JP5013320B2 - Method and apparatus for identifying nanobubbles - Google Patents

Description

  The present invention relates to a method and apparatus for identifying nanobubbles using an atomic force microscope.

  For example, nano-sized bubbles attached on a substrate in a wet process during the manufacturing process of nanodevices such as MEMS, semiconductor, and liquid crystal, that is, nanobubbles cause defects in the device. For this reason, it is important how to control the generation of nanobubbles, and for this purpose, a technique capable of accurately discriminating nanobubbles is required.

  Research on methods for discriminating nanobubbles has been actively conducted. For example, a method for discriminating nanobubbles from their shapes using an atomic force microscope (AFM) has been studied. However, nanobubbles have different properties from macrobubbles and have been reported to have a flat shape (Non-Patent Document 1), and it is very difficult to distinguish nanobubbles from other foreign substances from their shapes. It was difficult.

  In addition, it is conceivable to measure the interaction force by analyzing the agglomeration behavior by pushing the probe of the atomic force microscope into the object, and to discriminate between nanobubbles and other foreign substances. In the case of such a very soft substance, it was difficult to distinguish it from nanobubbles.

In addition, since repulsive force due to zeta potential works in the liquid, nanobubbles and other foreign substances cannot be distinguished by measuring the interaction repulsive force acting between the probe of the atomic force microscope and the object to be distinguished. There wasn't.
Lijuan Zhang, et al., Langmuir 2006, 22, 8109-8113.

  As described above, it has been difficult to reliably distinguish nanobubbles from other foreign substances using an atomic force microscope.

  Therefore, an object of the present invention is to provide a new discrimination method and apparatus capable of reliably discriminating nanobubbles from other foreign substances using an atomic force microscope.

  The nanobubble discrimination method of the present invention is a nanobubble determination method using an atomic force microscope equipped with a cantilever having a probe at the tip, when the tip of the probe is pressed against the slope of the object The displacement of the tip of the cantilever is measured, and when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object, it is determined that the object is a nanobubble.

  In addition, a change with time of the volume of the object is measured, and it is determined that the object is a nanobubble when the volume of the object is decreased.

  Further, the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is measured, and it is determined that the object is a nanobubble when the displacement rate is 0.05 N / m or less. And

  The nanobubble determination device of the present invention is a nanobubble determination device comprising an atomic force microscope equipped with a cantilever having a probe at the tip, when the tip of the probe is pressed against the slope of the object Displacement measuring means for measuring the displacement of the tip of the cantilever and determination means for determining that the object is a nanobubble when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object. It is characterized by.

  Further, the apparatus includes a volume measuring unit that measures a change in the volume of the object with time, and the determination unit is configured to determine that the object is a nanobubble when the volume of the object is decreased. And

  Further, the apparatus includes a displacement rate measuring means for measuring a displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object, and the determining means has the object when the displacement rate is 0.05 N / m or less. Is configured to be determined to be nanobubbles.

In addition , a lens for optically magnifying and observing the probe and nanobubbles is provided, and a circulation path for circulating gas saturated water is formed around the lens. .

Further, it is used for inspection of contamination or defects on the substrate surface.

  The program of the present invention is a program used in a nanobubble determination apparatus including an atomic force microscope having a cantilever having a probe at the tip, and presses the tip of the probe against the slope of the object. Displacement measuring means for measuring the displacement of the tip of the cantilever at the time, and a judging means for determining that the object is a nanobubble when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object Make it work.

  Further, the computer is caused to function as a volume measuring unit that measures a change in the volume of the object over time, and a determination unit that determines that the object is a nanobubble when the volume of the object decreases.

  Furthermore, the computer uses a displacement rate measuring means for measuring the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object, and the object is a nanobubble when the displacement rate is 0.05 N / m or less. It is made to function as a determination means that determines that

  According to the nanobubble discrimination method and apparatus of the present invention, the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object is measured, and the direction in which the probe is orthogonal to the slope of the object By determining that the object is a nanobubble when the tip of the cantilever is displaced, the nanobubble and other foreign substances can be distinguished.

  Further, by measuring a change in the volume of the object over time and determining that the object is a nanobubble when the volume of the object is reduced, it is possible to reliably discriminate the nanobubble from other foreign substances.

  Furthermore, by measuring the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object, and determining that the object is a nanobubble when the displacement rate is 0.05 N / m or less, Nanobubbles and other foreign substances can be discriminated more reliably.

  Therefore, it is possible to contribute to the analysis of the behavior of the nanobubbles for removing defects generated in the wet process during the nanodevice manufacturing process.

  Embodiments of a method and apparatus for identifying nanobubbles according to the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following Example, Various deformation | transformation implementation is possible.

  Using an atomic force microscope, the bubbles in the liquid adhering to the substrate were observed. Specifically, water saturated with carbon dioxide was dropped on an ArF resist substrate, microbubbles that could be observed with an optical microscope were generated on the substrate, and this was observed with an atomic force microscope. As the ArF resist substrate, an ArF resist was spin-coated on a Si (100) single crystal substrate at 2000 rpm for 60 seconds and subjected to a heat treatment for 90 seconds on a 130 ° C. hot plate.

For observation with an atomic force microscope, a cantilever having a tip made of Si ₃ N _{4 at} the tip was used. The spring constant of the cantilever was 0.082 N / m, and the radius of curvature of the tip of the probe was 8 nm.

  As an example of observation of bubbles, FIG. 1A shows an optical microscope image of micro bubbles near the cantilever of an atomic force microscope, and FIG. 1B shows an atomic force microscope image in contact mode. Moreover, the observation area | region by the atomic force microscope at this time is shown in FIG.1 (c). In the flat portion indicated as “in liquid” in FIG. 1B, the probe scans in the liquid.

  Hereinafter, a method for discriminating nanobubbles will be described in detail.

(1) Discrimination by measurement of change in volume of target object with time The change with time of the shape of microbubbles having a diameter of 10 μm was observed using an atomic force microscope. The result is shown in FIG. FIG. 2A is an image of bubbles 4 minutes and 20 seconds after water is dropped on the substrate. In addition, although it was spherical when observed with an optical microscope before scanning with an atomic force microscope, it was swept to the right in FIG. 2A and deformed by scanning with an atomic force microscope in contact mode. The scanning force by the probe at this time was 0.053 nN.

  2 (b), (c), and (d) show the images of bubbles after 4 hours and 38 minutes, 4 hours and 51 minutes, and 5 hours and 6 minutes after dropping water on the substrate, respectively. It was observed that the bubbles became smaller over time. In this way, bubbles in the liquid are dissolved, and the volume decreases with the passage of time.

  Therefore, the change with time of the volume of the object can be measured, and it can be determined that the object is a nanobubble when the volume of the object is reduced.

(2) Discrimination by measuring the displacement rate of the tip of the cantilever The force curve when the probe is brought close to the gas-liquid interface of the bubble, that is, the relationship between the distance between the tip of the probe and the bubble surface and the force acting on the probe Was measured. The measurement results are shown in FIG. In FIG. 3A, the horizontal axis represents the distance between the probe and the bubble surface, and the vertical axis represents the force acting on the probe, that is, the interaction force.

  Hereinafter, based on the force curve in FIG. 3A and the schematic diagram showing the state of deformation of the cantilever in FIG. 3B, the change in the interaction force between the probe and the gas-liquid surface is divided into four regions. Separately described.

  In the region 1 where the distance between the probe and the bubble surface was large, the interaction force showed a substantially constant value, and no particular change was observed. In the region 2 where the distance between the probe and the bubble surface is small, a repulsive force is applied between the probe and the bubble surface. In region 3 where the probe contacts the bubble surface, the probe was drawn into the bubble. Further, repulsive force was applied to the probe in the region 4 where the probe was inserted into the bubble. This repulsive force is considered to be due to Laplace force, that is, meniscus force.

  For comparison, the force curve when the probe was brought close to the ArF resist substrate was measured in the same manner as described above. The measurement results are shown in FIG. 4 (a), and FIG. 4 (b) shows how the cantilever is deformed. In the region 1 where the distance between the probe and the substrate surface was large, the interaction force showed a substantially constant value. In the region 2 where the distance between the probe and the substrate surface is small, a repulsive force is applied between the probe and the substrate surface. This repulsive force is due to the zeta potential of the electric double layer on the substrate. In the region 3 immediately before the probe contacts the substrate surface, the probe was attracted to the substrate surface. This attraction is due to van der Waals forces. When the probe further approaches the substrate surface, repulsive force is generated due to the overlap of electron orbits between atoms at the tip of the probe and molecules on the substrate surface. In the region 4 after the probe contacted the substrate surface, the value of the interaction force rapidly increased while the tip of the probe was in contact with the substrate surface.

  Next, the force curve when the probe is brought close to the bubble surface and the force curve when the probe is brought close to the ArF resist substrate are measured several times, changing the probe approach speed, and the probe is moved to the bubble. The displacement rate of the tip of the cantilever when pressed against the surface or the substrate surface, that is, the inclination in the region 4 in FIGS. 3A and 4A was obtained. The result is shown in FIG.

  The displacement rate of the cantilever obtained on the bubbles was 0.0132 to 0.0319 N / m, indicating a very soft object. On the other hand, the displacement rate of the cantilever obtained on the ArF resist substrate was close to the cantilever spring constant of 0.082 N / m, indicating that it was a hard object.

  Therefore, the displacement rate of the cantilever on the object is measured, and when the displacement rate is small, for example, 0.05 N / m or less, it can be determined that the object is a nanobubble.

(3) Discrimination by measuring the displacement of the tip of the cantilever While pressing the tip of the probe against the slope of the bubble while vibrating the cantilever up and down, the change over time in the deflection direction and the twist direction of the tip of the cantilever at that time It was measured. The measurement results are shown in FIG. FIG. 6A shows the displacement in the deflection direction, with the displacement value on the negative side when the probe is pressed against the bubble and the displacement value on the positive side when the probe leaves the bubble. FIG. 6B shows the displacement in the twist direction, and the time axis corresponds to FIG. In FIG. 6B, the greater the displacement value, the greater the torsion of the cantilever, indicating that the probe is tilted.

  From the measurement results shown in FIG. 6, when the probe is pressed against the slope of the bubble, the cantilever may be displaced so that the probe faces the center of the bubble, that is, the probe is perpendicular to the bubble slope. confirmed. This is schematically shown in FIG. This is considered to be due to the Laplace force resulting from the angle at which the side surface of the probe and the bubble contact, that is, the moment due to the meniscus force. That is, it is considered that the Laplace force acts in a direction in which the angle at which the side surface of the probe contacts the bubble is perpendicular. This phenomenon is considered to be a phenomenon peculiar to bubbles. This is because when the object is a solid, the probe is repelled by the surface of the solid, and a twist in the direction opposite to that of a bubble occurs.

  Therefore, the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object is measured, and when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object, the object It can be determined that it is a bubble.

(4) Method for discriminating nanobubbles of the present invention The method for discriminating nanobubbles of the present invention is based on discrimination among the above three discriminating methods by measuring the displacement of the tip of the cantilever. That is, a method for determining nanobubbles using an atomic force microscope equipped with a cantilever having a probe at the tip, and measuring the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object Then, when the tip of the cantilever is displaced in a direction in which the probe is orthogonal to the slope of the object, it is determined that the object is a nanobubble. Therefore, it is possible to reliably discriminate nanobubbles from other foreign substances.

  And in order to perform discrimination more reliably, a change with time of the volume of the object may be measured, and it may be determined that the object is a nanobubble when the volume of the object is reduced. In order to make a more reliable determination, the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is measured. When the displacement rate is 0.05 N / m or less, the object is a nanobubble. You may determine that there is.

  Further, according to the nanobubble discrimination method of the present invention, when the tip of the probe is pressed against the slope of the object, the tip of the cantilever was not displaced in a direction perpendicular to the slope of the object. In this case, when the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is 0.05 N / m or less, it is determined that the object is a soft solid such as a gel or a graft polymer. be able to.

  Furthermore, when the tip of the cantilever is not displaced in the direction perpendicular to the slope of the object when the tip of the probe is pressed against the slope of the object, the tip of the probe is pushed against the object. When the displacement rate of the tip of the cantilever at the time of contact exceeds 0.05 N / m, it can be determined that the object is a hard solid such as a nanoparticle.

  FIG. 8 summarizes the criteria for determining whether the object is a nanobubble, a soft solid such as a gel or graph and a polymer, or a hard solid such as a nanoparticle.

  The nanobubble discrimination device of the present embodiment will be described. Note that the nanobubble discrimination device of this example is composed of an atomic force microscope equipped with a cantilever having a probe at the tip, but the configuration of the atomic force microscope is the same as the conventional one, so Description is omitted.

  The nanobubble discrimination device 1 of the present embodiment is a nanobubble discrimination device including an atomic force microscope provided with a cantilever having a probe at the tip. Then, as shown in FIG. 9, the displacement measuring means 3 for measuring the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object, and the direction in which the probe is orthogonal to the slope of the object When the tip of the cantilever is displaced, there is provided determination means 2 for determining that the object is a nanobubble.

  The displacement measuring means 3 is configured to control the operation of the cantilever and measure the displacement of the tip of the cantilever.

  The determination unit 2 is configured to determine whether the object is a nanobubble based on the measurement data from the displacement measurement unit 3.

  Further, the nanobubble discrimination device 1 of the present embodiment includes a volume measuring unit 4 that measures a change in the volume of the object over time, and the judging unit 2 is configured such that the object is nano-sized when the volume of the object is reduced. It is comprised so that it may determine with it being a bubble.

  The volume measuring means 4 is configured to scan the object at a predetermined time interval with a cantilever and measure the volume of the object at each time point.

  The determination unit 2 is configured to determine whether the object is a nanobubble based on the measurement data from the volume measurement unit 4.

  Furthermore, the nanobubble determination apparatus 1 of the present embodiment includes a displacement rate measuring means 5 that measures the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object, and the determination means 2 includes: When the displacement rate is 0.05 N / m or less, the object is determined to be nanobubbles.

  The displacement rate measuring means 5 is configured to control the operation of the cantilever and measure the displacement rate of the tip of the cantilever.

  The determination unit 2 is configured to determine whether the object is a nanobubble based on the measurement data from the displacement rate measurement unit 5.

  The program of the present embodiment will be described. The program of this embodiment is a program for causing a computer to function as the determination unit 2, the displacement measurement unit 3, the volume measurement unit 4, and the displacement rate measurement unit 5.

  As shown in FIG. 10, in step S1, the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object is measured. In step S2, when the tip of the cantilever is displaced in a direction in which the probe is orthogonal to the slope of the object, the process proceeds to step S3. In step S2, when the tip of the cantilever is not displaced in the direction in which the probe is orthogonal to the slope of the object, it is determined that the object is not a nanobubble.

  Next, in step S3, the change with time of the volume of the object is measured. In step S4, when the volume of the object decreases, the process proceeds to step S5. In step S4, when the volume of the object does not decrease, it is determined that the object is not a nanobubble.

  In step S5, the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is measured. And in step S5, when a displacement rate is 0.05 N / m or less, it determines with a target object being a nano bubble in step S7. In step S5, when the displacement rate exceeds 0.05 N / m, it is determined that the object is not a nanobubble.

  This program can be provided by being recorded on a computer-readable recording medium.

  The method and apparatus for discriminating nanobubbles of the present invention can be used for inspection of contamination and defects on the surface of a substrate such as glass or semiconductor. Hereinafter, an example in which the nanobubble determination apparatus of the present invention is used as a defect inspection apparatus for a substrate surface will be described.

  In FIG. 11, 11 is a cantilever of an atomic force microscope, and a probe 12 is provided at the tip thereof. Above the cantilever 11, a lens 13 for optically enlarging and observing the cantilever and the nanobubbles 18 is provided. A circulation path 14 for circulating the gas saturated water 19 is formed around the lens 13. Then, the gas saturated water 19 is supplied and sucked from the circulation path 14, and a meniscus is formed between the lens 13 and the substrate 15 such as glass or semiconductor.

  Next, the operation will be described. If there is organic contamination 16 or nano defects 17 on the substrate 15, nano bubbles 18 are selectively generated in those portions. This nanobubble 18 is discriminated by the method of the present invention. The generation of bubbles is promoted by circulating the bubble saturated water 19. Further, by circulating the gas saturated water 19 having a temperature lower than that of the substrate 15, the generation of the nanobubbles 18 can be promoted.

  As described above, the nanobubble determination device of the present embodiment is provided with the lens 13 for optically magnifying and observing the probe 12 and the nanobubble 18, and around the lens 13 is a gas A circulation path 14 for circulating the saturated water 19 is formed. By scanning the nanobubble determination device on the substrate 15, the bubble generation distribution can be examined. As a result, contamination and defects on the surface of the substrate 15 can be inspected.

It is a schematic diagram (c) which shows the optical microscope image (a) of the micro bubble near the cantilever of an atomic force microscope, the atomic force microscope image (b) by contact mode, and the observation area | region by an atomic force microscope. It is an atomic force microscope image which shows a time-dependent change of the shape of a microbubble. It is a graph (a) which shows the interaction force when a probe is brought close to the gas-liquid interface of a bubble, and a schematic diagram (b) which shows the mode of deformation of a cantilever. FIG. 4 is a graph (a) showing an interaction force when a probe is brought close to an ArF resist substrate, and a schematic diagram (b) showing a state of deformation of the cantilever. It is a graph which shows the displacement rate of the front-end | tip of a cantilever when a probe is pressed on the bubble surface or the substrate surface. It is the graph (a) which shows the time-dependent change of the displacement of the bending direction of the front-end | tip of a cantilever, and the graph (b) which shows the time-dependent change of the displacement of a twist direction. It is a schematic diagram which shows a mode when a probe is pressed on the slope of a bubble. It is a table | surface which shows the reference | standard for judging whether a target object is solid solids, such as a nano bubble, gel, a graph, and a polymer, and hard solids, such as a nanoparticle. It is a block diagram which shows one Example of the discrimination device of the nanobubble of this invention. It is a flowchart which shows one Example of the program of this invention. It is a schematic diagram which shows one Example of the discrimination device of the nanobubble of this invention.

Explanation of symbols

2 Determination means 3 Displacement measurement means 4 Volume measurement means 5 Displacement rate measurement means
12 Probe
13 Lens
14 Circuit
18 nanobubbles
19 Gas saturated water

Claims (11)

A method for determining nanobubbles using an atomic force microscope equipped with a cantilever having a probe at the tip, measuring the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object, A method of determining a nanobubble, wherein the object is determined to be a nanobubble when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object. 2. The method for determining nanobubbles according to claim 1, wherein a change with time of the volume of the object is measured and it is determined that the object is a nanobubble when the volume of the object is reduced. The displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is measured, and it is determined that the object is a nanobubble when the displacement rate is 0.05 N / m or less. The method for determining nanobubbles according to claim 1 or 2 . A nanobubble determination device consisting of an atomic force microscope equipped with a cantilever with a probe at the tip, measuring the displacement of the tip of the cantilever when the tip of the probe is pressed against the slope of the object An apparatus for determining a nanobubble, comprising: a means for determining that the object is a nanobubble when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object. Volume measuring means for measuring a change with time of the volume of the object is provided, and the determination means is configured to determine that the object is a nanobubble when the volume of the object decreases. The nanobubble determination apparatus according to claim 4 . Displacement rate measuring means for measuring the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object is provided, and the determination means is configured such that the object is nano when the displacement rate is 0.05 N / m or less. 6. The nano-bubble determination device according to claim 4 , wherein the determination device is determined to be a bubble. A lens for optically magnifying and observing the probe and nanobubbles is provided, and a circulation path for circulating gas saturated water is formed around the lens. determination apparatus nanobubbles according to any one of 4-6. The apparatus for determining nanobubbles according to any one of claims 4 to 7, which is used for inspection of contamination or defects on a substrate surface. A program used in a nanobubble determination apparatus comprising an atomic force microscope having a cantilever having a probe at the tip, the tip of the cantilever when the tip of the probe is pressed against the slope of the object And a program for functioning as a determination means for determining that the object is a nanobubble when the tip of the cantilever is displaced in a direction perpendicular to the slope of the object. 10. The program according to claim 9, for causing a computer to function as a volume measuring unit that measures a change in the volume of an object over time, and a determination unit that determines that the object is a nanobubble when the volume of the object decreases. . Displacement rate measuring means for measuring the displacement rate of the tip of the cantilever when the tip of the probe is pressed against the object, and the object is a nanobubble when the displacement rate is 0.05 N / m or less The program according to claim 9 or 10 for functioning as a determination means for determining that the