Patent Number: 
Section: description

FIG. 1 is a block diagram showing an example of the control circuit for an ion-implanting device according to this invention. The entire configuration of the ion-implanting device, which is the same as those shown in FIGS. 2 and 3, will refer to the figures and the above-mentioned explanations to omit repeated explanations. Further, in the following explanation, like reference numerals and signs refer to like parts in the prior art described above. The differences of this invention from the conventional art will be mainly explained. The ion-implanting device according to this invention is provided with an implanting control device 26a which corresponds to the conventional implanting control device 26. The implanting control device 26a has the functions of controlling the sweep of the ion beam 4 by the sweeping magnet 12 and the scanning of the target 20 by the scan mechanism 16. Concretely, as described previously, the implanting control device 26a supplied the sweep signal S(t) which leads to the sweep current I(t) to the driving amplifier 30. Further, it controls the scan mechanism 16 through the scan control unit 32 to control the scan speed and number of times of scanning of the target 20. In addition to the functions described above, the implanting control device 26 also has the functions of changing a sweep frequency of the ion beam 4 to be swept by said sweeping magnet 12 according to at least one of the species and energy of the ion beam and of changing the minimum number of times of scanning of the target 20 to be scanned by said scan mechanism 16 according to the changing of the sweep frequency. In this example also, as described above, the ion species, energy, etc. of the ion beam 4 to be swept are also set through the man-machine-interface 28. Concretely, the changing of the sweep frequency of the ion beam 4 by the sweeping magnet 12 is carried out by changing the sweep frequency of the sweep signal S(t) supplied to the driving amplifier 30. As described above, the conventional ion-implanting device, the sweep frequency of the ion beam 4 and the minimum number of times of scanning of the target 20 are fixed. Therefore, as long as the beam current of the ion beam 4 and the implanting quantity for the target are fixed, even if the ion species and energy of the ion beam are varied, the number of times of scanning of the target 20 is basically identical. The number of times of scan is also identical. Therefore, even if it is intended that the beam current is increased to shorten the implanting time, as the case may be, it cannot be increased to reduce the fixed minimum number of times of scan. Generally, in order to improve the throughput of the apparatus, the beam current is set so that the aimed quantity can be implanted in the minimum number of times of scan. Therefore, the value of the minimum number of times of scan is desired as low as possible. On the other hand, in the ion-implanting apparatus according to this invention, the implanting control device 26a changes a sweep frequency of the ion beam 4 to be swept by said sweeping magnet according to at least one of the species and energy of the ion beam and changes the minimum number of times of scanning of the target 20 to be scanned by said scan mechanism 16 according to the changing of the sweep frequency, thereafter, drives(perform the ion implantation). An explanation will be given of a variation in the uniformity of implantation when the sweep frequency of the ion beam 4 has been changed in accordance with the ion species or energy of the ion beam. The variation in the uniformity of implantation will be examined for the case where the discharging in the ion source 2 occurs once during the implantation under, for example, the following condition and the ion beam 4 stops for 0.1 sec. Sweep frequency: 100 Hz Scan speed: 20 cm/s Implanting quantity: 5.0xc3x971012/cm2  Beam current: 150 xcexcA (this is due to the limitation by the minimum number of times of scan) Number of times : 4 times (minimum number of times of scan) Implanting time: 10 sec. The calculated value of the uniformity of implantation under the above condition is 0.248%. If the lowest satisfactory value of the uniformity is 0.25%, the 0.248% is at the very limit. Assuming that the uniformity of implantation when the discharge occurs once during single scan is A %, the uniformity of implantation is improved more greatly as the number of times of scan is increased. For example, the uniformity of implantation when the discharge occurs only once during n times of scan (n: number of times of scan) is represented by A/n %. Therefore, in the above example, if the number of times of scan is set for 3 times, the uniformity of implantation is 0.33% which results in failure. For this reason, the minimum number of times of scan is set for 4 times. Now, under the above condition, when the sweep frequency of the ion beam 4 is changed from 100 Hz (mode 1) into 200 Hz (mode 2) or 300 Hz (mode 3), as seen from Table 1, the uniformity of implantation is gradually improved. As seen from the Table 1, if the sweep frequency of the ion beam 4 is increased, the number of times of scan can be reduced while the uniformity of implantation is kept within a prescribed successful range. Therefore, the beam current of the ion beam 4 can be increased. An example thereof is indicated in Table 2. In the conventional ion-implanting apparatus, since the sweep frequency of the ion beam 4 is fixed, only the mode 1 in Table could be selected. On the other hand, in the ion-implanting apparatus according to this invention, the mode 2 or mode 3 can be selected by changing the sweep frequency. As a result, the implanting time can be shortened to improve the throughput. As described above, the sweep frequency of the ion beam 4 is limited by the energy and ion species of the ion beam 4 to be swept. Specifically, the ion beam to be swept having a lower energy and light ion species can be more easily bent by the sweeping magnet 12. Therefore, the sweep current I(t) therefor may be reduced. Correspondingly, dI/dt in the above Equation [1] is reduced so that the sweep frequency can be increased. In other words, under the implanting condition that the ion beam has a high energy and heavy (i.e. large mass number) ion species, the sweep frequency cannot be increased to exceed the limit. Therefore, the implanting time has no great difference from the case where the sweep frequency is fixed. However, under the implanting condition that the ion beam has a low energy and a light (i.e. small mass number) ion species, as described above, the sweep frequency can be increased to reduce the minimum number of times of scan. Thus, when various implanting conditions (recipes) are dealt with, as a whole, this invention can improve the throughput of the apparatus as compared with the case where the sweep frequency is fixed. In addition, since the implanting condition can be dealt with by changing the sweep frequency, it is hardly necessary to change the specification such as boosting the maximum output voltage of the driving amplifier 30 or decreasing the inductance L of the coil 13. Namely, it is not necessary to change devices relative to sweeping of the ion beam. Thus, the ion beam with high energy and heavy ion species can be simply dealt with. The following relationship stands between the sweep current I of the ion beam 4 and the upper limit F of the sweep frequency. Therefore, using this relationship, the sweep frequency can be easily calculated. Ixe2x88x9d{(mass of an ion)xc3x97(energy)}/valence of the ion}xe2x88x9dFxe2x80x83xe2x80x83[2] As a practical example, with the parameter Table 3 as shown in Table 3 being stored in the ion-implanting control apparatus 26a, in order to deal with the ion species (concretely, mass number and valence of the ion) and energy which are set through the man-machine interface 28, it is possible to effect the changing of the sweep frequency of the ion beam 4 and changing the minimum number of scanning of the target 20 according to the parameters of the parameter Table. The sweep frequency may be increased from 3 manners so that the parameter table of Table 3 may be further subdivided. In the case of dealing with the ion with higher energy, a parameter of the sweep frequency lower than 100 Hz has only to be added. As understood from the description hitherto made, in accordance with this invention, since the sweep frequency of the ion beam is changed according to at least one of the ion species and energy of the ion beam to be swept, even if at least one of the ion species and energy of the ion beam is changed, the ion beam can be swept normally within the capability of the devices relative to sweeping of the ion beam. Therefore, without changing the devices relative to sweeping of the ion beam, the ion beam with a wide variety of energies and ion species can be swept normally. Further, as the ion beam to be swept is lower in the energy and lighter in the ion species, it can be more easily bent by the sweeping magnet. Therefore, the sweep current therefor may be reduced. Correspondingly, the sweep frequency can be increased. Thus, the minimum number of times of scanning of the target can be reduced to assure prescribed uniformity of implantation. Correspondingly, the implanting time can be shortened to improve the throughput of the apparatus. While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.