JPH0740476B2 - Charge beam current measurement mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a Faraday structure for measuring a beam current of a target when the target is being irradiated with a charged beam. For the Faraday structure of No. 1, by electrically disconnecting the second Faraday structure for measuring the current value of the charged beam other than when the charged beam is irradiated to the target to the ground potential, the instability of the dose amount is eliminated. In addition to the prevention, it is possible to shorten the vacuum recovery time after the target replacement.

[Industrial application field]

The present invention relates to a charged beam current measuring mechanism, and more particularly to a Faraday mechanism for measuring a beam current of a target in an ion implanter when the target is irradiated with an ion beam.

Ion implanters are required to accurately measure the dose to the wafer on the target, and therefore a charged beam current measuring mechanism is required to measure the beam current as accurately as possible.

[Conventional technology]

An example of a conventional charged beam current measuring mechanism is shown in FIG. 3 (final diagram). In the figure, 1 is a target (rotating disk), on the surface of which a plurality of wafers 2 are mounted in the circumferential direction. Reference numeral 3 denotes a rear Faraday electrode, which is provided to measure the current value of the ion beam with which the target 1 is irradiated.

Further, on the ion beam incident side of the rear Faraday electrode 3,
A rear bias electrode 4, a beam gate 5, and a front Faraday electrode 6 are provided in that order. The rear bias electrode 4 constitutes the first Faraday structure together with the rear Faraday electrode 3. The beam gate 5 is made of aluminum, has a carbon layer on the ion beam entrance surface, and has an opening 5a and a non-opening 5b.
It is configured to be movable in the vertical direction. Beam gate 5
The size of the opening 5a is set to an appropriate size so that the ion beam does not hit the outer end surfaces of the openings of the rear bias electrode 4 and the rear Faraday electrode 3, and also serves as a beam mask.

The front Faraday electrode 6 also serves as a bias electrode, and together with the beam gate 5, constitutes a second Faraday structure for measuring the ion beam current value except when the target 1 is irradiated with the ion beam.

A bias power source 7 applies a negative DC voltage as a bias voltage to each of the rear bias electrode 4 and the front Faraday electrode 6. Further, the positive side terminal of the bias power source is connected to the beam ammeter 8 together with the target 1, the rear Faraday electrode 3 and the beam gate 5.

In the conventional hybrid scan type charged beam current measuring mechanism having the above-described configuration, the ion beam to be implanted is to be known in advance in advance, and the ion beam is normally scanned with respect to the wafer 2. In order to confirm whether or not the ion implantation is performed on the wafer 2, the beam gate 5 is moved upward in the drawing to be extracted from an ion beam source (not shown) into an external vacuum. The ion current that has passed through the inside of the front Faraday electrode 6 is measured with a coarse accuracy while the non-opening 5b of the beam gate 5 prevents the ion beam from passing beyond the rear bias electrode 4. In this case, the beam ammeter 8 is instructed of the beam current value corresponding to the ion beam that has collided with the non-opening portion 5b of the beam gate 5.

When the outline of the beam current value due to the ion beam to be implanted is known and it is confirmed that the scanning is normally performed, then the beam gate 5 is moved downward in the drawing to move the beam. The opening 5a of the gate 5 and the openings of the front Faraday electrode 6, the rear bias electrode 4, and the rear Faraday electrode 3 are made to communicate with each other.
As a result, the ion beam passes through the front Faraday electrode 6, the opening 5a of the beam gate 5, the rear bias electrode 4, and the rear Faraday electrode 3 in this order, and is irradiated onto the wafer 2.

At this time, the target 1 is rotating in a fixed direction, for example, at 1000 rpm, and the ion beam is horizontal in a range slightly larger than the diameter of one wafer 2, for example, one round trip.
Reciprocal scanning is performed at a rate of 10 seconds. Also, wafer 2
The beam current due to the ion beam irradiated above is measured by the beam ammeter 8.

Here, the rear bias electrode 4 is biased by a negative DC voltage from the bias power source 7 so that the current due to the secondary electrons generated when the ion beam collides with the target 1 and the wafer 2 is not added as the beam current. Therefore, only the beam current due to the implanted ion beam is measured.

[Problems to be solved by the invention]

However, in the above-mentioned conventional charged beam current measuring mechanism, during implantation of the ion beam, a part of the implanted ion beam collides with a portion other than the opening 5a of the beam gate 5 and passes to the rear bias electrode 4. May be blocked. In this case, the beam current due to a part of the ion beam colliding with the beam gate 5 other than the opening 5a is
Since the ion beam is supplied to the beam ammeter 8 via the beam current meter, a part of the ion beam is measured as the beam current even though the target 1 and the wafer 2 are not irradiated, and a dose amount error (insufficient) Had the problem of causing

Moreover, the dose error is due to the opening 5a of the beam gate 5.
Because the amount of ion beam that hits other places is different each time,
It was indefinite, and the dose amount became unstable with the change in beam size.

The present invention was created in view of the above points, and an object thereof is to provide a charged beam current measuring mechanism capable of measuring a beam current with a small dose error.

[Means for solving problems]

The charged beam current measuring mechanism of the present invention is a mechanism including first and second Faraday structures and an ammeter, and is a first mechanism provided on the charged beam incident side of the first Faraday structure during irradiation of the target with the charged beam. The second Faraday structure is electrically separated from the first Faraday structure to provide a ground potential.

[Action]

The second Faraday structure is provided on the charged beam incident side of the first Faraday structure for measuring the current value of the charged beam during irradiation of the target, and the charged beam passes through the opening during irradiation of the charged beam to the target. When the charge beam current value is guided to the first Faraday structure and the target is not irradiated with the charged beam, the non-aperture portion prevents the charged beam from passing through the first Faraday structure. That is, the second Faraday structure has a shutter function of passing or blocking the charged beam to or from the first Faraday structure, and also has a structure which doubles as a beam mask of the first Faraday structure by the opening. ing.

The above-mentioned second Faraday structure is electrically separated from the first Faraday structure during the irradiation of the target with the charged beam to be at the ground potential. As a result, during irradiation of the target with the charged beam, even if a part of the charged beam hits the second Faraday structure and is not irradiated to the target, the beam current for the charged beam hitting the second Faraday structure is The beam current is not supplied to the ammeter, and a beam current corresponding to the charged beam actually applied to the target flows through the ammeter.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of the mechanism of the present invention. In the figure, the same components as those of FIG. 3 are designated by the same reference numerals, and the description thereof will be appropriately omitted. In FIG. 1, the ion beam is horizontally scanned (scanned) by a scan magnet or the like (not shown) and is irradiated so as to cover the width of the wafer 2. Therefore, in the rear Faraday electrode 3, the rear bias electrode 4, the opening 5a of the beam gate 5, and the front Faraday electrode 6, the cross-sectional shape of these openings (passages) in the direction perpendicular to the ion beam implantation direction is laterally long. Become.

Further, S ₁ and S ₂ are switches each having two fixed contacts a and b, and are configured to be switched in conjunction with the vertical movement of the beam gate 5. The fixed contact a of the switch S ₁ is connected to the connection point between the rear bias electrode 4 and the negative side terminal of the bias electrode 7. The fixed contact b of the switch S _{1 and} the fixed contact b of the switch S ₂ are both grounded.

Further, the fixed contact a of the switch S ₂ is connected to a common connection point of the target 1, the rear Faraday electrode 3, the non-grounded side terminal of the beam ammeter 8 and the positive side terminal of the bias power supply 7. Furthermore, the common contact of the switch S ₁ is connected to the front Faraday electrode 6, and the common contact of the switch S ₂ is connected to the beam gate 5.

FIG. 1 shows that the beam 1 is opened, that is, the ion beam passes through the opening of the beam gate 5, and further passes through the rear bias electrode 4 and the rear Faraday electrode 3, respectively.
The state where the ion beam is irradiated is shown above.
At this time, ion beam implantation is performed, and the beam ammeter 8 displays the beam current of the ion beam with which the target 1 is irradiated, as described above. At this time, switch the switch as shown in Fig. 1.
Both S ₁ and S ₂ are connected to the fixed contact b side.

On the other hand, when measuring the beam current value with the ion beam to be implanted before starting the ion implantation,
The beam gate 5 is moved upward in FIG. 1 and its non-opening 5b prevents the ion beam passing through the front Faraday electrode 6 from passing through to the rear bias electrode 4 (that is, the beam gate is closed). Will be).

When the beam gate is closed, the switches S ₁ and S ₂ are switched and connected to the fixed contact a side in conjunction with the movement of the beam gate 5. Therefore, when the beam gate is closed, the wiring is the same as that of the conventional mechanism shown in FIG. 3, so the description thereof is omitted, and the operation in the case of opening the beam gate different from the conventional mechanism will be described below. .

When the beam gate is opened, the switches S ₁ and
Since S ₂ is switched and connected to the fixed contact b side, the front Faraday electrode 6 and the beam gate 5 are electrically disconnected from the rear bias electrode 4 and the rear Faraday electrode 3, respectively, and are set to the ground potential.

On the other hand, at this time, the ion beam from the ion beam source (not shown) sequentially passes through the front Faraday electrode 6, the opening 5a of the beam gate 5, the rear bias electrode 4 and the rear Faraday electrode 3, respectively, and the target 1 and The wafer 2 is irradiated, but a part of the injected ion beam may hit a portion other than the opening 5a of the beam gate 5 and be blocked from passing therethrough.

In this case, the beam gate 5 is set to the ground potential via the switch S ₂ , and the rear Faraday electrode 3,
Since the rear bias electrode 4 and the beam ammeter 8 are electrically separated from each other, the beam current due to a part of the implanted ion beam whose passage is blocked by the beam gate 5 flows to the beam ammeter 8. There is no such thing. Therefore, the beam ammeter 8 accurately measures only the beam current of the ion beam with which the target 1 is irradiated.

By the way, in order to eliminate a beam current measurement error caused by a part of the implanted ion beam hitting a portion other than the opening 5a of the beam gate 5 when the beam gate is opened,
Only the beam gate 5 is switched to the ground potential when the beam gate is opened, and the connection of the front Faraday electrode 6 is not switched.
It is also conceivable to always connect to the negative terminal of the above (this is referred to as method A for convenience of explanation).

However, in this method A, secondary ions generated when the beam beam 5 is irradiated with the ion beam and low-energy ions generated from the residual gas in the beam line flow into the front Faraday electrode 6, which causes a beam ammeter. The present inventor has found that the measured beam current of No. 8 increases from the beam current value of the ion beam with which the target 1 is irradiated, which causes the error of the dose amount and the instability of the dose amount.

Since the problem of the method A is that the bias power supply 7 for the front Faraday electrode 6 and the rear bias electrode 4 is shared, the bias power supply for supplying the negative DC voltage to the front Faraday electrode 6 is the bias power supply. It is conceivable that the positive side terminal of the bias power source provided separately from No. 7 is not connected to the beam ammeter 8 (this is referred to as method B for convenience of explanation).

According to this method B, the above-mentioned secondary ions and low-energy ions are bypassed by the front Faraday electrode 6 which is negatively biased by the above-mentioned other bias power source, which is apparently convenient. However, in this method B, when the degree of vacuum is poor and the amount of residual gas is large, some of the ions lose their charge in the ion beam and become a neutral beam, but the kinetic energy is not lost, so the dose amount is There is no change. Therefore, the value of the beam current to be measured measured by the beam ammeter 8 is reduced, so that the final dose amount is increased, and a dose amount error is generated.

On the other hand, according to the present invention, the problems of the methods A and B can be solved, which will be described in more detail with reference to FIG.

FIG. 2 shows the relationship between the measured beam current I _B and the pressure of the beam measuring mechanism. In the case of the method A, as shown by the curve I, when the pressure is low (that is, high vacuum), The residual gas is extremely small, and the measured beam current I _{B of} a predetermined value corresponding to a constant dose amount can be obtained. However, as the pressure increases (that is, the degree of vacuum decreases), the residual gas increases, and the low-energy ions generated thereby increase the measured beam current I _{B as} described above, and the constant beam current IV shown in FIG. The measured beam current value greatly differs with respect to the dose amount. As a result, in the method A, since the amount of ion beam to be injected is controlled so that the measured beam current value becomes the predetermined value in the high vacuum, the dose amount becomes lower than the original value to be injected.

On the other hand, in the case of method B, as shown by the curve II in FIG. 2, the measured beam current of a predetermined value corresponding to the dose amount at low pressure.
Although I _B obtained, when the pressure becomes higher (the degree of vacuum is degraded), an increase in the neutral beam generated by the ion beam, the value of the measured beam current corresponds to a certain dose indicated by a broken line IV The beam current value is much lower than that. As a result, in the method B, since the amount of ion beam to be injected is controlled so that the measured beam current value becomes the predetermined value in the high vacuum, the dose amount becomes larger than the original value to be injected. Therefore, in the cases of the methods A and B, a dose amount error occurs and the dose amount is unstable.

On the other hand, according to the present invention, at the time of ion implantation, both the beam gate 5 and the front Faraday electrode 6 are electrically separated from the rear Faraday electrode 3 and the rear bias electrode 4 to the ground potential. If it gets worse, an increase in the measured beam current I _B due to the inflow of low-energy ions into the rear bias electrode 4 and a decrease in the measured beam current I _B due to an increase in the neutral beam occur at the same time,
It was confirmed by the inventor's trial manufacture experiment that these are substantially offset.

Therefore, according to the present invention, the measured beam current I _B at the time of ion implantation has an error corresponding to a constant dose amount (shown by a broken line IV) as shown by a solid line III in FIG. An extremely small current value of is obtained.

This means that according to the present invention, the dose amount measurement accuracy can be secured even in a state where the degree of vacuum is poor and the residual gas pressure is relatively high (eg, 10 ⁻⁵ Torr order). Thereby, the vacuum is temporarily broken when the target 1 or the wafer 2 is replaced, but in the present invention, the vacuum degree recovery time after the replacement of the target 1 or the wafer 2 can be shortened and the throughput can be increased.

The present invention is not limited to the above-described embodiment, and can be applied to a Faraday mechanism using magnetic field suppression instead of the Faraday mechanism using electrostatic suppression as in the embodiments. Further, the present invention can be applied to a beam current measuring mechanism for a charged beam other than the ion beam.

〔The invention's effect〕

As described above, according to the present invention, even when a part of the charged beam hits the second Faraday structure and is not irradiated to the target during irradiation of the charged beam to the target,
Since the beam current of the charged beam with which the target is actually irradiated can be measured, accurate beam current measurement without dose error or dose instability can be performed. Further, even if the degree of vacuum is poor, a predetermined dose amount measurement accuracy can be secured, the vacuum recovery time after target conversion can be shortened, and thus the processing amount of ion implantation or the like can be increased. It has a number of features.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the mechanism of the present invention, FIG. 2 is a diagram showing the measured beam current vs. pressure characteristics of the mechanism of the present invention and another mechanism, and FIG. It is a block diagram which shows an example. In the figure, 1 is a target (rotary disk), 2 is a wafer, 3 is a rear Faraday electrode, 4 is a rear bias electrode, 5 is a beam gate, 5a is an opening, 5b is a non-opening, 6 is a front Faraday electrode, Reference numeral 7 is a bias power source, 8 is a beam ammeter, and S ₁ and S ₂ are switches.

Claims (1)

[Claims] 1. A first Faraday structure (3, 4) for measuring a current value of a charged beam during irradiation of a target (1).
Is provided on the charged beam incident side of the first Faraday structure (3, 4), and while the target (1) is being irradiated with the charged beam, the charged beam passes through the opening also serving as a beam mask. When the current value of the charged beam is guided to the Faraday structure (3, 4) and the target (1) is not irradiated with the charged beam, the first Faraday structure (3, 4, Charged beam current measurement comprising a second Faraday structure (5, 6) for blocking passage to 4) and an ammeter (8) connected to the first and love 2 Faraday structures (3-6) In the mechanism, during the irradiation of the charged beam to the target (1), the second
Charged beam current, characterized in that means (S ₁ , S ₂ ) for electrically disconnecting all Faraday structures (5, 6) from the first Faraday structure (3, 4) to ground potential are provided. Measuring mechanism.