JP3280369B2 - How to collimate a particle beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The field of the invention is that of particle beam systems such as electron microscopes, electron beam projection lithography systems, and electron beam direct writing lithography systems.

[0002]

BACKGROUND OF THE INVENTION In the past, brute force techniques have been used in the art to verify the collimation of a particle beam, and the beam cross-section must be distanced several times to ensure that the beam cross-section remains constant. Had to be measured at

[0003]

However, there is a need for a technique that is better suited for real-time evaluation and adjustment.

[0004]

SUMMARY OF THE INVENTION The present invention guides a beam along one edge of a set of apertures, sweeps the beam over a corresponding edge of a selected lower aperture, and sets an aperture set. Collimating the particle beam by repeating the procedure at the opposite edge of the particle beam. The current in the collimating electromagnetic lens (or the voltage in the collimating electromagnetic lens. Both the current and the voltage are generally the same) until the oscilloscope trace of the particle beam current interrupted on the plate containing the lower aperture satisfies the given criteria. (Referred to as control).

A feature of the present invention is that the operator can adjust the collimating lens while looking at a direct oscilloscope trace that immediately displays the effect of the adjustment.

[0006] Another feature of the present invention is that this procedure can be automated by digitizing the scope trace.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a simplified schematic of an electron beam system for projecting a circuit pattern on a semiconductor wafer is shown, wherein a light source 110 is positioned along a column axis 101. Generate a guided electron beam.
The light source imaging ray trace is shown by the dotted line 190 in FIG. The first condenser lens 120 is an electron source (crossover)
The focus of 110 is adjusted to the back focal plane aperture 135 of the illumination lens 130. The illumination lens 130 finally ensures a parallel and uniform illumination of the reticle 145. A second condenser lens 140 centered on the plane of the reticle further focuses the light source on the contrast aperture 150. Since the contrast aperture 150 is at the back focal plane of the projection lens 160, the illumination at the target plane 170 is also guaranteed to be parallel and uniform. Next, referring to the broken line 180 in FIG.
Imaging of the illumination aperture 115 on the reticle plane by the zero and the target plane 17 by the projection lens 160
Note the imaging of reticle 145 to zero. Projection lens 1
60 rear focal planes 150 (contrast aperture)
That the light source 110 is imaged on the target and the reticle 145 is imaged on the target plane 170 at the same time.
It is a characteristic of lighting.

The method of the present invention includes, but is not limited to, an electron probe forming column and an ion beam column.
It can be implemented in a number of other systems, this particular version being selected for convenience of explanation. Reticle 145 during collimation setup
Is removed and the magnetic field from such a lens is removed by the diagnostic aperture 235 in the aperture plane 230 (shown in FIG. 2).
If it overlaps with the magnetic field of a lens adjusted near the aperture 245 in the aperture plane 240, a nearby downstream lens (eg, the second condenser lens 140) may need to be turned off.

Referring now to FIG. 2, details of the system where the lens 130 to be adjusted is near the top of the drawing are shown. In a previous setup step, the image of the light source was formed in the plane of the aperture 135. The beam deflector 210 is arranged to pivot the beam in an aperture 135 at the back focal plane of the illumination lens 130. For convenience of the claim language, the upper beam deflector 210
The voltage (electrostatic plate) or current (magnetic coil) inside is referred to as offset or toggle deflection or scanning, and the voltage (electrostatic plate) or current (magnetic coil) in the lower deflector 220 is "swept deflection". I will call it.
Alternatively, when the beam deflector 210 includes two deflectors separated along the column axis 101, the position of the beam deflector 210 can be made wider. In that case, the ratio of the outputs of the two deflectors until the beam pivots about the illumination lens back focal plane aperture 135 (ie no motion of the beam is detected at this aperture when the deflector is activated). Will be adjusted.

The electron beam 205 is deflected by the deflector 210, so that it passes through the lens 130, and a part of the beam hits the left edge of the aperture 235. The blocking portion of the beam is not necessary for its broadest implementation of the invention, but ensures that the transmitted partial beam is aligned with the edge of the aperture 235. As beam 205 pivots in the back focal plane of lens 130, an unobstructed beam, called beamlet 251, travels parallel to axis 101 toward aperture 245. Aperture 24
5 is used as a diagnostic aperture. Aperture 23
5 and 245 have the same size and orientation in the plane of the paper, and both are aligned with the system axis. In some cases, an intermediate aperture may be used for convenience.

The particle beam column is designed such that the aperture 135 is at a distance from the lens 130 that corresponds to the desired focal length. Therefore, if the lens 130 is properly set up, the focal length of the lens will be set to match this distance. In that case, lens 130 collimates both the light source image and the "image" of deflector 210. When the pivot point of the deflector 210 is in the back focal plane of the lens 130, the collimated deflection causes the beam to be guided on a path parallel to the column axis 101. The accuracy of the parallel path depends on the adjustment of the focal length of the lens. Beamlet 251 advances into aperture 245, just grazing the left side of aperture plate 240. To verify this, the beamlets are apertured 245 using a deflector 220.
Sweeping on the left edge of the oscilloscope produces the oscilloscope trace described below.

This procedure is repeated by the biased deflector 210 such that a portion of the beam 206 strikes the right edge of the aperture 235. An unobstructed beam, called beamlet 252, travels toward aperture 245 parallel to column axis 101. Also in this case, the aperture 245 is a diagnostic aperture. As before, lens 1
With the proper setup of 30, the beam will just graze on the right side of aperture plate 240.
Using a square wave signal of appropriate magnitude and having a sub-hertz frequency input to deflector 210, aperture 2
It is possible to switch between the left and right edges of 35, and the beam is swept over the edge of aperture 245 using a triangular signal with much lower amplitude and frequency of several hertz.

Apertures 235 and 245 are preferably located not only to perform collimation adjustments, but also to assist in proper operation of the system. If the distance over which the beam is collimated is large, it may be desirable to provide more than two apertures along the beam axis. As the aperture spacing increases, the sensitivity of this setup technique increases.

A suitable oscilloscope signal trace and associated adjustment criteria are described below. Referring to FIGS. 3 and 4, oscilloscope traces of beam current impinging on aperture plate 240 when the beam is swept from left to right on both sides of aperture 245 are shown. Using an oscilloscope provides an effective and relatively quick set-up procedure, but other methods are possible. An alternative procedure that adds extra preparatory work but requires less expertise in operation is to digitize the aperture plate blocking current and deflection drive signal and provide data to a computer for signal analysis. The following description also applies to a scenario in which a number sequence representing a trace is used instead of an oscilloscope trace. Both the scope trace and the number sequence are current expressions. The scope trace is a human-visible representation, similar to the histogram of the beam current displayed on a computer monitor.

Initially, the beam is offset by deflector 210 to the left of aperture 235, resulting in beamlet 251 of FIG. Beamlet 251
Is swept by the deflector 220 on the left edge of the aperture 245 (from left 251 'to right 251 "in the figure). The beam current interrupted by the aperture plate 240 is such that the beamlet 251' is fully apertured. From the total beam current when on the plate 240 (line 302 in FIG. 3), the zero current when the beamlet 251 ″ is completely on the aperture 245 (line 30 in FIG. 3)
It changes up to 3). The transition point when the edge of the beam just grazes the aperture plate is "knee"
It is expressed using the term.

The sloping intermediate region (310 in FIG. 3) represents the transition region when the beam passes over the edge of the aperture and is partially blocked by the aperture plate 240. The amount of sweep required to deflect the beam into the transition region represented by 310 is a measure of the size of the beamlet width. The corresponding trace 311 when the beam is offset to the right edge of the aperture 235 (and also swept from left to right) is shown in FIG. Note that the size of the beam must be smaller than the size of aperture 245 so that the aperture cutoff current equals zero at 303 and 305. This procedure does not depend largely on how well the offset deflection 210 is set up. In the critical "knee" region where the signal approaches ground level, as long as a beamlet of approximately correct size is generated,
The signal will be similar to FIGS.

5, 6 and 7, the deflector 210
A pair of representative stored oscilloscope traces are superimposed on one display by triggering the scope display with the toggle scan signal used to drive the oscilloscope. Dotted line 450 is the center of each sweep scan and corresponds to zero deflection from the nominal position. If the path of the partial beam is parallel to the system axis, the left beamlet 251 will have the aperture 24 just when the sweep comes to line 450.
5 completely, and the right beamlet 252 shows that when the sweep comes to line 450,
Enter completely within 45. Beamlet 2 for column shape
51 and 252 from aperture 235 to aperture 2
If following a path parallel to the system axis 101 over an axial distance to 45, the beam will be collimated in this area.

FIG. 6 shows that the beam is
The case where the beam approaches (ie converges) the system axis when passing through 45 is shown. Trace segments 423 and 424 overlap horizontally by the amount indicated by number 414. Physically, this is a distance 414 for the beamlet to reach the edge of the aperture 245.
Requires an extra deflection corresponding to の, ie, trace 423 passes line 450 before the current interrupted by plate 240 begins to increase. Since the spot size of the converging beam is smaller at the distant aperture, the additional sweep required to bring the beam sufficiently above the aperture plate 240 after the beamlet blocks at the aperture plate 240 is Less is needed. Thus, the slope of the transition region is steeper than for a collimated beam.

Conversely, the diverging deflection is greater,
Fewer sweeps are required to bring the beamlets onto aperture plate 240. That is, in the case of zero deflection, there is already a finite current hitting plate 240. The corresponding separation of the traces is numbered 4 in FIG.
Indicated at 16. Correspondingly, the slope of the trace will be smaller than for the collimated beam.

FIG. 5 shows the case of accurate deflector collimation.
Shown in In FIG. 5, the narrow gap 41 between 421 and 422
As shown at 2, the transition of the signal trace from ground is rarely isolated. It has been found that maintaining the small spacing of the signals shown in FIG. 5 increases the reproducibility from which collimation can be determined when using the oscilloscope tracing method. Thus, in the preferred embodiment, the reference for the collimated beam is that the knees of the two traces are almost touching, ie, separated by approximately the trace width. In an automated embodiment, the slope and horizontal intercept are calculated, where the criterion is that both intercepts have the same (nominally zero) deflection current or voltage.

The use of two traces facilitates visual observation, but generally is not required. By adjusting the lens current until the knee at the top of the trace is at zero deflection, equivalent results are obtained (with more effort). In certain cases where the apertures are not aligned, the exemplary procedure allows for proper collimation and is therefore preferred. In this case, as shown in FIG. 8, in a single trace adjustment where the plate 240 is shifted to the left,
Improper lens setup may occur. Here, a divergent beam is obtained by using only the beamlet 551. (Note that when the beamlets 551 are just inside the aperture, the beamlets 552 are well above the plate 240.) As shown in FIG. 9, deflection of the beamlets 553 and 554 to properly align the beamlets 553 and 554 Some offset on deflector 220 relative to the nominal center will be required.

By repeating the procedure for additional apertures along the system axis, as shown in FIGS. 10 and 11, errors due to size differences between apertures can be averaged. FIG. 10 shows the error resulting from the larger lower aperture 645. Beamlet 65
The "exact" positions of 1 and 652 result in a diverging beam. In FIG. 11, the errors due to the larger and smaller apertures 655 at 645 are averaged.
In this figure, the exact positions of beamlets 651 and 652 determined at aperture 655 and the beamlets 65 determined at aperture 655 are shown.
A compromise is made regarding the exact position of 3 and 654 to obtain a better overall position of beamlets 657 and 658 on both apertures. The separation of the upper and lower apertures is large (generally about 250 mm) compared to the tolerance (about 0.05 mm) that can be achieved during aperture creation and alignment, so that the collimation error is small (about 0.1 mrad).

Although the trace is shown as a trace from the beam striking the aperture, the method can also be used with a detector. The detector is downstream of the aperture 245 and indicates the current passing through the aperture and hitting the detector. The trace is the inverse of the trace shown in FIGS. The phrase "sense current" in the appended claims encompasses both alternatives.

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

(1) A method of collimating a particle beam using a magnetic lens in a particle beam system having a diagnostic aperture in a diagnostic aperture plate, wherein both the magnetic lens and the diagnostic aperture are system axes. A) traveling therethrough, wherein: a) the beam passes through the lens at a first offset distance from the system axis in a first direction with respect to the system axis. Guiding a beam at the upper focal plane of the lens; b) sweeping the beam over a first edge of the diagnostic aperture by a sweep deflection, and a first from the beam having a first knee. Observing a current trace; c) the first offset distance from the system axis in a second direction with respect to the system axis. Guiding said beam at said upper focal plane of said lens in said second direction with respect to said system axis, opposite said first direction, so that said beam passes through said lens; D) sweeping the beam by the sweep deflection on a second edge of the diagnostic aperture different from the first edge, and removing a second current trace from the beam having a second knee. Observing and adjusting a lens controller in the lens until the first knee and the second knee coincide when the sweep deflection is zero. (2) The method of (1) above, wherein the observing step comprises displaying a human-visible representation of the first and second traces. (3) the offset distance from the system axis is such that the beam is partially obstructed by an upstream aperture disposed about the system axis, such that a portion of the beam passes through the upstream aperture; The method according to (1), wherein the distance is a distance. (4) the offset distance from the system axis is such that the beam is partially obstructed by an upstream aperture disposed about the system axis, such that a portion of the beam passes through the upstream aperture; The method according to (2), which is a distance. (5) the beam is swept over the first edge of the diagnostic aperture in a first direction, and the beam is swept in a second direction opposite the first direction; 2. The method according to (1), wherein the edge is swept over the edge. (6) the beam is swept over a first edge of the diagnostic aperture in a first direction and the beam is swept in a second direction of the diagnostic aperture in a second direction opposite the first direction; 3. The method according to (2), wherein the edge is swept over the edge of. (7) the beam is swept over the first edge of the diagnostic aperture in a first direction and the beam is swept in a second direction of the diagnostic aperture in a second direction opposite to the first direction; 3. The method according to (3), wherein the edge is swept over the edge of. (8) the beam is swept over the first edge of the diagnostic aperture in a first direction and the beam is swept in a second direction of the diagnostic aperture in a second direction opposite to the first direction; The method of (4) above, wherein the edge is swept over the edge of. (9) A method of collimating a particle beam using a magnetic lens in a particle beam system having a diagnostic aperture in a diagnostic aperture plate, wherein both the magnetic lens and the diagnostic aperture are along a system axis. A particle beam traveling therethrough, a) passing the beam through the lens at a first offset distance from the system axis in a first direction with respect to the system axis. Guiding at the upper focal plane of the lens; b) sweeping the beam over a first edge of the diagnostic aperture by sweeping deflection, detecting current from the beam, having a first knee; Forming a first representation of the current; c) the first offset from the system axis in a second direction relative to the system axis; Guiding the beam at the upper focal plane of the lens in the second direction with respect to the system axis, opposite the first direction, such that the beam passes through the lens at a distance; D) sweeping the beam by the sweep deflection on a second edge of the diagnostic aperture different from the first edge, detecting a current from the beam, having a second knee; Forming a second representation of the current and adjusting a lens controller in the lens until the first knee and the second knee coincide when the sweep deflection is zero. (10) the step of forming a representation of the current includes digitizing the value of the current to form a digitized current value; and storing the digitized current value. Calculating the value of the sweep deflection at the first and second knees. (11) The method of (9), wherein forming an expression comprises displaying human-visible first and second expressions of the current. (12) The method of (10) above, wherein forming a representation comprises displaying first and second human-visible representations of the current. (13) the offset distance from the system axis is
The method of claim 9, wherein the beam is partially obstructed by an upstream aperture disposed about the system axis, such that a portion of the beam passes through the upstream aperture. (14) the offset distance from the system axis is:
The method of claim 10, wherein the beam is partially obstructed by an upstream aperture disposed about the system axis, such that a portion of the beam passes through the upstream aperture.

[Brief description of the drawings]

FIG. 1 shows a simplified version of a particle beam system used to implement the present invention.

FIG. 2 is a diagram showing details of FIG. 1;

FIG. 3 illustrates an exemplary oscilloscope trace from a particle beam sweep on the lower aperture of FIG. 2;

FIG. 4 illustrates an exemplary oscilloscope trace from a particle beam sweep on the lower aperture of FIG.

FIG. 5 is a diagram showing a standard of collimation of a particle beam.

FIG. 6 is a diagram showing criteria for collimation of a particle beam.

FIG. 7 is a diagram showing a standard of collimation of a particle beam.

FIG. 8 is a diagram illustrating correction of an aperture having a misalignment.

FIG. 9 is a diagram illustrating correction of an aperture having a mismatch.

FIG. 10 illustrates the correction of an incorrectly dimensioned aperture.

FIG. 11 illustrates the correction of an incorrectly dimensioned aperture.

[Explanation of symbols]

 101 Column axis 110 Light source 115 Illumination aperture 120 First condenser lens 130 Illumination lens 135 Back focal plane aperture 140 Second condenser lens 145 Reticle 150 Contrast aperture 160 Projection lens 170 Target plane 190 Light source imaging ray trace

──────────────────────────────────────────────────の Continued on the front page (72) Paul F. Petrick, Inventor, United States 94588 Pleasanton, California Apartment 206 Andrews Drive 3440 (72) Inventor, Christopher F. Robinson United States 12538-3117 Hyde, New York Park Shaker Lane 15 (56) References JP-A-60-10720 (JP, A) JP-A-54-68149 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 504 G03F 7/20 521

Claims (14)

(57) [Claims] 1. A method of collimating a particle beam using a magnetic lens in a particle beam system having a diagnostic aperture in a diagnostic aperture plate, wherein both the magnetic lens and the diagnostic aperture are in a system axis. A) a particle beam traveling therethrough, a) the beam such that the beam passes through the lens at a first offset distance from the system axis in a first direction with respect to the system axis. B) sweeping the beam over a first edge of the diagnostic aperture by a sweeping deflection, and a first current from the beam having a first knee. Observing a trace; and c) measuring the first offset distance from the system axis in a second direction with respect to the system axis. Guiding the beam at the upper focal plane of the lens in the second direction, relative to the system axis, opposite the first direction, such that the beam passes through the lens at a filter. D) sweeping the beam by the sweep deflection on a second edge of the diagnostic aperture different from the first edge, and removing a second current trace from the beam having a second knee. Observing and adjusting a lens controller in the lens until the first knee and the second knee coincide when the sweep deflection is zero. 2. The method according to claim 1, wherein said observing step comprises:
2. The method of claim 1, comprising displaying a human-visible representation of the trace. 3. The offset distance from the system axis is such that the beam is partially obstructed by an upstream aperture disposed about the system axis, such that a portion of the beam passes through the upstream aperture. The method of claim 1, wherein the distance is such. 4. The method according to claim 1, wherein said offset distance from said system axis is such that said beam is partially obstructed by an upstream aperture disposed about said system axis, whereby a portion of said beam passes through said upstream aperture. The method of claim 2, wherein the distance is such. 5. The diagnostic instrument of claim 1, wherein the beam is swept over a first edge of the diagnostic aperture in a first direction, and the beam is swept in a second direction opposite the first direction. The method of claim 1, wherein the method is swept over a second edge. 6. The diagnostic aperture of claim 1, wherein said beam is swept over said first edge of said diagnostic aperture in a first direction and said beam is swept in a second direction opposite to said first direction. 3. The method of claim 2, wherein the method is swept over a second edge. 7. The diagnostic aperture of claim 1, wherein the beam is swept over a first edge of the diagnostic aperture in a first direction and the beam is swept in a second direction opposite to the first direction. 4. The method of claim 3, wherein the method is swept over a second edge. 8. The diagnostic apparatus of claim 1, wherein the beam is swept over the first edge of the diagnostic aperture in a first direction, and the beam is swept in a second direction opposite the first direction. 5. The method of claim 4, wherein the method is swept over the second edge. 9. A method for collimating a particle beam using a magnetic lens in a particle beam system having a diagnostic aperture in a diagnostic aperture plate, wherein both the magnetic lens and the diagnostic aperture are in a system axis. A) a particle beam traveling therethrough, a) the beam such that the beam passes through the lens at a first offset distance from the system axis in a first direction with respect to the system axis. B) sweeping the beam over a first edge of the diagnostic aperture by sweeping deflection, detecting current from the beam, and having a first knee. Forming a first representation of the current; c) the first direction from the system axis in a second direction relative to the system axis. Guiding the beam at the upper focal plane of the lens in the second direction with respect to the system axis, opposite the first direction, such that the beam passes through the lens at a set distance. D) sweeping the beam by the sweep deflection on a second edge of the diagnostic aperture different from the first edge, detecting a current from the beam, and having a second knee. Forming a second representation of the current, and adjusting a lens controller in the lens until the first knee and the second knee coincide when the sweep deflection is zero. 10. The step of forming a representation of the current includes digitizing the value of the current to form a digitized current value; and storing the digitized current value. Calculating the value of the sweep deflection at the first and second knees therefrom. 11. The method of claim 9, wherein forming the representation comprises displaying first and second human-visible representations of the current. 12. The method of claim 10, wherein forming the representation comprises displaying first and second human-visible representations of the current. 13. The system according to claim 1, wherein said offset distance from said system axis is such that said beam is partially obstructed by an upstream aperture disposed about said system axis, whereby a portion of said beam passes through said upstream aperture. 10. The method of claim 9, wherein the distance is such. 14. The system according to claim 1, wherein said offset distance from said system axis is such that said beam is partially obstructed by an upstream aperture disposed about said system axis so that a portion of said beam passes through said upstream aperture. 11. The method of claim 10, wherein the distance is such.