Charged particle beam device and method for adjusting same

Abstract

The objective of the present invention is to provide a charged particle beam device that has a simple configuration and is provided with a charged particle beam source capable of generating a stable charged particle beam over an extended period of time, and to provide a method for adjusting the charged particle beam device. The means for achieving the above objective is as follows. The charged particle beam device comprises: a charged particle beam source for emitting a charged particle beam; a charged particle gun chamber in which the charged particle source is placed; a first vacuum pump for evacuating the inside of the charged particle gun chamber; a sample chamber in which a sample to be irradiated with the charged particle beam is placed; a second vacuum pump for evacuating the sample chamber; a wall part separating the charged particle gun chamber and the sample chamber; and a differential evacuation opening part which is provided in the wall part and which allows the charged particle beam to pass. The charged particle beam device includes a shielding part provided between the charged particle beam source and the differential evacuation opening part, the shielding part shielding at least a part of an area on an extension line of the optical axis of the charged particle beam emitted from the charged particle beam source toward the sample.

Description

Charged particle beam device and adjustment method thereof

[0001] The present invention relates to a charged particle beam device.

[0002] Charged particle beam devices, which focus and accelerate charged particles such as electrons and ions using lenses composed of magnetic coils, irradiate the object to be observed, and form an image of the reflected charged particles for observation, are indispensable for research applications and semiconductor manufacturing processes. Such charged particle beam devices must be designed to ensure stable emission of primary charged particles over long periods of time. In particular, the semiconductor inspection process in semiconductor manufacturing requires continuous inspection of multiple semiconductor wafers over long periods of time, making the stability of the charged particle beam source a critical factor.

[0003] Charged particle beam sources pose a challenge in stable operation over long periods of time because the amount of charged particle beams emitted is reduced by gas molecules adsorbed on the surface. Charged particle beam devices are therefore designed to reduce the amount of gas adsorbed to the charged particle beam source by using a differential pumping structure aimed at lowering the pressure around the charged particle beam source. However, it is known that gas molecules entering through the differential pumping opening travel in a straight line within the molecular flow region, colliding with the charged particle beam source located directly above the differential pumping opening and adsorbing the gas molecules, thereby reducing the amount of charged particle emission.

[0004] To solve this problem, Patent Document 1 proposes a charged particle gun having a charged particle source and an extraction electrode that extracts a charged particle beam from the charged particle source and connected to a pump that evacuates the inside of the charged particle gun, the charged particle gun having an opening through which the charged particle beam passes and a barrier provided in a region connecting the charged particle source and the opening. This technology prevents molecules present in a downstream vacuum chamber with a lower vacuum level from passing through the opening and adsorbing to the charged particle source, thereby reducing current noise and enabling stable operation of the charged particle beam device.

[0005] JP 2011-014244 A

[0006] The technology described in Patent Document 1 can reduce the amount of gas molecules adsorbed to the charged particle beam source, thereby improving the stability of the charged particle beam source. The graphene film used as a barrier in Patent Document 1 is suitable as a barrier material because it is impermeable to gases but allows beams to pass through. However, it is susceptible to heat. Charged particle beam devices inevitably become contaminated by gas molecules adsorbed to structures within the beam column during use, necessitating a process of periodically heating the structures to expel the gas molecules.

[0007] Graphene films are sensitive to heat, making it difficult to eliminate contamination caused by heating. Another issue is that the thickness of a single graphene layer means that the film has low mechanical strength.

[0008] An object of the present invention is to provide a charged particle beam device with a simple configuration that allows stable observation over a long period of time, and a method for adjusting the same.

[0009] The present invention has the following configuration to achieve the above object.

[0010] a first vacuum pump that evacuates the inside of the charged particle gun chamber; a sample chamber in which a sample to be irradiated with the charged particle beam is placed; a second vacuum pump that evacuates the sample chamber; a wall that separates the charged particle gun chamber from the sample chamber; and a differential pumping opening provided in the wall that allows the charged particle beam to pass through, wherein the charged particle beam device has a shielding portion between the charged particle beam source and the differential pumping opening that shields at least a portion of an extension of an optical axis of the charged particle beam irradiated from the charged particle beam source toward the sample.

[0011] According to the present invention, it is possible to provide a charged particle beam device that has a simple configuration and is capable of stable observation over a long period of time, and a method for adjusting the same. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0012] Schematic diagram of a charged particle beam imaging device equipped with a charged particle beam aperture (annular aperture) Diagram showing a configuration in which two differential pumping chambers are provided and a differential pumping aperture is added between the two differential pumping chambers Plan view showing example aperture shapes, No. 1 Plan view showing example aperture shapes, No. 2 Plan view showing example aperture shapes, No. 3 Plan view showing the configuration of a charged particle beam aperture Side view showing parts necessary for determining the dimensions of the gas molecule shielding part Flowchart diagram showing the procedure for adjusting the optical axis Flowchart diagram showing the procedure for adjusting the optical axis Plan view showing a GUI screen during optical axis adjustment (comparison example) Schematic diagram of a charged particle beam imaging device equipped with a charged particle beam aperture (single-hole aperture)

[0013] The following describes a charged particle beam device according to the present invention, using an example device that uses an electron beam as the charged particle beam, with reference to the drawings. Note that the charged particle beam may be any type of charged particle beam that can be accelerated by an electromagnetic lens, such as an ion particle beam (e.g., argon ions), in addition to an electron beam. In addition, common components in the various figures are designated by the same reference numerals.

[0014] FIG. 1 shows an outline of a charged particle beam device equipped with a diaphragm shown in the right diagram of FIG. 3A (hereinafter, abbreviated as an "annular diaphragm." The configuration of the annular diaphragm will be described in detail later) as a charged particle beam diaphragm according to the present invention. an electron gun chamber 101 and an electron beam source 102 disposed therein; an extraction electrode 103 for extracting an electron beam from the electron beam source; an acceleration electrode 104 for accelerating the electron beam; a first vacuum pump 105 for evacuating the inside of the electron gun chamber; a differential pumping chamber 106 for realizing a differential pumping structure; an annular diaphragm (including a moving mechanism for moving the position of the diaphragm) 107 for shielding gas molecules from collisions with the electron beam source; a first focusing lens 108 for focusing the electron beam diffused from the electron beam source; a second vacuum pump 109 for evacuating the inside of the differential pumping chamber; an objective movable diaphragm 110 for adjusting the amount of electron beam reaching the sample; a differential pumping diaphragm 112 at a differential pumping opening for restricting the inflow of gas and generating a pressure difference; an outermost trajectory 111 of gas molecules passing through the differential pumping diaphragm 112 and heading toward the electron beam source 102; a charged particle beam path 113; a second focusing lens 114 for adjusting the aperture angle of the charged particle beam relative to the sample; The device is composed of a lens 115, a sample chamber 116 in which the sample and detector are placed, a third vacuum pump 117 that evacuates the sample chamber, a display 118 that displays the control software GUI of the device, a controller unit 119 that controls the device's controller, an electron beam source controller 120 that controls the electron beam source, an acceleration electrode controller 121 that controls the acceleration voltage, a first focusing lens controller 122 that controls the focal position of the first focusing lens, a second focusing lens controller 123 that controls the focal position of the second focusing lens, an objective lens controller 124 that controls the focal position of the objective lens, a detector controller 125 that reads signals detected by the detector, a sample 126, an electron beam detector 127 that detects the electron beam emitted from the sample, a first deflector 128 that controls the electron beam to pass through the center of the differential pumping aperture, a second deflector 129 that scans the electron beam over the objective movable aperture, and a third deflector 130 that passes the electron beam through the center of the objective lens. In the claims, the differential pumping diaphragm 112 is referred to as a "differential pumping opening," and the partition wall (without a reference numeral in FIG. 1) to which the differential pumping diaphragm 112 is attached is referred to as a "wall."

[0015] When the annular diaphragm 107 is installed, gas molecules entering through the differential pumping aperture collide with the shielding portion at the center of the annular diaphragm, thereby suppressing collisions of gas molecules with the charged particle beam source. For the purpose of protecting the charged particle beam source, the annular diaphragm 107 can be disposed between the accelerating electrode 104 and the differential pumping aperture 112 of the differential pumping aperture.

[0016] 2 shows a configuration in which two differential pumping chambers 401 and 402 are provided, with a differential pumping diaphragm 403 added between the two differential pumping chambers. Since the configuration is the same as that shown in FIG. 1 except for the fact that there are two differential pumping chambers, some of the configuration shown in FIG. 1 is omitted. In the claims, the differential pumping diaphragm 403 is referred to as the "second differential pumping opening," and the partition wall (without a reference number in FIG. 2) to which the differential pumping diaphragm 403 is attached is referred to as the "second wall portion."

[0017] Changing the acceleration voltage at the acceleration electrode 104 changes the beam diameter of the electron beam (the diameter of the optical axis of the charged particle beam) and also changes the focal position. The focusing lens 400 has a function of controlling the beam diameter (the diameter of the optical axis of the charged particle beam) so that the beam diameter is minimized by the differential pumping aperture 403 regardless of changes in the acceleration voltage. This function makes it possible to reduce the diameter of the differential pumping aperture 403, thereby making it possible to reduce the shielding portion of the annular aperture 107 and strengthen the differential pumping function.

[0018] 3A to 3C show examples of aperture shapes. The right diagram in FIG. 3A is the annular aperture 107. A gas molecule shielding portion 301 (referred to as a shielding portion in the claims) is provided at the center of the aperture, and the outside of the gas molecule shielding portion 301 has a structure with a circular ring-shaped hole (a structure corresponding to the "gap portion" in the claims). To hold the gas molecule shielding portion 301, a holding portion 302 (corresponding to the "support member" in the claims) is provided. While the annular aperture 107 has four holding portions 302, there are no restrictions on the number or shape of the holding portions as long as they can hold the gas molecule shielding portion 301. As shown in FIG. 3B, there may be three or two holding portions. Furthermore, as shown in FIG. 3C, the diameter of the gas molecule shielding portion 301 may be large or small.

[0019] As will be described later, it is possible to theoretically derive the dimensions of the gas shielding portion that most efficiently shields gas molecules. However, providing a gas shielding portion results in a portion of the electron beam for sample observation being unused. Depending on the sample being observed, it may be desirable to observe under the brightest possible conditions, even if this results in a slight increase in gas molecule adsorption. In such cases, an annular aperture with a small diameter gas shielding portion, as shown in the right diagram of Figure 3C, is useful. Furthermore, some samples generate a lot of gas. In such cases, gas molecules may collide with each other in the differential pumping chamber, causing the gas molecules to travel in a non-theoretical manner and possibly extending beyond the outermost orbit 111 of the gas molecules in Figure 1. In such cases, an aperture with a large diameter gas molecule shielding portion, as shown in the left diagram of Figure 3C, may be more effective. Note that the outer diameter of the aperture in Figure 3C is also larger than that in Figure 3A. The outer diameter of the annular aperture can be freely changed depending on the amount of beam to be transmitted. In the left diagram of Figure 3C, the outer diameter is 250 μm.

[0020] The charged particle beam aperture (annular aperture) is preferably made of a metal such as molybdenum. By making the aperture out of metal, it is possible to heat the aperture appropriately, thereby suppressing the adhesion of contamination to the aperture. A general electric heater can be used as the aperture heating mechanism.

[0021] FIG. 4 shows the configuration of the charged particle beam aperture. Multiple charged particle beam apertures are arranged side by side on a single plate (preferably made of a metal such as molybdenum, as described above). The plate can be moved vertically or horizontally with respect to the optical axis of the charged particle beam using a movable mechanism, allowing for easy replacement or position adjustment of the charged particle beam apertures. The movable mechanism may be manual or may include an electric unit that moves the apertures with a motor via gears. This structure allows for easy replacement of the annular aperture 107 when it becomes dirty, or for switching from the annular aperture 107 to the single-aperture aperture 201 when increasing the amount of charged particle beam reaching the sample. There are no restrictions on the type or order of apertures arranged on the plate. A sensor that detects the movement of the aperture may be attached to the movable mechanism, and the type and location of the set aperture may be displayed on a GUI.

[0022] 5 shows a side view of the portion necessary for determining the dimensions of the gas molecule shielding portion. If the distance from the electron beam source 102 to the annular diaphragm 107 is A, the distance from the electron beam source 102 to the differential pumping aperture 112 is B, and the aperture radius of the differential pumping aperture 112 is C, then the radius X of the gas molecule shielding portion of the annular diaphragm 107 can be calculated by X >= (A × C) / B. The above formula is a condition for preventing gas from being blown up in a linear manner while maximizing the amount of charged particle beam passing through the annular diaphragm. The "radius X of the gas molecule shielding portion" referred to here corresponds to the "radius of the approximately circular plate-like member" in the claims.

[0023] It is possible to increase or decrease the radius of the gas barrier of the annular diaphragm from the above calculation result X, but the maximum effect cannot be achieved because the amount of charged particle beam passing through the annular diaphragm will decrease or gas molecules will collide with the charged particle beam source. However, as mentioned above, the annular diaphragm not only blocks gas molecules but also has the function of transmitting the charged particle beam for sample observation.

[0024] Just as measurement conditions such as the acceleration voltage of the electron source are changed depending on the sample to be observed, it is effective to select an aperture to be used from among annular apertures having various shielding diameters. Note that the upper limit of the radius X of the gas barrier of the annular aperture 107 may be set to C>X in relation to the opening radius C of the differential pumping aperture 112. The annular aperture 107 is disposed closer to the electron beam source 102 than the differential pumping aperture 112, and even if the opening radius C of the differential pumping aperture 112 is smaller than the opening radius C of the differential pumping aperture 112, it is possible to increase the amount of charged particle beam passing through the charged particle beam aperture while preventing gas from being blown up.

[0025] Fig. 6 shows the procedure for adjusting the optical axis of the annular diaphragm in the charged particle beam instrument equipped with the annular diaphragm shown in Fig. 1. Note that it is desirable to perform the optical axis adjustment of the annular diaphragm after performing the optical axis adjustment of the other optical systems.

[0026] First, observation is started with the first focusing lens 108 turned off (step S61). Note that adjustment can also be performed with the first focusing lens turned on, but adjustment is easier with the first focusing lens turned off. The annular diaphragm 107 is moved in a direction perpendicular to the optical axis to find a position where the brightness of the observed image changes from bright to dark to bright, and the annular diaphragm is adjusted to the darkest position therein (step S62).

[0027] The first focusing lens 108 is turned on (step S63). The objective lens is scanned over the sample while periodically varying the excitation strength (step S64a). The position of the charged particle beam is adjusted using the first deflector 128 disposed below the annular diaphragm 107 so that the movement of the image field of view is stopped (step S65). Instead of adjusting the charged particle beam using a deflector, the optical axis can also be adjusted by moving the position of the annular diaphragm in a direction perpendicular to the optical axis.

[0028] By periodically varying the acceleration voltage, the same effect as periodically varying the excitation of the objective lens in step S64a can be obtained, and similar adjustments can be made (step S64b). However, since changing the acceleration voltage changes the electron beam diameter, which may require adjustment of the electromagnetic lens, it is simpler to perform the adjustment using S64a.

[0029] 7, a procedure for adjusting the optical axis of the annular diaphragm, different from that shown in FIG. 6, will be described. It is desirable to perform the optical axis adjustment of the annular diaphragm after performing the optical axis adjustment of the other optical systems. First, the charged particle beam is scanned over the objective movable diaphragm 110 by the second deflector 129, and the image passing through the objective movable diaphragm is observed (step S71). Note that the above procedure may also be performed by scanning over the differential pumping aperture without the objective movable diaphragm, and observing the image passing through the differential pumping aperture.

[0030] FIG. 8 shows the GUI screen during optical axis adjustment observed in step S71. While viewing the annular image displayed on the display 118, the horizontal position of the annular aperture is adjusted so that the shielding portion of the annular aperture is aligned with the center of the optical axis (step S72). The objective lens excitation is periodically varied from strong to weak while scanning the sample (step S73a). The charged particle beam is moved using the first deflector 128 positioned below the charged particle beam aperture so that the image movement stops (step S74). Alternatively, the optical axis can be adjusted by moving the position of the annular aperture in a direction perpendicular to the optical axis, rather than adjusting the position of the charged particle beam using a deflector. Adjustment can also be achieved by periodically changing the acceleration voltage, as in step S73a described above (step S73b).

[0031] 9 shows an outline of a charged particle beam device equipped with a single-aperture diaphragm as a charged particle beam diaphragm. That is, the annular diaphragm 107 in FIG.

[0032] The electron gun chamber 101 is vacuum pumped －７ The pressure is kept at a pressure of 100 Pa or less, and there is a pressure difference between the differential pumping chamber and the differential pumping opening. As in Fig. 1, the pressure difference generated at the differential pumping opening causes gas molecules to invade from the differential pumping opening on a linear trajectory. In the case of Fig. 2, gas molecules invading from the differential pumping diaphragm 112 of the differential pumping opening move along gas molecular orbits 111 and collide with the electron beam source 102, causing the gas molecules to be adsorbed to the electron beam source 102 and attenuating the charged particle beam.

[0033] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with each other configuration.

[0034] 101...electron gun chamber, 102...electron beam source, 103...extraction electrode, 104...acceleration electrode, 105...first vacuum pump, 106...differential evacuation chamber, 107...charged particle beam aperture (annular aperture), 108...first focusing lens, 109...second vacuum pump, 110...objective movable aperture, 111...gas molecular orbital, 112...differential evacuation aperture, 113...charged particle beam path, 114...second focusing lens, 115...objective lens, 116...sample chamber, 117...third vacuum pump, 118...display, 119...controller unit, 120...electron beam source controller, 121...acceleration electrode controller, 122...first focusing lens controller, 123...second focusing lens controller, 124...objective lens controller, 125...detector controller, 126...sample, 127...electron beam detector, 128...first deflector, 129...second deflector, 130...third deflector, 201...charged particle beam aperture (single aperture), 301...gas molecule shielding section, 302...holding section.

Claims

1. A charged particle source that emits charged particle beams, A charged particle gun chamber on which the charged particle source is placed, A first vacuum pump for exhausting the inside of the charged particle gun chamber, A sample chamber in which the sample to be irradiated with the charged particle beam is placed, A second vacuum pump for evacuating the aforementioned sample chamber, A wall separating the charged particle gun chamber and the sample chamber, A differential exhaust opening provided in the wall portion for allowing the charged particle beam to pass through, A charged particle beam apparatus equipped with, Between the charged particle source and the differential exhaust opening, The shielding portion has a shield that blocks at least a portion of the extension of the optical axis of the charged particle beam irradiated from the charged particle source toward the sample, The shielding portion consists of a plate-shaped member that is generally perpendicular to the optical axis, and has a gap in contact with the plate-shaped member for allowing the charged particle beam to pass towards the sample. The plate-like member is generally circular in shape, the annular gap surrounds the generally circular plate-like member, and the annular gap is surrounded by a support member that supports the generally circular plate-like member. A charged particle beam apparatus characterized in that the support member has a plurality of shielding portions of the plate-shaped member which is generally circular.

2. (delete)

3. (delete)

4. In the charged particle beam apparatus according to claim 1, Let X be the radius of the plate-like member which is roughly circular. The distance between the wall and the charged particle source is B. When the radius of the differential exhaust opening is C, A charged particle beam apparatus characterized by X ≥ (A × C) / B.

5. In the charged particle beam apparatus according to claim 4, Furthermore, a charged particle beam apparatus characterized in that X < C.

6. In the charged particle beam apparatus according to claim 1, A charged particle beam apparatus characterized by comprising a moving mechanism for moving the shielding portion in a plane perpendicular to the optical axis of the charged particle beam.

7. (delete)

8. In the charged particle beam apparatus according to claim 1, A charged particle beam apparatus characterized by comprising a display mechanism that indicates which of the plurality of shielding parts is installed on the optical axis of the charged particle beam.

9. In the charged particle beam apparatus according to claim 1, A charged particle beam apparatus characterized by comprising a heating mechanism for heating at least the shielding portion.

10. In a charged particle beam apparatus according to any one of claims 1, 4 to 6, 8, or 9, A second wall is provided between the aforementioned wall and the shielding portion, separating the charged particle gun chamber and the sample chamber. The second wall portion has a second differential exhaust opening that allows the charged particle beam to pass through, A focusing lens is provided between the second wall portion and the shielding portion to adjust the optical axis diameter of the charged particle beam. The charged particle beam apparatus is characterized in that the focusing lens is equipped with an adjustment mechanism that adjusts the optical axis diameter at the second differential exhaust aperture to the minimum even when the acceleration voltage for accelerating the charged particle beam changes.

11. A method for adjusting a charged particle beam apparatus comprising: a charged particle beam source that emits charged particle beams; a charged particle beam gun chamber on which the charged particle beam source is placed; a first vacuum pump for exhausting the inside of the charged particle beam gun chamber; a sample chamber on which a sample to be irradiated with the charged particle beams is placed; a second vacuum pump for exhausting the sample chamber; a wall separating the charged particle beam gun chamber and the sample chamber; and a differential exhaust opening provided in the wall for allowing the charged particle beams to pass through; wherein between the charged particle beam source and the differential exhaust opening, there is a shielding portion that shields at least a portion of the extension of the optical axis of the charged particle beams irradiated from the charged particle beam source toward the sample; a deflector provided on the sample side of the shielding portion for polarizing the charged particle beams; an objective lens for focusing the charged particle beams toward the sample; and a charged particle beam detector for detecting charged particle beams emitted from a sample as a result of the charged particle beams being irradiated from the charged particle beam source toward the sample; The steps include: moving the shielding portion perpendicular to the optical axis to find a position where the brightness of the image detected by the charged particle beam detector changes from bright to dark to bright, and then aligning the shielding portion with the position where it becomes the darkest; Either step (a) or (b) below, (a) A step of scanning the sample while periodically changing the strength of the excitation of the objective lens, (b) A step of scanning the sample while periodically changing the accelerating voltage for accelerating the charged particle beam, Either step (c) or (d) below, (c) A step of adjusting the position of the charged particle beam using the deflector so that the movement of the image within the field of view is minimized. (d) Moving the charged particle beam so that the image movement stops by moving the position of the shielding portion in a direction perpendicular to the optical axis, A method for adjusting a charged particle beam apparatus, characterized by including the following:

12. The system comprises a charged particle source that emits charged particle beams, a charged particle gun chamber on which the charged particle source is placed, a first vacuum pump for exhausting the inside of the charged particle gun chamber, a sample chamber on which a sample to be irradiated with the charged particle beams is placed, a second vacuum pump for exhausting the sample chamber, a wall separating the charged particle gun chamber and the sample chamber, and a differential exhaust opening provided in the wall for allowing the charged particle beams to pass through, wherein between the charged particle source and the differential exhaust opening, there is a shielding portion that shields at least a portion of the extension of the optical axis of the charged particle beams irradiated from the charged particle source toward the sample, and electron beams reaching the sample A method for adjusting a charged particle beam apparatus, comprising: a charged particle beam aperture for adjusting the amount; a first deflector for controlling the electron beam to pass through the center of a differential exhaust opening located closer to the sample than the charged particle beam aperture; a second deflector for scanning the charged particle beam; an objective lens for focusing the charged particle beam onto the sample; an objective movable aperture for adjusting the electron dose reaching the sample; a charged particle beam detector for detecting charged particle beams emitted from a sample due to irradiation of the sample with charged particle beams from the charged particle beam source; and a display for displaying the information detected by the charged particle beam detector as an image. The steps include scanning the charged particle beam with the second deflector, observing the image passing through the movable objective aperture on the display, and adjusting the horizontal position of the shielding portion so that the shielding portion displayed on the display aligns with the optical axis center, Either step (a) or (b) below, (a) A step of scanning the sample while periodically changing the strength of the excitation of the objective lens, (b) A step of scanning the sample while periodically changing the accelerating voltage for accelerating the charged particle beam, Either step (c) or (d) below, (c) A step of adjusting the position of the charged particle beam using the first deflector so that the movement of the image within the field of view is minimized. (d) Moving the charged particle beam so that the image movement stops by moving the position of the shielding portion in a direction perpendicular to the optical axis, A method for adjusting a charged particle beam apparatus, characterized by including the following:

13. In the charged particle beam apparatus according to claim 1, A charged particle beam apparatus characterized in that the radii of multiple shielding portions of the generally circular plate-shaped member of the support member are different.