The method of moving the probe scanning microscope - nanolithography in the field of coarse x-y positioner

 

(57) Abstract:

The invention relates to precision measuring technology and nanotechnology and is intended for use in a scanning probe microscope, the probe nanolithography, probe storage device of large capacity. The technical result of the invention is to improve the accuracy and linearity of the positioning of the probe over a large area of the sample surface. The first movement is accomplished through precise positioner until it reaches the border of its range. Then searched and binding of the probe to the nearest surface features. After this coarse positioner moves in such a direction that follows the exact positioner has been moved to the opposite border of its range. After reaching this limit the above-described procedure is repeated cyclically until the arrival of the probe at a point on the surface, separated from the source at a specified distance. 1 Il.

The invention relates to precision measuring technology and nanotechnology, it is intended for use in a scanning probe microscope (SPM), and made on the basis of the SPM positioner [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], providing within its own maximum field (the area on the surface that is available for research after the installation of the sample) initial placement of precise moves with some fairly major step, the amount usually not exceeding the working range is accurate. The direction, magnitude, speed, and the step of moving the coarse positioner set by the operator manually.

Because of the errors associated primarily with uneven step coarse positioner, the effect of hysteresis, thermal drift, creep and coupling, as well as with the subjective factor introduced by the installations of the operator, it is impossible to move from one point in the available fields on the sample surface in any other lying outside the current range of the exact scanner (here it is assumed that the exact scanner is able to perform a linear motion with high accuracy and almost not sensitive to drift and creep, see [13, 14, 15] ). Thus, most current tools cannot accurately determine the relative position of scans performed accurate positioner microscope in different places of the field of coarse and, therefore, the right to take out of them a whole Zobrazi would be eliminated, occurs in nanolithography with characteristic sizes of elements from several tens of nanometers to a few angstroms. In the considered technology as objects of manipulation are atomic clusters, individual molecules [16] and atoms [17].

Another promising application of the method can become SPM control of topological dimensions larger elements of nanoelectronics, such as a transistor with high electron mobility, a bipolar transistor with a heterojunction lasers heterostructures and other devices [18]. The inventive method can be used in probe storage device of large capacity [19] for the precise movement of the probe read/write on a large surface area media.

In the present study and the process accessible surface area of hundreds of square millimeters, where possible atomically-smooth areas of micron size. Therefore, to obtain higher integration of elements on the same substrate must be able to accurately move the probe within the field of coarse positioner, the right to associate individual scans performed in different places accessible surface, to be able INR the ptx2">

To solve these problems, the coarse positioner is required to provide a linear X-, Y-position sensors and to form a closed-loop servo system like the measuring precision positioner [13-15]. The main difference between these systems will be the type of sensors used. The sensor positioner have high sensitivity and low range sensors coarse positioner opposite have low resolution, but a large range of measured displacements. Typically, sensors coarse positioner constructed on the basis of the interferometer, able to work in fractions of a strip.

In practice, the use of two tracking systems: one for coarse positioner, the other for the exact leads to a sharp rise in the cost of equipment, as well as to other problems (calibration, alignment, parasitic interference). Therefore, sacrificing resolution, build a system in which the same interference sensor serves as an accurate and coarse positioners. An example of this approach can serve as a wide-field microscope [1], which is selected as a prototype of the invention.

It should be noted that this microscope is a unique, very expensive measuring instrukcii accuracy characteristics of the elements of the device are mounted in the housing, made of Zerodur (Zerodur), a material with a low coefficient of thermal expansion ( = 0.0510-6K-1). The microscope is placed inside covering each other membranes functions: passive vibration control, acoustic insulation, the vacuum chamber (residual pressure of 10-7PA), active vibration control, camera stabilization (temperature accuracy of 1 MK).

The measuring part of the device is a Metrology frame of Zerodur with the strengthened specimen. In case built-mirror differential interferometers. Relative to the sample along the guides move in X-, Y-carriage on which is mounted a tubular manipulator probe and the remaining parts of the interferometers: lasers, mirrors, prisms and detectors. The carriages are driven by stepper motors.

Disadvantages used in the prototype of the method of positioning are:

1. The high cost and complexity of manufacturing Metrology boxes (hard requirements for straightness and orthogonality, as well as to the materials used).

2. Expensive and complicated to manufacture coarse positioner (guides, a carriage, a stepper motor).

K for SPM limit the resolution of the device (to a great extent limited by the vibrations due to low-frequency mechanical resonances of the coarse positioner, and noise interferometric sensors).

5. The high cost and complexity of the interference of the sensors, a great complexity of the alignment optical system.

Thus, to date, have not created a fairly simple and affordable systems capable of precise movement of the probe on the large field of coarse positioner. The proposed method allows to eliminate the mentioned disadvantages by performing bindings probe microscope for surface features and the joint movement of fine and coarse X-Y positioners.

In the drawing, as an example, presents the sequence of actions (POS. 2-6), provides precise movement of the probe microscope, But the available fields in the point D at a distance of more than one of the exact range of the positioner. Legend: TP - precision positioner, SE - coarse positioner. The dotted line on the surface of the sample shows the splitting field of coarse positioner adjacent ranges are accurate. The arms in the positions of the probe and represent surface features.

Next, for the sake of definiteness we will assume that the sample is fixed on a precise positioner, and the tip - to coarse. For simplicity, Rossmoor, proposed in this application to use in systems like [13-15], program management microscope should be supplemented by the so-called pairing process. The main function of this procedure is to constantly compensate for the negative influence of disturbing factors, to hold the tip over the selected surface. Usually this place is some kind of local feature type "hill" or "the pit". Since this method is the recognition [20] askanianova image, the topography should be understood in a broad sense. Physically, depending on the varieties probe microscope, they may represent a region of the magnetization, the localization of the electric charge, etc.

Binding of the probe is performed by scanning the exact positioner small surrounding area (segment) of the selected features, the recognition of this features in the received image, the coordinates of its position and movement of the probe through the same exact positioner in place with the found coordinates. It is easy to see that the pairing process is essentially a digital servo system implemented by software.

The advantage of software-binding is the ability to apply complex algorithms for processing and use as features of individual molecules and atoms that make the system [21] is difficult because of the noise and limitations on the resolution (the radius of the circle scan should be small compared to the size of the used features). In General, for proper positioning does not matter how you're actually binding, it is important that the probe microscope was securely "attached" to some place surface run-time move the coarse positioner.

So, in the initial state (Ref. 1) the tip is located at the point And the surface. Through precise positioner will move it relative to the surface in the direction of point D until then, until "put our" end of the range (see Ref. 2 point). Then produce the search and capture features closest to the point C. Further in the direction of point D takes a step coarse poses the conditions, which through accurate positioner tries to compensate for the resulting error.

Next, move the coarse positioner, and with it the exact, until exhaustion of the exact range of the positioner. Thus, the joint movement of the positioner the positioner returns the exact opportunity to further move the probe to the right (relative to the surface). This is followed by repetition of the above steps (see Ref. 4, 5), in which the probe moves to the right along the surface of one exact range of the positioner and reaches point C. Finally, through accurate positioner (POS. 6) the touch probe moves to the specified point D.

Thus, whenever the SPM probe reaches the edge of the exact range of the positioner, the work enters the coarse positioner. His task is to move the field scan accurate positioner to a new location on the sample surface. Moreover, in step coarse positioner cannot afford losing probe current features (offset coarse positioner is for a procedure binding disturbing effect), since otherwise two adjacent areas on the sample can be correctly tie ereatest, in the next cycle of binding of the capture probe instead of the current features one of her neighbors.

The step size coarse positioner should be determined by the size of the captured features, the minimum distance to the nearest features, located in the direction of movement and speed of drift of the head of the microscope. The moving speed of the coarse positioner must be limited so that the pairing process was able to detect and compensate for the resulting error. After step coarse positioner must wait for the completion of the transition process, the end of which corresponds to the establishment of a mismatch value comparable to the value of the natural drift of the instrument.

Since the direction of motion and the average step coarse positioner is known in advance, then "bundle" of positioners can be moved with greater speed, if you move the exact positioner synchronously and with the same step, and rough. After each step you must perform a sequence of bindings, clarifying the position of the probe relative to the "center of gravity" features. Note that the RMSE move coarse positioner Prezista structures coarse positioners should distinguish three types of devices: "walking" (walker, louse) [2-5], "crawling" (inchworm) [5-7] and inertial [8-10], the main advantage of which is essentially unlimited range of movement. The analysis shows that of these three types, the most suitable for use in the described method should be considered walking positioners. Creeping positioners have approximately the same characteristics, but originally a one-dimensional devices, are more cumbersome when creating two-dimensional X-Y designs. Coarse positioners inertial type, as a rule, have low resolution, develop large accelerations, less convenient, because of greater sensitivity to the quality and purity of the rubbing surfaces have significantly more uneven, poorly regulated step; a slight tilt positioner may interfere with the operation of the device. As creepy, inertial positioner often able to move only in one direction.

Any type of coarse positioner in one way or another characteristic errors and non-linearity of movement, usually their absolute values are orders of magnitude higher than similar parameters precise positioners. The feature of the proposed method lies in the fact that the cut is P CLASS="ptx2">

During the movement of the ligament due to nparalleled lateral plane rough walking positioner exact plane, Z-components of thermal drift and creep, parasite relations of the type X-->Z, Y>Z both positioners, as well as instabilities in the vertical plane of the coarse positioner is a change of coordinates Z of the probe. Instability in the vertical plane, as well as unwanted rotation in the plane of the sample can occur in moments of electrostatic fixation or release supports. The reason is the asperities and dirt, leading to slippage.

The change in the vertical coordinates can be measured and then adjusted the introduction of amendments. Rotation in the plane of the sample leads to incorrect mutual position corresponding field in the microscope, where the scanning is performed with a needle. In this case, the procedure bindings instead of the segment should scan aperture - area, covering nearest neighbor features, in order to change the positions of neighboring features in the sequence of cycles bindings to be able to detect the angle of rotation. If the angle is known, it is not easy to collect the ol bindings in the process of moving.

Thus, the described method allows to solve up to date the problem of nanometrology [1] - measurement of surface topography over a large area with a high degree of accuracy and linearity.

In the above discussion it was assumed that the drift velocity (thermococcales + creep) is much less than the speed of movement of the coarse manipulator and that the characteristic time of the control loop binding drift does not cause significant displacement features. However, with the utmost features of the surface atoms drift becomes much more visible and therefore should be considered when selecting the size of the segment and the pitch of the coarse positioner.

When searching distributed across the field of the scanner calibration factors important to the structure of the pattern at each point field scanner was unchanged, which in practice is not always feasible because of defects. The proposed method for simultaneous movement of the positioner allows pre-selected the "correct" surface pattern to move across the field of precision scanner. Thus, it is possible to calibrate the entire field of the scanner is a small area of the standard.

This way the joint move of the reasons the b part. By fine tubular positioner performed full-scale simulation of the movement of coarse. As a result of the experiments fully confirmed the ability of the pairing process in real time to compensate for the displacement of the probe.

As features were atoms on the surface of high-oriented pyrolytic graphite. It was shown that the retention of the probe realizable when the step size coarse positioner 1 and the moving speed of not more than 1 on the background drift is not more than 0.1 Because retention was possible to separate the atoms, then there is no doubt that it will be feasible on any other "large" objects.

Some difficulties when using the walking coarse positioner in the process of moving on an atomically smooth surface can occur in moments of fixation and release bearings. Here the influence of the unwanted random motions can be negated if the voltage on the electrostatic clamps serve not abruptly, but smoothly, so that the tracking system was able to compensate for the resulting error.

Sources of information

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[5] K. Takata, S. Hosoki, S. Hosaka, T. Tajima, Scanning tunneling microscope with reliable coarse positioners, Rev. Sci. Instrum., vol. 60, 4, p. 789, 1989.

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[7] T. Kato, F. Osaka, I. Tanaka, S. Ohkouchi, A scanning tunneling microscope using a dual-axes inchworms for the observation of a cleaved semiconductor surface, J. Vac. Sci. Technol. B, vol. 9, 4, p. 1981, 1991.

[8] K. Besocke, An easily operable scanning tunneling microscope, Surf. Sci., vol.181, p.145,1987.

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[10] S. S. Meepagala, F. Real, C. B. Reyes, A. Novoselskaya, Z. Rong, E. L. Wolf, Compact scanning tunneling microscope with easy-to-construct X-Z inertial sample translation, J. Vac. Sci. Technol. A, vol. 8, 4, p. 3555, 1990.

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[14] R. A. Green, D. A. Grigg, P. E. Russell, A scanning tunneling microscope with a capacitance-based position monitor, J. Vac. Sci. Technol. B, vol. 8, 6, R. 2023, 1990.

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[18] M. Sundaram, S. A. Chalmers, P. F. Hopkins, A. C. Gossard, New quantum structures, Science, vol. 254, p. 1326, 1991.

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The method of moving the probe scanning microscope-nanolithography in the field of coarse X-Y positioner based on the use of coarse positioner and accurate, capable of providing linear motion, characterized in that at the moment of reaching the boundaries of the exact range of the positioner through accurate positioner search and seizure nearest features pay the positioner is moved to the opposite border of its range while performing the pairing process, holding the probe on the selected feature of the surface, after reaching the opposite end of the range exact positioner described procedure is repeated cyclically until the arrival of the probe at a point on the surface, separated from the source at a specified distance.

 

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