JP3473219B2 - Ion beam generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an ion implantation apparatus, an ion doping apparatus (non-mass separation type ion implantation apparatus), and a thin film forming apparatus using both ion irradiation and vacuum deposition. The present invention relates to an ion beam generator used for performing a process by irradiating an object to be processed with an ion beam as in the above. FIG. 9 is a sectional view showing an example of an ion implantation apparatus using a conventional ion beam generator. In this ion implantation apparatus, an ion source 2 of an ion beam generator having an ion source 2 for emitting an ion beam 40 and a power supply 30 for applying a voltage for extracting an ion beam to the ion source 2 is mounted on an upper part of a processing chamber 42. It has a structure. In the processing chamber 42, a holder 44 for holding a substrate 46 which is an example of an object to be processed is provided. The processing chamber 42 is evacuated by a not-shown evacuation device. [0004] The ion source 2 is a high-frequency ion source in the illustrated example, and a plasma source 4 for generating a plasma 14 by introducing a gas and ionizing the same by high-frequency discharge, and a portion near the outlet of the plasma source 4. And an extraction electrode system 20 for extracting the ion beam 40 from the plasma 14 in the plasma source unit 4 by the action of an electric field. [0005] The plasma source section 4 includes a plasma generation vessel 6 having a side wall 6a and a back plate 6b attached thereto via an insulator 8 therein. Gas is introduced from the downstream side. In this example, the side wall 6a and the back plate 6b
Also serve as electrodes (discharge electrodes), and a high-frequency power supply 16 is connected between them via a matching circuit 18.
However, the gas may be directly introduced into the plasma generation container 6 in some cases. In this example, the extraction electrode system 20 has a first electrode 21, a second electrode 22, a third electrode 23 and a fourth electrode 24 arranged from the most plasma side to the downstream side. 26 is an insulator. These electrodes 21 and 2
Reference numeral 4 denotes a porous electrode in this example, but may have an ion extraction slit. The first electrode 21 is provided with an ion beam 4 to be extracted.
In this example, a positive high voltage is applied from the first power supply 31 constituting the power supply device 30 with reference to the ground potential. The first electrode 21 and the plasma source unit 4 (more specifically, the plasma generation container 6 constituting the same) are connected to each other and have the same potential. The second electrode 22 is an electrode which generates a potential difference between the first electrode 21 and the ion beam 40 from the plasma 14 by an electric field caused by the potential difference. In this example, a second power supply 32 constituting the power supply device 30 is used. From the first electrode 2
A negative voltage is applied with reference to the potential of 1. The third electrode 23 is an electrode for suppressing backflow electrons from the downstream side. In this example, a negative voltage is applied from a third power supply 33 constituting the power supply device 30 with reference to the ground potential. . The fourth electrode 24 is grounded. An operation example of the ion implantation apparatus shown in FIG. 9 will be described. The plasma source section of the ion source 2 is held while a desired substrate 46 is held on a holder 44 in the processing chamber 42 and the processing chamber 42 is evacuated. When a desired gas is introduced from the downstream side of the extraction electrode system 20 into the inside 4 and high-frequency power of a frequency of, for example, 13.56 MHz is supplied from the high-frequency power supply 16 between the side wall 6a and the back plate 6b, the gap between the side wall 6a and the back plate 6b A high-frequency discharge occurs in the gas, whereby the gas is decomposed and the plasma 14
Is made. The ions in the plasma 14 are extracted by the extraction electrode system 20 as an ion beam 40. The extracted ion beam 40 is directly irradiated onto the substrate 46 without performing mass separation, and ion implantation (ion doping) is performed. When a polycrystalline silicon thin film transistor is manufactured, for example, it is necessary to perform implantation at a low dose of the order of 10 ¹¹ to 10 ¹² ions / cm ² . In order to use the ion beam generator for such low dose implantation, the ion current density of the ion beam 40 extracted from the ion source 2 must be reduced. The apparatus has a limit in reducing the ion current density. This is because, in the plasma 14 generated in the plasma source unit 4, the moving speed of the electrons constituting the plasma 14 is much higher than that of the ions. Since the first electrode 21 has a negative potential with respect to the plasma 14, and from a different viewpoint, the plasma 14 has a positive potential with respect to the plasma generation container 6 and the first electrode 21. This is because, even if it is 0, ions are extracted due to the potential difference existing between the plasma 14 and the first electrode 21, and the ion current density of the ion beam 40 cannot be reduced to 0. Therefore, conventionally, when the ion current density of the ion beam 40 is reduced, the density of the plasma 14 is also reduced. However, in order to reduce the density of the plasma 14, the power supplied to the plasma 14, It is necessary to reduce the power supplied to the plasma 14 from 16, and if this is done, the plasma 14 cannot be maintained, or if it can be maintained, there is a lower limit that can be maintained. Had limitations. FIG. 10 illustrates the above situation. If the power supplied to the plasma 14 is reduced below the lower limit of plasma maintenance, the plasma disappears and the ion beam 40 cannot be extracted. If the ion current density of the ion beam 40 cannot be made too small, when performing a low dose implantation,
The injection time is, for example, several seconds or less than one second, and the controllability and reproducibility for performing the predetermined dose injection deteriorate. An ion beam generator capable of solving such problems of the prior art has been previously proposed by the same applicant (Japanese Patent Application No. 7-136003). One example is shown in FIG. In this ion beam generator, in the above-mentioned ion source 2, between the first electrode 21 constituting the extraction electrode system 20 and the plasma source section 4 (more specifically, the plasma generation vessel 6). Is provided with an insulator 50,
The first electrode 21 and the plasma source unit 4 are electrically insulated from each other, and the first electrode 21 is positive or negative with respect to the plasma source unit 4 in a power supply device 30a corresponding to the conventional power supply device 30. A DC bias power supply 38 for applying the bias voltage VB is provided. By increasing the bias voltage VB to a positive or negative value, the ion current density can be further reduced from the conventional lower limit without reducing the power supplied to the plasma 14 as shown in FIG. Can be. This is because when the bias voltage VB is made positive and a positive potential is applied to the first electrode 21, the plasma 1
When a part of the ions to be extracted from the first electrode 21 is repelled by the first electrode 21 having the positive potential, and when the bias voltage VB is made negative and a negative potential is applied to the first electrode 21, the plasma source 4 Some of the ions to be extracted from the plasma 14 inside the first electrode 21 having the negative potential
This is considered to be because the amount of ions that can be absorbed and extracted can be reduced. By the way, the bias voltage VB
Is 0, the ion current density J ₁ or J ₂ corresponds to the conventional lower limit. In the above-described ion beam generator of the prior art, if a positive or negative bias voltage VB is applied to the first electrode 21, the ion current density can be certainly reduced. , Lowering the ion current density
As can be seen from FIG. 12, even when a more effective positive bias voltage VB is applied, the lower limit of the ion current density is about one third at most as compared with the case of 0 bias.
It was about 0 to 60 nA / cm ² . In this case, in order to perform low dose implantation, for example, implantation of 10 ¹¹ ions / cm ^2, it may not always be sufficient to secure controllability and reproducibility. Accordingly, it is a main object of the present invention to provide an ion beam generator capable of extracting a lower density ion beam by further improving the above-described prior art apparatus. According to the present invention, there is provided an ion beam generating apparatus, comprising: an ion source which is connected between a plasma-side first electrode and a plasma source portion among electrodes constituting an extraction electrode system of the ion source. And a DC bias power supply for applying a positive bias voltage to the first electrode with respect to the plasma source portion. A second electrode immediately downstream of the first electrode has a direct-current control power supply for applying a positive control voltage with respect to the plasma source. According to the above configuration, the potential of the second electrode serves as a barrier for extracting ions from the plasma in the plasma source portion, and the potential of the second electrode is fixed between the second electrode and the potential fixed by the bias voltage. The presence of one electrode does not affect the plasma potential. Therefore, by increasing the potential of the second electrode by the control voltage,
It becomes possible to extract a lower density ion beam. FIG. 1 is a sectional view showing an example of an ion implanter using an ion beam generator according to the present invention. Parts that are the same as or correspond to those of the conventional example of FIG. 9 and the preceding example of FIG. 11 are denoted by the same reference numerals, and differences from the preceding example will be mainly described below. Also in this embodiment, in the above-mentioned ion source 2, the first electrode 21 constituting the extraction electrode system 20 and the plasma source section 4 (more specifically, the plasma generation vessel 6; the same applies hereinafter). An insulator 50 is provided therebetween to electrically insulate the first electrode 21 from the plasma source 4. Further, in this embodiment, the power supply 3
0a, and includes a power supply device 30b having the following configuration that constitutes an ion beam generator together with the ion source 2. That is, the power supply device 30b includes a DC bias power supply 37 for applying a positive bias voltage VB to the first electrode 21 with reference to the plasma source section 4, and a downstream side immediately downstream of the first electrode 21. A DC control power supply 39 for applying a positive control voltage VS with respect to the plasma source unit 4 to the second electrode 22. This power supply device 30b
Further, as in the case of the preceding example, the first power supply 3 for applying a positive high voltage to the plasma source section 4 with reference to the ground potential.
1 and a third power supply 33 for applying a negative voltage to the third electrode 23 with reference to the ground potential. The bias power supply 37 and the control power supply 39
Variable output voltage is preferable because of better controllability. Whether the output voltages V1 to V3 of the first power supply 31 and the third power supply 33 are variable or fixed is arbitrary. As an example of the magnitude of each of the above voltages, the output voltage V1 is, for example, about 30 kV to 100 kV,
3 is, for example, about 500 V to 1 kV, the bias voltage VB is, for example, about 0 to 200 V, and the control voltage VS is, for example, 0 to 2 kV.
It is about 00V. FIG. 2 shows an example of the potential distribution in the ion source 2 when such a power supply device 30b is used. The potential of the plasma source section 4 is determined by the output voltage V1 of the first power supply 31, and the first electrode 2 is placed at a position higher than the output voltage of the bias power supply 37 (that is, the bias voltage VB).
1 and the potential of the second electrode 22 where the output voltage of the control power supply 39 (that is, the control voltage VS) has risen from the plasma source unit 4 is the potential of the second electrode 22, and the potential of the third electrode 23 is the third potential.
It is determined by the output voltage V3 of the power supply 33. As described above, the plasma 14 has a positive potential with respect to the plasma generation container 6 including the back plate 6b and the side wall 6a. In the ion beam generator of the prior art shown in FIG. 11, even when a positive bias voltage VB is applied to the first electrode 21, the ion current density is reduced to one third of that at zero bias.
The reason why it could only be reduced to a certain extent is probably due to the following reasons. That is, a positive bias voltage V is applied to the first electrode 21.
The ion current density when B is applied depends on the potential difference ΔV between the potential of the plasma 14 and the potential of the first electrode 21,
When it is small, the ion current density also becomes small. FIG. 13 shows the potential distribution when the bias voltage VB is small in the prior art device, and FIG. 14 shows the potential distribution when the bias voltage VB is large. As shown in FIG. 14, even when the bias voltage VB is increased. In addition, since the potential of the plasma 14 facing the first electrode 21 also rises by being dragged by the potential of the first electrode 21, the above-mentioned potential difference ΔV does not become very small, which is why the ion current density cannot be lowered much. It is considered to be. On the other hand, in this embodiment, as described above, the positive control voltage VS is also applied to the second electrode 22 with reference to the plasma source section 4. The potential of 22 does not affect the potential of the plasma 14 because the first electrode 21 whose potential is fixed by the bias voltage VB is present therebetween. Therefore, the potential of the second electrode 22 can be made closer to or higher than the potential of the plasma 14 by the control voltage VS. In the example of FIG. 2, the plasma 14 and the second electrode 22
Is almost zero. This second electrode 2
Since the potential of the second electrode 2 becomes a barrier for extracting ions from the plasma 14, by increasing the potential of the second electrode 22 as described above, the ion beam 4 extracted from the ion source 2 is increased.
The lower limit of the ion current density of 0 can be made smaller than in the case of the preceding example, and the ion beam 40 with lower density can be extracted. FIG. 3 shows an example of the results of actual measurement of the relationship between the control voltage VS and the ion current density. This shows that the high-frequency power supplied to the ion source 2 is 10 W and the output voltage V 1 is 1
0 kV and the output voltage V3 is 0.2 kV. From this figure, it is possible to control the ion current density by the control voltage VS. For example, if the control voltage VS is set to about 80 V or more, the ion current density can be further reduced to 0 as compared with the previous example. I understand. From FIG. 3, it can be seen that increasing the bias voltage VB makes the slope of the curve gentler, so that it is easier to control the ion current density by the control voltage VS. As described above, the ion current density of the ion beam 40 extracted from the ion source 2 can be made even smaller than the lower limit of the previous example. Since the time can be made longer, controllability and reproducibility when performing a predetermined dose injection are further improved. FIGS. 4 to 7 are diagrams each showing another example of the power supply device constituting the ion beam generator according to the present invention. In each case, the bias power source 3
7, a positive bias voltage VB is applied to the first electrode 21 with reference to the plasma source section 4 and a control power supply 39 is used to apply a positive control voltage VS to the second electrode 22 with reference to the plasma source section 4. Since the ion beam 40 can be extracted in the state, the ion current density of the ion beam 40 can be made smaller than the lower limit of the preceding example, as in the example shown in FIG. Of these,
In the examples of FIGS. 5 to 7, the potential of the second electrode 22 with respect to the plasma source unit 4 is the sum of the bias voltage VB and the control voltage VS. It can be smaller than in the example of FIG. The output voltage of the control power supply 39, that is, the control voltage VS, may be switched between positive and negative, and may be output. It is possible to cope with both the dose implantation and the high dose implantation by increasing the ion current density. The former case is as described above, and the latter case will be described here. When the control voltage VS is made negative, the potential distribution in the ion source 2 becomes, for example, as shown in FIG.
Since the potential difference ΔV ′ between the plasma 14 and the second electrode 22 increases, the ion beam 4 extracted from the ion source 2
The ion current density of 0 is large and can therefore be applied to high dose implants. In this case, the bias voltage VB may be set to 0, for example. The plasma source 4 of the ion source 2
The method is not limited to the method in which the gas is ionized by the high-frequency discharge to generate the plasma 14 as in the above-described example, and the other method, for example, the method in which the gas is ionized by the microwave discharge to generate the plasma 14. Or a method of generating plasma 14 by ionizing a gas by DC arc discharge. The number of electrodes constituting the extraction electrode system 20 of the ion source 2 is not limited to four as in the above example, but may be a plurality of other electrodes, for example, two or three.
Five or the like may be used. As described above, according to the present invention, the potential of the second electrode is brought closer to or lower than the potential of the plasma in the plasma source portion by the positive control voltage output from the control power supply. Since the height can be increased, the lower limit of the ion current density of the ion beam extracted from the ion source can be further reduced as compared with the case of the preceding example, and an ion beam with a lower density can be extracted. Therefore, when such an ion beam generator is used for, for example, ion implantation, the implantation time can be made longer when a low dose is implanted into the substrate. Controllability and reproducibility are further improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an example of an ion implantation apparatus using an ion beam generator according to the present invention. FIG. 2 is a diagram showing an example of a potential distribution in the ion source in FIG. FIG. 3 is a diagram showing an example of a measurement result of a relationship between a control voltage applied to the ion source in FIG. 1 and an ion current density. FIG. 4 is a diagram showing another example of the power supply device constituting the ion beam generator according to the present invention. FIG. 5 is a diagram showing another example of the power supply device constituting the ion beam generator according to the present invention. FIG. 6 is a diagram showing another example of the power supply device constituting the ion beam generator according to the present invention. FIG. 7 is a diagram showing another example of a power supply device constituting the ion beam generator according to the present invention. FIG. 8 is a diagram showing an example of a potential distribution in the ion source in FIG. 1 when a high dose is implanted. FIG. 9 is a cross-sectional view illustrating an example of an ion implantation apparatus using a conventional ion beam generator. 10 is a schematic diagram showing an example of a relationship between input power and ion current density in the ion source in FIG. FIG. 11 is a cross-sectional view illustrating an example of an ion implantation apparatus using the ion beam generator of the prior art. FIG. 12 is a diagram showing an example of a measurement result of a relationship between a bias voltage applied to the ion source in FIG. 11 and an ion current density. 13 is a diagram showing an example of a potential distribution when a bias voltage is small in the ion source in FIG. 14 is a diagram illustrating an example of a potential distribution when a bias voltage is increased in the ion source in FIG. 11; [Description of Signs] 2 Ion source 4 Plasma source unit 6 Plasma generation container 14 Plasma 16 High frequency power supply 20 Extraction electrode system 21 First electrode 22 Second electrode 23 Third electrode 24 Fourth electrode 30b Power supply device 31 First power supply 33 3 power supply 37 bias power supply 39 control power supply 40 ion beam 42 processing chamber 46 substrate 50 insulator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/203 H01L 21/203 Z 21/22 21/22 E 21/265 21/265 F (58) Fields surveyed (Int. (Cl. ⁷ , DB name) H01J 27/16 H01J 37/08 H01J 37/317

Claims (1)

(57) [Claim 1] A plasma source section for introducing a gas and ionizing the same by discharge to generate plasma, and extracting an ion beam from the plasma in the plasma source section by the action of an electric field. An ion source having an extraction electrode system having a plurality of electrodes, and a power supply device for applying a voltage for extracting an ion beam to the electrodes constituting the extraction electrode system of the ion source; In the ion source, an insulator is provided between the most plasma side first electrode of the electrodes constituting the extraction electrode system and the plasma source portion to electrically insulate them from each other. A DC bias power supply for applying a positive bias voltage to the first electrode with respect to the plasma source, and a DC bias power supply immediately downstream of the first electrode. 2
An ion beam generator, comprising: a DC control power supply for applying a positive control voltage with respect to a plasma source section to an electrode.