JP2006261066A - Doping device and doping method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a doping device wherein impurities can be introduced so that a sample can electrically keep neutrality by irradiating a neutral particle beam having low energy to the surface of the sample. <P>SOLUTION: This doping device 10 dopes the impurities by irradiating the neutral particles to the sample 18. The doping device 10 is equipped with a holding stand 44 to hold the sample 18, a plasma chamber 14 to generate charged particles as plasma, an electrode 32 to accelerate the charged particles toward the sample, and a neutralizing chamber 16 to generate the neutral particles by neutralizing the charged particles which have been accelerated. In addition, this doping device 10 is equipped with deflection electrodes 60 provided between the neutralizing chamber 16 and the sample 18 to remove the charged particles 54 which have not been neutralized in the neutralizing chamber 16, and measuring means 64, 66, 68 and 70 each measuring the amount of dope irradiated to the sample 18 by measuring the charged particles 54 which have been removed from the deflection electrodes 60. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a doping apparatus and a doping method for introducing impurities into a solid surface or an extremely shallow region, and particularly in the field of semiconductor manufacturing, a high-energy impurity is irradiated by irradiating a large-area sample with a low-energy neutral particle beam. The present invention relates to a doping apparatus and a doping method to be introduced.

  FIG. 1 is a schematic view showing a conventional doping apparatus. As shown in FIG. 1, a conventional doping apparatus has a plasma chamber 500 for generating charged particles, a neutralization chamber 502 for neutralizing charged particles, and a holding for holding a sample 504 to be doped. A table 506 and a sample chamber 508 in which a holding table 506 is arranged are provided.

Charged particles generated in the plasma chamber 500 are accelerated by the extraction mesh electrode 510 and reach the neutralization chamber 502. A gas for neutralization is introduced into the neutralization chamber 502 from the gas feed 503, and the pressure of the neutralization chamber 502 is maintained at a level of 10 ⁻³ Pa. Here, a part of the charged particles is neutralized by charge exchange collision to become a neutral particle beam. The neutral particle beam reaches the surface of the sample 504 in the sample chamber 508, and the sample 504 is doped with impurities. The The charged particles that have not been neutralized in the neutralization chamber 502 are removed by the suppressor 512 provided in front of the sample 504, and only the neutral particle beam reaches the sample 504.

  In the field of low energy doping of impurities, the target sample is often an insulator such as glass having a large area, and when the insulator sample is doped with charged particles, the surface of the sample is charged. Arise. Since the charged particles are repelled by this charging, the dope amount per unit time is reduced, the processing time is increased, and the productivity is lowered. Furthermore, when the charging proceeds, almost all charged particles are repelled, and doping cannot be performed.

  In order to prevent such charging, there is a method of relaxing charging by charged particles, for example, by emitting thermoelectrons near the surface of the sample 504. However, according to this method, for example, it is difficult to perform uniform charge suppression on a sample having a large area with a diameter exceeding 200 mm, and non-uniform doping tends to occur on the entire surface of the sample. In general, tungsten filaments are often used for thermionic emission, but there is a problem of sample contamination due to evaporation of tungsten.

  As a method for preventing the sample from being charged in the low energy doping of impurities, there is a method of irradiating a low energy neutral particle beam as shown in FIG. According to this method, it is possible to perform low-energy doping of impurities while preventing charging on the surface of a sample having a large area. However, since the gas for neutralization is introduced from the sample chamber 508, the pressure in the sample chamber 508 increases, and the trajectory of the neutral particle beam is scattered. Therefore, the dope amount per unit time is lowered, and the productivity is lowered.

  Further, since there is almost no difference in conductance between the neutralization chamber 502 and the sample chamber 508, there is almost no pressure difference between the neutralization chamber 502 and the sample chamber 508. Therefore, the neutralization of the charged particles by the charge exchange collision is not completely performed in the neutralization chamber 16 and is also performed in the sample chamber 508. Thus, it cannot be said that the neutralization chamber 16 of the conventional doping apparatus shown in FIG. 1 sufficiently performs the function for neutralization.

  Next, when the voltage applied to the suppressor 512 is greater than about 100 V, abnormal discharge is likely to occur when the neutralizing gas is introduced, and when abnormal discharge occurs, the material of the suppressor 512 is changed. Sputtering occurs and the sample 504 is contaminated. Similarly, the suppressor 512 is sputtered by the charged particles that have come in, the element of the substance constituting the suppressor 512 is doped into the sample 504 as a contaminant, and the yield decreases. Furthermore, since there is no function for monitoring the dope amount, the dope amount is not constant between batches, and the yield decreases.

Japanese Patent No. 3170792

  The present invention has been made in view of such problems of the prior art, and irradiates a sample with a low energy neutral particle beam to introduce impurities so that the sample is electrically neutral. It is an object of the present invention to provide a doping apparatus and a doping method that can be used.

  In order to achieve the above object, according to the first aspect of the present invention, the surface of the sample is irradiated with a low-energy neutral particle beam, and impurities can be introduced so that the sample is electrically neutral. A possible doping apparatus is provided. This doping apparatus is for doping impurities by irradiating a sample with neutral particles. The doping apparatus includes a holding table for holding the sample, plasma generating means for generating charged particles as plasma, acceleration means for accelerating the charged particles toward the sample, and neutralizing the accelerated charged particles. And neutralizing means for generating neutral particles. The doping apparatus is provided between the neutralizing means and the sample, and removes charged particles that have not been neutralized by the neutralizing means, and the charged particle removing means. And measuring means for measuring the amount of dope to the sample by measuring the charged particles removed by the above.

  The neutralizing means cannot neutralize all the charged particles emitted from the plasma generating means, and some charged particles pass through the neutralizing means as they are. For this reason, it is preferable that the charged particle removing unit bends the trajectory of the charged particles with a magnetic field and / or an electric field so that the charged particles do not reach the sample.

  The doping apparatus includes a plasma chamber that generates the charged particles, a sample chamber in which the holding table is disposed, a neutralization chamber that is disposed between the plasma chamber and the sample chamber, and the charging chamber. It is preferable to further include a neutralization gas introduction port for introducing a neutralization gas for neutralizing particles into the neutralization chamber.

  Further, the doping apparatus reduces the conductance with respect to a gas introduced from the outside between the plasma chamber and the neutralization chamber and between the neutralization chamber and the sample chamber, and You may further provide the electrode which neutralizes particle | grains. Thereby, while reducing the conductance of the introduced gas, the charged particles or the neutralized beam can be efficiently passed through the electrode, and the neutralization efficiency and the straightness of the beam can be improved.

The doping apparatus may further include an exhaust pump disposed on at least one of the upstream side and the downstream side of the neutralization chamber. Thereby, mixing with the gas introduced into the plasma chamber can be avoided. Moreover, the pressure of the sample chamber which performs doping can be maintained lower than 10 ⁻⁵ Pa or 10 ⁻⁵ Pa.

  Further, according to the second aspect of the present invention, there is provided a doping method capable of irradiating a sample surface with a low energy neutral particle beam and introducing impurities so that the sample is electrically neutral. Is done. The doping method includes a step of generating charged particles as plasma, a step of accelerating the charged particles toward a sample, a step of neutralizing the accelerated charged particles to generate neutral particles, A step of removing charged particles that have not been formed, a step of irradiating the sample with the neutral particles to dope impurities, and a step of controlling the amount of doping to the sample.

  Moreover, the said doping method may further have the process of measuring the dope amount to the said sample by measuring the said removed charged particle.

  According to the present invention, the surface of the sample can be irradiated with a low energy neutral particle beam, and impurities can be introduced so that the sample is electrically neutral.

  Hereinafter, embodiments of a doping apparatus according to the present invention will be described in detail with reference to FIGS. 2 to 7, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 2 is a schematic diagram showing the doping apparatus 10 according to the first embodiment of the present invention. As shown in FIG. 2, the doping apparatus 10 includes a cylindrical vacuum vessel 12. Inside the vacuum vessel 12, a plasma chamber 14 in which plasma is generated and a charge in the plasma in the plasma chamber 14 are included. A neutralization chamber 16 for generating a neutral particle beam from particles and a sample chamber 20 for processing a sample 18 such as a semiconductor substrate, glass, organic matter, and ceramics are formed. The plasma chamber 14, the neutralization chamber 16, and the sample chamber 20 are isolated from the outside by the vacuum vessel 12. FIG. 2 shows an example in which the plasma chamber 14, the neutralization chamber 16, and the sample chamber 20 are integrally formed by the vacuum vessel 12. However, the plasma chamber 14, the neutralization chamber 16, and the sample chamber are illustrated. 20 may be formed by separate vacuum vessels, and may be connected to another chamber via a flange or the like. In addition, although the cylindrical shape was shown as the example as a shape of the vacuum vessel 12, a cross section may be a rectangle or a shape similar to them.

  The doping apparatus 10 generates plasma composed of charged particles in the plasma chamber 14, then neutralizes the charged particles in the neutralization chamber 16 to generate a low energy neutral particle beam, and is disposed in the sample chamber 20. It is configured to dope impurities by irradiating the surface of the sample.

  A process gas introduction port 22 for introducing a process gas into the vacuum chamber 12 is provided in the upper part of the plasma chamber 14, and this process gas introduction port 22 is connected to a process gas supply source 24. Further, a vacuum pump 28 is connected to the plasma chamber 14 via an exhaust valve 26.

  Connected to the plasma chamber 14 is a plasma generating power source 30 as plasma generating means for generating charged particles as plasma in the plasma chamber 14, and between the plasma chamber 14 and the neutralizing chamber 16 is charged. A first electrode 32 that accelerates the energy of the particles is disposed. A first power source 34 is connected to the first electrode 32. As described above, the first electrode 32 and the first power source 34 constitute acceleration means for accelerating charged particles in the plasma toward the sample 18.

  The neutralization chamber 16 is provided with a neutralization gas introduction port 36 for introducing a neutralization gas into the neutralization chamber 16. The neutralization gas introduction port 36 is a neutralization gas supply source. 38. With such a configuration, the neutralizing gas is introduced into the neutralizing chamber 16 through the neutralizing gas introduction port 36. A second electrode 40 for removing residual charged particles that have not been neutralized in the neutralization chamber 16 is disposed between the neutralization chamber 16 and the sample chamber 20. A second power source 42 is connected to the electrode 40. Thus, the charged particle removal means which removes the charged particle which was not neutralized by the neutralization means by the 2nd electrode 40 and the 2nd power supply 42 is comprised.

  A holding table 44 that holds the sample 18 is disposed in the sample chamber 20, and the sample 18 is placed on the upper surface of the holding table 44. A vacuum pump 48 is connected to the sample chamber 20 in the vicinity of the holding table 44 via an exhaust valve 46. The sample chamber 20 is maintained at a predetermined pressure by the vacuum pump 48. A vacuum pump 52 is also connected to the vicinity of the second electrode 40 in the sample chamber 20 via an exhaust valve 50.

  The sample chamber 20 is provided with a deflection electrode 60 for forming a deflection electric field for removing the residual charged particles 54 that could not be removed by the second electrode 40. The deflection electrode 60 is used for generating a deflection electric field. The power source 62 is connected. In this way, the charged electrode removing means for removing the charged particles that have not been neutralized by the neutralizing means is constituted by the deflection electrode 60 and the deflecting electric field generating power source 62.

  In the sample chamber 20, a target 64 to which charged particles removed by the deflection electrode 60 are irradiated is installed. The target 64 is connected to an ammeter 66 for measuring a current due to charged particles irradiated on the target 64. The ammeter 66 is connected to the controller 70 via an amplifier 68. The controller 70 calculates the doping amount of the sample 18 based on the current value measured by the ammeter 66 and controls the plasma power supply 30 to adjust the generation amount of charged particles. As described above, the target 64, the amplifier 68, the ammeter 66, and the controller 70 constitute measuring means for measuring the amount of dope to the sample by measuring the charged particles removed by the charged particle removing means. .

Next, the operation of the doping apparatus 10 in this embodiment will be described. First, the sample 18 is placed on the holding table 44 in the sample chamber 20. Then, by operating the vacuum pump 28 and the vacuum pump 48, the inside of the vacuum vessel 12 is evacuated, and the pressure in the plasma chamber 14 and the sample chamber 20 is maintained at 10 ⁻⁴ Pa or less, preferably 10 ⁻⁵ Pa level. To do. Then, the exhaust valve 26 is closed and, for example, AsH ₃ , B ₂ H ₆ or the like is introduced as a process gas containing impurities from the process gas introduction port 22 into the plasma chamber 14, and the pressure in the plasma chamber 14 is set to 10 ⁻² Pa. Or it maintains on the 10 ^<-1 > Pa level.

  Next, energy is applied to the inside of the plasma chamber 14 by the plasma generation power source 30 to generate plasma. For example, inductively coupled plasma can be used as plasma generating means for applying energy to the inside of the plasma chamber 14 to generate plasma inside the plasma chamber 14. Since inductively coupled plasma can generate high-density plasma with a simple structure, it has been actively used in recent semiconductor manufacturing apparatuses. As the power source for generating plasma, a commercial frequency of 13.56 MHz or 2.45 GHz, or a high frequency intermittent application of such a high frequency can be used. Alternatively, energy may be applied to the inside of the plasma chamber 14 using an AC electric field, a pulse electric field, a DC electric field, a magnetic field, a laser, a shock wave, contact thermal ionization, or the like having other frequencies.

  Then, charged particles are released from the generated plasma. As a method for discharging charged particles from plasma, divergence of the plasma itself can be used. As the substance is heated (energy added), the solid (first state of the substance) to the liquid (second state of the substance) and the liquid (second state of the substance) to the gas (third of the substance) The state changes to the state of (2), but when more energy is applied, plasma is generated. Thus, the plasma is in a high energy state called the fourth state of matter. Using the high energy of the plasma, charged particles can be emitted from the plasma itself.

  However, the divergence (natural diffusion) of charged particles from the plasma itself is limited by space charge, and therefore efficient doping cannot be performed even if the plasma density is increased for the purpose of improving productivity. Therefore, in order to perform efficient doping on the sample 18, the energy of charged particles may be accelerated from several tens of volts to several hundred volts, up to several kilovolts. In the example shown in FIG. 2, the first power source 34 applies a voltage to the first electrode 32 to accelerate charged particles from the plasma in the plasma chamber 14.

  When charged particles are generated by inductively coupled plasma, the plasma potential of the plasma is approximately several volts to 100 volts, although it varies depending on the power for discharge, the type of gas, the pressure, and the like. Accordingly, the initial energy of the charged particles is approximately several eV to 100 eV when the potential of the first electrode 32 is the ground potential. This is because an ion sheath is formed at the portion where the plasma contacts the first electrode 32, and the charged particles in the plasma are accelerated by energy equivalent to the plasma potential.

  In order to further increase the energy of the charged particles, it is preferable to apply a voltage exceeding the plasma potential to the first electrode 32. For example, when it is desired to increase the energy of charged particles to about 1 keV, a voltage of about 1 kV may be applied to the first electrode 32. Conversely, when it is desired to accelerate lower energy charged particles from plasma at a relatively high plasma potential, such as 100 V, a potential control electrode (not shown) is provided inside the plasma chamber 14 to control the potential. What is necessary is just to apply a voltage to the electrode for use and lower the plasma potential.

  The charged particles to be accelerated include positive ions having a positive charge and negative ions having a negative charge. When a positive ion is desired to be accelerated, a negative voltage is applied to the first electrode 32 and the negative ions are applied. A positive voltage is applied to the first electrode 32 to accelerate the acceleration. The first electrode 32 not only determines the acceleration energy of the charged particles, but also has a role of reducing the gas conductance of the plasma chamber 14 and the neutralizing chamber 16 and neutralizing the charged particles.

  FIG. 3 is a perspective view showing an example of the structure of the first electrode 32. In the example shown in FIG. 3, the first electrode 32 is configured by a honeycomb structure 82 in which a large number of hexagonal columnar slits 80 are combined. The honeycomb structure 82 has a structure like a honeycomb slit used for a photomultiplier tube, and has a high optical aperture ratio with respect to all openings.

In addition, the honeycomb structure 82 shown in FIG. 3 has a small conductance with respect to the gas because the slit 80 has a long length and a high aspect ratio with respect to the opening area of one slit 80. For example, when the hexagonal diagonal length of the slit 80 is 1 mm and the length of the slit 80 is 10 mm, the conductance of one honeycomb slit 80 is about 1.2 × 10 ⁻⁵ (m ³ / s). There is only. The conductance value was calculated with reference to “Vacuum Handbook” (Nippon Vacuum Technology Co., Ltd. (currently ULVAC, Inc.), Ohm Co., First Edition, P. 35-40).

  These honeycomb slits 80 have a high transmissivity for a beam having good straightness although the conductance with respect to gas is small. Among the charged particles, charged particles having a beam component with good straightness are neutralized by charge exchange collision with residual gas molecules when passing through the honeycomb slit 80. Since the residual gas is the same as the plasma generation process gas, it is composed of the same element as the charged particles generated in the plasma chamber 14. Therefore, the cross-sectional area where charge exchange is performed is maximized, and the neutralization efficiency is high. The residual gas or residual gas molecule here is a discharge process gas that has flowed out of the plasma chamber 14 without becoming charged particles inside the plasma chamber 14 of the discharge process gas introduced into the plasma chamber 14. Gas or discharge process gas molecules.

  Charged particles that are diffused isotropically among the charged particles collide with the inner wall of the honeycomb slit 80, and are neutralized by reattaching electrons in the case of positive ions, and neutralized by desorption of electrons in the case of negative ions. It becomes. Thus, neutralization of charged particles in plasma can be performed by the first electrode 32.

  FIG. 4 is a perspective view showing another example of the structure of the first electrode 32. In the example shown in FIG. 4, the first electrode 32 is configured by a multicapillary structure 182 in which a large number of thin cylindrical tubes 180 are bundled. In the case of a cylindrical tube having a normal thickness, the conductance with respect to the gas can be reduced, but the neutral particle beam that can reduce the optical transmittance is reduced. In order to avoid such a problem, a thin-walled cylindrical tube is used in the example shown in FIG.

  FIG. 5 is a perspective view showing another example of the structure of the first electrode 32. The first electrode 32 shown in FIG. 5 has a structure in which a large number of holes 282 are formed in one plate 280 by machining or electric discharge machining. In the example shown in FIG. 5, one plate is used, but a plurality of holes may be formed in a plurality of plates.

  Note that the first electrode having the structure shown in FIGS. 4 and 5 can achieve the same effect as the first electrode having the structure shown in FIG. That is, while maintaining a small conductance with respect to the gas, the transmittance with respect to a beam having good straightness is high, and neutralization of charged particles is efficiently performed in the cylindrical slit.

Since the Debye length becomes shorter as the plasma generated in the plasma chamber 14 becomes higher in density, when the first electrode 32 is a thin plate-like electrode having many small holes, the representative dimension of the opening is used. Even for small holes whose diameter is less than 1 mm (for example, a diameter in the case of a circular opening and a diagonal length in the case of a honeycomb opening), the plasma leaks out. Here, the Debye length is a length determined by the plasma density and the electron temperature, and is used as one of dimensions representing plasma. The Debye length λ _D (cm) is expressed by the following equation, where the electron temperature is kTe (eV) and the electron density (plasma density) is ne (cm ³ ).
λ _D = (kTe / 4πne ² ) ^1/2 (cm)
For example, when the plasma density is 10 ¹¹ cm ³ and the electron temperature is 4 eV, the Debye length is about 47 μm.

  The Debye length is the range covered by the Debye shielding effect resulting from the property of maintaining the quasi-neutral state of the plasma. Debye shielding means that when a foreign object such as metal is inserted into the plasma, charged particles in the plasma surround the foreign object, creating a potential barrier around the foreign object, and the potential from the foreign object penetrates into the plasma. It means trying to prevent (= shielding). For example, when a positively charged metal rod is inserted into the plasma, negatively charged particles (electrons) are surrounded by the metal rod so that the electric field generated by the positively charged metal rod does not penetrate the entire plasma. Shield.

  In general, it is known that if there is a gap having a mechanical dimension longer than the Debye length, the plasma passes through the gap and oozes out to the outside. For example, when the first electrode 32 as shown in FIGS. 3 to 5 is used, it is originally necessary to make a hole having a diameter smaller than the Debye length, but the first electrode has a thickness exceeding several mm. It is not practical to form a hole with a diameter of less than 1 mm in 32 on a surface with a diameter of more than several tens of mm. Therefore, by making the first electrode 32 have a structure having an aspect ratio in which the length of the hole is 2 to 50 times, preferably about 10 times the hole diameter, it is possible to prevent the seepage of plasma. Further, as described above, charged particles are neutralized by charge exchange between charged particles and residual gas molecules in the holes. Therefore, by making the structure of the first electrode as shown in FIGS. 3 to 5, it is possible to simultaneously realize the three functions of lowering the conductance with respect to gas, preventing leakage of plasma, and neutralizing.

In the example shown in FIG. 5, the hole diameter (diagonal length in the case of honeycomb shape or rectangular shape) varies depending on the aspect ratio and the density of plasma generated in the plasma chamber 14, but should be 0.5 mm to 10 mm. More preferably, it is good to set it as 1 mm to 2 mm. For example, the first electrode 32 in which the density of plasma generated in the plasma chamber 14 is 10 ¹¹ / cm ³ , the hole diameter is 1 mm, the slit length is 10 mm, and the holes 282 are formed in a staggered pattern at a pitch of 1.33 mm on the plate electrode 280. When used, it was possible to prevent the plasma from leaking into the neutralization chamber 16.

Then, the same type of gas as that introduced into the plasma chamber 14, such as AsH ₃ or B ₂ H ₆ , is introduced into the neutralization chamber 16, and the internal pressure of the neutralization chamber 16 is changed from 10 ⁻³ Pa to 10 ⁻³ Pa. ^-1 Pa level is maintained. Neutralization of charged particles in the neutralization chamber 16 is performed by charge exchange collision. Since the collision cross section of the charge exchange collision is the largest among the same gas molecules, it is effective to introduce the same gas as the plasma chamber 14 into the neutralization chamber 16, but different types of gases such as argon and neon are used. Gas may be introduced.

Further, all the gas introduced into the plasma chamber 14 enters the neutralization chamber 16 unless the exhaust valve 26 connected to the vacuum pump 28 provided between the plasma chamber 14 and the neutralization chamber 16 is opened. Inflow. Furthermore, since the conductance of the second electrode 40 provided between the neutralization chamber 16 and the sample chamber 20 with respect to the gas is small, the flow rate of the gas introduced into the neutralization chamber 16 is small, or the neutralization chamber. Even if there is no gas to be introduced into 16, the pressure inside the neutralization chamber 16 can be maintained on the order of 10 ⁻³ Pa to 10 ⁻¹ Pa.

  The second electrode 40 is for removing residual charged particles that could not be neutralized by the first electrode 32 and the neutralization chamber 16 among the charged particles in the plasma accelerated by the first electrode 32. . All charged particles can be removed by applying, to the second electrode 40, a voltage having a reverse sign of a voltage equivalent to or higher than the energy accelerated by the first electrode 32. However, when the first electrode receives acceleration energy of several hundred volts or more, application of several hundred volts to the second electrode 40 may cause abnormal discharge due to the relatively high pressure in the neutralization chamber 16. In this case, there may be a disadvantage that the charged particles are regenerated. In such a case, it is necessary to suppress the voltage applied to the second electrode 40 to a voltage that does not cause abnormal discharge. When the voltage applied to the second electrode 40 is lowered, charged particles having energy exceeding the voltage pass through the second electrode 40. This contradiction can be solved as follows.

  That is, by making the second electrode 40 the same structure as the first electrode 32, neutralization of the charged particles is performed in the slit of the second electrode 40, and the charged particles passing through the second electrode 40 are reduced. Can do. Accordingly, charged particles can be effectively removed without raising the potential of the second electrode 40 to the potential of the first electrode 32. That is, the effect of making the second electrode 40 the same structure as that of the first electrode 32 is great, and it is possible to simultaneously improve the neutralization rate of the residual charged particles and the straightness of the neutral particle beam. .

  As shown in FIG. 2, a deflection electrode 60 that forms a deflection electric field for removing residual charged particles that could not be removed by the second electrode 40 is disposed in the sample chamber 20. For example, when the diameter of the sample is 300 mm, the deflection electrodes 60 having a length of 200 mm are arranged so that the electrode interval is 300 mm and the distance from the upper end of the deflection electrode 60 to the sample 18 is 500 mm. At this time, by applying a voltage of 850 V to the deflection electrode 60, for example, the deflection distance of the charged particles 501 accelerated at 500 V becomes 450 mm, and the charged particles 501 that attempt to reach the surface of the sample 18 are completely removed. be able to.

  In doping impurities with a neutral particle beam, the most serious problem is the control of the doping amount. This problem is caused by the fact that the doping amount cannot be detected as a current because the particles to be doped are not charged particles but neutral particles.

  Therefore, in this embodiment, the amount of dope is measured by measuring the residual charged particles that have passed through the second electrode 40 and reached the sample chamber 20 as current. The residual charged particles here are charged particles extracted from the plasma chamber 14 and still pass through the first electrode 32, the neutralization chamber 16, and the second electrode 40 and reach the sample chamber 20. A particle that exists as a charged particle.

  That is, the neutralization rate after passing through the second electrode 40 under the doping condition is obtained in advance, for example, the residual charged particles 54 deflected by the deflection electrode 60 are irradiated to the target 64, and the residual charge flowing into the target 64. The particles 54 are measured by an ammeter 66. The dope amount can be calculated based on the measured current value. For example, if a Faraday cup is used as the target 64, measurement errors due to secondary electrons can be eliminated, so it is preferable to use a Faraday cup.

  Depending on the current value measured by the ammeter 66, a signal is sent from the ammeter 66 via the amplifier 68 or directly to the controller 70. In the controller 70, the doping amount is determined based on the neutralization rate obtained in advance and the current value measured by the ammeter 66.

  When the doping amount reaches a predetermined value, a stop signal is sent from the controller 70 to the plasma generating power source 30 to stop plasma generation. When the plasma generation is stopped, the generation of charged particles is eliminated, so that the low energy neutral particle beam does not reach the sample 18 and the doping is completed. The dope amount can be controlled by performing such a series of operations.

  Further, the doping amount can be controlled without stopping the plasma generation in the plasma chamber 14. For example, a shutter (not shown) that can cover the entire surface of the sample 18 is disposed on the upstream side of the sample 18, and when the predetermined amount of dope is reached, the shutter is operated with power such as a motor or compressed air to It is also possible to physically terminate the irradiation of the 18 with a low energy neutral particle beam.

  FIG. 6 is a partially enlarged view of the doping apparatus in the second embodiment of the present invention. As shown in FIG. 6, a coil 160 that forms a deflection magnetic field for removing residual charged particles that could not be removed by the second electrode 40 is disposed in the sample chamber 20. When it is necessary to form a uniform magnetic field over a wide range, it is preferable to use a Helmholtz coil as the coil 160. This Helmholtz coil is composed of two circular coils having the same shape, and these two circular coils are arranged at the same interval as the diameter thereof. With such a configuration, the magnetic field distribution formed at the center of the two circular coils becomes uniform.

For example, when the distance from the second electrode 40 to the sample 18 is 500 mm and a sample having a diameter of 300 mm is doped with As, a Helmholtz coil 160 having a diameter of 300 mm is provided at the midpoint between the second electrode 40 and the sample 18. Deploy. If the magnetic field intensity by the Helmholtz coil 160 at this time is 0.05 Tesla and a uniform magnetic field is generated, the As ⁺ Larmor radius becomes 0.56 m, and for example, charged particles accelerated at 500 V can be completely removed. it can. Here, the Larmor radius is a rotation radius when the charged particles are rotated by a Lorentz force received in a magnetic field. The Larmor radius r is given by the following equation, where m is the mass of the charged particle, v is the velocity of the charged particle, Z is the valence of the charged particle, e is the charge of the electron, and B is the magnetic field.
r = mv / ZeB

  Moreover, it is good also as removing the residual charged particle which was not able to be removed with the 2nd electrode 40 using the ExB filter which combined the electric field and magnetic field mentioned above. In this case, as shown in FIG. 7, it is preferable to use a combination of a Helmholtz coil 160 capable of generating a uniform magnetic field and the deflection electrode 60. Further, residual charged particles can be removed by utilizing the resonance phenomenon of charged particles caused by a high-frequency electric field, but this is not practical when the beam diameter is relatively large (diameter 300 mm or more) as in this embodiment.

  Although the embodiments of the present invention have been described so far, it is needless to say that the present invention is not limited to the above-described embodiments and may be implemented in various forms within the scope of the technical idea.

It is a schematic diagram which shows the conventional doping apparatus. It is a schematic diagram which shows the doping apparatus in the 1st Embodiment of this invention. It is a perspective view which shows an example of the 1st electrode of the doping apparatus shown in FIG. It is a perspective view which shows the other example of the 1st electrode of the doping apparatus shown in FIG. It is a perspective view which shows the other example of the 1st electrode of the doping apparatus shown in FIG. It is the elements on larger scale of the doping apparatus in the 2nd Embodiment of this invention. It is a schematic diagram which shows the doping apparatus in the 3rd Embodiment of this invention.

Explanation of symbols

10 Doping device 14 Plasma chamber 14
16 Neutralization chamber 18 Sample 20 Sample chamber 24 Process gas supply source 28, 48, 52 Vacuum pump 30, 34, 42, 62 Power source 32, 40 Electrode 44 Holding table 54 Residual charged particles 60 Deflection electrode 64 Target 66 Ammeter 70 Controller 160 Helmholtz coil

Claims (7)

A doping apparatus for irradiating a sample with neutral particles to dope impurities,
A holding table for holding the sample;
Plasma generating means for generating charged particles as plasma;
Accelerating means for accelerating the charged particles toward the sample;
Neutralizing means for generating neutral particles by neutralizing the accelerated charged particles;
A charged particle removing unit that is provided between the neutralizing unit and the sample and removes charged particles that have not been neutralized by the neutralizing unit;
Measuring means for measuring the dope amount to the sample by measuring the charged particles removed by the charged particle removing means;
A doping apparatus comprising:   2. The doping apparatus according to claim 1, wherein the charged particle removing unit bends the trajectory of the charged particles by a magnetic field and / or an electric field so that the charged particles do not reach the sample. A plasma chamber for generating the charged particles;
A sample chamber in which the holding table is disposed;
A neutralization chamber disposed between the plasma chamber and the sample chamber;
A neutralization gas introduction port for introducing a neutralization gas for neutralizing the charged particles into the neutralization chamber;
The doping apparatus according to claim 1, further comprising:   Electrodes for neutralizing the charged particles by reducing conductance with respect to a gas introduced from the outside between the plasma chamber and the neutralization chamber and between the neutralization chamber and the sample chamber The doping apparatus according to claim 3, further comprising:   The doping apparatus according to claim 3, further comprising an exhaust pump disposed on at least one of an upstream side and a downstream side of the neutralization chamber. Generating charged particles as plasma;
Accelerating the charged particles toward the sample;
Neutralizing the accelerated charged particles to produce neutral particles;
Removing charged particles that have not been neutralized;
Irradiating the sample with the neutral particles to dope impurities;
Controlling the amount of dope to the sample;
A doping method characterized by comprising:   The doping method according to claim 6, further comprising a step of measuring a dope amount to the sample by measuring the removed charged particles.

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