ω ₀ of the cantilever 3, / 2 of the second AC voltage Va ₂ is added. These superimposed voltages are applied to the cantilever 3. Now, the force acting between the probe 2 and the sample surface is, as described above,

[0074]

(Equation 20)

Is as follows. Assuming that the surface potential of the sample 1 is Vs, the potential difference V between the probe 2 and the surface of the sample is

[0076]

(Equation 21)

Is obtained. Thus, the electrostatic attractive force Fes between the tip of the probe 2 and the sample surface is

[0078]

(Equation 22)

Is obtained. ω is 1 of the mechanical resonance frequency ω ₀
Since the frequency is equal to or lower than / 3, no resonance oscillation is caused by Fes. Therefore, the output v of the preamplifier 10 representing the vibration of the cantilever 3 is

[0080]

(Equation 23)

## EQU1 ## which indicates the same-phase vibration proportional to Fes. The lock-in amplifier 45 is a narrow-band amplifier, and since the frequency of the reference signal is ω, amplifies only the ω component of the second term of the output v of Expression (31). The phase difference of each sine function in the second term is a phase difference based on the AC voltage of the frequency ω applied to the probe 2. The second terms are π /
It has a waveform in which a sine wave whose phase is shifted by 2 is superimposed. Since the lock-in amplifier 45 here is of a two-phase type, a sine wave whose phase is shifted by π / 2 is separated,
The respective outputs V ₁ and V ₂ are

[0082]

(Equation 24)

Thus, a DC voltage proportional to the amplitude of the AC voltage is output. A ₁ and A ₂ are proportional constants. Thus, the two terms in the parentheses of the second term of the equation (31) can be separated. Ω in the equation (31) is a vibration frequency that is non-resonant with the mechanical resonance frequency ω ₀ of the cantilever 3, and as in the case of vibrating the cantilever 3 at the resonance frequency as in the prior art, The phase of the vibration of the cantilever 3 does not greatly change due to a slight change in the resonance frequency due to the influence of temperature, humidity, atmospheric pressure, and the like. Therefore, the measurement result of the surface potential and the surface shape does not interfere with each other due to the phase change of the vibration waveform and appears as a non-negligible error, and the sample 1 with stable and accurate error is less. Of the surface potential and the surface shape can be measured. In this case, by applying the feedback to Vb so that voltages V ₁ becomes zero, it is possible to know the surface potential Vs from the value of Vb. In addition, since the probe voltage and the DC bias voltage of the surface potential become equal, even if the distance between the probe 2 and the sample surface is shortened in order to increase the resolution, a discharge phenomenon may occur between them. Measurement in a non-destructive state. Further, by feeding back the Z-axis actuator 16 so that the value of V ₂ becomes constant, the distance between the probe 2 and the sample surface can be kept constant. Even if it is present, the collision between the probe 2 and the sample surface can be prevented, and the fluctuation of the resolution can be suppressed.

Next, a modification of the present embodiment will be described. Here, the feedback to the adder 6 and the Z-axis actuator 16 is not performed, and the outputs V ₁ and V ₂ of the lock-in amplifier 45 are sent to the personal computer 17 as shown in FIG. By taking the output data into the personal computer 17 in this manner, the surface potential of the sample 1 and the probe 2
The distance between the sample and the sample surface can be measured. That is, if the capacity of the insulating film of the sample 1 is sufficiently larger than the capacity of the tip of the probe 2 and the cantilever, (∂C / ∂Z) is a function of the distance between the probe 2 and the sample surface. The distance between the probe 2 and the sample surface can be calculated from V ₂ and calculated. Also, (∂C / ∂Z) obtained from V ₂ ,
From V _1, the surface potential Vs of the sample 1 can be calculated and calculated using the equation (11). Note that Vb at this time is 0.

As described above, the frequency ω of the voltage applied to the probe 2 by the probe voltage applying means 44 is
For being different non-resonant vibration frequency and the mechanical resonance frequency omega _0, conventional mechanical resonance frequency omega ₀ as
Ambient temperature, as if the cantilever 3 was vibrated at
A slight change in the mechanical resonance frequency ω ₀ due to the influence of humidity, atmospheric pressure or the like prevents the phase of the vibration of the cantilever 3 from largely changing. Thereby, the cantilever 3
Measurement of physical quantities (sample surface potential and sample surface shape) without the measurement results of surface potential and surface shape interfering with each other due to the phase change of the vibration waveform of the sample and appearing as non-negligible errors Can always be performed accurately in a stable state.

An embodiment of the present invention will be described with reference to FIGS. The description of the same parts as those of the conventional technique (see FIG. 8) is omitted, and the same parts are denoted by the same reference numerals.

At a position close to the cantilever 3, a distance meter 46 is provided as a distance measuring means for measuring a distance between the probe 2 and the surface of the sample 1. The distance meter 46 and the base 4 holding the cantilever 3 are mechanically and firmly held by a common fixed base 47. The distance meter 46 may be any type, but an optical distance meter with high measurement accuracy,
For example, a non-contact laser displacement meter is desirable, and its output is preferably linear and has a constant sensitivity to the distance to be measured. Such a distance meter 46 is connected to the personal computer 17. In the personal computer 17, a distance control means for determining the distance between the probe 2 and the surface of the sample 1 based on the output value of the distance meter 46 and controlling the operation of the coarse actuator 16a during approach (FIG. (Not shown).

In such a configuration, the distance meter 4
6 and the function of the distance control means will be mainly described. First, the sample 1, the Z-axis actuator 16, and the photoreceptor sample 1 are integrally moved by the moving rail 48 below the charger 49 and the laser writing system 50. At this position, the sample 1 is charged by the charger 49, and thereafter, the laser writing system 5
Exposure by 0. Thus, an electrostatic latent image of a pattern irradiated with the laser light is formed on the surface of the sample 1.
Thereafter, the sample 1 and the Z-axis actuator 16 are moved below the cantilever 3 and the distance meter 46 by the moving rail 48. Then, at this position, the distance meter 46 measures the distance between the distance meter itself and the sample surface. This distance meter 46
Has a linear and constant sensitivity to distance,
Even if the distance meter 46 and the sample surface are separated by a few mm, the distance meter 46 has sufficient sensitivity to a change in distance. Further, since the distance meter 46 and the base 4 of the cantilever 3 are firmly held by the common fixed table 47, the tip of the probe 2 and the surface of the sample 1 are determined from the output value of the distance meter 46. Is uniquely determined. At this time, the personal computer 17 reads the output value of the distance meter 46 immediately after the sample 1 has moved directly below the probe 2, and measures the distance ds between the probe 2 and the sample surface at this time.
This distance ds indicates an accurate value because the measured value has sufficient sensitivity to the distance. After that, the personal computer 17
Is determined from the distance d ₀ between the tip of the probe 2 and the surface of the sample 1 at the time of measurement, which is determined in advance.
There calculates the distance ds-d ₀ to be moved at the time of approach,
The coarse movement actuator 16a is moved by this distance to approach the sample 1, and the distance between the tip of the probe 2 and the surface of the sample 1 is set to ds. At this time, since the distance to move the coarse movement actuator 16a is accurately known, the coarse movement actuator 16a can be drive-controlled in an open loop without applying feedback. Thus, the approach operation can be performed at a high speed without collision between the probe 2 and the surface of the sample 1.

Further, the personal computer 17 approaches while monitoring the output of the distance meter 46, and the tip of the probe 2 and the sample 1
When the distance to the surface becomes d ₀ at the time of measurement,
The coarse actuator 16a may be stopped (negative feedback is applied). In this case, the output of the distance meter 46 is a straight line with respect to the distance between the tip of the probe 2 and the surface of the sample 1, and the sensitivity is constant. The tip of the probe 2 does not collide with the surface of the sample 1.

Next, a modification of this embodiment will be described. Consider a case in which the output of the comparator 14 that outputs the deviation between the output of the lock-in amplifier 12 and the target reference voltage is always integrated by the integrator 15 (see FIG. 8), and the Z-axis actuator 16 is fed back. Here, a feedback circuit 51 is provided instead of the integrator 15 of FIG. FIG. 4 shows the feedback circuit 5
1 shows a configuration of an internal circuit. The feedback circuit 51 includes a first voltage adjustment unit 52, a comparator 53, a second voltage adjustment unit 54,
And an integrator 55.

Now, the probe 2 and the sample 1 at the time of approaching
The distance between the probe 2 and the surface of the sample 1 is represented by d _{0, and} the distance between the probe 2 and the surface of the sample 1 is controlled by V ₂₁ to keep the distance (d ₀ ) constant. And the movement of the coarse movement actuator 16a which approaches to For this reason, feedback control is applied twice,
Extremely unstable operation. Therefore, in order to eliminate such an inconvenience, the previous approaches completion leave manual control state of the voltage Vr ₁ by the first voltage adjustment unit 52, after the approach completion (by coarse actuator 16a of the probe 2 and the sample 1 after it is no longer possible to change the distance between the surface), shifts to the feedback control state of the automatic due to the DC voltage V _11. Thereby, double feedback control is not applied, and stable operation can be performed.

As described above, by controlling the distance between the probe 2 and the surface of the sample 1 using the distance control means based on the output value of the distance meter 46, the coarse movement It is not necessary to control the distance between the probe 2 and the sample surface by the actuator 16a and the Z-axis actuator 16, so that the approach operation can be performed at high speed without collision between the probe 2 and the sample surface. It becomes possible. For this reason, the time until the start of the measurement of the physical quantity can be further shortened, whereby, for example, the measurement of the surface potential of the photoconductor can be performed with high accuracy.

Next, the light source used for the distance meter 46 will be described. The light source preferably has an emission wavelength that does not have sensitivity to the photoreceptor, and the light receiving element also preferably has sensitivity to the emission wavelength. As an example, a case where the photoconductor is a photoconductor used for electrophotography will be described.

FIG. 5 shows the spectral sensitivity of a well-known typical photosensitive member used in an electrophotographic apparatus. Thus, at around 400 nm, Se and a mixture of zinc sulfide and cadmium sulfide have particularly high sensitivity. In the vicinity of 600 nm, LPC (Layered Photo
Conductor) ｛Chlorodiane blue and di of about 0.1μm thickness
Membrane CGL of mixture with phenylhydrazone (Charge Gener
CTL (Charge Tra)
nsport Layer) has a particularly high sensitivity. Organic photoreceptors (polyvinylcarbazole and t
A substance obtained by mixing rinitrofluorenone in a ratio of 1: 1 and having a positive charge has a sensitivity at around 600 nm, and an organic photoreceptor (having a similar substance negatively charged) has a sensitivity of 400 nm.
It has sensitivity in the range of nm to 600 nm.

From this, it is understood that the photosensitive member has no sensitivity to light having a wavelength of 600 nm or more. Therefore,
For this reason, a measurement laser light source that emits light having a wavelength of 600 nm or more and a light receiving element having sensitivity of this wavelength of 600 nm or more are used. In addition, from the viewpoint of giving a certain margin to the spectral sensitivity, a light source and a light receiving element made of a material corresponding to light having a wavelength of 900 nm or more are preferably used. Materials for the light source and the light receiving element corresponding to the wavelength of 900 nm or more include those shown in Tables 1 and 2 below.

[0096]

[Table 1]

[0097]

[Table 2]

Further, as the material of the light source and the light receiving element corresponding to the wavelength of 600 nm or more, in addition to the light source and the light receiving element corresponding to the wavelength of 900 nm or more, those shown in the following Tables 3 and 4 can be used. is there.

[0099]

[Table 3]

[0100]

[Table 4]

Further, in FIG. 5, since the substance is low in sensitivity to a wavelength of 400 nm or less, a light source having a wavelength of 400 nm or less and a light receiving element having sensitivity to this wavelength are used. Materials for the light source and the light receiving element corresponding to the wavelength of 400 nm or less include those shown in Tables 5 and 6 below.

[0102]

[Table 5]

[0103]

[Table 6]

As described above, the light having a wavelength which does not have the spectral sensitivity of the photosensitive member is used, and the light emitting wavelength and the material having the spectral sensitivity coincide with each other from the various materials of the light source and the light receiving element. By configuring the total 46, the state of the electrostatic latent image on the photoconductor is not disturbed,
As a result, the measurement of the surface potential or the like can be accurately performed without a measurement error.

[0105]

According to the first aspect of the present invention, when the probe approaches and departs from the surface of the sample, the distance control means controls the distance between the probe and the surface of the sample based on the output value of the distance measuring means. The approach distance can be controlled so that the approach operation can be performed at high speed and without collision between the probe and the sample surface, thereby shortening the time until the start of the physical quantity measurement, For example, the surface potential of a photoreceptor as a sample can be measured accurately.

According to a second aspect of the present invention, the distance measuring means comprises:
A light source that emits light of a wavelength that does not have the spectral sensitivity of the sample, and a light receiving element that is sensitive to the wavelength of the light emitted by the light source, the optical measurement means consisting of a combination of the sample, for example, on the photoreceptor Without disturbing the state of the electrostatic latent image,
The measurement of the surface potential and the like can be accurately performed without a measurement error.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a physical quantity measuring device according to a reference example of the present invention.

FIG. 2 is a configuration diagram when a personal computer is added to the apparatus of FIG.

FIG. 3 is a configuration diagram illustrating a physical quantity measurement device according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a feedback circuit.

FIG. 5 is a characteristic diagram showing the sensitivity of a photoconductor to wavelength.

FIG. 6 is a configuration diagram showing a physical quantity measuring device as a first conventional example.

FIG. 7 is a configuration diagram showing a physical quantity measuring device as a second conventional example.

FIG. 8 is a configuration diagram showing a physical quantity measuring device as a third conventional example.

FIG. 9 is a configuration diagram showing a physical quantity measuring device as a fourth conventional example.

FIG. 10 is a perspective view showing a fifth conventional example of a physical quantity measuring device.

FIG. 11 is an explanatory diagram illustrating an operation principle of signal detection.

FIG. 12 shows a physical quantity measuring device according to a sixth conventional example,
(A) is a perspective view, (b) is an aa cross-sectional view.

FIG. 13 is a perspective view showing a basic configuration of a Mach-Zehnder interferometer that detects a signal by a phase change.

FIG. 14 shows the operating principle of a Mach-Zehnder interferometer,
(A) is a schematic diagram showing the operation in the in-phase, and (b) is a schematic diagram showing the operation in the opposite phase.

FIG. 15 is a perspective view showing another example of detecting a signal by a phase change.

16A and 16B show the operation principle of FIG. 15, wherein FIG. 16A is a schematic diagram showing an operation at the same phase, and FIG. 16B is a schematic diagram showing an operation at the opposite phase.

FIG. 17 is a configuration diagram showing a surface potential measurement meter.

FIG. 18 is a side view showing a configuration of a micro cantilever.

FIG. 19 is a characteristic diagram showing a surface potential distribution.

FIG. 20 is a side view showing a state where a potential difference is generated between the sample surface and the cantilever.

FIG. 21 is a characteristic diagram showing a potential difference between a sample surface and a probe and a state of a discharge starting voltage.

[Explanation of symbols]

 1 sample 2 probe 46 distance measuring means

Claims (2)

[Claims] 1. A physical quantity measuring device for measuring a physical quantity of a sample by bringing the probe close to a surface of a sample to be measured, wherein a distance measuring means for measuring a distance between the probe and the surface of the sample. Distance control means for controlling a distance between the probe and the surface of the sample based on an output value of the distance measuring means when the probe approaches and departs from the surface of the sample. A physical quantity measuring device characterized by comprising: 2. The distance measuring means is an optical measuring means comprising a combination of a light source emitting light of a wavelength having no spectral sensitivity of the sample and a light receiving element sensitive to the wavelength of the light emitted by the light source. The physical quantity measuring device according to claim 1, wherein: