JPS632653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion implantation apparatus that accelerates target ions to high energy and implants them into a substance (object to be processed).

2. Description of the Related Art In the manufacture of semiconductor devices and the like, there is a process of implanting conductivity type determining impurities such as boron, phosphorus, arsenic, etc. into semiconductor thin plates (wafers) as ions, and an ion implantation device is generally used for this process. As shown in Figure 1, this ion implantation device extracts three ion beams from an ion source using two extraction electrodes.Generally, in the ion source, ion species other than the target ions are also generated at the same time. Therefore, the extracted ion beam number 3 contains, for example, five types of ions, which are separated into five types from 5-1 to 5-5 by means of magnetic field analysis in the next 4 ion beam analysis section. Now, if the ion beam of 5-3 is the target ion, then 5-1,
5-2 is an ion beam with a smaller mass than this and is deflected greatly by the magnetic field, and ion beams 5-4 and 5-5 are ion beams with a larger mass than the target ion beam and are deflected slightly. 5
-6 shows the neutral particle beam generated in the ion extraction section. The ion beam separated in this way collides with the tube wall of the magnetic field analysis tube as shown in 5-1 and 5-5, and is blocked by the slit 6 as shown in 5-2 and 5-4. In the end, only the target 5-3 ion beam is taken out, enters the next 7 acceleration tube, and is accelerated to the target energy. This accelerated ion beam is 8 and 9
The ion beam is electrically scanned in the X and Y directions by the ion beam scanning electrode, and expanded so that the ions are uniformly implanted over the entire surface of the silicon wafer to be implanted. What is noteworthy here is the neutral particle deflection plate No. 10, which is used when the ion beam passes through an accelerator tube, etc., and high-speed neutral particles that have lost their charge due to collision with residual gas fly away with the ion beam. In order to prevent the ion beam from being implanted into the silicon substrate, the ion beam is deflected at an angle of about 7 to 10 degrees in the direction of travel.
-2 high-velocity neutral particles. The ion beam 11-1 separated in this way is implanted into the silicon substrate 13, while the neutral particle beam 11-2 separated from the ion beam collides with the deflection plate 10, If this deflection plate were not provided, neutral particles would be locally concentrated and blocked. The ion implantation method shown in FIG. 1 is generally used in an ion beam implantation device with an ion beam current of up to about 500 μA.
The ion beam is also scanned by a magnetic field. This method of scanning the ion beam by electric field scanning or magnetic field scanning is called electrical scanning, and is contrasted with mechanical scanning, which will be described next.

FIG. 2 shows a method applied to a relatively large ion beam implantation device with an ion beam current of 1 mA or more. The principle from the ion source 1 to the acceleration tube 7 is the same as in Figure 1. However, the only difference is the structure of the ion source 1 to generate a large current. The ion beam accelerated in the acceleration tube is directly implanted into the silicon wafer on the next cylindrical rotating implantation part, and the ion beam is rotated in the X and Y directions by the electric field as in the case of Fig. 1. not be scanned by
There are two reasons why this electrical scanning is not performed. One is due to the inherent properties of the ion beam. When the beam current reaches 1 mA, the electrons generated when the residual gas is ionized are transferred into the ion beam. It is thought that the ion beam is taken in and becomes an ion beam in a state of so-called "beam plasma." When an electric field is applied to this, the electrons taken in are slow, so they flow toward the positive electrode side of the applied electric field, creating a very large load on the electrode, making scanning impossible in some cases. In addition, the ion beam whose electrons are absorbed in this way generates a positive space charge and causes the beam to diverge, making it impossible to maintain the beam focus on the implanted silicon substrate, which is necessary for uniform beam scanning. This is due to reasons such as. The above describes scanning using an electric field among electrical scanning methods.
This is not the case with magnetic field scanning, but it is not commonly used due to cost and complexity. Another reason is heat generation. When a large amount of ion beam is implanted onto a single silicon substrate (13 in Figure 1) and the implantation energy is converted into heat, the temperature of the silicon substrate will rise excessively. This is because it interferes with the element manufacturing process.

Therefore, if the implanted ion beam current exceeds 1 mA, for example, the second
As shown in FIG. 14, a large number of silicon substrates are pasted onto the rotating body implantation part on a cylinder numbered 14,
As shown in Figure 2, the ion beam is rotated around its axis and moved left and right at the same time, so that even if the ion beam is fixed, the ion beam effectively scans uniformly over the many silicon wafers attached. That's what I do. At the same time, the generated heat is applied to a rotating cylinder with a large surface area and heat capacity, which has the effect of not causing a rise in the temperature of the silicon substrate. This scanning of the implanted substrate without scanning the ion beam is called mechanical scanning. In this case, the high-speed neutral particle beam that caused the problem in FIG. 1 will naturally be generated, and this beam will be implanted into the cylindrical silicon substrate. However, in this case, since the ion beam is also fixed, the high-speed neutral particle beam is uniformly dispersed and implanted into multiple silicon substrates, and the proportion of this is considerably less than 1% of the total implantation amount, as shown in Figure 1. Neutral particles will not be locally concentrated as would be the case if beam deflection was not performed.

In this way, the scanning method used for uniform implantation differs between electrical scanning and mechanical scanning depending on the magnitude of the ion beam current used. Recently, the application of ion implantation to semiconductor device manufacturing processes has become more popular, and in particular, for the formation of high-concentration junctions, a method of implanting with a beam current of 1 mA or more, as shown in Figure 2, is increasingly being used. Ta. Along with this, as the number of applications for this high-concentration implantation increases, many cases have come to be discovered that are extremely inconvenient and unfavorable in terms of semiconductor device manufacturing under the current state. This is contamination of the silicon substrate by movable impurity ions such as sodium, which is caused by high-concentration ion implantation. As a result of research, the cause of this contamination was found to be due to the following causes.

(1) Substances containing very large amounts of sodium, etc. (mainly substances mainly composed of hydro and carbon) from the extraction part of the ion source in Figs. 1 and 2 to the analysis tube parts 4 and 6 and the slit part. is attached.

(2) This hydrocarbon is caused by oil that is decomposed and attached to the ion beam due to back diffusion from the vacuum pump that exhausts the ion source.
Sodium, etc. adsorbed to this part are released from the constituent materials of the ion source, especially the filament, etc. due to heating during discharge, and trace amounts of sodium adhering to the vacuum pump may accumulate in this part over time. Various studies have shown that this accumulation and concentration, which is considered to be accumulation and concentration, reaches a non-negligible amount in about 3 to 6 months under normal usage conditions of the device.

(3) If this ion implantation device is operated in such a state, the ion beam will collide with the inside of the magnetic field analysis tube as shown in Figures 5-1 and 5-5 in Figures 1 and 2, causing damage to the inside of the analysis tube. Contaminants containing sodium etc. attached to the tube are spattered, or the analysis tube is heated due to the collision of the ion beam and the temperature rises, causing this contaminant to evaporate, resulting in a considerable concentration of contaminants in the analysis tube. Therefore, in this state, diffusion occurs in the ion implantation area on the high vacuum side due to the difference in density between the inside and outside of the slit hole 6.

(4) Figure 3 shows this state after the 6th slit, and in addition to the target ion beam 5-3, there are 14 cylindrical rotary body implanting parts that implant ions through the 6th slit 15. This ion implantation area shows that “contaminants including sodium etc.” have arrived at ~1×
Since it is evacuated to an extremely high vacuum of about 10 ^-7 Torr, it is assumed that this material will travel straight because the distance between the slit hole 6 and the rotating body implantation part of the mechanical scanning 14 is much shorter than the mean free path. good. However, since this substance is only diffused, it has only a small amount of thermal energy.

(5) The material that has arrived at the implantation area 14 in this way reaches and adheres to this surface, causing contamination such as sodium, but the ion beam does not irradiate the implantation area 14, including the silicon substrate. The surface is then activated by the ion beam, further increasing the deposition rate of this substance.

As mentioned above, in the ion implantation method with the configuration shown in Figure 2, in addition to the ion beam and neutral particles, as shown in Figure 8, "contaminants including sodium etc." (hereinafter also abbreviated as contaminants) are ejected from the analysis tube section. It has become clear that the ion implantation element is blown away by thermal kinetic energy and adheres to the surface of the ion implantation element, causing contamination with sodium and the like. Particularly, it has become clear that the area that is irradiated with the ion beam adsorbs a large amount of this contaminant. This is of course the first
This occurs in the configuration shown in the figure, but the amount is relatively small.
This is because the configuration shown in Figure 1 has a small amount of ion beam, so the amount of spatter or evaporation is smaller than that of the analysis tube section, and also because the ion beam deflection plate 10 is used to remove neutral particles. Here, since it has the effect of blocking to some extent,
This is because the amount of contaminants that fly to the silicon substrate 13 for ion implantation is small. However, various experiments have revealed that this contaminant accumulates in the ion beam deflector when used for a long time, and this contaminant is spattered by the ion beam and neutral particles, causing contamination of the silicon substrate used for ion implantation. It has also been found to cause Since neutral particles have almost the same energy as the ion beam, this deflection plate either blocks the neutral particles by shooting them into the deflection plate, or removes most of their energy when reflecting them. Since the primary purpose is to reduce the energy to an extremely weak level that can be ignored even if it reaches the substrate, the configuration is not necessarily suitable for blocking contaminants containing sodium, etc. This is because it is useless against spatter and re-evaporation.

Is the current configuration shown in Figures 1 and 2 ineffective against contamination with sodium, etc.?
Or talked about less. When considering solutions to this problem, the following can be considered.

(1) Evacuate the ion beam analysis section to prevent contamination with sodium, etc. (for example, an exhaust pump is installed in the processing chamber where the ion source section, analysis section, and implantation section are located). Use a cryopump, terpo molecular pump, etc., and be very careful not to use sodium, etc. in the constituent materials of the ion source. This measure is considered to be effective to some extent. However, it is nearly impossible to eliminate the opportunity to come into contact with sodium, etc. during various handling processes, and as mentioned in the section on causes, no matter how much you try to avoid contact with sodium, etc., a small amount of sodium, etc. can accumulate in the analysis tube. Even if there is an effect of prolonging the time during which this occurs, it is impossible to prevent the accumulation. Therefore, it is difficult to provide a concrete solution. However, many commercially available devices actually use cryopumps.

(2) An exhaust pump is installed in the slit section and analysis tube section where contaminants are generated to quickly exhaust the generated contaminants, and the exhaust pump is also used in the processing chamber on the ion implantation section side to provide a powerful exhaust system. Exhaust. However, due to the structure of the apparatus, the slit section, analysis tube section, etc. are located at high positions, making it difficult to directly attach a large and heavy exhaust pump. For this reason, it is desirable to make the exhaust pump disposed in the processing chamber of the ion implantation part more powerful. However, since a slit consisting of a small hole is provided between the processing chamber of the ion implantation section and the analysis tube section, the exhaust efficiency is poor. Therefore, it is possible to narrow down the ion beam without reducing the vacuum conductance by forming the slit by combining several slit plates arranged in series.

Accordingly, an object of the present invention is to provide an ion implantation apparatus that can prevent contamination of a workpiece.

In order to achieve such an object, the present invention analyzes ions emitted from an ion generation section in an analysis section, narrows down only desired ions using a slit, accelerates them, and guides them to an ion implantation section. In an ion implantation device for implanting desired ions into the surface of a workpiece disposed in a section, an exhaust pump with a large displacement is disposed in the vicinity of the slit and in a processing chamber in which the ion implantation section is disposed. , the slit is made up of several slit pieces arranged in series that partially block the conduit, and is configured such that a narrow aperture hole through which ions pass is formed only when all the slit pieces are overlapped. The present invention will now be explained with reference to Examples.

FIG. 4 is a schematic diagram of an ion implantation apparatus according to an embodiment of the present invention. In this embodiment, in the high output ion implantation apparatus shown in Fig. 2, two exhaust pumps _P4 and _P5 are installed in addition to the conventional exhaust pumps _P1 to _P3 , and a slit It is made up of two slit pieces as shown in FIG. That is, the entire device is covered with a cover 16 that forms each chamber, and the inside of the cover forms a vacuum system. Inside the cover 16, along the ion flying direction,
An ion source 1, an extraction electrode 2, an ion beam analysis section 4, a conduit 17 equipped with a slit 6, an acceleration tube 7,
A processing chamber 18 in which the driving section 14 is arranged is provided. Further, exhaust pumps P ₁ and P ₂ are provided on the ion source side and the upper part of the ion beam analysis section 4, respectively, and a pipe line 1 near the slit 6 is provided.
7 and analysis section 4 where ion beams collide violently.
Exhaust pumps P ₄ and P ₅ are installed on the wall.
Further, the processing chamber 18 is also provided with an exhaust pump _P3 . These exhaust pumps P ₁ to _{P 5} are oil-free cryopumps or turbo molecular pumps. For this reason, processing chamber 1
8. There is no oil diffusion into the analysis section 4, and contamination is reduced. Further, P ₃ to _{P 5} have a large displacement (evacuation capacity), making it easy to maintain a vacuum inside the cover.

On the other hand, as shown in FIG. 5, the slit 6 provided in the conduit 17 consists of two semicircular slit pieces 19, and a thin semicircular notch hole 20 is provided in the center of the semicircle. It is being Further, both slit pieces 19 are fixed to the inner wall of the pipe at a distance from each other. At this time, both slit pieces 19 are arranged at 180 degree intervals, and when both are overlapped in this state, a small hole is formed by both notches 20. The desired ions pass through this hole.

According to such an ion implantation device, since oil and the like do not diffuse from the exhaust pump, there is little contamination of the vacuum system. In addition, contaminants such as impurities contained in the ion source, etc. that adhere to the inner walls of the analysis section and the slit, and contaminants generated by ions colliding with these or by thermal evaporation, can be removed by exhaust gas with a large exhaust volume. Since the pumps P ₄ and P ₅ quickly exhaust the air, contamination of the analysis section and contamination of the processing chamber by impurities diffused from the analysis section into the processing chamber is reduced. Furthermore, the processing chamber is always kept at a high degree of vacuum, that is, at a high degree of cleanliness, by an exhaust pump with a large displacement. Therefore, contamination of the wafer (workpiece) is extremely low. Moreover, since each slit piece is semicircular, approximately half of the cross-sectional area of the conduit is open. Therefore, the gas flow is better than in the conventional slit, and the degree of vacuum in the analysis section is improved, that is, the cleanliness of the analysis section is improved.

Note that the present invention is not limited to the above embodiments. For example, the number of slit pieces may be increased to improve the vacuum conductance.
In other words, by making three slit pieces with an angle slightly over 120 degrees and arranging the slit pieces at 120 degree intervals, approximately 2/3 of the pipe cross section can be
can be used as a flow path for vacuuming.

As described above, according to the ion implantation apparatus of the present invention, contamination of the object to be processed can be prevented. Therefore, if applied to the manufacture of semiconductor devices, semiconductor devices with excellent characteristics can be manufactured.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of a conventional ion implantation device, and FIG. 3 is an explanatory diagram similarly showing a contaminated state.
FIG. 4 is a schematic diagram of an ion implantation apparatus according to an embodiment of the present invention, and FIG. 5 is a schematic perspective view showing a slit. 1... Ion source, 2... Extraction electrode, 3... Ion beam, 4... Ion beam analysis section, 5...
Analyzed ion beam (from 5-1 to 5-5),
6... Slit, 7... Accelerator tube, 8... X direction scanning electrode, 9... Y direction scanning electrode, 10... Deflection plate for neutral particles, 11-1... Deflected ion beam, 11- 2... Neutral particle beam, 13... Silicon substrate, 14... Cylindrical rotating body implantation part, 15
...Diffusing substances containing sodium, etc., 16...
Cover, 17...Pipeline, 18...Processing chamber, 19...
...Slit piece, 20...Notch hole.

Claims (1)

[Scope of Claims] 1. The ions emitted from the ion generation section are analyzed by the analysis section, and only the desired ions are narrowed down with a slit and are accelerated and guided to the processing chamber where the ion implantation section is installed. In an ion implantation device for implanting desired ions into the surface of a workpiece disposed in a section, an exhaust pump with a large displacement is disposed in the vicinity of the slit and in a processing chamber in which the ion implantation section is disposed. , the slit is comprised of several slit pieces arranged in series that partially block the conduit, and is configured such that a narrow aperture hole through which ions pass is formed only when all the slit pieces are overlapped. Ion implantation equipment. 2. The ion implantation apparatus according to claim 1, wherein the exhaust pump is an oil-free vacuum pump such as a turbo molecular or cryopump.