JPH0613014A - Ion implantation device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of implantation error by detecting an error if it exists in the measured value of beam current during the operation of ion implantation, and by making a suppresser current indicating change greater than that in the measured value of beam current an object to be detected. CONSTITUTION:When an error occurs in the measured value of beam current, a suppresser current flows between a suppresser electrode 5 and a grounding part corresponding to the error. A suppresser current detection resistance 9 is provided between the suppresser electrode 5 and the grounding part, and the voltages on both terminals of the detection resistance 9 are monitored by a suppresser current detection circuit 11. When a voltage no less than 100mV (corresponding to 1muA of suppresser current) is detected by the detection circuit 11, an output relay 12 works and a relay contact point 13 is closed, whereby interlocking is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus for uniformly implanting impurity ions into an object to be ion-irradiated such as a wafer, and more particularly to measuring ion beam current and controlling the ion implantation amount based on the measurement result. The present invention relates to an ion implanter for performing the above.

[0002]

2. Description of the Related Art An ion implanter, in which ions are generated in a vacuum, is extracted as an ion beam, and the desired ion beam is selectively extracted by mass spectrometry using a magnetic field. By irradiating a target such as a wafer after accelerating the energy to a predetermined energy, impurities are implanted into the target, and the impurities that determine the characteristics of the device in the semiconductor process can be controlled at an arbitrary amount and depth with good controllability. Because it can be injected
It has become an important device in the manufacture of current integrated circuits.

In the above-mentioned ion implantation apparatus, as shown in FIG. 4, irradiation of the target 53 with the ion beam 58, that is, ion implantation is carried out in an ion implantation chamber in the target chamber 51 held in a high vacuum state. And
The beam current of the ion beam 58 reaching the target 53 is measured by the beam current measuring system, and the implantation controller (not shown) controls the ion implantation amount based on the measurement result.

When the target beam 53 is irradiated with the ion beam 58, secondary electrons and secondary ions are generated (mainly secondary electrons are generated). A Faraday cage 52 that collects is used. The Faraday cage 52 is installed around the target 53, and a suppressor electrode 55 to which a negative voltage (for example, -600V) is applied from the suppressor power supply 56 is usually provided near the beam incident part 52a. The suppressor electrode 55 suppresses the movement of electrons between the inside and the outside of the Faraday cage 52,
Only the secondary electrons jumping out from the target 53 by the irradiation of the ion beam 58 are surely absorbed by the Faraday cage 52.

The beam current measurement by the beam current measurement system is performed by collecting the electric charges of the ions reaching the Faraday system and measuring them by the current integrator 54. That is, the ion beam 58 enters the Faraday cage 52 through the suppressor electrode 55 and reaches the target 53. The charge of the ions reaching the target 53 is the charge injected into the target 53 and the charge at that time. This is the sum of the charges of secondary electrons and secondary ions emitted from the beam irradiation surface, and the beam current measurement value is obtained by the current integrator 54 connected to the target 53 and the Faraday cage 52.

[0006]

By the way, when the ion beam 58 passes through the ion implantation chamber, residual gas molecules in the ion implantation chamber collide with the ion beam 58, and the gas molecules are ionized into ions and electrons. To do. Among the ions generated by this impact ionization, especially the suppressor electrode 5
Those near 5 are absorbed by the suppressor electrode 55 to which a negative voltage is applied. Then, a phenomenon occurs in which some of the electrons generated by ionization enter the Faraday cage 52, and as a result, the measured value of the current integrator 54 becomes smaller than the actual beam current (hereinafter, This is called a negative measurement error).

Particularly, when the degree of vacuum in the target chamber 51 is lowered, collision ionization of gas molecules is increased,
The electrons generated by impact ionization are also Faraday cages 52.
Since a large amount of intrusion occurs inside, the negative measurement error also increases. Further, if there is a dirty surface near the suppressor electrode 55, this dirty surface is charged to a negative potential, and this negative charged surface (dirty surface) acts as if the suppressor electrode 55 becomes wide. As the charging of the dirty surface progresses, the adsorption action of ions generated by impact ionization and the repulsion action of electrons are enhanced, and the intrusion of electrons into the Faraday cage 52 also increases, so that the negative measurement error also increases.

As described above, when the negative measurement error becomes large due to the influence of the degree of vacuum in the ion implantation chamber or internal contamination, the implantation amount control different from the desired implantation amount (that is, the implantation amount). The injection amount is controlled such that the injection amount becomes excessive, resulting in a large difference (injection error) between the set injection amount and the actual injection amount.

However, in the above conventional configuration, even if the above situation occurs, it is indistinguishable from the decrease of the beam current due to the change of the state of the ion source. Therefore, during the ion implantation operation, ions are generated by impact ionization. There is a problem that it is not possible to detect that electrons generated in the injection chamber enter the Faraday system and a negative measurement error occurs.

When the implantation operation is completed or interrupted, the ion beam 58 is deflected so that the target 53 is not irradiated with the ion beam 58 (so as not to enter the Faraday cage 52). If a large number of generated electrons have entered the Faraday cage 52, the measured value of the current integrator 54, which should be 0 (zero), becomes negative. Therefore, in the related art, the negative measurement is performed during the implantation operation by detecting that the measurement value of the current integrator 54 becomes negative immediately after the ion beam 58 is deflected and the beam irradiation to the target 53 is stopped. It is configured to detect that an error has occurred and to take measures such as prohibiting subsequent injection operation and alarm operation.

However, in this case, it cannot be detected that the measured value of the current integrator 54 is negative unless a large number of electrons generated by the impact ionization enter the Faraday cage 52, and the injection is performed. Compared with during operation, the amount of electrons that intrude into the Faraday cage 52 is overwhelmingly smaller at the time of completion or interruption of the injection operation, so the detection accuracy is very low. In this case, if there is a measurement error during the injection operation, the most important problem is that the measurement error during the injection operation cannot be detected even though the injection error immediately occurs.

The present invention has been made in view of the above, and an object thereof is that during the implantation operation, electrons generated in the ion implantation chamber enter the Faraday system to cause a negative measurement error. An object of the present invention is to provide an ion implantation apparatus capable of preventing an implantation error from occurring by performing detection with high accuracy.

[0013]

In order to solve the above-mentioned problems, an ion implantation apparatus of the present invention includes a Faraday cage surrounding a target to be irradiated with an ion beam in an ion implantation chamber in a high vacuum state, and the Faraday cage. Of the suppressor electrode provided with a negative voltage, and a beam current measuring means for measuring the current amount of the ion beam injected into the Faraday cage, and the beam current measuring means An ion implanter in which the amount of ion implantation is controlled based on the beam current measurement value, and the following means are taken.

That is, the suppressor current detecting means for detecting the suppressor current flowing between the suppressor electrode and the ground portion is provided.

[0015]

In the above structure, the residual gas molecules in the ion implantation chamber are ionized by collision with the ion beam, and among the ions generated by the collision ionization, those near the suppressor electrode are the suppressor electrode to which a negative voltage is applied. On the other hand, some of the electrons generated by ionization enter into the Faraday cage while being absorbed in the Faraday cage, which causes a measurement error (negative measurement error) of the beam current measuring means. When the above phenomenon occurs, a suppressor current corresponding to the amount of ions absorbed by the suppressor electrode flows between the suppressor electrode and the ground portion. This ion implanter is equipped with suppressor current detection means for detecting this suppressor current, and is adapted to monitor the change state of the suppressor current during the ion implantation operation. It can be detected during the ion implantation operation that a negative measurement error has occurred by penetrating into the cage.

The suppressor current shows a change about 100 times larger than the change in the beam current measurement value (negative measurement error), and the change in the beam current measurement value can be magnified and detected. The detection accuracy is very high. Therefore, it is possible to detect that a negative measurement error has occurred long before the change (which can be detected) in the beam current measurement value occurs.
It is possible to prevent an injection error from occurring.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, the ion implantation apparatus according to this embodiment includes a target chamber 1 forming an ion implantation chamber 7 in an end station section. The ion implantation chamber 7 is kept in a high vacuum state, and a target 3 holding an ion irradiation target such as a wafer is provided in the ion implantation chamber 7. And this target 3
The ion implantation process is performed by irradiating the ion beam 8 extracted from an ion source (not shown) and subjected to acceleration, shaping, deflection, scanning, etc., if necessary.

A beam profile monitor (not shown) for measuring a beam profile such as a beam current density or a beam shape is provided behind the target 3 in the traveling direction of the ion beam 8. Target 3 above
Is rotatable between an implantation position for receiving the irradiation of the ion beam 8 (shown by a solid line in the figure) and a retracted position (shown by a dotted line in the figure) out of the trajectory of the ion beam 8. It has become. The target 3 is arranged at the implantation position during the implantation operation, and is arranged at the retracted position when the beam profile is measured at the time of starting the beam or when the wafer is exchanged.

Around the target 3, charged particles (secondary electrons, secondary ions, and secondary electrons, which predominantly fly out from the beam irradiation surface of the target 3 during the injection operation, are overwhelmingly abundant. There is a Faraday cage 2 for collecting A suppressor electrode 5 to which a negative voltage (for example, −600 V) is applied from a suppressor power supply 6 is provided near the beam entrance portion 2 a of the Faraday cage 2. The suppressor electrode 5 serves as an electron (that is, an ion beam 8) generated inside the Faraday cage 2.
The secondary electrons emitted from the irradiation surface of 1) are prevented from escaping to the outside of the cage, and the electrons generated outside the Faraday cage 2 are prevented from entering the cage.

The target 3 and the Faraday cage 2 are connected to the grounded current integrator 4, and the current flowing through the current integrator 4 is
The current value of the ion beam 8 reaching the target 3 is measured. Then, the measured value of the beam current by the current integrator 4 is fetched by an implantation controller (not shown), and the implantation controller controls the ion implantation amount based on the measured value of the beam current.

By the way, residual gas molecules in the ion implantation chamber 7 are ionized by collision with the ion beam 8, and among the ions generated by this collision ionization, those near the suppressor electrode 5 are absorbed by the suppressor electrode 5, while Some of the electrons generated by ionization enter the Faraday cage 2 and
This is a factor that causes a measurement error (negative measurement error) in the current integrator 4, as described in the related art.

When the above phenomenon occurs, the suppressor electrode 5 is placed between the suppressor electrode 5 and the ground portion.
A current flows according to the amount of ions absorbed in the
This is called suppressor current). Here, FIG. 2 shows a temporal change of the beam current measurement value I _B by the current integrator 4 during the ion implantation operation, and FIG. 3 shows a temporal change of the suppressor current I _S at this time. The change over time of the suppressor current I _S shown in FIG. 6B is measured by connecting a current measuring device (not shown) between the suppressor electrode 5 and the grounding portion. As is clear from the figure, the suppressor current I _S is gradually increasing from a time point far before the time point when it becomes clear that the measured beam current value I _B is decreasing. Therefore, by monitoring the suppressor current, it is possible to detect that the electrons generated in the ion implantation chamber 7 enter the Faraday cage 2 to cause a negative measurement error.

Factors that cause negative measurement errors include
Other than the above (eg 2 emitted from target 3
It is possible that the secondary ion escapes from the Faraday cage 2), but the chance of being affected by other factors is small compared to the above factors. Therefore, a relatively strong correlation is normally established between the beam current measurement value I _B and the suppressor current I _S, and a current of about 1/100 of the suppressor current I _S decreases on the beam current measurement side. (There is a negative measurement error).

Therefore, the ion implanter of the present invention is constructed so as to detect the occurrence of a negative measurement error by detecting that a suppressor current of a predetermined value or more is flowing, as described below. Has become. That is, the positive terminal of the suppressor power source 6 is grounded via a suppressor current detecting resistor (suppressor current detecting means) 9 of 10 kΩ and a non-linear resistor such as a Zener diode 10 having a Zener voltage of 3 to 5 V. In addition, the detection resistor 9
The voltage across the Zener diode 10 is applied to the input terminal of the suppressor current detection circuit (suppressor current detection means) 11. The suppressor current detection circuit 11 is 100 mV (suppressor current 1 μA
(Corresponding to the above), a detection signal is output when an input voltage above is detected. When the suppressor current detection circuit 11 outputs a detection signal, the output relay 1
2 operates to close the relay contact 13, thereby interlocking and alarming.

If there is no decrease in the degree of vacuum in the ion implantation chamber 7 or internal contamination, the suppressor current flowing during the ion implantation operation is about 50 nA and 100 nA.
It does not exceed. If the degree of vacuum in the ion implantation chamber 7 is reduced or there is internal contamination, the suppressor current increases,
Although the negative measurement error becomes large, if the detection level is set to about 1 μA (the detection level in the presser current detection circuit 11 is 100 mV) as in the present embodiment, the difference in suppressor current between the normal state and the abnormal state is large. Is sufficient and stable operation is possible. Further, when the suppressor current becomes 1 μA, the negative measurement error corresponds to about 10 nA, and normally, the measurement error below this does not pose a problem. Of course, the detection level is 1
By setting the value to μA or less, it is possible to detect a negative measurement error with higher sensitivity.

As described above, the ion implantation apparatus of this embodiment is designed to monitor the change state of the suppressor current during the ion implantation operation, so that a negative measurement error can be reliably detected during the ion implantation operation. it can. In addition, since the suppressor current that shows a change about 100 times larger than the change in the beam current measurement value (negative measurement error) is targeted for detection, it is possible to magnify and detect the change in the beam current measurement value. It is possible to detect that a negative measurement error has occurred long before the change in the measurement value (detectable) occurs, and the detection accuracy is very high. Therefore, the injection error can be prevented.

Further, in this embodiment, since a nonlinear resistance such as the Zener diode 10 is connected between the suppressor power supply 6 and the ground portion, and the voltage fluctuation of the suppressor power supply 6 is suppressed to several V, an excessive suppressor is provided. Even if a current flows, the suppressive effect of electrons by the suppressor electrode 5 hardly changes.

Conventionally, when the suppressor power supply is overloaded and the voltage drops, a method of interlocking by detecting a voltage shortage has been used.
If a suppressor current of 0 mA does not flow, the lack of voltage of the suppressor power supply cannot be detected, and the effect of the suppressor (suppression of electrons) is lost due to the decrease in voltage. The effect of being able to detect the measurement error of and to prevent the injection error in advance cannot be expected.

In this embodiment, the interlock is applied when the suppressor current reaches a predetermined level (about 1 μA), but the following structure is also possible. That is, as described above, a relatively strong correlation is established between the beam current measurement value and the suppressor current (a value of about 1/100 of the suppressor current causes a negative measurement error on the beam current measurement side). Therefore, the current integrator 4 corrects the beam current measurement value based on the suppressor current measurement value, and the implantation controller controls the ion implantation dose based on the corrected value.

[0031]

As described above, the ion implantation apparatus of the present invention is provided in the Faraday cage surrounding the target to be irradiated with the ion beam in the ion implantation chamber in the high vacuum state, and in the vicinity of the beam incidence portion of the Faraday cage. , A suppressor electrode to which a negative voltage is applied, and a beam current measuring means for measuring the current amount of the ion beam incident in the Faraday cage, and the ion current is measured based on the beam current measurement value of the beam current measuring means. An ion implanter in which the amount of implantation is controlled, which is configured to include suppressor current detection means for detecting a suppressor current flowing between the suppressor electrode and the ground portion.

Therefore, the fact that the electrons generated in the ion implantation chamber penetrate into the Faraday cage to cause a measurement error (negative measurement error) in the beam current measurement value of the beam current measuring means during the ion implantation operation. Can be detected. In addition, the change in beam current measurement value is approximately 100
Since the suppressor current that shows twice the large change is targeted for detection, it is possible to magnify and detect the change in the beam current measurement value.
The detection accuracy is very high.

Therefore, it is possible to detect the occurrence of a negative measurement error long before a change that can be detected in the beam current measurement value occurs, and to prevent an injection error from occurring. Play.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a schematic configuration diagram showing a main part of an end station section in an ion implantation apparatus.

FIG. 2 is a graph showing changes over time in beam current measurement values by a current integrator during an ion implantation operation.

FIG. 3 is a graph showing changes in suppressor current with time during an ion implantation operation.

FIG. 4 illustrates a conventional example and is a schematic configuration diagram illustrating a main part of an end station unit in an ion implantation apparatus.

[Explanation of symbols]

1 Target Chamber 2 Faraday Cage 2a Beam Injector 3 Target 4 Current Integrator (Beam Current Measurement Means) 5 Suppressor Electrode 6 Suppressor Power Supply 7 Ion Implantation Chamber 8 Ion Beam 9 Suppressor Current Detection Resistor (Suppressor Current Detection Means) 10 Zener Diode 11 Suppressor Current detection circuit (suppressor current detection means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G21K 5/04 C 8707-2G H01J 37/04 A H01L 21/265 // H05H 7/00 9014- 2G

Claims (1)

[Claims] 1. A Faraday cage that surrounds a target that is irradiated with an ion beam in an ion implantation chamber in a high vacuum state, and a suppressor electrode that is provided in the vicinity of the beam incidence portion of the Faraday cage and to which a negative voltage is applied.
In the ion implantation apparatus, which comprises a beam current measuring means for measuring the current amount of the ion beam incident into the Faraday cage, and in which the ion implantation amount is controlled based on the beam current measurement value of the beam current measuring means, An ion implanter comprising a suppressor current detecting means for detecting a suppressor current flowing between the suppressor electrode and the ground portion.