JPH04267044A - Ion implanter - Google Patents

Abstract

PURPOSE:To decelerate the ion speed in the high-vacuum area and suppress the generation of high-energy neutral particles by providing ion deceleration electrodes in a space exhausted by a high exhaust pump between a mass spectrometer and a post-deflection accelerator. CONSTITUTION:A space formed between a mass spectrometer 3 and a target 5 is kept vacuum via an exhaust hole 7. The ion speed is decelerated to a preset value by electrodes 10, 11 provided in the space, and ions fed to the target 5 are controlled to the preset speed by a post-deflection acceleration section 8. The running distance is shortened when ions are decelerated, ions are decelerated in the proper-vacuum area, thus the collision probability between ions and residual gas is decreased, and the generation of neutral particles can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus capable of implanting low energy ions to form a shallow PN junction in a semiconductor substrate.

Ion implantation is widely applied to the formation of PN junctions in VLSI manufacturing processes because of its excellent controllability regarding the implantation depth and concentration of impurities into an implanted target such as a semiconductor substrate. conventionally,
For example, boron (B), phosphorus (
Impurity ions such as P) and arsenic (As) were implanted into the silicon substrate to form a PN junction with a depth of about 0.3 μm, but in order to form a shallow PN junction of about 0.1 μm required for VLSI, For this reason, technology for implanting impurity ions with low energy of about 10 KeV has become important.

0003

[Prior Art] Normally, an ion beam for ion implantation consists of an ion source that generates impurity ions consisting of a desired element or molecule, an extraction electrode (pre-acceleration electrode) for extracting ions from the ion source, and a desired mass and mass. After passing through a post-acceleration section that includes a magnet forming a mass spectrometer for extracting charged ions and electrodes for decelerating or accelerating the velocity of ions from the mass spectrometer to a predetermined value, the ions are transferred to the target semiconductor substrate. irradiated. This will be explained with reference to FIG.

[0004] That is, ions generated by the ion source 1 are transferred to an extraction electrode 2 disposed opposite to the ion source 1.
After being accelerated to 30 to 60 KeV (pre-acceleration), the ions are deflected by the magnetic field of the mass spectrometer 3, and only ion species having a desired charge pass through a slit (not shown) and enter the post-acceleration section 4. These ion species are decelerated or accelerated by a post-acceleration unit 4 and adjusted to a predetermined energy, and then transferred to a semiconductor substrate 5 such as a silicon wafer.
is injected into. At this time, the amount of implantation is controlled by measuring the current flowing through the semiconductor substrate 5. Note that the reference numeral 6 in the figure indicates a plurality of semiconductor substrates 5 into which ions are sequentially implanted.
This is a rotary support disk 6 on which a is mounted. Also, if the above-mentioned pre-stage acceleration voltage is lowered to about 20 KeV or less,
Since ions with sufficient beam current cannot be extracted from the ion source 1, the acceleration voltage is set within the above range.

[0005]

[Problems to be Solved by the Invention] When a voltage that decelerates ions is applied to the electrodes in the conventional post-acceleration section 4, there is a problem in that the controllability of the implantation depth of impurities deteriorates. The reason for this is thought to be as follows. That is, when ions collide with residual gas, charge transfer occurs and the ions become neutral particles. For example, boron ion (B+
), B+ + n → B0 + n+ where,
n represents a residual gas molecule, and B0 represents a neutralized boron ion.

Neutral particles B0 produced as described above
Since B is not decelerated in the rear acceleration section 4,
It maintains almost the same initial velocity as B+, and is therefore injected deeper than B+, which has been slowed down. FIG. 5 shows the results of an experiment conducted to confirm this phenomenon. The figure shows that B+, which has been pre-accelerated to 35KeV,
This is the profile of boron impurity in the silicon wafer when it is implanted after being decelerated to 5 KeV in the post-acceleration section 4, where the horizontal axis is the depth from the surface (nm) and the vertical axis is the boron concentration (atoms/cm3). ). In addition,
The injection amount at this time was 6×10 13 cm −2 . The parameter is the residual gas pressure immediately before the deceleration electrode of the post-acceleration section 4, and the pressure for sample 1 is 3.2 x 10-5 Torr.
In the case of sample 2, the pressure is 3.8 x 10-6 Torr.

As shown in the figure, in sample 1, 5
In addition to the main peak corresponding to B+ of KeV, 3
A sub-peak corresponding to B+ of 5 KeV exists at a position approximately 150 nm from the surface. On the other hand, in sample 2, this subpeak is not significant. From the area of this sub-peak, the residual gas pressure is 3.2×10
In the case of −5 Torr, it is estimated that approximately 0.7% of B+ is converted to B0 by the above mechanism. In this way, it is clear that a deep PN junction is formed by the neutral particles B0 which are hardly decelerated by the post-acceleration section 4.

In order to reduce the generation of neutral particles as described above, 1) lower the residual gas pressure in the space in which ions travel before deceleration; 2) shorten the distance in the space in which ions travel before deceleration; Either of the following measures can be considered. Regarding the former (2), exhaust devices are installed at various locations along the ion travel space. In particular, as shown in FIG. 6, a large-capacity turbomolecular pump (not shown) is generally connected between the mass spectrometer 3 and the post-acceleration section 4 through the exhaust hole 7.
is connected. However, the inside of the second-stage acceleration tube 4 is not structured to directly exhaust gas, and furthermore, gas leakage from the end station where the semiconductor substrate 5 and the support disk 6 are installed cannot be ignored.
The degree of vacuum is not necessarily high. On the other hand, regarding the latter ■,
The electrode of the post-acceleration unit 4, that is, the post-acceleration electrode 8, is located away from the mass spectrometer 3. This is because the density of the ion beam incident on the semiconductor substrate 5 can be maintained at a high level by having the latter stage acceleration electrode 8 close to the semiconductor substrate 5. Therefore, the distance traveled by the ions before deceleration has to increase. Note that in the figure, the reference numeral 31 is the injection slit 31 of the mass spectrometer 3.

As described above, in conventional ion implantation equipment, it is inevitable that the probability of collision between ions and residual gas increases, which causes the generation of high-energy neutral particles, which is a problem in low-energy ion implantation. .

It is an object of the present invention to provide an ion implantation device in which high-energy neutral particles generated by collisions between ions and residual gas are not implanted, and in particular, to provide an ion implantation device that does not implant high-energy neutral particles caused by collisions between ions and residual gas, and in particular, without losing versatility regarding ion acceleration and deceleration. An object of the present invention is to provide an ion implantation device having a structure capable of reducing the generation of neutral particles by shortening the space in which the ions travel and maintaining the degree of vacuum in this space at a high level.

[0011]

[Means for Solving the Problems] The above object is an apparatus for injecting atomic or molecular ions into a target to be processed, which comprises an ion source for generating the ions, and an ion source for generating the ions generated by the ion source. A mass spectrometer for analysis, a target into which the analyzed predetermined ions are injected, and a space defined between the mass spectrometer and the target in proximity to the mass spectrometer, the space The present invention is characterized by comprising a space provided with an exhaust hole for maintaining the ion in a vacuum, and an electrode provided in the space for decelerating the velocity of the analyzed ions to a predetermined value. This is achieved by such an ion implantation device.

0012

[Operation] An electrode used mainly for decelerating ions is provided in the space between the mass spectrometer and the post-accelerator, which is generally evacuated by a high exhaust pump. As a result, deceleration is performed in a region with a good degree of vacuum, so the probability of collision between ions and residual gas is reduced, and the generation of neutral particles as described above is reduced.

[0013]

[Embodiment] FIG. 1 is an explanatory diagram of one embodiment of the present invention.
Separately from the latter-stage acceleration electrode 8, an electrode 10 is installed. This space is maintained at high vacuum through the exhaust hole 7 by a turbo molecular pump (not shown), as in the conventional ion implanter. The electrode 10 is the latter acceleration electrode 8
Similarly, it has a structure supported by an insulator 9. Note that the second-stage accelerating electrode 8 usually includes a plurality of electrodes 81 arranged along the ion traveling direction as shown in the figure.
It has a multi-stage structure consisting of 82, 83, ...
A divided voltage is applied to these electrodes 81, 82, 83, . . . , and the electrode closest to the ion implantation target such as a semiconductor substrate is at the same potential as the support disk 6 (see FIG. ). For this reason, these electrodes 81, 82, 83, ...
They are electrically isolated from each other by an insulator 9.

[0014] In order to decelerate ions that have been pre-accelerated at 30 to 60 KV as described above to, for example, 5 KeV, +25 to 55 KV is applied to the electrode 10 relative to the extraction electrode 2 (see FIG. 4). . Note that usually
An electrode 11 is provided immediately in front of the electrode 10, and the same potential as the extraction electrode 2 is applied to the electrode 11. As a result,
The spatial distance through which ions are decelerated is shortened, reducing the frequency of collisions with residual gas. When deceleration is performed using the electrode 10, a weak reverse potential is applied to the second stage accelerating electrode 8 in order to converge the ion beam. On the other hand, when acceleration is also performed at the post-acceleration electrode 8 as in a normal ion implantation process, a weak reverse potential is applied to the electrode 10 to converge the ion beam.

As shown in FIG. 2, the space in which the electrode 10 is installed and the post-acceleration tube 4 surrounding the post-acceleration electrode 8 runs through a cylinder with an inner diameter of 200 mm and an exhaust pipe with a diameter of 200 mm provided close to the electrode 10. When exhausting through the hole 7 with a turbo molecular pump having a pumping speed of 1000 liters/sec, the effective pumping speeds at the positions of the electrode 10 and the post-acceleration electrode 8 are 90 liters/sec, respectively.
6 Liter/sec and 595 Liter/sec
sec. In an actual ion implanter,
Since the greatest amount of gas is released from the end station where the semiconductor substrate to be ion-implanted is installed, in the ion implanter of the present invention, the degree of vacuum in the region where deceleration is performed is lower than that in conventional ion implanters. This results in an improvement of approximately 1.5 times. In addition, the deceleration electrode 10 is inserted through the slit provided on the output side of the mass spectrometer 3.
The distance from the slit to the rear acceleration electrode 8 is approximately 1/4 of that from the slit to the rear acceleration electrode 8 in a conventional device. Therefore, according to the present invention, the probability of generating neutral particles due to collisions between ions and residual gas can be reduced to about 1/6 of that of conventional ion implanters.

[0016] Although the focusing ability of the ion beam is improved by deceleration by the electrode 10, in the present invention, in order to more efficiently transport slow ions to the semiconductor substrate,
We propose a configuration in which a magnetic field is applied to the ion travel space after the mass spectrometer 3. That is, as shown in FIG.
A magnet 20 surrounds the electrode 8 of the second stage acceleration tube 4 from
Place. The ion beam is focused by the magnet 20 by applying a coaxial magnetic field in the direction in which the ions travel.

The following configurations are possible for the magnet 20. That is, ■ a plurality of annular magnets whose central axes are arranged coaxially with the direction of ion travel and are separated from each other by insulators 9; including the case where these annular magnets constitute the tube wall of the post-acceleration tube 4; : ■Each annular magnet in ■ above, as shown in Figure 3(b),
A structure in which the ring magnet in the above ■ or the divided magnet in the ■ is divided in parallel to the traveling direction of the ions; For example, the one closest to the mass spectrometer 3 is an electromagnet, and the others are replaced with paramagnetic materials; ■ The above A ring magnet, a segmented magnet, or a paramagnetic material is placed in front of the semiconductor substrate 5 into which ions are implanted or on the support disk 6 (Fig. 4).
Reference) is additionally installed at the rear (on the opposite side of the rear acceleration tube 4 with respect to the support disk 6); and so on.

[0018] Since the second stage accelerator tube 4 is made of a non-magnetic material, it does not have any influence on the formation of the magnetic field as described above.

[0019]

[Effects of the Invention] According to the present invention, the degree of vacuum in the space in which mass-analyzed ions travel until they are decelerated is improved.
Additionally, because the distance in this space is shortened, the generation of high-energy neutral particles due to collisions between ions and residual gas is reduced, making it possible to form shallow junctions using low-energy ion implantation. As a result, it has the effect of promoting the practical application of high-density integrated circuits.

[Brief explanation of the drawing]

[Fig. 1] An explanatory diagram of a structural example of the ion implantation device of the present invention

[Figure 2] Explanatory diagram for improving the degree of vacuum in the ion deceleration space in the present invention

[Fig. 3] An explanatory diagram of another structural embodiment of the ion implantation device of the present invention

[Figure 4] Diagram explaining the basic configuration of the ion implantation device

[Figure 5
] Diagram explaining the injection phenomenon of high-energy neutral particles in deceleration ion implantation

[Figure 6] Diagram explaining problems in deceleration ion implantation using conventional equipment

[Explanation of symbols]

1 Ion source
8 Post-acceleration electrode 2 Extraction electrode
9 Insulator 3 Mass spectrometer 10 Electrode 4 Post-acceleration tube
11 Electrode 5 Semiconductor substrate
20 Magnet 6 Support disk
31 Injection slit 7 Exhaust hole

Claims (6)

[Claims] 1. An apparatus for injecting atomic or molecular ions into a target to be processed, comprising an ion source 1 for generating the ions, and a mass spectrometer for analyzing the ions generated by the ion source 1. a target 5 into which the analyzed predetermined ions are implanted, and the mass analyzer 3.
A space defined near the mass spectrometer 3 between the target 5 and the target 5, and a space provided with an exhaust hole 7 for maintaining the space in a vacuum, and the velocity of the analyzed ions. An electrode 1 provided in the space to reduce the speed to a predetermined value.
0. An ion implantation device characterized by comprising: 0. 2. A post-acceleration section 8 is provided between the electrode 10 and the target 5 for controlling the velocity of the ions entering the target 5 to a predetermined value. 1. The ion implantation device according to 1. 3. The ion implantation apparatus according to claim 1, wherein the electrode 10 is arranged closer to the mass spectrometer 3 than its support. 4. The ion implantation apparatus according to claim 1, further comprising means 20 for applying a coaxial magnetic field to the path of the analyzed ions. 5. The magnetic field applying means 20 is configured to apply a magnetic field to the electrode 10.
5. The ion implantation apparatus according to claim 4, further comprising a plurality of magnets arranged around the post-acceleration section. 6. A method for manufacturing a semiconductor device, comprising the step of implanting ions decelerated to a predetermined speed by the electrode 10 into the target 5 in the ion implantation apparatus according to any one of claims 1 to 5. .