JPH08273896A - Acceleration for ion beam - Google Patents

Abstract

PURPOSE: To suppress the increase of the acceleration voltage to a minute value, suppress the decrease of the potential of a focus electrode resulting from the inflow of the secondary electrons from the ground side to the focus electrode, and maintain required acceleration voltage and focus voltage stably. CONSTITUTION: In the acceleration device 1 of an ion implanter used in the manufacturing process of semiconductors and the like, a focus electrode P3 is provided between the acceleration electrodes P1, P2 of input and out put both ends sides, and a potential variable focus power source 22 is connected between the acceleration electrode P1 and the focus electrode P3 together with an acceleration power source 21 between the acceleration electrodes P1, P2. The resistance value of a potential division resistor R2 between the electrodes P3, P2 is set to be larger by two digits than the potential division resistor R1 between the electrodes P1, P3, and the resistance value of the resistor R1 is set to such a value as to sufficiently cope with the inflow of secondary electrons from the ground 25 side to the electrode P3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion beam accelerating apparatus which is suitable for use in an ion implantation apparatus used in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art The ion implantation apparatus is for implanting a sample such as ionized boron into a target such as a silicon wafer to obtain desired electrical characteristics. In the ion implanter, the accelerator accelerates the desired ions extracted from the ion source and extracted by the analyzing electromagnet to a velocity corresponding to the desired implantation depth of the target wafer by passing through the electric field. It is for doing.

The accelerator has, for example, two gaps in which an acceleration electrode is provided at each of the input and output ends of the accelerator, and a focus electrode is arranged between the acceleration electrodes. A predetermined focus voltage is applied between the focus electrodes and an acceleration voltage corresponding to the implantation depth is applied between the acceleration electrodes.

In such an accelerating device, a potential dividing resistor is connected between each of the accelerating electrodes and the focus electrode. By supplying a current to the potential dividing resistance, the potential of each electrode can be maintained at a desired value even if ions collide with the electrodes.

[0005]

In a typical prior art accelerating device, the potential dividing resistor is a potential dividing resistor that connects a focus electrode and an accelerating electrode on the input end side, and the focus electrode and the output end side. The potential dividing resistors for connecting the accelerating electrode and the accelerating electrode are selected to have the same resistance value. Therefore, there is a problem that the acceleration voltage increases when the ion beam becomes minute.

That is, for example, pure water for cooling the ion source and the ion source and the analyzing electromagnet are supported between the high voltage portion provided with the ion source and the analyzing electromagnet and the ground. There is a miscellaneous resistance component due to the insulator and so on. Therefore, due to the current flowing from the focus power source through the miscellaneous resistance component to the potential dividing resistor interposed between the focus electrode and the acceleration electrode on the output end side, only the inter-terminal voltage generated in the miscellaneous resistance component is accelerated. There is a problem of rising.

When secondary electrons emitted from the target by injecting the ion beam into the target flow into the focus electrode from the ground side, the focus voltage becomes almost equal to the acceleration voltage, and the focus voltage is further exceeded. There is also a problem that it becomes impossible to lower the value.

An object of the present invention is to provide an ion beam accelerating device capable of obtaining a stable accelerating voltage and focus voltage at a desired voltage.

[0009]

According to a first aspect of the present invention, there is provided an ion beam accelerating device between an accelerating electrode provided on at least both input / output end sides of an ion beam and both accelerating electrodes on both input / output ends. A focus electrode that is provided, an accelerating power supply that applies an accelerating voltage between the accelerating electrodes on both input and output sides, and a focus that can be arbitrarily changed between the accelerating electrode on the input end side and the focus electrode. A focus power supply for applying a voltage, a first potential division resistor connecting between the input end side acceleration electrode and the focus electrode, and a second potential connection between the focus electrode and the output end side acceleration electrode. And the resistance value of the second potential dividing resistor is selected to be larger than the resistance value of the first potential dividing resistor by two digits or more.

According to a second aspect of the present invention, in the ion beam accelerating device, a first electric field shaping device is provided between the accelerating electrode on the input end side and the accelerating electrode on the output end side and the focus electrode.
And a second shaping electrode are respectively arranged, and the first potential dividing resistor and the second potential dividing resistor are connected to the first and second shaping electrodes, respectively, at a point where the resistance value becomes 1/2. It is characterized by being done.

Furthermore, in the ion beam accelerating device according to a third aspect of the present invention, the first and second potential division resistors have an extraction voltage of 40 (kV) and a focus voltage of 50.
(KV), when the resistance value of the miscellaneous resistance component between the accelerator and the ground is 180 (MΩ), 400 (MV)
Ω) and about 60 (GΩ).

[0012]

According to the invention of claim 1, in the ion beam accelerating device having at least two gaps, the accelerating electrodes are provided on both input and output sides of the ion beam, and the focus electrodes are provided between the accelerating electrodes. Between the acceleration electrode on the input end side and the focus electrode, together with an acceleration power supply for applying a desired acceleration voltage between both the input and output ends to accelerate the ion beam to a desired speed. A focus power supply for applying a focus voltage is provided, a focus voltage that can be arbitrarily changed by the focus power supply can be generated, and the speed and divergence of the ion beam can be controlled.

On the other hand, a potential division resistor is connected between the electrodes, and a current flowing through the potential division resistor stably holds each electrode at a desired voltage even if ions collide with the electrodes. can do. In the present invention, of the potential dividing resistors, the resistance value of the first potential dividing resistor that connects the acceleration electrode and the focus electrode on the input end side is relatively small, and The resistance value of the second potential division resistor that connects the focus electrode and the acceleration electrode on the output end side is increased by two digits or more, for example, 14
Choose about 0 times.

Therefore, even if the accelerating voltage is small and the beam current of the ions is small, the focus is caused by the miscellaneous resistance component between the accelerating electrode on the input end side and the ground which is generated through the ion source or the analyzing electromagnet. Even if a current path from the power source to the second potential dividing resistor via the miscellaneous resistance component is formed, the resistance value of the second potential dividing resistor is sufficiently large and therefore the current value is small, so that the miscellaneous resistance component The voltage generated between the terminals is extremely small, and therefore the acceleration voltage does not undesirably increase.

Further, even if secondary electrons from the ground flow into the focus electrode, the first potential division resistance has a resistance value sufficiently smaller than that of the second potential division resistance, and the current due to the secondary electrons is After passing, the potential of the focus electrode can be stably maintained at the value defined by the first and second potential dividing resistors.

According to a second aspect of the present invention, first and second shaping electrodes are provided between the accelerating electrode and the focus electrode, respectively, and the first and second potential dividing resistors are It is connected to the corresponding first and second shaping electrodes in that the resistance value becomes 1/2.

Therefore, the electric fields from the accelerating electrode on the input end side to the focus electrode and from the focus electrode to the accelerating electrode on the output end side can be made to be uniform electric fields capable of suppressing the divergence of the ion beam. it can.

Further, according to the invention of claim 3, for example, the extraction voltage is 40 (kV) and the focus voltage is 50.
(KV), and the resistance value of the miscellaneous resistance component is 180 (MΩ), the first and second potential division resistors are 4 respectively.
Select about 00 (MΩ) and 60 (GΩ).

Therefore, as described above, the second potential dividing resistor has a resistance value sufficiently higher than that of the first potential dividing resistor, and when the beam current is small, the second potential dividing resistor passes through the miscellaneous resistance component to the second potential dividing resistor. It is possible to suppress the current value of the loop formed by the potential dividing resistance, suppress the voltage generated in the miscellaneous resistance component by the current of the loop, and prevent the acceleration voltage from undesirably rising. . Moreover, even if a large amount of secondary electrons flow into the focus electrode from the ground side, a current flows corresponding to the secondary electrons through the first potential dividing resistor having a relatively small resistance value, and the secondary electrons are generated. It is possible to suppress a decrease in the potential of the focus electrode due to the inflow of electrons.

[0020]

EXAMPLE An example of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram for explaining the structure of an accelerator 1 according to an embodiment of the present invention, and FIG. 2 is a plan view showing the overall structure of an ion implanter 2 using the accelerator 1 in a simplified manner. It is a figure.

In this ion implanter 2, the ions extracted from the ion source 3 are extracted by the analyzing electromagnet 4 into only desired ions, and then input to the accelerator 1.
In the accelerator 1, the ion beam is accelerated or decelerated to a desired speed corresponding to the implantation depth into the target so as not to diverge. The ion beam from the accelerator 1 is swept to have a desired beam width by a sweep magnet 6 after the energy contamination is removed by a FEM (Final Energy Magnet) 5, and a target is passed through a collimator magnet 7 It is injected into the target 9 in the chamber 8.

The target 9 is, for example, a silicon wafer, and the target 9 carried into the end station 10 by an operator is the transfer robot 1.
The target 9 that has been loaded into a predetermined loading position on the platen in the target chamber 8 by 1 and has undergone ion implantation is taken out by the transfer robot 11 to the end station 10.

Referring to FIG. 1, the accelerating device 1 includes a first accelerating electrode P1 provided at an input end on the analyzing electromagnet 4 side and an F
A two-gap strong electric field type acceleration device including a second accelerating electrode P2 provided at the output end on the side of the ground structure 15 such as EM5 and a focus electrode P3 arranged between these accelerating electrodes P1 and P2. Yes, each acceleration electrode P1, P
2 and the focus electrode P3 between the shaping electrodes P4 and P5.
Are respectively arranged and configured. The acceleration electrode P
An accelerating voltage Vacc from the accelerating power supply 21 is applied between 1 and P2. Further, a focus voltage Vf, which can be changed arbitrarily, from the focus power supply 22 is applied between the acceleration electrode P1 and the focus electrode P3.

Therefore, by changing the acceleration voltage Vacc, the implantation depth of ions into the target wafer can be controlled, and the focus voltage Vf can be controlled.
The focus adjustment that causes the ions to diverge or focus can be performed by changing the. In this way, the accelerator 1 also functions as an electron lens capable of adjusting the intensity, and can control the beam shape on the target to a desired value regardless of the ion species, energy, and beam current. . Furthermore, the shaping electrode P
By 4, P5, the potential gradient between the electrodes P1, P3; P3, P2 can be adjusted.

The acceleration electrode P1 and the focus electrode P3 are connected by a first potential dividing resistor R1, and the focus electrode P3 and the acceleration electrode P2 are connected by a second potential dividing resistor R2. It is connected. Potential dividing resistor R1
Is two partial resistors R11 and R1 having the same resistance value.
2 and the connection point of these resistors R11 and R12, that is, the resistance value of the potential dividing resistor R1 is 1/2.
Is connected to the shaping electrode P4. Similarly, the potential dividing resistor R2 is composed of two partial resistors R21 and R22, and the connection point of the partial resistors R21 and R22 is connected to the shaping electrode P5. Each electrode P1 to P5
The spaces are electrically insulated from each other and fixed by the insulators Q1 to Q4.

On the other hand, a voltage higher than the acceleration voltage Vacc by the extraction voltage Vex generated by the extraction power source 23 whose voltage can be changed is applied to the ion source 3. The ion source 3 and the analyzing electromagnet 4 are composed of a conductive housing 2
4 is housed in the housing 4, and the housing 24 is connected to the acceleration electrode P.
1 is electrically connected, that is, the acceleration voltage Vacc is applied to the housing 24. For this reason, the housing 24 is installed on the ground 25 in an electrically insulated manner via an insulator 26 such as an insulator. Therefore, between the ion source 3 and the ground 25, there is a miscellaneous resistance component Retc of about 180 (MΩ) due to the pure water for cooling circulating inside the ion source 3 and the insulator 26. It will be. On the other hand, the ground structure 15 to which the acceleration electrode P2 is electrically connected is directly provided on the ground 25.

FIG. 3 is an equivalent circuit diagram when the set value of the acceleration voltage Vacc is higher than the set value of the focus voltage Vf at the steady beam current of the accelerator 1 configured as described above. An acceleration power source 21 is provided between the acceleration electrodes P1 and P2.
Is applied with an acceleration voltage Vacc, for example 160 (kV), and the focus power source 2 is applied between the electrodes P1 and P3.
2 is applied with a focus voltage Vf, for example, 125 (kV), whereby the potential dividing resistors R1 and R2 are applied.
Currents i1 and i2 flow in the respective channels. Further, in addition to the acceleration voltage Vacc, the extraction voltage Vex, for example, 40 (kV) is applied by the extraction power supply 23, and the beam current indicated by reference numeral ib flows.

The beam current ib depends on the degree of vacuum and the like.
In contrast, it functions as shown by the resistance Rb. Further, the miscellaneous resistance component Retc is interposed between both terminals of the acceleration power supply 21. Furthermore, the focus power supply 22 is
A focus current indicated by reference sign if is supplied between the electrodes P1 and P3 at the focus voltage Vf. Also, the electrode P3
A current IE corresponding to secondary electrons flowing from the electrodes P2 to P3 flows from the electrode P2 to the electrode P2, and a barrier between the electrodes P2 and P3 with respect to the electrode IE is indicated by reference symbol Re.

Therefore, the potential gradient from the ion source 3 to the end of the accelerator 1 is as shown by reference numeral α1 in FIG.

On the other hand, FIG. 5 shows an equivalent circuit diagram when the acceleration voltage Vacc is set to 0 and the beam current ib is set to a small value, which is 0 in this embodiment. Since ib = 0, as shown in FIG. 5, the switch S1 is interposed in the path of the beam current ib and the switch S1 is opened. Since ib = 0, the acceleration electrode P
There is no secondary electron inflow from 2 to the focus electrode P3,
Therefore, the current path indicated by the reference numeral IE can be ignored.

Here, the extraction voltage Vex = 40 (kV), the acceleration voltage Vacc = 0 (kV), and the focus voltage Vf = 5.
If 0 (kV), the current i1 flows through the potential dividing resistor R1 due to the focus voltage Vf, and the potential dividing resistor R1
2 forms a current loop by the focus power source 22 and the miscellaneous resistance component Retc, and the current i2 flows.

Therefore, when the beam current is very small and the setting value of the acceleration voltage Vacc is also small as described above, the potential gradient as shown by reference numeral α3 in FIG. The voltage Vetc generated across the terminals causes the change indicated by the reference numeral α4, that is, the acceleration voltage Vacc changes.

On the other hand, in the prior art, the potential dividing resistor R
1 and R2 have mutually equal values, for example, 640 (MΩ)
Is selected as 1.28 (GΩ) in which two commercially available resistors are connected in series. On the other hand, in the present invention, first, the resistance value of the potential dividing resistor R2 is selected to be a large value as follows in order to suppress the influence of the voltage Vetc. That is, the deviation ΔE of the ion beam energy E determined by the voltage Vetc is set to be, for example, 0.5% or less, and the sum of the extraction voltage Vex and the acceleration voltage Vacc, which is the energy E, is 40 (kV). ), ΔE = E × 0.005 = 40 (kV) × 0.005 = 0.2 (kV) (1) is obtained. When the resistance values of the potential dividing resistor R2 and the miscellaneous resistance component Retc are represented by the same symbols as the reference symbols, i2 = (Vacc-Vf) / R2 (2) and ΔE = i2 × Retc ((2)) 3), and Retc = 180 (MΩ), Vf as described above.
= 50 (kV), R2 = (Vf / i2) = {Vf / (ΔE / Retc)} = 45 (GΩ) (4) is obtained. Therefore, select 60 (GΩ) with a commercially available resistor.

Table 1 shows the respective parameters when R2 = 60 (GΩ) is selected and when R2 = 1.28 (GΩ) of the prior art.

[0036]

[Table 1]

Next, corresponding to the potential dividing resistor R2,
The resistance value of the potential dividing resistor R1 is obtained as follows.
At the connection point 30 between the potential dividing resistors R1 and R2, the current flowing out is the sum of i2, if, and IE with respect to the current i1 flowing into the connection point 30, and therefore i1 = i2 + if + ie (5) Further, i1 = Vf / R1 ...
(6) i2 = (Vacc-Vf) / R2 ...
(7) Therefore,

[0038]

[Equation 1]

Is required.

On the other hand, depending on the inflow of the secondary electrons, the potential gradient indicated by reference numeral α1 in FIG.
2, and if the current ie (> 0) is in the range of tens to hundreds of tens (μA), if≈0 and Vf≈Vacc. Therefore, in order to prevent Vf.apprxeq.Vacc, the value of R2 / R1 may be increased.

Generally, from the ground potential, the focus electrode P3
When secondary electrons flow into the
It is experimentally required to be about 0 (μA).
On the other hand, when Vacc> Vf, the focus voltage Vf is generally used at 60 (kV) or more, and therefore, even if secondary electron inflow occurs, it is 40% (2/3 of that). The goal is to maintain voltage control in the range above about kV). Therefore, by using R2 = 60 (GΩ) obtained as described above, R1 = Vf · R2 / {Vacc + (if + ie) · R2-Vf} (9) is obtained from the above equation 8, and Vacc, Vf And if ・ R2 is ie ・ R
Since it can be almost ignored compared to 2, R1≈400
(MΩ) is required. Therefore, the existing 640 (M
In the past, two resistors of (Ω) were connected in series and used, whereas three sets of the series circuit were used in parallel to obtain 427
Used as (MΩ).

Minimum value of focus voltage Vfm at this time
in becomes about 42 (kV). The ratio of the potential dividing resistors R2 and R1 at this time is about 140 times.

Thus, in the accelerator 1 according to the present invention,
In order to make the focus voltage Vf variable, the potential dividing resistor R1 between the focus electrode P3 and the first accelerating electrode P1 on the input end side is different from the potential dividing resistor R2 between the accelerating electrode P2 on the output end side. It is possible to prevent the ion accelerating voltage from undesirably rising when the accelerating voltage setting value is 0 and the minute beam is set, by setting the resistance value of 1 to be sufficiently high. Further, by selecting the resistance value of the potential dividing resistor R1 so that the resistance value of the potential dividing resistor R2 becomes two digits or more, for example, 140 times, secondary electrons flow from the ground side to the focus electrode P3 side. However, the desired focus voltage Vf can be obtained by maintaining the potential of the focus electrode P3 so as not to decrease. Thus, the acceleration voltage Vacc and the focus voltage Vf are
A desired voltage can be obtained stably.

The accelerating electrodes may be provided in multiple stages, and the present invention is not limited to the ion implantation apparatus 2 described above.
The present invention can be suitably applied to an accelerating device of another beam application device having a variable potential electrode between both accelerating electrodes.

[0045]

As described above, in the ion beam accelerating device according to the first aspect of the present invention, a focus electrode having a variable potential focus voltage is applied between the accelerating electrodes provided at the input and output ends of the ion beam. In the accelerating device configured to provide, the resistance value of the first potential dividing resistor between the acceleration electrode on the input end side and the focus electrode is relatively small, and the resistance value between the focus electrode and the acceleration electrode on the output end side is relatively small. The resistance value of the second potential dividing resistor is set to be two digits or more larger than the resistance value of the first potential dividing resistor.

Therefore, even when the acceleration voltage is small and the acceleration voltage is increased due to the miscellaneous resistance component between the acceleration electrode on the input end side and the ground when the beam is minute, the current flowing through the miscellaneous resistance component has a resistance value. Is a very small value via the second potential dividing resistor having a large value. Therefore, the amount of increase in the acceleration voltage can be suppressed to a small value. Further, even if secondary electrons flow into the focus electrode from the ground side, the first potential dividing resistor having a smaller resistance value than the second potential dividing resistor supplies a current corresponding to the secondary electron, As a result, the potential of the focus electrode is not dragged down to the potential of the accelerating electrode on the output end side, that is, the ground potential, and can be stably maintained at the value defined by the potential dividing resistance.

In the ion beam accelerating device according to the second aspect of the present invention, as described above, the first and second shaping electrodes are provided between the accelerating electrodes and the focus electrode, respectively.
The first and second shaping electrodes are connected at the point where the resistance values of the first and second potential dividing resistors become 1/2.

Therefore, the electric field from the acceleration electrode on the input end side to the focus electrode, and from the focus electrode to the acceleration electrode on the output end side is a regular electric field capable of suppressing the divergence of the ion beam. be able to.

In the ion beam accelerator according to the third aspect of the present invention, as described above, for example, the extraction voltage is 40 (kV), the focus voltage is 50 (kV), and the resistance value of the miscellaneous resistance component is 180 ( MΩ), the first and second potential dividing resistors are 400 (MΩ) and 6 respectively.
Select 0 (GΩ).

Therefore, the second potential dividing resistor has a resistance value sufficiently higher than that of the first potential dividing resistor, and suppresses the voltage generated by the miscellaneous resistance component at the time of the minute beam to suppress the increase of the acceleration voltage. be able to. Further, even if secondary electrons flow into the focus electrode from the ground side, a current corresponding to the secondary electrons is supplied via the first potential division resistor, and 2
It is possible to suppress a decrease in the potential of the focus electrode due to the inflow of secondary electrons.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an accelerator according to an embodiment of the present invention.

FIG. 2 is a simplified plan view for explaining the overall configuration of an ion implanter in which the accelerator shown in FIG. 1 is used.

FIG. 3 is an equivalent circuit diagram when the beam current is in a steady state when the acceleration voltage setting value of the accelerator shown in FIG. 1 is higher than the focus voltage setting value.

FIG. 4 is a graph showing a potential gradient from the ion source to the accelerator in the state shown in FIG.

5 is an acceleration voltage set value of the accelerator shown in FIG. 1 is 0,
It is an equivalent circuit diagram when the beam current is very small.

6 is a graph showing a potential gradient in the state shown in FIG.

[Explanation of symbols]

 1 Accelerator 2 Ion Implanter 3 Ion Source 4 Analysis Electromagnet 6 Sweep Magnet 8 Target Chamber 9 Target 10 End Station 15 Earth Structure 21 Acceleration Power Supply 22 Focus Power Supply 23 Extraction Power Supply 24 Housing 25 Earth 26 Insulator P1 Acceleration Electrode P2 Acceleration Electrode P3 Focus electrode P4 Shaping electrode P5 Shaping electrode R1 Potential dividing resistor R2 Potential dividing resistor

Claims (3)

[Claims] 1. An accelerating electrode provided on at least both input and output sides of an ion beam; a focus electrode provided between both accelerating electrodes on both sides of the input and output; and a focus electrode between both accelerating electrodes on both sides of the input and output. An acceleration power supply that applies an acceleration voltage, a focus power supply that applies a focus voltage that can be changed arbitrarily between the acceleration electrode on the input end side and the focus electrode, and an acceleration electrode and a focus electrode on the input end side. And a second potential dividing resistor connecting between the focus electrode and the acceleration electrode on the output end side, and a resistance value of the first potential dividing resistor. An ion beam accelerating device characterized in that the resistance value of the second potential dividing resistor is selected to be larger by two digits or more. 2. A first electric field shaping device between the acceleration electrode on the input end side and the acceleration electrode on the output end side and the focus electrode.
And a second shaping electrode, respectively, and the first potential dividing resistor and the second potential dividing resistor are
2. The points at which the resistance value is halved are connected to the first and second shaping electrodes, respectively.
The described ion beam accelerator. 3. The first and second potential division resistors have an extraction voltage of 40 (kV) and a focus voltage of 50 (k).
V), when the resistance value of the miscellaneous resistance component between the accelerator and the ground is 180 (MΩ), it is selected to be about 400 (MΩ) and 60 (GΩ), respectively. 2. The ion beam accelerator according to 2.