JPH10302707A - Ion implantation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion implantation device which can exclude a light ion including only a hydrogen element and can implant all other ions in a wafer in the case of using hydrogen compound gas as source gas. SOLUTION: This ion implantation device comprises: an ion source which produces a long ion beam having a smaller width 2a larger length T, a diameter of an object sample 6; a longitudinal yoke 10 having a passage of a longitudinal ion beam; main coils M1, M2 wound on the middle of the yoke 10; first auxiliary coils A1, A2 wound on the middle of the yoke 10; first auxiliary coils A1, A2 wound on one of the ends of the yoke 10, in line with the main coils M1, M2; and second auxiliary coils B1, B2 wound on the other end of the yoke 10, in line with the main coils M1, M2. Further, this device comprises: a long mass analysis magnet which generates a magnetic field in a longitudinal direction of longer side of the ion beam passage; and a shutter which shuts a light ion separated by the mass analysis magnet; a sample maintaining structure which maintains the sample so that the ion beam of ions other than the light ion separated by the mass analysis magnet may be implanted therein and which moves the sample to a direction orthogonal to the longitudinal direction of the ion beam. The magnetic field in the longitudinal direction is uniformly distributed in the longitudinal direction by controlling a ca coil current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor wafer,
The present invention relates to an ion implantation apparatus for realizing high-current ion implantation into a large workpiece such as a glass substrate. In the case of a Si wafer, ions are often implanted to dope p-type and n-type impurities such as boron, phosphorus, and arsenic. In order to increase the throughput, a device for doping with a uniform implantation distribution and at a high speed is desired. Further, implantation of hydrogen ions or the like has an adverse effect such as an excessive rise in temperature. Therefore, it is desirable to remove hydrogen ions or the like.

[0002]

2. Description of the Related Art Conventional large current ion implanters are roughly classified into two types. One is to analyze a thin (zero-dimensional spread) high-density ion beam by mass spectrometry using a sector magnet and irradiate only the desired ion species to a workpiece (wafer) placed on a rotating target that rotates and translates. It is. Since it is a thin ion beam, it is easy to separate the mass by a sector magnet. However, since the beam itself has no spread, it is necessary to translate and rotate the wafer to irradiate the entire surface of the wafer. It is necessary to move the wafer two-dimensionally at the end station supporting the wafer.

Another method 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 the large-diameter ion beam is generated, there is no need to scan the wafer.

[0004]

[Problems to be solved by the invention]

1. In the method using a rotating target, a thin 0-dimensional beam is generated, so that the beam optical system is simple. However, the structure of the end station which must perform the rotational translation is complicated. The disk on which the wafer is mounted must perform high-speed rotation and translation speed control in such a manner as to be proportional to the ion beam current and inversely proportional to the beam position. When the beam current density at the wafer increases, the charge-up phenomenon of the wafer becomes significant. Charge-up means that charge does not escape when positive or negative ion beam is implanted,
This is a phenomenon in which electric charges are accumulated on a surface such as a wafer. This can destroy the devices on the surface of the wafer, which is undesirable. At present, this rotary target method is actually used as a method for ion implantation into a large-diameter wafer, but has such disadvantages.

[0005] 2. Since the beam optical system of the large-aperture ion source non-mass separation system is only an ion extraction system, the apparatus configuration is much 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 implanted into the wafer without being distinguished. Desired characteristics may not be obtained by implantation of impurity ions. Further, since the ions are implanted not only in the form of ions but also in the form of molecules, the implantation depth distribution changes depending on the state of the plasma. Since the implantation depth is difficult to be constant, there is also a disadvantage that device characteristics are difficult to be constant.

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

[0007] 3. The disadvantage of the large-diameter ion source system is not only that. When ion implantation is to be performed on a large-area substrate such as an 8-inch wafer or a 12-inch wafer, implantation uniformity within several percent is required everywhere on the wafer surface. It is extremely difficult 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 implantation uniformity.

[0008] 4. As an ion implantation method without mass spectrometry, 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. B
12 (2), (1994) p962. This is a method in which a Si wafer is exposed to plasma, ions are accelerated in a sheath region by applying a negative voltage to the wafer, and injected into the wafer. Since the sheath voltage is used to extract the ion beam, no extraction electrode is required. Often, the impurities are sputtered electrodes. In this method, there is no possibility that impurities generated from the electrodes are mixed. Therefore, it is not necessary to perform mass spectrometry.

[0009] However, it is not possible to remove unnecessary ions from elements contained in the source gas. In the case of the boron doping, diborane is used as a source gas, and hydrogen ions are implanted into the wafer. Both hydrogen ions and boron ions have the same acceleration energy. The wafer is overheated by the hydrogen ion implantation. If the implantation time is shortened to increase the throughput, the temperature rise due to hydrogen implantation becomes significant.
Therefore, the injection time cannot be shortened too much. To one wafer,
It is reported that ion implantation at a density of 1.9 × 10 ¹⁵ cm ^{−2 took} 10 minutes. This results in too low throughput. I want to implant ions within one minute. In fact, this method does not appear to be practical.

[0010] 5. So far, a method of mass analyzing a beam of a 0-dimensional beam (point in cross section) and injecting the beam into a two-dimensionally scanned wafer has been described. The method of implanting the wafer into the stationary wafer and the PIII method of implanting the ion into the wafer in the plasma without using the ion source have been described. The problem should be solved if mass spectrometry can be performed in the second large-diameter ion beam method. However, no attempt has been made to mass analyze a large beam.

It is a first object of the present invention to provide an ion implantation apparatus capable of removing light elements such as hydrogen by mass separation. It is a second object of the present invention to provide an ion implantation apparatus having a high ion utilization rate capable of implanting different ions which can be doped with the same element. It is a third object of the present invention to provide an ion implantation apparatus with high throughput.

The first object and the second object are common. When the raw material gas becomes plasma, various ions are generated. If the raw material gas contains a certain element, all of them are ion-implanted to effectively use the gas. Light ions containing only hydrogen (H ⁺ , H ₂ ⁺ , H ₃ ⁺ )
Need to be removed. This does not meet the original purpose of doping with p-type impurities or n-type impurities. In addition, the temperature of the wafer is too high due to the hydrogen ion implantation. Thus, an eclectic mass spectrometry that excludes only light ions (up to H ₃ ⁺ ) is performed.

There are various requirements for mass spectrometry.
Others strictly require that only one type of ion be implanted. Others find mass spectrometry unnecessary. The present invention is intermediate between these.
Any ion species as long as it contains the target element is implanted, and those containing only hydrogen that does not contain the target element are to be eliminated.

For example, when doping a silicon wafer with P as an n-type impurity, the source gas is PH ₃ .
This _{^{P +, PH +, PH 2}} +, H +, H 2 +, causing ions such as H ₃ ^+. In the present invention, H ⁺ , H ₂ ⁺ , H ₃ ⁺
Except for the above, all other ions are implanted into the sample. If ions of a compound of P are implanted, after implantation, H will eventually escape and become an n-type impurity, so that there is no waste. That mass spectrometry of the present invention, the ion (M certain threshold M ₀ smaller mass M <M ₀₎ is excluded, all ions of greater mass M than a threshold (M> M ₀₎ and selects.

[0015]

SUMMARY OF THE INVENTION An ion source for producing a vertically long ion beam having a width 2d smaller than the diameter D of a target sample and a longer width T larger than the diameter w, and a vertically long ion beam having a passage for the vertically elongated ion beam. A yoke, main coils M1 and M2 wound around the center of the yoke, and first auxiliary coils A1 and A2 wound around one end of the yoke side by side with the main coil
A vertically elongated mass analysis magnet that generates a magnetic field in the vertical direction, the second auxiliary coil being wound around the other end of the yoke along with the main coil, and light ions separated by the mass analysis magnet And a sample holding mechanism for holding the sample so that an ion beam other than light ions separated by the mass analysis magnet is injected, and moving the sample in a direction orthogonal to the longitudinal direction of the ion beam.

The first feature of the apparatus of the present invention resides in that a vertically elongated ion beam is first generated. Since a vertically long beam larger than the diameter of the sample is used, it is sufficient that the sample is moved only in the lateral direction of the beam. Therefore, the injection time can be shortened and the throughput is improved. However, although it is said that the sample is vertically long, it is needless to say that the sample may be moved in the vertical direction by applying a magnetic field in the horizontal direction and performing mass analysis in the short side direction. Here, the magnetic field is vertical and the beam is also vertical.

However, when a vertically elongated beam is to be bent by a magnet, the distance between magnetic poles is extremely long, so that a uniform magnetic field is hardly generated. If the magnetic field is not uniform, the cross section of the beam will be distorted because the bending angle differs depending on the place, and mass analysis cannot be performed correctly. Therefore, the present invention is devised so that a uniform magnetic field can be formed at a long magnetic pole interval. A uniform magnetic field is generated between long magnetic poles by a combination of a main coil, a first auxiliary coil, and a second auxiliary coil wound around a yoke.

The longitudinal beam is bent to the short side by a uniform longitudinal magnetic field, and ions are separated by mass. A shutter is provided to remove only light ions, and a beam bent at a certain angle or more is cut off by the shutter. All the remaining beams are injected into the sample. The sample moves in a direction orthogonal to the long side of the beam, and the ion beam can be implanted over the entire surface of the sample.

[0019]

FIG. 1 is a schematic structural view of an ion implantation apparatus according to the present invention. A vertically elongated ion source 1 generates a band-shaped (vertically elongated) beam 3 from a vertically elongated ion extraction port 2. Assuming that the diameter of the sample (wafer) is W, the vertical length T of the beam is larger than W, and the horizontal width 2d of the beam is smaller than W (T>W> 2d). In the path of the beam 3, a vertical magnetic field By parallel to the long side T of the beam is formed. Here, the coordinate system is defined. The traveling direction of the beam is the z direction, the direction of the short side of the vertically long beam is the x direction, and the direction of the long side of the beam is the y direction. The strip beam 3 receives Lorentz force due to the longitudinal magnetic field By and bends in the x direction. When the radius of curvature is R,

ByR = (2MV / q) ^1/2 (1)

## EQU1 ## q is the charge, V is the extraction voltage, and M is the mass. Heavy ions have a large R. That is, it is hard to bend. Light ions have a small R. That is, it is easy to bend. Light ions bend greatly like beam 5. Heavy ions hardly bend like beam 4. Light ions mean hydrogen ions (H ⁺ , H ₂ ⁺ , H ₃ ⁺ ) and the like. The heavy ions are P ⁺ , PH ⁺ , PH ₂ ^{+ and the} like in the example of the P doping described above. The light ions 5 are cut off by moving the shutter 7 forward and backward during the course. Not a slit,
Since it is a shutter, all ions above a certain mass pass through.

The heavy ion beam 4 not blocked by the shutter 7 is injected into the surface of the object (wafer) 6.
Since the beam 4 includes a plurality of ion species, the beam 4 spreads on the surface of the wafer 6. Due to the existence of a plurality of ion species, the width Δx of the implantation surface 8 becomes wider than the original beam width 2d (Δx>
2d).

It is relatively easy to create a uniform magnetic field in the short side direction (x direction) of the beam. This is because the magnetic pole interval is small. Instead, the present invention attempts to create a uniform magnetic field By in the long side direction (y-direction) of the beam and thereby mass analyze the beam. Since the distance between the magnetic poles is long, it is not possible to form a uniform magnetic field due to a magnetic flux leaking from the yoke surface when a coil is wound around a slender closed loop yoke. The magnetic field is strong at the center and weak at both ends. y
The beam bends strongly near = 0, and weakly away from y = 0. Then, the beam is curved on the wafer surface as shown in FIG. In addition to bending, a part of the beam of the heavy ion P ⁺ and a part of the beam of the light ion H ₃ ⁺ overlap at a position away from y = 0. Here, the mass separation becomes incomplete.

Therefore, the present invention takes special measures to form a uniform vertical magnetic field. FIG. 2 is a longitudinal sectional view of the ion implantation apparatus of the present invention, and FIG. 3 is a plan view of the same. Ion source 1
Denotes a vertically elongated ion source, and a vertically elongated ion outlet 2
From which a beam 3 having a cross section that is long in the y direction and short in the x direction is extracted. The beam travels in the z direction and enters the yoke 10. A uniform longitudinal magnetic field By exists inside the yoke 10. This causes the light ions 5 to bend strongly and the heavy ions to bend weakly. A shutter 7 and a position detector 11 are provided so as to freely enter and exit the beam path. This is shown in FIGS. 1 and 3.

The position detector 11 is for initially examining the spatial distribution of the ion beam. It may be in front of the shutter, behind it, or behind the wafer. This is a two-dimensional or one-dimensional detector extending in the xy plane. When a one-dimensional detector is used, it is moved in a direction perpendicular to the sensor array to form a substantially two-dimensional sensor. First, the position detector 11 is taken out to the beam path, and the ion distribution in the xy directions of the straight beam when the magnetic field is 0 is examined. Further, the magnetic field is applied to monitor the distortion of the ion profile, and the auxiliary coil current is adjusted so that the ion beam is not distorted.

Similarly, the position detector 11 and the shutter 7 can advance and retreat in the x direction. When performing ion implantation, the position detector 11 is pulled in, and the shutter 7 is extended instead. Light ions bend strongly and are blocked by the shutter 7. Heavy ions enter the wafer 6 without touching the shutter 7 because the ions are hardly bent. The end station 9 includes a support mechanism that supports the wafer 6 and can move in the x direction.

FIG. 4 shows the yoke 10 and the six coils. The yoke constitutes a ferromagnetic closed magnetic path. It is rectangular and long in the y direction and short in the x direction. The yoke portion in the x direction is called an X frame, and the yoke portion in the y direction is called a Y frame. The Y frame is provided with six coils, M1, M2, A1, A2, B1, and B2. The central main coils M1 and M2 are coils having the largest number of turns. The winding directions are the same, and all generate an upward magnetic flux in the yoke 10. York 1
It does not cause the circulation magnetic flux to be directed vertically to zero.
Below the main coil are first auxiliary coils A1 and A2. Also in this case, the winding directions are the same, and both generate an upward magnetic flux. Above the main coil, the second auxiliary coils B1, B
There are two. This also generates an upward magnetic flux.

That is, the yoke has a closed curve magnetic path, but the magnetic flux generated by the coil does not travel through the yoke along the closed curve. 3 wrapped around the left Y frame
Each of the coils B1, M1, and A1 provides an upward magnetic flux. The three coils B2, M2, and A2 in the right Y frame also generate an upward magnetic flux. The magnetic flux collides at the center U of the X frame and jumps out of the yoke up and down.

The object that has jumped upward goes around the yoke greatly and returns to the center D of the X frame on the opposite side. This is a loss of magnetic flux. What protrudes downward has a downward magnetic flux density B. It penetrates vertically through the mass analysis space 12 and returns into the yoke at the center D of the lower X frame. in this way,
The yoke 10 has magnetic poles at the midpoints U and D of the upper and lower X frames.

The magnetic flux on the right side passes through A2, M2, and B2 from below, goes down from the middle point U of the upper frame of the yoke 10, passes through the beam 3, returns to the middle point D of the lower frame, and then returns to A2, M2. M2
Draw a closed loop passing through B2.

The magnetic flux on the left side passes through A1, M1 and B1 from below, descends from the middle point U of the upper frame of the yoke 10, passes through the beam 3, returns to the middle point D of the lower frame, and further moves A1, M1 and B1. M
1. Draw a closed loop passing through B1.

As described above, since the magnetic flux collides strongly at the midpoints U and D of the X frame and the magnetic field energy increases here, the leakage of the magnetic flux from the yoke in the vicinity thereof is large. This is the problem. If there is only a pair of main coils M1 and M2,
By is not uniform in the y direction due to magnetic flux leakage in the middle of the yoke.

FIG. 6 shows that only the main coils M1 and M2 have 5000
A current of 0 AT flows, and the auxiliary coils A1, A2, B1, B
2 shows the distribution of the magnetic flux density By (y) in the y direction when no current flows. AT is originally a unit of the magnetic field H in the MKS unit system, but here, the coil magnetomotive force is expressed by the product of the number of turns N of the coil and the current I as giving the magnetomotive force generated in the yoke. If the yoke forms a closed magnetic path and there is no leakage magnetic flux, the magnetic field H in the yoke is a value obtained by dividing the value of AT by the magnetic path length.

However, the magnetic field in the yoke is not the AT divided by the magnetic path length because of the magnetic flux leakage in the use of the present invention. Therefore, there is no simple proportional relationship between AT / m and the magnetic flux density B. Since the current flowing through the coil is large, a sufficient magnetic flux density B can be generated even if the magnetic poles are separated. If the AT is large, the saturation of the yoke may occur.
However, if the yoke has a sufficient cross-sectional area, the magnetic flux density can be several k
Since it is of the order of G, there is no fear of saturation occurring.

The length of the yoke opening in the y direction is 40c.
Assuming that m is 1600 gauss at the center y = 0. However, at both ends y = ± 20 cm, it is only 720 gauss. By becomes non-uniform in the y direction. A beam passing near y = 0 is strongly bent, while a beam passing near y = ± 20 cm has small bending.

Therefore, auxiliary coils are provided on both sides, and a large current is supplied to these coils to enhance the magnetic field at both ends. FIG.
Indicates the magnetic flux density By (y) in the y direction when a current of 25000 AT flows through the main coils M1 and M2 and a current of 12,500 AT flows through the auxiliary coils A1, A2, B1 and B2, respectively. Although it is 1040 gauss at y = 0 cm, it is uniform up to y = ± 20 cm, and a flat magnetic flux density distribution is realized. Thus, the auxiliary coil A,
By exciting B, the magnetic field in the y direction can be made uniform. If the magnetic field is uniform, the bending of the beam can be equalized regardless of the difference in the position in the y direction.

As shown in FIG. 8B, if the beam has a rectangular cross section at first, the cross section of P and the cross section of H ₃ also become rectangular on the wafer surface. FIG.
Taking shutter at the boundary of the P and H _3,
All light ions such as H ₃ ⁺ , H ₂ ⁺ and H ⁺ are dropped, and all ions such as P ⁺ , PH ⁺ , PH ₂ ⁺ and PH ₃ ⁺ having a mass of P or more can be implanted into the wafer. . FIG.
Although (b) in the region of the P region and H ₃ are in contact, both spaced apart sufficiently when shifted back a little wafer.

First, a position detector 11 having a two-dimensional resolution
The distribution of the ion beam is determined by using a Faraday cup or the like, the boundary between the P and H ₃ beams is determined, and the shutter is positioned at the boundary. Since the irradiation area 8 becomes known, the wafer 6 may be scanned in the x → −x direction. This is done by the support mechanism of the wafer. The beam can be uniformly injected over the entire surface of the wafer only by translation in one direction. Compared with the conventional ion implantation apparatus for large-diameter wafers, which simultaneously performs high-speed rotation and translational motion, the operation is greatly simplified.

[0039]

EXAMPLE A case where a silicon wafer having a diameter of 30 cm is doped with P ions will be described. Source gas is PH ₃
Gas. This is introduced into the ion source to form plasma,
It is extracted as an ion beam by the action of the extraction electrode.
A band-shaped ion beam having a height of 40 cm and a width of 10 cm is generated from a vertically long ion source 1. A two-dimensional position detector 11 is arranged in front of the beam. Thus, the two-dimensional distribution of the ion beam in the x and y directions is examined.

For example, a Faraday cup having a two-dimensional detection function is used. In order to provide two-dimensional resolution, for example, a Faraday cup in which a large number of 1 cm-diameter ion detectors are arranged in a grid pattern is suitable. Instead of the two-dimensional detector, a one-dimensional position detector extending in the y-direction may be moved in the x-direction. Alternatively, the one-dimensional position detector extending in the x direction can be moved in the y direction. The two-dimensional signals of these beam intensities can be read out in parallel or serially through a gate and subjected to appropriate mathematical processing by a personal computer to display the two-dimensional distribution of the beam on a CRT. In this state, hydrogen ions and phosphorus ions form overlapping peaks.

Next, the main coils M1 and M2 are energized to generate a vertical magnetic field By from the yoke. The magnetic field distribution is as shown in FIG. The ion beam bends in the x direction and the peak splits into two. As shown in FIG. 8A, the H ₃ beam and the P beam are separated at the center, but overlap each other at the ends. Although the original beam has a rectangular shape of 40 cm × 10 cm, the beam is distorted because the magnetic field is strong at the center and weak at the ends.

Further, auxiliary coils A1, A2, B1, B2
To excite it. The auxiliary coil current is increased while balancing the currents of the main coils M1 and M2.
It is only necessary that the beam distribution be rectangular as shown in FIG. At this time, a uniform magnetic field as shown in FIG. 7 is formed.

When the implantation angle becomes a problem, the substrate 6 is tilted so that the phosphorus ion beam becomes a right angle. Under these conditions, the incident angle of phosphorus ions is about 10 degrees, and that of hydrogen ions is about 40 degrees. Therefore, the wafer 6 may be incident at an angle of about 10 degrees. If the incident angle can be tilted by about 10 degrees, the wafer need not be tilted. Since the beam cross section is a rectangle that is long in the y direction,
The substrate 6 is translated in the x direction and is ion-implanted over the entire surface.

The saturation of the yoke has been described above. Here, an example of parameters for an example of phosphorus doping will be described. FIG. 5 shows how a vertically long beam having a width of JHG (2d) is bent by the Faraday force of a magnetic field. Let L be the width of the region where the effective magnetic field exists. The hydrogen H ₃ ⁺ ion draws an arc with a small radius R _{H about} the point C. _{Let the} central angle be ΘH. Since the H ₃ ⁺ beam has a JHG spread at the entrance,
At the exit, it extends to the SQP range. Center point H to z
Let F be the intersection of the line drawn in the direction and the line at the end of the area. Phosphorus ions an arc of large radius R _P about the point E.
The central angle and Θ _P. Since the P ⁺ beam has a width of JHG at the entrance, it also has a NMK spread at the exit.

The point N has the largest value of x in the exit distribution of the phosphor beam. Point P has the smallest x in the exit distribution of the H ₃ beam. Thus, if X _N <X _P , all the H ₃ can be dropped by placing the shutter between PN. Of course, since the beam angle is different, there is actually more room.

R _H = (M _H V) ^1/2 /0.69B (2)

[0047] _{R H = (M P V)} 1/2 /0.69B (3)

[0048] Here, the unit of the radius R cm, the unit of magnetic flux density tesla, MH (3), MP ( 31) is the mass number _{(M H = 3, M P} = 31). The unit of acceleration voltage V is 10k
eV. Central angle of beam bending in magnetic field region L
P, ΔH are

[0049] _{R H sinΘ H = L (4} )

[0050] _{R P sinΘ P = L (5} )

Is determined by

[0052] _{FN = R P -R P cosΘ P} + d (6)

[0053] _{FP = R H -R H cosΘ H} -d (7)

Is as follows. Since the condition of separation is FP> FN,

[0055] _{R H -R H cosΘ H -d>} R P -R P cosΘ P + d (8)

Any method can be used. Specifically, the width L of the magnetic field region
Is 50 cm, the beam half width d is 5 cm, the beam energy is 100 keV, and the ions to be separated are H ₃ ions and P ions, the required magnetic flux density is about 1000 gauss. At this time (B = 0.1 Tesla), R _H = 7
9 cm, Θ _H = 39 ゜, R _P = 253 cm, Θ _P = 11
It becomes ゜. At this time, the inequality (8) is satisfied. It is possible to generate such a longitudinal magnetic field. As shown in FIG. 7, the main coil has 25000AT and the auxiliary coil has 1250AT.
When a current of 0 AT flows, B = 1040 gauss.

FIG. 9 shows the beam spread when the auxiliary coil current is set to zero. FIG. 9 (a) shows that phosphorus ions
It is a beam when accelerating to 00 keV. Since the beam originally has a width (2d: GHJ in FIG. 5), three beam trajectories at the center and left and right are shown. Each of them is separated into three lines because the magnetic field By in the y direction varies. FIG. 9B shows the locus of H ₃ ions at 100 keV. The bend is more pronounced because it is a light ion. Again, the beam is separated into three or more beams due to the non-uniformity of By.

FIG. 10 shows the beam spread when the auxiliary coil current is passed and By is made uniform. FIG.
It is a locus of phosphorus ions of 0 keV. Since By is uniform in the y-direction, the beams do not separate. FIG.
It is the locus of H ₃ ion of 0keV. This is because, although slightly separated, By is slightly non-uniform in a large range of x.

FIG. 11 shows that the main coil current is 50,000 A
T shows the distribution of the lines of magnetic force between the yokes and the magnetic poles when the auxiliary coil current is 0 (the same conditions as in FIG. 6). The frame outside the yoke is a frame for setting a virtual boundary condition instead of an infinite circle.
Since the magnetic field lines are continuous, the magnetic field lines cannot be calculated without such boundary conditions. Actually, the yoke may be surrounded by such a box made of ferromagnetic material, but may not be surrounded. Such a boundary condition does not have a strong influence on the internal magnetic field line distribution. Since only the main coil is excited, there is much leakage from the yoke, and the lines of magnetic force are not completely parallel between the magnetic poles.

FIG. 12 shows the distribution of the lines of magnetic force between the yokes and the magnetic poles when a current of 25,000 AT flows through the main coil and 12,500 AT through the auxiliary coil (under the same conditions as in FIG. 7). It can be seen that the lines of magnetic force are completely parallel between the magnetic poles.

[0061]

According to the present invention, ions are mass-analyzed by bending a band-like ion beam in the direction of the short side with a magnet. When the source gas is an ion, if it contains unnecessary light ions and necessary heavy ions, it is separated to remove unnecessary light ions. It generates less heat and has less adverse effects due to impurity implantation as compared to non-mass spectrometry type ion implanters.
When there are plural kinds of necessary heavy ions, all of them can be ion-implanted, so that the raw material can be effectively used and the implantation processing ability is large. Since the object (wafer) needs to be reciprocated only in one direction, the structure of the end station is simplified.

In the case of this type of end station, the injection uniformity cannot be guaranteed unless the wafer is overscanned by the length of the beam width, but the beam profile on the wafer surface can be controlled by the current of the correction coil. Therefore, the overscan width can be made narrower than that without the correction coil. Thereby, the injection time can be reduced. The bending angle is small and the beam line can be short. Therefore, the beam divergence due to the space charge effect is small, so that the beam loss is small.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an ion implantation apparatus of the present invention.

FIG. 2 is a longitudinal sectional view of the ion implantation apparatus of the present invention.

FIG. 3 is a cross-sectional plan view of the ion implantation apparatus of the present invention shown in FIG.

FIG. 4 is a front view showing a relationship between a yoke and a coil of a longitudinal beam mass analysis magnet used in the present invention.

FIG. 5 is an explanatory view showing that light ions H ₃ ⁺ composed of hydrogen and ions containing phosphorus P can be mass-analyzed by bending a vertically long beam in a horizontal direction by a magnet.

FIG. 6 is a graph showing a y-direction distribution of a magnetic flux density By in a yoke opening when a current of 50,000AT is applied only to a main coil. At y = 0, the magnetic flux density becomes excessive, and as the distance increases, the magnetic flux density becomes too small.

FIG. 7: 25000AT for main coil and 12 for auxiliary coil
5 is a graph showing a y-direction distribution of a magnetic flux density By in a yoke opening when a current of 500 AT flows. The magnetic flux density is uniform in the y direction.

FIG. 8 is a diagram for explaining how a magnetic field generated by an auxiliary coil affects a beam profile. (A)
Indicates a case where the auxiliary coil current is 0, and (b) indicates a case where an appropriate current is flowing through the auxiliary coil.

FIG. 9 is a beam trajectory diagram illustrating how the mass analysis magnet affects the ion beam trajectory when there is no auxiliary coil current. (A) is a trajectory diagram of phosphorus ions accelerated to 100 keV when the auxiliary coil current is 0.
(B) is a locus diagram of H ₃ ions accelerated to 100 keV when the auxiliary coil current is 0. Each is separated into three beams.

FIG. 10 is a beam trajectory diagram for explaining how a mass analysis magnet affects an ion beam trajectory when an appropriate current is applied to an auxiliary coil. (A) is a trajectory diagram of phosphorus ions accelerated to 100 keV when the auxiliary coil current is 0. (B) is 100 when the auxiliary coil current is 0;
locus plot of accelerated H ₃ ions keV. Since the magnetic flux density is uniform in the y direction, the beams do not separate.

FIG. 11 is a diagram showing a calculation result regarding distribution of lines of magnetic force formed in the yoke by the coil current when the main coil current is 50000AT and the auxiliary coil current = 0. Assuming a magnetic circuit forming a closed magnetic circuit outside the yoke, a boundary condition that the magnetic field lines do not spread to infinity is imposed. The lines of magnetic force are curved between the magnetic poles.

FIG. 12 is a diagram showing the distribution of magnetic lines of force formed in the yoke by the coil current when the main coil current is 25000AT and the auxiliary coil current is 12500AT. Assuming a magnetic circuit forming a closed magnetic circuit outside the yoke, a boundary condition that the magnetic field lines do not spread to infinity is imposed. The lines of magnetic force are straight between the magnetic poles.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 vertically elongated ion source 2 ion outlet 3 band ion beam 4 beam containing heavy ions 5 beam containing light ions 6 wafer 7 shutter 8 irradiation region of heavy ions 9 end station 10 yoke of mass analysis magnet 11 position detector 12 mass Analysis space

Claims (1)

[Claims] A width smaller than a diameter of a sample to be treated;
An ion source for generating a vertically elongated ion beam having a longitudinal width larger than the diameter, a vertically elongated yoke having a passage for the vertically elongated ion beam, and main coils M1 and M wound around the center of the yoke
2, first auxiliary coils A1 and A2 wound on one end of the yoke side by side with the main coil, and second auxiliary coils B1 and B2 wound on the other end of the yoke side by side with the main coil. A longitudinally elongated mass analysis magnet that generates a magnetic field in the longitudinal direction that is the long side of the ion beam path, a shutter that blocks light ions separated by the mass analysis magnet, and light ions separated by the mass analysis magnet And a sample holding mechanism for holding the sample so that the ion beam is injected and moving the sample in a direction orthogonal to the longitudinal direction of the ion beam.