SE0800670A0 - Nanoscale charge carrier mapping - Google Patents

Description

10 P17703SEOO SIMS (secondary ion mass spectrometry) provides a solution for determining the chemical structure and depth profile of the sample; however, this method is not suitable for small structures since it provides only a few micrometers of resolution at best.

There is thus a need for an instrument that can provide both a macro and nano scale positioning while at the same time being able to determine the electrical and / or chemical properties of the sample.

SUMMARY OF THE lNVENTlON lt is the object of the present invention to provide such instrumentation. This is achieved in a number of aspects of the present invention, in which a first is a device for measuring charge carrier maps in situ of an electron microscope using a scanning probe microscopy technique simultaneously with acquiring images with the electron microscope. In a second aspect of the present invention, a method is provided for measuring these charge carrier maps in situ of an electron microscope.

Furthermore, the present invention is realized as a measurement device for characterization of physical properties of a nano sized structure of any semiconductor device, comprising a probe, a probe holder for holding the probe, a probe positioning unit, and a control unit, wherein the probe positioning unit is arranged to position the probe holder in relation to a sample and where the control unit is arranged to send control signals to the positioning unit for positioning of the probe in relation to the sample and in such a way as to provide simultaneous imaging using an electron microscope, acquire at at least one measurement signal relating to at least one physical property of the nano sized structure.

The physical property may comprise electrical properties of the structure. The measurement signal may be a plurality of measurements of electrical current flowing between the probe and sample at given voltages.

The device may further be arranged to acquire a charge carrier density map of an area of the sample.

P17703SE00 3 Another aspect of the present invention is a system for determining a charge carrier map of an area of the nano sized structure of the semiconductor device, comprising a measurement device as described above and an analysis unit.

Yet another aspect of the present invention is a method of testing and verifying nano sized structures of any semiconductor device, comprising the steps of: positioning an electrically conducting probe in relation to a sample; determining the position of the probe relative to the sample using an electron microscope; monitoring the position of the probe in relation to the sample while positioning the probe at a measurement position of the sample; acquiring measurement signals from the probe; The method may further comprise a step of scanning an area and acquiring a charge carrier density map of the area.

LETTER DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a measurement system according to the present invention; Fig. 2 schematically illustrates a measurement device according to the present invention; Fig. 3 schematically illustrates the probe / sample area in a close up of Fig. 2; Fig. 4 illustrates schematically in a block diagram a method according to the present invention; and Fig. 5 schematically illustrates an l-V curve according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODlMENTS ln Fig. 1 reference numeral 1 generally indicate a measurement system comprising a measurement device 2, control / measurement electronics 3, and optionally a control and analysis processing device 4. The measurement device may be built as a microscope P17703SEOO 4 sample holder for an electron microscope 5, for instance for transmission electron microscope (TEM) or for a scanning electron microscope (SEM) and include a sample holding structure 11 and a probe holding structure 12. One of the sample and the probe holding structure is located in mechanical cooperation with a nano positioning device such as a piezo electric device. The piezo electric device changes its mechanical dimensions when a voltage is applied to it. The control / measurement electronics is arranged to control signals applied to the piezo and / or other positioning devices. The control / measurement device 3 is further arranged to receive signals from measurements perfonned at the sample / probe area. lt should be noted that pre conditioning electronics may be present close to the sample / probe area on the microscope sample holder depending on type of measurement to be done, since in some cases the measurements are subject to electrical and / or mechanical disturbances. In some configurations the piezo electric device is complemented with some others electromechanical device for operating the sample or the probe on a macroscopic scale (up to a few millimeters of range). The total operating range will thus be from a few angstroms (or even smaller) and up to a few millimeters. ln one embodiment of the present invention the piezo electric device is arranged to operate with a movement solution that operates within the entire displacement range for the relative position between the probe and the sample. This is shown in relation to Fig. 2.

The components of the measurement solution are in mechanical connection to a frame 22 of an electron microscope sample holder. A positioning device (e.g. controlled by a piezo electric tube 24) is at one end in fixed mechanical connection to the frame (directly of indirectly). A probe holder receiving structure (e.g. a structure with part of the outer circumferential surface being spherical) 23 is attached to the piezo tube and in turn a probe holder 12 is clamped to the probe holder receiving structure 23 using clamping structures pressing on the receiving structure 23. A probe 20 may be attached to the probe holder 12. The operation of the positioning device may be as follows: by applying a voltage to one or several electrodes on the piezo tube it will be elongated, retracted, or bent in some suitable direction: this type of dispiacement operate in the sub Angstrom range. By rapid changes of the applied voltage it is possible to displace the probe holder relative the probe holder 12 receiving structure 23 using the mechanical inertia of the probe holder: this type of displacement may provide movement in the range of several mm using repeated changes of the voltage (each change may for example give a P1 77035500 displacement of the order a few micrometers depending on applied voltage change).

Furthermore, a sample 28 is attached to the sample holder 11 which in turn is fi xed 21 to the frame 22. Both the sample and the probe may be electrically connected (indirectly via sample holder and probe holder) with electrical connections 26 and 27 respectively. The electrical connections may be connected to an optional pre conditioning unit 25 before being connected to the control and measurement electronics. Further, electrical connections may be present to the piezo tube for applying voltages to suitable electrode of the piezo tube, for grounding purposes, or for other physical measurements available in the setup.

The control / measurement electronics may optionally be connected to a processing device, e.g. a computer. This may be provided with software for interfacing with the electrical control and measurement electronics and with the user of the system. The processing device may be arranged to analyze measurement data and to control the overall operation of the system while the control and measurement electronics may be arranged to control operation the measurement setup on a local scale, i.e. action feedback loops, taking of measurements, noise cancellation, pre conditioning of signals, and so on as understood by the skilled person.

A suitable probe is positioned close to the sample and the electrical interaction between the probe and the sample surface is measured using at least one of the available techniques. ln one embodiment the probe is pressed against the sample, preferably with a known force and / or known distance into the sample. This ensures a good and reproducible contact configuration enabling reproducible measurements to be done of the electrical and / or chemical properties of the sample relative the probe position on the sample.

However, in order to measure small structures the probe need to have a tip that has small enough dimensions. STM tips made of Ptlr, etched W or similar can not be reproducibly manufactured with small enough tip. ln the solution according to the present invention it is suggested to use probe tips that has been manufactured using FIB process (Focused Ion Beam) or a tip with a functionalized tip end (e.g. with a nanotube attached to the end or a chemically of physically "grown" surface at the end). Furthermore, the sample tip may also be functionalized with respect to other characteristics such as chemical or magnetic interactions.

P17703SE00 The sample requires some preparation also in some cases, for instance if a TEM is to be used the sample need to be prepared by reducing it to suitable dimensions for fitting in the sample holder and reducing the thickness so as to allow electrons to pass through it (i.e. make it electron transparent) in order to view the structures of the sample. Also in the case of using a SEM, the sample might need cleaning and / or dimensioning (i.e. reduced in dimensions so as to fit in the sample holder). ln one embodiment a TEM is used for locating a structure which is of interest to characterize. When the structure has been located the probe is positioned close to or in contact with the structure while still imaging with the TEM in order to verify the location of the probe during the characterization. This ensures the relevance of the data (at least with respect to the geometrical location). The TEM may also be used to determine the distance the probe enters into the sample which may be used for reproducing similar depths between different samples or different structures on the same sample: thus again ensuring the reproducibility of the technique.

Using a force sensing device in relation to the probe or the sample, it is possible to determine the force exerted when the probe makes contact with the surface. This has the advantage of allowing for a reproducible measurement between measurements (i.e. the same measurement repeated several times, different structures on the same sample, or different structures on different samples) and / or determining the mechanical Characteristics of the interaction area of the sample, for instance by comparing the force exerted and the depth of the probe in to the sample, the mechanical hardness may be determined. ln Fig. 3 is shown a setup with a probe 30 positioned in relation to a sample 31. ln or on the sample is located a number of structures 32, 32 ', and 32 ”which are of interest to characterize. Furthermore, a force sensing device 33 is located as to measure the force exerted on the sample by the probe. However, it should be understood by the skilled person that the force sensor may be located in relation to the sample instead of the probe in some configurations. When dealing with nano sized structures on or in semiconductor or nems / mems devices, it is of interest to determine the depth information of the nano sized structures, for instance doping profiles of n- or p-doped structures.

P17703SEO0 When the probe is close to or in contact with the surface, the system may perform different types of measurements depending on the type of probe. ln one embodiment an electrical conducting tip is used and the voltage is scanned over a range and the resulting current through the probe / sample system is detected, generating an I-V curve. This l-V curve may be used to determine for instance the electrical and / or chemical characteristics of the structure. With appropriate signal analysis the depth profile may be obtained. The probe may be scanned over the surface producing a 2 dimensional map around the structure of interest. By stopping a number of points during the scan and taking l-V curves for each point, a 2 dimensional map with depth information or charge carrier information may be obtained. This so called CC-map (charge carrier map) may be used to understand the electrical (or chemical) performance or behavior of the structure in question. The structure may be any type of semiconductor structure, conducting structure or insulating structure as used in small scale electrical devices.

Fig. 5 shows a typical l-V curve obtained from a probelsurface measurement according to the present invention.

Scanning spreading resistance microscopy and scanning capacitance microscopy are methods suitable for two-dimensional profiling of localized resistance / conductance on a semiconductor surface of nano / micro scaled structures. These methods may provide depth profiles from bulk structures due to that the bulk structures may provide a surface signature affecting the surface sensitive measurement.

SCM measures capacitance variations between a metallized probe and a sample, e_g. a semiconductor sample while scanning in eg. contact mode. Since the variations are directly related to carrier concentration, the SCM may generate a 2D image with contrast corresponding to near-surface variations in carrier density.

Fig. 4 schematically illustrates a measurement process according to the present invention with the steps of, 401. Locating the probe in relation to the sample. 402. Determining the location of the probe in relation to the sample using the electron microscope. 403. Positioning the probe in relation to a structure of the sample.

P17703SE00 8 404. Continuously monitoring the probelsample area during measurements. 405. Measuring electrical or chemical characteristics in relation to the structure of the sample. 406. Optionally repeating measurements for several structures. 407. Removing the probe from the sample.

The present invention is advantageously used in sample Characterization of production grade samples of for instance any semiconductor structure devices (semiconductor may be Si based, GaAs based or any other semi conducting device), i.e. devices manufactured in a batch or series production in professional fabrication facilities or in laboratories. The measurement solution according to the present invention may be used for instance for quality analysis of random inspection samples of production series of semiconductor devices, integrated circuits, or nems / mems devices. lt should be noted that the word "comprising" does not exclude the presence of others elements or steps than those listed and the words “a” or “an“ preceding an element do not exclude the presence of a plurality of such elements. lt should further be noted that any reference signs do not limit the scope of the claims, and that several "means", "devices", and “units” may be represented by the same item of hardware.

The above mentioned and described embodiments are only given as examples and should not be iimiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art.

Claims (1)

10 15 20 25 30 P17703SEOO CLAIMS 1. A measurement device for Characterization of physical properties of a nano sized structure of any semiconductor device, comprising a probe, a probe holder for holding the probe, a probe positioning unit, and a control unit, wherein the probe positioning unit is arranged to position the probe holder in relation to a sample and wherein the control unit is arranged to send control signals to the positioning unit for positioning of the probe in relation to the sample and in such a way as to provide simultaneous imaging using an electron microscope, acquire at least one measurement signal relating to at least one physical property of the nano sized structure. The device according to claim 1, wherein the physical property comprises electrical properties of the structure. The device according to claim 1, wherein the measurement signal is a plurality of measurements of electrical current flowing between the probe and sample at given voltages. The device according to claim 1, further arranged to acquire a charge carrier density map of an area of the sample. A system for determining a charge carrier map of an area of the nano sized structure of the semiconductor device, comprising a measurement device according to claim 1 and an analysis unit. A method of testing and verifying nano sized structures of any semiconductor device, comprising the steps of: - positioning an electrically conducting probe in relation to a sample; - determining the position of the probe relative to the sample using an electron microscope; - monitoring the position of the probe in relation to the sample while positioning the probe at a measurement position of the sample; - acquiring measurement signals from the probe; P17703SE00 10 7. The method according to claim 6, further comprising a step of scanning an area and acquiring a charge carrier density map of the area.