JP3236472B2 - Electromagnetic field superimposition type objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high resolution electromagnetic field superimposition type objective lens which is optimally used for an objective lens such as a scanning electron microscope.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become finer and more complex, it has become increasingly necessary to observe large and flat objects such as wafers and masks from all directions in shape inspections in the manufacturing process of these devices. ing. The present inventor has commercialized a lens described in Japanese Patent Application Laid-Open No. 1-298566 as an objective lens for a scanning electron microscope meeting this object, and has already obtained certain results.

FIG. 1 shows the invention of the prior application. In the figure, 1 is a conical bobbin having an electron beam passage hole P, 2 is a coil, 3 is a yoke, 4 is a flat sample such as a wafer.
Are inclined along the yoke 3. With this configuration, the number of windings of the coil 2 wound over several layers outside the conical bobbin 1 is changed for each layer.
As a result, the distribution of the number of windings along the axis of the coil is configured to be larger on the electron beam emission side than on the electron beam incidence side of the objective lens. With this configuration, the lens main surface and the magnetic field peak can be made closer to the sample 4.

The configuration shown in FIG. 2 is a modification of the configuration of FIG. 1, and the same reference numerals as those in FIG. 1 indicate the same components. In the configuration of FIG. 2, a funnel-shaped bobbin 5 is provided as a bobbin. Then, the number of turns of the coil 2 wound around the outside of the funnel-shaped bobbin 5 (hatched portion) over several layers is changed for each layer so that the outer surface of the coil formed by the coil 2 is formed in a substantially conical shape. Make up. For this reason, the distribution of the number of windings along the axis of the coil 2 gradually decreases toward the electron beam incident side and the electron beam exit side of the objective lens.

In the case of the axial magnetic field distribution of the objective lens shown in FIG. 2, the lens main surface and the magnetic field peak are closer to the sample 4 than the axial magnetic field distribution of the objective lens of FIG. improves.

The objective lens shown in FIGS. 1 and 2 has an outer shape of a truncated cone having an apex angle of 60 °.
That is, after the sample can be tilted up to 60 °, the winding distribution of the coil is increased at the top surface of the truncated cone and decreased toward the bottom surface. With such a configuration,
The main surface of the objective lens was made as close as possible to the top surface of the truncated cone. As is well known, the aberration of the magnetic field type lens becomes smaller as the lens main surface is closer to the sample.
A small aberration can be achieved even at an inclination of 0 °.

However, the degree of integration of semiconductors has been rapidly improved, and a scanning electron microscope has been required to further improve the resolution. FIG. 3 shows a cross-sectional view of a recently proposed electromagnetic field superimposition type objective lens, which is a superposition of a magnetic field lens and an electric field lens (deceleration bipotential type).

In FIG. 3, reference numeral 6 denotes a lower yoke of a magnetic lens, 7 denotes an upper yoke, and 8 denotes a coil. One electrode 9 of the electric field lens is arranged inside the upper yoke 7 of the magnetic lens, and this electrode 9 is formed in a conical cylindrical shape. The other electrode 10 of the electric field lens is provided at the tip of the lower yoke 6, and although not shown, a voltage is applied between the electrodes 9 and 10.

FIG. 3 shows the cross section of the objective lens. The cross section is actually symmetrical in shape. In the figure, the left cross section shows the electric field lens and the equipotential lines of the electric field, and the right side shows the same. Figure 3 shows the magnetic lens and the equipotential lines of the magnetic field.

This lens is (4 + α) m from the tip of the electrode.
At position m, the sample can be tilted up to 50 °. Here, α is a mechanical clearance for preventing the sample from contacting the lens outer wall when the sample is inclined by 50 °.
For example, when the working distance WD is 4 mm and the reduction ratio Vi / Vo = 1/17, this lens has a spherical aberration Cs = 3.7 mm and a chromatic aberration Cc =
It is assumed that 1.8 mm was obtained. Here, Vi is the accelerating voltage of the electron beam (= potential of the sample viewed from the emitter), Vo
Is an intermediate acceleration voltage (based on the emitter).

[0011]

The objective lens having the structure shown in FIG. 3 has a very high performance of about 1/10 of the above-mentioned aberration value as compared with the lenses shown in FIGS. 1 and 2. Has the drawbacks described below. First, set the sample at 50 °
It can only be tilted to a degree. As the tiltable angle of the sample is larger, the information obtained from scanning electron microscope observation increases, and it is considered that 50 ° is insufficient, and about 60 ° is desirable.

Second, the sample cannot be redesigned to be tilted up to 60 ° for the following four reasons. When the lower magnetic pole 6 has a vertical angle of 60 ° and the inner diameter of the upper magnetic pole 7 and the tip position are kept the same, the lower magnetic pole 6 and the lower magnetic pole 6 are too close to each other, and magnetic saturation occurs at a relatively low excitation. Therefore, the usable maximum acceleration voltage must be reduced.

For the reasons described above, if the tip position is raised upward, magnetic saturation can be avoided, but the main surface of the magnetic lens shifts upward, and the performance as a superposition field lens deteriorates.

If the inner diameter of the upper magnetic pole 7 is reduced for the above-described reason, magnetic saturation can also be avoided, but this time, it will be close to the high voltage electrode, and the discharge is likely to occur, which is not practical. Also, if the electrode inner diameter is reduced,
Discharge can be avoided, but lens performance will deteriorate significantly.

If the upper electrode voltage Vo is lowered for the reasons described above, discharge can be avoided, but the reduction ratio Vi /
Vo becomes large, and the performance is greatly deteriorated. Third, the performance of the magnetic lens alone is worse than the lenses shown in FIGS. In the lens shown in FIG. 3, the ground voltage (Vo-Vi) of the high-voltage pipe is constant because of the electrode withstand voltage. Therefore, when the acceleration voltage Vi is increased, the reduction ratio Vi / Vo increases. For example, Vi = 50
When 0 V and Vo-Vi = 8 kV, Vi / Vo = 1 /
17, but when Vi = 15 kV, Vi / Vo =
15/23 = 1 / 1.53. In this case, the performance of the superimposed field lens is almost equal to that of the magnetic field only lens. The magnetic field lens of FIG. 3 has a traditional shape before the appearance of the lenses of FIGS. 1 and 2 and does not pursue the highest performance as a magnetic field lens at a tilt of 50 °. Of course.

FIG. 4 shows the ground voltage (Vo-V) of the high voltage pipe.
i) is fixed at 8 kV, and Vi is 0.5 kV to 15 kV.
FIG. 6 is a graph showing Cs and Cc when varied. In this graph, two curves are drawn for both Cs and Cc. Curve A corresponds to the case where the sample is placed at the position where the apex of the cone and the optical axis intersect (working distance WD = 4 mm). Corresponds to the case where the sample is lowered by 2 mm from that position.

The dashed line in the figure shows the values of Cs and Cc at the position where the lens can be tilted by 60 ° (position including the mechanical clearance) in the lens having the configuration shown in FIG. As can be seen from this graph, when the acceleration voltage is 4.4 kV or more,
Cs is worse than the lens of FIG. This is because the performance of the superimposed magnetic lens is poor.

The present invention has been made in view of such a point, and an object of the present invention is to reduce the values of Cs and Cc to realize a high-resolution electromagnetic field superimposed type objective lens.

[0019]

According to a first aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and an electron beam. And a high-resistance element disposed inside the insulator so as to surround the passage, wherein a voltage is applied to both ends of the high-resistance element.

According to a second aspect of the invention, in the electromagnetic field superposition type objective lens according to the first aspect, the high-resistance body is formed in a film shape. According to a third aspect of the present invention, in the electromagnetic field superposition type objective lens according to the first aspect, the high-resistance body is formed in a pipe shape.

According to a fourth aspect of the invention, in the electromagnetic field superimposition type objective lens according to the first aspect, a large number of conductive pipes are arranged inside the high-resistance body. Claim 5
The present invention is characterized in that, in the electromagnetic field superimposition type objective lens according to any one of claims 1 to 4, a material for heat radiation is provided between the coil and the high-resistance body.

According to a sixth aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a ring-shaped part disposed inside the insulator. It comprises a member in which a high resistance body and a conductor are laminated, and is characterized in that a voltage is applied to both ends of this member.

According to a seventh aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a plurality of rings disposed inside the insulator. And a member formed by laminating high-resistance elements in a ring shape. A metal is sandwiched between the high-resistance elements in a ring shape, and a voltage is applied to both ends of the high-resistance element.

[0024]

According to the first aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and an insulating member surrounding the electron beam path. A high-resistance element disposed inside the body, and configured to apply a voltage to both ends of the high-resistance element, so that the electrostatic lens action occurs on the sample side from the magnetic flux density peak position of the magnetic lens. .

According to a second aspect of the present invention, in the electromagnetic field superposition type objective lens according to the first aspect, the high-resistance body is formed in a film shape. According to a third aspect of the present invention, in the electromagnetic field superposition type objective lens according to the first aspect, the high-resistance body is formed in a pipe shape.

According to a fourth aspect of the present invention, in the electromagnetic field superimposition type objective lens according to the first aspect, a number of conductive pipes are arranged inside the high-resistance body, and the equipotential surface accompanying the non-uniformity of the high-resistance body. Was corrected.

According to a fifth aspect of the present invention, in the electromagnetic field superimposition type objective lens according to the first to fourth aspects, a heat-dissipating material is provided between the coil and the high-resistance element to efficiently radiate heat generated by the coil.

According to a sixth aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil arranged inside the magnetic pole, an insulator arranged inside the coil, and a ring-shaped inside formed inside the insulator. It has a member in which a high-resistance body and a conductor are laminated, and is configured to apply a voltage to both ends of the member, so that the electrostatic lens action occurs on the sample side from the magnetic flux density peak position of the magnetic lens. .

According to a seventh aspect of the present invention, there is provided a magnetic pole formed substantially in a conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a plurality of rings disposed inside the insulator. A high-resistance member laminated in a ring shape, a metal is sandwiched between the high-resistance ring members, and a voltage is applied to both ends of the member. The magnetic flux density was generated on the sample side from the peak position of the magnetic flux density of the lens.

[0030]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 shows an electromagnetic field superimposition type objective lens according to the present invention, in which 11 is a magnetic pole formed of a conical magnetic material. The conical magnetic pole 11 is formed to be thin, and the coil 12 is wound in a thin shape along the inner wall of the magnetic pole 11. Inside the coil 12, a heat radiating member 13 made of copper or the like which also serves as a winding frame of the coil 12 and a heat radiating path is arranged. These magnetic poles 11,
The coil 12 and the heat radiating member 13 form a conical magnetic lens.

A hollow insulating member 14 made of ceramic or the like is provided inside the heat radiating member 13 coaxially with the conical magnetic lens. Inside the insulating member 14, a film 15 of a high resistance material such as silicon carbide is formed. A voltage is applied from a power supply 16 between both ends of the film 15. As a result, a high voltage is applied to the upper end (electron gun side) of the high resistance film 15 and a ground potential or a small voltage is applied to the lower end (sample side) of the high resistance film 15.

The upper inner wall portion 17 of the insulating member 14
Has been subjected to a metallizing process, and the insulating member 1
An electrode 18 connected to the high-resistance film 15 is provided at the lower end of 4, and the metallization processing unit 17 and the electrode 15 are actually connected to a power supply 16. The operation of such a configuration will now be described.

When a current is applied to the coil 12, an axially symmetric magnetic field is generated inside the magnetic lens. The resulting on-axis magnetic flux density (B
z) The distribution has a peak near the lower end of the magnetic pole 11 as shown in FIG. Accordingly, the lens main surface as the magnetic field lens approaches the sample (disposed below the lens), and for example, a smaller aberration is obtained as compared with the lens of FIG.

When a high voltage is applied from the power supply 16 to the high-resistance film 15, a minute current flows from the upper end to the lower end of the high-resistance film 15, and the high-resistance film 15 extends in the longitudinal direction (the optical axis direction of the electron beam). ) Causes a voltage drop. At this time, since the shape and thickness of the high-resistance film 15 are symmetrical with respect to the optical axis, the equipotential surface is axially symmetric. FIG. 7 shows equipotential lines (FIG. 7A) in the internal space of the high-resistance film 15 and an axial potential distribution (FIG. 7A).
(A)) is shown.

In the configuration shown in FIG. 5, the on-axis magnetic flux density B, the on-axis potential V, the electron orbit T, and the integrand Rcs in the integral formula of Cs and Cc when the electric field and the magnetic field are simultaneously excited.
FIG. 8 shows an example of (z) and Rcc (z). In the example of FIG. 8, the ground voltage V1 applied to the upper end of the high resistance film 15
Is applied to the lower end of the high-resistance film 15 at 7 kV.
2 is set to 0 V, and the calculation is performed for electrons having an acceleration voltage Vi of 500 V.

In this figure, Z = 0 indicates a position at which the sample can be tilted by 60 ° including the mechanical clearance. In addition,
The required ampere turn (AT) is about 500AT
Met. The values of Cs and Cc obtained in this example are:
They are 8.0 mm and 3.6 mm, respectively, which are equivalent to the values when the acceleration voltage Vi of the lens in FIG. 3 is 0.5 kV and α = + 2.

Here, the on-axis magnetic flux density B of the lens shown in FIG.
FIG. 9 shows the integrands Rcs (z) and Rcc (z) in the integral formula of the on-axis potential V, the electron trajectory T, and Cs and Cc. As can be seen from this figure, the electric field is generated only between the electrodes at the tip of the lens, and the first half of this electric field acts as a diverging lens. By this action, the trajectory of the electrons is once increased in the radial direction, and then focused on the sample by the focusing action in the latter half.

On the other hand, the potential distribution of the lens of FIG. 5 is distributed over a wide range of the Z axis, as can be seen from FIG. The orbital divergence effect of this lens is extremely small, so that it can hardly be recognized in FIG. As is well known,
Since the integral formula of the spherical aberration of the electron lens includes a component proportional to the fourth power of the orbital radius, a high-resistance pipe-type electrostatic lens having a small orbital diverging effect is more spherical than a gap-type electrostatic lens. Small aberration.

If the upper pole and the lower pole are separated from each other in a gap form, it seems that the range of existence of the electric field can be increased, but this is not the case. That is, there is a magnetic lens around the gap (the same potential as the lower pole potential), and most of the potential drop occurs near the upper pole tip. Therefore, raising the upper pole to widen the gap is substantially the same as moving the entire electric field lens away from the sample, and significantly degrades the performance.

As can be seen from FIGS. 8 and 9, the focusing action by the electrostatic lens occurs after the primary electrons have been sufficiently decelerated. That is, the electrode 18 in FIG.
In the vicinity of the electrode 10. Since this position is set closer to the sample than the peak position of the magnetic flux density, the focal length of the compound lens is shortened, and the aberration coefficient is greatly improved.

FIG. 10 shows another embodiment of the present invention. The same or similar components as those in the embodiment of FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, a cylindrical high-resistance pipe 20 is arranged inside the insulating member 14 instead of the high-resistance film. Further, a metal electrode or an electrode 21 formed by metallizing the inner surface of the insulating body is provided on the upper inside of the insulating member 14.

The high-resistance pipe 20 may be a high-resistance pipe having a specific resistance in a range of about 10 ⁶ Ω · cm to 10 ⁹ Ω · cm.
For example, Si, SiC, CaZrO ₃ or the like is used. These high-resistance materials are stable even in the air, it is difficult to form an oxide insulating layer, and even if scattered electrons collide,
It has the characteristic of not being charged.

The embodiment shown in FIG. 10 has an advantage that it is easy to manufacture because only the straight cylindrical portion is formed by the high-resistance pipe 20. Of course, this advantage also occurs when a high resistance film is used instead of the high resistance pipe 20. In the configuration of FIG. 10, the electric field becomes the strongest between A and B in the figure.
Between B, a homogeneous insulator occupies the space, and the dielectric strength is higher than the vacuum gap. Therefore, a larger voltage can be applied to a narrow space than in the case where a vacuum gap is used. / Vo A lens with a small size becomes practical.

FIG. 11 shows another embodiment of the present invention. In this embodiment, a plurality of electric field correcting metal rings 22 are arranged in parallel inside the high resistance body 20. In some cases, the electric field cannot be accurately formed axially symmetrically due to the thickness of the high-resistance body pipe 20 being partially different. It corrects the disturbance of the equipotential surface due to the non-uniformity of the body.
When the metal ring 22 is formed, a number of thin metal rings may be fitted inside the high-resistance pipe 20, and then the metal rings may be cut off at a constant pitch.

FIG. 12 also shows another embodiment of the present invention. In this embodiment, the high-resistance body ring 23 and the metal ring 24 are stacked and arranged inside the insulating member 14, and as a result, the high-resistance film 15 in the embodiment of FIG.
The same effect as that of the high resistance pipe 20 in the embodiment is obtained.

FIG. 13 shows another embodiment of the present invention. In this embodiment, the high resistance rings 25 are laminated and arranged inside the insulating member 14, but one or both surfaces of each ring are subjected to a metallizing process.

[0047]

As described above, the electromagnetic field superimposition type objective lens according to the first aspect of the present invention has a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, and a coil inside the coil. And a high-resistance body disposed inside the insulator so as to surround the electron beam path, and configured to apply a voltage to both ends of the high-resistance body, thereby forming an electrostatic lens. Was generated on the sample side from the peak position of the magnetic flux density of the magnetic lens. As a result, Cs and Cc
Can be made extremely small, and a high-resolution objective lens can be provided.

According to the second aspect of the present invention, in the electromagnetic field superimposition type objective lens according to the first aspect, since the high-resistance body is formed in a film shape, the same effect as the first aspect of the invention can be obtained. According to a third aspect of the present invention, in the electromagnetic field superimposition type objective lens according to the first aspect, the high-resistance body is formed in a pipe shape.

According to a fourth aspect of the present invention, in the object lens of the first aspect, a large number of conductive pipes are arranged inside the high-resistance body, and the equipotential surface accompanying the non-uniformity of the high-resistance body. Was corrected.

According to a fifth aspect of the present invention, in the electromagnetic field superimposition type objective lens according to the first to fourth aspects, a heat-dissipating material is provided between the coil and the high-resistance element to efficiently radiate heat generated by the coil. The effect of heat was prevented.

According to a sixth aspect of the present invention, there is provided a magnetic pole formed in a substantially conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a ring-shaped part disposed inside the insulator. It has a member in which a high-resistance body and a conductor are laminated, and is configured to apply a voltage to both ends of the member, so that the electrostatic lens action occurs on the sample side from the magnetic flux density peak position of the magnetic lens. . As a result, Cs and Cc
Can be made extremely small, and a high-resolution objective lens can be provided.

According to a seventh aspect of the present invention, there is provided a magnetic pole formed substantially in a conical shape, a coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a plurality of rings disposed inside the insulator. A high-resistance member laminated in the shape of a ring, a metal is sandwiched between the high-resistance ring members, and a voltage is applied to both ends of the member. It was generated on the sample side from the magnetic flux density peak position of the lens. As a result, the values of Cs and Cc can be made extremely small, and a high-resolution objective lens can be provided.

[Brief description of the drawings]

FIG. 1 is a view showing a conventional conical objective lens.

FIG. 2 is a diagram showing a conventional conical objective lens.

FIG. 3 is a diagram showing a conventional electromagnetic field superimposition type objective lens.

FIG. 4 shows spherical aberration Cs and coma Cc according to an acceleration voltage.
FIG.

FIG. 5 is a diagram showing an embodiment of an electromagnetic field superimposition type objective lens according to the present invention.

FIG. 6 is a diagram showing an on-axis magnetic flux density of the objective lens of FIG. 5;

FIG. 7 is a view showing equipotential lines and on-axis potentials in a high-resistance body internal space in the lens of FIG. 5;

FIG. 8 shows the on-axis magnetic flux density B, on-axis potential V,
It is a figure which shows the integrand R (Cs) and R (Cc) in the electron orbit T and the integral formula of Cs, Cc.

9 shows an on-axis magnetic flux density B, an on-axis potential V,
It is a figure which shows the integrand R in the electron orbit T and the integral formula of Cs, Cc.

FIG. 10 is a diagram showing another embodiment of the present invention.

FIG. 11 is a diagram showing another embodiment of the present invention.

FIG. 12 is a diagram showing another embodiment of the present invention.

FIG. 13 is a view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Magnetic pole 12 Coil 13 Heat dissipation member 14 Insulation member 15 High resistance film 16 Power supply 17 Metallization processing part 18 Electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 37/12-37/145 H01J 37/28

Claims (7)

(57) [Claims] A magnetic pole formed in a substantially conical shape;
A coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a high-resistance element disposed inside the insulator so as to surround the electron beam path; An electromagnetic field superimposition type objective lens configured to apply a voltage to the objective lens. 2. The objective lens according to claim 1, wherein the high-resistance element is formed in a film shape. 3. The objective lens according to claim 1, wherein the high-resistance body is formed in a pipe shape. 4. The objective lens according to claim 1, wherein a number of conductive pipes are arranged inside the high-resistance body. 5. The objective lens according to claim 1, wherein a material for heat radiation is provided between the coil and the high-resistance element. 6. A magnetic pole formed in a substantially conical shape,
A coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a member in which a ring-shaped high-resistance body and a conductor are laminated inside the insulator are provided. An electromagnetic field superimposition type objective lens configured to apply a voltage to the objective lens. 7. A magnetic pole formed in a substantially conical shape,
A coil disposed inside the magnetic pole, an insulator disposed inside the coil, and a member in which a number of ring-shaped high-resistance elements are laminated inside the insulator; An electromagnetic field superimposition type objective lens in which a metal is sandwiched between resistors and voltage is applied to both ends of the member.