Electricity: motive power systems – Positional servo systems – Multiple mode systems
Patent
1989-06-07
1991-03-19
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Multiple mode systems
318593, 318594, 250306, G05B 1118
Patent
active
050014099
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an apparatus for obtaining surface information of a sample by bringing a probe-tip close to the sample and obtaining the surface information on the basis of physical parameters such as a current that occur between the probe-tip and the sample. More particularly, the present invention relates to a surface metrological apparatus which can provide topography by scanning a probe-tip at a high speed, can observe a large area and can provide fine characterization.
BACKGROUND ART
A scanning tunneling microscope (STM) is known in the past as a system effective for observing a crystal structure of a solid surface with a sub-angstrom resolution (.ANG.=10.sup.-10 m).
The conventional STM apparatus employs the system wherein a probe-tip is fixed to the tip of a 3-dimensional fine actuator, and after the distance between the sample and the probe-tip is reduced to some dozens of angstroms to, a few angstroms by use of a coarse actuator (inchworm system) in a Z direction, the position of the probe-tip is subjected to servo control in such a manner as to keep a tunnel current flowing through the probe-tip constant while the inchworm system is fixed and the probe-tip is being scanned in the X and Y directions, in order to display the displacement of the probe-tip at that time. Such a system is disclosed, for example, in U.S. Pat. Specification No. 4,343,993.
On the other hand, a method of obtaining topography during high speed scanning by STM is discussed in Appl. Phys. Lett. 48 (1986), pp. 832-834.
The approaching method of the probe-tip and the sample and the observation area selecting method in accordance with the prior art are described in Appl. Phys Lett. 40 (1982), pp. 178-180.
Incidentally, the principle of STM is described in Scientific American (Japanese version), Oct. 1, 1985, pp. 10-17, and the like.
When high speed scanning is made in accordance with the prior art technique described above, the gap between the probe-tip and the sample is held at an arbitrary distance and after gap control is suspended, the probe-tip is moved on the sample surface and the tunnel current or field emission obtained from the change of the gap is used as the surface information. For this reason, the prior art technique involves the problems in that the structural information of topology cannot be obtained correctly and in that the probe-tip impinges against the sample when any corrugations exist inside the scanning area or the inclination between the scan surface and the sample surface is at least 10 .ANG. or the sample surface grows such as crystal growth especially in the case of large scanning area.
Furthermore, the conventional STM is not free from the problem in that when high speed scanning is made, a fine structure cannot at all be measured because a servo system or a piezo device cannot respond to a high frequency range.
Still another problem of the prior art technique lies in that it does not consider any counter-measure when the change of relative positions between the probe-tip and the sample resulting from the inclination of the sample and its warp exceeds the movable range of the Z-direction fine actuator of the probe-tip or the digitizing error of data. This results in the problems such as the impingement of the sample and the probe-tip and suspension and nullification of measurement.
The prior art technique does not either consider the approach of the probe-tip having a sharp tip to the sample or instability of the tunnel current, and the approach of the probe-tip to the sample while its tip is kept sharp and selection of the observation area have left problems yet to be solved. Disclosure of Invention
It is an object of the present invention to provide a surface metrological apparatus capable of high speed fine characterization even for a sample having a large area.
Unlike the prior art technique which does not subject the probe-tip to servo control in fast scanning but moves it on a predetermined plane to represent a current image, the first action of the present inventi
REFERENCES:
patent: 4772817 (1988-09-01), Aida et al.
patent: 4870352 (1989-09-01), Koechner
Hosaka Sumio
Hosoki Shigeyuki
Kondou Hitoshi
Ohtake Masatoshi
Takata Keiji
Bergmann Saul M.
Hitachi , Ltd.
Shoop Jr. William M.
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