JPH0340360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for double deflection scanning of charged particles, and more particularly to a single electromagnet with multiple gaps for achieving double deflection scanning of a charged particle beam. be.

Charged particle beam devices typically incorporate a charged particle source, an accelerator tube, a separator or momentum resolver unit, and a target. The target is sometimes moved relative to the fixed beam to uniformly distribute the charged particle beam across the target or to reduce heating. This is reflected in the U.S. patent by Arndt Giunia et al.
No. 3983402 (title of the invention “Ion Implanter”) or U.S. Patent No. 3983402 by G.I. Robertson.
No. 3778626 (title: "Mechanical scanning device for ion implantation"). Alternatively, the beam may be scanned about the target using electromagnets. See page 171 of "Ion Implantation, Sputtering and Their Applications" by B.D. Townsett et al. (Publisher: Academy Press, 1976). The latter method inherently provides a variable angle of incidence of the beam on the target. If the target is a processed semiconductor wafer inside the ion implanter, this variable incidence angle can change the depth of penetration due to channeling effects, and can even make it non-uniform. This result is enhanced with increasing semiconductor wafer diameter. Such variations in penetration depth are undesirable in semiconductor devices (see, G.R. Brewer, U.S. Pat. No. 3,569,757, col.
~line 59).

The variation of the angle of incidence of charged particles scanned using an electromagnet is achieved in conventional techniques by deflecting the beam transversely to the beam path and then opposing it in order to remove the transverse component of the beam's velocity. This can be substantially eliminated by deflecting the beam in the opposite direction. The initial velocity component of the beam (the velocity component at the beam source towards the target) is not disturbed and the charged particles are forced to move laterally. References are shown below. “Ion Implantation” by G. Deianeire et al., pages 404-406 (1973), U.S. patent no. by G.R. Brewer.
No. 3,569,757 (title: “Accelerator for implanting ions into materials”), U.S. Pat. ”, by M. Thomson, “Aberrations and Tolerances in Dual Polarization Electron Beam Scanning Devices” (Journal of Science and Technology, Volume 12, Page 1156 (1975)). These double polarization In the device, a set of charged plates is used to achieve electrostatic deflection or an electromagnet is used to achieve magnetic deflection, thus achieving a perfect double deflection. This would require two sets of plates for electrostatic deflection and one set of electromagnets for magnetic deflection.To achieve deflection in both the X and Y directions, multiple Twice as many plates or electromagnets are required for each deflection means and for each deflection means to achieve deflection in these dual deflection devices, and to use separate means to further achieve re-deflection. The geometry and placement of the electrical circuitry in conjunction with the In general, the use of a large number of elements leads not only to a considerable initial cost increase but also to an increase in energy consumption during operation.

It is therefore an object of the invention to achieve dual deflection scanning of a charged particle beam by a single electromagnetic means.

Furthermore, it is an object of the invention to achieve dual deflection scanning of a charged particle beam without aberrations and errors.

Furthermore, it is an object of the present invention to provide one electromagnet with multiple gaps to accomplish both deflection and re-deflection in a dual deflection scanning mode.

A uniform electromagnet with two gaps is provided for charged particle beam dual deflection scanning. These gaps are provided in the magnet to allow the charged particles to trace a continuous aiming path through these gaps. In order to improve the linear scanning of the beam, the depth of the magnetic poles of the magnets that define the space (2B to 4)
In Figure B, the length of the magnetic pole in the Y direction) is larger than the length of the magnetic pole in the lateral direction (the length of the magnetic pole in the Z direction in Figures 2B to 4B). Modes of scanning include axial sweep scanning, off-center scanning, and split scanning.
These modes are determined by the shape of the electrical waveform used to energize the electromagnet.

Preferred Embodiment As described above, there are two approaches to transmit uniformly focused charged particles to a target. In ion implanters, these approaches include either mechanically scanning the wafer across a fixed ion beam path, or electromagnetically scanning the ion beam across the surface of a fixed semiconductor to generate an even portion of ions. This is an attempt to add this to semiconductor wafers. The first example presents a different mechanical problem in obtaining a lateral back-and-forth scan, and further limits the scan speed due to the required accelerations and decelerations at the ends of each scan. Precise electromagnetic scanning over the entire area of the wafer is difficult because the electrostatic plate displacement or magnet gap length needs to be large for good scanning. This leads to high electromagnetic field strengths, ineffective energy, and fringe electromagnetic fields that in turn cause undesirable effects. A hybrid scanning system that incorporates the best features of both approaches offers advantages over employing the individual approaches. When such a device incorporates rotational scanning of a target, for example a fixed object to which a semiconductor is mounted, high scanning speeds are essentially achieved by precise navigation of the rotating target in one linear direction. However, the horizontal scanning height will not increase. See, for example, G. I. Robertson's discussion of pattern figures in US Pat. No. 3,778,626. The transverse scanning is a sawtooth waveform or an oscillatory function (which is subject to the modulation discussed next) and is best accomplished by magnetic means, particularly dual deflection magnetic scanning. This scanning is possible because the deflection force is applied to the moving ion in a direction perpendicular to the direction of the magnetic field B→ and also perpendicular to the direction of the velocity of the moving ion. Since the deflection (and re-deflection) occurs in a plane that equally divides the two gaps,
The gap may be relatively small. On the other hand, electrostatic deflection requires a larger gap to be used since the deflection force is applied in the direction of the electric field E→ and scanning occurs along the length of the gap. Instead of a combination of magnetic scans, a first transverse scan is performed by magnetic means and a second longitudinal scan is obtained by electrostatic means. In any combination,
The target is either precisely mounted perpendicular to the impinging ion beam or oriented at a slight angle to the direction of the beam. The single (integral) magnet for dual deflection scanning of the present invention is therefore easily adaptable for integration into one of these hybrid scanning devices.

As mentioned above, dual deflection scanning is a natural technique for producing lateral displacements of the beam with the desired accuracy. Wide beam heights are not ideally suited for magnetic scanning because the gap lengths become large and require very high magnetic field strengths. For such dual deflection scans, careful alignment of the deflection and re-deflection by the magnetic field must be obtained if ion mass uniformity is important. This alignment is essential if separate magnets are used, since typically the ion mass must be maintained within 1% error. The single electromagnet of the present invention has double gaps positioned to provide the ion beam with a line of sighting path through the two gaps so that the ion beam traverses the length of the gap. , will pass through each gap in a plane completely perpendicular to the magnetic field B→. The geometry establishing this condition is shown in FIG. Since electromagnets draw closed curves as magnetic field lines, the same magnetic flux occurs in the deflecting and re-deflecting forces. This alignment is inherent as long as the pole faces and gap lengths are the same or approximately balanced. The waveform for energizing the electromagnet is such that the same flux traverses each gap in the magnet. Since it creates a magnetic field B→, it does not need to conform to any standards. The waveform simply determines the position of the ion beam on the wafer, but not the angle of incidence. This single magnet for dual deflection does not require separate magnets and precision electrical circuitry, and can be more easily and concisely constructed.

With reference to FIG. 1, the structure of a single magnet of the present invention can be seen. Closed curve electromagnet 10 has two U
It is composed of glyph-shaped cores 11 and 12. core 1
The size and shape of 1, 12 are matched so as to form gaps 13, 14 at their ends. Preferably the length of their gap (distance from pole to pole)
are equal. In this case, the windings 15, 16 are symmetrically located and carry the same current. The length of the gap is typically on the order of 4 cm. The depth of the pole face (the face perpendicular to the drawing) is also the width of the pole face (the face facing the drawing)
It is also on the order of 30cm. The total width of the U-shaped core, ie the distance between the outer sides of the two pole faces, is of the order of 100 cm.

1 to 4, the direction of the magnetic field and the forces acting on the positively charged ions are shown. The force acting on negatively charged ions is in the opposite direction. In FIG. 1, the direction of the magnetic field B→ in the gap 13 is from the bottom pole to the top pole. Since the ion beam moves from left to right, the force field F→ is the direction toward which the drawing is directed (indicated by the tip of the arrow). Conversely, the magnetic field B→ in the gap 14 is from the upper pole to the lower pole, and its force field F→ is in the direction of the drawing (indicated by the arrowheads). The directions of the magnetic and force fields for comparison are also shown in FIGS. 2 to 4, and at any time t ₁ ,
This is clearly shown in Figure A.

The operation of the single magnet of the present invention can be understood with reference to the side view of FIG. A diverging ion beam 33 from an ion source 30 (point source or parallel source as shown) is focused onto a momentum resolving magnet 34
I will provide a. Ions of the appropriate type, such as As ⁺ with an energy of 80 kev, are selectively redirected based on charge, energy and mass so that the ions exit the momentum resolving magnet 34 as a focused beam 35. Species with different masses, energies, and charges cannot be redirected into this converging beam. single magnet 10
is positioned to direct a focusing beam 35 through one of its magnetic gaps. If the relative distance between the magnets is chosen optimally, the beam will converge at the center of a single magnet 10. This tends to eliminate any possible optical effects of the single magnet in the plane in which the beam is deflected and re-deflected (the Y-Z plane in FIG. 1). A focal point that is such a point (the center of a single magnet that becomes like a source)
allows the use of the most concise magnets. A parallel series of foci will achieve the same result with the foci being at the center of a single magnet. The initial height of the beam, ie the vertical deviation of the plane of deflection and re-deflection, will be highly dependent on the optical properties of the incident beam. The uniform magnet 10 is desirably optically inert with respect to the beam, so that the magnet exerts a force in the X-Z plane that deflects and re-deflects the beam. Optical properties may come into play, for example, if it is desired to intentionally cause channeling in a semiconductor wafer. This can be done by varying the area of the gap or by shaping the faces of the poles. What is shown in FIGS. 2-4 is Y-direction scanning with a magnet having an infinite focus. If a particular beam height is obtained, the relative positions of the single magnet and momentum resolver can be changed to defocus the beam and increase its height. If a rotating disk is used to attach a semiconductor wafer, the interaction of rotational scanning and transverse scanning of a semiconductor wafer mounted on rotating disk 32 can be compared to the pattern geometry discussed in Robertson, US Pat. No. 3,778,626.

A series of single magnet embodiments of the invention are illustrated in FIGS. 2-4. These views are drawn along the gap in FIG. 1 (lines 2-4). The differences in the figures are due to the point of incidence of the ion beam and the waveform used to energize the electromagnet windings. Elaborating on the differences between these figures can result in very different and useful embodiments.

In the first embodiment shown in FIGS. 2A and 2B, the ion beam is
It is introduced along a line in the Z plane. A triangular waveform (shown in Figure 2A) is used to energize the electromagnet. Each half period of the triangular waveform causes the second pole to scan from one side to the other side. Its amplitude is such that it directs the beam to move from one end of the second pole face to the other. The effective depth of the scan will be less than the geometric depth of the plane of the pole. Its depth is typically on the order of 2/3 of the geometric depth. Since the magnetic field B is opposite in direction and of the same strength in the second gap, the lateral velocity in the Y-Z plane applied by the first pole field is removed by the second pole field. Will. Therefore,
A scanning width W is obtained.

In the second embodiment shown in FIGS. 3A and 3B, the ion beam is introduced into the X-Z plane along one end of the first gap pole face. One period of the triangular waveform now causes the beam to scan from one end of the pole face to the other and back in the second gap. The advantage of this method is that the uncharged particles generated along the initial beam axis will impinge on a single point on the target along the incident axis, which can also be chosen not to coincide with the semiconductor wafer area.

In a third embodiment, shown in Figures 4A and 4B, the waveform is chosen to have a built-in bias. Basically, a sawtooth waveform function has alternating positive and negative biases superimposed. This waveform allows scanning of isolated areas,
In other words, it performs divided scanning, and therefore separate local areas can be used. The magnetization switch is ideally instantaneous and can allow deflection from one locality to another.

In all of the embodiments described above for performing transverse scanning magnetically, the scanning speed is shown to be constant, so that the waveform is a sawtooth function with perfectly linear sections. If the rate of scan transition in the direction perpendicular to the transverse scan is not constant, such as in the case of a rotating target where the rotational transverse scan rate varies with the radius of the beam impact point, the scan rate will undergo a change. The transverse scan velocity is kept inversely proportional to this radius to obtain a uniform distribution of ions.
This is accomplished by modulating the basic sawtooth waveform used to energize the electromagnet. Storage means, such as programmable read-only storage, or real-time feedback means may be used to determine the position of the beam at any point in time to permit appropriate modulation of the basic sawtooth function by the waveform generation means. good. Alternatively, the beam intensity may be varied by the source of the charged particles according to input from a storage means or feedback means to compensate for changes in scanning speed, so that a uniform quantity of ions is produced per unit area. will be joining. U.S. Patent No. by G.I. Robertson
See discussion in No. 3778626, entitled "Mechanical Scanning Apparatus for Ion Implantation."

[Brief explanation of the drawing]

FIG. 1 is a side view of an electromagnetic device of the invention illustrating the reception of charged particles from a momentum resolving unit, the passage of the beam through the device, and the delivery of the beam to a target; FIG. 2A is an embodiment of the invention; an electrical waveform diagram for energizing the electromagnetic coil according to
2B is a plan view of the electromagnet of FIG. 1 illustrating the scanning accomplished by the waveform of FIG. 2A;
Figure 3B is a diagram of electrical waveforms for energizing an electromagnet according to a second embodiment of the invention; Figure 3B illustrates the scan obtained by utilizing the waveforms of Figure 3A; 4A is a top view of the electromagnet; FIG. 4A is another electrical waveform diagram for energizing the electromagnet according to a third embodiment of the invention; FIG. 4B illustrates the scan obtained using the waveforms of FIG. 4A; FIG. 2 is a plan view of the embodiment of FIG. 1; 10... Electromagnet, 11, 12... Core, 13,
14... Gap, 15, 16... Winding wire, 30... Source, 31... Focusing point, 32... Target,
33...Divergent beam, 34...Momentum resolving magnet,
35... Focused beam, W... Scanning width.

Claims (1)

[Scope of Claims] 1. A single device for double deflection scanning of a charged particle beam, comprising a set of generally U-shaped cores, the ends of which define a set of They are placed opposite each other so that the
an electromagnet comprising a core through which said charged particles can traverse, and a winding associated with each of said gaps; and means for energizing said winding to scan said beam; A single device in which the polarity of the magnetic field across one of the gaps is of opposite polarity to the magnetic field across the other gap. 2. A unitary device as claimed in claim 1, wherein the windings associated with each of the poles are arranged symmetrically and have equal current carrying capacity. 3. A unitary device according to claim 1, further comprising a charged particle beam source located adjacent to said one gap for introducing said beam into the center of one of said gaps. 4. A unitary device according to claim 1, comprising a charged particle beam source arranged adjacent to said one gap for introducing said beam along an edge of said one gap. . 5. A charged particle beam source disposed adjacent to the one gap in order to introduce the beam into the central plane of the one gap, and a charged particle beam source placed adjacent to the one gap, and the beam in the middle of both poles of the other gap. 2. A unitary device as claimed in claim 1, comprising: means for energizing the windings of the electromagnet capable of producing a waveform having a sub-scan of . 6. A unitary device according to claim 1, wherein only the electromagnet exerts a force on the beam in the plane of the scanning beam. 7. A unitary device according to claim 1, wherein the particles in the scanning beam move along parallel paths occurring between said other beams.