JP4640521B2 - Plasma doping method - Google Patents

Description

  The present invention relates to a plasma doping method for introducing impurities into the surface of a solid sample such as a semiconductor substrate.

  As a technique for introducing impurities into the surface of a solid sample, for example, as shown in Patent Document 1, a plasma doping method is known in which impurities are ionized and introduced into a solid with low energy.

  Hereinafter, a plasma doping method as a conventional impurity introduction method will be described with reference to FIG.

FIG. 6 shows a schematic configuration of a plasma doping apparatus used in a conventional plasma doping method. In FIG. 6, a sample electrode 6 for placing a sample 9 made of a silicon substrate is provided in the vacuum vessel 1. A gas supply device 2 for supplying a doping source gas containing a desired element, for example, B ₂ H _6, into the vacuum vessel 1 and a pump 3 for reducing the pressure inside the vacuum vessel 1 are provided. Can be kept at a pressure of. Microwaves are radiated from the microwave waveguide 19 into the vacuum chamber 1 through the quartz plate 7 as a dielectric window. A magnetic field microwave plasma (electron cyclotron resonance plasma) 20 is formed in the vacuum chamber 1 by the interaction between the microwave and a DC magnetic field formed from the electromagnet 14. A high frequency power source 10 is connected to the sample electrode 6 via a capacitor 21 so that the potential of the sample electrode 6 can be controlled.

In the plasma doping apparatus having such a configuration, the doping source gas introduced from the gas supply apparatus 2, for example, B ₂ H _6, is converted into plasma by the plasma generating means including the microwave waveguide 19 and the electromagnet 14, and the plasma 20 Boron ions are introduced into the surface of the sample 9 by the high frequency power source 10.

  After forming the metal wiring layer on the sample 9 into which impurities are introduced in this way, a thin oxide film is formed on the metal wiring layer in a predetermined oxidizing atmosphere, and then the sample 9 is formed by a CVD apparatus or the like. When a gate electrode is formed thereon, for example, a MOS transistor is obtained.

Incidentally, a gas containing impurities that become electrically active when introduced into a sample such as a silicon substrate, such as a doping source gas made of B ₂ H ₆ , generally has a high risk.

In the plasma doping method, all of the substances contained in the doping source gas are introduced into the sample. Taking a doping source gas made of B ₂ H ₆ as an example, boron is the only effective impurity when introduced into the sample, but hydrogen is also introduced into the sample at the same time. When hydrogen is introduced into the sample, there is a problem that lattice defects occur in the sample during subsequent heat treatment such as epitaxial growth.

  Therefore, an impurity solid containing impurities that become electrically active when introduced into the sample is placed in a vacuum vessel, and plasma of a rare gas is generated in the vacuum vessel, and the impurity solid is sputtered by ions of the inert gas. Thus, a method of separating impurities from the impurity solid has been considered. FIG. 7 shows the configuration of a plasma doping apparatus for performing doping by such a method. In FIG. 7, a sample electrode 6 for placing a sample 9 made of a silicon substrate is provided in the vacuum vessel 1. A gas supply device 2 for supplying an inert gas into the vacuum vessel 1 and a pump 3 for depressurizing the inside of the vacuum vessel 1 are provided, and the inside of the vacuum vessel 1 can be maintained at a predetermined pressure. Microwaves are radiated from the microwave waveguide 19 into the vacuum chamber 1 through the quartz plate 7 as a dielectric window. A magnetic field microwave plasma (electron cyclotron resonance plasma) 20 is formed in the vacuum chamber 1 by the interaction between the microwave and a DC magnetic field formed from the electromagnet 14. A high frequency power source 10 is connected to the sample electrode 6 via a capacitor 21 so that the potential of the sample electrode 6 can be controlled. An impurity solid 22 containing an impurity element such as boron is provided on a solid holding table 23, and the potential of the solid holding table 23 is controlled by a high frequency power supply 25 connected via a capacitor 24.

  In the plasma doping apparatus having such a configuration, an inert gas such as argon (Ar) introduced from the gas supply apparatus 2 is converted into plasma by the plasma generating means including the microwave waveguide 19 and the electromagnet 14, and the impurity solid 22 A part of the impurity element jumping out into the plasma by sputtering is ionized and introduced into the surface of the sample 9. Such a configuration is described in detail in Patent Document 2.

US Pat. No. 4,912,065 JP 09-1115851 A JP 2000-309868 A JP 2004-47695 A

  However, the conventional method has a problem that low concentration doping cannot be stably performed. In order to perform low-concentration doping using a doping source gas, it is necessary to lower the pressure in the vacuum vessel and reduce the partial pressure of the doping source gas. In this case, the doping source gas is generally diluted with helium, which is an inert gas. This is because helium ions have an advantage that the ion irradiation damage to the sample is small because the sputtering yield is small. However, helium gas has a drawback that discharge is difficult to start at a low pressure, and it has been difficult to process under desired low-concentration doping conditions.

  Also, when performing low concentration doping using impurity solids without using a doping source gas, it is necessary to lower the pressure in the vacuum vessel. When argon is used as the inert gas, although discharge is likely to start even at a lower pressure than helium, it is difficult to process under the desired low concentration doping conditions as in the case of using the doping source gas. is there.

  On the other hand, Patent Document 3 describes a method of reliably performing ignition by increasing the pressure in the vacuum vessel in the ignition step in a sputtering apparatus using argon gas. It cannot be directly applied to a process extremely sensitive to impurities.

  In view of the above-described conventional problems, an object of the present invention is to provide a plasma doping method capable of stably performing low concentration doping.

The plasma doping method of the present gun onset Ming, a plasma doping method for introducing impurities into the film of the sample or sample surface, a first step of placing a sample on a sample electrode in the vacuum chamber, the vacuum vessel The vacuum vessel is evacuated while supplying a gas containing an inert gas other than helium, and high-frequency power is supplied to the plasma source while controlling the inside of the vacuum vessel to the first pressure, thereby generating plasma in the vacuum vessel. In the second step of generating the gas, while the plasma is being generated, the vacuum vessel is evacuated while supplying a gas containing helium, and the second pressure is controlled while the vacuum vessel is controlled to the second pressure. And a third step of supplying a high-frequency power larger than the high-frequency power in the step to the plasma source.

In this gun onset bright plasma doping method, preferably, it is more desirable than the first pressure toward the second pressure low. In this case, it is more preferable that the first pressure is 1 to 10 Pa and the second pressure is 0.01 to 1 Pa. More preferably, the first pressure is 2 to 5 Pa and the second pressure is 0.01 to 0.5 Pa.

  A plasma doping method capable of stably performing low concentration doping can be provided.

Sectional drawing which shows the structure of the plasma doping apparatus used in the 1st thru | or 4th embodiment of this invention. Sectional drawing which shows the structure of the plasma doping apparatus used in other embodiment of this invention. Sectional drawing which shows the structure of the plasma doping apparatus used in other embodiment of this invention. Sectional drawing which shows the structure of the plasma doping apparatus used in other embodiment of this invention. Sectional drawing which shows the structure of the plasma doping apparatus used in other embodiment of this invention. Sectional drawing which shows the structure of the plasma doping apparatus used in the conventional example Sectional drawing which shows the structure of the plasma doping apparatus used in the conventional example

  Hereinafter, a first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows a cross-sectional view of the plasma doping apparatus used in the first embodiment of the present invention. In FIG. 1, while introducing a predetermined gas from a gas supply device 2 into a vacuum vessel 1, exhaust is performed by a turbo molecular pump 3 as an exhaust device, and the inside of the vacuum vessel 1 is maintained at a predetermined pressure by a pressure regulating valve 4. However, by supplying high frequency power of 13.56 MHz to the coil 8 provided in the vicinity of the dielectric window 7 facing the sample electrode 6 from the high frequency power source 5, inductively coupled plasma is generated in the vacuum vessel 1, Plasma doping treatment can be performed on the silicon substrate 9 as a sample placed on the sample electrode 6. In addition, a high frequency power source 10 for supplying high frequency power to the sample electrode 6 is provided, and the potential of the sample electrode 6 can be controlled so that the substrate as a sample has a negative potential with respect to plasma. It is like that. The turbo molecular pump 3 and the exhaust port 11 are disposed immediately below the sample electrode 6, and the pressure regulating valve 4 is a lift valve positioned directly below the sample electrode 6 and directly above the turbo molecular pump 3. . The sample electrode 6 is fixed to the vacuum vessel 1 by four support columns 12. The main component of the dielectric window 7 is quartz glass.

After the substrate 9 is placed on the sample electrode 6, while maintaining the temperature of the sample electrode 6 at 10 ° C., 50 sccm of helium gas and 3 sccm of diborane (B ₂ H ₆ ) gas as a doping source gas are supplied into the vacuum chamber 1. Then, while controlling the pressure in the vacuum vessel 1 to the first pressure = 3 Pa, 800 W was supplied to the coil 8 as the plasma source to generate plasma in the vacuum vessel 1. After 1 second after the plasma is ignited, after the plasma is stabilized, the inside of the vacuum vessel 1 is controlled to a second pressure = 0.3 Pa lower than the first pressure (3 Pa) while the plasma is generated. Boron could be introduced in the vicinity of the surface of the substrate 9 by supplying high frequency power of 200 W to the sample electrode for 7 seconds. The doping concentration was 2.5 × 10 ¹³ atm / cm ² .

  In this way, it is possible to realize stable ignition by performing plasma ignition at a pressure higher than that in the doping process, and stable using a plasma mainly composed of helium with little ion irradiation damage to the sample. As a result, low concentration doping can be performed.

  In the first embodiment of the present invention described above, an inert gas other than helium may be supplied in the step of igniting plasma. In this case, since an inert gas other than helium generally has a lower ignition lower pressure than helium, there is an advantage that plasma can be ignited at a lower pressure.

  In the step of igniting the plasma, the high frequency power supplied to the plasma source may be reduced. In this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  Further, in the step of igniting the plasma, the doping source gas may not be supplied into the vacuum vessel. Also in this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  Since the basic operation of the plasma doping apparatus shown in FIG. 1 has been described in detail in the first embodiment of the present invention, description thereof is omitted here.

After the substrate 9 is placed on the sample electrode 6, while keeping the temperature of the sample electrode 6 at 10 ° C., 50 sccm of argon gas and 3 sccm of diborane (B ₂ H ₆ ) gas as a doping source gas are supplied into the vacuum chamber 1. Then, while controlling the pressure in the vacuum vessel 1 to the first pressure = 0.8 Pa, 800 W was supplied to the coil 8 as a plasma source to generate plasma in the vacuum vessel 1. One second after the plasma was ignited, while the plasma was still generated, 50 sccm of helium gas was supplied into the vacuum chamber 1 and the supply of argon gas was stopped. After the plasma was stabilized, the sample was maintained for 7 seconds. Boron could be introduced in the vicinity of the surface of the substrate 9 by supplying high-frequency power of 200 W to the electrodes. The doping concentration was 4.2 × 10 ¹³ atm / cm ² .

  In this manner, by performing plasma ignition with a gas containing an inert gas (argon) other than helium, it becomes possible to realize stable ignition, and a helium-based plasma with small ion irradiation damage to the sample can be realized. It has become possible to perform low concentration doping stably.

  In the second embodiment of the present invention described above, the pressure in the vacuum vessel may be increased in the step of igniting plasma. In this case, there is an advantage that plasma can be ignited more stably.

  In the step of igniting the plasma, the high frequency power supplied to the plasma source may be reduced. In this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  Further, in the step of igniting the plasma, the doping source gas may not be supplied into the vacuum vessel. Also in this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  Next, a third embodiment of the present invention will be described with reference to FIG.

  Since the basic operation of the plasma doping apparatus shown in FIG. 1 has been described in detail in the first embodiment of the present invention, description thereof is omitted here.

After the substrate 9 is placed on the sample electrode 6, while maintaining the temperature of the sample electrode 6 at 10 ° C., 50 sccm of helium gas and 3 sccm of diborane (B ₂ H ₆ ) gas as a doping source gas are supplied into the vacuum chamber 1. Then, while controlling the pressure in the vacuum vessel 1 to the first pressure = 3 Pa, 100 W was supplied to the coil 8 as the plasma source to generate plasma in the vacuum vessel 1. 1 second after the plasma is ignited, the vacuum vessel 1 is controlled to a second pressure lower than the first pressure (3 Pa) = 0.3 Pa in a state where the plasma is generated, and supplied to the coil. Boron could be introduced in the vicinity of the surface of the substrate 9 by increasing the power to 800 W and supplying 200 W of high frequency power to the sample electrode for 7 seconds after the plasma was stabilized. The doping concentration was 2.4 × 10 ¹³ atm / cm ² .

  In this way, using a helium-based plasma that reduces ion irradiation damage to the sample while reducing the negative effects on the sample in the ignition step by reducing the power supplied to the plasma source in the step of plasma ignition. As a result, low concentration doping can be stably performed.

  In the third embodiment of the present invention described above, the second pressure may be the same as the first pressure. Even in this case, the adverse effect on the sample in the ignition step can be reduced.

  Further, an inert gas other than helium may be supplied in the step of igniting plasma. In this case, since an inert gas other than helium generally has a lower ignition lower pressure than helium, there is an advantage that plasma can be ignited at a lower pressure.

  Further, in the step of igniting the plasma, the doping source gas may not be supplied into the vacuum vessel. Also in this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  Next, a fourth embodiment of the present invention will be described with reference to FIG.

  Since the basic operation of the plasma doping apparatus shown in FIG. 1 has been described in detail in the first embodiment of the present invention, description thereof is omitted here.

After placing the substrate 9 on the sample electrode 6, while maintaining the temperature of the sample electrode 6 at 10 ° C., 50 sccm of helium gas is supplied into the vacuum vessel 1, and the pressure in the vacuum vessel 1 is set to the first pressure = 3 Pa. Plasma was generated in the vacuum chamber 1 by supplying high frequency power of 800 W to the coil 8 as a plasma source while controlling. One second after the plasma is ignited, the inside of the vacuum chamber 1 is controlled to a second pressure lower than the first pressure (3 Pa) = 0.3 Pa while the plasma is being generated, and as a doping source gas The boron can be introduced near the surface of the substrate 9 by supplying 3 sccm of diborane (B ₂ H ₆ ) gas and supplying 200 W of high frequency power to the sample electrode for 7 seconds after the plasma is stabilized. It was. The doping concentration was 2.3 × 10 ¹³ atm / cm ² .

  In this way, by using a gas that does not contain a doping source gas in the step of performing plasma ignition, while using a helium-based plasma that reduces ion irradiation damage to the sample while reducing adverse effects on the sample in the ignition step. The low concentration doping can be performed stably.

  In the fourth embodiment of the present invention described above, the second pressure may be the same as the first pressure. Even in this case, the adverse effect on the sample in the ignition step can be reduced.

  Further, an inert gas other than helium may be supplied in the step of igniting plasma. In this case, since an inert gas other than helium generally has a lower ignition lower pressure than helium, there is an advantage that plasma can be ignited at a lower pressure.

  In the step of igniting the plasma, the high frequency power supplied to the plasma source may be reduced. In this case, there is an advantage that adverse effects on the sample in the ignition step can be reduced.

  In the embodiment of the present invention described above, only a part of various variations regarding the shape of the vacuum vessel, the method and arrangement of the plasma source, and the like are only illustrated in the application range of the present invention. It goes without saying that various variations other than those exemplified here can be considered in applying the present invention.

  For example, a configuration as shown in FIG. 2 in which the coil 8 is planar may be used.

  Further, a configuration as shown in FIG. 3 using an antenna 13 and an electromagnet 14 as a magnetic field forming device instead of the coil 8 is also possible. In this case, helicon wave plasma can be formed in the vacuum vessel, and plasma with a higher density than inductively coupled plasma can be generated. A direct current magnetic field or a low frequency magnetic field having a frequency of 1 kHz or less may be applied in the vacuum vessel by controlling the current flowing through the electromagnet.

  Further, a configuration as shown in FIG. 4 using an antenna 13 and an electromagnet 14 as a magnetic field forming device instead of the coil 8 is also possible. In this case, a magnetic neutral loop plasma can be formed in the vacuum vessel by flowing reverse currents through the two electromagnets 14, and a plasma with a higher density than the inductively coupled plasma can be generated. A direct current magnetic field or a low frequency magnetic field having a frequency of 1 kHz or less may be applied in the vacuum vessel by controlling the current flowing through the electromagnet.

  Further, a configuration as shown in FIG. 5 is also possible. In FIG. 5, while introducing a predetermined gas from the gas supply device 2 into the vacuum vessel 1, exhaust is performed by a turbo molecular pump 3 as an exhaust device, and the inside of the vacuum vessel 1 is maintained at a predetermined pressure by a pressure regulating valve 4. However, by supplying high frequency power of 13.56 MHz to the coil 8 provided in the vicinity of the dielectric window 7 facing the sample electrode 6 from the high frequency power source 5, inductively coupled plasma is generated in the vacuum vessel 1, Plasma doping treatment can be performed on the silicon substrate 9 as a sample placed on the sample electrode 6. In addition, a high frequency power source 10 for supplying high frequency power to the sample electrode 6 is provided, and the potential of the sample electrode 6 can be controlled so that the substrate as a sample has a negative potential with respect to plasma. It is like that. The turbo molecular pump 3 and the exhaust port 11 are disposed immediately below the sample electrode 6, and the pressure regulating valve 4 is a lift valve positioned directly below the sample electrode 6 and directly above the turbo molecular pump 3. . The sample electrode 6 is fixed to the vacuum vessel 1 by four support columns 12. The main component of the dielectric window 7 is quartz glass, but contains boron as an impurity.

  A high frequency power source 16 is provided for supplying high frequency power having a frequency of 500 kHz to the bias electrode 15 disposed between the coil 8 and the dielectric window 7. The bias electrode 15 has a spoke shape (in which strip-shaped electrodes are arranged radially) and is arranged in a line direction substantially perpendicular to the winding direction of the coil 8, so that the high-frequency electromagnetic field from the coil 8 can be It is devised so as not to disturb the radiation in 1. On the other hand, the bias electrode 15 covers almost the entire area of the dielectric window 7, and the amount of diffusion of boron as an impurity into the plasma can be controlled by sputtering the dielectric window 7.

  In addition, a band pass filter 17 is provided as a circuit for preventing the influence of modulation by the high frequency power of 500 kHz on the reflected wave detection circuit system of the high frequency power of frequency 13.56 MHz. This eliminates the effect of the sheath thickness of the surface of the dielectric window 7 varying at 500 kHz due to the supply of high-frequency power having a frequency of 500 kHz. Of the reflected waves of high-frequency power having a frequency of 13.56 MHz, 13.56 MHz It is for extracting and detecting only components. In such a configuration, by performing processing while monitoring the reflected wave of the high frequency power having the frequency of 13.56 MHz with the reflection wave meter 18, it is possible to detect the matching state and the trouble of the high frequency power source having the frequency of 13.56 MHz in real time. It becomes possible.

  By adopting such a configuration, the doping source gas generated from solid impurities (dielectric window) is not supplied into the vacuum vessel, and impurities are introduced into the sample or the film on the sample surface. It becomes possible to introduce. This configuration is described in detail in Patent Document 4.

  In the embodiment of the present invention described above, when the second pressure is lower than the first pressure, the first pressure is 1 to 1 in order to ensure ignition and realize low concentration doping. It is desirable that the pressure is 10 Pa and the second pressure is 0.01 to 1 Pa. Furthermore, it is desirable that the first pressure is 2 to 5 Pa and the second pressure is 0.01 to 0.5 Pa.

  In addition, when using an inert gas other than helium, it is desirable to use at least one of neon, argon, krypton, or xenon (zenon). These inert gases have the advantage that the adverse effect on the sample is smaller than other gases.

  In addition, when reducing the high-frequency power supplied to the plasma source in the ignition step, the ignition is performed in order to ensure the ignition and to suppress the adverse effect on the sample in the ignition step, and to realize the low concentration doping. The high frequency power supplied to the source is preferably 1/100 to 1/2 of the high frequency power supplied to the plasma source in the doping step. Further, it is desirable that the high frequency power supplied to the plasma source in the ignition step is 1/20 to 1/5 of the high frequency power supplied to the plasma source in the doping step.

  In addition, when the doping source gas is supplied into the vacuum vessel, the partial pressure of the doping source gas is 1/1000 to 1/5 of the pressure in the vacuum vessel in the doping step in order to realize low concentration doping. It is desirable. Furthermore, it is desirable that the partial pressure of the doping source gas is 1/100 to 1/10 of the pressure in the vacuum vessel in the doping step.

  Further, although the case where the sample is a semiconductor substrate made of silicon has been exemplified, the present invention can be applied when processing samples of various other materials.

  Further, although the case where the impurity is boron is illustrated, the present invention is effective when the sample is a semiconductor substrate made of silicon, particularly when the impurity is arsenic, phosphorus, boron, aluminum, or antimony. This is because a shallow junction can be formed in the transistor portion.

The present invention is effective when the doping concentration is low, and is particularly effective as a plasma doping method aiming at 1 × 10 ¹¹ / cm ^{2 to} 1 × 10 ¹⁷ / cm ² . In addition, as a plasma doping method aiming at 1 × 10 ¹¹ / cm ^{2 to} 1 × 10 ¹⁴ / cm ² , there is a particular effect.

  The present invention is also effective when using electron cyclotron resonance (ECR) plasma, but is particularly effective when not using ECR plasma. This is because ECR plasma has an advantage that the plasma is easily ignited even at a low pressure. However, since the DC magnetic field in the vicinity of the sample is large, charge separation of electrons and ions is likely to occur, and the doping amount is not uniform. . That is, by applying the present invention to a plasma doping method using another high-density plasma source without using ECR plasma, low-concentration doping with excellent uniformity can be realized.

  The present invention relates to a plasma doping method for introducing impurities into the surface of a solid sample such as a semiconductor substrate.

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Gas supply apparatus 3 Turbo molecular pump 4 Pressure regulating valve 5 High frequency power supply 6 Sample electrode 7 Dielectric window 8 Coil 9 Substrate 10 High frequency power supply 11 Exhaust port 12 Strut

Claims (1)

A plasma doping method for introducing impurities into a sample or a film on a sample surface,
A first step of placing a sample on a sample electrode in a vacuum vessel;
The vacuum vessel is evacuated while supplying a gas containing an inert gas other than helium in the vacuum vessel, and the high frequency power is supplied to the plasma source while controlling the inside of the vacuum vessel to the first pressure. A second step of generating a plasma within,
High-frequency power larger than the high-frequency power in the second step while supplying the gas containing helium into the vacuum vessel and exhausting it while controlling the inside of the vacuum vessel to the second pressure with the plasma generated. And a third step of supplying a plasma source to the plasma source.

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