JP2000228164A - Particle beam system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrically adjust the optical axis of a coil by including at least two focus coils arranged around a beam axis in a variable axis focus coil, and by providing at least one of them with a geometrical center displaced from a system axis in a plane perpendicular to the system axis. SOLUTION: A system axis (Z-axis) of a two-axis variable focus coil extends vertically to the paper surface and penetrates all coils arranged around the system axis. That is, each of the coils extends around the system axis, the respective four coils are expressed as circles. The canter of the coils is referred to as a geometrical center and is displaced from the system axis in two planes (an X-Z plane and a Y-Z plane). The magnitude of coil X1-X2 and Y1-Y2 currents can be so set as to position a magnetic axis at any place in an open area (shaded area). Therefore, a displaced variable focus coil can be composed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to particle beam systems, and more particularly to systems used for semiconductor lithography or micromachining.

[0002]

2. Description of the Prior Art Referring to FIG.
A prior art electron beam projection system as disclosed in US Pat. No. 9,851 is shown in schematic partial cross-sectional view.
This system incorporates a variable axis immersion lens (VAIL) system disclosed in US Pat. No. 4,544,846.

The projection system in FIG. 5 has at its top a box 5 which schematically represents an electron gun and accelerating voltage means for generating a beam of electrons and directing it along the system axis 101. Representation. "Direct writing"
In the system, a narrow beam (having a dimension on the order of 1-2 μm with a minimum feature size of about 0.15 μm) is operated by the lower part of the system, and the desired beam is placed on a work piece 59, illustratively a semiconductor wafer Write out the pattern. In general, the beam can be a character or cell projection (see US Pat. No. 4,213,053) or a subsystem that allows for a shaped beam (see US Pat. No. 4,243,866), or US Pat. , 466,904, which can be patterned in an upstream subsystem 5, which can include a subfield projection system.

[0004] In this generalized example, beam B is optionally focused between an upstream subsystem and a downstream subsystem. The downstream subsystem includes a collimating lens indicated by reference numeral 47 on the left side of the figure and an immersion lens indicated by reference number 12 on the lower left side of the figure, and auxiliary components.

At the top of the downstream subsystem, a magnetic collimating lens 47 having non-zero inner diameter annular pole pieces 49 and 51 and an excitation coil 53 for the collimating lens 47 are arranged. You. Lens 47
The effect is to collimate beam B to provide a telecentric function (meaning that the beam along a beam axis parallel to the system axis hits the work piece). The term "lens" as used herein refers to iron,
A magnetic lens with magnetically permeable pole pieces made of ferrite or other common materials. At the bottom of the downstream subsystem, non-zero inner diameter annular pole pieces 13 and 14
In addition, a magnetic projection lens 32 having an exciting coil 41 is arranged. In general, lenses with such poles have a large inductance and their magnetic fields change fast enough to provide an acceptable throughput to compensate for the field curvature when deflecting the beam. Can not.

Within the aperture in the annular pole piece 49 is an upper beam deflection stage including a set of multipole electrostatic deflection plates 72, preferably a 12 pole (12 plates per set) multipole deflector. is there. Within and below the opening in the annular pole piece 51, a second set of multipolar electrostatic deflection plates 7 is provided.
3, there is preferably a 12 pole (12 plates per set) multipole deflector. The deflection plates 72 and 73 can be located elsewhere, but only before the lower beam deflection stage, i.e. the main deflection yokes 43 and 45, which provide the main magnetic field for controlling the deflection of the beam B. No. The plates 72 and 73 perform the function of deflecting the beam such that it intersects the axis 101 at the front focus of the projection lens 32, thus producing a telecentric electrical deflection.

The lower deflection stage includes a pair of main deflection yokes 43 and 45, which
9 to pre-deflect the projected beam B to the left as shown. It is desirable that both the upper deflection yoke 43 and the lower deflection yoke 45 are ring magnets. Collimating lens 4
7 stigmator placed below
Reference numeral 71 performs astigmatism correction of the electron beam B. The pole piece of the collimating lens 47 is provided with a dynamic focus coil 69, which refocuses the beam when it is deflected (also called field bending) and / or height fluctuations in the work piece To compensate. It will be apparent to those skilled in the art that other locations can be used for the stigmeter and / or dynamic focus coil.

The projection lens 32, which focuses beam B onto the wafer 59, is provided by an upper magnetic path including a non-zero inner diameter upper pole piece 13 and a return path section 19 and a lower pole piece, ie, a zero inner diameter section 14. Including the lower magnetic path formed. One surface of the projection lens 32 has an upper pole piece 13 above and a lower pole piece 1 below.
Principal plane PP on the object side of the lens 32 with
It is. The projection lens 32 is a thick lens and therefore
It also has a main plane on the image side of the projection lens 32.
This main plane is not shown in FIG.

The VAIL system is a VAIL assembly 1
2, the VAIL assembly comprising a combination of the projection lens 32 and the magnetic compensation yoke 11. The shield legs 18 include an alternating arrangement of magnetic and non-magnetic sections, thereby preventing magnetic lines of force from the yoke 11 from passing through the windings 41, thus preventing unwanted eddy currents. Also, the shield legs 18 reduce the amount of magnetic field leaking from the center of the lens. The magnetic circuit of projection lens 32 is formed in section 19 and lower pole piece (zero inner diameter section) 14 to allow magnetic flux to reach lower pole piece 14 with a minimum amount of reluctance and fringe. A single magnetic compensation yoke 11 provides a magnetic field proportional to the first derivative of the axial magnetic field generated by the projection lens 32 multiplied by the deflection distance between the axes 101 and 105 (represented by arrow 100). , Thereby effectively shifting the center of the lens field to reduce distortion away from the system axis 101.

FIG. 5 shows target holding, processing and step means. A target 59 is provided on a target holder consisting of a wafer clamping mechanism and a wafer stage 16 for accurate registration of the target in the electron beam projection system. The wafer clamp mechanism and the wafer stage move within the opening 21.

The system of FIG. 5 uses dynamic correction to correct for astigmatism and magnetic field curvature. A block 61 in the right part of the figure is a power supply for the exciting coil 53. Block 63 is a power supply for exciting coil 41. The driver 65 represents a computer-controlled driver for exciting the deflection yokes 43 and 45. The deflection yokes 43 and 45 have two sets of magnetic deflection coils, which together deflect the electron beam B in both the X and Y directions according to the usual practice. The deflection yokes 43 and 45 generally comprise a plurality of annular coils. The driver 65 operates the magnetic compensation yoke 11 composed of a pair of X and Y magnetic deflection yokes. The magnetic compensation yoke 11 may consist of a simple saddle coil or may be an annular yoke. The XY current sent to the magnetic compensation yoke 11 is proportional to the XY current sent to the deflection yokes 43 and 45, and the same driver 65
May be supplied by Driver 67 represents a computer controlled driver for exciting the dynamic focus and stigmator coil.

In a first method, the magnetic field of the compensation yoke 11 is projected along a line 105 parallel to the geometric (symmetric) axis 101 of the lens 32 but laterally displaced from that geometric axis. Compensates for the radial component of the magnetic field generated by. Since the radial magnetic field component caused by the superposition of the magnetic fields of the compensation yoke 11 and the projection lens 32 is zero,
The magnetic axis 105 defines the shifted electron optical axis. A lens having this characteristic is called a variable axis lens in the field. The shifted position of the electron optical axis 105 is scanned so that the deflected beam is “on-axis”. The displacement of optical axis 105 from axis of symmetry 101 in variable axis lens system 12 is proportional to the current in compensation yoke 11 and deflection cokes 43 and 45.

In the absence of a sub-field deflection signal applied to the electrostatic deflection plates 72 and 73,
That is, when the voltage at the plates 72 and 73 is set to zero, the position of the beam B on the immersion lens 12 exactly matches the shifted electron optical axis 105. Furthermore,
Beam B enters immersion lens assembly 12 as a collimated collimated beam representing an object at infinity. The blurring effect is caused by the fact that electrons of different energies in the beam are deflected by different amounts.
The two states of beam B that cause removal of effect are: (1) the beam axis coincides with the shifted electron optical axis 105 (the beam axis extends from the top to the bottom of beam B); And (2) the object is at infinity.

This blur effect is referred to in the art as lateral chromatic aberration. Since lateral chromatic aberration is a major limitation in the performance of more common deflectors, the removal of this chromatic aberration is considered to be of fundamental importance.

If a sub-field deflection is applied to plates 72 and 73, ie, if the voltages at plates 72 and 73 are non-zero, the position of beam B in immersion lens assembly 12 will deviate from the ideal situation described above. Slightly offset. Since the sub-field deflection is seen as a small perturbation in the main field deflection, this deviation from the ideal state has only a small effect and contributes only a small chromatic aberration and blurring effect.

US Pat. No. 4,544,846, column 7, 5
As described in lines 4-68, the dynamic astigmatism correction coil assembly 71 and the dynamic focus coil 69 compensate for chromatic aberration and magnetic field curvature, respectively. The dynamic astigmatism correction coil assembly is preferably a dual quadrupole element driven by a driver 67. The dynamic focus coil 69 is driven by a separate output of the driver 67 to supply a current suitable for producing the desired correction. Driver 67 receives an input signal proportional to the current supplied to the X and Y main deflection yokes 43 and 45 and generates signals applied to the various elements by techniques well known to those skilled in the art.

To maintain vertical landing (telecentricity) for electrostatic subfield deflection, the system crosses the deflected beam across optical axis 101 at the rear focus of VAIL lens assembly 12. Must be given. When the beam is deflected, for example, from axis 101 to axis 105, there is a series of focal points. These series of focal points form one plane called the back focal plane. The excitation voltage ratio for the deflection stages 72 and 73 (located before the magnetic yoke of the variable axis polarizing lens system according to the invention shown in FIG. 5) depends on the axial position of the beam in its rear focal plane. Can be adjusted to cross the optical axis. Since the deflected beam traverses the optical axis at the back focal plane, the deflection is telecentric, so that it arrives on the work piece at right angles, ie, at a perpendicular angle, but is displaced from the optical axis.

It is important that the rays strike the work piece 59 at a normal projection angle, ie, parallel to the axis 105. It is only in this state that a beam can be hit on the target (workpiece) 59, regardless of unavoidable errors in the height of the wafer. This is very beneficial because the positional height of the target is difficult to control. The wafer is generally not flat but tilted.

The "back focal plane" BFP is the plane that contains the back focal point for all passes of beam B, and is perpendicular to axes 105 and 101. To obtain a pivot point to coincide with the back focus, the ratio of the electrical intensities at the upper 12 poles and the lower 12 poles is adjusted. This moves the pivot point up and down along axis 105. When the beam hits the target at normal incidence, it is known when the two points coincide. Techniques for measuring the angle of incidence by measuring the distance between fiducial marks on a tilted substrate are known in the art.

In the case of coil 69, the coil is nominally centered about system axis 101. Mechanical errors are inevitable, and the alignment between the beam and the system axis is not perfect. As a result, the beam moves on the target surface 59 when the coil 69 is excited. The prior art used mechanical displacement, such as with an adjustable support. Similarly, in the prior art, it is calibrated to the extent that beam movement at the target is repeatable. In modern systems, space is at a premium and there is no room for adjustable elements or no access is available for adjustment.

Since the VAIL lens 12 has a large inductance, its current cannot be changed quickly. When the beam hits the wafer 59, and elsewhere in the system, it is an improvement if a rapidly adjustable low inductance dynamic focus coil is available to adjust the beam focus. Will be.

[0022]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a particle beam system using a dynamic focus coil for electrically adjusting the optical axis of the coil.

[0023]

SUMMARY OF THE INVENTION A feature of the present invention is that an xy
The use of an electrically adjustable focus coil consisting of at least two coils that partially overlap in a plane. Both of the at least two coils are penetrated by the system axis, and at least one of the coils is displaced from the system axis.

[0024]

Referring to FIG. 4, a particle beam system employing the present invention is shown in simplified form. Box 5 at the top of the figure represents the upstream subsystem as shown in FIG. The present invention relates to direct writing, character projection, cell projection shaped beams, and U.S. Pat.
It can be used with many different types of particle beam systems, such as the sub-field projection shown in US Pat.

Below the box 5, an intermediate surface 7, for example
There is a variable axis focus coil 202 according to the invention for dynamically adjusting the focus of the beam on the reticle in the case of a projection lithography system. It will be apparent to those skilled in the art that multiple focus coils distributed along the optical axis may be used. Polarizer 72 and stigmator 71 perform the same function as their counterparts in FIG. For convenience of explanation, corresponding elements are denoted by the same reference numerals. Now, the dynamic focus coil 69 'is a variable axis focus coil configured according to the present invention.

The polarizers 43 and 45 and the compensation coil 11 of the lens 12 are the same as their counterparts in the prior art. For clarity, the core support and biasing coils have been omitted. At the bottom of the figure, the dynamic focus coil 206 performs the final focus adjustment on the beam to compensate for height variations of the work piece 59 or variations due to magnetic field curvature. According to the invention, these focus coils are variable axis and can be installed under polarizers 43 and 45. The focus coil can be activated synchronously with the polarizer so that the optical axis of the focus coil is aligned with the deflected beam axis 105.

The term "focus coil" is used to refer to a helical wire (which may have only one turn), as is common in the art. The helical wire generates a magnetic field near the center of the helix with a radial component that increases with distance from the center, thereby imparting a focusing effect on the electrons passing through it. The term "variable axis focus coil" is used in Figure 1.
3 is used to refer to the combination of focus coils as shown in FIG.

Referring to FIGS. 2 and 3, there is shown a simple single axis version of a variable axis focus coil having a plurality of similar coils, each driven by a current of different magnitude and direction. FIG. 2 which is a schematic plan view
Shows two partially superposed coils X1 and X2. Each is displaced along the X axis by the same amount. The schematic side view in FIG. 3 shows the two coils as being adjacent along the Z axis. Each of the coils will have a coil length along the system axis and will be positioned at an axial position which means the portion of the system axis along which the coil extends.
It will be apparent to those skilled in the art that the combination of the fields of two coils with the same or opposite polarities will produce a focusing field. By appropriate selection of the currents of coils X1 and X2, the magnetic axis of the focus coil system will be set in the marked area at the center of those coils.

Referring now to FIG. 1, there is shown a schematic plan view of a two-axis variable axis focus coil according to the present invention. The system axis (Z axis) extends perpendicular to the plane of the paper and passes through all the coils. A coil through which the system axis passes may be said to be "disposed around" the system axis. That is, the coil extends around its axis. Each of the four coils is represented as a circle. The centers of these coils are called the geometric centers of the coils and are displaced from the system axis in two planes (XZ plane and YZ plane in this figure). As will be readily apparent to those skilled in the art, coils X1-X2 and Y1-Y2
The magnitude of the current can be set to place the magnetic axis of the variable axis focus coil somewhere within the shaded area labeled "open area."

It will be apparent to those skilled in the art that various modifications may be made to these examples, if necessary. For example, by centering one coil on the system axis and displacing the other coil to one side,
A "biased" variable axis focus coil is configurable.

Referring to FIG. 6, another embodiment of the present invention that occupies less space along the system axis is shown. FIG. 6 shows a schematic cross-sectional view of a "mixed" single axis variable axis focus coil. These coils can be said to overlap along the system axis, and their axial positions can be said to overlap. The coil 201 displaced to the upper left of the system axis 101 has windings alternating with the winding of the coil 203 displaced to the lower right. in this case,
As represented by the dashed lines, each winding of the coil passes through the plane of the figure at the same height, and the step down from one winding to the next is out of the page.

Although the present invention has been described in terms of two embodiments, it will be apparent to those skilled in the art that the present invention may be embodied in various versions within the spirit of the invention.

In summary, the following items are disclosed regarding the configuration of the present invention.

(1) a particle beam system for directing a beam of particles to a work piece, source means for generating and directing the particle beam along a system axis;
Beam control means for directing the beam to a target location on the work piece, wherein the particle beam system further comprises at least one variable axis focus coil for focusing the particle beam; The coil has at least two focuses
Wherein the at least two focus coils are disposed about a beam axis, and at least one of the at least two focus coils is displaced from the system axis in a plane perpendicular to the system axis. A particle beam system having a geometric center. (2) The particle beam system according to (1), wherein each of the at least two focus coils has a geometric center displaced from the system axis in a plane passing through the system axis. (3) a first coil of the at least two focus coils extends along the system axis by a first coil length at a first axis position, and a second coil of the at least two focus coils; Extends along the system axis by a second coil length at a second axis position different from the first axis position, such that the first and second coils are separated from each other along the system axis. The particle beam system according to the above (2), wherein (4) a first coil of the at least two focus coils extends along the system axis by a first coil length at a first axis position, and a second coil of the at least two focus coils; Extends along the system axis by a second coil length at a second axis position overlapping the first axis position, such that the first and second coils overlap one another along the system axis. The particle beam system according to (2), wherein: (5) a first coil of the at least two focus coils includes at least two windings, a second coil of the at least two focus coils along the system axis of the first coil; The particle beam system of claim 4, including at least two windings alternating with the at least two windings. (6) the focus coil includes at least four focus coils, all of the at least four focus coils being arranged around the system axis;
A first of the at least four focus coils
The pair has first and second geometric centers displaced from the system axis in a first plane passing through the system axis, and a second pair of the at least four focus coils passes through the system axis. The particle beam system of claim 1, having third and fourth geometric centers displaced from the system axis in two planes. (7) the first coil of the first pair extends along the system axis by a first coil length at a first axis position;
The second coil of the first pair extends along the system axis by a second coil length at a second axis position different from the first axis position, such that the first and second coils are coupled to the system. Spaced apart from each other along an axis, the third coil of the second pair extends along the system axis by a third coil length at a third axis position different from the first and second axis positions; The fourth coil of the second pair extends along the system axis by a fourth coil length at a fourth axis position different from the first, second and third axis positions, whereby the first, The particle beam system of claim 6, wherein the second, third, and fourth coils are separated from each other along the system axis. (8) the first coil of the first pair extends along the system axis by a first coil length at a first axis position;
The second coil of the first pair extends along the system axis by a second coil length at a second axis position that overlaps the first axis position, whereby the first and second coils are coupled to the system. Superimposed along the axis, the second
The third coil of the pair extends along the system axis by a third coil length at a third axis position different from the first and second axis positions, and the fourth coil of the second pair includes the third coil position. A fourth coil length extending along the system axis at a fourth axis position overlapping the position,
The particle beam according to (6), wherein the first and second coils overlap along the system axis, and the third and fourth coils overlap along the system axis. system. (9) the first coil of the first pair extends along the system axis by a first coil length at a first axis position;
The second coil of the first pair extends along the system axis by a second coil length at a second axis position that overlaps the first axis position, whereby the first and second coils are coupled to the system. Superimposed along the axis, the second
The third coil of the pair extends along the system axis by a third coil length at a third axis position overlapping the first and second axis positions, and the fourth coil of the second pair includes the third axis. A fourth coil length extending along the system axis at a fourth axis position overlapping the position,
The particle beam system according to (6), wherein the first, second, third, and fourth coils overlap each other along the system axis. (10) The beam control means has at least one deflector and a variable optical axis for deflecting the beam from a first beam axis to a second beam axis, and intercepts the beam along the second beam axis. A current driver adapted to shift the variable optical axis of the variable axis focus coil to interrupt the second beam axis. (6), wherein the variable axis focus coil acts on the beam as the beam travels along the second beam axis.
A particle beam system according to claim 1.

[Brief description of the drawings]

FIG. 1 shows a two-axis dynamic focus system according to the present invention.
FIG. 2 shows a schematic plan view of the coil.

FIG. 2 shows a schematic plan view of a single-axis dynamic focus coil.

FIG. 3 shows a schematic side view of a single axis dynamic focus coil.

FIG. 4 illustrates a system using the invention, partially in a drawing format and partially in a schematic format.

FIG. 5 illustrates a prior art system using a variable magnetic lens, partially in a drawn form and partially in a schematic form.

FIG. 6 illustrates another embodiment of the present invention.

Continued on the front page (72) Inventor Michael E. Gordon 10540 United States, Dayton Drive, Lincolndale, NY 7

Claims (10)

[Claims] 1. A particle beam system for directing a beam of particles to a work piece, source means for generating and directing the particle beam along a system axis, and a target on the work piece. Beam control means for directing a position, wherein the particle beam system further comprises at least one variable axis focusing device for focusing the particle beam.
A coil, wherein the variable axis focus coil includes at least two focus coils, each of the at least two focus coils being disposed about a beam axis, and at least one of the at least two focus coils. A particle beam system having a geometric center displaced from the system axis in a plane perpendicular to the system axis. 2. The particle beam system according to claim 1, wherein each of said at least two focus coils has a geometric center displaced from said system axis in a plane passing through said system axis. 3. A first coil of said at least two focus coils extends along said system axis by a first coil length at a first axis position, and said first coil of said at least two focus coils. The two coils extend along the system axis by a second coil length at a second axis position different from the first axis position, such that the first and second coils are mutually reciprocal along the system axis. 3. The particle beam system of claim 2, wherein the particle beam system is remote. 4. A first coil of the at least two focus coils extends along the system axis by a first coil length at a first axis position, and a first coil of the at least two focus coils. The two coils extend along the system axis by a second coil length at a second axis position that overlaps the first axis position, such that the first and second coils are mutually connected along the system axis. 3. The particle beam system according to claim 2, wherein the particle beams overlap. 5. The first of the at least two focus coils includes at least two windings, and the second of the at least two focus coils includes a first coil along the system axis. 5. The particle beam of claim 4 including at least two windings alternating with said at least two windings of a coil.
system. 6. The focus coil includes at least four focus coils, wherein the at least four focus coils are all disposed about the system axis, and wherein the first of the at least four focus coils is
The pair has first and second geometric centers displaced from the system axis in a first plane passing through the system axis, and a second of the at least four focus coils.
The particle beam system according to claim 1, wherein the pair has third and fourth geometric centers displaced from the system axis in a second plane passing through the system axis. 7. The first coil of the first pair extends along the system axis by a first coil length at a first axis position, and the second coil of the first pair is located at a first axis position relative to the first axis position. Extending along the system axis by a second coil length at a different second axis position, such that the first and second coils are separated from each other along the system axis, and the second and third coils of the second pair The three coils extend along the system axis by a third coil length at a third axis position different from the first and second axis positions, and the fourth coil of the second pair includes the first, second, and third coils. A fourth coil position extending along the system axis at a fourth axis position different than the third axis position, such that the first, second, third and fourth coils extend along the system axis. A contract characterized by being separated from each other Particle beam system according to claim 6. 8. The first coil of the first pair extends along the system axis by a first coil length at a first axis position, and the second coil of the first pair overlaps the first axis position. Extending along the system axis by a second coil length at a second axis position where the first and second coils overlap along the system axis and the third pair of third pairs of the second pair. A coil extends along the system axis by a third coil length at a third axis position different from the first and second axis positions, and the fourth coil of the second pair overlaps the third axis position. A fourth coil length extends along the system axis at a fourth axis position, whereby the first and second coils overlap along the system axis, and the third and fourth coils overlap the system axis. Superimposed along the axis Particle beam system of claim 6, characterized in that. 9. The first coil of the first pair extends along the system axis by a first coil length at a first axis position, and the second coil of the first pair overlaps the first axis position. Extending along the system axis by a second coil length at a second axis position where the first and second coils overlap along the system axis and the third pair of third pairs of the second pair. A coil extends along the system axis by a third coil length at a third axis position overlapping the first and second axis positions, and the fourth coil of the second pair overlaps the third axis position. A fourth axial position extends along the system axis by a fourth coil length, whereby the first, second, third and fourth coils overlap along the system axis. Claim 6
A particle beam system according to claim 1. 10. The beam control means controls the beam to a first beam.
At least one deflector for deflecting from a beam axis to a second beam axis and a variable axis focus coil having a variable optical axis and arranged to block the beam along the second beam axis. The beam control means further includes current driver means adapted to shift the variable optical axis of the variable axis focus coil to block the second beam axis, whereby the variable axis focus coil 7. The particle beam system of claim 6, wherein said beam acts on said beam as said beam travels along said second beam axis.