Patent Application
20110217830
The present invention relates to a plasma doping method and apparatus for implanting impurities into the surfaces of samples.
For example, in fabrication of a MOS transistor, a thin oxide film is formed on the surface of a silicon substrate as a sample, and then a gate electrode is formed on the sample using a CVD apparatus or the like. Thereafter, impurities are implanted thereto by a plasma doping method as described above, using the gate electrode as a mask. By implanting impurities, for example, a metal wiring layer is formed on the sample where source and drain areas are formed in the sample to provide a MOS transistor.
As a technique for implanting impurities into the surface of a solid sample, there has been known a plasma doping method for implanting ionized impurities into a solid with low energy (refer to Patent Document 1, for example).
In the plasma processing apparatus having such a structure, the introduced doping material gas, such as B2H6, is changed into plasma by the plasma generating means constituted by the microwave waveguide 121 and the electromagnet 123, and boron ions in the plasma 124 are implanted into the surface of the sample 107 by the high-frequency power supply 112.
As aspects of the plasma processing apparatus for use in plasma doping, there are known one which uses a helicon-wave plasma source (refer to Patent Document 2, for example), one which uses an inductively-coupled plasma source (refer to Patent Document 3, for example), and one which uses a parallel-plate plasma source (refer to Patent Document 4, for example), as well as the aforementioned apparatus which uses an electron cyclotron resonance plasma source.
However, these conventional methods have an issue of poor reproducibility of the amount of implanted impurities (the amount of dose).
The present inventors have found, from various experiments, that the poor reproducibility is caused by the increase in the density of boron-based radicals within plasma. As plasma doping processing is successively performed, a thin film containing boron (boron-based thin film) is gradually deposited on the inner wall surface of the vacuum container. It is considered that, in a case of using B2H6 as the doping material gas, along with the increase in the thickness of the deposited film, the probability of adsorption of boron-based radicals to the inner wall surface of the vacuum container is gradually decreased, and accordingly, the density of boron-based radicals in plasma is gradually increased. Further, ions within plasma are accelerated by the potential difference between the plasma and the inner wall of the vacuum container and then impinge on the boron-based thin film deposited on the inner wall surface of the vacuum container, thereby causing sputtering. The sputtering thus caused gradually increases the amount of particles containing boron which are supplied into the plasma. Consequently, the amount of dose is gradually increased. The degree of the increase is significantly large, and after plasma doping processing is repeatedly carried out several hundreds of times, the amount of dose has been increased to about 3.3 to 6.7 times the amount of dose that is implanted in plasma doping processing performed just after the cleaning of the inner wall of the vacuum container with water and an organic solvent.
Along with the generation of plasma and stoppage thereof, the temperature of the inner wall surface of the vacuum container is varied, which also changes the probability of adsorption of boron-based radicals to the inner wall surface. This also causes the change in the amount of dose.
The present invention is made in view of the aforementioned issues in the prior art, and an object of the present invention is to provide a plasma doping method and apparatus which are capable of controlling the amount of impurities implanted to sample surfaces with higher accuracy and providing highly reproducible impurity concentration.
In accomplishing these and other aspects, according to a first aspect of the present invention, there is provided a plasma doping method comprising:
placing a sample on a sample electrode within a vacuum container;
supplying an electric power to the sample electrode, while supplying a plasma doping gas into the vacuum container, exhausting gas from the vacuum container, and controlling an inside of the vacuum container to a plasma doping pressure, and generating plasma between a surface of the sample and a surface of a counter electrode within the vacuum container; and
performing plasma doping processing to implant impurities into the surface of the sample, in a state where a following equation (1) is satisfied, where S is an area of the surface which is faced to the counter electrode, out of surfaces of the sample, and G is a distance between the sample electrode and the counter electrode.
0.1√{square root over ((S/π))}G
0.4√{square root over ((S/π))} (1)
With this structure, it is possible to realize the plasma doping method having excellent reproducibility of the concentration of impurities implanted to the surfaces of samples.
According to a second aspect of the present invention, there is provided the plasma doping method as defined in the first aspect, wherein a high-frequency electric power is supplied to the counter electrode which is placed opposite the sample electrode.
With this structure, it is possible to prevent the adsorption of generated plasma to the counter electrode.
According to a third aspect of the present invention, there is provided the plasma doping method as defined in the second aspect, wherein, after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode,
a high-frequency electric power is supplied to the counter electrode while a pressure within the vacuum container is maintained at a plasma generating pressure which is higher than the plasma doping pressure, to generate plasma between the surface of the sample and the surface of the counter electrode within the vacuum container, gradually decreasing a pressure within the vacuum container to the plasma doping pressure after the plasma is generated, and supplying the electric power to the sample electrode after the pressure within the vacuum container reaches the plasma doping pressure.
According to a fourth aspect of the present invention, there is provided the plasma doping method as defined in the second aspect, wherein, after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode,
supplying a plasma generating gas which causes discharge at a lower pressure more easily than a dilution gas used for diluting an impurity material gas in the plasma doping gas into the vacuum container, supplying the high-frequency electric power to the counter electrode while the pressure within the vacuum container is maintained at the plasma doping pressure, generating plasma between the surface of the sample and the surface of the counter electrode within the vacuum container, switching a gas supplied into the vacuum container to the plasma doping gas after the plasma is generated, and supplying the electric power to the sample electrode after the gas inside the vacuum container has been switched to the plasma doping gas.
According to a fifth aspect of the present invention, there is provided the plasma doping method as defined in the second aspect, wherein, after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode,
relatively moving the sample electrode and the counter electrode to separate the sample electrode from the counter electrode such that a distance G between the sample electrode and the counter electrode is larger than a range defined by the equation (1), and in this state, supplying the high-frequency electric power to the counter electrode while a plasma doping gas is supplied into the vacuum container, gas is exhausted from the vacuum container, and the inside of the vacuum container is controlled to the plasma doping pressure, generating plasma between the surface of the sample and the surface of the counter electrode within the vacuum container, relatively moving the sample electrode and the counter electrode after the plasma is generated to restore a state where the distance G satisfies the equation (1), and thereafter, supplying the electric power to the sample electrode.
According to a sixth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to fifth aspects, wherein a concentration of impurity material gas within the gas introduced into the vacuum container is equal to or less than 1%.
According to a seventh aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to fifth aspects, wherein a concentration of impurity material gas within the gas introduced into the vacuum container is equal to or less than 0.1%.
According to an eighth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to seventh aspects, wherein the gas introduced to the vacuum container is a mixed gas prepared by diluting an impurity material gas with a rare gas. Further, as defined in a ninth aspect of the present invention, there is provided the plasma doping method as defined in the eighth aspect, wherein the rare gas is He.
With this structure, it is possible to realize the plasma doping method with excellent reproducibility while realizing both accurate control of the amount of dose and a low sputtering property.
According to tenth and eleventh aspects of the present invention, there is provided the plasma doping method as defined in any one of the first to ninth aspects, wherein the impurity material gas within the gas is BxHy (x and y are natural numbers) or PxHy (x and y are natural numbers).
With this structure, it is possible to prevent implantation of undesirable impurities into the surfaces of samples.
According to a twelfth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to eleventh aspects, wherein the plasma doping processing is performed while the gas is ejected toward the surface of the sample through gas ejection holes provided in the counter electrode.
With this structure, it is possible to realize the plasma doping method with more excellent reproducibility of the concentration of impurities implanted to the sample surface.
Further, according to a thirteenth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to twelfth aspects, wherein the plasma doping processing is performed in a state where the surface of the counter electrode is made of silicon or a silicon oxide.
With this structure, it is possible to prevent implantation of undesirable impurities into the surfaces of samples.
According to a fourteenth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to thirteenth aspects, wherein the plasma doping processing is performed in a state where the sample is a semiconductor substrate made of silicon. According to a fifteenth aspect of the present invention, there is provided the plasma doping method as defined in any one of the first to fourteenth aspects, wherein impurities in the impurity gas contained in the gas is arsenic, phosphorus, or boron.
As the impurities, it is also possible to employ aluminum or antimony.
According to a sixteenth aspect of the present invention, there is provided a plasma doping apparatus comprising:
a vacuum container;
a sample electrode placed within the vacuum container;
a gas supply device for supplying gas into the vacuum container;
a counter electrode which is faced substantially in parallel to the sample electrode;
an exhaust device for exhausting gas from the vacuum container;
a pressure control device for controlling a pressure within the vacuum container; and
a power supply for supplying an electric power to the sample electrode, wherein
a following equation (2) is satisfied, where S is an area of a surface of the sample electrode, the surface being faced to the counter electrode and also being a placement region of the surface in which the sample is placed, and G is a distance between the sample electrode and the counter electrode.
0.1√{square root over ((S/π))}G
0.4√{square root over ((S/π))} (2)
With this structure, it is possible to realize the plasma doping apparatus with excellent reproducibility of the concentration of impurities implanted to the surfaces of samples.
According to a seventeenth aspect of the present invention, there is provided the plasma doping apparatus as defined in the sixteenth aspect, further comprising a high-frequency power supply for supplying a high-frequency electric power to the counter electrode.
With this structure, it is possible to prevent the adsorption of generated plasma to the counter electrode.
According to an eighteenth aspect of the present invention, there is provided the plasma doping apparatus as defined in the seventeenth aspect, wherein the pressure control device is capable of controlling the pressure within the vacuum container in such a way as to switch between a plasma doping pressure and a plasma generating pressure higher than the plasma doping pressure,
after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode, the high-frequency electric power is supplied from the high-frequency power supply to the counter electrode while the pressure within the vacuum container is maintained at the plasma generating pressure which is higher than the plasma doping pressure by the pressure control device, to generate plasma between the surface of the sample and a surface of the counter electrode within the vacuum container, after the plasma is generated, the pressure within the vacuum container is gradually decreased to the plasma doping pressure by the pressure control device, and after the pressure within the vacuum container reaches the plasma doping pressure, the electric power is supplied from the power supply to the sample electrode.
According to a nineteenth aspect of the present invention, there is provided the plasma doping apparatus as defined in the seventeenth aspect, wherein the gas supply device is capable of supplying the plasma doping gas and plasma generating gas which causes discharge at a lower pressure more easily than a dilution gas used for diluting an impurity material gas in the plasma doping gas, in a switchable manner,
after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode, the plasma generating gas which causes discharge at a lower pressure more easily than the dilution gas used for diluting the impurity material gas in the plasma doping gas is supplied into the vacuum container by the gas supply device, and the high-frequency electric power is supplied from the high-frequency power supply to the counter electrode while the pressure within the vacuum container is maintained at a plasma doping pressure by the pressure control device, to generate plasma between the surface of the sample and the surface of the counter electrode within the vacuum container, after the plasma is generated, the gas supplied into the vacuum container is switched to the plasma doping gas, and after the gas inside the vacuum container has been switched to the plasma doping gas, the electric power is supplied to the sample electrode.
According to a twentieth aspect of the present invention, there is provided the plasma doping apparatus as defined in the seventeenth aspect, further comprising a distance-adjustment driving device for relatively moving the sample electrode with respect to the counter electrode,
after the sample is placed on the sample electrode within the vacuum container and before the electric power is supplied to the sample electrode, the sample electrode and the counter electrode are moved relative to each other, by the distance-adjustment driving device, to separate the sample electrode from the counter electrode such that the distance G between the sample electrode and the counter electrode is larger than a range defined by the equation (2), and in this state, the high-frequency electric power is supplied from the high-frequency power supply to the counter electrode while a plasma doping gas is supplied into the vacuum container, gas is exhausted from the vacuum container, and the inside of the vacuum container is controlled to a plasma doping pressure to generate plasma between the surface of the sample and the surface of the counter electrode within the vacuum container, after the plasma is generated, the sample electrode and the counter electrode are moved relative to each other by the distance-adjustment driving device to restore a state where the distance G satisfies the equation (2), and thereafter, the electric power is supplied to the sample electrode.
According to a twenty-first aspect of the present invention, there is provided the plasma doping apparatus as defined in any one of the sixteenth to twentieth aspects, wherein the gas supply device is adapted to supply the gas through gas ejection holes provided in the counter electrode.
With this structure, it is possible to realize the plasma doping apparatus with more excellent reproducibility of the concentration of impurities implanted to the surfaces of samples.
Further, according to a twenty-second aspect of the present invention, there is provided the plasma doping apparatus as defined in any one of the sixteenth to twenty-first aspects, wherein the surface of the counter electrode is made of silicon or a silicon oxide.
With this structure, it is possible to prevent implantation of undesirable impurities into the surfaces of samples.
According to a twenty-third aspect of the present invention, there is provided a plasma doping method comprising:
placing a sample on a sample electrode within a vacuum container;
relatively moving the sample electrode and the counter electrode to separate the sample electrode from the counter electrode such that a distance G between the sample electrode and the counter electrode opposite the sample electrode is larger than a distance for plasma doping processing, and in this state, supplying the high-frequency electric power to the counter electrode while supplying a plasma doping gas into the vacuum container, exhausting a gas from the vacuum container, and controlling an inside of the vacuum container to a plasma doping pressure, to generate plasma between a surface of the sample and a surface of the counter electrode within the vacuum container;
after the plasma is generated, relatively moving the sample electrode and the counter electrode to restore the distance G to a distance for plasma doping processing, and thereafter, supplying the electric power to the sample electrode; and
performing plasma doping processing to implant impurities into the surface of the sample, in a state where the distance G between the sample electrode and the counter electrode is maintained at the distance for plasma doping processing, where S is an area of the surface which is faced to the counter electrode, out of surfaces of the sample.
These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.
Hereinafter, embodiments of the present invention will be described in detail, with reference to the drawings.
Hereinafter, a first embodiment of the present invention will be described with reference to
A plasma doping apparatus according to the first embodiment of the present invention is a plasma doping apparatus including a vacuum container (vacuum chamber) 1, a sample electrode (first electrode) 6 placed within the vacuum container 1, a gas supply device 2 for supplying plasma doping gas into the vacuum container 1, a counter electrode (second electrode) 3 which is placed within the vacuum container 1 and is opposed substantially in parallel to the sample electrode 6, a turbo pump 8 serving as one example of an exhaust device for exhausting gas in the vacuum container 1, a pressure adjustment valve 9 serving as one example of a pressure control device for controlling the pressure within the vacuum container 1, and a sample-electrode high-frequency power supply 12 serving as one example of a power supply for supplying a high-frequency power to the sample electrode, as illustrated in the cross-sectional views of
That is, referring to
Further, the gas supplied from the gas supply device 2 to the vacuum container 1 is exhausted from the vacuum container 1 by the turbo molecular pump 8 as an example of the exhaust device through an exhaust opening 1a, and also the degree of opening of the exhaust opening 1a is adjusted by the pressure adjustment valve 9 as an example of the pressure control device, so that the pressure within the vacuum container 1 is maintained at a predetermined pressure (a plasma doping pressure). Further, the turbo molecular pump 8 and the exhaust opening 1a are placed just below the sample electrode 6, and also the pressure adjustment valve 9 is a liftable valve positioned just below the sample electrode 6 and just above the turbo molecular pump 8. Furthermore, the sample electrode 6 is fixed at a middle portion of the vacuum container 1 with the four insulation supporting columns 10. By supplying a high-frequency electric power with a frequency of 60 MHz to the counter electrode 3 from the counter-electrode high-frequency power supply 11, it is possible to generate capacitive-coupled plasma between the counter electrode 3 and the sample electrode 6. Further, there is provided the sample-electrode high-frequency power supply 12 for supplying a high-frequency electric power with a frequency of 1.6 MHz to the sample electrode 6, and the sample-electrode high-frequency power supply 12 functions as a bias-voltage source which controls the electric potential of the sample electrode 6 such that the substrate 7 as an example of the sample is maintained at a negative potential with respect to the plasma. Instead of using the sample-electrode high-frequency power supply 12, a pulse power supply can also be used to supply a pulse power to the sample electrode 6 to control the potential of the substrate 7. An insulation member 13 is for galvanically isolating the counter electrode 3 from the vacuum container 1 which is grounded. In this manner, by accelerating ions within plasma toward the surface of the substrate 7 as an example of the sample to cause these ions to impinge thereon, it is possible to treat the surface of the substrate 7 as an example of the sample. By using a gas containing diborane or phosphine as the plasma doping gas, it is possible to perform the plasma doping processing.
In a case of performing the plasma doping processing, the flow rates of gases each including an impurity material gas are controlled to predetermined values, by flow-rate control devices (mass-flow controllers) (for example, first to third mass-flow controllers 31, 32, and 33 in
Further, in
As an actual example, the substrate 7 used herein is a silicon substrate with a circular shape (having a notch at a portion thereof) and a diameter of 300 mm. Further, there will be described in the following, as an example, plasma doping processing in the case where the distance G between the sample electrode 6 and the counter electrode 3 is set to 25 mm.
In performing plasma doping using the aforementioned plasma processing apparatus, at first, the inner walls of the vacuum container 1 including the surface of the counter electrode 3 are cleaned using water and an organic solvent.
Next, a substrate 7 is placed on the sample electrode 6.
Next, a high-frequency electric power of 1600 W is supplied from the counter-electrode high-frequency power supply 11 to the counter electrode 3, while the temperature of the sample electrode 6 is maintained at, for example, 25 C.°. B2H6 gas diluted with He, and He gas, for example, are supplied at flow rates of 5 sccm and 100 sccm, respectively, from the gas supply device 2 into the vacuum container 1, and also, the pressure within the vacuum container 1 is maintained at 0.8 Pa by the pressure adjustment valve 9, to generate plasma between the counter electrode 3 and the substrate 7 on the sample electrode 6 within the vacuum container 1. Also, a high-frequency electric power of 140 W is supplied from the sample-electrode high-frequency power supply 12 to the sample electrode 6 for 50 seconds to cause boron ions within the plasma to impinge on the surface of the substrate 7, thus implanting boron to the vicinity of the surface of the substrate 7. Then, the substrate 7 is taken out from the vacuum container 1 and activated, and thereafter, the surface resistance (a value relating to the amount of dose) is measured.
Under the same conditions, plasma doping processing is successively applied to the substrates 7. As a result, first several substrates exhibit decreasing surface resistance after activation, and the substrates subsequent thereto exhibit a substantially constant surface resistance, as illustrated by a curve “a” in
Further, after the surface resistance reaches a substantially constant value, the surface resistance is varied within an extremely small width.
For comparison, the same processing is conducted using an inductively-coupled plasma source as in the prior-art example (in the prior-art example, the distance between the quartz plate which is dielectric and the electrode is in the range of 200 mm to 300 mm). As a result, first several tens of substrates exhibit moderately-decreasing surface resistance, and the substrates subsequent thereto exhibit surface resistance asymptotically approaching a constant value, as illustrated by a curve “b” in
Further, in the prior-art example, after the surface resistance substantially reach a constant value, the surface resistance is varied within a relatively large variation width, which is several times the variation width of the present first embodiment.
Hereinafter, there will be described reasons for the fact that the aforementioned difference is observed.
In the prior-art example, during successively performing the plasma doping processing just after the cleaning of the inner wall of the vacuum container 1, a thin film containing boron is gradually deposited on the inner wall surface of the vacuum container 1. It is considered that this phenomenon occurs since boron-based radicals (neutral particles) produced within the plasma are adsorbed to the inner wall surface of the vacuum container, and also boron-based ions are accelerated by the potential difference between the plasma potential (=approximately 10 to 40 V) and the potential of the inner wall of the vacuum container (usually, since the inner wall of the vacuum container is dielectric, a floating potential=approximately 5 to 20 V) and then impinge on the inner wall surface of the vacuum container, so that a thin film containing boron is grown thereon due to thermal energy or ion impingement energy. It is considered that, along with the increase in the thickness of this deposited film, the probability of adsorption of boron-based radicals to the inner wall surface of the vacuum container is gradually decreased, and therefore, the density of boron-based radicals within the plasma is gradually increased, in the case of using B2H6 as a doping material gas. Further, ions within the plasma are accelerated by the aforementioned potential difference and then impinge on the boron-based thin film deposited on the inner wall surface of the vacuum container, which causes sputtering, thereby gradually increasing the amount of particles containing boron which are supplied to the plasma. Consequently, the amount of dose is gradually increased, which gradually decreases the surface resistance after activation. Further, the temperature of the inner wall surface of the vacuum container is varied along with the generation of plasma or the stoppage thereof, which varies the probability of adsorption of boron-based radicals to the inner wall surface, thereby causing the surface resistance after activation to be largely varied.
On the other hand, in the present first embodiment, the distance G between the sample electrode 6 and the counter electrode 3 is as small as 25 mm as compared with the area of the sample electrode 6 in which a wafer with a diameter of 300 mm as an example of the substrate 7 is placed, so that so-called narrow-gap discharge is caused. Further, the processing is performed while the gas is ejected toward the surface of the substrate 7 through the gas ejection holes 5 provided in the counter electrode 3. In this case, the surface condition of the inner wall surface of the vacuum container 1 (except the surface of the counter electrode 3) exerts significantly small influence on the density of boron-based radicals and the density of boron ions within the plasma. This is mainly for the following four reasons.
(1) Due to the narrow-gap discharge, the plasma is mainly generated only between the counter electrode 3 and the substrate 7, and therefore, boron-based radicals are very unlikely to be adsorbed to the inner wall surface of the vacuum container 1 (except the surface of the counter electrode 3), so that a thin film containing boron is less likely to be deposited thereon.
(2) The area of the inner wall surface of the vacuum container 1 (except the surface of the counter electrode 3) relative to the substrate 7 is smaller than that of the prior-art example, which reduces the influence of the inner wall surface of the vacuum container 1.
(3) Due to the application of the high-frequency electric power to the counter electrode 3, a self-bias voltage is generated at the surface of the counter electrode 3, and therefore, boron-based radicals are very unlikely to be adsorbed thereto, so that the condition of the surface of the counter electrode 3 is hardly changed even when the doping processing is successively performed.
(4) The gas is flowed along the surface of the substrate 7 in a single direction from the center of the substrate 7 to the periphery thereof, which attenuates the influence of the inner wall surface of the vacuum container 1 on the substrate 7.
Further, the present inventors determine a preferable range for the distance between the sample electrode 6 and the counter electrode 3. Assuming that the area of the surface of the substrate 7 (the surface which is faced to the counter electrode 3 or the surface of the sample electrode 6 which is faced to the counter electrode 3 and also the placement region on which the substrate 7 is to be placed) is S, in the case where the substrate 7 has a circular shape, the radius thereof is (S/π)−1/2. Assuming that the distance between the sample electrode 6 and the counter electrode 3 is G, under a condition where the following equation (3) holds, namely under a condition where the inter-electrode distance G falls within the range of 0.1 time to 0.4 time the radius of the substrate 7, a preferable impurity concentration reproducibility is obtained.
0.1√{square root over ((S/π))}G
0.4√{square root over ((S/π))} (3)
When the inter-electrode distance G is excessively small (smaller than 0.1 time the radius), plasma could not be generated within a pressure range suitable for performing the plasma doping (equal to or less than 3 Pa). On the contrary, when the inter-electrode distance G is excessively large (larger than 0.4 time the radius), several tens of substrates were required until the surface resistance after activation is stabilized just after wet cleaning, as in the prior-art example. Further, after the surface resistance is substantially stabilized, the surface resistance is varied within a large variation width.
As described above, generating the narrow-gap discharge through the application of the high-frequency electric power to the counter electrode 3 using the high-frequency power supply 11 is extremely important in ensuring the processing reproducibility. This is a particularly prominent phenomenon in plasma doping. In a case where the variation in etching property due to the deposition of a carbon-fluoride-based thin film on the inner wall of the vacuum container is problematic in applying dry etching to an insulation film, narrow-gap discharge may be utilized, wherein the concentration of carbon-fluoride-based gas within mixed gas introduced into the vacuum container is about several percentages, and the influence of the deposited film is relatively small. On the other hand, in the case of the plasma doping, the concentration of impurity material gas within inert gas introduced into the vacuum container is 1% or less (0.1% or less, particularly in a case where it is desired to control the amount of dose with higher accuracy), which causes the influence of the deposited film to be relatively large. In the case where the concentration of impurity material gas within inert gas exceeds 1%, it is impossible to provide a so-called self-regulation effect, thereby inducing malfunction that the amount of dose cannot be controlled accurately. Accordingly, the concentration of impurity material gas within inert gas is set to be 1% or less. It is necessary that the concentration of impurity material gas within inert gas introduced into the vacuum container be equal to or more than 0.001%. If it is smaller than 0.001%, processing should be performed for an extremely long time to attain a desired amount of dose.
Further, the use of the present invention offers the advantage of improvement in the accuracy of controlling the amount of dose, dose monitoring utilizing in-situ monitoring techniques such as emission spectroscopy and mass spectrometry, and the like. This is because of the following reason. That is, it is known that the saturation amount of dose in the so-called self-regulation phenomenon depends on the concentration of impurity material gas within mixed gas introduced into the vacuum container, wherein the self-regulation phenomenon is a phenomenon that, in processing a single substrate, the amount of dose is saturated along with the elapse of processing time. According to the present invention, it is possible to obtain relatively easily measurement values strongly relating to particles such as ions and radicals generated by dissociation or electrolytic dissociation of impurity material gas within plasma through in-situ monitoring, regardless of the condition of the inner wall of the vacuum container.
Further, in the plasma doping apparatus described in the Patent Document 4, the counter electrode (anode) provided opposite to the sample is maintained at a ground electric potential, which causes a thin film containing boron to be deposited on the counter electrode, when plasma doping processing is successively performed. Further, the Patent Document 4 only describes that the distance (gap) between the counter electrode (anode) and the sample electrode (cathode) “can be adjusted with respect to different voltages”.
In the aforementioned first embodiment of the present invention, there have been exemplified only portions of various variations of the shape of the vacuum container 1, the structure and placement of the electrodes 3 and 6, and the like, within the applicable scope of the present invention. It goes without saying that the present invention can be implemented in various variations, as well as the aforementioned examples.
Further, there has been exemplified a case where the high-frequency electric power with a frequency of 60 MHz is supplied to the counter electrode 3, and where the high-frequency electric power with a frequency of 1.6 MHz is supplied to the sample electrode 6, these frequencies are merely illustrative. A preferable frequency of the high-frequency electric power supplied to the counter electrode 3 is substantially within the range of 10 MHz to 100 MHz. If the frequency of the high-frequency electric power supplied to the counter electrode 3 is lower than 10 MHz, it is impossible to provide a sufficient plasma density. On the contrary, if the frequency of the high-frequency electric power supplied to the counter electrode 3 is higher than 100 MHz, it is impossible to provide a sufficient self-bias voltage, which tends to cause a thin film containing impurities to be deposited on the surface of the counter electrode 3.
A preferable frequency of the high-frequency electric power supplied to the sample electrode 6 is substantially within the range of 300 kHz to 20 MHz. If the frequency of the high-frequency electric power supplied to the sample electrode 6 is lower than 300 kHz, it is impossible to attain high-frequency matching easily. On the contrary, if the frequency of the high-frequency electric power supplied to the sample electrode 6 is higher than 20 MHz, this will tend to induce an in-plain distribution in the voltage applied to the sample electrode 6, thereby degrading the uniformity of doping processing.
Further, the surface of the counter electrode 3 can be made of silicon or a silicon oxide, which can prevent the implantation of undesirable impurities into the surface of a silicon substrate as an example of the substrate 7.
Further, in the case where the substrate 7 is a semiconductor substrate made of silicon, the substrate 7 can be utilized in fabrication of fine transistors, by using arsenic, phosphorus, or boron as the impurities. Also, the substrate 7 may be made of a compound semiconductor. Aluminum or antimony can be used as the impurities.
Further, a known heater and a known cooling device can be incorporated to respectively control the temperature of the inner wall of the vacuum container 1 and the temperatures of the counter electrode 3 and the sample electrode 6, which enables controlling, with higher accuracy, the probability of adsorption of impurity radicals to the inner wall of the vacuum container 1, the counter electrode 3, and the surface of the substrate 7, thereby further increasing the reproducibility.
Further, while there has been exemplified a case where a mixed gas prepared by diluting B2H6 with He is used as plasma doping gas to be introduced into the vacuum container 1, generally, it is also possible to use a mixed gas prepared by diluting an impurity material gas with a rare gas. As an impurity material gas, it is possible to use BxHy (x and y are natural numbers) or PxHy (x and y are natural numbers). These gases have the advantage of containing, as impurities, only H which will have less influence on the substrate even if it is intruded into the substrate, in addition to B or P. It is also possible to use other gasses containing B, such as BF3, BCl3, or BBr3. Also, it is possible to use other gasses containing P, such as PF3, PF5, PCl3, PCl5, or POCl3. Further, He, Ne, Ar, Kr, Xe, or the like can be used as the rare gas, but He is most preferable. This is for the following reason. The use of He can prevent the implantation of undesirable impurities into the surfaces of samples and also can realize a plasma doping method with excellent reproducibility while realizing both accurate control of the amount of dose and a low sputtering property. By using a mixed gas prepared by diluting an impurity material gas with a rare gas, it is possible to significantly reduce the change in the amount of dose caused by the film containing impurities such as boron which has been formed on the chamber inner wall. This enables controlling the distribution of the amount of dose with higher accuracy, by controlling the gas ejection distribution. This makes it easier to ensure preferable in-plain uniformity of the amount of dose. Ne is the most preferable rare gas next to He. Ne has the advantage of easily causing discharge at a low pressure, while having the drawback of having a sputtering rate slightly higher than He.
It should be noted that the present invention is not limited to the first embodiment and can be implemented in various modes.
For example, while, in the first embodiment, there has been exemplified a case where B2H6 gas diluted with He, and He gas are supplied from the gas supply device 2 at flow rates of 5 sccm and 100 sccm, respectively, and the high-frequency electric power of 1600 W is supplied to the counter electrode 3 from the counter-electrode high-frequency power supply 11 while the pressure within the vacuum container 1 is maintained at 0.8 Pa by the pressure adjustment value 9, thus generating plasma between the counter electrode 3 and the substrate 7 on the sample electrode 6 within the vacuum container 1, there are cases where it is difficult to generate plasma at a low pressure in a state where the partial pressure of He gas is high. In this case, it is effective to appropriately employ the following methods as modifications of the first embodiment of the present invention.
A first method is a method which changes the pressure. At first, a high-frequency electric power is supplied to the counter electrode 3 from the counter-electrode high-frequency power supply 11, while the pressure within the vacuum container 1 is maintained, through the pressure adjustment valve 9, at a plasma-generating pressure which is equal to or higher than 1 Pa (typically, 10 Pa) and higher than the plasma doping pressure, to generate plasma between the counter electrode 3 and the substrate 7 on the sample electrode 6 within the vacuum container 1. At this time, the sample electrode 6 is not supplied with a high-frequency electric power from the sample-electrode high-frequency power supply 12. After the plasma is generated, the pressure within the vacuum container 1 is gradually reduced to the plasma doping pressure which is equal to or lower than 1 Pa (typically, 0.8 Pa), by adjusting the pressure adjustment valve 9. A similar procedure can be possibly used in the case of using a so-called high-density plasma source such as an ECR (electron cyclotron resonance plasma source) or an ICP (inductively coupled plasma source). However, in the structure of the apparatus according to the modification of the first embodiment of the present invention, the volume of plasma is significantly smaller than that in the case of using a high-density plasma source, and accordingly, it is necessary to decrease the pressure more slowly by the pressure adjustment valve 9 in order to prevent the generated plasma from being lost. However, if the pressure is decreased excessively slowly, this will extend the total processing time and also may cause contamination on the substrate 7. Accordingly, it is preferable to decrease the pressure by taking about 3 to 15 seconds using the pressure adjustment valve 9. After the pressure within the vacuum container 1 is decreased to the plasma doping pressure, a high-frequency electric power is supplied to the sample electrode 6 from the sample-electrode high-frequency power supply 12.
A second method is a method which changes the types of gases. As illustrated in
A third method is a method which changes the distance G between the sample electrode 6 and the counter electrode 3. As another modification of the first embodiment, in order to move the sample electrode 6 and the counter electrode 3 relative to each other to control the distance G between the sample electrode 6 and the counter electrode 3, for example, as illustrated in
If the distance G is excessively small (smaller than 0.4 time the radius), plasma may not be generated. On the contrary, if the distance G is excessively large (larger than 1.0 time the radius), this will excessively increase the volume of the vacuum container 1, resulting in insufficient pump exhaust ability.
Also, two or more methods out of the aforementioned three methods may be combined.
Note that, in the case of using an ICP (inductively-coupled plasma source), in order to reduce the number of substrates required until the surface resistance after activation is stabilized from just after the wet cleaning is finished, it is effective to perform processing in a state where the distance G between the sample electrode 6 and the dielectric window facing to the sample electrode 6 satisfies the following equation (5).
Also, in the aforementioned modification, the bellows 40 as an example of the sample-electrode lifting/lowering driving device may be provided between the bottom surface of the vacuum container 1 and the sample electrode 6 within the vacuum container 1, and also, the bellows 40 as an example of the counter-electrode lifting/lowering driving device may be provided between the upper surface of the vacuum container 1 and the counter electrode 3 within the vacuum container 1 for lifting and lowering the counter electrode. Thus, both the sample electrode 6 and the counter electrode 3 may be moved to move the sample electrode 6 and the counter electrode 3 relative to each other, in order to control the distance G between the sample electrode 6 and the counter electrode 3.
Also, in the case where the present invention is applied to an ECR (electron cyclotron resonance plasma source) or an ICP (inductively-coupled plasma source), the distance between the counter electrode and a dielectric plate or a surface including gas ejection holes may be set as G, instead of setting the distance between the sample electrode and the aforementioned counter electrode as G.
Further, while, in the present invention, the distance G has been described as being the distance between the electrodes, it is necessary that the distance G be defined as the distance between the substrate and the electrode in a strict sense. However, the substrate is significantly smaller than the distance, and accordingly, there is no problem in describing the distance G as the distance between the electrodes without taking into consideration the thickness of the substrate in the embodiments and examples.
By properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by the embodiments can be produced.
According to the present invention, there are provided a plasma doping method and apparatus having excellent reproducibility of the concentration of impurity implanted into the surfaces of samples. Accordingly, the present invention can be applied to fabrication of thin-film transistors for use in liquid crystals and the like, including impurity doping processing for semiconductor devices.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-271605 | Oct 2006 | JP | national |
This is a continuation application of International Application No. PCT/JP2007/069287, filed Oct. 2, 2007.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12137897 | Jun 2008 | US |
| Child | 13108625 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2007/069287 | Oct 2007 | US |
| Child | 12137897 | US |
