JP3376857B2 - Ion implanter - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor wafer,
The present invention relates to an ion implantation apparatus for realizing large-current ion implantation into a large processed product such as a glass substrate. In the case of a Si wafer, ion implantation is often performed to dope p-type and n-type impurities such as boron, phosphorus and arsenic. In order to increase the throughput, a device for uniform doping distribution and high-speed doping is desired.

[0002]

2. Description of the Related Art Conventional high current ion implanters are roughly classified into two types. One is to perform mass analysis of a thin (zero-dimensional spread) high-density ion beam with a fan-shaped magnet and irradiate only a desired ion species onto a processed product (wafer) placed on a rotating target that rotates and translates. Is. Since the ion beam is thin, it is easy to perform mass separation with a fan magnet. However, since the beam itself has no divergence, it is necessary to translate and rotate the wafer in order to irradiate the entire surface of the wafer. It is necessary to move the wafer two-dimensionally on the side of the end station supporting the wafer.

The other is to extract a large-diameter ion beam from a large-diameter ion source and irradiate the wafer without mass analysis. The diameter of the wafer is W, and the diameter of the ion beam extracted from the ion source is D. D> W
Since a large-diameter ion beam is generated, it is not necessary to scan the wafer.

[0004]

[Problems to be Solved by the Invention]

1. In the method using the rotating target, the beam optical system is simple because a thin 0-dimensional beam is generated. However, the structure of the end station, which has to perform rotational translation, is complicated. The disk on which the wafer is placed must be rotated at high speed and controlled in translational speed in proportion to the ion beam current and inversely proportional to the beam position. When the beam current density at the wafer becomes high, the charge-up phenomenon of the wafer becomes remarkable. Charge-up is a phenomenon in which charges do not escape when a positive or negative ion beam is injected and the charges accumulate on the surface of a wafer or the like. This may destroy devices on the surface of the wafer, which is undesirable. Currently, the rotary target method is practically used as a method for implanting ions into a large-diameter wafer, but there are such drawbacks.

2. In the large-aperture ion source non-mass separation method, the beam optical system is only an ion extraction system, and therefore the apparatus configuration is simpler. The structure of the end station is also simple. However, since a large-diameter ion beam cannot be subjected to mass analysis, ion species other than desired ions are not distinguished and are injected into the wafer. The desired characteristics may not be obtained due to the implantation of the impurity ions. Further, the implantation depth distribution changes depending on the plasma state because the implantation is performed in the form of molecules instead of ions. Another difficulty is that the device characteristics are difficult to maintain because the implantation depth is difficult to maintain.

Regarding the former, for example, when boron is injected, diborane (B ₂ H ₆ ) is used as a source gas. At this time, hydrogen ions are also injected into the wafer together with boron. Since the injected hydrogen has a high speed, it may penetrate through the gate oxide film and be injected into the channel layer. This can cause lattice defects in the channel below the gate electrode. All the ion energy is converted into heat, but if ions other than the desired ion species (for example, hydrogen ions) are injected, the sample will be overheated. The device on the sample may be destroyed due to the temperature rise.

3. That is not the only drawback of the large-diameter ion source system. When an ion is to be implanted into a large-area substrate such as an 8-inch wafer or a 12-inch wafer, the uniformity of implantation within several percent is required everywhere on the wafer surface. It is a very difficult technique to realize an ion source having such a large area and uniform beam density. Large diameter ion sources can currently only be used for small area wafers with less demanding implant uniformity.

4. Further, as an ion implantation method without mass spectrometry, the PIII method (Plasma ImmersionIon Implantation)
) Has been proposed. Shu Qin and Chung C
han, "Plasma immersion ion implantaion doping exper
iments for microelectronics ", J.Vac.Sci.Technol.B12
(2), (1994) p962. This is a method in which a Si wafer is exposed to plasma and a negative voltage is applied to the wafer to accelerate ions in the sheath region and inject them into the wafer. No extraction electrode is required because a sheath voltage is used to extract the ion beam. Often the impurities are sputtered electrodes. In this method, there is no possibility that impurities generated from the electrodes will be mixed. Therefore, it is not necessary to do mass spectrometry. However, it is not possible to remove unnecessary ions from the elements contained in the source gas.

In the case of boron doping, diborane is used as a source gas, but hydrogen ions are injected into the wafer. Both hydrogen ions and boron ions have the same acceleration energy. The wafer is overheated by hydrogen ion implantation. When the injection time is shortened to increase the throughput, the temperature rise due to hydrogen injection becomes remarkable. Therefore, the injection time cannot be shortened too much. It has been reported that a single wafer was ion-implanted at a density of 1.9 × 10 ¹⁵ cm ^-2 in 10 minutes. This is too low a throughput. 1
I want to implant ions within 1 minute. In fact, this method does not seem to be in practical use.

5. USP 5,350,926 "Compact
"High Current Broad Beam Ion Implanter" and Japanese Patent Laid-Open No. 6-342639 "Compact High Current Wide Beam Ion Implanter" are the first masses for deflecting an ion beam expanding horizontally from a horizontally long ion source by about 90 degrees. Pass it through the analysis magnet to a single point, pass through a hole with a small slit, eliminate unnecessary ions, and pass a second mass analysis magnet that deflects the divergent beam by about 90 degrees to form a parallel flat beam with a width, Suggests a way to inject. The wafer is adapted to scan in a direction orthogonal to the longitudinal direction of the beam. In other words, this is a method of mass-analyzing a beam having a unitary spread (having a width) and injecting it into a wafer which is one-dimensionally scanned. Since this is a mass spectrometric analysis of a one-dimensional beam (belt), there is no risk of impurities being mixed in. Since a band-shaped beam is formed, it is not necessary to perform two-dimensional scanning on the wafer side, and one-dimensional scanning is sufficient. There are such advantages.

However, this also requires a complicated mechanism to scan the wafer in one dimension. Further, in this method, the beam is converged and passed through the slit of a small hole at the converging point, so that only ions having one mass number and one charge amount are selected. In many cases, ion species that are better to be ion-implanted are mixed even if the mass numbers are different. Such ionic species will also be dropped. So mass spectrometry is too strict. Moreover, this mechanism is poorly flexible. If the ion species is changed, the constant of the magnet should be changed, but this is not easy.

More gradual and flexible mass spectrometry is desired. After all, the difficulty of the band-shaped beam method is that the wide beam emitted from the ion source is converged to one point. Unlike narrowing the beam emitted from one point of the ion source to a single point, a wide beam is bent by a magnetron, so even ions of the same energy do not converge to one point. That is, it is not possible to introduce all of the desired ion species into the slit holes. This is a fundamental difficulty in beam optics.
For this reason, most of the ions are excluded by the slit. Useful ions with similar mass numbers are also excluded. On the contrary, the desired ionic species may also be removed.

6. So far, the method of mass-analyzing a 0-dimensional beam (point of cross-section) and injecting the beam into a wafer that is two-dimensionally scanned, and mass-analysis of a large-diameter two-dimensional beam (circular with wide cross-section) The method of implanting into a stationary wafer, the PIII method of implanting ions into a wafer in a plasma without using an ion source, and the method of mass-analyzing two one-dimensional beams (cross sections are line segments) with a magnet. did. The problem should be solved if mass spectrometry can be performed in the second large-diameter ion beam method. However, attempts to mass-analyze large-diameter beams have yet to be realized.

If a large-diameter ion beam is mass-analyzed by a fan-shaped magnet, the gap between the magnets becomes extremely wide. The magnet becomes larger and the required current becomes larger. Not only that. Since the gap is wide, it cannot be said that the magnetic field is uniform anywhere in the gap, resulting in non-uniformity. As a result, the beam diverges and beam loss occurs. Further, the magnetic poles and walls are sputtered by the beam, which causes contamination. Since such concerns are a concern from the beginning, methods such as mass spectrometric analysis of large-diameter beams have not yet been implemented.

It is a first object of the present invention to provide an ion implantation apparatus which is free from the risk of impurities being mixed by mass separation. It is a second object of the present invention to provide an ion implantation apparatus capable of implanting an ion beam with high uniformity over the entire wafer. It is the third object of the present invention to provide an ion implantation apparatus which can simplify the structure of the end station and reduce the apparatus cost. It is a fourth object of the present invention to provide an ion implanter capable of coping with various ion species energies. It is a fifth object of the present invention to provide an ion implanter without the possibility of charge-up.

[0016]

The ion implantation apparatus of the present invention comprises an ion source for extracting a laterally long ion beam whose horizontal width is larger than the lateral width of an object, and a fan-shaped central angle θj.
A plurality of fan-shaped magnets that are continuously provided for mass analysis by bending an oblong beam in the horizontal direction with n values that give the inclination of the magnetic field in the direction perpendicular to the beam and ε that gives the curvature of the magnetic field in the same direction as parameters The magnet is composed of a slit which is provided in the substantially central portion of the magnet and through which only a necessary ion beam passes, and a sample support mechanism which holds an object with respect to the beam and moves the object in a direction orthogonal to the width direction of the beam.

When a horizontally long beam is generated, it is not necessary to scan the beam in the horizontal direction, and it suffices to relatively move the sample vertically (vertical scanning). That is, since the time of ion implantation is shortened, the throughput is improved. The mass of the transverse beam is bent by a magnet in the horizontal direction. Since a beam having a lateral width is bent laterally, the magnetic pole spacing may be narrow. This point is convenient. However, since the beam having a width in the lateral direction is bent in the lateral direction to separate the beams due to the difference in mass, the radius of curvature is inevitably large. Not only that, the bending center angle must be large.
It is difficult to bend a wide beam uniformly horizontally. It is necessary to use a large magnet to obtain a magnetic field spread over a wide space. However, even if a large magnet is used, the magnetic field tends to be non-uniform.

Therefore, in the present invention, the mass separating magnet is divided into a plurality of magnets instead of a single magnet, and a plurality of fan-shaped magnets are continuously arranged to bend a lateral beam uniformly in the horizontal direction. A slit with a small hole is provided at approximately the midpoint of the beam path to eliminate unnecessary ions. To enable such sorting, only the desired ions should be focused just before the slit. This is the condition for mass separation. That is not all.
It is desirable that the ion beam is not diffused at the exit and is kept substantially parallel so that it is vertically incident on the wafer.

In order to satisfy such requirements, a simple magnet is not enough. This has two meanings. First, even if a uniform magnetic field is applied to give a uniform radius of curvature, it is not easy when the beam has a large area. At the end of the magnet, the magnetic field lines bend toward the outside, weakening the magnetic field. Therefore, even if a large magnet is used, a uniform magnetic field cannot be formed. It is not easy to create a uniform magnetic field, which is one, and there are aberrations, so it is necessary to correct the magnetic field in order to create a uniform magnetic field. But not only that. The present invention does not suffice with a uniform magnetic field. Since the beam spreading in the lateral direction is mass-separated by the slit, the beam position at the slit changes depending on the location at the entrance. Therefore, a uniform magnetic field is not enough because it is necessary to focus the divergent beam at the beginning. Since it is necessary to bend the ion beam with different history depending on the place, a uniform magnetic field is not enough.

Since such a complicated control is aimed at, each fan-shaped magnet has not only a dipole (double pole) component but also a quadrapole (quadrupole) component and a sector pole (hexapole). Must also be given as a parameter. That is, according to the present invention, the laterally long beam is bent, mass analysis is performed, unnecessary ions are removed, and the horizontally long beam is irradiated to the sample. However, selective placement of magnets is the most demanded. The sector magnet has a central angle θj and an n value n that gives a magnetic field gradient.
j, βj (or εj) that gives the bending of the magnetic field, etc. are parameters. That is, a series of magnets have the same magnetic field in the 0th-order approximation (non-perturbation), but have different primary and secondary coefficients.
It is necessary to determine this to the optimum value for each magnet. Since the transverse beam is bent by four magnets here, it is necessary to determine the parameters of the four magnets.

[0021]

BACKGROUND OF THE INVENTION The present invention combines a plurality of magnets and bends a flat ion beam in a flat direction to perform mass analysis through a slit.
The parameters of the magnet are no longer simple and their action is not straightforward. It is difficult to understand the effect. Therefore, the matters necessary for the magnet in order to carry out the present invention will be clarified first. First, the coordinate system is defined. The traveling direction of the ion beam is the z axis. The direction in which the ion beam bends is the x-axis direction. Since the ions bend due to the Faraday force q (v × B) of the magnetic field, B has a y component. By is the main component. This is a constant if the magnetic field is uniform. But a uniform magnetic field is not enough. Therefore, primary and secondary coefficients are provided in the direction (x direction) orthogonal to the beam. Since the magnetic flux density B starts with an approximation that it has no x component, the beam size in the y direction is almost unchanged in the traveling direction. Therefore, the spread of the beam in the x direction becomes the main concern.

Since the beam bends in an arc, the orbit spreads in the xz plane and has a z component perpendicular to the beam direction. Then, it is inappropriate to express this as the spread in the x direction. Therefore, a further improvement is made to define the z coordinate along the central axis of the magnet. The central axis of the magnet is the z axis itself. z is an arc coordinate along the reference radius R. The direction orthogonal to the beam is always the x and y directions, but the bending direction is x and the non-bending direction is y. The central axis of the magnet is x = 0 and y = 0. It is a coordinate in which the x component and the z component of normal three-dimensional Cartesian coordinates are mixed. y
Since the directions are not mixed, it is the same in the rectangular coordinate system and the circular coordinate system. (X, y, z) in this arc coordinate system, in the Cartesian coordinate system (X, Y, Z),

[0023]     X = xcos (z / R) -R + Rcos (z / R) (1)     Y = y (2)     Z = xsin (z / R) + Rsin (z / R) (3)

It will be understood that, although it is a special coordinate, it is intuitively easy to understand. Further, in the 0th-order approximation, each magnet gives the same longitudinal magnetic field By (constant), so that a desired ion writes a circle having a radius R. This is the reference circle. The reference radius R is RBy =
Given by (2MV / q) ^1/2 . M is the desired ion mass, V is the acceleration voltage, and q is the charge of the ion.
That is, R is the radius of curvature of the arc drawn by the desired ion in the uniform longitudinal magnetic field.

The expansion of the magnetic field can be given as a coefficient of x / R. Magnetic field By formed by the magnet required in the present invention
Can be written as

By (x) = B ₀ {1- (Nx / R) + (βx ² / R ² ) + ...} (4)

B ₀ is a uniform dipole component. This is common to the plurality of sector magnets M1 to Mm. The non-perturbative system means the magnetic field of this term only.
There are two methods to generate such an anisotropic magnetic field. One is to devise the magnetic pole shape of the yoke. The other is to combine coils in a complicated way. FIG. 1 shows the shape of the magnetic poles of the yoke, which can include magnetic field changes up to the second order. First-order change of x by deforming the shape of the magnetic pole,
A quadratic change can be given. However, it is difficult to deform the magnetic pole of the yoke and it lacks flexibility. Even if a plurality of coils are combined while utilizing a flat magnetic pole, similar x dependence can be given.

FIG. 2 is a diagram showing the relationship between the coil cross section and the magnetic field formation. In the cross section of the air-core coil, the plus sign indicates the direction in which the current is boiled up from the paper surface, and the minus sign indicates the direction in which the current flows downward. A magnetic field is generated in the direction in which the right-hand screw travels with respect to the flow of the coil current.

FIG. 2A shows a simple cylindrical coil in which an electric current is passed, and a substantially uniform upward magnetic field is generated in the coil. This is the same as a magnetic field that can be formed by facing flat magnetic poles at right angles to the coil. It is a magnetic field with uniform direction strength in the coil, and is called a dipole magnetic field because it is created by a dipole. Since the magnetic flux density created by this is uniform, it can be written as B ₀ .

FIG. 2B shows a combination of two conical air-core coils with their bottoms facing each other. The coil on the upper left produces a conical magnetic flux density in the coil that is directed obliquely downward to the right. The lower right conical coil produces an upper left magnetic flux density. x
The change in magnetic flux density on the axis is positive for x> 0 and negative for x <0. The magnetic flux density created by this can be written as Nx / R. N is a coefficient indicating the slope. Since two coils are combined, it is called a quadrupole magnetic field.

In FIG. 2 (c), three coils are vertically combined. The middle cylindrical coil produces a uniform upward magnetic field. The upper and lower cone coils produce a downward inhomogeneous magnetic field. Since these cancel each other out, a large magnetic field is generated at the center of the coil and at the end of the coil. This is given by a quadratic function of βx ² / R ² . It is called a hexapole (sector pole) magnetic field because it combines three coils. β / R ²
May be expressed by ε.

Regarding the variation in the x direction, it has been explained that the 0th-order magnetic field can be provided by the dipole, the 1st-order magnetic field by the quadrupole, and the 2nd-order magnetic field by the sector pole. These use an air-core coil and describe the case where there is no yoke. The presence of the yoke limits the shape of the yoke itself. There are also restrictions on how to wind the coil around the yoke.

FIG. 1 shows that a similar anisotropic magnetic field is generated depending on the shape of the magnetic pole of the yoke. Since the N pole is on the upper side and the S pole is on the lower side, a 0th-order magnetic field B is generated from the upper side to the lower side.
This is due to the dipole. This also occurs in a flat magnetic pole. That is not all. On the right side (x> 0) of the magnetic poles in FIG. 1, the distance between the magnetic poles becomes wide,
The spacing is narrower on the left side (x <0). The magnetic field decreases as it goes in the x (right side) direction. This is N
Is equivalent to the quadrupole effect (Nx / R) when is positive. That is, the gradient of the magnetic pole in FIG. 1 is equal to that of the quadrupole.

Further, the magnetic pole of FIG. 1 is not a flat surface, but a convex curved surface protruding at the central portion. This curve is x = 0
It means that the magnetic field is strong in the vicinity of and becomes weaker when it leaves, so β is made negative and the term of (βx ² / R ² ) is given. In other words, the curved surface of the magnetic pole causes 3 in FIG.
It can have the same effect as two coils.

When the magnetic poles are geometrically deformed as shown in FIG. 1, a simple coil can have a quadrupole (Nx / R) action and a hexapole action (βx ² / R ² ). However, since the pole shape of the yoke is fixed, changing the beam type or changing the energy makes it no longer applicable. The present invention therefore does not take the route of directly deforming the magnetic pole as in FIG. Instead, the yoke magnetic pole structure is made simple and flat, and the coil distribution is complicatedly devised. Increase the number of coils to enable quadrupole and hexapole action.

By combining a plurality of fan-shaped magnets having such a complicated action, the laterally long beam is directly subjected to mass analysis.

The number m of the fan-shaped magnets is four here,
It can be set to 3 to 20 pieces. The total central angle (ΣΘ) of the sector magnet is 126.5 ° in the embodiment, but is not limited to this. The central angle may be set within the range of 100 ° to 240 ° so as to meet the purpose.

The parameters of the magnet here are Θ, N, ε.
(= Β / R ² ). Optimal values for these parameters are calculated by imposing conditions at the entrance, exit and slit. Therefore, it is necessary to analyze the beam trajectory in the magnet.

Six variables X _j (s) representing one ray are defined, and changes in these variables are calculated for each coordinate divided in the flow direction s. When the division in the flow direction is made fine, the value of the variate at the k + 1th division point can be expressed by a linear combination of the values at the immediately previous division points.

X ₁ = x, X ₂ = θ, X ₃ = y, X ₄ =
Let φ, X ₅ = 1 and X ₆ = δ.

In the 1st order analysis, the coordinates of the division points are obtained by the calculation of linear linear combination.

X _i (s + 1) = ΣR _ij X _j (s) (5)

R _ij depends on B ₀ , N, Θ, etc. The variable at the magnet outlet can be obtained by calculating the sum of products. In the calculation of the 2nd order, including the aberration,

X _i (s + 1) = ΣR _ij X _j (s) + ΣT _ijk X _j (s) X _k (s) (6)

The following calculation is performed. T _ijk is B
₀ , N, Θ, ε, etc.

By performing such calculation, the beam variable at the exit of the mass analysis magnet is calculated. The variable at the slit can also be calculated. This is an analysis of each beam,
Calculate for all required ticks. Each magnet M1 to Mm
For Θ j, N j, ε j such that the desired result is obtained at the slit and exit.

[0047]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows a schematic structure of an ion implantation apparatus of the present invention. The ion source 1 introduces a raw material gas, turns it into plasma by microwaves or electric discharge, applies a voltage, and extracts it as an ion beam. The shape of the outlet and electrode has been devised so that a horizontally long beam can be generated. Since the x axis is in the horizontal direction and the y axis is in the vertical direction, it means that a beam having a cross section that is long in the x direction and short in the y direction is generated. For example, a ribbon-shaped (strip-shaped) parallel ion beam having a width of 40 cm and a thickness of 5 cm is generated. Energy can be freely given by the extraction voltage. For example, it has an energy of several tens keV to several hundreds keV. The horizontally long beam enters the mass analysis magnet 3 composed of a plurality of sector magnets M1, M2, M3, M4. At the entrance 2, a parallel beam extending in the x-direction, which is bent by the magnetic field.
An arc in which the central beam (x = 0) is bent by the common magnetic field By ₀ is defined as a reference arc R. The z-axis is defined along this.

If the magnetic field is uniform, ions of desired mass travel in the magnetic field space in the magnet with the same radius R. The beam located at x> 0 at the entrance is x <0 at the exit
Go out. A slit 4 having a hole of an appropriate width is provided here because it converges substantially in the middle of the path in the magnet. Only ions with the desired mass can pass through the slit. Ions having other masses collide with this slit and are injected into the slit plate or scattered backward so that they do not enter the beam line after the slit.

The beam that has once converged and passed through the slit diverges and becomes a parallel horizontally long beam at the exit of the mass analysis magnet 3 with its distribution in the x direction being substantially inverted. It passes through the short vacuum path 7 and is incident vertically on the wafer 8. Since the beam width T (here, 40 cm) is longer than the wafer diameter W (here, 30 cm) (T> W), ion implantation can be performed over the entire lateral width of the wafer. The wafer is translated in the vertical direction (y direction) and ion-implanted on the front surface. The two-dimensional position detector 9 is located behind the wafer and can directly measure the current density of the oblong beam. This can be configured by a Faraday cup or the like having sensors arranged two-dimensionally.

FIG. 4 shows the end station part in more detail. The traveling direction of the beam is opposite to that in FIG. Wafer transfer device from cassette at W1 1
1 through the intermediate point W2 and the ion implantation point W
Carry to 3. The carrier now redirects the wafer to a vertical orientation so that the surface is at right angles to the beam. The wafer is translationally scanned in the y direction. As a result, the ion beam is injected onto the entire surface of the wafer. The wafer after the injection is carried to the cassette position W5 by the carrying device 11 and sequentially accommodated therein.

The parameters of the sector magnets M1 to M4 of the mass analysis magnet 3 are adjusted so that the beam flies in a trajectory like steam. Therefore, 1st order analysis is performed. Ion beam is incident parallel at the entrance,
In the analysis slit 4, by imposing a constraint condition that ions of a desired mass converge on the hole of the slit, central angles Θ1 and Θ2 of M1 and M2 and N1 and N2 that give inclinations are determined. Since it is a parallel beam having a spread of 30 cm to 40 cm in the x direction at the entrance, even ions of desired mass do not converge at the slit in the uniform magnetic field. Therefore, it is necessary to change the magnetic field in the direction perpendicular to the longitudinal direction. Therefore, a plurality of fan-shaped magnets are used to give different magnetic field gradients N to force the desired ions to converge at the slit.

Next, the horizontal beam size and beam divergence angle on the wafer and the vertical beam size are designated as the beam divergence angle. In addition, the conditions for a parallel beam are included. The central angles Θ3 and Θ4 and the inclination values N1 and N2 of the fan-shaped magnet (magnet section) are determined so as to satisfy these constraint conditions. If an ion beam of a desired mass that is forcibly converged at the slit is bent as it is with a uniform magnetic field, it will not be conveniently parallel at the exit and the spread in the x direction will not be sufficient. The beam must be forced out and parallel at the exit. Therefore, it is necessary to devise the N value of the sector magnet.

It is not the only one. Fine adjustment of the x squared term is required. This is an analysis of the 2nd order. First, the radius of curvature of the pole piece at the magnet entrance and the values of ε in the fan-shaped magnets (magnet sections) M1 and M2 are determined so as to minimize the contribution of the secondary aberration in the analysis slit. Further, the radius of curvature of the pole piece at the magnet exit and the value of ε in the fan-shaped magnets M3 and M4 are determined so that the secondary aberration in the wafer is also minimized. By the 1st order analysis, Θ of the fan-shaped magnet,
N is determined by the analysis of the 2nd order. In order to realize these parameters, a large number of coils are wound around the yoke and an appropriate current is passed.

Next, it will be shown whether the parameters of the optical system obtained by the beam trajectory analysis can be produced by an actual magnet.

Magnetic field analysis was carried out based on the actual shape of the magnet, and it was examined how the parameters of the optical system varied depending on the product of the number of turns of the coil (ampere turn). The yoke shape of the magnet is fan-shaped, and its size is defined by the central angle Θ. Further, the coil is provided in the yoke as shown in FIG. Here, a total of 16 coils are attached. The yoke forms a square-shaped closed magnetic circuit. The long side is parallel to the x direction and the short side is parallel to the y direction.

Since each coil is wound around the yoke, two surfaces obtained by dividing the coil wire at right angles appear in the cross section of the yoke surface. Sections of the same pair of coils have the same reference numerals. The same symbols and numbers are attached, but they are distinguished by plus and minus symbols. In the cross section marked with plus, the electric current flows so as to boil up from the paper surface. In the cross section with a minus sign, the current flows in the direction in which it is drawn into the paper. An upward magnetic flux density is generated in the yoke when the positive coil is viewed on the right and the negative coil is viewed on the left.

The 16 coils are divided into a dipole coil, a quadrupole coil and a sector pole coil. In FIG. 2, the anisotropic magnetic field formation is described by the conical air-core coil. Actually, it is not possible to wind a conical coil around the yoke. A cylindrical coil with a core parallel to the yoke will be used. Even with a cylindrical coil, the magnetic fields of a quadrupole and a hexapole can be equivalently formed by combining some of them.

Since the horizontally long beam is bent in the horizontal direction, the horizontally long yoke 12 is used. A yoke 12 is provided so as to surround a vacuum container 13 through which the beam passes. York is left vertical frame 1
4, a lower horizontal frame 15, a right vertical frame 16, and an upper horizontal frame 17. Since the yoke 12 is fan-shaped in the xz plane, the thickness of the yoke differs depending on the location. Categorize coils by application.

Dipole coil: 1,5 Quadrapole coil: 2, 3, 4, 6, 7, 8 Sector pole: s1, s2, s3, s4, s5, s6,
s7, s8

The coils 1 and 5 produce an upward magnetic flux density in the vertical frames 14 and 16 of the yoke. This becomes the downward magnetic flux density at the midpoint U of the upper horizontal frame 17, propagates downward in the vacuum, and becomes the lateral magnetic flux density at the midpoint D of the lower horizontal frame 15. This creates a dipole magnetic field B0. Magnetic field 2 of FIG. 2 (a)
It is equivalent to 1. The currents of the coils 1 and 5 are always the same or increase or decrease in proportion.

The coils 3 and 7 face to the horizontal frames 17 and 15 to the right,
Creates a leftward magnetic flux density. This corresponds to the upward rightward magnetic field 22 and the downward leftward magnetic field 23 in FIG. The coils 2 and 8 generate a downward magnetic flux density in the left vertical frame 14.
This corresponds to the magnetic flux density 25 in FIG. The coils 4 and 6 generate an upward magnetic field in the right vertical frame 16. This corresponds to the magnetic flux density 24 in FIG. Thus, the six coils can transparently generate the quadrupole magnetic field. This gives a linear dependence of x such as B ₀ Nx / R.

In FIG. 2B, the quadrupole magnetic field is created by two conical air core coils, but six coils are required to create the same magnetic field distribution by the coils wound around the quadrilateral yoke. The currents in these six coils can also be controlled separately. However, in order to always form a proper quadrupole magnetic field, the respective coil currents must always increase or decrease in proportion. Here, the product of current turns is 6
The N value that gives the magnetic field gradient is controlled by increasing / decreasing so that the two coils are equal.

FIG. 6 is a graph showing changes in the N value when the current turns product of the quadrupole coil is increased or decreased. This is a common current change for all of the coils 3, 7, 2, 4, 6, 8. The product of the number of turns of electric current and the N value are clearly in direct proportion. For example, N = 1 at 9000 AT.

In FIG. 5, the remaining coils all generate a hexapole magnetic field. s2 and s3 are adjacent to each other, and the current directions are opposite to each other. There are four such coil sets. s3 and s4 are yoke frames 15, 16 and 1
A counterclockwise magnetic field is generated at 7. This produces the magnetic field 26 of FIG. 2 (c) (the signs are opposite). Adjacent s2 and s5 generate a clockwise magnetic field in the same framework. Since this cancels the magnetic field, the small magnetic field 27 in FIG. 2C is left.

FIG. 7 is a graph showing the relationship between the product of the coil current turns of the hexapole and ε. This is also all related coils s1
The current of s8 is changed to be the same. 400
At 0 AT, ε is about 0.00075.

The central angle Θ, N value, and ε of the fan-shaped magnet were obtained by the above analysis. Θ defines the geometrical shape of the magnet and is a constant value. The N value and ε define the coil current. The desired N value and ε can be freely given by the current. It is highly flexible because it gives a magnetic field gradient and curvature by an electric current. It is possible to freely change these values and respond to changes in implanted ions and energy. An example of magnet parameters is shown below.

(1) Reference radius R = 60 cm (2) Total center angle of four sector magnets 126.5 ° (3) Radius R1 = 72.14 cm at mass analysis magnet inlet (4) At mass analysis magnet outlet Radius R2 = 76.34 cm (5) Fan magnet M1: Θ1 = 42 °, N1 = −1.01
006, ε1 = −4.9576 × 10 ⁻⁴ (6) Fan magnet M2: Θ2 = 23.5 °, N2 = 1.0
9953, ε2 = 2.0544 × 10 ⁻³ (7) Fan magnet M3: Θ3 = 19 °, N3 = 2.773
4, ε3 = 3.3142 × 10 ⁻³ (8) Fan magnet M4: Θ4 = 42 °, N4 = −1.32.
62, ε4 = −6.317 × 10 ⁻⁴

With such a combination of magnets, it has become possible to mass-analyze ions and inject only necessary ions into the wafer. By this example,
The beam emittance diagrams at the wafer when the beam is mass analyzed and transported to the wafer are shown in FIGS. 8 and 9. FIG. 8 shows the beam spread in the x direction at the wafer. The horizontal axis is the x coordinate (cm), and the vertical axis is the beam divergence angle in the x direction (unit: mr: milliradian). The lateral spread of the beam is about 40 cm. The divergence angle is about 16 mr. FIG. 9 shows the spread in the y direction. The vertical axis represents the y coordinate (cm), and the horizontal axis represents the spread angle in the y direction. The width in the y direction is 5 cm. The spread angle is 40 mr. That is, about 40c on the wafer surface
The beam has a rectangular cross section of m × 5 cm. Since the divergence angle is small, the beam has excellent parallelism and can be vertically incident on the wafer.

The reason why the beam is balanced as described above is that the beam trajectory is forcibly corrected by the fan magnet. Fig. 10 shows aberration correction of magnet (secondary correction).
The beam intensity distribution on the wafer when not performing (ε = 0) is shown. The wafer is 50 downstream from the outlet of the analysis magnet.
in cm. The horizontal axis is the x coordinate and the depth is the y coordinate. The height represents the intensity distribution. It can be seen that the beam intensity is unevenly distributed when x> 0. In this case, it is impossible to uniformly implant ions on the wafer surface.

FIG. 11 shows the intensity distribution in the wafer when the secondary aberration of the magnet is corrected. That is, a finite value of ε is given and a finite current is passed through the coils of s1 to s8. The horizontal axis is the x coordinate and the depth is the y coordinate. It can be seen that the intensity distribution is almost uniform along the x coordinate. Although the value of ε is small,
The correction effect by that is large. Unless corrected by ε, uniform ion implantation cannot be performed.

With the same settings, the beam envelope along the flow was determined. The actual flow direction follows the arc, but is drawn straight again. FIG. 12 is a beam envelope surface in the yz plane. The beam at (z = 0) from the ion source has a thickness of about 5 cm. This is z = 30cm-160c
It is bent in the x direction by a magnet provided between m.
There is almost no change in the thickness in the y direction. A slit is installed at z = 100 cm. There is a wafer at 210 cm. Again, the y-direction thickness is about 5 cm.

FIG. 13 is a beam envelope surface in the xz plane.
Initially, a parallel beam having a spread of about 40 cm in the x direction emerges from the ion source. Z = 30 cm to 16 with magnet present
The beam draws an arc between 0 cm. Since the radii of the arcs are approximately the same, the parallel beams converge weakly near the midpoint (z = 100 cm). Since a uniform magnetic field does not converge to a single point, an anisotropic magnetic field is adopted to force the convergence just before the slit. After convergence, it diverges and exits z =
At 160 cm, the beam becomes almost parallel.

[0073]

In the ion implantation apparatus of the present invention, an ion beam having a lateral width T larger than the object (wafer) diameter W is applied to the wafer, so that the wafer need only be translated in the beam thickness direction. The drive mechanism of the wafer is not a complicated combination of rotation and translation as in the past,
Only a simple translational movement is needed. The structure of the end station is simple and the cost can be reduced.
Further, the injection time can be shortened and the throughput can be improved.

The wafer is irradiated with the ion beam subjected to mass spectrometry. Ions other than the desired ions are not injected into the object. Compared with the conventional non-mass separation type ion implantation, the concern about contamination of impurities can be largely eliminated.

Conventionally, when attempting to implant ions into a large area substrate, two elements, a mass separation function and a beam shaping function, were required. In the present invention, one magnet has both a mass analysis function and a beam convergence correction function. Therefore, the system configuration is simple.

A combination of a plurality of linear magnets whose coefficients of dipole, quadrapole and sector pole can be freely set is combined, and the beam can be made substantially parallel at the exit of the mass analysis magnet. Since the beam at the magnet exit can be made parallel, the distance from the magnet to the wafer can be shortened. Since the path is short, it is possible to suppress generation of neutral particles due to collision with gas molecules existing in the vacuum path.

Each linear magnet has dipole, quadrupole and sector pole elements.
It does not deform the geometric shape of the poles. The magnetic poles are flat planes, but their high-order effects are exhibited by a complicated combination of coils. Since the magnetic pole itself is not inclined or curved, the beam acceptance can be increased. Further, the magnetic field gradient and the magnetic field curvature are not fixed and can be arbitrarily changed by the current.

The distance of the drift space is very short from the ion source to the magnet and from the magnet to the wafer. Therefore, the beam divergence due to the space charge effect can be suppressed. When the beam is converged in the drift space, beam divergence tends to occur remarkably due to space charge neutralization, but in the present invention, since the beam cross-sectional area can be increased and the current density can be lowered, the space charge effect is difficult to appear, Less consideration is given to functions such as a plasma flood gun for space charge neutralization.

A large number of multipole coils that can independently control the current are arranged on the yoke. Since the currents of the respective coils can be controlled independently, the parameters of the beam optical system are not fixed. It can be dynamically controlled freely.
If a large area ion beam is mass analyzed and transported by a magnet, the aberration of the magnet optical system is large and it is difficult to adjust the parameters. With fixed parameters,
It was impossible to compensate when the state of the ion source setup changed. The present invention can flexibly cope with such a state change of the ion source.

Since the beam area is large, the effective beam current density can be lowered. Therefore, the charge-up phenomenon of the wafer can be suppressed. For example, in a normal high-current ion implanter, when the beam size is a 5 cm square type (cross-sectional area 25 cm ² ), the ion current is often set to about 10 mA. In this case, the current density of the ion beam is 400 μA / cm ² .

On the other hand, in the present invention using a laterally long beam, for example, the beam cross section can have a width of 30 cm and a thickness of 5 cm (cross sectional area 150 cm ² ). If the ion current is 10 mA, the current density is only 70 μA / cm ² , so that charge-up does not occur. Since the present invention has a margin for charge-up, the total current can be further increased. Throughput can be increased by increasing the current. Since the beam current density extracted from the ion source is low, there is no fear of beam divergence due to the space charge effect.

[Brief description of drawings]

[Figure 1] Double pole (dipole), quadrupole (quadrapo-
2) and a sectional view showing the shape of a magnetic pole capable of forming a hexapole (sector pole) magnetic field. It is possible to give a primary component of a magnetic field by giving an inclination to a magnetic pole (pole) shape of a yoke and give a secondary component by giving a curvature. The coil that gives the magnetomotive force to the yoke is a simple ordinary coil. This can give a correction magnetic field but cannot change freely because the coefficient is fixed.

FIG. 2 is a diagram illustrating that a multipole magnetic field can be generated by a combination of coils. In (a), a double-pole magnetic field is generated by one cylindrical coil. (B)
Generates a quadrupole magnetic field Nx / R by combining two conical coils. In (c), a hexapole magnetic field βx ² / R ² is formed by three coils.

FIG. 3 is a schematic configuration diagram of an ion implantation apparatus of the present invention. A horizontally long beam emitted from an ion source is bent by a plurality of fan-shaped magnets, mass analysis is performed by a slit, and a parallel beam is formed before irradiation on an object (wafer).

FIG. 4 is a configuration diagram of an ion implantation apparatus of the present invention including an end station.

FIG. 5 is a distribution diagram of yokes and coils of a fan-shaped magnet used for mass spectrometry in the present invention. The coil is shown by a sectional view taken along a plane parallel to the yoke surface. Two cross-sections of the same coil are marked with the same numerical symbols. "+" Indicates that the current is flowing upward in the drawing. "-"
The presence of a current means that the electric current is flowing downward in the drawing.
1 and 5 are the largest coils and generate a dipole magnetic field in the yoke. Reference numerals 2, 3, 4, 6, 7, and 8 are coils that generate a quadrupole magnetic field in the yoke. s1, s
2, s3, s4, s5, s6, s7, and s8 are coils that generate a sector pole magnetic field.

FIG. 6 is a view showing a coil of FIG. 5 in which the same current is simultaneously applied to coils 2, 3, 4, 6, 7, and 8 for generating a double pole to generate a gradient of a magnetic field in the x direction, and a gradient coefficient N. The graph which shows the result of having measured the relationship between a value and coil current. The horizontal axis is the current winding product (ampere turn: AT) of the double pole coil. The vertical axis represents the coefficient N of Nx / R. It can be seen that the coil current and the slope N have a clean linear relationship.

FIG. 7 is a diagram showing coils s1, s2, s3, s4, s5, s6, s7, s8 for generating quadrupoles in the coil of FIG.
The same current is applied to the two simultaneously to generate a magnetic field curvature in the x direction,
The graph which shows the result of having measured the relationship of the coefficient ε of bending and the coil current. The horizontal axis represents the product of the coil current and the number of turns (AT), and the vertical axis represents ε. The bending magnetic field is expressed as εx ² = βx ² / R ² as a function of x. The coil current for the quadrupole and ε have a linear relationship.

FIG. 8 shows an emittance diagram in the x direction on a wafer. The horizontal axis is the beam divergence (cm) in the x-axis direction on the wafer, the vertical axis is the beam divergence angle (unit: milliradian: 1 mr = 0.057 °) in the x-axis direction, and the contour lines are the same beam density ( x, dx) are connected. Lateral (x direction) spread -20 cm ~ +
At 20 cm, the divergence angle of the beam is roughly constant (10 m
It can be seen that the beam has a band-shaped cross section with excellent convergence at about r).

FIG. 9 shows an emittance diagram in the y-direction on a wafer. The vertical axis represents the beam divergence (cm) in the y direction on the wafer. The beam divergence width in the vertical direction is about 5 cm. The horizontal axis represents the beam divergence angle in the y direction on the y coordinate (unit is milliradian: 1 mr = 0.057).
゜). Contour lines have the same beam density (y, dy)
It is something that Vertical beam divergence is 5 cm
It is in the range of 3 cm that the density is particularly high. The spread angle is about ± 20 mr. The spread angle in the y direction is larger than that in the x direction. This is because the magnetic field (Bx) that gives convergence in the y direction is not particularly used, but since the divergence in the y direction is suppressed by the multipole magnetic field By, the divergence angle is suppressed to such a small divergence angle.

FIG. 10 is a three-dimensional graph showing the xy intensity distribution of the beam on the wafer when the aberration of the mass analysis magnet is not corrected. The horizontal axis is the x-axis taken on the wafer. Depth is y
It is an axis. The vertical axis represents the beam intensity distribution. The beam is unevenly distributed on the side of x> 0 (outside) with respect to the center of the wafer.
This is because the ion beam transmitted through the slit holes often has an outward velocity component and cannot be corrected by a uniform magnetic field.

FIG. 11 is a three-dimensional graph showing the xy intensity distribution of the beam on the wafer when the aberration of the mass analysis magnet is corrected.
The horizontal axis is the x-axis taken on the wafer. Depth is the y-axis taken on the wafer. The vertical axis represents the beam intensity.
The beams are distributed almost evenly on both sides of x = 0. This is because there is an anisotropic magnetic field that bends the ion beam that has passed through the slit holes inward.

FIG. 12 is an envelope diagram showing a change in width in the y direction of a beam along a reference arc (z axis) by redrawing the z axis into a straight line.
The horizontal axis is the z-axis along the reference arc. z = 0 cm is the outlet of the ion source. z = 220 cm is the position of the wafer surface. The mass analysis magnet is provided in the range of z = 30 cm to 160 cm. A slit is provided in the middle part of z = 100 cm. The y-width is about 5 cm at the ion source and slightly widens in the middle part, but when it exceeds this, it begins to decrease and becomes about 5 cm on the wafer surface. That is, when passing through the mass analysis magnet, the ion beam trajectory hardly changes in the y direction.

FIG. 13 is an envelope diagram showing a change in width in the x direction of a beam along a reference arc (z axis) by redrawing the z axis into a straight line.
The horizontal axis is the z-axis along the reference arc. z = 0 cm is the outlet of the ion source. z = 220 cm is the position of the wafer surface. Since the mass analysis magnet is provided in the range of z = 30 cm to 160 cm, the ion beam draws an arc in this range. The parameters of the magnet are devised so that the ions having the desired mass are localized in the x direction at the intermediate portion of z = 100 cm. A slit is provided at a position where the predetermined beam is sufficiently narrowed in the x direction. Beams of other mass hit the plate surface of the slit and cannot pass through the hole. Since the reference arc R is linearly extended, the positions of the beam on the inlet side and the outlet side in the x direction are reversed. Magnet inlet z =
The beam at x = 20 cm at 30 cm has an exit z = 1.
At 60 cm it is at x = -20 cm. Beam is z = 10
Since it converges once around the 0 cm slit, mass spectrometry is possible.

[Explanation of symbols] 1 ion source 2 Mass analysis magnet inlet 3 Mass analysis magnet 4 slits 5 Mass analysis magnet outlet 6 ion beam 7 Vacuum path 8 wafers 9 Position detection device

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-6-342639 (JP, A) JP-A-10-283977 (JP, A) JP-A-9-129173 (JP, A) JP-A-55- 104800 (JP, A) JP 7-37536 (JP, A) JP 6-162977 (JP, A) JP 4-209460 (JP, A) JP 50-797 (JP, A) JP-A-8-124515 (JP, A) JP-A-4-253149 (JP, A) JP-A-59-54161 (JP, A) JP-A-11-500573 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37/05 H01J 37/09 H01J 37/317 H01L 21/265 603

Claims (2)

(57) [Claims] 1. An ion source for extracting a laterally long ion beam having a horizontal width larger than the lateral width of an object, a central angle Θj of a sector, and Nj giving a gradient of a magnetic field in a direction perpendicular to the beam.
A plurality of sector-shaped magnets M1 continuously provided along an arc locus for mass analysis by bending a laterally long beam in a horizontal direction using εj as a parameter, which gives a curvature of a magnetic field in the same direction.
Mj ..., Mm, a slit provided in the substantially central portion of the sector magnet for passing only a necessary ion beam, and a sample support mechanism for holding an object with respect to the beam and moving it in a direction orthogonal to the width direction of the beam. Ion implanter characterized by 2. Each of the sector magnets Mj comprises a yoke made of a ferromagnetic material, a dipole coil provided around the yoke for generating a dipole magnetic field, a quadrupole coil for generating a quadrupole magnetic field, and a hexapole. It consists of a sector pole coil that produces a polar magnetic field, and the dipole coil, quadrupole coil, and sector pole coil currents can be controlled independently, and the magnitudes of the zero-order magnetic field component, the primary magnetic field component, and the secondary magnetic field component of the sector magnet can be controlled independently. The ion implanter according to claim 1, wherein the ion implanter is adjustable.