WO2005119205A1 - Instrument for electrical characterisation on a nanometric scale - Google Patents

Instrument for electrical characterisation on a nanometric scale Download PDF

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Publication number
WO2005119205A1
WO2005119205A1 PCT/ES2005/000308 ES2005000308W WO2005119205A1 WO 2005119205 A1 WO2005119205 A1 WO 2005119205A1 ES 2005000308 W ES2005000308 W ES 2005000308W WO 2005119205 A1 WO2005119205 A1 WO 2005119205A1
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Prior art keywords
sample
measurement
tip
instrument
afm
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PCT/ES2005/000308
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Spanish (es)
French (fr)
Inventor
Francisco Javier Blasco Jimenez
Montserrat NAFRÍA MAQUEDA
Francisco Javier Aymerich Humet
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Universitat Autonoma De Barcelona
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Publication of WO2005119205A1 publication Critical patent/WO2005119205A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/30—Scanning potential microscopy
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders
    • G01Q60/40—Conductive probes

Definitions

  • the present invention refers to an instrument for topographic and electrical characterization on a nanometer scale whose particular configuration allows for significantly higher performance than the instruments that have been used up to now.
  • the characterization instrument of the invention essentially comprises an atomic force microscope (hereinafter, AFM).
  • An AFM is based on the measurement of the force between a nanometer-sized tip that acts as a probe and the surface of the sample to be analyzed. Said tip sweeps the surface of the sample and the variation in force between the tip and the sample is detected. The successive changes of the tip-sample force in the swept region are used by a control unit to generate a topographic image of the sample.
  • CAFM conductive tip atomic force microscope
  • Conductive AFM conductive AFM
  • a CAFM basically consists of an AFM to which the necessary elements have been added to apply a voltage between the tip (probe), made of an electrically conductive material, and the sample, and to measure the current flowing through the tip.
  • the main features of the atomic force microscope are the measurement of the topography of the sample with a lateral resolution of a few nm and a vertical resolution below one nanometer, and the possibility of operating under ambient conditions.
  • AFM and related techniques such as CAFM to become a very useful tool in many fields of science and technology, such as microelectronics, health sciences, material sciences, chemistry, or biology, among others.
  • CAFM the drawbacks of the CAFM is that, for certain applications, its electrical performance is not sufficient.
  • the current that passes through the gate oxide when it is polarized produces a degradation of its electrical properties, causing large current variations.
  • the door oxide layer loses its insulating properties.
  • the present invention proposes an electrical characterization instrument on a nanometric scale, hereinafter, ECAFM, with which it is possible to overcome the aforementioned limitations in relation to the state of the art.
  • the electrical characterization instrument of the invention includes an atomic force microscope (AFM) which incorporates a scanning device, at least one tip, and a support for the sample to be analyzed. According to the invention, there are also means for voltage generation and current measurement, and/or for current generation and voltage measurement connected to said tip of the
  • the aforementioned means comprise one or more source-measurement units (SMU, "Source Monitor Unit”).
  • SMU Source Monitor Unit
  • An SMU is capable of sourcing voltage and measuring current, or sourcing current and measuring voltage.
  • the measurement element has a variable and self-selectable dynamic range.
  • at least one of said SMUs is connected to the tip of the AFM and the other to the sample holder. If only one SMU is used, it can be connected to the tip, while any voltage is applied to the sample (or sample holder). Alternatively, the SMU can be connected to the sample (or sample holder), while any voltage is applied to the tip.
  • one of said units is connected to said tip of the AFM and the other of said units is connected to the sample (or to the sample holder).
  • the main advantages of the invention are obtaining a dynamic range in the measurement of the current that is several orders of magnitude higher; the possibility of new electrical tests; and greater flexibility in the definition of electrical tests.
  • the invention provides an effective solution to the limitations described above in relation to the state of the art.
  • Figure 1 is a schematic view illustrating the conventional configuration of an AFM before modifications to convert it into the electrical characterization instrument object of the invention, ECAFM;
  • Figure 2 is a schematic view illustrating the configuration of a CAFM;
  • Figure 3 is a schematic view illustrating the configuration of an embodiment of an electrical characterization instrument according to the invention, ECAFM;
  • Figure 4 is a schematic view illustrating the configuration of an alternative embodiment of the instrument of the invention in which several SMU Measurement Source Units are arranged, forming part of a semiconductor parameter analyzer (SPA), illustrating the control of the SMUs and the management of the data acquired by said SMUs, according to the invention;
  • Figure 5 is an example of a measurement made with the instrument of the invention (ECAFM).
  • ECAFM semiconductor parameter analyzer
  • An atomic force microscope designated collectively by (10) has been illustrated, which typically comprises a probe or tip (20) that scans the surface of a sample (30) arranged on a support (40).
  • the AFM (10) includes means for attenuating the vibrations to which the AFM (10) may be subjected, as well as means (50) for detecting the force between the tip (20) and the sample (30).
  • Said detection means (50) comprises, in the illustration shown, a laser (60) and a photodiode
  • a three-dimensional relative movement means (80) is also provided between the tip (20) and the sample (30).
  • Said three-dimensional relative movement means (80) comprises, in the illustration shown, a piezoelectric actuator (90) and control electronics for its management.
  • control unit (100) that includes control electronics (110) and a computer (120), as well as the specific software for controlling the AFM (10).
  • the tip (20) of the AFM (10) sweeps the surface of the sample (30).
  • the variation in force between the tip (20) and the sample (30) is detected by the laser (60) which is focused on the tip (20) and is reflected by the photodiode (70).
  • a change in force between the tip (20) and the sample is detected by the laser (60) which is focused on the tip (20) and is reflected by the photodiode (70).
  • the control unit (100) allows the user to configure the parameters of the measurement to be carried out, as well as the representation and processing of the measurements made.
  • figure 2 of the drawings a schematic view of the elements included in a typical configuration of a conductive tip atomic force microscope is shown.
  • CAFM which has been jointly designated by
  • the equipment (CAFM) (200) is equipped, in this case, with a conductive tip (210) and has means to apply voltage between the tip (210 ) and the sample (30) .
  • Said means for applying tension between the tip (210) and the sample (30) typically comprise a variable tension source
  • FIG. 220 which belongs to the control electronics, and means (230) to measure the current passing through the sample (30).
  • Said means (230) typically comprise a current-voltage converter connected to an analog input of the control electronics (240).
  • the tip-sample assembly and said current measurement means (230) are normally located inside a Faraday box (250) to minimize the contribution of electrical noise in current measurements.
  • the CAFM (200) can measure topography and current simultaneously.
  • Figure 3 shows a schematic view illustrating an embodiment of an electrical characterization instrument (ECAFM) according to the present invention, which has been collectively designated by (300). Starting from the configuration of the AFM (10) described above with reference to figure 1 of the drawings, the ECAFM (300) that is illustrated is equipped with a conductive tip (210).
  • EAFM electrical characterization instrument
  • the conductive tip (210) is connected to a source-measure unit (SMU), designated by (310).
  • Sample (30) is connected to another SMU, designated by (320).
  • the SMUs (310, 320) are capable of sourcing voltage and measuring current, or of sourcing current and measuring voltage.
  • the dynamic range of the element measure is variable and self-selectable. As can be seen, if one starts from the configuration of a CAFM (200) as illustrated in Figure 2, the two SMUs (310, 320) replace, in the aforementioned CAFM (200) configuration, the means (220) necessary to apply a voltage between the tip (210) and the sample (30) and to the means (230) to measure the current passing through the sample (30).
  • the SMUs (310, 320) are managed from a control computer application developed for this purpose.
  • the values generated and measured by the SMUs (310, 320) can be controlled and managed from the control computer application.
  • the ECAFM (300) includes means (330) for the simultaneous and synchronized measurement of the topographic and electrical properties of the sample (30). Through said means (330) it is possible to obtain electrical and topographic maps simultaneously and of the same area of said sample (30).
  • the voltage that is applied to the piezoelectric actuator 90 to control the sweep pattern is used as the timing parameter.
  • the tip-sample assembly (210, 30) is located inside a Faraday box (250) to minimize the contribution of electrical noise in the measurements. current.
  • the SMUs (310, 320) can be located inside or outside said Faraday box (250). Using a restricted configuration of the SMUs (310, 320), the measurements typical of a conventional CAFM (200) can be performed.
  • the features and types of measurements that a CAFM (200) allows can be considered as a very particular case within the features and tests that the ECAFM (300) of the invention allows.
  • FIG 4 shows another possible embodiment of the ECAFM (300) of the present invention with a specific implementation of the SMUs and their control and management means.
  • SMUs 310, 320, 340, 350
  • the semiconductor parameter analyzer (400) which includes said SMUs (310, 320, 34.0 , 350)
  • SPA semiconductor parameter analyzer
  • the graph of Figure 5 shows an example of a measurement made with the instrument of the invention (ECAFM) (300).
  • Said graph shows the current passing through a 3.5 nm thick layer of silicon oxide through the contact area between the tip (210) and the sample (30), which is about 300 square nm. This is measured through an SMU (310) connected to the tip (210) of the ECAFM (300) when a linearly increasing voltage is applied between the tip (210) of the ECAFM (300) and the sample (30). This measurement is compared with the same test carried out using CAFM (200) . Said graph shows the greatest dynamic range of current measurement obtained with the ECAFM (300) of the present invention.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
  • Microscoopes, Condenser (AREA)

Abstract

The invention relates to an instrument for electrical characterisation on a nanometric scale. The inventive instrument consists of an atomic force microscope (AFM) comprising a scanning device, at least one tip, a support for the sample and voltage-generating and current-measuring means, and/or current-generating and voltage-measuring means, with an auto-selectable and variable dynamic measuring range, the latter means being connected to the tip of the AFM and/or to the sample support and comprising at least one source measurement unit (SMU). According to the invention, different SMUs can form part of a semiconductor parameter analysis instrument (SPA) and the aforementioned AFM can take the form of an atomic force microscope with a conducting tip (CAFM). In addition, the invention comprises means for the simultaneous and synchronised measurement of the topographic and electrical properties of the sample. Moreover, the current measurement orders of magnitude are increased and a high degree of flexibility is obtained in terms of electrical test definition, while maintaining nanometric resolution in topographic and electrical measurements.

Description

INSTRUMENTO DE CARACTERIZACIÓN ELÉCTRICA A ESCALA NANOMÉTRICA ELECTRICAL CHARACTERIZATION INSTRUMENT AT NANOMETRIC SCALE
La presente invención se refiere a un instrumento de caracterización topográfica y eléctrica a escala nanométrica cuya particular configuración permite conseguir unas prestaciones notablemente superiores respecto a las de los instrumentos que se venían utilizando hasta ahora. El instrumento de caracterización de la invención comprende esencialmente un microscopio de fuerzas atómicas (en lo sucesivo, AFM) . Un AFM se basa en la medida de la fuerza entre una punta de tamaño nanométrico que actúa como sonda y la superficie de la muestra a analizar. La citada punta barre la superficie de la muestra y se detecta la variación de la fuerza entre la punta y la muestra. Los sucesivos cambios de la fuerza punta-muestra en la región barrida son utilizados por una unidad de control para generar una imagen topográfica de la muestra. Posteriormente, han aparecido diversas técnicas basadas en el AFM que permiten la medida simultánea a la topografía de alguna otra magnitud, como, por ejemplo, el microscopio de fuerzas atómicas de punta conductora (CAFM) ( " Conductive AFM" ) que permite obtener imágenes topográficas y eléctricas de la muestra simultáneamente. Un CAFM consiste básicamente en un AFM al cual se le han añadido los elementos necesarios para aplicar una tensión entre la punta (sonda) , realizada con un material conductor eléctrico, y la muestra, y medir la corriente que circula por la punta. Las principales características del microscopio de fuerzas atómicas son la medición de la topografía de la muestra con una resolución lateral de pocos nm y una resolución vertical por debajo del nanómetro, y la posibilidad de funcionamiento en condiciones ambiente. Estas características han permitido que el AFM y técnicas afines como el CAFM se conviertan en una herramienta muy útil en muchos campos de la ciencia y de la técnica, tales como la microelectrónica, ciencias de la salud, ciencias de los materiales, química, o biología, entre otras. Sin embargo, uno de los inconvenientes que presenta el CAFM es que, para determinadas aplicaciones, sus prestaciones eléctricas no son suficientes. A modo de ejemplo, la medida de la corriente eléctrica que atraviesa localmente el óxido de puerta ultra delgado de estructuras metal-óxido- semiconductor (propias de tecnologías microelectrónicas) cuando se le aplica una tensión. La corriente que pasa a través del óxido de puerta cuando está polarizado produce una degradación de sus propiedades eléctricas, provocando grandes variaciones de corriente. Además, bajo ciertas condiciones la capa de óxido de puerta pierde sus propiedades aislantes. Tras producirse este fenómeno, conocido como ruptura dieléctrica, la corriente puede ser varios órdenes de magnitud mayor que antes. Por lo tanto, las configuraciones estándar del CAFM, con un rango dinámico de medida de corriente que típicamente es de tres órdenes de magnitud (de fA a pA, de pA a nA o de nA a μA, dependiendo del equipo de medición) no puede adquirir toda la evolución de la corriente en una única medida . Otra limitación del CAFM (y complementaria a la citada anteriormente) es la baja flexibilidad en la definición de los ensayos eléctricos. La mayoría de losThe present invention refers to an instrument for topographic and electrical characterization on a nanometer scale whose particular configuration allows for significantly higher performance than the instruments that have been used up to now. The characterization instrument of the invention essentially comprises an atomic force microscope (hereinafter, AFM). An AFM is based on the measurement of the force between a nanometer-sized tip that acts as a probe and the surface of the sample to be analyzed. Said tip sweeps the surface of the sample and the variation in force between the tip and the sample is detected. The successive changes of the tip-sample force in the swept region are used by a control unit to generate a topographic image of the sample. Subsequently, various techniques based on the AFM have appeared that allow the simultaneous measurement of some other magnitude to the topography, such as the conductive tip atomic force microscope (CAFM) ("Conductive AFM") that allows topographic images to be obtained. and electrical sample simultaneously. A CAFM basically consists of an AFM to which the necessary elements have been added to apply a voltage between the tip (probe), made of an electrically conductive material, and the sample, and to measure the current flowing through the tip. The main features of the atomic force microscope are the measurement of the topography of the sample with a lateral resolution of a few nm and a vertical resolution below one nanometer, and the possibility of operating under ambient conditions. These features have allowed AFM and related techniques such as CAFM to become a very useful tool in many fields of science and technology, such as microelectronics, health sciences, material sciences, chemistry, or biology, among others. . However, one of the drawbacks of the CAFM is that, for certain applications, its electrical performance is not sufficient. By way of example, the measurement of the electric current that locally passes through the ultra-thin gate oxide of metal-oxide-semiconductor structures (typical of microelectronic technologies) when a voltage is applied to it. The current that passes through the gate oxide when it is polarized produces a degradation of its electrical properties, causing large current variations. Furthermore, under certain conditions the door oxide layer loses its insulating properties. After this phenomenon, known as dielectric breakdown, occurs, the current can be several orders of magnitude higher than before. Therefore, standard CAFM configurations, with a dynamic current measurement range that is typically three orders of magnitude (fA to pA, pA to nA, or nA to μA, depending on the measurement equipment) cannot Acquire the entire evolution of the current in a single measurement. Another limitation of the CAFM (and complementary to the one mentioned above) is the low flexibility in the definition of electrical tests. Most of the
CAFM solamente permiten aplicar una rampa de tensión (para medir curvas corriente-tensión) . Aunque pueden obtenerse importantes parámetros eléctricos de este tipo de mediciones, para otros parámetros relevantes son necesarios otro tipo de ensayos. La presente invención propone un instrumento de caracterización eléctrica a escala nanométrica, en lo sucesivo, ECAFM, con el cual se consiguen superar las limitaciones citadas anteriormente con relación al estado de la técnica. El instrumento de caracterización eléctrica de la invención incluye un microscopio de fuerzas atómicas (AFM) el cual incorpora un dispositivo de barrido, por lo menos una punta y un soporte para la muestra a analizar. De acuerdo con la invención, se disponen también medios para la generación de tensión y medición de corriente, y/o para la generación de corriente y medición de tensión conectados a la citada punta delCAFM only allow applying a voltage ramp (to measure current-voltage curves). Although important electrical parameters can be obtained from this type of measurement, for other relevant parameters other types of tests are necessary. The present invention proposes an electrical characterization instrument on a nanometric scale, hereinafter, ECAFM, with which it is possible to overcome the aforementioned limitations in relation to the state of the art. The electrical characterization instrument of the invention includes an atomic force microscope (AFM) which incorporates a scanning device, at least one tip, and a support for the sample to be analyzed. According to the invention, there are also means for voltage generation and current measurement, and/or for current generation and voltage measurement connected to said tip of the
AFM (ahora conductora) y al soporte de dicha muestra. En particular, los medios citados anteriormente comprenden una o varias unidades de fuente-medida (SMU, " Source Moni tor Uni t" ) . Una SMU es capaz de generar tensión y medir corriente, o generar corriente y medir tensión. El elemento de medida dispone de un rango dinámico variable y autoseleccionable. En la invención, por lo menos una las citadas SMU se conecta a la punta del AFM y la otra al soporte de la muestra. En caso de utilizar únicamente una SMU, ésta puede conectarse a la punta, mientras que a la muestra (o al soporte de la muestra) se le aplica una tensión cualquiera. Alternativamente, la SMU puede conectarse a la muestra (o al soporte de la muestra) , mientras que a la punta se le aplica una tensión cualquiera. En caso de utilizar dos o más SMU, una de dichas unidades se conecta a la citada punta del AFM y la otra de dichas unidades se conecta a la muestra (o al soporte de la muestra) . Las principales ventajas de la invención son la obtención de un rango dinámico en la medida de la corriente que es de varios órdenes de magnitud superior; la posibilidad de nuevos ensayos eléctricos; y una mayor flexibilidad en la definición de los ensayos eléctricos. En otras palabras, con la configuración descrita es posible ampliar ventajosamente los intervalos u órdenes de magnitud de medida de corriente, a la vez que se obtiene una elevada flexibilidad en la definición de los ensayos eléctricos, manteniendo la resolución nanométrica tanto en las medidas topográficas como eléctricas. Por lo tanto, la invención proporciona una solución eficaz para las limitaciones descritas anteriormente con relación al estado de la técnica. Las características y las ventajas del instrumento de caracterización eléctrica a escala nanométrica (ECAFM) objeto de la presente invención resultarán más claras a partir de la descripción detallada de una realización preferida. Dicha descripción se dará, de aquí en adelante, a modo de ejemplo no limitativo, con referencia a los dibujos. En dichos dibujos: La figura n° 1 es una vista esquemática que ilustra la configuración convencional de un AFM antes de las modificaciones para convertirlo en el instrumento de caracterización eléctrica objeto de la invención, ECAFM; La figura n° 2 es una vista esquemática que ilustra la configuración de un CAFM; La figura n° 3 es una vista esquemática que ilustra la configuración de una realización de un instrumento de caracterización eléctrica de acuerdo con la invención, ECAFM; La figura n° 4 es una vista esquemática que ilustra la configuración de una realización alternativa del instrumento de la invención en la cual se disponen varias Unidades de Fuente Medida SMU formando parte de un analizador de parámetros de semiconductores (SPA) , ilustrándose el control de las SMU y de la gestión de los datos adquiridos por dichas SMU, de acuerdo con la invención; y La figura n° 5 es un ejemplo de medida realizado con el instrumento de la invención (ECAFM) . De acuerdo con la figura n° 1 de los dibujos, se ha ilustrado un microscopio de fuerzas atómicas (AFM) designado en conjunto por (10) , el cual comprende típicamente una sonda o punta (20) que barre la superficie de una muestra (30) dispuesta sobre un soporte (40) . El AFM (10) incluye un medio de atenuación de las vibraciones a las que puede estar sometido el AFM (10) , así como un medio de detección (50) de la fuerza entre la punta (20) y la muestra (30) . Dicho medio de detección (50) comprende, en la ilustración mostrada, un láser (60) y un fotodiodoAFM (now host) and the support of said sample. In particular, the aforementioned means comprise one or more source-measurement units (SMU, "Source Monitor Unit"). An SMU is capable of sourcing voltage and measuring current, or sourcing current and measuring voltage. The measurement element has a variable and self-selectable dynamic range. In the invention, at least one of said SMUs is connected to the tip of the AFM and the other to the sample holder. If only one SMU is used, it can be connected to the tip, while any voltage is applied to the sample (or sample holder). Alternatively, the SMU can be connected to the sample (or sample holder), while any voltage is applied to the tip. In the case of using two or more SMUs, one of said units is connected to said tip of the AFM and the other of said units is connected to the sample (or to the sample holder). The main advantages of the invention are obtaining a dynamic range in the measurement of the current that is several orders of magnitude higher; the possibility of new electrical tests; and greater flexibility in the definition of electrical tests. In other words, with the configuration described it is possible to extend advantageously the intervals or orders of magnitude of current measurement, at the same time that a high flexibility is obtained in the definition of the electrical tests, maintaining the nanometric resolution both in the topographic and electrical measurements. Therefore, the invention provides an effective solution to the limitations described above in relation to the state of the art. The characteristics and advantages of the electrical characterization instrument at the nanometer scale (ECAFM) object of the present invention will become clearer from the detailed description of a preferred embodiment. Said description will be given, hereinafter, by way of non-limiting example, with reference to the drawings. In said drawings: Figure 1 is a schematic view illustrating the conventional configuration of an AFM before modifications to convert it into the electrical characterization instrument object of the invention, ECAFM; Figure 2 is a schematic view illustrating the configuration of a CAFM; Figure 3 is a schematic view illustrating the configuration of an embodiment of an electrical characterization instrument according to the invention, ECAFM; Figure 4 is a schematic view illustrating the configuration of an alternative embodiment of the instrument of the invention in which several SMU Measurement Source Units are arranged, forming part of a semiconductor parameter analyzer (SPA), illustrating the control of the SMUs and the management of the data acquired by said SMUs, according to the invention; and Figure 5 is an example of a measurement made with the instrument of the invention (ECAFM). According to figure 1 of the drawings, An atomic force microscope (AFM) designated collectively by (10) has been illustrated, which typically comprises a probe or tip (20) that scans the surface of a sample (30) arranged on a support (40). The AFM (10) includes means for attenuating the vibrations to which the AFM (10) may be subjected, as well as means (50) for detecting the force between the tip (20) and the sample (30). Said detection means (50) comprises, in the illustration shown, a laser (60) and a photodiode
(70) . Se dispone también un medio de movimiento relativo tridimensional (80) entre la punta (20) y la muestra (30) . Dicho medio de movimiento relativo tridimensional (80) comprende, en la ilustración mostrada, un actuador piezoeléctrico (90) y una electrónica de control para la gestión del mismo. Se dispone también una unidad de control (100) que comprende una electrónica de control (110) y un ordenador (120) , así como el software específico para el control del AFM (10) . La punta (20) del AFM (10) barre la superficie de la muestra (30) . La variación de la fuerza entre la punta (20) y la muestra (30) se detecta mediante el láser (60) que se focaliza en la punta (20) y se refleja en el fotodiodo (70) . Un cambio en la fuerza entre la punta (20) y la muestra(70) . A three-dimensional relative movement means (80) is also provided between the tip (20) and the sample (30). Said three-dimensional relative movement means (80) comprises, in the illustration shown, a piezoelectric actuator (90) and control electronics for its management. There is also a control unit (100) that includes control electronics (110) and a computer (120), as well as the specific software for controlling the AFM (10). The tip (20) of the AFM (10) sweeps the surface of the sample (30). The variation in force between the tip (20) and the sample (30) is detected by the laser (60) which is focused on the tip (20) and is reflected by the photodiode (70). A change in force between the tip (20) and the sample
(30) provoca una deflexión de la punta (20) que cambia el reflejo en el fotodiodo (70) y, por tanto, la potencia óptica que éste recibe. La tensión de salida del fotodiodo (70) depende de la potencia óptica y, por los tanto, de la fuerza entre la punta (20) y la muestra (30) . Dicha tensión es utilizada por la unidad de control (100) para acercar o separar la punta (20) a la muestra (30) y generar un patrón de barrido mediante el actuador piezoeléctrico (90) del citado medio de movimiento relativo tridimensional (80) . La unidad de control (100) permite al usuario configurar los parámetros de la medida a realizar, así como la representación y procesado de las medidas realizadas. De acuerdo con la figura n° 2 de los dibujos, se muestra una vista esquemática de los elementos comprendidos en una configuración típica de un microscopio de fuerzas atómicas de punta conductora(30) causes a deflection of the tip (20) that changes the reflection on the photodiode (70) and, therefore, the optical power that it receives. The output voltage of the photodiode (70) depends on the optical power and, therefore, on the force between the tip (20) and the sample (30). Said tension is used by the control unit (100) to bring the tip (20) closer to or separate from the sample (30) and generate a sweep pattern by means of the piezoelectric actuator (90) of said three-dimensional relative movement means (80). . The control unit (100) allows the user to configure the parameters of the measurement to be carried out, as well as the representation and processing of the measurements made. According to figure 2 of the drawings, a schematic view of the elements included in a typical configuration of a conductive tip atomic force microscope is shown.
(CAFM) , el cual ha sido designado en conjunto por(CAFM), which has been jointly designated by
(200) . Partiendo de la configuración del AFM (10) mostrada en la figura n° 1, el equipo (CAFM) (200) está equipado, en este caso, con una punta conductora (210) y dispone medios para aplicar tensión entre la punta (210) y la muestra (30) . Dichos medios para aplicar tensión entre la punta (210) y la muestra (30) comprenden típicamente una fuente de tensión variable(200) . Starting from the configuration of the AFM (10) shown in figure 1, the equipment (CAFM) (200) is equipped, in this case, with a conductive tip (210) and has means to apply voltage between the tip (210 ) and the sample (30) . Said means for applying tension between the tip (210) and the sample (30) typically comprise a variable tension source
(220), la cual pertenece a la electrónica de control, y medios (230) para medir la corriente que atraviesa la muestra (30) . Dichos medios (230) comprenden típicamente un conversor corriente-tensión conectado a una entrada analógica de la electrónica de control (240) . El conjunto punta-muestra y los citados medios (230) de medida de la corriente se sitúan normalmente en el interior de una caja de Faraday (250) para minimizar la contribución del ruido eléctrico en las medidas de corriente. El CAFM (200) puede medir topografía y corriente simultáneamente. En la figura n° 3 se muestra una vista esquemática que ilustra una realización de un instrumento de caracterización eléctrica (ECAFM) de acuerdo con la presente invención, el cual ha sido designado en conjunto por (300) . Partiendo de la configuración del AFM (10) anterior descrita con referencia a la figura n° 1 de los dibujos, el ECAFM (300) que se ilustra va equipado con una punta conductora (210) . La punta conductora (210) se conecta a una unidad fuente-medida (SMU) , designada por (310) . La muestra (30) se conecta a otra SMU, designada por (320) . Las SMU (310, 320) son capaces de generar tensión y medir corriente, o bien de generar corriente y medir tensión. El rango dinámico del elemento de medida es variable y autoseleccionable. Como puede apreciarse, si se parte de la configuración de un CAFM (200) tal como se ha ilustrado en la figura n° 2, las dos SMU (310, 320) substituyen, en la citada configuración del CAFM (200) , a los medios (220) necesarios para aplicar una tensión entre la punta (210) y la muestra (30) y a los medios (230) para medir la corriente que atraviesa la muestra (30) . En la realización ilustrada en dicha figura n° 3, las SMU (310, 320) se gestionan desde una aplicación informática de control desarrollada a tal fin. Los valores generados y medidos por las SMU (310, 320) pueden ser controlados y gestionados desde la aplicación informática de control. El ECAFM (300) incluye medios (330) para la medida simultanea y sincronizada de las propiedades topográficas y eléctricas de la muestra (30) . A través de dichos medios (330) es posible obtener mapas eléctricos y topográficos simultáneamente y de la misma zona de dicha muestra (30) . En la realización mostrada se utiliza como parámetro de sincronización la tensión que se aplica al actuador piezoeléctrico (90) para controlar el patrón de barrido. Como en el caso del CAFM (200) ilustrado en la figura n° 2, el conjunto punta-muestra (210, 30) se sitúa en el interior de una caja de Faraday (250) para minimizar la contribución del ruido eléctrico en las medidas de corriente. En el caso de la realización de la invención ilustrada a modo de ejemplo en la figura n° 3, las SMU (310, 320) pueden situarse dentro o fuera de dicha caja de Faraday (250) . Utilizando una configuración restringida de las SMU (310, 320) se pueden realizar las medidas propias de un CAFM convencional (200) . Pueden considerarse las prestaciones y tipos de medidas que permite un CAFM (200) como un caso muy particular dentro de las prestaciones y ensayos que permite el ECAFM (300) de la invención. En la figura n° 4 se muestra otra posible realización del ECAFM (300) de la presente invención con una implementación concreta de las SMU y su medio de control y gestión. En esta realización, se disponen varias SMU (310, 320, 340, 350) que forman parte de un instrumento analizador de parámetros de semiconductores (SPA) , el cual ha sido designado en conjunto por (400) en dicha figura n° 4. El analizador de parámetros de semiconductores (400) , que comprende dichas SMU (310, 320, 34.0, 350), puede ser operado manualmente, o desde una aplicación informática en la unidad de control (410) mediante un bus de comunicaciones (420) , que en la realización es un bus GPIB. En la gráfica de la figura n° 5 se ha ilustrado un ejemplo de medida realizado con el instrumento de la invención (ECAFM) (300) . En dicha gráfica se muestra la corriente que atraviesa una capa de óxido de silicio de 3,5 nm de grosor a través del área de contacto entre la punta (210) y la muestra (30), que es de unos 300 nm cuadrados. Esto se mide a través de una SMU (310) conectada a la punta (210) del ECAFM (300) cuando se aplica una tensión linealmente creciente entre la punta (210) del ECAFM (300) y la muestra (30) . Esta medida se compara con el mismo ensayo realizado mediante CAFM (200) . En dicha gráfica se puede observar el mayor rango dinámico de medida de corriente obtenido con el ECAFM (300) de la presente invención. Conclusiones La disposición de un ECAFM (300) resultado de la integración en el mismo de un AFM (10) y una o más SMU (310, 320, 340, 350) proporciona un instrumento de caracterización eléctrica a escala nanométrica mejorado respecto a los instrumentos que hasta la fecha se venían utilizando para el mismo fin. Las mediciones realizadas en capas de Si02 ultra delgadas que se presentan en esta memoria ilustran algunas de las ventajas mencionadas del ECAFM (300) de la invención respecto a otros instrumentos como el CAFM (200) . A modo de ejemplo, dichas mediciones muestran que el ECAFM (300) de la invención es capaz de reproducir los resultados del CAFM (200) pero con un margen dinámico para la medición de la corriente mucho mayor y una mayor flexibilidad en la definición de los ensayos eléctricos . Las prestaciones eléctricas extendidas del ECAFM (300) hacen previsible que el citado instrumento pase a convertirse en herramienta muy útil para la comunidad de usuarios que actualmente utiliza el CAFM (200) . Descrito suficientemente en qué consiste el instrumento de caracterización eléctrica a escala nanométrica (ECAFM) de la presente invención en correspondencia con los dibujos adjuntos, se comprenderá que podrán introducirse en el mismo cualquier modificación de detalle que se estime conveniente, siempre y cuando las características esenciales de la invención resumidas en las siguientes reivindicaciones no sean alteradas. (220), which belongs to the control electronics, and means (230) to measure the current passing through the sample (30). Said means (230) typically comprise a current-voltage converter connected to an analog input of the control electronics (240). The tip-sample assembly and said current measurement means (230) are normally located inside a Faraday box (250) to minimize the contribution of electrical noise in current measurements. The CAFM (200) can measure topography and current simultaneously. Figure 3 shows a schematic view illustrating an embodiment of an electrical characterization instrument (ECAFM) according to the present invention, which has been collectively designated by (300). Starting from the configuration of the AFM (10) described above with reference to figure 1 of the drawings, the ECAFM (300) that is illustrated is equipped with a conductive tip (210). The conductive tip (210) is connected to a source-measure unit (SMU), designated by (310). Sample (30) is connected to another SMU, designated by (320). The SMUs (310, 320) are capable of sourcing voltage and measuring current, or of sourcing current and measuring voltage. The dynamic range of the element measure is variable and self-selectable. As can be seen, if one starts from the configuration of a CAFM (200) as illustrated in Figure 2, the two SMUs (310, 320) replace, in the aforementioned CAFM (200) configuration, the means (220) necessary to apply a voltage between the tip (210) and the sample (30) and to the means (230) to measure the current passing through the sample (30). In the embodiment illustrated in said figure 3, the SMUs (310, 320) are managed from a control computer application developed for this purpose. The values generated and measured by the SMUs (310, 320) can be controlled and managed from the control computer application. The ECAFM (300) includes means (330) for the simultaneous and synchronized measurement of the topographic and electrical properties of the sample (30). Through said means (330) it is possible to obtain electrical and topographic maps simultaneously and of the same area of said sample (30). In the shown embodiment, the voltage that is applied to the piezoelectric actuator 90 to control the sweep pattern is used as the timing parameter. As in the case of the CAFM (200) illustrated in figure 2, the tip-sample assembly (210, 30) is located inside a Faraday box (250) to minimize the contribution of electrical noise in the measurements. current. In the case of the embodiment of the invention illustrated by way of example in figure 3, the SMUs (310, 320) can be located inside or outside said Faraday box (250). Using a restricted configuration of the SMUs (310, 320), the measurements typical of a conventional CAFM (200) can be performed. The features and types of measurements that a CAFM (200) allows can be considered as a very particular case within the features and tests that the ECAFM (300) of the invention allows. Figure 4 shows another possible embodiment of the ECAFM (300) of the present invention with a specific implementation of the SMUs and their control and management means. In this embodiment, there are several SMUs (310, 320, 340, 350) that are part of a semiconductor parameter analyzer (SPA) instrument, which has been designated as a whole by (400) in said figure 4. The semiconductor parameter analyzer (400), which includes said SMUs (310, 320, 34.0 , 350), can be operated manually, or from a computer application in the control unit (410) through a communications bus ( 420), which in the embodiment is a GPIB bus. The graph of Figure 5 shows an example of a measurement made with the instrument of the invention (ECAFM) (300). Said graph shows the current passing through a 3.5 nm thick layer of silicon oxide through the contact area between the tip (210) and the sample (30), which is about 300 square nm. This is measured through an SMU (310) connected to the tip (210) of the ECAFM (300) when a linearly increasing voltage is applied between the tip (210) of the ECAFM (300) and the sample (30). This measurement is compared with the same test carried out using CAFM (200) . Said graph shows the greatest dynamic range of current measurement obtained with the ECAFM (300) of the present invention. Conclusions The provision of an ECAFM (300) resulting from the integration in it of an AFM (10) and one or more SMUs (310, 320, 340, 350) provides an instrument for electrical characterization at the nanometric scale that is improved with respect to the instruments which to date had been used for the same purpose. The measurements carried out on ultra-thin Si0 2 layers presented in this report illustrate some of the mentioned advantages of the ECAFM (300) of the invention with respect to other instruments such as the CAFM (200). By way of example, these measurements show that the ECAFM (300) of the invention is capable of reproducing the results of the CAFM (200) but with a much larger dynamic range for current measurement and greater flexibility in defining the parameters. electrical tests. The extended electrical features of the ECAFM (300) make it foreseeable that the aforementioned instrument will become a very useful tool for the user community that currently uses the CAFM (200) . Having sufficiently described what the electrical characterization instrument at the nanometric scale (ECAFM) of the present invention consists of in correspondence with the attached drawings, it will be understood that any detail modification deemed appropriate may be introduced therein, as long as the essential characteristics of the invention summarized in the following claims are not altered.

Claims

REIVINDICACIONES : 1- Instrumento de caracterización eléctrica a escala nanométrica (300) que comprende un microscopio de fuerzas atómicas (AFM) (10) el cual incluye un dispositivo de barrido (90) , por lo menos una puntaCLAIMS: 1- Instrument for electrical characterization on a nanometric scale (300) comprising an atomic force microscope (AFM) (10) which includes a scanning device (90), at least one tip
(210) , y un soporte (40) para la muestra (30) a analizar, caracterizado en que dicho instrumento (300) incluye, además, medios (310, 320, 340, 350) para la generación de tensión y medición de corriente, y/o para la generación de corriente y medición de tensión, con rango dinámico de medida variable y autoseleccionable, estando conectados dichos medios (310, 320, 340, 350) a la citada punta (210) del AFM (10) y/o a dicho soporte(210), and a support (40) for the sample (30) to be analyzed, characterized in that said instrument (300) also includes means (310, 320, 340, 350) for voltage generation and current measurement , and/or for current generation and voltage measurement, with a variable and self-selectable dynamic range of measurement, said means (310, 320, 340, 350) being connected to the aforementioned tip (210) of the AFM (10) and/ or to said support
(40) de la muestra (30) . 2- Instrumento de caracterización eléctrica(40) of the sample (30). 2- Electrical characterization instrument
(300) según la reivindicación 1, caracterizado en que dichos medios para la generación de tensión y medición de corriente, y/o para la generación de corriente y medición de tensión, comprenden por lo menos una unidad de fuente-medida (SMU) (310, 320, 340, 350) conectada a una de las puntas (210) del AFM (10) y/o al soporte(300) according to claim 1, characterized in that said means for voltage generation and current measurement, and/or for current generation and voltage measurement, comprise at least one source-measurement unit (SMU) ( 310, 320, 340, 350) connected to one of the tips (210) of the AFM (10) and/or to the support
(40) de dicha muestra (30) . 3- Instrumento de caracterización eléctrica (300) según la reivindicación 1, caracterizado en que dichos medios para la generación de tensión y para la medición de la corriente, y/o para la generación de corriente y medición de la tensión, comprenden por lo menos dos unidades de fuente-medida (SMU) (310, 320, 340, 350), estando conectada como mínimo una de dichas unidades (310) a una de las puntas (310) del AFM (10) y estando conectada la otra de dichas unidades (320) al soporte (40) de dicha muestra (30) . 4- Instrumento de caracterización eléctrica (300) según la reivindicación 1, caracterizado en que dicho microscopio de fuerzas atómicas es un microscopio de fuerzas atómicas con punta conductora (CAFM) (200) . 5- Instrumento de caracterización eléctrica (300) según la reivindicación 2, caracterizado en que dichas unidades de fuente-medida (SMU) (310, 320, 340, 350) forman parte de un instrumento analizador de parámetros de semiconductores (SPA) (400) . 6- Instrumento de caracterización eléctrica (300) según la reivindicación 1, caracterizado en que incluye medios (330) para la medida simultanea y sincronizada de las propiedades topográficas y eléctricas de la muestra (30) . (40) of said sample (30). 3- Electrical characterization instrument (300) according to claim 1, characterized in that said means for voltage generation and current measurement, and/or for current generation and voltage measurement, comprise at least two source-measurement units (SMU) (310, 320, 340, 350), at least one of said units (310) being connected to one of the tips (310) of the AFM (10) and the other of said units (320) to the support (40) of said sample (30). 4- Electrical characterization instrument (300) according to claim 1, characterized in that said atomic force microscope is a conductive tip atomic force microscope (CAFM) (200). 5- Electrical characterization instrument (300) according to claim 2, characterized in that said source-measurement units (SMU) (310, 320, 340, 350) are part of a semiconductor parameter analyzer (SPA) instrument (400). 6- Electrical characterization instrument (300) according to claim 1, characterized in that it includes means (330) for the simultaneous and synchronized measurement of the topographic and electrical properties of the sample (30).
PCT/ES2005/000308 2004-06-01 2005-05-27 Instrument for electrical characterisation on a nanometric scale WO2005119205A1 (en)

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