JPH0125187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion implantation device that accelerates target ions to high energy and implants them into a material. The present invention relates to an ion implantation device for implanting conductivity type determining impurities such as boron, phosphorous, hisso, etc. as ions to perform desired doping.

First, the currently used method and apparatus that are the basis of the present invention will be described.

In Fig. 1, an ion beam numbered 3 is extracted from an ion source numbered 1 using an extraction electrode numbered 2.Generally, in an ion source, ion species other than the target ions are simultaneously generated, so the extracted ion beam numbered 3 is as follows: For example, it contains five types of ions. This is separated into five types from 5-1 to 5-5 by means of magnetic field analysis in the next four Ikan beam analysis sections.
Now, if the ion beam 5-3 is the target ion, ions 5-1 and 5-2 have smaller masses and are largely deflected by the magnetic field, and the ion beams 5-4 and 5-5 are the target ions. Reference numerals 5-6 shown here indicate neutral particle beams generated at the ion extraction portion, which are slightly deflected by the ion beam having a mass larger than the beam. The ion beams separated in this way collide with the tube wall of the magnetic field analysis tube as shown in 5-1 and 5-5, and 5-2 and 5
Some ion beams, such as -4, are blocked by the slit 6, and in the end, only the target ion beam 5-3 is taken out, enters the next acceleration tube 7, and is accelerated to the target energy. This accelerated ion beam is electrically scanned in the X and Y directions by ion beam scanning electrodes 8 and 9, and is 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 by about 7 to 10 degrees in the direction of movement as an ion beam 11-1, and is separated from the high-speed neutral particles 11-2. 11 separated in this way
The ion beam -1 is implanted into the silicon substrate 13, while the ion beam 11- is separated from the ion beam.
The 2 neutral particle beams collide with the 10 deflection plates and are blocked by being driven into the deflection plates.
If there is no deflection plate, neutral particles will be locally concentrated and implanted. In the ion implantation method shown in Figure 1, the ion beam current is
Commonly used in ion beam implantation equipment up to about 500μA. 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 discussed next.

Figure 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 is the same as in Figure 1 from the ion source 1 to the acceleration tube 7. The only difference is the structure of the ion source 1 to generate the current, and the ion beam accelerated in the acceleration tube 7 in FIG. The ion beam is implanted into the silicon wafer above, and the ion beam is not scanned in the X and Y directions by an electric field as in the case of Figure 1.
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, it effectively scans the ion beam uniformly over the multiple 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 first
The high-speed neutral particle beam that was the problem in the figure is naturally generated, and this beam is 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 this ion implantation to the semiconductor device manufacturing process has become more and more popular, and in particular, for the formation of high-concentration junctions, the method of implanting 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 extremely large amounts of sodium, etc. (mainly substances mainly composed of hydro and carpon) 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 under such conditions, the ion beam will collide with the inside of the magnetic field analysis tube as shown in 5-1 and 5-5 in Figures 1 and 2, causing damage to the inside of the analysis tube. Contaminants such as sodium adhering to the tube are spattered, or the ion beam collides with the tube, heating the tube and raising the temperature, causing these contaminants to evaporate. 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. In addition to the target ion beam 5-3, there are 14 cylindrical rotating body implanting parts that implant ions through the 6th slit. 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 3, "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 there is less spatter or evaporation than the analysis tube part, and also because there is an ion beam deflection plate 10 for removing neutrons, this airborne contaminant is absorbed here. hand,
This is because the amount of contaminants flying up to the silicon substrate 13 for ion implantation is small since it has the effect of preventing it to some extent. 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 and directs them to the substrate. The first step is to reduce the energy to an extremely weak and negligible amount even if it arrives.
This is because the configuration is not necessarily suitable for blocking contaminants containing sodium and the like, and is also useless against spatter and re-evaporation of these contaminants.

Is the current configuration shown in Figures 1 and 2 ineffective against contamination with sodium, etc.?
Or talked about less. There are three possible solutions to this problem:

(1) To prevent contamination with sodium, etc. from occurring in the ion beam analysis section, use a cryopump, terpo molecular pump, etc. for vacuum evacuation, and make sure that the constituent materials of the ion source do not contain sodium, etc. Be very careful. 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 not a concrete solution.

(2) Cleaning the ion beam analysis tube. Although this may have been effective at the time,
Generally, cleaning the analysis tube of an ion implanter is difficult due to its structure, and when contamination accumulates in an extremely short period of time in a 1:1 ratio during use,
This cleaning method does not provide a concrete solution. Another possibility is to heat the analysis tube for cleaning, but this is not a concrete solution.

(3) A deflection method is used that simultaneously deflects the ion beam and completely traps incoming contaminants, including sodium. Although this method appears to be similar in appearance to the configuration for removing neutral particles in FIG. 1, there is an essential difference in content. As described above, neutral particles are generated by charge exchange in an accelerated ion beam, and therefore have approximately the same energy as the ion beam.

Therefore, when an ion beam collides with a deflection plate, it is either driven into the deflection plate and comes to rest, or if the ion beam does not come to rest and collides with the deflection plate and is reflected, the energy of the ion beam is lost. If the energy of the ion beam becomes significantly different from the original ion beam energy, that is, if the energy becomes extremely small, there is no problem in practical use. In fact, when ions are implanted using an ion implantation device configured as shown in Figure 1, it is often observed that such low-energy neutral particles fly onto the silicon substrate surface. A commonly used technique is to form a thin oxide film of approximately 50 to 100 Å on the implantation area and perform ion implantation, thereby blocking low-energy neutral particles that could not be blocked by the deflection plate with this oxide film. has been done. However, pollutants containing sodium, etc. essentially fly away due to thermal kinetic energy due to diffusion. Therefore, when it collides with the deflection plate, it is very likely to be reflected, making it difficult to prevent it. Unlike the case of neutral particles mentioned above, when these particles fly onto the surface of a silicon substrate, it causes extremely inconvenient situations in the production of semiconductor devices. At the same time, the deposition rate of sodium-containing contaminants activated by the ion beam and blown onto the silicon substrate increases.

FIG. 4 shows an example of the configuration of an ion beam deflection section devised for the above purpose. 16 (1st
In FIGS. 2 and 3, both the ion beam 5-3) and the airborne contaminant 15 enter the wide entrance deflection section 18. At this deflection section, 16 ion beams exit from the deflection section, and this deflection section is characterized by having a slit with an exit number 17, and as shown in Fig. 4, the incoming materials are It is reflected inside the beam and does not proceed in the direction of the beam, but is prevented from adhering to the wall of the deflection section.

The beam can be deflected by a magnetic field applied externally to the deflection section, or by applying an electric field with a positive potential on the bottom and a negative potential on the top, using the two plates of the deflection section as opposing electrodes. There are two methods, one is to deflect the light and the other is to deflect it.

In the case of magnetic field deflection, it is necessary to change the strength of the applied magnetic field if the type or mass of the passing ion beam differs even if the energy is the same, but the convergence state of the ion beam does not change. In the case of electric field deflection, as described above, low-energy electrons that have been supplemented in the ion beam flow into the positive potential electrode, which not only increases the load on the power supply but also impairs beam convergence. Furthermore, it is necessary to attach the slit 19 in FIG. 4, which is a feature of this system, to the insulation, and the same applies to the upper and lower lids of the deflection section in FIG. In the case of magnetic field deflection, the slit and the upper and lower lids may be made of the same non-magnetic material and the same material composition as the deflection plate. As described above, the deflection section is characterized by having a wide entrance and a box-like structure as a whole, with only the exit of the beam being as narrow as possible.

FIG. 5 shows an ion implantation device according to the present invention which is an improved version of the device shown in FIG. It is a diagram in which a thin plate-shaped shielding plate, that is, a reflecting plate is attached. It is known that the efficiency of collecting such diffused flying substances is improved if the reflecting plate is not only perpendicular to the outer wall but also at a certain angle. Since it is best to make the beam passage part of the Nahoko reflector as small as possible, it can also be thought of as a stack of multiple exit slits, which is a feature of this method. Furthermore, in order to further improve the collection efficiency, it is better if the temperature of the surface that the flying substances collide with is lower. Figure 5 2
0 is a cooling pipe for cooling the outer wall of the deflection section,
It is cooled by cold water or, in some cases, liquid nitrogen, liquid helium, etc. This does not have to be a tubular cooling pipe, but may have a jacket-like structure in which a cooling liquid is poured for cooling.

Although the structure of the deflection section has been described above with a rectangular cross section, the cross section may be circular, oval, or a combination thereof, if necessary.

As explained above, contaminants containing sodium, etc., which come flying from the analysis tube of the ion beam due to diffusion, cannot be removed by the conventional deflection plate for removing neutral particles as shown in Figure 1. Flaws As explained in Figure 5, only the ion beam is allowed to pass through, and the flying substances are removed by a method that does not leave them outside the deflection unit.Contaminants containing sodium, etc., which are a common problem with ion implantation equipment, are removed from the silicon substrate surface. Contamination with sodium, etc. due to adhesion can be prevented.

In the structure shown in Figure 5, the ion beam is single, so the flying particles attached to the deflection part will not be hit by the ion beam and spatter, but there will be a small amount of neutral particles flying at the same time as the ion beam. may be spat out. For this reason, if a considerable amount of airborne contaminants adhere to the tube wall of the deflection section, it is necessary to remove the contaminants by removing them and cleaning them, or to replace the entire deflection section with a new one, but this work is done infrequently. It's easy.

As described above, the use of the apparatus for removing contaminants including sodium and the like using the ion beam deflection unit according to the present invention will be specifically considered.

As mentioned above, the configuration shown in Figure 1 is a configuration in which contamination of the silicon substrate by contaminants is unlikely to occur because the amount of ion beam used is small, but over time contaminants accumulate on the neutral particle deflection plate 10. do. In order to prevent this, it is necessary to position the ion beam deflection section of the present invention between the acceleration tube 7 and the X-direction scanning electrode 8 in FIG. At the position of the neutral particle deflection plate 10 in Figure 1, the ion beam is effectively expanded due to electrical scanning in the X and Y directions at 8 and 9, and this contaminant removal deflection unit is installed. There's nothing I can do. In other words, since the neutral particle deflection plate and the contaminant removal deflection section do not have the same function, it is necessary to position the contaminant removal deflection section in front of the electric scanning section.

In the configuration of FIG. 2, the contaminant removal deflection section is located between the accelerating tube 7 and the cylindrical rotary driving section or mechanical scanning section 14. This prevents contaminants from flying onto the silicon substrate surface and allows only the desired ions to be implanted.
As mentioned above, when the ion beam current exceeds 1 mA, scanning with an electric field is disadvantageous due to beam divergence, etc. However, if the ion beam is scanned with a magnetic field instead of an electric field, the beam can be A large amount of ion beam can be scanned without causing divergence. Therefore, this contaminant removal deflection section is positioned in front of the method that performs magnetic field scanning of a large amount of ion beam, and the ion beam that has passed through this deflection section to remove contaminants is subjected to magnetic field scanning. . In this case, the neutral particle deflection plate must be inserted after scanning, as in the case of FIG.

Considering the above, when scanning an ion beam by electric scanning, whether it is electric field scanning or magnetic field scanning, the contaminant removal deflection section is placed in front of the scanning section, and the neutral point is placed after scanning. A particle deflection plate must be installed, making the structure extremely complicated. If possible, it is desirable that the deflection section for removing contaminants and the deflection plate for neutral particles be the same, even if the structure is not perfect.

FIG. 6 shows a deflection section that was invented to serve these two purposes in one deflection section, and is characterized by having a wide entrance and exit for the ion beam. First, the tube wall of the deflection section is kept at a low temperature using a cooling liquid or the like to improve the effectiveness of trapping incoming contaminants. Then, the deflection angle θ is increased so that the deflection angle collides with the tube wall at a large angle. In addition, the length l of the collecting pipe wall is increased,
If the incident contaminant collides with the pipe wall for the first time and is reflected without being collected, the deflection angle θ and the collection pipe wall of the deflection section should be adjusted so that at least a second collision occurs on the pipe wall. Select length l. The length of the tube wall can be shortened by setting the deflection angle .theta. to about 90.degree. if the configuration permits, and if the deflection angle is small, the length of the tube wall must be increased. According to this structure, neutral particle removal measures are sufficient. This deflection section is designed so that it does not have a reflector inside that prevents the ion beam from passing, since it allows a thick ion beam that has been scanned by an electric field or a magnetic field, that is, has been effectively expanded by electrical scanning, to pass therethrough. However, it is also possible to improve the blocking ability by installing a reflector plate that does not prevent the passage of the beam and is useful for blocking neutral particles and reflective contaminants.
However, the combined system shown in FIG. 6 may have a slightly inferior contaminant removal ability compared to the system in which the contaminant removal deflection section and the neutral particle deflection plate are separated.

FIG. 7 shows the structure of a deflection section in which 22 pockets for confining 15 contaminants are attached to the tip of the straight path from the ion beam entrance in order to further improve the contaminant removal ability in this dual-use method. Not only can the effect be further improved by cooling the surrounding tube wall of No. 21 with the cooling pipe No. 20 or by attaching a reflective plate inside, but if the structure is such that this pocket can be removed, it is possible to prevent the incident contaminants from entering this pocket. If all of the pockets are configured to undergo the first collision, cleaning this pocket will remove most of the contaminants. Moreover, by making the bottom of this pocket not flat as shown in FIG. 7, but having a conical shape, for example, the collection efficiency can be further improved. In Nahoko's pocketed deflection section as shown in Figure 7, the deflection due to the electric field is due to disturbance of the electric field.
Although it is difficult and preferable to use a magnetic field for deflection, it is also possible to perform electric field deflection by correcting the disturbance of the electric field by, for example, pasting a metal mesh on the pocket entrance.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an ion implantation device currently in use with a maximum ion beam current of approximately 500μA, and Figure 2 is a diagram of an ion implantation device currently in use with an ion beam current of 1m.
A configuration diagram of an ion implantation device of A or higher. Figure 3 is an explanatory diagram showing how contaminants containing sodium diffuse from the analysis section in the configuration of Figure 2. Figure 4 shows the contaminants that fly in due to this diffusion. Fig. 5 is an explanatory diagram of the present invention which is an improved deflection part of Fig. 4, and Figs. FIG. 2 is an explanatory diagram of a deflection section according to the present invention that serves both as a removal deflection section and a neutral particle deflection plate. 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...
Ion beam, 17...Slit, 18...Deflection section for removing contaminants, 19...Reflection plate, 20...Cooling tube, 21...Deflection section with pocket, 22...Pocket.

Claims (1)

[Claims] 1. The ion beam extracted from the ion source is mass-analyzed by an ion beam analyzer, target ions are extracted, and the extracted ions are accelerated and implanted into the object to be treated with a predetermined impurity doping. In an ion implantation device with an ion beam current of 1 mA or more, contaminants flying to the workpiece during implantation are prevented and removed between the ion beam analysis section and the place where the workpiece is installed. A deflection section for removing contaminants is provided which has a curved path for removing contaminants, and the deflection section has a wide ion beam inlet and a narrowed ion beam exit, and has a reflector inside the deflection section that does not impede passage of the ion beam. An ion implantation device comprising: 2. The ion beam extracted from the ion source is subjected to mass analysis in the ion beam analyzer, the target ions are extracted, and the extracted ions are accelerated and implanted into the object to be processed to perform predetermined impurity doping. In an ion implantation device of 1 mA or more, a curved path is provided between the ion beam analysis section and the place where the object to be processed is installed to prevent and remove contaminants that fly to the object to be processed during implantation. An ion implantation apparatus comprising: a contaminant removal deflection section having a contaminant removal deflection section, the deflection section having a contaminant collection pocket at the tip of a straight path from an ion beam entrance. 3 The ion beam extracted from the ion source is subjected to mass analysis in the ion beam analyzer, the target ions are extracted, and the extracted ions are accelerated and implanted into the object to be processed to perform predetermined impurity doping. In an ion implantation device of 1 mA or more, a curved path is provided between the ion beam analysis section and the place where the object to be processed is installed to prevent and remove contaminants that fly to the object to be processed during implantation. A contaminant removal deflection section is provided, and the deflection section is configured to prevent at least a second collision if the flying contaminants are not collected on the inner wall of the deflection section and are reflected. An ion implantation device characterized by having a deflection angle of a deflection section, a length of a tube wall of the deflection section, and a cooling mechanism for cooling the outside of the deflection section.