JPH0384841A - Ion implanter - Google Patents

Abstract

PURPOSE:To detect beam hitting by measuring a current that flows through the circuit of a bias supply and comparaing the measured value with a reference value. CONSTITUTION:A bias voltage which is negative with respect to a wafer disk 4 system is applied from a bias supply 18 to a Faraday cup 12; under normal conditions, secondary electrons generated in the wafer disk 4 system are therefore made to flow into the Faraday cup 12 so that current flow through the circuit of the bias supply 18 is restrained. When an ion beam 2 spreads abnormalily and one part of it hits the Faraday cup 12, i.e., beam hitting occurs, a current is thereby caused to flow through the circuit of the bias supply 18 and is measured by a current measuring means 20. The measured current value is compared with a predetermined reference value by a comparing means 22; beam hitting is therefore detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion implantation device, and particularly to a method for preventing the occurrence of a phenomenon in which an ion beam collides with the inner wall of a Faraday cup that constitutes a Faraday system (so-called beam hitting). Concerning means for detecting.

[Conventional technology]

FIG. 3 is a diagram partially showing an example of a conventional ion implantation apparatus.

This ion implantation device is of a so-called mechanical scan type, and basically, ions are placed on a plurality of wafers 6 mounted on the peripheral edge of a wafer disk 4 that is rotated and translated in a vacuum container (not shown). It is configured to perform ion implantation into each wafer 6 by irradiating the beam 2.

On the path of the ion beam 2, in addition to the beam shaping slit 8, there is a ground for secondary electrons emitted when the ion beam 2 hits the wafer disk 4, etc., which together with the wafer disk 4 form a Faraday system. A Faraday cup (also called a neutral cup) 12 and a negative potential suppressor electrode 10 are placed on the front side of the wafer disk 4 to catch the ion beam 2 in its place when the wafer disk 4 is translated outward. A plate 14 is provided on each rear side of the wafer disk 4.

The wafer disk 4, Faraday cup 12, and catch plate 14 are electrically connected in parallel to each other and connected to a current measuring device 16 such as a current integrator, thereby controlling the beam current Ii+ of the ion beam 2. This allows for accurate measurements.

[Problem to be solved by the invention]

In the above-mentioned ion implantation apparatus, for example, as shown by the broken line in FIG. 3, the ion beam 2 may spread abnormally due to some reason (for example, if the focal point position of the ion beam 2 shifts on the upstream side). When a part of the beam enters the Faraday system and collides with the inner wall of the Faraday cup 12, that is, when beam hitting occurs, an abnormality in the amount of implantation (more specifically, an insufficient amount of implantation) for the wafer 6 occurs.

This is because although the portion of the ion beam 2 that collided with the Faraday cup 12 is not incident on the wafer 6, the beam current lit flows through the current measuring device 16 as if it were incident on the wafer 6, and based on this, This is because the injection amount is controlled.

Also, when beam hitting as described above occurs,
The so-called cross contour contour, in which the material forming the Faraday cup 12 is knocked out and adheres to the surface of the wafer 6, also becomes larger.

Therefore, if ion implantation is continued without such beam hitting, a large amount of defective lofts will occur.

Therefore, the main object of the present invention is to provide an ion implantation apparatus that can easily detect the occurrence of beam hitting as described above.

[Means to solve the problem]

In order to achieve the above object, the ion implantation apparatus of the present invention includes a bias power supply connected between the Faraday cup and the wafer disk system and applying a negative bias voltage to the former, and a bias power supply that flows through the circuit of this bias power supply. It is characterized by comprising a current measuring means for measuring current, and a comparing means for comparing the current value measured by the current measuring means with a predetermined reference value.

[Effect]

Since a negative bias voltage is applied to the Faraday cup from the bias power supply to the wafer disk system, under normal conditions, secondary electrons generated in the wafer disk system flow into the Faraday cup and the bias power supply It is possible to suppress the flow of current through the circuit.

On the other hand, when the ion beam spreads abnormally and a part of it collides with the Faraday cup, that is, when beam hitting occurs, a current flows through the bias power supply circuit, and this is measured by the current measuring means. By comparing this measured current value with a predetermined reference value in the comparison means, it is possible to detect that beam hitting has occurred.

〔Example〕

FIG. 1 is a diagram showing the main part of an ion implantation apparatus according to an embodiment of the present invention. The same reference numerals are given to the same or corresponding parts as in the example of FIG. 3, and the differences from the conventional example will be mainly explained below.

In this embodiment, a direct current is connected between the Faraday cup 12 as described above and a wafer disk system, that is, a system in which the wafer disk 4 and catch plate 14 are connected in parallel, with the Faraday cup 12 on the negative side. A bias power supply 18 is connected, thereby applying a negative bias voltage (9) to the Faraday cup 12 with respect to the wafer disk system.

The magnitude of this bias voltage VN is, for example, several volts to several tens of volts.
It is preferable to keep it at a certain level. This is because the distance between the lower end surface of the Faraday cup 12 and the surface of the wafer 6 on the wafer disk 4 is usually as small as several mm, so when the bias voltage vN exceeds several tens of square meters, the electric field This is because there is a concern that this may adversely affect the devices on the surface of the wafer 6.

The circuit of the bias power supply 18 includes a current measuring device 20 in this example as a current measuring means for measuring the current IN flowing therethrough.
are inserted in series.

Furthermore, a comparator 22 is provided in this example as a comparison means for comparing the current value measured by the current measuring device 20 with a predetermined reference value, and when the measured current value exceeds the reference value, a detection signal S is output. That's what I do.

FIG. 2 shows examples of curves of the current IN flowing through the current measuring device 20 when the magnitude of the bias voltage vN is selected from various values in the above configuration.

Curve A in the same figure shows the normal state when beam hitting does not occur, and when the bias voltage vN is zero or close to zero, the ion beam 2 hits the wafer disk 4.
The bias power supply 18 is activated by the secondary electrons emitted by the impact flowing into the Faraday cup 12.
negative (i.e. in the opposite direction to that shown in Figure 1)
Current ■, flows, but if the magnitude of bias voltage ■ is increased (for example, from several volts to several dozen sheets), secondary electrons are suppressed from flowing into the Faraday cup 12, so current ■8 becomes almost zero.

On the other hand, if the ion beam 2 abnormally spreads (for example, in the state shown by the broken line in FIG. 1 or spreads further) and a part of it collides with the Faraday cup 12, that is, if beam hitting occurs, the collision will occur. Since the beam current generated by the ion beam 2 flows through the circuit of the bias power supply 18, the curve of the current (2) 8 is shifted to the positive side by that amount, and becomes like curve B in FIG.

Therefore, the magnitude of the bias voltage 9 is set to several volts to several tens of volts, and the level of the reference value in the comparator 22 is set to, for example, the second level.
If the current value is set to correspond to the current shown in the figure, the detection signal S will not be output from the comparator 22 during normal operation, but the detection signal S will be output from the comparator 22 when beam hitting occurs. This makes it possible to immediately detect the occurrence of beam hitting.

By the way, even if the bias power supply 18 is not provided (this is equivalent to the case where the bias voltage vM is zero), the comparator 22
For example, the level of the reference value in 1i style ■2 in Figure 2
If you set it to something corresponding to the above current measuring device 20
Although it is not impossible to detect the occurrence of beam hitting by the comparator 22, the amount of secondary electrons generated when the ion beam 2 hits the wafer disk 4 etc. depends on the degree of contamination of the wafer disk 4, the energy of the ion beam 2, etc. Since it differs depending on the ion species, etc., in practice, correct detection of beam hitting is impossible unless the level of the reference value in the comparator 22 is changed accordingly, which is very troublesome. For example, it is necessary to accumulate data for various cases in advance and to automatically set reference values based on this database.

Therefore, it is preferable to provide the bias power supply 18 as in this embodiment to suppress the secondary electrons from flowing into the Faraday cup 12.
Current flowing in 1. Since the uncertain element is no longer included in
Setting the reference value in the comparator 22 becomes very simple.

Note that the detection signal S may be used, for example, by sending it to a higher-level control device of the ion implantation apparatus and using this as an interlock condition to immediately stop ion implantation. By doing so, it is possible to automatically prevent the occurrence of an abnormality in the amount of implantation into the wafer 6 and an increase in cross-contamination. Alternatively, in addition to or in lieu of the above,
An alarm may be issued based on the detection signal S during the preparation stage before actually implanting ions into the wafer 6.

Further, instead of using the current measuring device 20 and the comparator 22 as described above, a meter relay (ammeter with contact) or the like that serves as both a current measuring means and a comparing means may be used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to easily and immediately detect that the ion beam has spread abnormally and collided with the inner wall of the Faraday cup, resulting in beam hitting.

As a result, for example, it becomes possible to prevent an abnormality in the amount of implantation into a wafer and an increase in cross-contamination.

Furthermore, since a special structure such as a detection electrode for detecting beam hitting is not required, the configuration can be extremely simple.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main part of an ion implantation apparatus according to an embodiment of the present invention. FIG. 2 is a graph showing an example of the state of current flowing through the bias power supply circuit. FIG. 3 is a diagram partially showing an example of a conventional ion implantation apparatus. 2... Ion beam, 4... Wafer disk, 6
°°°Wafer, 12...Faraday cup, 18.
, - bias power supply, 20... current measuring device (current measuring means), 22... comparator (comparing means).

Claims (1)

[Claims] (1) A wafer disk that is rotated and translated in a vacuum container, together with which a Faraday system is constructed, a Faraday cup is provided on the front side of the wafer disk, and a wafer disk is provided on the rear side of the wafer disk. A bias power supply connected between the Faraday cup and the wafer disk system and applying a negative bias voltage to the wafer disk system in an ion implantation apparatus comprising a catch plate that receives the ion beam instead of the disk when the disk is translated. An ion implantation apparatus comprising: a current measuring means for measuring a current flowing through a circuit of the bias power supply; and a comparing means for comparing a current value measured by the current measuring means with a predetermined reference value.