JPH0754689B2 - Ion implanter - Google Patents

Description

The present invention relates to an ion implanter, and more particularly to a peripheral structure of an implanting object.

[Conventional technology]

FIG. 4 is a block diagram showing an outline of a conventional ion implanter, in which an ion beam 2 extracted from an ion source 1 separates unwanted ions from target ions in an analysis tube 3, and then an earth electrode 4 and a suppressor electrode. After passing through 5, it collides with an object to be implanted (for example, a semiconductor wafer) arranged in the Faraday cup 6 and ions are implanted.

This ion implantation is usually performed by scanning the ion beam in the X and Y directions. The driven object 7 is the Faraday cup 6.
The ion implanted into the object to be implanted rests in the object to be implanted, and its ionic charge becomes an ionic current, which is measured by the ammeter 8.

This measured current is a standard for knowing the dose amount of ions, and when the set dose amount is reached, the ion implantation is stopped.

By the way, the ion beam used for ion implantation is
Since the energy is high, secondary electrons and secondary ions are emitted from the hit object when it hits the hit object. If this secondary electron or secondary ion leaks to the outside of the Faraday cup, the ion current will fluctuate, making it impossible to accurately measure the ion current. Specifically, for example, the leakage (emission) of secondary electrons is measured in the same manner as the inflow of positive charges into the current measuring device 8 and is measured more than the actual amount of implanted ions.

Therefore, conventionally, as shown in FIG. 4, a Faraday cup 6 is used.
A suppressor electrode 5 is provided near the beam entrance of the. The suppressor electrode is set near the entrance to the Faraday cup on the negative side, so that secondary electrons (negative charges) that try to jump out of the Faraday cup through the entrance are returned to the cup by repulsive force, and secondary ions (positive Charge) and returned to the Faraday cup side again.

A conventional device of this type is, for example, US Pat.
There is one described in No. 11449.

[Problems to be Solved by the Invention]

The above-mentioned conventional technique fulfills a sufficient function in capturing secondary electrons and secondary ions generated from an object to be ion-implanted, and has an ion current value based on the original ion beam (primary ion). Was measured accurately, but when the object to be implanted was one in which gas was easily generated by ion implantation, there were the following points to be improved.

For example, if the ion beam current is 10 mA and there is a resinous film on the surface of the object to be implanted (specifically, if there is a resist film on the semiconductor wafer), the non-implanted object at the time of ion implantation From which organic gas is produced. Since the conventional Faraday cup has a gas escape port only at its ion beam inlet, the gas easily fills the Faraday cup, and the gas diffuses upstream of the ion beam line through the opening of the ion beam inlet. When such a phenomenon occurs, the ion beam collides with the gas before entering the Faraday cup, and a part of the ion beam is combined with free electrons contained in the gas to be neutralized. In addition, the gas collides with the ion beam in the Faraday cup and is ionized, and part of the gas is exhausted in the ion state, so the charge in the Faraday cup decreases and the same phenomenon as current leakage occurs. . In either case, the ion current to be measured fluctuates, and there is a problem that an accurate ion current cannot be measured.

Further, when the current measuring system has a high voltage electrode such as a suppressor electrode for secondary electrons or the like, discharge may occur due to a decrease in vacuum degree, which is likely to cause noise generation and power source damage.

In addition, the generated gas substance is mixed into the object to be implanted by the mixing action at the time of implanting the ion beam, and the gas substance collects and grows to a problematic size as a foreign matter. There is concern that it may have an adverse effect.

In order to deal with such a problem, for example, JP-A-60-23034
As disclosed in Japanese Patent Publication No. 7, a Faraday cup is composed of an inner cylinder having a large number of gas vent holes and an outer cylinder, and a positive potential is applied to the inner cylinder and a negative potential is applied to the outer cylinder. The gas in the cup is released to the outside through the hole, and the above-mentioned positive and negative potentials are trapped so that the secondary electrons and secondary ions generated during ion implantation in the Faraday cup do not mix with the gas and are not released (external leak). Techniques for doing so have also been proposed.

The object of the present invention is to discharge the gas at the time of ion implantation generated in the Faraday cup while trapping secondary electrons and secondary ions even without such a negative potential inner cylinder and a positive potential outer cylinder.
It is to solve the above-mentioned various problems caused by the generation of gas generated from an object to be ion-implanted.

[Means for Solving the Problems]

The present invention is basically an ion implanting device in which an object to be implanted is arranged in a Faraday cup, and an ion beam is introduced into the object to be implanted from a beam entrance of the Faraday cup to implant ions. The Faraday cup is composed of a ring-shaped shield plate assembly in which a large number of ring-shaped shield plates whose cross-section is bent in a "dogleg" shape are arranged in a cylindrical shape at intervals so that the outside cannot be seen. It is characterized in that a bent passage for discharging gas generated in the Faraday cup at the time of ion implantation from the gap between the plates to the outside is formed (this is the first means for solving the problem).

Further, there is also proposed such a ring shield plate assembly in which a magnet for forming a magnetic field around the Faraday cup is arranged around the Faraday cup (this is referred to as a second problem solving means).

[Action]

Action of First Problem Solving Means ... Since the gap between the annular shield plates of the annular shield plate assembly forming the Faraday cup constitutes a bent narrow passage having a "dogleg" cross section, the Faraday cup generated at the time of ion implantation The gas inside is released to the outside through this bent passage, but secondary electrons and secondary ions collide with the wall of the passage (annular shield plate) and are repelled or adsorbed in the process of passing through the bent passage.

In this case, since the particle energy colliding with the passage wall is low, there are few tertiary charged particles such as electrons and ions (herein, referred to as tertiary electrons and tertiary ions) generated from the passage wall, and The collision does not generate tertiary ions.

When the particles collide and bounce, the energy of the secondary particles decreases stochastically, and when collisions on the passage walls are repeated, most of the secondary ions and secondary electrons are finally adsorbed on the passage walls.

Further, according to the present invention, when the secondary electrons and secondary ions pass through the curved passage secured in the Faraday cup, the structure can collide with the passage wall several times without fail. Only the air can be exhausted and the charged particles can be captured.

Operation of Second Problem Solving Means ... A case where a magnetic field is formed by a magnet around the Faraday cup composed of such an annular shield plate assembly will be described.

The magnetic field has the property of bending the charged particle in the path direction. Therefore, if the magnetic field is strong enough, not only the charged particles can be bent, but also a U-turn can be made. Even if it is assumed that charged particles such as secondary ions are emitted from the Faraday cup, it can be changed. It is possible to pull it back to the Faraday cup side.

Here, the magnetic field strength required to trap secondary electrons experimentally will be calculated based on FIG.

In FIG. 3, A is a Faraday cup, B is an exhaust hole provided on the cylindrical surface of the Faraday cup (here, it is a straight hole so that secondary electrons can easily pass through it), and C is a secondary hole. The path of electrons, G indicates the direction of the magnetic force of the magnetic field. If the energy Ee of the secondary electron is several tens of eV and the length of the magnetic field in the particle passage direction is several cm, and if the radius of gyration R of the electron due to the magnetic field is smaller than L, the secondary electron is Can't pass through.

Ee = 100eV ・ R <1.0cm, the relational expression between charged particles and magnetic field is However, ME is the electron mass (atomic weight conversion) and B is the magnetic flux density (Gauss). Therefore, if there is a magnetic field of about 50 gauss near the exhaust hole of the Faraday cup, secondary electrons can be captured by the magnetic field.

The energy of the secondary electron ions seems to be almost the same as that of the secondary electrons, but since the mass is large, the straight exhaust hole may not be trapped by such a magnetic field and may pass through.

However, in the structure of the present means for solving the problem, since the Faraday cup is composed of the aggregate of the above-mentioned annular shield plate having the "dogleg" shape, the charged particles such as secondary electrons and secondary ions are exhausted from the exhaust. Is captured by a bent passage wall (annular shielding plate) for
However, since the secondary ions have a large mass, they may be discharged together with the gas when the gas pressure in the Faraday cup becomes high, but as described above, the secondary ions collide with the bent passage wall several times. Since the energy is attenuated, the secondary ions can be sufficiently pulled back to the Faraday cup side even if a magnetic field of the above-mentioned empirical formula is provided around the Faraday cup.

〔Example〕

 One embodiment of the present invention is shown in FIGS. 1 and 2.

FIG. 1 shows the vicinity of the Faraday cup of the ion implantation device, and FIG. 2 is a partially enlarged sectional view thereof.

In these figures, 20 is a Faraday cup, and the Faraday cup 20 is formed into a tubular shape with a predetermined interval such that a large number of annular shield plates 21 whose cross section is bent in a "dogleg" shape cannot be seen through. It is composed of an array of annular shielding plates. An exhaust passage 22 bent from the gap between the annular shield plates 21 was formed to allow the gas generated in the Faraday cup at the time of ion implantation to be released to the outside.

The Faraday cup 20 is grounded via the ammeter 8.

Reference numeral 25 is a ground electrode, and 26 is a suppressor electrode. These electrodes are arranged near the ion beam entrance (opening) 20b of the Faraday cup 20.

23 is the outer periphery of the Faraday cup 20 and the ion beam entrance
In addition to forming a magnetic field 24 around the Faraday cup 20 (outer side) with a magnetic field forming magnet (permanent magnet) provided on the outer side of the end plate-shaped wall (cylinder bottom) on the side opposite to 20b, inside the Faraday cup 20 A part of the magnetic field 24 is applied to. The magnetic flux of the magnetic field 24 is set in the same direction as the ion beam 2 entering the Faraday cup 20, and the ion beam 2 is set so as to pass through the magnetic flux inside the magnetic field 24.

Reference numeral 7 denotes an object to be driven (for example, a semiconductor wafer) set on the inner wall of the end plate in the Faraday cup 20.

The ion beam 2 from the ion source passes through the earth electrode 25 and the suppressor electrode 26, enters the Faraday cup 20, and is irradiated onto the implanting object 7.

According to the present embodiment, the gap between the annular shield plates 21 of the annular shield plate assembly that constitutes the Faraday cup 20 has a cross-section of "dogleg".
Since the curved narrow passage 22 is formed, the gas is discharged to the outside through the curved passage in the Faraday cup 20 generated at the time of ion implantation. Further, when the secondary electrons or secondary ions are mixed in the gas and pass through the bent exhaust passage 22, the secondary electrons or secondary ions collide with the passage wall (annular shield plate) and bounce or are adsorbed.

In this case, since the particle energy colliding with the passage wall is low, the number of tertiary charged particles such as electrons and ions (tertiary electrons, tertiary ions) generated from the passage wall is small, and the tertiary ions are generated only by the collision of electrons. Does not occur.

When the particles collide and bounce, the energy of the secondary particles decreases stochastically, and when collisions on the passage walls are repeated, most of the secondary ions and secondary electrons are finally adsorbed on the passage walls.

The secondary ions may be discharged together with the gas when the gas pressure in the Faraday cup becomes high because of the large mass. However, as described above, the secondary ions may be discharged to the bent passage wall several times. Since the energy is attenuated by the collision, the magnetic field formed in the Faraday cup 20 (about 50 Gauss is enough) makes it possible to make the secondary ions U-turn to the Faraday cup 20 side and pull back.

Therefore, according to the present embodiment, only the neutral gas is discharged through the large number of gas exhaust passages 22 provided on the peripheral surface of the Faraday cup to eliminate the gas filling in the Faraday cup 20 and the ion beam of the Faraday cup 20. The gas flowing out from the inlet 20b can be almost eliminated, and the leakage of secondary electrons and secondary ions can be prevented, so that the following effects can be obtained.

That is, it is possible to prevent a situation in which the degree of vacuum is lowered due to the gas generated by implanting an ion beam on a semiconductor wafer with a resist and the like, avoiding collision between the gas and the ion beam 2 as well as secondary electrons, secondary ions, etc. Since the charged particles are effectively captured near the cylindrical surface of the Faraday cup and the entrance of the ion beam, the current value of the ion beam can be accurately measured without fluctuation.

Further, the safety of the device can be improved without fear of electric discharge at the suppressor electrode or the like which occurs when the degree of vacuum is extremely lowered.

In addition, by eliminating the gas filling in the Faraday cup, the problem that the gas substance in the vicinity of the driving chamber is driven into the target by the mixing action of the ion beam is eliminated, and the contamination of the target by the mixing action and the gas It is possible to prevent a situation in which the substances are aggregated to form a foreign substance, which hinders the normal driving of the object to be driven. Further, it is possible to reduce the problem of fouling due to the gas substances adhering to the surrounding components, and thus maintenance.

Further, in the present embodiment, since the magnetic field lines of the magnetic field 24 are oriented in the same direction as the ion beam traveling direction and the ion beam passes through the magnetic field 24, the secondary electrons and the secondary electrons are also generated by the magnetic field inside the Faraday cup. Since the ions are restrained, it is difficult for the secondary electrons and secondary ions to reach the wall surface of the Faraday cup,
Furthermore, even when the implanting object is charged with ionic charge (positive charge) due to the generation of secondary electrons, the magnetic field line
Secondary electrons reach the object to be implanted, and the effect of suppressing charging can be expected.

〔The invention's effect〕

As described above, according to the present invention, it is possible to use the structure of the Faraday cup itself or an auxiliary magnetic field for the Faraday cup without using the conventionally proposed Faraday cup composed of the negative potential inner cylinder and the positive potential outer cylinder. By adding, the gas at the time of ion implantation is released while trapping secondary electrons and secondary ions,
It is possible to solve various problems caused by the generation of gas generated from an object to be ion-implanted and provide a highly accurate ion-implanting device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a partially enlarged cross-sectional view, FIG. 3 is an explanatory view schematically showing the magnetic field action given to charged particles, and FIG. 4 is a configuration diagram showing an example of a conventional ion implantation apparatus. 2 ... ion beam, 7 ... implant, 20 ... Faraday cup, 21 ... annular shield, 22 ... bent exhaust passage, 23 ... magnet, 24 ... magnetic field.

Claims (3)

[Claims] 1. An ion implanter in which an object to be implanted is arranged in a Faraday cup, and an ion beam is introduced into the object to be implanted from a beam entrance of the Faraday cup to implant ions, wherein the Faraday cup comprises: It is composed of an annular shield plate assembly in which a large number of annular shield plates whose cross section is bent in a "dogleg" shape are arranged in a cylindrical shape with a gap that does not allow the outside to be seen, and the gap between these annular shield plates. An ion implanting device, further comprising a bent passage for releasing a gas generated in the Faraday cup during ion implantation to the outside. 2. The ion implanting apparatus according to claim 1, wherein a magnet for forming a magnetic field around the Faraday cup is arranged around the Faraday cup. 3. A magnetic field line of a magnetic field formed by the magnet is oriented in the same direction as the ion beam, and a part of the magnetic flux is set so as to overlap with a passage path of the ion beam. Item 2. The ion implanter according to item 2.