JP3736086B2 - Ion source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides, for example, an ion implantation apparatus that performs ion implantation by irradiating an ion beam to a target, an ion doping apparatus that performs ion implantation by irradiating an ion beam without performing mass separation on the target (non-mass separation type ion) Implantation apparatus), an ion beam etching apparatus that irradiates an ion beam to a target, an ion beam etching apparatus that irradiates the target with an ion beam, and an ion source that is used to irradiate the target with an ion beam. The present invention relates to a means for improving uniformity.
[0002]
[Prior art]
A conventional example of this type of ion source is shown in FIG. An ion source similar to this is disclosed in, for example, JP-A-9-161704.
[0003]
In this example, the ion source 2 is a high-frequency ion source. The ion source gas 10 is introduced and ionized by high-frequency discharge to generate plasma 14, and in the vicinity of the outlet of the plasma source unit 4. And an extraction electrode system 20 that extracts an ion beam 28 from the plasma 14 in the plasma source section 4 by the action of an electric field. Since this ion source 2 has a plurality of permanent magnets 12 that form a cusp magnetic field for confining plasma in the plasma source section 4, it is also called a bucket ion source.
[0004]
The plasma source unit 4 includes a plasma generation vessel 6 having a side wall 6a and a back plate 6b attached thereto via an insulator 8, into which the ion source gas 10 is introduced. Further, in this example, the side wall 6a and the back plate 6b also serve as electrodes (discharge electrodes), respectively, and a frequency of, for example, 13.56 MHz or 100 MHz is provided between the both 6a and 6b via the matching circuit 18 from the high-frequency power supply 16. High frequency power is supplied. Of course, the plasma source unit 4 may be of a type other than the high-frequency discharge type, for example, a filament cathode type that generates an arc discharge between the filament for generating thermoelectrons and the plasma generation vessel 6 to generate the plasma 14.
[0005]
The extraction electrode system 20 includes four porous electrodes having a large number of electrode holes 21a to 24a for extracting ions at positions corresponding to each other.
[0006]
The plasma electrode 21 is disposed on the most plasma side (the most upstream side) and determines the energy of the ion beam 28 to be extracted. The plasma electrode 21 is supplied from a DC acceleration power supply 31 with a positive acceleration voltage V _{1 based on the} ground potential. Is applied. The plasma electrode 21 and the plasma source unit 4 (more specifically, the plasma generation container 6 constituting the plasma electrode unit 4) are connected to each other and have the same potential. The magnitude of the acceleration voltage V ₁ is, for example, about 3 kV to 100 kV.
[0007]
The extraction electrode 22 is disposed immediately downstream of the plasma electrode 21. The extraction electrode 22 is an electrode that generates a potential difference with the plasma electrode 21 and extracts the ion beam 28 from the plasma 14 by an electric field thereby. Therefore, a negative extraction voltage V ₂ is applied with reference to the potential of the plasma electrode 21. The magnitude of the extraction voltage V ₂ is, for example, about 1 kV to 3 kV.
[0008]
The suppression electrode 23 is an electrode that is disposed immediately downstream of the extraction electrode 22 and suppresses backflow electrons from the downstream side. The suppression electrode 23 receives a negative suppression voltage V ₃ from the DC suppression power supply 33 with reference to the ground potential. Is applied. The magnitude of the suppression voltage V ₃ is, for example, about 0.5 kV to 1 kV.
[0009]
The ground electrode 24 is disposed immediately downstream of the suppression electrode 23 and is set to the ground potential. That is, it is grounded.
[0010]
The operation example of the ion source 2 will be described. When a desired ion source gas 10 is supplied to the plasma source unit 4 and high-frequency power is supplied from the high-frequency power source 16, high-frequency discharge is generated in the plasma generation vessel 6, thereby The source gas 10 is ionized to generate a plasma 14, and an ion beam 28 is extracted from the plasma 14 by an extraction electrode system 20.
[0011]
The extracted ion beam 28 is irradiated to a target (for example, a semiconductor substrate or a liquid crystal substrate) 34 as it is without mass separation, for example, and used for ion implantation (ion doping) or the like.
[0012]
[Problems to be solved by the invention]
In recent years, the target 34 tends to have a large area, and the ion beam 28 extracted from the ion source 2 has a large area and uniformity in order to uniformly perform ion implantation or the like on the entire surface of the large area target 34. A thing with high (that is, uniformity of ion current density distribution) is required.
[0013]
The main factors that influence the uniformity of the ion beam 28 are: (1) the uniformity of the plasma 14 generated in the plasma source unit 4, (2) the uniformity when the ion beam 28 is extracted from the extraction electrode system 20, and (3) The divergence angle of the ion beam when extracted from the electrode holes 21a to 24a of the four electrodes 21 to 24 is mentioned.
[0014]
Here, paying attention to the uniformity when the ion beam 28 is extracted from the extraction electrode system 20 of (2), the conventional ion source 2 has a non-uniform region in the electric field distribution in the extraction electrode system 20, thereby It has been found that there is room for improvement in uniformity when the ion beam 28 is extracted from the electrode system 20.
[0015]
More specifically, in order to cope with an increase in the area of the ion beam 28, the four electrodes 21 to 24 constituting the extraction electrode system 20 have a large number of electrode holes 21a to 21a as shown in FIG. 24a is opened. Each of the electrode holes 21a to 24a is opened at a position corresponding to each other one to one.
[0016]
An example of the electric field distribution in the vicinity of the end of the extraction electrode system 20 having such four electrodes 21 to 24 is shown in FIG. Although a predetermined electric field is generated between the four electrodes 21 to 24 by the above-described voltages V _{1 to} V ₃ , the place where the largest electric field is generated is usually between the extraction electrode 22 and the suppression electrode 23. . That is, the voltage between the extraction electrode 22 and the suppression electrode 23 is (V ₁ −V ₂ + V ₃ ) as can be seen from FIG. 6, for example, V ₁ = 30 kV, V ₂ = 1 kV, V ₃ Assuming = 0.5 kV, it becomes 29.5 kV. Incidentally, in the case of the same voltages V _{1 to} V ₃ , the voltage between the plasma electrode 21 and the extraction electrode 22 is V ₂ = 1 kV, and the voltage between the suppression electrode 23 and the ground electrode 24 is V ₃ = 0.5 kV. .
[0017]
Since the electric field between the extraction electrode 22 and the suppression electrode 23 is particularly large in this way, it oozes out between the plasma electrode 21 and the extraction electrode 22 through each electrode hole 22a of the extraction electrode 22, and the electric field distribution there To change. An example of the situation is shown by an equipotential surface 40 in FIG. In FIG. 8, the equipotential surface 40 between the plasma electrode 21 and the extraction electrode 22 is more than the equipotential surface 40 between the extraction electrode 22 and the suppression electrode 23 in order to make the shape easy to understand. The intervals are shown in detail. The same applies to FIG.
[0018]
For the electrode hole 22a on the inner side of the outermost electrode hole 22a of the extraction electrode 22, as shown in FIG. 7, the adjacent electrode hole 22a is uniformly opened in the periphery, and the symmetry of the electrode hole arrangement is good. The bias of the electric field that oozes out from the downstream side of the extraction electrode 22 through the electrode hole 22a between the plasma electrode 21 and the extraction electrode 22 is small (that is, the symmetry is good). Therefore, the equipotential surface 40 near the portion A in FIG. 8 is substantially parallel to the electrode surface. Accordingly, an ion beam (not shown) can be extracted with good symmetry from the vicinity of the portion A, that is, from the electrode hole 22a inside the outermost electrode hole 22a. The symmetry of the ion beam is the symmetry around the central axis of the ion beam.
[0019]
On the other hand, the outermost electrode hole 22a does not have an electrode hole 22a on the outer side and lacks symmetry of the electrode hole arrangement, and therefore the electrode hole 22a is interposed between the plasma electrode 21 and the extraction electrode 22. There is a relatively large bias in the electric field that oozes out from the downstream side of the extraction electrode 22 (that is, the symmetry is poor). For example, the equipotential surface 40 near the portion B in FIG. 8 is inclined to the lower right with respect to the electrode surface. Therefore, as shown in FIG. 8, the ion beam 28 extracted from the vicinity of the portion B, that is, extracted through the outermost peripheral electrode hole 22a is deteriorated and becomes non-uniform. Specifically, ions taking a trajectory that spreads outward greatly increase, and the ion current density of the ion beam 28 is biased toward the outside.
[0020]
As a result, when viewed as a whole of the ion beam 28 extracted from the ion source 2, the ion current density at the peripheral portion of the ion beam 28 is particularly higher than the others, and the uniformity of the ion beam 28 is reduced. For example, as shown in FIG. 4 as a conventional example, a peak P due to the ion beam spreading outwardly through the outermost electrode hole 22a appears at the peripheral portion of the ion beam 28, and this is the entire ion beam 28. The uniformity is reduced.
[0021]
Accordingly, the main object of the present invention is to improve the uniformity of the ion beam extracted from the ion source by reducing the bias of the electric field distribution in the electrode hole forming region between the plasma electrode and the extraction electrode.
[0022]
[Means for Solving the Problems]
The ion source according to the present invention is a hole having substantially the same size as the electrode hole of the extraction electrode in the outer peripheral portion surrounding the electrode hole formation region of the extraction electrode, and no corresponding electrode hole exists in the plasma electrode. A dummy hole is provided.
[0023]
According to the above configuration, a dummy hole having substantially the same size as the electrode hole exists outside the outermost electrode hole of the extraction electrode. The symmetry of arrangement is improved. As a result, the bias of the electric field that oozes out from the downstream side of the extraction electrode between the plasma electrode and the extraction electrode is the same as that of the innermost electrode hole at the outermost electrode hole. Therefore, the bias of the electric field distribution in the electrode hole forming region between the plasma electrode and the extraction electrode is reduced. Even if the electric field distribution is biased in the upstream portion of the dummy hole, there is no corresponding electrode hole on the plasma electrode side, and no ion beam is extracted from the dummy hole. As a result, the uniformity of the ion beam drawn from the ion source can be improved.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view showing an example of an ion source according to the present invention together with its power source. FIG. 2 is a plan view showing an example of the extraction electrode in FIG. FIG. 3 is a diagram showing an example of the calculation result of the electric field distribution near the end of the extraction electrode system of the ion source of FIG. Portions that are the same as or correspond to those in the conventional example of FIGS. 6 to 8 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.
[0025]
In the ion source 2a, the electrode hole of the extraction electrode 22 is formed on the outer periphery surrounding the electrode hole forming region 36 of the extraction electrode 22 (that is, the region where the electrode hole 22a is formed) constituting the extraction electrode system 20 described above. A dummy hole 38 having substantially the same size as 22a is provided. Since they are substantially the same size, naturally they have substantially the same shape. Here, “substantially” means that a slight difference in manufacturing error is allowed. There is no electrode hole 21 a corresponding to the dummy hole 38 on the plasma electrode 21 side facing the extraction electrode 22.
[0026]
The structure of the other electrodes 21, 23 and 24 is the same as that of the conventional example shown in FIG.
[0027]
The dummy holes 38 may be provided in at least one row as in this embodiment, and may be provided in two or more rows. However, the effects described below are not significantly different from those in the case of one row.
[0028]
Further, it is optional whether or not to provide the electrode holes 23a and 24a corresponding to the dummy holes 38 on the suppression electrode 23 and the ground electrode 24 side, and even if they are provided, they are not used for extraction of the ion beam. Therefore, it is not provided in this embodiment.
[0029]
In this ion source 2a, a dummy hole 38 having substantially the same size as the electrode hole 22a exists outside the outermost electrode hole 22a of the extraction electrode 22. Also for 22a, the symmetry of electrode hole arrangement is improved. As a result, the deviation of the electric field that oozes out from the downstream side of the extraction electrode 22 between the plasma electrode 21 and the extraction electrode 22 is caused in the innermost electrode hole 22a even in the outermost electrode hole 22a. As little as the part. That is, as shown in FIG. 3, the equipotential surface 40 between the plasma electrode 21 and the extraction electrode 22 is also upstream of the innermost electrode hole 22a in the upstream portion B of the outermost electrode hole 22a. It is parallel to the electrode surface as much as the portion A. As a result, the bias of the electric field distribution in the electrode hole forming region 36 (see FIG. 2) between the plasma electrode 21 and the extraction electrode 22 is reduced.
[0030]
Incidentally, in the upstream portion C of the dummy hole 38, as in the case of the upstream portion B of the outermost electrode hole 22a of the conventional example, the electric field oozing out from the downstream side of the extraction electrode 22 is biased. Although the equipotential surface 40 is inclined to the lower right, the corresponding electrode hole 21a does not exist on the plasma electrode 21 side, and no ion beam is extracted from the dummy hole 38, so there is no problem.
[0031]
As a result, as shown in FIG. 3, the ion beam 28 drawn through the outermost electrode hole 22a has much better symmetry than the conventional example shown in FIG. Of course, the ion beam extracted from the electrode hole 22a inside the outermost periphery is not shown in FIG. 3, but its symmetry is good for the reasons described above. That is, the symmetry of the ion beam 28 extracted from the outermost electrode hole 22a is as good as the symmetry of the ion beam extracted from the inner electrode hole 22a. As a result, it is possible to prevent a peak from occurring in the peripheral portion of the ion beam 28 extracted from the extraction electrode system 20, and to improve the uniformity of the entire ion beam 28 extracted from the ion source 2a.
[0032]
An example of the result of measuring the uniformity of the ion beam 28 extracted from the ion source 2a, that is, the ion current density distribution is shown in FIG. The embodiment shown by the solid line in FIG. 4 is the case where the extraction electrode 22 having the dummy hole 38 shown in FIG. 6 is used as the extraction electrode 22, and the embodiment shown by the broken line is the conventional example shown in FIG. This is a case where the extraction electrode 22 is used. As the other electrodes 21, 23 and 24, the electrodes having the structure shown in FIG. As can be seen from FIGS. 2 and 7, the electrode hole forming region is rectangular here.
[0033]
As operating conditions, high-frequency power of 100 MHz and 100 W is applied from the high-frequency power source 16 to the plasma source unit 4, the acceleration voltage V ₁ is 30 kV, the extraction voltage V ₂ is 1 kV, the suppression voltage V ₃ is 0.5 kV, and the ion beam 28 Pulled out.
[0034]
The ion current density distribution of the ion beam 28 is such that seven Faraday cups are arranged in a line in the direction of the width W of the electrode (see FIG. 2) at a position 70 cm downstream of the ground electrode 24, and the Faraday cup is the length of the electrode. Scanning was performed in the L direction at once, and the ion current flowing through each Faraday cup at that time was measured. As a result, the ion current density distribution in two dimensions of the ion beam 28 could be measured. FIG. 4 shows the ion current density distribution in the length L direction in the vicinity of the center in the width W direction. In addition, although illustration is abbreviate | omitted, the tendency similar to FIG. 4 is shown also in the other position of the width W direction.
[0035]
As can be seen from FIG. 4, in the conventional example, a large peak P appears in the peripheral portion of the ion beam 28 and the uniformity is deteriorated. On the other hand, in the example, such a peak does not appear. The uniformity of the beam 28 is improved.
[0036]
The shape of the electrode hole forming regions of the four electrodes 21 to 24 is not limited to the rectangle as in the above example, but may be other shapes such as a square or a circle.
[0037]
Further, as in the example shown in FIG. 5, a voltage obtained by adding the extraction voltage V ₂ from the extraction power source 32 to the acceleration voltage V ₁ from the acceleration power source 31 may be applied to the plasma electrode 21.
[0038]
【The invention's effect】
As described above, according to the present invention, by providing the above-described dummy hole in the extraction electrode, the extraction electrode oozes out from the downstream side of the extraction electrode through the electrode hole of the extraction electrode between the plasma electrode and the extraction electrode. The bias of the electric field is reduced in the entire electrode hole formation region, thereby reducing the unevenness of the electric field distribution in the electrode hole formation region between the plasma electrode and the extraction electrode. Can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of an ion source according to the present invention together with its power source.
FIG. 2 is a plan view showing an example of an extraction electrode in FIG.
3 is a diagram showing an example of a calculation result of an electric field distribution in the vicinity of an end portion of an extraction electrode system of the ion source in FIG. 1. FIG.
FIG. 4 is a diagram showing an example of a result of measuring an ion current density distribution of an ion beam.
FIG. 5 is a diagram showing another example of how to connect power supplies.
FIG. 6 is a cross-sectional view showing an example of a conventional ion source together with its power source.
7 is a plan view showing an example of an electrode in FIG. 6. FIG.
8 is a diagram showing an example of a calculation result of an electric field distribution in the vicinity of the end portion of the extraction electrode system of the ion source in FIG. 6. FIG.
[Explanation of symbols]
2a Ion source 4 Plasma source part 20 Extraction electrode system 21 Plasma electrode 22 Extraction electrode 23 Suppression electrode 24 Ground electrode 21a-24a Electrode hole 28 Ion beam 36 Electrode hole formation area 38 Dummy hole

Claims (1)

Four porous electrodes comprising a plasma source section for generating plasma and an extraction electrode system for extracting an ion beam from the plasma, and the extraction electrode system having a number of electrode holes for extracting ions at positions corresponding to each other A plasma electrode which is arranged on the most plasma side and to which a positive voltage is applied with reference to the ground potential, and which is arranged immediately downstream of the plasma electrode and which is based on the potential of the plasma electrode An extraction electrode to which a negative voltage is applied, a suppression electrode that is disposed immediately downstream of the extraction electrode and to which a negative voltage is applied with reference to the ground potential, and is disposed immediately downstream of the suppression electrode An ion source having a ground electrode that is at a ground potential, and is substantially connected to an electrode hole of the extraction electrode on an outer peripheral portion surrounding an electrode hole formation region of the extraction electrode. A hole of the same size, an ion source, wherein the corresponding electrode holes in a plasma electrode is provided a nonexistent dummy hole.

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