JP2007212470A - Scanning probe microscope - Google Patents

Abstract

【Task】
To provide a scanning probe microscope capable of measuring distribution information regarding local characteristics of a sample simultaneously with accurate three-dimensional shape information of the sample without damaging the sample with high throughput.
[Solution]
An optical high-sensitivity proximity sensor is provided to control the approach between the sample and the probe, thereby speeding up the approach to each measurement location. In addition, sample height data is obtained while the probe is intermittently brought into contact with the sample so that the probe is not dragged on the sample. At the same time, a voltage is applied to the probe during the contact period with the sample. By measuring the response by oscillating and detecting the local light intensity on the sample surface, additional information regarding the material distribution on the sample can be obtained without reducing the scanning speed.
[Selection] Figure 1

Description

  The present invention relates to a scanning probe microscope, a sample observation method using the same, and a device manufacturing method.

  A scanning probe microscope (SPM: Scanning Probe Microscope) is known as a measurement technique for a fine three-dimensional shape. This is a technique for scanning a sample while controlling the probe with a sharp tip while keeping the contact force at a very small value, and is widely used as a technique capable of measuring a fine three-dimensional shape on the atomic order. Conventionally, various improvements have been made to the problem peculiar to a scanning probe microscope that it is difficult to increase the speed for physically scanning a sample.

  For example, JP-A-10-142240 and JP-A-2000-162115 disclose a technique for correcting shape data from both a deflection signal of a probe and a driving signal of a sample in order to achieve both high speed and resolution. Is disclosed. In Japanese Patent Laid-Open No. 6-74754, in order to bring the probe close to the sample at high speed, when the probe is brought close to the sample while being vibrated, the amplitude of the probe starts from a distance of about 5 micrometers due to acoustic interaction. A technique for making the probe close to the sample at high speed by utilizing the fact that it can be configured to decrease is disclosed.

  However, the above-mentioned technique can only be used with a scanning probe microscope apparatus configured to vibrate the probe, and because the proximity cannot be detected unless the sample is approached to several micrometers, the probe can be moved to a distance of several micrometers at high speed. There is a problem that another sensor is required to bring them closer.

  On the other hand, at present, in the fine pattern formation process of LSI, dimension management using a CD-SEM (measurement SEM) is performed, but the following limitations have come with the miniaturization of patterns. (1) Measurement accuracy problem. The gate width of a 90 nm node LSI, which is expected to become mainstream in 2003, is 80 nm. If the allowable variation is 10% and the measurement accuracy is 20%, the required measurement accuracy is 1.6 nm. (2) Request for profile measurement. The need for APC (Advanced Process Control) is increasing for high-precision control of line width, but this requires not only pattern line width but also cross-sectional shape measurement technology that greatly affects electrical characteristics. Has been. (3) Problem of measurement object. Measurement needs for materials having weak electron beam resistance such as resists for DUV (deep ultraviolet light) and low-k (low dielectric constant) film materials are increasing. Further, for the measurement of the pits of the next-generation high-density optical disc memory, the same needs such as the same measurement accuracy, the necessity for profile measurement, and the measurement of the resist pattern for creating the master are considered.

  The current CD-SEM cannot cope with the above problems. For this reason, scanning probe microscope technology appears promising. What is needed in this case is a scanning probe microscope technique that can reduce the damage to soft and brittle materials and obtain information on the surface material, in addition to speeding up the probe approach described above.

  On the other hand, in Japanese Patent Application Laid-Open No. 11-352135, the sample or the probe is vibrated with a constant amplitude, and the probe is scanned while periodically hitting the sample to reduce damage to the soft and brittle sample and the probe. A method is disclosed.

  Furthermore, Japanese Patent Application Laid-Open No. 2001-33373 discloses a scanning method of measuring the height by applying the servo of the probe only at the jumping measurement point and moving to the next measurement point with the probe pulled up, In this method, the contact pressure is further reduced, and the soft brittle sample and the probe are less damaged. Further, since the probe is not dragged, there is an advantage that the shape at the step portion can be measured faithfully. However, in the case of measuring a pattern such as a resist, it is desirable to measure the shape of the bottom of the pattern and to measure whether or not the resist remains on the bottom, but this need has been met. There wasn't.

  In order to increase the speed, it was necessary to increase the resonance frequency of the probe and reduce the inertia of the probe. To this end, however, it was necessary to reduce the cantilever at the tip of the probe. However, the conventional optical lever method requires an area of about 50 micrometers for securing and adjusting the reflecting surface of the laser, and there is a limit to speeding up.

JP-A-10-142240 JP 2000-162115 A JP-A-6-74754 Japanese Patent Laid-Open No. 11-352135 JP 2001-33373 A

  As described above, the prior art has a problem of speeding up the approach of the probe to the sample for improving the measurement throughput.

  An object of the present invention is to provide a scanning probe microscope having a high-sensitivity proximity sensor and a high-speed approach to a sample, and a data observation method using the same, in order to solve the above problems.

  Another object of the present invention is to obtain a three-dimensional image by using a scanning method with little damage to a fragile sample such as a resist pattern, and at the same time, add to the sample material, such as capacitance, elasticity, and optical properties. To obtain the distribution of the target information simultaneously with the stereoscopic image without reducing the throughput. Another object of the present invention is to provide a scanning probe microscope which can detect deflection and can be easily adjusted even if the cantilever size at the tip of the probe is reduced in order to increase the scanning speed according to this method.

  Another object of the present invention is to provide a probe tilt scanning function for measuring an accurate shape with respect to a sample step portion having a steep inclination.

  Another object of the present invention is to provide a stable and highly accurate device manufacturing method by measuring a pattern of a semiconductor sample and feeding it back to process conditions.

  In order to achieve the above-described object, in the present invention, the scanning probe microscope is provided with a high-sensitivity proximity sensor having an optical height detection function so that the probe can approach the sample at high speed. did.

  Further, according to the present invention, in the scanning probe microscope, the probe is intermittently brought into contact with the sample so that the sample height data is obtained while the probe is not dragged on the sample. You can apply additional voltage, measure the response by vibrating the probe, or detect the local light intensity on the sample surface to obtain additional information on the material distribution on the sample without reducing the throughput The configuration.

  Further, according to the present invention, in the scanning probe microscope, it is possible to measure the accurate shape of the stepped portion by scanning the sample stepped portion having a steep inclination while tilting the probe.

  Furthermore, in the present invention, in the method of manufacturing a sample having an extremely fine structure such as a semiconductor device, the above-described scanning probe microscope is used to observe the semiconductor pattern or the resist pattern, and the result of this observation is obtained from the process apparatus. By feeding back to the operating conditions, it was possible to stably manufacture devices with extremely fine structures such as semiconductor devices.

  According to the present invention, by providing a high-sensitivity proximity sensor, it is possible to realize a high-speed approach between the sample and the probe and to improve the measurement throughput.

  Further, according to the present invention, the sample height data is obtained while the probe is intermittently brought into contact with the sample so that the probe is not dragged on the sample, and at the same time, the material distribution on the sample is not reduced. There is an effect that additional information can be obtained.

  In addition, according to the present invention, it is possible to realize measurement of an accurate shape of the stepped portion by performing scanning while tilting the probe with respect to the stepped sample stepped portion.

  In addition, according to the present invention, a semiconductor pattern can be measured with high throughput, so that a highly accurate device can be stably manufactured.

  FIG. 1 is a diagram showing the configuration of a scanning probe microscope according to the present invention. FIG. 2 is an enlarged view of an embodiment around the probe. A sample 501 is placed on a sample stage 302 that can be driven in X, Y, and Z, and is controlled by the scanning control unit 201. Above this is the probe 103, and the probe moving mechanism 252 to which the probe 103 is attached is driven by X, Y, and Z under the control of the probe drive unit 202, thereby performing probe scanning of the scanning probe microscope. . Reference numeral 252 is attached to the probe holder 101, and the probe holder 101 is attached to the lens barrel 102 by the probe holder up-and-down mechanism 253, and is coarsely driven in the Z direction by control from the probe holder drive unit 203. Is done.

  The probe moving mechanism 252 is a fine movement mechanism, and since the operating distance is not large, the probe is moved closer to the sample by the probe holder up / down mechanism 253. Alternatively, as another example, a short needle may be approached to the sample by driving on the sample stage 302 side. Also, the probe scanning of the scanning probe microscope may be driven by the sample stage 302 side.

  The proximity sensor 204 is a sensor for measuring the height in the vicinity of the tip of the probe with high sensitivity, and by detecting the contact of the probe with the sample in advance and controlling the approach speed, the probe is detected. High speed access to the sample can be realized without hitting the sample.

  The proximity sensor 204 may use light as will be described later, but other sensors can be used as long as the detection range is several tens of micrometers or more and the sensor can detect the distance to the sample with a sensitivity of about 1 micrometer. Also good. For example, by applying an AC voltage between the sample holder 101 or the cantilever portion of the probe 103 and the sample 501, a capacitance sensor that measures the capacitance and detects the distance, or the sample holder 101 and the sample 501 You may use the air micro sensor which flows air between these and detects a pressure.

  The scanning control unit 201 controls the probe deflection detection sensor 205, the proximity sensor 204, the probe holder driving unit 203, the probe driving unit 202 and the sample stage 302 to realize the proximity of the probe, the scanning of the sample, and the like. At this time, the surface shape image of the sample is obtained by sending a signal at the time of scanning the sample to the SPM image forming apparatus 208.

  Further, the signal applying device 207 oscillates the probe at a high frequency and detects the response by the deflection detection sensor 205 to measure the elasticity of the surface, or applies an AC or DC voltage between the probe and the sample to apply current. To measure the capacitance or resistance. By performing this simultaneously with the scanning of the probe, it is possible to obtain a distribution image of additional properties in addition to the surface shape image in the SPM image forming apparatus 207.

  When the objective lens is incorporated in the probe holder 101, it can be used for simultaneous observation of the SPM measurement area by obtaining an optical image of the sample by the optical image sensor 206 and adjustment at the time of mounting the probe 103.

  The operation of the entire apparatus is controlled by the overall control apparatus 209, and an instruction from an operator can be received, or an optical image or an SPM image can be presented by the display / input apparatus 251.

  FIG. 3 is a diagram showing an embodiment of the optical system. Light emitted from the light source 111 is converted into parallel light by the lens 112, reflected by the mirror 113, enters the objective lens formed inside the probe holder 101, and is focused on the sample 501. Depending on the shape of the opening incorporated in the light source 111, an image having an arbitrary shape such as a spot or a slit can be formed.

  The light reflected by the sample passes through the objective lens again, is reflected by the mirror 114, and forms an image on the detector 116 by the imaging lens 115. The position of the image moves depending on the height of the sample 501. If the incident angle of the detection term 110 to the sample is θ, the imaging magnification by the lens 115 is m, and the height of the sample is Z, the amount of movement is 2 mZ tan θ. If this amount of movement is measured, the sample height Z Can be detected. The detector 116 may be anything such as a PSD (position sensitive device), a divided photodiode, or a linear image sensor, as long as it can detect the position of the image.

  In addition, the above description is an explanation of a configuration in which the detection light 110 passes through the objective lens. However, the detection light 110 passes through the outside of the objective lens and is bent by another mirror (not shown) to be placed on the sample. A configuration in which an image is formed is also conceivable. At this time, the lenses 112 and 115 are adjusted so that the light source 111 and the sensor 116 are in an imaging relationship with the sample 501, respectively. In this case, the amount of movement of the image on the sensor 116 is 2 mZsin θ.

  The probe deflection detection system will be described below. Light emitted from the light source 131 passes through the lens 132 and the beam splitter, passes through the beam splitter 134, passes through the objective lens, and is irradiated on the cantilever portion of the probe. The light reflected here returns along the same path, passes through the beam splitter 133, and irradiates the sensor 136 through the lens 135. The lens 135 is configured so that the exit pupil of the objective lens and the sensor 136 are in an imaging relationship, and thereby a position change proportional to the inclination of the reflecting surface of the cantilever is caused in the light on the sensor 136. By detecting this with a PSD (position sensitive device), a divided photodiode, a linear image sensor, or the like placed at the position 136, the inclination (deflection) of the cantilever can be detected.

  In addition, by using a two-dimensional PSD, an image sensor, and a four-division photodiode, it becomes possible to detect torsion at the same time as deflection. In order to separate the detection light 130 from the light of the sample observation system, it is desirable that the light source 131 is a monochromatic laser, and an interference filter is provided before and after the lens 135 so that only this light passes.

  In order to further increase efficiency, the beam splitter 134 may be a dichroic mirror. Further, by using the beam splitter 133 as a polarizing beam splitter, the polarization direction of the laser 131 is changed to S-polarized light reflected by 133, and a ¼ wavelength plate (not shown) is placed between the beam splitters 133 and 134, thereby making the S-polarized light. May be converted into circularly polarized light and applied to the reflecting surface of the probe 103, and the reflected light may be changed to P-polarized light again by the quarter wavelength plate and transmitted through the polarizing beam splitter 133.

  The sample observation system emits from the illumination light source 154, passes through the condenser lens 153, is reflected by the beam splitter 155, passes through the beam splitter 134, and illuminates the sample 501 through the objective lens in 101. The reflected light of the sample passes through the objective lens again, passes through the beam splitters 134 and 155, forms an image with the imaging lens 152, and is detected by the image sensor 151.

  As described above with reference to FIG. 3, the probe, the sample observation system, the sample height sensor, and the probe deflection detection optical system are configured coaxially, thereby enabling simultaneous observation of the SPM measurement position and adjustment of the probe. Simplification and high-speed access between the probe and the sample are possible. Further, since the probe deflection detection optical system is configured coaxially, it becomes possible to irradiate the detection light 130 even to a probe having a small cantilever width, and a probe that is lighter and has a high resonance frequency is used. As a result, the scanning speed can be increased. By detecting all through the objective lens 101, the objective lens can be brought close to the probe, and optical observation of the sample with high resolution becomes possible.

  On the other hand, using an objective lens with a long working distance, of course, an off-axis configuration is also conceivable in which at least one of the sample height sensor and the probe deflection sensor projects and detects light obliquely through the gap between the objective lens and the sample. .

  As another configuration, a method of detecting the deflection of the probe 103 using the heterodyne interferometry is also conceivable. A point light source having a frequency fo and a point light source having a frequency fo + f shifted by the frequency f are arranged at the position of the light source 131. For the arrangement of the point light source, the laser may be squeezed with a lens, or the output end of the fiber may be placed here. The optical system is adjusted so that this image is formed at two points of the probe 103.

  As shown in FIG. 9, one forms an image at the tip of the cantilever portion of the probe and the other forms an image at the root. Since this reflected light intersects at the position 136, when a photodiode is placed at 136, two The light interferes and generates a beat of frequency f. When the beat signal is detected by lock-in detection using the frequency f signal applied to the frequency shifter as a reference to determine the phase, the change in the phase becomes the change in the tilt of the cantilever. Thereby, the deflection of the cantilever can be detected. Alternatively, instead of using the signal applied to the frequency shifter, the light transmitted through the lens 132 and not reflected by the beam splitter 133 is detected by another photodiode (not shown) where the two beams cross. Thus, the reference signal of frequency f may be used.

  As another configuration, a signal that reflects a change in strain such as a strain gauge may be incorporated in the probe and used as an alternative to the optical deflection sensor.

  Hereinafter, the high-speed approach control between the probe and the sample using the sample height sensor according to the present invention will be described with reference to FIG. First, the probe fine movement mechanism (probe moving mechanism 252) is in an extended state (a state in which the probe fine movement height is low). Next, while monitoring the sample height sensor 204, the probe coarse movement mechanism (probe holder vertical mechanism 253) is lowered at a high speed (about 1 to 10 mm / s) (the probe coarse movement height is lowered). When the output of the sample height sensor 204 becomes 10 to several tens of micrometers, switching to low speed approach is performed (about 0.1 mm / s). The output of the probe deflection detection sensor 205 is monitored, and when this starts to increase, the probe fine movement mechanism is contracted at once (probe high-speed retraction in FIG. 8).

  Compared to the conventional approach of making the probe close to the SPM servo mode, it is difficult to increase the speed when approaching at a low speed due to the control band of the probe. There is an advantage that the speed of the low-speed approach can be increased by contracting at a moment at the moment of sensing.

  Thereafter, after the probe is retracted at high speed, the servo is turned on to slowly bring the probe into contact with the sample. Although the above description has been made on the assumption that the probe side is driven, it goes without saying that the same applies to the case where the probe is brought closer by driving the sample stage 302 side.

  Next, a probe scan mode suitable for measuring a soft and brittle material sample having a high aspect such as a resist pattern will be described with reference to FIG. As shown in (b), the probe is lifted and lowered to apply a servo (Tc interval) so that the contact pressure (ie, probe deflection) becomes constant. By repeating while changing, the height of the sample is measured only at the measurement points. The repetition period is Ts.

  Accordingly, since the probe does not drag the sample, damage to the sample is small, and probe scanning capable of faithfully measuring the shape at the stepped portion can be realized. Although this is a method disclosed in Japanese Patent Laid-Open No. 2001-33373, the following invention will be described as an example suitable for measuring a resist pattern and the like.

  The tip of the probe has a certain taper angle, and the shape of the stepped portion that stands out from this tip could not be accurately measured with a scanning probe microscope, but when a step was detected, as shown in FIG. Tilt the probe to make it scan.

  As a method of tilting the probe, there is a method of providing a micro-rotation mechanism in the probe holder, but “TR Albrecht, S. Akamine, M. J. Zdebrick, C. F. Quate, J. Vac. Sci. Technol. A8 (1), 317 (Jan./Feb., 1990) ", there is also a method using the piezoelectric thin film type cantilever shown in FIG. It has a so-called bimorph structure, and a piezoelectric body is provided above and below the intermediate electrode G, and electrodes A, B, C, and D are formed on the opposite side. Here, when a voltage change in the reverse direction is applied to AG, DG, BG, and CG, torsional deformation occurs, and the probe can be tilted. The twist of the probe can be easily detected by using a quadrant photodiode for the probe deflection detector 136.

  Further, there is a high need for detecting whether or not the resist remains at the bottom of the resist pattern for measuring the resist pattern. Further, in recent semiconductors, there is a growing need for knowing the boundary of the material for a pattern in which the planarized structure is generalized and the surface irregularities are eliminated by grinding. In order to meet these needs, it is necessary to have a technique for measuring the distribution of mechanical properties such as surface capacity, optical properties, elasticity, etc. simultaneously with measurement of the three-dimensional surface shape.

  In the scanning method described in FIG. 4B, there is a period Tc in which the probe is in contact with the sample surface during each measurement period Ts. By measuring various surface properties in synchronization with this period, Various physical property distribution measurements can be performed simultaneously with the surface shape image.

  FIG. 4C shows an embodiment in which a local capacitance is measured by applying an AC voltage between the probe and the sample and synchronously detecting the flowing current. In FIG. 4D, light is transmitted through the probe, the sample is illuminated, light is guided from the tip of the probe to the fiber 170 and guided to the sensor 172 via the lens 171 Tc. In this embodiment, the distribution of the local optical characteristics of the sample is obtained by detecting the amount of light during this period. In this way, as an example, observation and measurement can be performed on a flat sample obtained by embedding silicon oxide in silicon and polishing as shown in FIGS.

  FIG. 6 shows an embodiment in which the probe is vibrated with a period T during the period Tc. At this time, T is sufficiently smaller than Ts or Tc. The probe deflection signal at this time is obtained, synchronously detected with respect to the excitation input signal, and the amplitude and phase are obtained to obtain a distribution with respect to the local mechanical properties of the sample surface.

  Further, by illuminating the tip of the probe, the scattered light from the tip or the light operated by the optical system as shown in FIG. 4D is detected and detected synchronously with the vibration of the probe. The distribution of the local optical characteristics of the sample can also be obtained.

  Alternatively, as shown in FIG. 7, the height of the sample is detected by constantly vibrating the probe at a period T (where T << Tc) and detecting a decrease in amplitude due to contact of the probe with the sample. It is also possible.

  Next, an example in which a resist pattern is measured will be described with reference to FIG. In the measurement of the resist pattern, it is necessary to distinguish whether the pattern is cut vertically as shown in (a), whether the resist remains thin as shown in (b), or whether the lower part of the groove or hole is narrowed as shown in (c). There is. According to the present invention, these can be distinguished.

  Further, FIG. 11 shows a device manufacturing method using the present invention. The wafer 620 is flowed to the process apparatuses 601 and 601 'to form a device. The process devices 601 and 601 'may be an etcher, a CMP device, an exposure device, or a development device depending on circumstances. A pattern formed on the wafer is observed and measured by the scanning probe microscope 603 of the present invention using the extracted wafer or the dummy wafer 621 that has undergone these steps. Alternatively, since the throughput is large, all the wafers may be observed and measured with the scanning probe microscope 603 of the present invention.

  In the present invention, since the three-dimensional shape of the pattern and the distribution of the surface state can be accurately observed and measured without damaging the sample, the observation and measurement results are fed back to the process conditions of the process devices 601 and 601 ′. A highly accurate device can be manufactured stably. In some cases, a dedicated data processing server may be connected to the feedback path 610.

  In addition, the data obtained by observation / measurement with the scanning probe microscope 603 of the present invention is sent to another data processing apparatus via a line and processed in combination with the data obtained by another inspection / observation / analysis apparatus. You can also For example, by analyzing the data obtained by observing and measuring with the scanning probe microscope 603 of the present invention in combination with the analysis data of the sample obtained by other analyzers, two-dimensional defects and compositions on the sample surface are analyzed. More detailed information such as a target or three-dimensional distribution can be obtained.

It is a figure which shows the whole structure of a scanning probe microscope. It is an enlarged view of one Example around a probe. It is a figure which shows one Example of an optical system. It is a figure which shows the control method of a probe. It is a figure which shows the structure of the cantilever which can control the inclination of a probe. It is a figure which shows the state which vibrated the probe during the contact period of the sample and the probe. It is a figure which shows making it measure a sample height with the period Tc sufficiently slower than the frequency of a minute vibration, always making it minutely vibrate at a high frequency. It is a figure which shows the method of the high-speed approach control of the probe-sample distance. It is a figure which shows the principle which measures the deflection | deviation of a probe by heterodyne interference. It is a figure which shows the example of the resist pattern which can be discriminate | determined by this invention. It is a figure which shows the Example which performs the condition control of the process of a semiconductor by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Probe holder, 102 ... Lens tube, 103 ... Probe, 111 ... Light source, 112 ... Lens, 113 ... Mirror, 114 ... Mirror, 115 ... Lens, 116 ... Detector, 131 ... Light source, 132 ... Lens, 133 ... Beam splitter, 134 ... Beam splitter, 135 ... Lens, 136 ... Detector, 154 ... Illumination light source, 153 ... Condenser lens, 155 ... Beam splitter, 152 ... Imaging lens, 151 ... Image sensor, 170 ... Optical fiber, 171 ... Lens, 172 ... Detector, 201 ... Scanning control unit, 202 ... Probe drive unit, 203 ... Probe holder drive unit, 204 ... Proximity sensor, 205 ... Deflection detection sensor, 206 ... Optical image sensor, 207 ... Signal application device , 208... SPM image forming device, 250... Overall control device, 251... Input / display device, 252. Moving mechanism, 253 ... probe holder elevation mechanism, 302 ... sample stage 501 ... sample, 601 ... process equipment, 603 ... scanning probe microscope, 610 ... feedback information, 620 ... wafer, 621 ... extraction or dummy wafer

Claims (3)

  A driving mechanism capable of controlling the mutual position between the surface of the sample and the probe, a proximity sensor for measuring a distance between the sample and the probe, and a contact state between the sample and the probe. A scanning probe microscope comprising a probe deflection sensor for measuring, wherein the proximity sensor comprises a light source and an image sensor, and the irradiation light from the light source passes through an objective lens provided inside the probe holder, The probe holder is irradiated from a direction inclined with respect to a moving axis that moves up and down to form an image on the sample surface, and reflected light from the sample surface passes through the objective lens and forms an image on the image sensor. A scanning probe microscope, wherein the light source and the image sensor are arranged so as to cause   The scanning probe microscope according to claim 1, wherein the proximity sensor has a detection sensitivity of 1 micrometer and an operating distance of 10 micrometers or more.   The scanning probe microscope according to claim 1, wherein the image sensor is a position sensitive device (PSD) or a linear image sensor.

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