JPS63231202A - Charged beam device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a charged beam device that uses tunneling current or field emission current, and in particular, the present invention relates to a charged beam device that uses tunneling current or field emission current. The present invention relates to a charged beam device having a signal detecting means that maintains a constant distance from the charged beam device.

[Conventional technology]

Regarding the signal detection circuit of an electronic device that has the function of maintaining a constant distance between the electrodes that flow the above-mentioned current using tunnel current or field emission current or between the probe and the sample, please refer to Nikkei Microdevice November 1986 issue. It is discussed on pages 81 to 97. In the prior art, as shown in FIG. 2, the detected current is amplified by an amplifier 12, then logarithmically converted by a logarithmic converter 13, and then input to the servo circuit.

This logarithmic conversion is presumably used because the tunnel current or field emission current is proportional to an exponential function of the relative distance S between the electrodes. However, strictly speaking (1
), it is proportional to the product of - and an exponential function.

1 toe -exp (-k 2S )
(1) Taking the logarithm of equation (1) yields equation (2).

Q n Ito=-Q n5-kzs (
2) In equation (2), when nnS<kzs, the conventional method is effective. However, if the work function T is 4eV, then 4
i Lcz at tunnel current (= (2mY'),
The plane constant (m: electron mass) is 2.04 x IO', and a curve of QnS and kzs with respect to S is obtained as shown in Figure 3, so for a relative distance S of 10 to 1 person, uns < kz
The condition of s is not satisfied. That is, with the prior art, it is not possible to detect the error in the relative distance S more accurately than the detection current.

On the other hand, in the prior art, a desired relative distance is set from the reference power source 8' in order to keep the relative distance constant. It is difficult to specify an absolute value for this set distance due to substance dependence, etc. Therefore, it is also extremely difficult to keep the current constant.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the point of highly accurate position detection from tunnel current or field emission current, and the relative distance is determined by moving either the probe or the sample so as to keep the tunnel current etc. constant. To keep it constant, the error becomes large, and there is a problem that high resolution cannot be obtained in an electronic device such as a scanning tunneling microscope (STM) that has high position detection resolution in two directions.

An object of the present invention is to obtain a charged beam device that uses tunnel current or field emission current to maintain the distance between opposing electrodes or between a probe and a sample with high precision.

[Means for solving problems]

The above purpose is to provide a current detection means for servoing the signal detection circuit of the charged beam device so that the current is constant;
This is achieved by having a constant current setting means, an error current detecting means, and an error distance converting means for detecting a relative distance error from the error current with high precision according to equation (1).

[Effect]

The present invention is based on the concept of keeping the relative distance constant by controlling the relative distance so as to keep the tunnel current or field emission current constant, and has an error current detection means and an error distance conversion means from the error current. It is possible to maintain a constant distance with high precision. In particular, the above error distance conversion can be performed accurately by dividing the error current by the tunneling current or field emission current. This allows accurate error distance conversion by differentiating equation (1). The error current dIi from the set value is given as shown in equation (3).

From this, the distance error amount ds is expressed by the following equation.

Here, k2 is constant, and since S is controlled, it has a value close to constant. Moreover, at a relative distance of 5 Å or more, −<k2
, and equation (4) can be easily expressed as equation (5).

t This allows the theoretical formula (formula (1)) to be faithfully maintained, so by servoing the actuator that drives the probe or sample so that the tunnel current or field emission current is constant, the error operation can be reduced. It is possible to keep the relative distance constant.

〔Example〕

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

In the figure, the probe 2 is brought close to the sample 4 using an actuator L or another moving means, and a voltage Vt is applied to the probe 2 and the sample 4 to obtain a tunnel current or field emission current It. FIG. 2 is a block diagram of a servo circuit that is part of a charged beam device that has a function of maintaining a constant relative distance between the charged beam device and the charged beam device. This servo circuit is a current detector 5. Error current detection circuit 7. Error distance conversion circuit 9. Servo circuit 10. It is composed of a high voltage amplifier 11.

When vt (<O) is applied to the probe 2 through the current detector 5, electrons 3 flow from the probe 2 toward the sample 4.

This is a tunnel current when the voltage is low, and a field emission current It when the voltage is high. Note that in order to obtain a tunnel current, it is desirable that the relative distance between the probe 2 and the sample 4 be 10 Å or less.

At this time, a signal corresponding to It is output from the current detector 5, and is subtracted by the voltage corresponding to the desired current in the differential current detection circuit 7 to detect the differential current dIt. Note that the voltage corresponding to the desired current can be set using the reference power supply 8. Further, it is desirable that the reference power source 8 is variable. The detected dIt is converted into dS by the error position conversion circuit 9 according to equation (1). Based on this signal, the actuator 1 can be driven through the known servo circuit 10 and high voltage amplifier 11 so that ds becomes zero. That is, d
Setting S to zero means setting dIt to zero, so
The purpose of the present invention can be achieved. Further, the error position conversion circuit 9 can be easily implemented using equation (5), and can be realized using a commercially available division circuit.

FIG. 4 shows a specific example of the main part of the present invention. The figure shows a current detection section, an error current detection section, and a division section. The current detection unit 5 detects a voltage Va corresponding to It by the operational amplifier 5.
(= Rt・Workt) is detected.

The error current detection circuit 7 includes an operational amplifier 21 and resistors R2 to R5.
is formed in the subtractor by dVd(=CVa-Vr
)). These dV- and V- are input to the error distance detection circuit 9 composed of a dividing circuit 21, and Vo%lt (" d Va/ Va
" d I t / I t) can be obtained. Thereby, the distance error amount can be accurately calculated using the tunnel current or the field emission current.

That is, in the servo circuit as shown in FIG. 1, it is possible to keep the tunnel current etc. constant with high precision and also maintain the relative distance with high resolution.

The current detector 5 in Figure 4 uses a current-voltage conversion circuit, but in this case it is installed between the sample 4 and the ground rather than between the probe 2 and the power source 6 as in Figure 1. It is better to set it up. In the case of FIG. 1, a suitable method is to install a detection resistor between the probe 2 and the power source 6 and detect this back electromotive force. Furthermore, although the error distance conversion circuit 9 shown in FIG. 4 faithfully expresses equation (5), it is important to use equation (4) to make it even more precise, and the characteristics shown in FIG. Depending on the case, it is necessary to calculate the relative distance component using the electric current and calculate it in the error distance conversion circuit 9.

That is, if Ωn5)kzs, then the current is the component of the relative distance, while if Ωns<kzs, then QnIt
It is necessary to configure the arithmetic circuit so as to satisfy the equation (4) using .

In the configuration shown in Figure 1, the current detector 5 and power source 6 are connected to the probe 2.
These were installed between the ground and the probe 2, respectively.
Alternatively, the servo circuit 10 may be installed between the sample 4 and the ground, and the servo circuit 10 is determined by the one used for the actuator 1. For piezoelectric elements, proportional-integral control or proportional-integral-derivative control including an integral element is used.

Proportional control is preferable for voice coils, motors, etc.

An application of the present invention is a scanning tunneling microscope.

There are three-dimensional shape measuring devices that use field emission current, bit detection or reading of large-capacity files, and gap holding mechanisms between the head and the sample for writing. Furthermore, the scope of the present invention is also applicable to mechanisms that maintain minute gaps by using tunnel current or field emission current.
This does not depart from the invention. Although the specific example shows the case of electrons, the present invention is the same even when using not only electrons but also field emission ion current, such as in a liquid metal probe.According to this embodiment, tunnel current or field emission Since the amount of error in relative distance can be detected more accurately than the amount of error in current, relative distance can be maintained with high precision.

According to the embodiments described above, the tunnel current or field emission current can be servoed within ±5% using the actuator, so the relative distance between the electrodes or between the probe and the sample can be adjusted to within 0.1%. Can be held with precision.

In other words, it can be used for high-precision shape measurement like a scanning tunneling microscope and for reading out information as large-capacity, ultra-high-density files.

This has the effect of increasing measurement precision and miniaturizing information. moreover,
The present invention is also extremely effective in fields where a head and a sample are held at a very small distance or in close proximity to each other at a very small distance, such as when reading and writing files, because the head and sample can be held close to each other with the above-mentioned accuracy.

〔Effect of the invention〕

Since the present invention is configured as explained above,
It becomes possible to maintain a constant distance between electrodes or between a probe and a sample with high precision.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a servo circuit for maintaining a constant distance between the probe and sample according to an embodiment of the present invention, Fig. 2 is a block diagram of a servo circuit according to the prior art, and Fig. 3 is a block diagram of a servo circuit for maintaining a constant distance between the probe and the sample. Characteristics of QnS and kzs FIG. 4 is a specific electrical circuit diagram of the main part of the present invention. DESCRIPTION OF SYMBOLS 1... Actuator, 2... Probe, 3... Electron, 4... Sample, 5... Current detector, 6... Power supply,
7...Error current detection circuit, 8...Reference power supply, 9...
・Error distance detection circuit, 10... Servo circuit, 11...
・High voltage amplifier, 20゜21...Operational amplifier, 22...
・Division circuit. 1 bird

Claims (1)

[Claims] 1. In a charged beam device that uses tunneling current or field emission current to flow between electrodes placed opposite each other or between a tip and a sample, and to maintain a constant distance between the electrodes or between the tip and the sample, the above method is used. A means for detecting tunnel current or field emission current, a target value setting means for making the above current flow constant, a current error detecting means for detecting an error between the detected current and the target value, and a means for converting the current error into a distance error. 1. A charged beam device comprising a current distance converting means for converting a current distance.