JPH04319243A - Ion-implantation apparatus - Google Patents

Abstract

PURPOSE:To discharge remaining gas using an intense magnetic field of a mass spectrometer in an ion-implantation apparatus. CONSTITUTION:In an ion-implantation apparatus wherein various kinds of ions taken out of an ion source 6 are led to pass a mass spectrometer 12, and a desired ion is separated by the function of a magnetic field 38 of a magnet 10 here and implanted in an object to be treated, a large number of ion pumps 30 are installed in the inner wall of a chamber 31 of the mass spectrometer 12 and remaining gas is discharged by chemical adsorption and sputtering function while using the magnetic field 38.

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.

0002

2. Description of the Related Art Ion implantation equipment is used as an equipment for introducing impurities in the manufacturing process of semiconductor devices because it is possible to introduce impurities with precision and can be processed while keeping track of the number of ions. This ion implanter converts a gas such as a halide into a plasma state, extracts it by applying an electric field with an electrode installed in the middle, and then removes impurity ions by applying a predetermined magnetic field to the extracted beam. Mass spectrometry is performed to extract only predetermined ions, and the energy of the extracted ions is increased or decreased before being implanted into the object to be processed.

To explain this specifically based on FIG. 4, the ion implantation apparatus 2 has a gas box 4, and the gas in the gas box 4 is brought into a plasma state by an ion source 6 and ionized. taken out. The extracted ion beam B is accelerated and passes through a variable slit 8, and then passes through a mass analyzer 12 having a strong magnet 10, where only predetermined necessary ions are extracted and impurity ions are eliminated. . After passing through the mass slit 14, the extracted ions are further accelerated or decelerated in the acceleration tube 16 to have a predetermined energy, and are sent to the processing target attached to the wafer disk 22 in the disk chamber 20. injected into the body. Here, since the degree of vacuum has a great influence on the performance of the ion implanter, the ion source 6
, the mass slit 14 and the disc chamber 20 are each equipped with, for example, an oil diffusion pump 24, 1000 l/
A turbo molecular pump 26 and a cryopump (not shown) with a capacity of
It is maintained at a high vacuum of -6 Torr.

0004

[Problem to be Solved by the Invention] By the way, the maximum amount of ions that can be extracted from a unit area is limited by the space charge effect.
That is, in order to extract a large amount of ions, in order to increase the extraction area, the widths of the slit provided on the ion source 6 and the variable slit 8 are widened, and a large amount of gas is supplied to the ion source 6. I have to, but
When the width of the slit 8 is widened, the gas that is not turned into plasma on the ion source 6 side flows out to the mass spectrometer 12 side through the variable slit 8, even though the oil diffusion pump 24 is provided to create a vacuum. It becomes a trend. In addition, since the gas pressure on the ion source 6 side decreases due to the outflow of this gas, a larger amount of gas must be supplied in order to maintain the gas pressure and maintain the plasma state. Even so, the amount of gas flowing downstream tends to increase.

[0005] In this way, when the degree of vacuum inside the mass spectrometer 12 decreases, this outflow gas and the extracted ions collide and exchange charges, and as a result, the original ions become neutral. This results in a state where normal ions and ions are mixed. Then, when an attempt is made to further increase or decrease the energy of these ions on the accelerator tube 16 side in the latter stage, those that maintain the ion state are electrostatically accelerated or decelerated to a predetermined value, but in the middle of the process, The ions that have become neutral through charge exchange are injected into the object to be processed, such as a wafer, at the same speed without being accelerated or decelerated. There is an improvement in that a mixture of those with energy and those with unexpected energy are injected, resulting in so-called energy contamination.

[0006] Furthermore, a part of the ion beam bent by the mass spectrometer 12 collides with the chamber wall, and as a result, gas molecules are released and the internal vacuum level is deteriorated, or the residual gas molecules may become ion beams. This method has an improvement in that not only does the collision with the beam cause beam loss, but also that gas molecules are ionized due to the collision and are injected into the object to be processed as impurities. In order to solve this problem, it may be possible to provide a separate vacuum pump such as a cryopump in the mass spectrometer 12, which occupies a relatively large area.
However, since this part is equipped with a magnet 10 that generates a strong magnetic field, the vacuum pump cannot be installed because there is no extra space and the voltage is maintained at a high voltage. In particular, an early solution is desired for this type of ion implantation device, which requires a large current. The present invention focuses on the above problems, and
The present invention was devised to effectively solve this problem, and an object of the present invention is to provide an ion implantation device that can remove residual gas by using the magnetic field of a mass spectrometer.

[0007]

[Means for Solving the Problems] The present invention was made based on the finding that an ion pump can be constructed by utilizing the strong magnetic field generated by the magnet of a mass spectrometer. . In order to solve the above problems, the present invention passes various ions extracted from an ion source through a mass spectrometer equipped with a magnet to separate predetermined ions, and then separates the separated ions to be processed. In the ion implantation device for injecting into the body, the mass spectrometer is configured to form an ion pump using a magnetic field generated by the magnet.

[0008]

[Operation] Since the present invention is configured as described above, the magnetic field generated by the magnet of the mass spectrometer acts on the residual gas in the mass spectrometer, and this residual gas is adsorbed by the ion pump and removed. Become.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an ion implantation apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. The same parts as those in the device shown in FIG. 4 are given the same reference numerals. The overall configuration of the ion implantation apparatus according to the present invention is similar to that of the apparatus shown in FIG. 4, and the difference is that an ion pump 30 is formed in the mass spectrometer 12, as shown in FIG. Specifically, the mass spectrometer 12 has a chamber 31 formed in an L-shape, for example, about 1 m in length and width. The beam inlet 34 of the mass spectrometer 12 is connected to the ion source 6 and the oil diffusion pump 24 (see FIG. 4) in order to convert gases such as halides and phosphine into plasma, ionize them, and take them out. The beam exit 36 is connected to the acceleration tube 16 and turbo molecular pump 26 for accelerating or decelerating the ion beam B to a desired energy, and the size of the beam exit 36 is, for example, 30 cm in width.
The height is set to about 10cm. A strong magnet 10 is attached to surround the L-shaped chamber 31, and in the illustrated example, forms a strong magnetic field 38 of, for example, several K Gauss, directed perpendicular to the plane of the paper. It is configured so that it can be done. Therefore, the ion beam B introduced from the beam entrance 34 is bent approximately 90 degrees under the influence of the magnetic field 38 and exits from the beam exit 36.

[0010] The mass spectrometer 12 configured as described above includes:
The ion pump 30 described above will be provided. A large number of ion pumps 30 are arranged along the path of the ion beam B in the chamber 31 at locations where they do not interfere with the ion beam B (see FIG. 2). In actual arrangement, a plurality of ion pumps 30 are assembled into a module, and a plurality of these modules are installed adjacently in the chamber 31 and assembled so as to be electrically connected to each other. As is well known, the configuration of the ion pump 30 is as shown in FIG. For example, a pair of cathodes 42, 42 made of titanium is provided, and between these anodes 40 and cathodes 42, for example, 1 to 10K
It is configured to apply a DC power source 44 of about V. When a strong vertical magnetic field 38 is applied to such an ion pump, for example in a high vacuum of 10-3 to 10-10 Torr, the getter material sputters to form a new active film due to discharge within the magnetic field, and at the same time the generated ions It is structured so that it can also adsorb neutral molecules.

Therefore, when installing the ion pump 30, the magnetic field 38 generated by the magnet 10 of the mass spectrometer 12 is
is formed along the longitudinal direction of the cylindrical anode 40 of the ion pump 30. Further, although an ion pump normally requires a magnetic flux of 1K Gauss or more, the magnetic flux generated by the magnet 10 is, for example, about 5K Gauss, which is well within the operating range.

Next, the operation of this embodiment configured as above will be explained. First, by driving each vacuum pump of this ion implantation device, such as the oil diffusion pump 24 and the turbo molecular pump 26, the inside of the device is maintained at a predetermined vacuum state, and the ion beam B extracted from the ion source 6 is After passing through the variable slit 8, the ions are introduced into the mass spectrometer 12, where the direction is changed by 90 degrees under the action of the magnetic field 38 to extract only the desired ions, and the extracted ions are further accelerated or decelerated in the acceleration tube 16. and inject it into the object to be processed inside the disk chamber 20. Here, gas that has not been turned into plasma flows out from the ion source 6 side through the variable slit 8 to the mass spectrometer 12 side, or some of the ion beams collide with the chamber wall, causing gas molecules to In the chamber 31,
Although residual gas tends to remain, in the present invention, since a large number of ion pumps 30 are provided, the residual gas is removed. That is, as shown in FIG. 3, a vertical magnetic field 38 generated by the magnet 10 of the mass spectrometer 12 is applied to each ion pump 30, and electrons 46 generated by cold cathode discharge are wound around the magnetic field 38 and move in a spiral manner. These electrons collide with the residual gas molecules 48 existing in the space and ionize the gas molecules. At this time, the ejected electrons are again wrapped around the magnetic field 38 and repeat the same movement. Therefore, at the beginning of the movement, the number of electrons is small, but
After a certain period of time, a considerable number of electrons exist and the level reaches a certain level.

On the other hand, the ions 50 generated from the gas molecules due to the collision are powered by a DC power source 44, for example, at 5KV.
Accelerated by an electric field, the particles collide with a cathode 42 made of a getter material such as titanium and sputter it, forming an active sputtered titanium film with a strong chemical adsorption effect on the surface of the cathode 42 and the anode 40. As a result, neutral gas molecules present in the space collide with this active sputtered film and are chemically adsorbed, thereby exhibiting an exhaust effect. Since the cathode 42 is constantly sputtered, a new sputtered film is always formed on the anode 40 and the cathode 42, and the exhaust performance does not deteriorate. Furthermore, when the ions 50 collide with the cathode 42, the gas molecules adsorbed on the surface of the cathode 42 are knocked into the interior of the cathode 42, thereby exhibiting an exhaust effect. In this way, a large number of ion pumps 30 that utilize the strong magnetic field from the magnet 10 are incorporated into the mass spectrometer 12, so that the chambers, which conventionally had small conductance and could not be fully pumped by the oil diffusion pump 24 or the turbomolecular pump 26, can be used. The residual gas in the chamber 31 can be exhausted by chemical adsorption, and it becomes possible to raise the degree of vacuum by one order of magnitude or more, for example, from the conventional limit of 10-6 Torr to 10-7 Torr.

Since the degree of vacuum can be improved in this way, it is possible to eliminate energy contamination as shown in the graph of FIG. That is, FIG. 5 shows the concentration of implanted boron with respect to the depth of the wafer as the object to be processed. In order to extract a large amount of ions, a high voltage is applied during extraction, and then the implantation is performed with the energy decelerated to a predetermined level. It is. As shown in the figure, the solid line a obtained in this example shows the case where ion implantation was performed in a high vacuum of about 10-7 Torr, and only one peak appeared at a depth of 0.1 μm, indicating ideal characteristics. However, as the degree of vacuum deteriorates as indicated by the wavy lines b and c, a second peak appears, and the second peak value becomes larger, indicating that the characteristics deteriorate.

In the above embodiment, a large number of ion pumps 30 are arranged on both sides of the path of the ion beam B, which is most effective since ions travel only in a straight line, but the present invention is not limited to this. , may be provided on all the upper and lower sides of the inner wall of the chamber 32. Furthermore, it can be applied not only to ion implantation equipment but also to any high vacuum equipment that uses a magnetic field, such as ECR (Electron Cyc
It can also be applied to lotron Resonance) devices.

[0016]

[Effects of the Invention] As described above, according to the present invention, the following excellent effects can be exhibited. The remaining gas in the chamber of the mass spectrometer, which could not be removed by conventional vacuum pumps, can be evacuated using chemical adsorption, making it possible to maintain a high vacuum inside the chamber. Therefore, it is possible not only to suppress the occurrence of energy contamination and obtain a processed object with good characteristics, but also to reduce beam loss. Further, since it is possible to prevent impurity ions from being implanted into the object to be processed, it is possible to obtain an object to be processed with better characteristics than this point.

[Brief explanation of drawings]

FIG. 1 is a top sectional view showing a mass spectrometer of an ion implanter according to the present invention.

FIG. 2 is a sectional view taken along line AA in FIG. 1;

FIG. 3 is a configuration diagram showing an ion pump used in the present invention.

FIG. 4 is a top sectional view showing a conventional ion implantation device.

FIG. 5 is a graph showing the relationship between wafer depth and boron concentration when the degree of vacuum is changed.

[Explanation of symbols]

6 Ion source 10 Magnet 12 Mass spectrometer 30 Ion pump 31 Chamber 38 Magnetic field 40 Anode 42 Cathode B Ion beam

Claims (1)

[Claims] 1. An ion implantation apparatus that passes various ions extracted from an ion source through a mass spectrometer having a magnet to separate predetermined ions, and injects the separated ions into an object to be processed. An ion implantation device characterized in that an ion pump using a magnetic field generated by the magnet is formed in an analyzer.