JPH09219173A - Ion injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform high-current ion injection possible, by making an oblong ion beam advance straight and deflect by a wien filter, to radiate a specimen and a detector, and the scanning speed for the specimen is controlled according to an observation result of the uniformity and irradiation quantity by the detector to restrain a temperature rise. SOLUTION: By a wien filter 3, a slitlike (belt-like) ion beam 2, drawn by an ion source 1, is mass-separated into ion beam 4 and 5, advanced straight and deflected to be outputted. The beam 4 passes through the slender hole 7 of a slit 6 to be radiated to a specimen 9 on a placing mount 8, and current quantity is measured by a Faraday cup 11 for receiving the beam 5. By this measured result, the current and the uniformity in a lateral direction of the beam 4, entered into the specimen 9, is observed, and a scanning speed in the Y-direction of the mount 8 is controlled by a scanning mechanism, in accordance with this observation result. This can remove unnecessary ion injection of the specimen 9, to restrain a temperature rise, thereby performing high-current ion injection uniform in a lateral direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ions capable of performing high-current ion implantation into a large-sized workpiece such as a semiconductor wafer with high efficiency without damaging the device by suppressing heat generation by extra ions. Regarding injection device.

[0002]

2. Description of the Related Art An ion implanter is a device for implanting an ion beam into a semiconductor, an insulator or the like at high speed. In the case of a semiconductor, it is used to change the conduction type by implanting p-type or n-type impurities into an object. The implantation depth can be controlled by the acceleration voltage of the ion beam. There are two types of conventional ion implanters. One is to ion-implant a target surface having a large area by separating a thin beam into masses and effectively scanning the beams vertically and horizontally. The other is to extract a wide ion beam from a large-diameter ion source and directly hit the irradiation target without mass separation.

The former scanning method will be described. The beam itself may be shaken for scanning, or the object to be processed may be shaken left and right. Either may be used. When the target is a semiconductor wafer, a rotating disk having a plurality of rotatable disks on its circumference is used. Attach the semiconductor wafer to the disk. In some cases, the disk is moved left and right and up and down while the disk is rotated, and the thin ion beam is sequentially irradiated onto the entire surface of the rotating wafer so as to be uniform. This is called a rotary target method. The wafer undergoes both rotational and translational scanning.

In the beam scanning system, since the beam is thin, the mass is separated by a mass separation device composed of a fan-shaped magnet immediately after it is emitted from the ion source. As a result, unnecessary ions can be removed and only the necessary ions can be applied to the wafer. In an ion source, a gas of a compound containing necessary ions is used as a raw material, and this is turned into plasma and extracted as an ion beam, so that unnecessary ions and ions harmful to the target are also contained in the ion beam. Therefore, mass separation is performed and only the necessary ions are selected and applied to the target irradiation object. The fan-shaped magnetic poles are opposed to each other, and a current is applied to the coil wound around the magnetic core to generate a strong magnetic field between the magnetic poles. Since the ion beam runs so as to cut the lines of magnetic force at a right angle, the Faraday force bends the ion path. Bending acceleration is proportional to velocity and inversely proportional to mass. Even if the energy is the same, the bending angle is different because the mass and velocity are different. This causes mass separation.

Since the mass separation is performed, it is possible to prevent unnecessary ions, ions having a harmful influence, etc. from entering the object to be processed. This is an advantage in terms of affecting the object.
Another benefit is that fever can be effectively prevented. When unnecessary ions, such as hydrogen-containing ions, are irradiated onto the object to be processed, a large amount of heat is generated because all the kinetic energy is converted into heat. Since no unwanted ions are incident, there is an advantage that less heat is generated.

The method of directly irradiating the irradiation object with the ion beam extracted from the large-diameter ion source has an advantage of high throughput. If the size of the ion beam is set to be slightly larger than the size of the wafer, it is not necessary to move (scan) the wafer in ion implantation of one wafer. When multiple wafers are attached to the rotating target, the rotating target is kept stationary during the processing of each wafer, and when the processing of one wafer is completed, the target is rotated by one and the next wafer is processed. You can do it.

[0007]

In the beam scanning system, the beam optical system is relatively simple. However, the end station becomes complicated. For example, a disk on which a wafer is placed must be subjected to high-speed rotation and translational speed control. The translational velocity control is a motion that is proportional to the ion beam current and inversely proportional to the distance between the center of the disk and the center of the beam, and is quite complicated in itself. This complex end station mechanism adds to the cost of the device. Moreover, the operation itself of ion implantation is made difficult. In addition, a beam with a high current density is often used to increase the processing speed, but when the current density is increased, the charge-up phenomenon becomes prominent. There is a possibility of element destruction due to charge-up. Therefore, there is a limit to increase the current density.

The one using the large-diameter ion source and not scanning the beam is simpler than the above-mentioned one because the beam optical system is only the ion extracting system. However, the large-diameter non-scanning device has the following disadvantages. Since mass separation of ions is not performed, impurities from the electrode are injected into the object to be processed. Since the molecules are injected, the injection depth changes depending on the plasma state. Therefore, the characteristics of the device vary. Since unnecessary ions emitted from the ion source are also injected into the object to be processed, the temperature of the object to be processed rises significantly. Since the temperature rise is suppressed, the upper limit of the current density can be suppressed. Therefore, the throughput cannot be further increased.

The above problem will be further described. For example, S
When boron (B) is injected into i, diborane (B ₂ H ₆ ) is used as a source gas. Hydrogen ions H ⁺ , H ^{2+ and the} like are extracted from the ion source together with boron ions. Since no mass separation is performed, hydrogen ions also enter the Si wafer. Kinetic energy becomes all heat here. Since the kinetic energy is almost equal to the acceleration energy qV, the energy per ion is almost the same for both hydrogen ions and boron ions. Ions containing boron are valid ions, but hydrogen ions not containing boron are invalid ions. Not only invalid but also heat the wafer to raise the temperature.

Since a resist film and the like have already been formed on the wafer, the characteristics deteriorate when heated. Eg 400
There are restrictions such as not to exceed K.
In the case of the large-diameter ion source non-mass separation method, about half of all the ions are invalid hydrogen ions. The temperature of the wafer rises excessively due to the incidence of hydrogen ions. If hydrogen ions are removed from the ion beam, the heat generation can be halved. However, since hydrogen ions have a high diffusion coefficient, they escape from the wafer by annealing. Therefore, it does not have a bad influence on the wafer, but it has a drawback of unnecessarily increasing the substrate temperature during irradiation.

Then, it seems that mass separation should be performed even for a large-diameter beam. As is the case, in the case of a beam having a large cross-sectional area, mass separation using a fan-shaped cross-section magnet as in the past requires a huge magnet having a very large magnetic pole and generating a strong magnetic field. This is not economically feasible, if not impossible. Therefore, in the case of a large-diameter beam, no mass separation device is provided. As a method for implanting ions into a large-diameter wafer without mass separation, the PIII method (Plasma Immersion
Ion Implantation) has been proposed. Plasma Source Sci. Technol. 1 (1992) p1-6.

It is said that a wafer biased with a negative voltage is exposed to plasma, ions are accelerated in a sheath region, and ions are injected into the wafer. A wafer is put in the ion source and the plasma is accelerated by the negative bias of the wafer, which is a skillful method. No extraction electrode is required because it is not necessary to extract ions. Since there is no extraction electrode, no impurities are generated from it. The above problems can be solved.

However, this problem is still powerless. When doping with boron, diborane (B
₂ H ₆ ) is used, but it is unavoidable that hydrogen ions are mixed into the wafer. In addition to the heating by the implantation of boron, the heating by the implantation of hydrogen ions causes a remarkable increase in the substrate temperature. Therefore, the current density cannot be increased above a certain level. Since the ion current cannot be increased, the throughput is low. In this paper, there is a description that one Si wafer was doped with 1.9 × 10 ¹⁵ / cm ² for 10 minutes. However, in the current semiconductor industry such slow processing cannot be adopted. One wafer should be processed in about 1 minute. In other words, the throughput is too low. For that reason, the above PIII method has not been industrially adopted at present.

Why is mass separation not possible in large-diameter ion beams? Although mass separation is performed by an electromagnet having a fan-shaped magnetic pole, if the beam diameter is large, the magnetic pole must be increased and the magnetic force must be increased, which is industrially difficult. However, in order to finally solve the problem of heating due to the incidence of unnecessary ions such as hydrogen ions on the wafer, it is necessary to mass-separate the large-diameter ion beam.

The first object of the present invention is to provide an ion implantation apparatus provided with means for mass-separating a large-diameter ion beam.
Is the purpose of. A second object of the present invention is to provide an ion implantation apparatus in which unnecessary ions do not enter the sample and are not heated by mass separation.
A third object of the present invention is to provide an ion implantation apparatus capable of increasing throughput by suppressing heating of a sample by a beam. Spatial uniformity of the beam,
It is a fourth object of the present invention to provide an ion implantation apparatus equipped with means capable of measuring temporal fluctuations in real time.
It is a fifth object of the present invention to provide an ion implantation apparatus provided with a device capable of monitoring when the spatial uniformity of a beam is deteriorated and stopping the ion implantation.

[0016]

The ion implantation apparatus of the present invention is an ion source capable of extracting a strip-shaped ion beam having a rectangular cross section having short sides and long sides, and a strip beam in the long side direction of the cross section. A plurality of Wien filters that can apply an electric field to the magnetic field in the direction of the short side and mass-separate band-shaped ion beams by a combination of perpendicular magnetic fields and electric fields; A support table further downstream of the slit for supporting the irradiation target, a plurality of ion detection devices provided on the path of unnecessary ions whose path is bent by the Wien filter, and the support table of the slit. The scanning mechanism moves in the direction of the short side of the hole.

The present invention first differs from conventional devices in the ion source. The ion source of the present invention emits a beam of elongated cross section. The beam of the present invention is neither a narrow beam having a round cross section as in the above-mentioned scanning method nor a wide square beam as in the large-diameter ion beam described above. It is a strip-shaped beam with an elongated cross section. Let W be the diameter of the irradiation object. The scanning beam effectively scans a circular cross-section beam with a small r = b to the left, right, front, and back (b <W). In the case of the large aperture non-scanning beam system, the beam cross section is Q × R, and both Q and R are larger than the aperture W of the wafer (Q> W, R> W). Although the ion beam of the present invention has a cross section of c × D, c is smaller than the diameter W of the wafer. D is greater than W. c <W <D. Therefore, it becomes a band-shaped beam. The scanning is also different from the conventional example. Do not scan two-dimensionally vertically and horizontally. However, it is not completely non-scanning. The present invention scans in the direction of the short side c,
The long side D is not scanned. Performs one-dimensional scanning.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION For example, a horizontally long ion beam is extracted from the ion source with energy proportional to the extraction voltage. FIG. 1 shows the outline of the configuration of the present invention. The ion source 1 is provided with a mechanism in which a source gas to be made into ions is introduced, the gas is made into plasma by discharge, and an extraction voltage is applied to extract the ions in the plasma as an ion beam 2 to the outside. The shape of the extraction electrode is devised so that a slit-shaped (strip-shaped) beam can be extracted. The direction of the longer side of the beam cross section is taken as the X axis, and the direction of the shorter side is taken as the Y axis. The traveling direction of the beam is the Z axis. The beam has a length width of D in the X direction and c in the Y direction.

The Wien filter 3 separates the band-shaped ion beams by the difference in mass. Ions to be irradiated on the sample (object to be treated) go straight, and other ions are refracted. A slit 6 having an elongated hole 7 is provided in front of the Wien filter 3. Ion source outlet,
The center of the Wien filter and the hole 7 are on a straight line. Ions having a predetermined mass can go straight through the hole 7. Ions having other masses hit the plate surface of the slit 6. Since the ions having different masses are not irradiated on the sample, it is possible to prevent the temperature of the sample from rising. This is the greatest advantage of the present invention.

The ions having passed through the hole 7 are applied to a sample (wafer) 9 fixed on a mounting table 8. The projection of the beam on the wafer surface is a c × D elongated rectangular shape. D>
If W, the beam spread in the X direction is sufficient. Then, the mounting table is scanned in the Y direction. There is a scanning mechanism for that purpose, but it is not shown here. The beam can be injected over the entire surface of the wafer by scanning in the Y direction. The ion beam current is measured by the ammeter 20.

A Faraday cup 11 is installed below the hole 7 of the slit 6. It receives ion beams of different mass and measures the amount of current. With the same source gas, the amount of desired ions is proportional to the amount of unnecessary ions. The ion beam current entering the Faraday cup allows the ion beam current entering the sample to be evaluated.

Further, by providing a plurality of Faraday cups at equal intervals in the beam spreading direction (X direction), the distribution of unwanted ion beams in the X direction can be known from time to time. If the same gas is used, the amounts of the necessary ion beam and the unnecessary ion beam are proportional to each other, so that the uniformity of the ion beam can be monitored. The spatial beam uniformity is monitored, and if non-uniform, the ion source and Wien filter are adjusted. If the adjustment is not successful, stop ion implantation.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a laterally long (c × D) ion beam is extracted from an ion source with energy corresponding to the extraction voltage. This is separated by the Wien filter 3 so as to take different paths depending on the mass. An electric field Ey is applied parallel to the short side of the beam, and a magnetic field Bx is applied parallel to the long side of the beam. By the action of the electric field and the magnetic field which are orthogonal to each other, only the ions of desired energy and mass are made to go straight. The Faraday force F is represented by F = q (E + v × B).

Assuming that the magnetic field and electric field are uniform inside the Wien filter, the x component of the Faraday force is 0 and the y component is Fy = q (Ey-wBx). w =
Only Ey / Bx ions have Fy = 0 and can go straight through the Wien filter. Although w is the velocity in the z direction, since the acceleration energy is the same, those having the same mass receive the same force. If only necessary ions, for example, boron, are adjusted to have a predetermined velocity Ey / Bx, only boron can go straight through the Wien filter.

Electrostatic shielding does not occur because the electric field is parallel to the short side of the beam. Instead, a strong magnet is required because the direction of the magnetic field is parallel to the long side of the beam cross section. A magnetic pole having a large distance between magnetic poles and a strong end face magnetic field is used. Although the beam is thick in the direction of the magnetic field, the magnetic field is not shielded by charged particles as much as the electric field, and the force of the magnetic field extends to the inside of the beam. Therefore, a magnetic field is applied in the wide direction and an electric field is applied in the narrow direction.

For example, the case of implanting boron ions will be described as an example. The energy of the beam is assumed to be 50 keV. For example, let the magnetic field strength B be 1 kG (0.1 Tesla). The electric field for moving the boron straight is 93326.
It becomes 6V / m. For example, when the electrode gap is 10 cm, the voltage to be applied between the electrodes is about 9.3 kV. The spacing of the pole pieces must be longer than the long side of the beam in order to create a magnetic field along the longer side of the ion beam. Take, for example, 30 cm.
The magnet grows accordingly.

Boron is made to go straight by a combination of such electric and magnetic fields. Diborane is used as a source gas when boron (molecular weight 11) is injected, but the most abundant ion emitted from the ion source is hydrogen molecular ion. However, hydrogen ions are unnecessary ions for the purpose of boron doping. Without mass separation, when hydrogen molecular ions collide with the sample with energy of 50 keV, the same amount of heat is generated. The sample is heated significantly due to unnecessary ions. In the case of the present invention, since the mass separation is performed by the Wien filter, hydrogen molecules are not injected into the sample.

FIG. 2 shows the calculation result of how the molecular hydrogen ions are deflected inside the Wien filter.
The horizontal axis is the distance z (m) from the entrance of the Wien filter. If the axial length k of the filter is 20 cm,
The deviation of hydrogen molecular ions (molecular weight 2) at the outlet of the filter is 25 mm. Here, since the hydrogen molecule ions have a flow direction inclined from the Z axis, the hydrogen molecule ions are further deviated in the slit. If the distance from the center of the Wien filter to the slit is L, the deviation amount Δ is Δ = 0.025L
(M).

The production ion implantation apparatus is required to have high throughput. At present, an 8-inch wafer requires a processing capacity of 100 sheets per hour when the dose amount is 5 × 10 ¹⁵ / cm ² . That is, the processing time per sheet is 36 seconds. Since the time for transportation is also included, the time available for ion implantation is 30 seconds or less per sheet.

In order to realize such a high throughput, a necessary number of wafers are fixed to a circular mounting table,
The entire mounting table is translated in the direction of the short side of the beam. That is, it moves in parallel in the y direction. At this time, it is necessary to change the translation speed according to the change in the current amount of the ion beam.
Since the ion beam current is constantly monitored, the translation speed can be controlled by feeding back the current value.

The wafer mounting table fixes the wafer and cools the wafer. The wafer is irradiated with the ion beam accelerated to a high voltage and all of its kinetic energy is converted into heat, so that the substrate is heated significantly. If left unattended, the semiconductor device formed on the wafer will be destroyed or deteriorated. Cooling of the wafer is essential to avoid heating. As a cooling method, there are a cooling device utilizing electrostatic attraction and a gas cooling device. Either cooling device may be used. In any case, the cooling capacity is limited. The limit of cooling capacity defines the throughput. However, in the present invention, since unnecessary ions are not injected into the sample, the amount of heat injection for that amount is small. An example will be given.

Ion current I after mass separation is 20 mA, and beam size R is 20 cm × 5 cm (c = 50 mm, D =
200 mm). It is assumed that the implantation area S (area of the wafer) is 20 cm × 25 cm. The dose amount Φ is 5 × 10 ¹⁵ cm ^-2 as described above. Since the length of one side of the beam is equal to the length of one side of the wafer, the required implantation time T _imp is simply represented by T _imp = qΦS / I.

For the above parameters, the injection time per sheet is T _imp = 20 seconds. It is assumed that the loss time required from wafer implantation to wafer implantation is 10 seconds. This is a sufficiently realizable value. Then, it takes 30 seconds to process one wafer and the throughput is 120 hours / hour.
It becomes a sheet. The throughput is sufficiently satisfactory. When the ion beam current cannot be obtained by a predetermined value, or when the ion beam current cannot be increased so much as to avoid the temperature rise of the wafer, two wafers can be processed at a time to increase the throughput. In this case, it is necessary to double the dimension of the beam in the longitudinal direction.

Ions having a desired mass pass through the through hole 7 of the slit 6. However, ions with other masses are deflected by the mass separator. For example, hydrogen ions are strongly deflected. The ion beam deflected by the mass separator collides with the slit plate 6 installed in front of the wafer. By installing the Faraday cup 11 in front of the slit plate 6, the ion beam can be monitored. Although only one Faraday cup appears in FIG. 1, a plurality of Faraday cups are actually installed side by side in the X direction. This is shown in FIG.

In this example, four Faraday cups 11
a, 11b, 11c, and 11d are arranged at equal intervals on a straight line having the same Y and Z coordinates. Of course, the number of Faraday cups may be increased. Not all ion beams that cannot pass through the through hole 7 enter the Faraday cup. However, the amount of ion beam A passing through the through hole, the amount of ion beam B entering the Faraday cup without passing through the through hole, and the ion beam not entering the Faraday cup without passing through the through hole
The amount C is proportional, and their component ratios should be the same. What I want to know is A, but this can be detected by B. The currents flowing through the four Faraday cups are obtained by the respective ammeters 20a, 20b, 20c and 20d. This is converted into a digital signal by the A / D converter 21.

This is displayed on the display 22. The screen shows a bar graph of the height proportional to the ion beam entering each Faraday cup. This is proportional to the beam density along the longitudinal direction (X direction) of the elongated ion beam that has passed through the Wien filter. That is, this shows the density distribution in the X direction of the ion beam passing through the through hole 7. As a result, the spatial uniformity and non-uniformity of the ion beam can be immediately known. Since the amount of unnecessary beam is observed, the dose of necessary ions does not decrease. Since the spatial variation of the ion beam can be monitored online, it is extremely excellent in controllability and immediacy.

The Faraday cup is movable in a direction parallel to the slit plate. It is necessary to appropriately change the distance from the through hole of the Faraday cup depending on the type of ion beam deflected and detected and the acceleration energy of the ion source. It is most convenient to detect hydrogen ions because hydrogen ions have the largest number of unnecessary ions (not passing through holes). Even in that case, the acceleration energy of the ion source is different, so the position of the Faraday cup must be adjusted.

The spatial distribution is monitored, and if the uniformity of the beam deteriorates, an alarm can be issued and the ion implantation can be interrupted. The injection can also be stopped by inserting a beam shutter in the beam path and blocking it. However, in the case of the present invention, by changing the conditions of the Wien filter, it is possible to make the ions that have been injected hit the slit plate without passing through the through holes or enter the Faraday cup. The spatial uniformity of the ion beam deteriorates because the ion source is in poor condition. The parameters of the ion source are examined and readjusted to improve uniformity. When the work is completed, the ion implantation is started again.

[0039]

EFFECT OF THE INVENTION Mass separation is performed on a large area ion beam using a Wien filter. For this reason, it is possible to perform ion implantation without impurities, as in the conventional ion implantation apparatus that handles thin ion beams. High quality ion implantation processing becomes possible. Unless mass separation is performed as in the conventional method, the substance generated from the ion source contaminates the object to be treated. Therefore, the electrode material of the ion source, the wall material, and other materials of the member are limited, and moreover, the surface treatment has to be performed. In the case of the present invention, the degree of freedom of the material of the ion source is increased, and special processing such as surface treatment is unnecessary.

Unnecessary ion beam, especially hydrogen ion beam
The object to be processed is not irradiated. Therefore, the temperature rise of the object becomes smaller. Although depending on the type and energy of the ions, for example, the ion current injected is reduced to about half, and the amount of heat given to the object to be processed is also halved. Then, cooling becomes easy. The cooling mechanism is also simplified. On the contrary, if the temperature can be raised to the same temperature, the ion beam current can be increased about twice.

The greatest feature of the present invention is that the temperature rise is suppressed. A concrete calculation example is shown to illustrate this point. The temperature rise in the case of performing mass separation as in the present invention and in the case of not performing mass separation will be compared. The beam parameters were adjusted so that the implantation time was the same, and the difference in the temperature rise of the wafer was investigated. An example is a case where boron as a p-type impurity is ion-implanted into Si. Since hydrogen gas and diborane gas are used, hydrogen ions are mixed in addition to boron ions. When mass separation is not performed, when boron is doped, hydrogen ions are mixed in addition to boron ions, and the hydrogen ions are also injected into the object to be processed.

A typical value is boron ion: hydrogen ion = 1: 1. Therefore, about half of the ion beams are hydrogen ions. Since the hydrogen ions are injected, the wafer is heated excessively and the temperature rises. By the way, the ion implantation amount (or dose amount) is actually determined by the boron ion implantation amount. Therefore, the implantation time must be calculated by the amount of boron ion beam. Here, in order to evaluate the difference between the case with mass separation and the case without mass separation, the beam parameters were adjusted so that the injection time was the same, and the wafer temperature rise was analyzed.

It is assumed that the energy of the beam extracted from the ion source without mass separation is 50 keV. The ion current density j of boron is 30 μA / cm ² . The desired boron concentration Φ is 5 × 10 ¹⁵ / cm ² . This is FE
It is a normal concentration for making the source and drain of T.
The size of the object to be processed is 8 inches square. This amount of boron ions is collectively doped. The injection time T _imp is

T _imp = qΦ / j

Is given by q is a charge unit (1.
6 × 10 ^-19 C). According to this calculation, the injection time is 27 seconds. However, the expression “substantial ion current density” only represents boron ions in this case. If boron and hydrogen are 50 and 50, the ion current density extracted from the ion source is 60 μ, which is twice the above density.
It is about A / cm ² . Since it is 8 inches square, the area is multiplied by this, and the total ion current is 24 mA, and the substantial current of boron is 12 mA.

The power P of the ion beam applied to the wafer is 3 W / cm ² because P = Vj. The temperature rise of the wafer at this time was measured. This result is shown in FIG. The horizontal axis is time, and the vertical axis is temperature. A 10 second injection raises the temperature by about 120 ° C. The temperature rise is saturated in about 20 seconds and rises by about 150 ° C. At 27 seconds, the temperature is almost 450K, that is, 177 ° C. This is the temperature rise of the sample when mass separation is not performed.

Consider a case where mass separation is performed as in the present invention. Since a Wien filter is used, 8 inch square (20c
It is impossible to use a large-diameter beam (m × 20 cm) as it is. A beam with a narrower strip cross section is used. Let's use an ion beam with a cross section of 20 cm x 5 cm with one side being common. The implantation area is set to 20 cm × 25 cm in consideration of overscan. If the implantation time of 27 seconds is maintained under this condition, the beam amount I is 15 mA. This is a value obtained by I = qΦS / t.
15 mA is the boron ion current. In the present invention, since mass separation is performed, the total ion current emitted from the ion source is
It is 0 mA.

The ion beam power applied per unit area of the wafer is 1.5 W / cm ² . This is half the value of 3 W / cm ² when the mass separation is not performed. Since hydrogen ions do not enter, 1.5W /
It is reduced by cm ² . Predetermined infusion time (27 seconds)
Then, the injection should be completed by two reciprocating scans. Scan speed is 25 x 4/27 = 3.7 cm
/ S.

When the temperature change of the wafer is measured under such conditions, it becomes as shown in FIG. When a region is irradiated with a beam, its temperature rises sharply. However, when the beam moves away, the temperature drops due to heat dissipation (heat conduction and radiation). The temperature has a sawtooth variation as shown in FIG. This is a measurement of temperature change up to 100 seconds. In this example, the desired doping of 5 × 10 ¹⁵ / cm ² can be completed in 27 seconds.
Ion implantation may be terminated in seconds. Sample temperature is 3 at the beginning
It goes up to 80K and goes down to 315K. Further 390
It goes up to K and goes down to 320K. Finally, there is only a temperature change from room temperature to 100 ° C or less. In the case of FIG. 4, the temperature monotonously increases and reaches 450K. In the case of the present invention, it is lower than that by 50 ° C or more.

The cause is that the hydrogen ion beam is separated and does not enter the sample. Since the ion beam becomes about half, the degree of heating becomes weak. The other is that the beam must be thin in the shape of a strip and must be scanned in the direction of the short side, and heat is easily dissipated due to the scanning.
Since the temperature rise is small, the device is not destroyed. This is a great advantage of the present invention. The values are shown in a table for this example.

[0051]

[Table 1]

Table 1 reveals the advantages of the present invention in which mass separation is performed on a large-diameter ion beam.
The temperature rise of the sample is smaller than that without mass separation. In this example, since the ratio of hydrogen ions to boron ions is 1: 1, the amount of heat given to the sample is almost halved.
Even in cases other than this, it is possible to prevent unnecessary ions such as hydrogen ions from being injected into the sample, so that the temperature rise of the sample can be effectively suppressed.

The end station does not have to have a complicated mechanism for performing a combined motion of rotation and translation as in the conventional case, but only a translation mechanism. As a result, the structure of the end station can be simplified, and the cost can be reduced. Even if the translational movement is performed, it is sufficient to follow only the ion beam amount, and therefore the control becomes simple.

In the conventional mechanism, a rotating target was used and the beam was focused on the sample for irradiation. However, the present invention does not require the beam to be focused. Therefore, the current density of the beam in the wafer can be made smaller. It is possible to suppress charge-up. For example, in the case of a normal rotating target system,
A beam having a current density of about 0.6 mA / cm ^{2 to 1} mA / cm ² is irradiated, but in the case of the present invention, it is 0.15 mA / cm ^2.
The degree is sufficient, and a current density of half or less is sufficient. For rotating targets, the beam must be focused
This is because if the beam size is large compared to the implantation area of the rotating target, implantation uniformity is not guaranteed.

The present invention basically advances the ion beam straight. This is because mass separation is performed using a Wien filter. Since the beam that goes straight is handled, it is not necessary to consider the correction of the beam optical system. The design of the optical system is easy.
It is sufficient that the magnetic field strength and the electric field strength in the Wien filter are uniform in the beam existing region. In order to obtain the uniformity of the electric field, for example, a protrusion is attached to the end of the electrode. The projections correct the electric field strength and improve the uniformity.

Further, the beam is a beam having a rectangular cross section consisting of a short side and a long side, and the long side is parallel to the magnetic field direction.
Therefore, it is not necessary to increase the distance from the filter to the slit. This is also a great advantage. Since the unselected beam bends in the direction of the electric field (Y direction), if it is thin in the direction of the electric field, the beam can be separated with a slight displacement.
FIG. 6 illustrates this. In the present invention as shown in FIGS. 6A and 6B, the beam is flat and thin in the electric field direction and thick in the magnetic field direction.

Since the beam is mass-separated in the thin direction, the distance from the filter to the slit can be shortened. If, on the contrary, the beam is thin in the direction of the magnetic field (Fig. 6 (c),
(D)), the distance from the filter to the slit must be increased in order to separate the beams. This is the selection of the beam cross-section by skillfully utilizing the asymmetry between the magnetic field and the electric field of the Wien filter. It is not just the elimination of unwanted ions. By positively utilizing this, a Faraday cup is installed in front of the slit plate to monitor the spatial uniformity of the beam. Beam instability can be detected and immediately addressed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of ion implantation of the present invention.

FIG. 2 is a diagram of a beam trajectory drawn by a hydrogen ion beam inside a Wien filter. The horizontal axis represents the distance in the beam traveling direction inside the filter, and the vertical axis represents the amount of displacement from the central axis of the hydrogen ion beam.

FIG. 3 is a schematic view of a Faraday cup group provided in front of a slit plate.

FIG. 4 is a graph showing the time transition of the temperature rise of the wafer when mass separation is not performed. The horizontal axis is the time of ion implantation, and the vertical axis is the temperature.

FIG. 5 is a graph showing a time transition of wafer temperature rise in the present invention in which mass separation is performed. The horizontal axis is the time of ion implantation, and the vertical axis is the temperature.

FIG. 6 is a diagram for explaining that a beam line required for separation is different depending on a direction of a beam in a Wien filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ion source 2 Ion beam 3 Wien filter 4 Straight ion beam 5 Deviating ion beam 6 Slit plate 7 Ion beam through hole 8 Wafer mounting table 9 Wafer 11 Faraday cup 20 Ammeter 21 A / D converter 22 display

Claims (1)

[Claims] 1. An ion beam extracted from a plurality of strip-shaped ion extraction ports is caused to go straight by an ion to be injected by a Wien filter, and other ions are mass-separated, and the separated ions are arranged at equal intervals. Measured by Faraday cup, monitoring the uniformity and dose of ion beam, holding the sample by the end station, scanning the sample against the beam only in the short side direction of the ion beam cross section, and measuring the ion current value An ion implanter characterized in that the scanning speed is controlled by.