JP4204902B2 - Charged particle beam device with aberration correction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention corrects aberrations such as chromatic aberration and spherical aberration in a charged particle optical system that focuses a charged particle beam of an electron beam device such as a scanning electron microscope or an ion beam device such as an ion microprobe and irradiates a sample. The present invention relates to a charged particle beam apparatus including an aberration correction apparatus.
[0002]
[Prior art]
In a scanning electron microscope or a transmission electron microscope, an aberration correction apparatus is incorporated in an electron optical system for the purpose of observing a high resolution image or increasing a probe current density. As this aberration correction apparatus, a method has been proposed in which chromatic aberration is corrected by a combination of an electrostatic quadrupole and a magnetic quadrupole, and spherical aberration is corrected by a four-stage octupole. The principle is introduced in detail in the following documents.
[0003]
[1] H. Rose, Optik 33, Heft 1 (1971) 1-24
[2] J. Zach, Optik 83, No. 1 (1989) 30-40
[3] J. Zach and M. Haider, Nucl. Instr. And Meth. In Pyhs. Res.
A 363 (1995) 316-325
Here, an outline of the principle of the aberration correction apparatus will be described with reference to FIG. In FIG. 1, an aberration correction device C is disposed upstream of the objective lens 7 and downstream of the objective lens aperture 8. The aberration correction device C generates a magnetic potential distribution similar to the potential distribution generated by the four-stage electrostatic quadrupole 1, 2, 3, 4 and the second and third stages of the electrostatic quadrupole. Two-stage magnetic quadrupoles 5, 6 that form a superimposed magnetic field and four-stage electrostatic octupoles 11, 12, that form an electric field superimposed on the electric field formed by the four-stage electrostatic quadrupole. 13 and 14.
[0004]
In the figure, the first-stage electrostatic quadrupole 1 and the first-stage electrostatic octupole 11 are drawn in an overlapping manner. Similarly, the second-stage electrostatic quadrupole 2, the second-stage electrostatic octupole 12, and the first magnetic field-type quadrupole 5 are drawn in an overlapping manner. Similarly, a third-stage electrostatic quadrupole 3, a third-stage electrostatic octupole 13, and a second magnetic field-type quadrupole 6 are drawn in an overlapping manner. Similarly, a fourth-stage electrostatic quadrupole 4 and a fourth-stage electrostatic octupole 14 are drawn in an overlapping manner.
[0005]
Further, 9 is an operation display unit, 10 is a power source for electrostatic quadrupoles, 15 is a power source for magnetic field type quadrupoles, 17 is a power source for objective lenses, 18 is a power source for electrostatic octupoles, and 19 is a control unit. . Further, FFP is the front focal position of the objective lens 7, and PP is the principal surface position of the objective lens.
[0006]
In such a configuration, the charged particle beam incident from the left side of the figure forms a reference charged particle beam trajectory by the four-stage electrostatic quadrupoles 1, 2, 3, 4 and the objective lens 7. The charged particle beam is focused on the sample surface 20. In FIG. 1, the orbit R in the X direction of the particle beam_xAnd Y-direction trajectory R_yIs schematically drawn on a plane.
[0007]
The reference trajectory is a paraxial trajectory and a trajectory R in the Y direction by the quadrupole 1_yPasses through the center of the quadrupole 2 and the trajectory R in the X direction by the quadrupole 2_xIs a trajectory through which the charged particle beam is focused on the sample surface 20 by the quadrupoles 3 and 4 and the objective lens 7 at the end. In practice, these mutual adjustments are necessary for complete focus.
[0008]
Next, chromatic aberration correction by the aberration correction apparatus C will be described. In order to first correct chromatic aberration with the system shown in FIG. 1, the potential φ of the electrostatic quadrupole 2 is set so as not to change the reference trajectory._q2[V] and magnetic field type quadrupole 5 excitation J₂[AT] (or magnetic position) is adjusted, and the chromatic aberration in the X direction is corrected to 0 for the entire lens system. Similarly, the potential φ of the electrostatic quadrupole 3 so as not to change the reference trajectory._q3[V] and excitation of magnetic field type quadrupole 6_Three[AT] is adjusted, and the chromatic aberration in the Y direction is corrected to 0 for the entire lens system.
[0009]
Next, spherical aberration correction (third-order aperture aberration correction) will be described. When correcting spherical aberration, the potential Φ of the electrostatic octupole 12 is corrected after correcting chromatic aberration in the X and Y directions._O2[V] corrects the spherical aberration in the X direction to 0 as the whole lens system, and the potential φ of the electrostatic octupole 13 is corrected._O3To correct the spherical aberration in the Y direction to zero.
[0010]
Next, the spherical aberration in the direction in which XY is synthesized is corrected to 0 by the electrostatic octupoles 11 and 14. In practice, alternate repeated adjustments are required. In addition, the superposition of the potential and excitation of the quadrupole and octupole uses a single twelve pole to change the potential and excitation applied to each of the twelve poles, thereby dipole, quadrupole, hexapole, octupole, etc. Has been synthesized and put into practical use. In this way, the positive aberration of the objective lens 7 that operates as a convex lens is canceled by the negative aberration of the aberration correction device C that operates as a combination of a concave lens and a convex lens.
[0011]
The spherical aberration correction can be performed without correcting the chromatic aberration. For example, when the acceleration voltage is high, chromatic aberration has a relatively smaller influence than spherical aberration, and thus only spherical aberration may be corrected.
[0012]
In the following description, when the expression of potential φ (or voltage) is used for an electrostatic multipole, it represents the value on the + side of the multipole having a standard arrangement as shown in FIGS. 2a and 2b. To do. Similarly, when the expression magnetic field type excitation J is used, it represents the excitation [AT] on the + side.
[0013]
In the aberration correction apparatus C shown in FIG. 1, the results of the above-described theory of aberration correction and the results of experiments actually performed correct chromatic aberration and spherical aberration almost completely, and the superiority of the aberration correction system is recognized. It is done.
Incidentally, the aberration correction apparatus C shown in FIG. 1 is composed of quadrupoles and octupoles. However, there is an aberration correction apparatus composed of hexapoles for correcting spherical aberration. Used on the image forming side of the microscope (the side on which the image of the sample is enlarged). Further, when an aberration correction apparatus composed of this hexapole is used on the imaging side of a transmission electron microscope, a transfer lens is provided between the aberration correction apparatus and the objective lens, and a coma free point (coma aberration) of the aberration correction apparatus is provided. It is considered that the blur due to image distortion and coma aberration is reduced by conjugating the objective lens with a coma free point. Further, by providing such a transfer lens, a physical distance can be secured without increasing the optical distance between the aberration correction apparatus and the objective lens.
[0014]
For example, as an aberration correction apparatus, a spherical aberration correction apparatus using two hexapoles is provided, and when correcting chromatic aberration, a method of arranging a chromatic aberration correction apparatus between hexapoles is described in the following document [4]. It is shown.
[0015]
[4] H. Rose, Optik 84, No.3 (1990) 91-107
Further, the following document shows a method using two transfer lenses having a focal length f.
[0016]
[5] H. Rose, Optik 85, No.1 (1990) 19-24
[6] USP No. 5,084,622
In the optical systems shown in these documents, the position Z where there is no coma aberration of the objective lens._OLC(In the case of an imaging system, it is said that it substantially coincides with the back focal position of the objective lens) and the position Z of the surface without the coma aberration of the aberration corrector_CCWhere L = 4f, the position Z where there is no coma aberration of the objective lens_OLCF is the distance between the main surface of the transfer lens and the front transfer lens, 2f is the distance between the main surfaces of the front transfer lens and the rear transfer lens, and there is no coma aberration in the aberration correction device. Position Z_CCThe distance between and is f.
[0017]
Also, the following US patent
[7] USP No. 6,191,423
As described in, the position Z of the surface without coma aberration of the objective lens_OLC(In the case of an imaging system, it is said that it substantially coincides with the back focal position of the objective lens) and the position Z of the surface without the coma aberration of the aberration corrector_CCAnd L = 4f, the position Z of the surface free from coma aberration of the aberration corrector_CCThe distance Z between the main surface of the transfer lens and the main surface of the transfer lens is 2f, and the position Z of the main surface of the transfer lens and the surface without the coma aberration of the objective lens_OLCAnd the distance is 2f.
[0018]
[Problems to be solved by the invention]
In the results based on the theory of aberration correction described above and experiments actually performed, chromatic aberration and spherical aberration are almost completely corrected by the aberration correction method shown in FIG. 1, and the superiority of the aberration correction system is recognized. However, from the viewpoint of practical use, sufficient consideration has not been given to the stability of the aberration correction system, the range of applied voltage, and the optimum conditions. For example, the following problems have occurred.
[0019]
First, in the configuration as shown in FIG. 1, when the acceleration voltage is low, even if the amount of aberration for correction generated by the aberration correction apparatus C is somewhat large, the acceleration voltage is low. Since the voltage applied to the type of multipole (such as a quadrupole or octupole) is not set so high, there is no problem with the withstand voltage of the multipole. However, when the conditions of the apparatus are changed from a low acceleration voltage to a high acceleration voltage in this optical system, the correction voltage for correction is naturally larger than that when the acceleration voltage is low. As a result, the voltage applied to the multipole becomes higher and the withstand voltage of the multipole may be exceeded.
However, if the device is designed so that the withstand voltage of the multipole is not exceeded when the acceleration voltage is high, the applied voltage to the multipole naturally becomes low when the acceleration voltage is low. It becomes easy to be affected by fluctuations in the power supply and the like, making it difficult to correct aberrations appropriately.
On the other hand, in a charged particle beam apparatus that focuses a charged particle beam and irradiates a sample, such as a general-purpose scanning electron microscope or an electron probe apparatus equipped with an element analysis function, the acceleration voltage ranges from a low acceleration voltage to a high acceleration voltage. Since this is necessary, the above becomes a practical problem.
[0020]
Second, in order to further improve the performance, higher-order aberrations remaining after correction of chromatic aberration and spherical aberration, for example, fifth-order aperture coefficient C5 (proportional to the fifth power of the incident angle α of the particle beam on the sample) Aberrations) and the fourth-order aberration coefficient, the third-order aperture / chromatic aberration coefficient C3c (proportional to the cube of the incident angle α to the sample and proportional to the energy width of the particle beam). It is also necessary to consider the aberration coefficient.
[0021]
Third, in a charged particle beam apparatus that focuses a charged particle beam and irradiates a sample, a deflection apparatus, an astigmatism correction apparatus, or the like is disposed between the aberration correction apparatus C and the objective lens 7. Requires space. However, if the space (distance) is simply opened, the following problems occur. That is, the correction of the aberration is performed by causing the aberration correction apparatus C to generate the opposite aberration on the sample surface when the aberration correction apparatus C is not performing the aberration correction. If the space (distance) between the two is simply increased, higher-order aberrations (C5, C3c, etc.) generated by combining the aberration of the aberration correction apparatus C and the aberration of the objective lens 7 become large values. End up. That is, these higher order combined aberrations increase in proportion to the distance between them.
[0022]
The present invention has been made in view of the above points, and an object thereof is to realize a stable and optimum aberration correction and to obtain a minimum probe diameter of a charged particle beam. Is to realize.
[0023]
[Means for Solving the Problems]
  A charged particle beam apparatus provided with an aberration correction apparatus according to the present invention is disposed inside an optical system of a charged particle beam apparatus, and has two electrostatic quadrupoles at the center of the four stages and two at the center of the four electrostatic quadrupoles. Aberration correction apparatus having a two-stage magnetic quadrupole that superimposes a magnetic potential distribution similar to the potential distribution of the four-stage electrostatic quadrupole, and a power supply that supplies a voltage to each of the four-stage electrostatic quadrupole A power source for supplying a current to each of the two-stage magnetic field type quadrupoles; an objective lens for focusing a charged particle beam that is arranged downstream of the aberration correction device and irradiates the sample; a power source for the objective lens; A transfer lens that is disposed between the aberration correction device and the objective lens, and includes at least one transfer lens for transmitting an image plane formed by the aberration correction device to a position of an object plane of the objective lens. An operation unit for changing at least one of a power supply for the transfer lens system, an acceleration voltage for applying predetermined energy to the charged particle beam, and a working distance that is a distance between the objective lens and the sample, and the operation unit The power supply for supplying voltage to each of the four-stage electrostatic quadrupoles, the power supply for supplying current to each of the two-stage magnetic quadrupoles, the power supply for the objective lens, and the transfer A control unit that controls the lens power supply is provided, and the composite magnification of the transfer lens system and the objective lens can be adjusted.The transfer lens system is arranged asymmetrically with respect to a plane perpendicular to the optical axis through an intermediate point between the main surface of the final stage multipole element of the aberration correction apparatus and the front focal point of the objective lens.It is characterized by that.
[0024]
A charged particle beam apparatus provided with an aberration correction apparatus according to the present invention,A four-stage electrostatic octupole that superimposes an octupole potential on the potential distribution of the four-stage electrostatic quadrupole, a power supply that supplies a voltage to the four-stage electrostatic octupole, A control unit for controlling the power supply of the four-stage electrostatic octupole based on operation or setting is provided.It is characterized by that.
[0025]
In the charged particle beam apparatus including the aberration correction apparatus according to the present invention, the transfer lens system is an enlargement type or a reduction system.It is characterized by that.
[0026]
A charged particle beam apparatus provided with an aberration correction apparatus according to the present invention,When the object plane of the transfer lens system is set as the main surface of the final stage multipole element of the aberration correction apparatus, and the image plane conjugate to this is set at the front focal position of the objective lens, the transfer lens with respect to the conjugate point The transfer lens system is arranged at a position where the magnification of the system is 1/3 to 3 times.It is characterized by that.
[0028]
The charged particle beam apparatus equipped with the aberration correction apparatus according to the present invention has a fifth-order aperture coefficient C5 or fourth-order aberration on the sample surface by adjusting the combined magnification of the transfer lens system and the objective lens. The absolute value of the tertiary aperture / chromatic aberration coefficient C3c is minimized..
[0029]
The charged particle beam apparatus equipped with the aberration correction apparatus according to the present invention has components X5 and C5y in the X and Y directions of the fifth-order aperture aberration coefficient C5 on the sample surface or X of the aperture / chromatic aberration coefficient C3c which is the fourth-order aberration. , Y-direction components C3cx, C3cy have the same magnitude so that the positions of the transfer lens system and the objective lens with respect to the aberration correction device are determined..
[0030]
The charged particle beam apparatus including the aberration correction apparatus according to the present invention has a 12-pole potential for correcting the fifth-order aberration coefficient in the focus potential, chromatic aberration correction potential, and spherical aberration correction potential of the multipole of the aberration correction apparatus. Characterized by overlapping.
[0031]
A charged particle beam apparatus including an aberration correction apparatus according to the present invention includes a power source for applying a voltage to a sample surface, and the aberration is caused by decelerating the charged particle beam irradiated to the sample surface by the application of the voltage. By reducing the spherical aberration coefficient and chromatic aberration coefficient of the objective lens before correction, the fifth-order aperture aberration coefficient and the third-order aperture / chromatic aberration coefficient after aberration correction can be reduced..
[0032]
In addition, a charged particle beam apparatus including another aberration correction apparatus according to the present invention includes a power source for applying a voltage to the sample surface, and decelerates the charged particle beam irradiated to the sample surface by applying the voltage. As a result, the aberration coefficient before aberration correction was reduced.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 5 shows the basic configuration of the present invention (first embodiment). In an apparatus for irradiating a sample with a part of a charged particle beam as a probe, a four-stage electrostatic type is used to correct chromatic aberration. Two-stage magnetic quadrupoles 5 and 6 that superimpose magnetic potential distributions similar to the potential distribution of the quadrupoles 1, 2, 3, and 4 and the central two-stage electrostatic quadrupoles 2 and 3, and the objective lens 7 Transfer lens 27a, transfer lens 27b, objective diaphragm 8 provided in a part of the optical path, acceleration voltage for applying predetermined energy to the charged particle beam, and distance between objective lens 7 and sample surface 20. An operation display unit 9 for changing the working distance, a power supply 10 for supplying voltage to the four-stage electrostatic quadrupoles 1 to 4, a power supply 15 for exciting the two-stage magnetic quadrupoles 5 and 6, and an objective lens Power supply 17 for transfer lens and operation display section Control unit 19 for controlling the power 10,15,17 based on the operation or settings are provided.
[0034]
Further, in order to correct spherical aberration, in addition to the above-described components, a four-stage electrostatic type 8 that superimposes an octupole potential on the potential distribution of the four-stage electrostatic quadrupoles 1, 2, 3, 4 is used. A pole 18, 12, 13, 14, a power source 18 that supplies voltage to the four-stage electrostatic octupole, and a controller 19 that controls the power source 18 based on the operation or setting of the operation display unit 9 are provided. ing.
[0035]
Such an aberration correction apparatus C is incorporated in a scanning electron microscope or the like as shown in FIG. Reference numeral 100 denotes a lens barrel whose inside is in a vacuum atmosphere. Inside the lens barrel 100, an electron gun 101 that generates an electron beam and applies energy to the electron by an acceleration voltage, a condenser lens 102 for limiting the current of the electron beam generated by the electron gun 101 to an appropriate value, and an objective aperture 103, an aberration correction device C, a transfer lens system T, a deflector 104 for deflecting and scanning an electron beam in two dimensions, an objective lens 105 for focusing the electron beam and irradiating the sample 106, and a sample 106 are placed. Then, a sample stage 107 that can arbitrarily drive the sample 106 so that the electron beam is irradiated / scanned at a desired location, and a detection that detects a signal such as a secondary electron generated from the sample 106 due to the irradiation / scanning of the electron beam. A device 108 and the like are provided.
However, in an actual apparatus, the arrangement relationship between the transfer lens system T and the deflector 104 does not always match this figure. Note that the electron gun 101 to the objective lens 107 may be called an electron beam optical system. Furthermore, when a deceleration potential for the electron beam is applied to the sample 106 via the sample stage 107, the electron gun 101 to the sample 106 may be referred to as an electron beam optical system.
[0036]
FIG. 12 shows an example in which the aberration correction apparatus C is incorporated in a scanning electron microscope or the like. A transmission electron microscope having a function of irradiating a sample by two-dimensionally scanning an electron beam in the same manner as the scanning electron microscope. In the example in which the aberration correction apparatus C is incorporated in the sample stage 107, a sample system 107 includes a lens system for enlarging a transmission image formed by an electron beam transmitted through the sample 106 in FIG. What is necessary is just to think that it is provided below.
[0037]
Further, the positional relationship between the objective lens 7 and the transfer lens system will be described with reference to FIG. First, the focal length f_aThe distance L between the transfer lens 27a and the principal surface of the electrostatic quadrupole 4 can be obtained.₁F_aTo the extent. Also, the focal length f_bThe distance L between the transfer lens 27b and the main surface of the transfer lens 27a₂F_a+ F_bTo the extent. Further, the objective lens 7 is moved to a distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7._ThreeIs f_bArrange so that it is about.
[0038]
With the configuration described above, the particle probe is focused on the sample surface 20 by the control of the power supply 17 for the objective lens 7 and the transfer lens. Where f_aDegree, f_a+ F_bDegree, f_bThe expression “degree” does not indicate mechanical tolerance accuracy, and in order to configure the apparatus conveniently, even if it is intentionally shifted by about 10 to 20% from these reference values, it will affect the performance. In other words, the positions of the transfer lenses 27a and 27b and the objective lens 7 can be configured.
[0039]
Incidentally, as a very special case of FIG. 5, an arrangement of transfer lenses as shown in FIG. 3 can be considered. That is, the distance L between the transfer lens 27a from which the focal length f is obtained and the principal surface of the electrostatic quadrupole 4 is obtained.₁Is f. Similarly, the distance L between the transfer lens 27b and the main surface of the transfer lens 27a from which the focal length f can be obtained.₂Let f + f = 2f. Further, the objective lens 7 is moved to a distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7._ThreeIs arranged so that becomes f. In this case, the magnification of the transfer lens system formed by the transfer lens 27a and the transfer lens 27b is 1 ×.
[0040]
The arrangement of the transfer lens shown in FIG. 3 is the transfer lens in the case of the imaging side (side for enlarging the sample image) of the transmission electron microscope by combining the hexapole and the transfer lens previously shown as the prior art. Is similar to the arrangement. Actually, in the case of the aberration correction device provided on the imaging side of the transmission electron microscope, the transmitted image of the sample has a finite size (area), so depending on the arrangement of the transfer lens, the image is distorted to the off-axis image. And inconvenience such as blur due to coma aberration occur. In order to reduce the distortion, blur, and the like, it is necessary to keep the relationship between the focal length f of the transfer lens and the arrangement of the transfer lens strictly.
On the other hand, in the case of the apparatus to which the present invention is applied to irradiate the focused beam onto the sample surface 20, even if the relationship between the focal length f of the transfer lens and the arrangement of the transfer lens is not strict, The inventors have found that no inconvenience arises. According to this discovery, it can be seen that firstly the arrangement of the transfer lens becomes free, and secondly, when the transfer lens is arranged in a certain arrangement, no problem occurs even if the magnification of the transfer lens is changed.
However, since the aberration of the optical system increases if the arrangement is shifted too much, it is safe to limit the limit of the position of the transfer lens system to about 50% of the focal length of the transfer lens. That is, in the case of FIG. 3, if the position of the transfer lens system is shifted by about 50% of the focal length of the transfer lens, the realizable transfer lens system magnification is about 1/3 to 3 times. .
Similarly, the magnification of the transfer lens has the following limitations. First, since changing the magnification of the transfer lens changes the focus of the charged particle beam on the sample surface, it is necessary to adjust the magnification of the objective lens so that the charged particle beam is just focused on the sample surface. is there. Second, when the magnification of the transfer lens is changed, the combined magnification of the magnification of the transfer lens and the magnification of the objective lens changes, and the correction amount at the position of the sample surface changes. Therefore, it is necessary to perform an operation such as adjusting the correction amount generated by the aberration correction device again so that the correction amount just cancels the aberration at the position of the sample surface. In the present invention, this limitation is utilized as an advantage for solving the problem rather than a defect.
The operation of the basic configuration shown in FIG. 5 will be described below with reference to FIG.
[0041]
In order to simplify the explanation, the positional relationship among the aberration correction device C, the transfer lenses 27a and 27b, and the objective lens 7 in the configuration of FIG. 5 is set by controlling the objective lens / transfer lens power source 17 to transfer lenses 27a and 27b. Focal length f of each_a, f_bFor the following relationship.
[0042]
L₁= F_a, L₂= F_a+ F_b, L_Three= F_b                        ... (1)
That is, this is a special case of FIG.
[0043]
First, the method of making the reference trajectory of the particle beam in the aberration correction apparatus is performed by the method described in the section of the prior art. That is, as a paraxial orbit (orbit considered as having no aberration), the quadrupole 1 causes the orbit R in the y direction._yPasses through the center of the quadrupole 2 and the trajectory R in the X direction by the quadrupole 2_xPasses through the center of the quadrupole 3, and the quadrupoles 3 and 4 are controlled so that the image plane positions in the X and Y directions of the charged particle beam emitted from the quadrupole 4 coincide. This state is adjusted by adjusting the focus states in the X and Y directions at the same time.
[0044]
Next, the aberration correction device is adjusted so that the beam incident on the transfer lens 27a is parallel to the optical axis. In this way, the beam emitted from the transfer lens 27a is f from the main surface of the transfer lens 27a._aIt passes through a focus position TFP that is far away from the lens and enters the transfer lens 27b. The beam emitted from the transfer lens 27b becomes parallel to the optical axis (however, FIG. 5 is not necessarily the same as the relationship of the above formula (1) and is not drawn in parallel), Incident.
[0045]
Note that it is not a necessary condition to adjust the aberration correction apparatus C so that the beam incident on the transfer lens 27a is “parallel” to the optical axis. That is, if the transfer lens and objective lens are set so as to have a designed focal length, and the above-mentioned focus is matched in the X and Y directions, there is no need to stick to parallelism. This is to make it easier to understand.
[0046]
Next, the objective lens / transfer lens power source 17 is controlled to focus the beam on the sample surface 20. The lens operation for obtaining such a paraxial trajectory is based on a standard concept applying the conventional method. Magnification M with respect to the conjugate point of the transfer system having the lens arrangement satisfying the expression (1)_TLIs f_a= F_bIt becomes 1 at. When correcting chromatic aberration and spherical aberration in this state, it can be performed by the method shown in the above-described conventional example or the method shown in the prior patent application 2001-328776.
[0047]
The method described in the above-mentioned prior patent application 2001-328776 will be briefly described. In the conventional method, the aberration correction amount is adjusted by adjusting the potential and excitation applied to each multipole element of the aberration correction apparatus C. In the method of Japanese Patent Application No. 2001-328776, the objective lens 7 and the objective lens are adjusted. 7 and the combined magnification of the lens or lens system closest to the upstream (transfer lens 27b or transfer lenses 27a and 27b in the present invention) is also adjusted. The adjustment of the aberration correction apparatus C and the adjustment of the composite magnification of the objective lens 7 and the nearest lens can be performed together to greatly widen the range of aberration correction that can be adjusted. However, in the following, the method in the conventional example will be described.
[0048]
That is, when correcting the chromatic aberration, the potential φ of the electrostatic quadrupole 2 is set so as not to change the reference trajectory._q2[V] and magnetic field type quadrupole 5 excitation J₂[AT] (or magnetic position) is adjusted, and the chromatic aberration in the X direction is corrected to 0 for the entire lens system. Similarly, the potential φ of the electrostatic quadrupole 3 so as not to change the reference trajectory._q3[V] and excitation of magnetic field type quadrupole 6_Three[AT] is adjusted, and the chromatic aberration in the Y direction is corrected to 0 for the entire lens system.
[0049]
Next, when correcting spherical aberration, the potential φ of the electrostatic octupole 12 is corrected after correcting chromatic aberration in the X and Y directions._O2[V] corrects the spherical aberration in the X direction to 0 as the whole lens system, and the potential φ of the electrostatic octupole 13 is corrected._O3To correct the spherical aberration in the Y direction to zero. Next, the spherical aberration in the direction in which XY is synthesized is corrected to 0 by the electrostatic octupoles 11 and 14. In practice, alternate repeated adjustments are required.
[0050]
Next, the focal length f of the objective lens 7 is maintained while the control of the aberration correction device C and the transfer lens 27a is left as it is._OLAnd the focal length f of the transfer lens 27b_bTo adjust the total magnification M of the lens system so that the particle beam is focused on the sample surface 20._x, M_ychange. In order not to change this new reference trajectory, the method of correcting chromatic aberration of the aberration correction apparatus described in the above section of the prior art, the correction method of spherical aberration, or the prior patent application 2001-328776 Correct chromatic aberration and spherical aberration by this method.
[0051]
At this time, the fifth-order aperture aberration coefficient C5 and the third-order aperture / chromatic aberration coefficient C3c after correcting the chromatic aberration / spherical aberration are changed to the focal length f of the transfer lens 27b._bFIG. 6 is a plot with respect to. In this example, f_bIs L₃Different from f_mBy the way, it is the smallest. That is, depending on the structure of the aberration corrector C, the operating condition of the aberration corrector C greatly contributes to C5 and C3c, and the vicinity of the main surface of the aberration corrector is not necessarily conjugate with the front focus of the objective lens 7. It shows that it is not good to do.
[0052]
This is because, for the purpose of reducing C5 and C3c, the arrangement of the transfer lenses 27a and 27b is strictly as shown in US Pat. No. 5,084,622, which is an application example similar to the transfer lens of FIG. This shows that it is better to arrange the transfer lenses 27a and 27b and adjust the focal length of the transfer lens 27b and the objective lens 7 for the convenience of the apparatus configuration.
[0053]
As described above, in the first embodiment of the present invention, first, the transfer lenses 27a and 27b can be arranged according to the design convenience, and secondly, the focal length of the transfer lens is made variable. High-order aberrations can be optimally corrected mainly for the second reason. Furthermore, with the second reason, the combined magnification of the magnification of the transfer lens system and the magnification of the objective lens has become variable. By utilizing this, the amount of aberration on the sample surface can be increased or decreased by adjusting the composite magnification, so that the range of increase or decrease in the voltage applied to the multipole of the aberration correction device C accompanying the change in the acceleration voltage or the like can be reduced. It became so. In this way, the control unit 19 uses the probe acceleration voltage V set in the operation display unit 9._a, Working distance WD, probe current I_pAre set to the aberration correction apparatus C, the transfer lens 27b, and the objective lens 7 so that C5 or C3c calculated (or stored) in the operation display unit 9 is minimized. Here, the focal length of the transfer lens 27a may be fixed.
[0054]
In this basic configuration, when the length of the entire lens system is limited to a predetermined length, the distance between the transfer lens 27b and the objective lens 7 becomes relatively small. For this reason, it is not preferable to dispose all of the deflection device and the astigmatism correction device, which should originally be disposed between the aberration correction device C and the objective lens 7, between the transfer lens 27 b and the objective lens 7. Therefore, for example, it is preferable that the deflection device is disposed between the transfer lenses 27a and 27b, and the astigmatism correction device is disposed between the aberration correction device C and the transfer lens 27a.
[0055]
The basic configuration (first embodiment) of the present invention has been described above with reference to FIGS. 5 and 6. In this embodiment, the focal length of the transfer lens 27a is f._aThe distance L between the main surface of the fourth-stage electrostatic quadrupole 4 and the main surface of the transfer lens 27a₁Is f_aAn example of an arrangement such that
[0056]
However, in FIG. 5 of the basic configuration of the present invention (first embodiment), as shown in FIG. 7, depending on the operating conditions of the aberration correction apparatus, the X and Y direction components C5 of C5_x, C5_yAnd the X and Y direction components C3c of C3c_x, C3c_yWhere the magnitude (absolute value) is equal, L₁= F_aNot always there.
[0057]
Accordingly, when the X and Y components of C5 and C3c cannot be simultaneously reduced to 0, the blur of the particle probe is as symmetrical as possible (that is, the blur due to the X component and the blur due to the Y component are reduced to the same extent). L) such that the size of the components in the X and Y directions is approximately the same.₁= L₀Can be selected. This is the second embodiment. However, L₁Is actually difficult to make variable, so L₀Is obtained by calculation or experiment, and this is calculated as a design distance L.₀And it is sufficient. Further, as shown in FIG._b= F_mAnd L under this condition₁L by setting₁= L₀Can also be obtained.
[0058]
In the first and second embodiments described above, a system using two stages of transfer lenses has been described, but the same effect can be obtained even if a single stage of transfer lens is used. This will be described as a third embodiment with reference to FIG. In this case, the following two conditions are assumed. First of all, the focal length f_bThe distance L between the transfer lens 27b and the main surface of the fourth-stage electrostatic quadrupole 4 can be obtained.₂2f_bTo the extent.
[0059]
Secondly, the objective lens 7 has a distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7.₃Is 2f_bArrange so that it is about. Under such conditions, the particle probe is focused on the sample surface 20 under the control of the objective lens / transfer lens power source 17.
[0060]
Where 2f_bThe expression “degree” does not indicate mechanical tolerance accuracy, but in order to configure the apparatus conveniently, even if it is intentionally shifted from these reference values by about 10 to 20%, the performance is not improved. It shows that the positions of the transfer lens 27b and the objective lens 7 can be determined so as not to affect.
[0061]
Incidentally, as an extremely special case of FIG. 8, an arrangement of transfer lenses as shown in FIG. 4 is conceivable. In other words, the distance L between the transfer lens 27b from which the focal length f is obtained and the principal surface of the electrostatic quadrupole 4 is obtained.₂Is 2f. Further, the objective lens 7 is moved to a distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7._ThreeTo be 2f. In this case, the magnification of the transfer lens system formed by the transfer lens 27b is 1 ×. In this case as well, the arrangement of the transfer lens shown in FIG. 4 can be shifted as shown in FIG. 8. However, for the reason described above, it is safe to limit the limit to the focal length of the transfer lens. is there. That is, in the case of FIG. 4, when the position of the transfer lens is shifted by the same distance as the focal length of the transfer lens, the realizable transfer lens system has a magnification of about 1/3 to 3 times.
[0062]
Next, the principle of operation for minimizing higher-order aberration coefficients will be described with reference to FIG. In order to simplify the explanation, the positional relationship among the aberration corrector C, the transfer lens 27b, and the objective lens 7 is determined by controlling the objective lens / transfer lens power source 17 and the focal length f of the transfer lens 27b._bOn the other hand, it is assumed that they are arranged as follows.
[0063]
L₂= 2f_b, L_Three= 2f_b                                  ... (2)
First, the method of making the reference trajectory of the particle beam in the aberration correction apparatus is performed by the method described in the section of the prior art. Next, the beam incident on the transfer lens 27b is transmitted from the main surface of the transfer lens 27b by the aberration correction device._bThe aberration correction device C is adjusted so that it passes through a point CFP on the optical axis that is far away (so that the focus position of the aberration correction device is CFP). In this way, the beam emitted from the transfer lens 27b is parallel to the optical axis (however, FIG. 8 is not necessarily the same as the relationship of the above equation (2), so it is not drawn in parallel). , Enters the objective lens 7.
[0064]
Next, the objective lens / transfer lens power source 17 is controlled to focus the beam on the sample surface 20. The lens operation for obtaining such a paraxial trajectory is based on a standard concept applying the conventional method. The magnification M with respect to the conjugate point of the transfer lens system in this case_TLBecomes 1. In this state, chromatic aberration and spherical aberration can be corrected by the method shown in the prior art or the method shown in the prior patent application 2001-328776.
[0065]
Next, the focal length f of the objective lens 7_OLAnd the focal length f of the transfer lens 27b_bTo maintain the condition that the particle beam is focused on the sample surface 20, and the overall magnification M of the lens system_x, M_ychange. In order not to change this new reference trajectory, chromatic aberration and spherical aberration are corrected by the method shown in the section of the prior art using an aberration correction device or the method shown in the prior patent application 2001-328776.
[0066]
At this time, the fifth-order aperture aberration coefficient c5 and the third-order aperture chromatic aberration coefficient C3c after correction of chromatic aberration and spherical aberration are converted into the focal length f of the transfer lens 27b.₂Is plotted against f as in FIG._bIs L₃Different from f_mBy the way, it is getting minimum. That is, depending on the structure of the aberration corrector, the operating condition of the aberration corrector contributes more to C5 and C3c, and the vicinity of the main surface of the aberration corrector C does not necessarily need to be conjugate with the front focus of the objective lens 7. .
[0067]
This is because, for the purpose of reducing C5 and C3c, the transfer lens 27b is not required to have a strict positional relationship as shown in FIG. 4, but rather the transfer lens 27b is arranged for the convenience of the apparatus configuration. It shows that it is better to adjust the focal length of the objective lens 7b and 27b.
[0068]
In addition, the following is supplemented just in case. F in FIG._aIndicates the focal length of the transfer lens 27a on the side adjacent to the aberration correction apparatus C. In FIG. 8, since 27a does not exist, the focal length of the transfer lens 27b is indicated. That is, in the third embodiment shown in FIG._aIs f in FIG._bCorresponding to L in FIG.₁Is L in FIG.₂It corresponds to.
[0069]
As described above, in the first, second, and third embodiments of the present invention described so far, the acceleration voltage V set in the operation display unit 9 is set._a, Working distance WD, probe current I_pFor the above, the operation condition that C5 or C3c calculated (or stored) in the operation display unit 9 is minimized is set in the aberration correction device C, the transfer lens 27b, and the objective lens 7. .
[0070]
In the configuration shown in the third embodiment of the present invention, when the length of the entire lens system is limited to a predetermined length, the distance between the transfer lens 27b and the objective lens 7 is relatively small. When all of the deflection device and the astigmatism correction device cannot be inserted between the transfer lens 27b and the objective lens 7, the aberration correction device C and the transfer lens 27b are used for arranging these devices. Is done.
[0071]
In each of the embodiments described with reference to FIGS. 5 to 8, the magnification M with respect to the conjugate point of the transfer lens system._TL9 has been considered, but the fact that it can be configured to have a magnification other than this will be described below as a fourth embodiment with reference to FIG. In this case, the focal length f_bThe distance L between the transfer lens 27b and the main surface of the fourth-stage electrostatic quadrupole 4₂1.5f_bThe distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7_ThreeIs 3f_bThe particle probe is focused on the sample surface 20 under the control of the objective lens / transfer lens power source 17.
[0072]
Here, the expressions of 1.5 fb and 3 fb do not indicate mechanical tolerance accuracy, and are intentionally shifted by 10 to 20% from these reference values in order to conveniently configure the apparatus. However, the position of the transfer lens 27b and the objective lens 7 can be configured so as not to affect the performance.
[0073]
Hereinafter, the operation principle for minimizing the higher-order aberration coefficient will be described with reference to FIG. In order to simplify the explanation, the positional relationship among the aberration correction device C, the transfer lens 27b, and the objective lens 7 is arranged as follows with respect to the transfer lens 27b set by controlling the objective lens / transfer lens power source 17. Suppose that
[0074]
L₂= 1.5f_b, L_Three= 3f_b                            ... (3)
That is, this is a special case of FIG.
[0075]
First, the method of creating the reference trajectory of the particle beam in the aberration correction apparatus C is performed by the method shown in the section of the prior art or the method shown in the prior patent application 2001-328776. Next, the beam incident on the transfer lens 27b is transmitted from the main surface of the transfer lens 27b to the aberration correction device C by f._bThe aberration correction device C is adjusted so that it passes through a point CFP on the optical axis that is far away (so that the focus position of the aberration correction device is CFP).
[0076]
In this way, the beam emitted from the transfer lens 27b is parallel to the optical axis (however, FIG. 9 is not necessarily drawn in parallel because the relationship of the above equation (3) is not necessarily the same). And enters the objective lens 7. Next, the objective lens / transfer lens power source 17 is controlled to focus the beam on the sample surface 20. The magnification M with respect to the conjugate point of the transfer lens system in this case_TLBecomes 2. The method of minimizing the magnitude of the fifth-order aperture aberration coefficient C5 and the third-order aperture / chromatic aberration coefficient C3c after correcting chromatic aberration and spherical aberration in this state is the third embodiment described with reference to FIG. Can be done in the same way.
[0077]
In the fourth embodiment, 1 <M_TLL which becomes₂, L_ThreeTherefore, C5 and C3c increase compared to the third embodiment. However, the distance between the aberration corrector C and the objective lens 7 is L without the transfer lens 27b.₂+ L_Three(Or 4f) compared to the device in the case of L₂+ L_ThreeDepending on the size of (or 4f), C5 and C3c can be made smaller by using a transfer lens, and a deflection device and an astigmatism correction device are arranged between the transfer lens 27b and the objective lens 7 in the space. It is convenient because it can be done.
[0078]
8 and 9, the example in which the image plane CFP of the aberration correction device C is between the aberration correction device C and the transfer lens 27b has been shown, but this is the same as the transfer lens 27b as shown in FIG. Obviously, it may be between the objective lenses 7 (TF).
[0079]
Similarly, FIG. 13 illustrates a fifth embodiment that can be configured so that the magnification of a transfer lens system composed of two-stage transfer lenses is a magnification other than one. When the distance between the exit point of the aberration correction device C and the front focal point of the objective lens 7 is 4f, the focal length f_aThe distance L between the transfer lens 27a that provides the main surface of the fourth stage electrostatic quadrupole 4₁F_a= About 0.5f, focal length f_bThe distance L between the transfer lens 27b and the main surface of the transfer lens 27a₂F_a+ F_b= 2f, and the objective lens 7 has a distance L between the main surface of the transfer lens 27b and the front focal position FFP of the objective lens 7._ThreeIs f_bThe particle probe is focused on the sample surface 20 under the control of the objective lens / transfer lens power source 17. At this time, the magnification by the transfer lens system, that is, the magnification by the transfer lens system at the front focal position of the objective lens 7 with respect to the emission position of the aberration correction apparatus C is 3.
[0080]
Here, the expression of about 0.5f, 2f, and 1.5f does not indicate mechanical tolerance accuracy, and is intentionally shifted by about 10 to 20% from these reference values in order to construct the apparatus conveniently. It shows that the positions of the transfer lenses 27a and 27b and the objective lens 7 can be configured so that the arrangement does not affect the performance.
[0081]
Hereinafter, an operation principle for minimizing higher-order aberration coefficients will be described with reference to FIG. In order to simplify the explanation, the positional relationship among the aberration corrector C, the transfer lenses 27a and 27b, and the objective lens 7 is as follows with respect to the transfer lenses 27a and 27b set by controlling the objective lens / transfer lens power source 17. Is arranged as follows.
[0082]
L₁= 0.5f, L₂= 2f, L_Three= 1.5f (4)
That is, this is a special case of FIG.
[0083]
First, the method of creating the reference trajectory of the particle beam in the aberration correction apparatus C is performed by the method shown in the section of the prior art or the method shown in the prior patent application 2001-328776. Next, the aberration correction apparatus C is adjusted so that the beam incident on the transfer lens 27a is parallel to the optical axis. In this way, the beam emitted from the transfer lens 27a passes through the focus position TFP separated by 0.5f from the main surface of the transfer lens 27a and enters the transfer lens 27b. The beam emitted from the transfer lens 27b is parallel to the optical axis (however, FIG. 13 is not necessarily the same as the relationship of the above formula (4) and is not drawn in parallel), and the objective lens 7 Incident.
[0084]
Next, the objective lens / transfer lens power source 17 is controlled to focus the beam on the sample surface 20. The magnification M with respect to the conjugate point of the transfer lens system in this case_TLBecomes 3. The method of minimizing the magnitude of the fifth-order aperture aberration coefficient C5 and the third-order aperture / chromatic aberration coefficient C3c after correcting chromatic aberration and spherical aberration in this state is the third embodiment described with reference to FIG. Can be done in the same way.
[0085]
In the fifth embodiment, 1 <M_TLL which becomes₁, L₂, L_ThreeTherefore, C5 and C3c increase compared to the third embodiment. However, without the transfer lenses 27a and 27b, the distance between the aberration corrector C and the objective lens 7 is L.₁+ L₂+ L_Three(Or 4f) compared to the device in the case of L₁+ L₂+ L_ThreeDepending on the size of (or 4f), the use of the transfer lens can reduce C5 and C3c, and the space between the transfer lenses 27a and 27b and 27b and the objective lens 7 can have a deflecting device or astigmatism. Since a correction device can be arranged, it is convenient.
[0086]
FIG. 10 shows a sixth embodiment. In this embodiment, in order to decelerate the particle probe incident on the sample 20 in the vicinity of the sample, the structure for applying a potential for decelerating the particle probe to the sample surface or the vicinity thereof is described in the first to fifth embodiments. (However, the combination with the third embodiment is shown as a representative example in FIG. 10). The effect by deceleration is shown by the following literature, for example.
[0087]
[8] E. Munro et al., J. Vac. Sci. Technol. B6 (6), Nov / Dec (1988) 1971-1976
That is, in this document, as a most realistic example, when a voltage is applied to the sample surface 20 and the incident energy is reduced to ¼ by the deceleration voltage, the chromatic aberration coefficient Cc is attenuated to about 1/4. The spherical aberration coefficient Cs can be attenuated to about 1 / 2.5. It is also shown that the effect is further increased by increasing the voltage on the sample surface 20 and further increasing the degree of deceleration.
[0088]
In the sixth embodiment of the present invention, a decelerating voltage power supply 30 is provided to supply a voltage for decelerating the particle probe to or near the sample surface, and the above-mentioned properties are used to provide an objective lens before aberration correction. 7 chromatic aberration coefficient Cc and spherical aberration coefficient Cs can be reduced.
[0089]
As a result, the above-mentioned C5 and C3c, which are higher-order aberration coefficients generated as combined aberrations after aberration correction, can be made small. As an example, it was confirmed by simulation that these aberration coefficients can be reduced to 1/5 to 1/10 when the incident energy is reduced to 1/4.
[0090]
Therefore, by using the transfer lens 27b and the present deceleration voltage power supply 30, the high aberration coefficient C5 and C3c after aberration correction can be reduced by about two orders of magnitude compared to the case where these are not used at all. This makes it possible to obtain a finer probe diameter.
[0091]
FIG. 11 shows a seventh embodiment of the present invention. In this embodiment, the effects of the sixth embodiment described above can be further utilized. That is, in the sixth embodiment shown in FIG. 10, the configuration has been described in which the fifth-order aperture aberration coefficient can be reduced on the order of two digits. However, when the value becomes so small, the fifth-order using a 12-pole field is used. Is practical (for example, [9] H. Rose, Optik 34, Heft 3 (1971) 285-311). That is, although not described in detail, a quadrupole field or an octupole field is obtained by synthesizing a field formed by each pole using twelve or more multipoles. More multipoles can be used as a 12-pole for correcting the original fifth-order aperture aberration.
[0092]
Therefore, if the first to fourth stage 12-poles 31 to 34 working as described above and the power supply 35 for the 12-pole are connected to this, the fifth-order aperture aberration can be corrected by the 12-pole. In FIG. 11, the first-stage electrostatic quadrupole 1, the first-stage electrostatic octupole 11 and the first-stage electrostatic twelve pole 31 are drawn in an overlapping manner. Similarly, the second stage electrostatic quadrupole 2, the second stage electrostatic octupole 12, the first magnetic field type quadrupole 5, and the second stage electrostatic twelve pole 32 are stacked. It is drawn. Similarly, the third stage electrostatic quadrupole 3, the third stage electrostatic octupole 13, the second magnetic field type quadrupole 6, and the third stage electrostatic twelve pole 33 are overlapped. It is drawn. Similarly, a fourth stage electrostatic quadrupole 4, a fourth stage electrostatic octupole 14, and a fourth stage electrostatic twelve pole 34 are depicted in an overlapping manner.
[0093]
Hereinafter, this method will be described. The fifth-order aperture aberration correction method can be implemented in the same manner as the conventional spherical aberration correction. That is, as the most basic (primary) method, the adjusting means according to the next step is used.
[0094]
In the first step, C5 which is the X component of C5_xIs corrected by the second 12-pole element 32. At this time, since the orbit in the Y direction passes through the center of the second stage 12-pole, C5 which is a component in the Y direction_yThere is little impact on.
[0095]
Next, in the second step, C5 which is the Y component of C5_yIs corrected by the 12th stage 33 of the third pole. At this time, since the orbit in the X direction passes through the center of the 12th stage of the third stage, C5 which is a component in the X direction._xThere is little impact on.
[0096]
Next, in the third step, the component in which the X and Y directions are combined is corrected by the first and fourth stage 12-pole elements 31 and 34. For example, the opening angle α in the X and Y directions of the particle probe incident on the sample_x, Α_yThe aperture aberration is α_x ^Threeα_y ²Is corrected by the first stage 12-pole element 31, and the aperture aberration is α._x ²α_y ^ThreeIt is also possible to correct the component proportional to the?
[0097]
Next, in the fourth step, C5 is corrected by the correction in the third step._x(Aberration is α_x ^FiveCoefficient proportional to C) and C5_y(Aberration is α_y ^FiveSince the coefficient proportional to is affected, the first step and the second step are adjusted again. This adjustment also reduces α_x ^Threeα_y ²And α_x ²α_y ^ThreeSince the component proportional to is affected, the third step is adjusted again. In practice, this alternate adjustment is repeated.
[0098]
By repeating the first to fourth steps several times, the fifth-order aperture aberration coefficient can be further reduced to 1/100 after aberration correction with respect to the value before aberration correction by the 12-pole field. This indicates that substantially all fifth-order aperture aberration coefficients can be made substantially zero.
[0099]
In this way, since it is not affected by the fifth-order aperture aberration coefficient C5, the aberration that substantially determines the probe diameter is ideally only the diffraction aberration and C3c, and a remarkable effect is obtained.
[0100]
By the way, in FIG. 11, the first-stage electrostatic quadrupole 1 and the first-stage electrostatic octupole 11 are replaced with electrostatic twelve poles, which are also used as electrostatic twelve poles 31. Two-stage electrostatic quadrupole 2 and second-stage electrostatic octupole 12, third-stage electrostatic quadrupole 3 and third-stage electrostatic octupole 13, fourth-stage electrostatic type The quadrupole 4 and the fourth-stage electrostatic octupole 14 are respectively replaced with electrostatic twelfth poles to serve as the electrostatic twelfth poles 32, 33, and 34. In theory, the power source 35 and the power sources 10, 15 , 18 may be combined. However, in practice, it should be possible to operate as if the power supplies 10, 15 and 18 are independent of the power supply 35. Otherwise, the above adjustment work becomes extremely difficult.
[0101]
In the above embodiment, a charged particle beam apparatus having both a function for correcting chromatic aberration by a quadrupole field in which an electric field and a magnetic field are superimposed and a function for spherical aberration by an octupole field will be described. did. However, depending on the characteristics of the charged particle beam apparatus to which the aberration correction apparatus of the present invention is actually applied, either the function of correcting chromatic aberration or the function of spherical aberration can be omitted. For example, in a device with a high acceleration voltage, chromatic aberration is relatively small compared to spherical aberration, and correction of chromatic aberration may be practically omitted. Similarly, in a device with a low acceleration voltage, spherical aberration is relatively small compared to chromatic aberration, and correction of spherical aberration may be practically omitted.
[0102]
Although FIG. 9 shows the case where the magnification of the transfer lens system is 2, when this magnification is further increased, higher-order aberrations, for example, fifth-order aperture aberration coefficient C5 are also greatly increased. On the other hand, when the fifth-order aperture aberration coefficient C5 is large, the voltage for creating the 12-pole field becomes extremely large (for example, 10 times), and it is difficult to correct C5 by the 12-pole. Even if C5 can be corrected, an aberration coefficient of 6th order or higher (for example, 7th order aperture aberration coefficient) is increased by a large aberration correction voltage, and an opening angle α incident on the sample in an attempt to reduce the diffraction effect._x, Α_yIs increased, the influence of these aberrations cannot be ignored, and it is not practical as a means for obtaining a microprobe. Therefore, when high order aberrations are taken into consideration, the practical upper limit is about 3 times the magnification at which the effect of the transfer lens system can be expected.
[0103]
【The invention's effect】
As described above, the charged particle beam apparatus including the aberration correction apparatus according to the first aspect of the present invention includes: (a) a four-stage electrostatic quadrupole disposed inside the optical system of the charged particle beam apparatus; An aberration correction device having a two-stage magnetic quadrupole that superimposes a magnetic potential distribution similar to the potential distribution of the two-stage electrostatic quadrupole in the center of the four-stage electrostatic quadrupole; (b)) An objective lens that is arranged downstream of the aberration correction device and focuses the charged particle beam irradiated on the sample; and (c) an image that is arranged between the aberration correction device and the objective lens and is formed by the aberration correction device. A transfer lens system comprising at least one stage transfer lens for transmitting the surface to the object surface position of the objective lens, and (d) a four-stage electrostatic quadrupole power source and a two-stage magnetic field quadrupole power source And objective lens power supply and transfer lens power supply, (e) An operation unit that changes at least one of an acceleration voltage that gives predetermined energy to the particle beam and a working distance that is a distance between the objective lens and the sample; and (f) based on the operation or setting of the operation unit. It is characterized by comprising a control unit for controlling a four-stage electrostatic quadrupole power source, a two-stage magnetic quadrupole power source, an objective lens power source, and a transfer lens power source.
[0104]
In such a system, since the transfer lens of the transfer lens system arranged between the aberration correction device and the objective lens is relatively freely arranged, the deflection device and the astigmatism correction between the aberration correction device and the objective lens are arranged. The degree of freedom for arranging the devices and the like increases.
[0105]
Furthermore, since the magnification of the transfer lens system can be set relatively freely, the combined magnification of the magnification of the transfer lens system and the magnification of the objective lens can be adjusted without changing the focus of the beam on the sample. As a result, when the accelerating voltage is low, the composite magnification is adjusted to be low so that the amount of aberration generated by the aberration correction device does not become too small, reducing the effects of noise and power supply fluctuations on the applied voltage. However, when the acceleration voltage is high, the composite magnification is adjusted to be high so that the amount of aberration does not become so large that the problem of the withstand voltage of the multipole is reduced.
[0106]
Similarly, since the magnification of the transfer lens system can be set relatively freely, higher-order aberrations remaining after correction of chromatic aberration and spherical aberration, for example, fifth-order aperture coefficient C5 and fourth-order aberration coefficient, third-order aperture It is possible to optimally correct higher-order aberration coefficients such as the chromatic aberration coefficient C3c so that the charged particle beam irradiated on the sample surface has a minimum probe diameter.
[0107]
Further, a component C5 in the X and Y directions of the fifth-order aperture aberration coefficient C5 on the sample surface._x, C5_yAlternatively, the component C3c in the X and Y directions of the aperture chromatic aberration coefficient C3c, which is a fourth-order aberration_x, C3c_ySince the positions of the transfer lens system and the objective lens with respect to the aberration correction apparatus are determined so that the size of the aberration correction device is approximately the same, the symmetry of the probe diameter of the charged particle beam irradiated on the sample surface is improved and the smallest probe is obtained. It can be made to become a diameter.
[0108]
Furthermore, a 12-pole potential for correcting a fifth-order aberration coefficient was superimposed on the focus potential, chromatic aberration correction potential, and spherical aberration correction potential of the multipole of the aberration correction apparatus. With such a configuration, the fifth-order aperture aberration coefficient can be made substantially zero, and the probe diameter of the charged particle beam irradiated on the sample surface can be minimized. it can.
[0109]
Furthermore, a power supply for applying a voltage to the sample surface is provided, and the aberration coefficient before aberration correction is reduced by decelerating the charged particle beam irradiated to the sample surface by the application of the voltage. C5 and C3c can be reduced to 1/5 to 1/10, and the probe diameter of the charged particle beam irradiated on the sample surface can be made the minimum probe diameter.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of a charged particle beam apparatus including an aberration correction apparatus that corrects chromatic aberration with a combination of an electrostatic quadrupole and a magnetic quadrupole and corrects spherical aberration with a four-stage octupole. FIG.
FIG. 2 is a diagram showing a standard arrangement of electrostatic multipole elements.
FIG. 3 is a diagram showing a charged particle beam apparatus including an aberration correction apparatus in which a two-stage transfer lens is arranged in a very special case according to the first embodiment of the present invention.
FIG. 4 is a diagram showing a charged particle beam apparatus including an aberration correction apparatus in which a one-stage transfer lens is arranged in a very special case according to a third embodiment of the present invention.
FIG. 5 is a diagram showing a charged particle beam apparatus including an aberration correction apparatus in which a two-stage transfer lens according to the first embodiment of the present invention is arranged.
FIG. 6 shows changes in the magnitude (absolute value) of fifth-order aperture coefficient C5 and third-order aperture / chromatic aberration coefficient C3c after correction of chromatic aberration and spherical aberration, and the focal length f of transfer lens 27b._bFIG.
FIG. 7 L₁X, Y direction component C5 of C5_x, C5_yAnd the X and Y direction components C3c of C3c_x, C3c_yIt is a figure which shows the change of.
FIG. 8 is a diagram showing a charged particle beam apparatus including an aberration correction apparatus in which a one-stage transfer lens according to a third embodiment of the present invention is arranged.
FIG. 9 is a diagram showing another example of a charged particle beam apparatus including an aberration correction apparatus in which the one-stage transfer lens according to the fourth embodiment of the present invention is arranged asymmetrically.
FIG. 10 is a diagram showing a charged particle beam apparatus including an aberration correction apparatus that decelerates a particle probe incident on a sample according to a sixth embodiment of the present invention.
FIG. 11 is a diagram showing a charged particle beam device including an aberration correction device on which a dodecapole field is superimposed according to a seventh embodiment of the present invention.
FIG. 12 is a diagram for explaining a scanning electron microscope provided with an aberration correction apparatus.
FIG. 13 is a diagram showing another example of a charged particle beam apparatus including an aberration correction apparatus in which two-stage transfer lenses according to the fifth embodiment of the present invention are arranged asymmetrically.
[Explanation of symbols]
1,2,3,4 Electrostatic quadrupole
5,6 Magnetic field type quadrupole
7 Objective lens
8 Objective aperture
9 Operation display
10, 15, 18, 17, 30, 35 Power supply
11, 12, 13, 14 Electrostatic octupole
19 Control unit
20 Sample surface
27a, 27b Transfer lens

Claims (10)

Magnetic potential distribution similar to the potential distribution of the four-stage electrostatic quadrupole and the two-stage electrostatic quadrupole in the center of the four-stage electrostatic quadrupole, disposed inside the optical system of the charged particle beam apparatus Aberration correction apparatus having a two-stage magnetic quadrupole that superimposes, a power supply that supplies a voltage to each of the four-stage electrostatic quadrupole, and a current to each of the two-stage magnetic quadrupole A power supply, disposed downstream of the aberration correction device, and an objective lens for focusing the charged particle beam irradiated on the sample; a power supply of the objective lens; disposed between the aberration correction device and the objective lens; A transfer lens system comprising at least one stage of transfer lens for transmitting the image plane formed by the aberration correction device to the position of the object plane of the objective lens, a power supply for the transfer lens system, and a predetermined charged particle beam An operation unit that changes at least one of an acceleration voltage that gives energy and a working distance that is a distance between the objective lens and the sample, and the four-stage electrostatic type based on the operation or setting of the operation unit A power supply for supplying a voltage to each of the quadrupoles; a power supply for supplying a current to each of the two-stage magnetic quadrupoles; a control unit for controlling the power supply of the objective lens and the transfer lens power supply; The magnification of the system and the objective lens can be adjusted, and a plane perpendicular to the optical axis passes through an intermediate point between the main surface of the final stage multipole element of the aberration correction apparatus and the front focal point of the objective lens. On the other hand, a charged particle beam apparatus provided with an aberration correction apparatus , wherein the transfer lens system is arranged asymmetrically .   A four-stage electrostatic octupole that superimposes an octupole potential on the potential distribution of the four-stage electrostatic quadrupole, a power supply that supplies a voltage to the four-stage electrostatic octupole, The charged particle beam apparatus having an aberration correction apparatus according to claim 1, further comprising a control unit that controls a power source of the four-stage electrostatic octupole based on an operation or setting.   3. The charged particle beam apparatus having an aberration correction apparatus according to claim 1, wherein the transfer lens system is an enlargement type or a reduction system.   When the object plane of the transfer lens system is set as the main surface of the final stage multipole element of the aberration correction apparatus, and the image plane conjugate to this is set at the front focal position of the objective lens, the transfer lens with respect to the conjugate point 4. A charged particle beam apparatus having an aberration correction apparatus according to claim 3, wherein the transfer lens system is arranged at a position where the magnification of the system is 1/3 to 3 times. By adjusting the composite magnification of the transfer lens system and the objective lens, the absolute value of the fifth-order aperture aberration coefficient C5 or the fourth-order aberration third-order aperture / chromatic aberration coefficient C3c on the sample surface is minimized. forming charged particle beam apparatus having an aberration correction device according to one of claim 2 to 4 characterized in that the. The magnitudes of the X- and Y-direction components C5x and C5y of the fifth-order aperture aberration coefficient C5 on the sample surface or the X- and Y-direction components C3cx and C3cy of the fourth-order aberration and the chromatic aberration coefficient C3c are the same. a charged particle beam having an aberration correction device according to one of claim 2 to 4, characterized in that defining the position of the transformer fir lens system and the objective lens with respect to the aberration correcting device apparatus. Focus potential of the multipole of the aberration correcting device, the chromatic aberration correction potential, any one of claims 2 to 4, characterized in that the fifth-order aberration coefficients to the spherical aberration correction potential obtained by superimposing a 12-pole potential for correcting A charged particle beam apparatus comprising the aberration correction apparatus according to any one of the above. A power source for applying a voltage to the sample surface is provided, and the charged particle beam applied to the sample surface is decelerated by applying the voltage, thereby reducing the spherical aberration coefficient and chromatic aberration coefficient of the objective lens before aberration correction. The aberration correction according to any one of claims 1 to 7 , wherein the fifth-order aperture aberration coefficient and the third-order aperture / chromatic aberration coefficient after aberration correction can be reduced by setting Charged particle beam device equipped with the device. The transfer lens system, charged particle beam apparatus having an aberration correction device according to one of claim 1 to 8, characterized in that consists of the transfer lens of the first stage. The transfer lens system, charged particle beam apparatus having an aberration correction device according to one of claim 1 to 8, characterized in that consists of the transfer lens of the second stage.

Images