JP3838397B2 - Semiconductor manufacturing method - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a manufacturing method for realizing a desired process in a plasma process without introducing defects into a substrate.
[0002]
[Prior art]
With the increase in the degree of integration of semiconductor integrated circuits and the reduction in device dimensions, there is a demand for a high-quality and high-speed plasma process that suppresses the introduction of defects into a base substrate. However, for example, by etching the silicon oxide film (SiO ₂ ) using C ₄ F ₈ , CO, O ₂ , Ar, impurities such as carbon (C), fluorine (F), and oxygen (O) are formed on the underlying silicon substrate. A depth of 20-50 nm is also introduced as shown in FIG. As a result, when a wiring metal film is formed immediately after etching, the contact resistance of the source / drain layer increases, and the device speed deteriorates. For this reason, the surface of the Si substrate must be removed by several tens of nm after the SiO ₂ etching, and then a wiring metal film must be formed, leading to an increase in the number of processes, that is, an increase in manufacturing cost. In addition, with the miniaturization of MOS devices, the source / drain layer must be made extremely shallow to several tens of nm in order to suppress the short channel effect. However, with the current technology, the silicon layer of several tens of nm must be removed after etching. It is impossible to realize.
[0003]
Also, in order to increase the speed of LSI, the sheet resistance of the gate electrode of the MOS device must be 1 Ω / □ or less, but the current high-concentration silicon surface is silicided to several Ω / □. Is the limit. Furthermore, when the salicide technique in which silicide is formed in a self-aligning manner is used, there is a problem that the sheet resistance increases due to the fine line effect when the gate width is 0.2 μm or less. Therefore, in order to reduce the sheet resistance by using pure metal for the gate electrode, there is a demand for a metal film forming method that does not introduce defects into the substrate.
[0004]
[Problems to be solved by the invention]
In order to solve the problems of the conventional example, the present invention dramatically reduces defects introduced due to ion irradiation in a substrate or a film and a substrate newly deposited / formed on the substrate. An object of the present invention is to provide a plasma processing method.
[0005]
[Means for Solving the Problems]
The semiconductor manufacturing method of the present invention dramatically reduces defects introduced into the substrate due to the plasma process by changing the gas species used during the plasma process and changing the ion species incident on the substrate surface. It is characterized by making it. Since the amount of defects introduced into the substrate by ion irradiation increases as the atomic weight or molecular weight of ions increases, the use of atoms / molecules with large atomic weight as the process gas, and the gas flow rate and gas type during the process The amount of defects introduced into the substrate is controlled by changing the above.
[0006]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0007]
Example 1
This example shows an example in which the present invention is used in a magnetron plasma etching apparatus.
[0008]
FIG. 2 is a schematic view showing an example of a plasma apparatus according to the present invention. In FIG. 2, 206 is a vacuum vessel, 207 is an electrode I, 208 is a substrate, 209 is a focus ring, 210 is a shower plate, 211 is an electrode II, 212 is a gas inlet, 213 is a magnetic field applying means, and 214 is a vacuum pump. Reference numeral 215 denotes a matching circuit I, 216 denotes a high-frequency power source I, 217 denotes a matching circuit II, and 218 denotes a high-frequency power source II.
[0009]
In the plasma apparatus of FIG. 2, a dipole ring magnet in which a plurality of permanent magnets are arranged in an annular shape is used as the magnetic field applying means 213. The permanent magnets that make up the dipole ring magnet are arranged in such a way that the magnetization direction rotates once while the position of the permanent magnet is half-circular, and generates a magnetic field parallel to the substrate in the vacuum vessel, thereby reducing the plasma density. There is an effect to raise.
[0010]
The gas introduced from the gas inlet 212 is discharged into the process space from a large number of small holes in the shower plate 210. The introduced gas and the reaction product gas released from the substrate surface pass through a space sandwiched between magnetic field applying means 213a and 213b on the side of the substrate, and are exhausted from the plurality of vacuum pumps 214 to the outside. A relatively wide space is provided above the vacuum pump 214 so as not to lower the gas conductance.
[0011]
The high frequency power output from the 13.56 MHz high frequency power source I216 is applied to the electrode I217 through the matching circuit I215 to generate plasma. High-density plasma is efficiently realized by the magnetic field of the dipole ring magnet. However, since the uniformity of the plasma is lost due to electron drift, high frequency power of another frequency is supplied to the upper electrode II211 on the ring.
[0012]
The electrode II211 is a ring-shaped metal plate here, and is provided to improve the in-plane uniformity of the plasma near the surface of the substrate 208. The high frequency power output from the 100 MHz high frequency power supply II 218 is applied to the electrode II 211 through the matching circuit II 217. By balancing the drift of electrons on the surface of the electrode II211 and the drift of electrons on the surface of the substrate 208 caused by applying a magnetic field by applying an appropriate high frequency power to the electrode II211, the plasma near the surface of the substrate 208 is almost completely uniform. It becomes.
[0013]
Using this apparatus, an experiment for etching a BPSG film was conducted. As a substrate to be plasma-treated, an insulating film BPSG is formed to a thickness of 1.5 μm on a Si wafer having a diameter of 200 mm, and a mask material 0.7 μm called a resist is applied thereon, followed by exposure and development processes. A hole pattern having a diameter of 0.18 μm was prepared.
[0014]
Etching conditions are: high frequency power (13.56 MHz) 2000 W applied to electrode I, high frequency power (100 MHz) 400 W applied to electrode II, process pressure 40 mTorr, process gas flow rate C ₄ F ₈ : 10 sccm, CO: 50 sccm, Ar : 200 sccm, O ₂ : 5 sccm. By realizing uniform plasma, high-speed etching at 850 nm / min was achieved with in-plane uniformity of 2% or less.
[0015]
However, after forming the contact hole, after wet cleaning, the wiring metal (Al-Si (1%)) was formed, patterned and etched, and the contact resistance between the wiring metal and the underlying high-concentration silicon layer was measured. The contact resistivity was, on average, 2.5 × 10 ⁻⁵ Ωcm ² , which was 1 to 2 digits larger than that obtained conventionally.
[0016]
When the base silicon substrate after etching was measured by a secondary ion mass spectrometer (SIMS), impurities such as carbon (C), fluorine (F), and oxygen (O) had a depth of 20 to 50 nm as shown in FIG. It was found that was also introduced. Since these impurities were introduced, the carrier concentration in Si near the surface decreased, leading to an increase in contact resistance. Therefore, conventionally, several tens of nm of the underlying silicon layer has been removed after etching to obtain a low contact resistance.
[0017]
When the process is performed under the above etching conditions, most of the ion species incident on the substrate surface is Ar ⁺ and the incident energy is about 500 eV. On the other hand, the substrate surface is always covered with a thin fluorocarbon (C _x F _y ) polymer film, and BPSG etching proceeds by irradiating the polymer film with high-energy Ar ions.
[0018]
When all of the BPSG is etched and the underlying silicon layer appears, the deposition rate of the polymer film increases, and the etching of the underlying Si layer stops or the etching rate decreases significantly due to the balance with the etching by high energy Ar ion irradiation. As a result, the underlying silicon layer can be left without being etched.
[0019]
In the actual process, overetching of about 20 to 40% is generally performed in order to surely etch the underlying silicon layer. Therefore, high energy Ar ions are irradiated in a state where a thin C _x F _y polymer layer is present on the silicon layer. At this time, carbon (C) and fluorine (F) contained in the polymer layer are irradiated. Impurities such as oxygen (O) are introduced into the substrate.
[0020]
The plasma etching method of the present invention is characterized in that the amount of impurities introduced into the underlying silicon layer is reduced by using Xe having a large atomic weight instead of Ar. FIG. 3 shows an impurity profile in Si when Xe is used as a dilution gas. It can be seen that the amount of impurities introduced and their depth are greatly reduced. This is because the atomic radius of Xe is as large as 2.17 Å compared to the atomic radius of Ar being 1.88 、, and it is difficult to be implanted into the polymer and Si substrate, and energy can be efficiently transferred only to the substrate surface. Because. Further, the atomic weights of Ar and Xe are 39.95 and 131.3, respectively, and Xe is heavier than Ar, and has the effect that the transmission efficiency of energy and momentum to the substrate surface is low, making it difficult to create defects. The results as shown in Fig. 1 were obtained.
[0021]
However, when Xe is used, the etching rate is 530 nm / min, which is lower than 850 nm / min when Ar is used. This is because Xe is harder to be driven into the substrate than Ar, and energy and momentum transmission efficiency to the substrate surface is low. A decrease in the etching rate leads to a decrease in throughput and a decrease in apparatus productivity. Therefore, when etching the contact hole, Ar / C ₄ F ₈ / CO / O ₂ is used until 90% of the BPSG film thickness is etched, and then Ar is switched to Xe to perform etching. While suppressing the introduction of impurities into the substrate, the increase in process time could be suppressed. This also led to a reduction in the amount of expensive Xe used, thereby reducing costs.
[0022]
Needless to say, the same effect can be obtained when the present invention is applied to a plasma apparatus using a different plasma source or other process conditions.
[0023]
(Example 2)
In this example, an example in which the present invention is applied to a magnetron sputtering apparatus is shown.
[0024]
FIG. 4 is a schematic diagram showing a cross-sectional view of the element manufactured in this example and a measurement system for the withstand voltage of the element. In FIG. 4, the element whose dielectric strength is measured is composed of the base body 4001 made of an n-type Si wafer, a field oxide film 4002, a gate oxide film 4003, and a gate electrode 4004. Reference numeral 4005 denotes a probe used for measuring the withstand voltage, 4006 denotes a voltmeter, 4007 denotes a voltage applying means, and 4008 denotes an ammeter.
[0025]
The formation of the element shown in FIG. 4 and the measurement of the withstand voltage were performed according to the following procedure.
[0026]
(1) A field oxide film 4002 (thickness: 500 nm) made of SiO _{2 is} deposited on an n-type Si wafer 4001 by a thermal oxidation method [(H ₂ + O ₂ ) gas, H ₂ = 1 l / min, O ₂ = 1 l / min, the temperature of the object to be processed = 1000 ° C.], a part of the field oxide film 4002 was wet-etched to expose the surface of the n-type Si wafer 4001.
[0027]
(2) Only on the exposed surface of the n-type Si wafer 4001, a gate oxide film (SiO ₂ ) 4003 (area = 1) by a thermal oxidation method [O ₂ gas, 2 l / min, temperature of the object to be processed = 900 ° C.] 0.0 × 10 ⁻⁴ cm ² , thickness = 10.2 nm).
[0028]
(3) A gate electrode material 4004 (thickness = 200 nm) was formed, and a gate electrode was formed by a lithography process and an etching process. Note that polycrystalline silicon doped with Ta and phosphorus by about 10 ²⁰ cm ⁻³ was used as the gate electrode material. All film thicknesses are 200 nm. The Ta film forming conditions are shown separately. The conditions for forming the polycrystalline silicon film are as follows: the substrate temperature is 650 ° C., the pressure is 100 Torr, the type of gas used and the flow rate are N ₂ : SiH ₄ : PH ₃ = 9950 sccm: 50 sccm: 0.5 sccm. Annealing is performed at 850 ° C. for 30 minutes in an N ₂ atmosphere.
[0029]
(4) An interlayer insulating film SiO ₂ (thickness: 400 nm) was deposited at 400 ° C. by an atmospheric pressure CVD method, and contact holes were formed by a lithography process and an etching process.
[0030]
(5) An Al electrode was formed, and finally sintering annealing was performed at 400 ° C. for 30 minutes in an N ₂ / H ₂ = 1.8 slm: 0.2 slm atmosphere.
[0031]
(6) A voltage at which the probe 4005 is brought into contact with the electrode 4010 and a DC voltage is applied to the object 4001 made of an n-type Si wafer via the gate electrode 4004, and the gate oxide film 4003 breaks down (ie, withstand voltage). Was measured with a voltmeter 4006.
[0032]
FIG. 5 shows a schematic diagram of the plasma apparatus used when sputtering Ta film as the gate electrode of the MOS diode. The plasma apparatus shown in FIG. 5 includes two parallel plate type electrodes I402 and II403 in a vacuum vessel 401, a Ta target 404 is deposited on the electrode II, and a film is deposited on the electrode I. A silicon wafer 405 is mounted, a matching circuit I406, a matching circuit II412, a high-frequency power source I408, a high-frequency power source for the purpose of introducing a source gas into the container and applying a high frequency to the electrode I and the electrode II II 413 is connected. In order to control the film forming speed, a DC power source 417 is connected to the electrode II via a low-pass filter 416.
[0033]
A dipole ring magnet 414 in which a plurality of permanent magnets are arranged in an annular shape to apply a magnetic field to the target surface is provided outside the container, and is generated near the target surface in a region outside the outer peripheral edge of the target. Auxiliary electrode A410 provided with a means for adjusting the junction impedance provided at the portion that is electrically joined to the electrode II for the purpose of making the plasma density uniform is provided, and in the region outside the outer peripheral edge of the target, Auxiliary to which high frequency power independent from the high frequency applied to the electrodes I and II is applied to a position separated from the electrode II for the purpose of equalizing the density of plasma generated near the target surface. An electrode B411 is provided.
[0034]
The gas introduced into the container passes through a space sandwiched between magnetic field applying means 414a and 414b on the side of the substrate, and is exhausted from the plurality of vacuum pumps 415 to the outside. A relatively wide space is provided above the vacuum pump so as not to lower the gas conductance.
[0035]
The frequency of the high frequency power applied to the electrode I was 13.56 MHz, the frequency applied to the electrode II was 42.4 MHz, and the frequency applied to the auxiliary electrode B was 100 MHz. The frequency of the high frequency applied to each electrode is not limited to the above value, but the frequency of the high frequency applied to the auxiliary electrode B lowers the self-bias potential applied to the auxiliary electrode B, and causes its own sputtering. It is preferable to set as high as possible to avoid.
[0036]
The sputter deposition conditions for forming bcc tantalum are shown below. In general, when Ta is formed by sputtering, a thin film having a crystal structure different from that of a bulk having a large specific resistance of 160 μΩcm called b-Ta is formed.
[0037]
In this example, the ion irradiation conditions, that is, the ion irradiation amount and the ion irradiation energy are independently and precisely controlled by the supply power of the high frequency power supply II 413 and the supply power of the high frequency power supply II 408, respectively, and the specific resistance is 14 μΩcm, one digit. As described above, a Ta film having a small bcc structure was formed. The Ta film was formed in two cases using Ar plasma and Xe plasma.
[0038]
(1) Ar plasma gas pressure: 7 mTorr
Gas flow rate: 250sccm
High frequency power I (target): 1000W
High frequency power II (substrate): 0W
High frequency power B (auxiliary electrode B): 200 W
Target voltage: -70V
Energy of ions incident on the substrate: 20 eV
[0039]
(2) Xe plasma gas pressure: 7 mTorr
Gas flow rate: 250sccm
High frequency power I (target): 1000W
High frequency power II (substrate): 250W
High frequency power B (auxiliary electrode B): 100 W
Target voltage: -95V
Energy of ions incident on the substrate: 45 eV
[0040]
FIG. 6 is a graph showing the measurement result of the withstand voltage when Ta is used as the gate electrode. Compared to the case of using Ar, when the film is formed using Xe, the breakdown voltage distribution has a higher value. This is because the atomic radius of Xe is as large as 2.17 Å compared to the atomic radius of Ar being 1.88 、, and it is difficult to be implanted into the substrate, and energy can be efficiently transmitted only to the substrate surface. . In addition, the atomic weights of Ar and Xe are 39.95 and 131.3, respectively, and Xe is heavier than Ar and has the effect of low energy and momentum transfer efficiency to the substrate surface, making it difficult to create defects in the gate insulating film. There was also a result as shown in FIG.
[0041]
FIG. 7 is a schematic view showing a cross-sectional view of the element prepared in this example and a measurement system for the dielectric breakdown injection charge amount of the element. In FIG. 7, the element whose dielectric breakdown injection charge was measured is the same as the element shown in FIG. The dielectric breakdown injection charge amount was measured according to the following procedure.
[0042]
(1) The probe 5005 is brought into contact with the Al electrode 5010, and a constant current is supplied from the constant current source 5007 through the gate electrode 5004 so that the current density is 100 mA / cm ^2. And the time for the gate oxide film 5003 to break down was measured. The current density value multiplied by this time is the dielectric breakdown injection charge amount.
[0043]
FIG. 8 is a graph showing the measurement results of the dielectric breakdown injection charge amount. In FIG. 8, the horizontal axis represents the injected charge amount, and the vertical axis represents the cumulative frequency of the element from which each injected charge amount was obtained. As a gate electrode material, a Ta thin film formed by sputtering using Ar plasma and Xe plasma, and polycrystalline silicon doped with about 10 ²⁰ cm ^{−3 of} phosphorus were used. All film thicknesses are 200 nm. The following points became clear from FIG.
[0044]
(1) An element in which a Ta gate electrode is produced by Ar plasma has a wide distribution of injected charge amount (that is, the uniformity of the film quality of the gate oxide film is poor) and the average charge injection amount is C / cm ² . It was low.
[0045]
(2) An element in which a Ta gate electrode is produced with the Xe plasma of the present invention has a narrow distribution of injected charge amount (that is, good uniformity in film quality) and a high average charge injection amount of C / cm ^2. The result is equivalent to that using crystalline silicon for the gate electrode. Furthermore, when Ta is used for the gate electrode, the sheet resistance of the gate can be reduced to 0.7Ω / □, which is a target of 1Ω / □ or less, and the speed of the device can be increased.
[0046]
From the results of the dielectric breakdown characteristics and dielectric breakdown injection charge amount characteristics of the gate insulating film described above, when the metal gate electrode is formed by sputtering film formation, it is applied to the base gate oxide film by using Xe plasma instead of Ar plasma. It is possible to eliminate almost no damage. This is because Xe ions are less likely to enter the substrate than Ar ions, and it is easy to effectively supply energy to the substrate surface, and Xe ions are more efficient in transferring energy and momentum to the substrate surface than Ar ions. This also has the effect of making it difficult to form defects in the gate insulating film, and the results shown in FIGS. 6 and 8 were obtained.
[0047]
The elucidation of the above mechanism is further clarified from the results of sputtering film formation using He, Ne, Kr plasma in addition to Ar and Xe, and Xe having the largest atomic number among the rare gases excluding the radioactive element Rn Is optimal. However, Xe has an atmospheric content of 0.087 ppm by volume, which is very small compared to 9340 ppm by volume of Ar, and the price of Xe gas is more than 100 times that of Ar gas. Therefore, switching the gas during the process is suitable from the viewpoint of cost reduction.
[0048]
In the gate electrode formation step, the initial step of starting to deposit the gate electrode on the gate oxide film is most likely to damage the gate insulating film and is important. Therefore, the first 20 nm is formed with Xe plasma, and thereafter When the gas was switched and the remaining 180 nm was deposited with Ar plasma, the same results as those obtained with the Xe plasma were obtained.
[0049]
Therefore, when the gate electrode is formed on the gate insulating film, an initial process is performed with Xe plasma, and thereafter, a method using a rare gas different from Xe is suitable from the viewpoint of cost reduction. From the viewpoints of sputtering rate, conditions for forming Ta of the bcc structure, and the price of gas, a method using Ar after Xe is most suitable. Alternatively, if the cost is reduced by providing means for collecting and reusing the rare gas used in the process from the latter stage of the pump, the same running cost can be realized even if the process is performed using Xe.
[0050]
Needless to say, the same effect can be obtained when the present invention is applied to a plasma apparatus using a different plasma source or a plasma film formation of a different material.
[0051]
Example 3
In this example, the present invention is applied to a plasma oxidation process in which a radial line slot antenna plasma apparatus is used and a silicon substrate surface is oxidized at a low temperature.
[0052]
First, FIG. 9 shows a schematic diagram of a plasma apparatus used in a silicon direct oxidation experiment. This plasma apparatus has a vacuum vessel 901, a source gas inlet 902 necessary for generating plasma in the vessel, and a vacuum pump 903 for exhausting the source gas introduced into the vessel. A part of the wall portion is a dielectric plate 904 made of a material that can transmit microwaves with substantially no loss, and an antenna 905 that radiates microwaves is installed outside the container across the dielectric plate. ing.
[0053]
An electrode 906 for placing a substrate 908 to be processed is provided inside the container, and the microwave radiation surface of the antenna and the surface on which the substrate is subjected to plasma processing are opposed substantially in parallel. Are arranged. The electrode 906 is provided with a heating mechanism so that the substrate temperature can be raised during the process.
[0054]
A reflector 909 is provided for the purpose of preventing the microwave radiated from the antenna from propagating to the exhaust port side and generating plasma uniformly only on the substrate. Further, in order to make the introduction of the source gas uniform, the source gas of this apparatus is introduced into the process space through a large number of small holes through the shower plate 907. This source gas is exhausted from the plurality of vacuum pumps 903 to the outside. A relatively wide space is provided above each vacuum pump so as not to lower the conductance of the gas.
[0055]
As described above, when a plurality of vacuum pumps arranged at substantially equal intervals on the side of the substrate are exhausted, a gas flow on the substrate that is uniform in the rotation direction can be realized with almost no decrease in gas conductance.
[0056]
In this example, a radial line slot antenna is used as a microwave antenna, and the present invention is applied to a plasma oxidation process in which a silicon substrate surface is oxidized at a low temperature.
[0057]
Here, a case will be described in which a Si wafer is used as the substrate, and the gate oxide film is formed by directly oxidizing the surface of the Si wafer with gas plasma containing O ₂ . FIG. 10 is a schematic diagram showing a cross-sectional view of the element manufactured in this example and a measurement system for the withstand voltage of the element. In FIG. 10, the element whose dielectric strength is measured is composed of the base 6001 made of an n-type Si wafer, a field oxide film 6002, a gate oxide film 6003, and a gate electrode 6004. Reference numeral 6005 denotes a probe used for measuring the withstand voltage, 6006 denotes a voltmeter, 6007 denotes a voltage applying means, and 6008 denotes an ammeter.
[0058]
The formation of the element shown in FIG. 10 and the measurement of the withstand voltage were performed according to the following procedure.
[0059]
(1) A field oxide film 6002 (thickness: 800 nm) made of SiO _{2 is} deposited on an n-type Si wafer 6001 by a thermal oxidation method [(H ₂ + O ₂ ) gas, H ₂ = 1 l / min, O ₂ = 1 l / min, the temperature of the object to be processed = 1000 ° C.], a part of the field oxide film 6002 was wet-etched to expose the surface of the n-type Si wafer 6001.
[0060]
(2) Only the exposed surface of the n-type Si wafer 6001 is directly oxidized using the plasma processing apparatus according to the present invention, and a gate oxide film 6003 made of SiO ₂ (area = 1.0 × 10 ⁻⁴ cm ^2). , Thickness = 7.6 nm). The film forming conditions at that time are as follows: the film forming gas is Ar / He / O ₂ , the gas pressure is 30 mTorr, the partial pressure ratio is Ar: He: O ₂ = 68%: 30%: 2%, the microwave power is 700 W, the oxidation The treatment time was 20 minutes, the substrate was kept in an electrically floating state, and the temperature of the object to be treated was 430 ° C. However, the film forming conditions are not limited to this.
[0061]
(3) A gate electrode 6004 (thickness = 1000 nm) made of Al was formed on the field oxide film 6002 and the gate oxide film 6003 by an evaporation method.
[0062]
(4) A probe 6005 is brought into contact with the gate electrode 6004, a DC voltage is applied to the object 6001 made of an n-type Si wafer via the gate electrode 6004, and a voltage at which the gate oxide film 6003 breaks down (that is, withstand voltage) ) Was measured with a voltmeter 6006.
[0063]
Prior to the plasma oxidation of (2), the substrate surface was irradiated with low energy ions in a non-oxidizing atmosphere to desorb impurities adsorbed on the substrate surface. Also, after plasma oxidation, low energy ion irradiation was performed under the same conditions to improve the denseness of the film. The pressure at that time is 300 mTorr, the microwave power is 150 W, and the ion irradiation energy is 4 eV. This surface cleaning and post irradiation were performed using He, Ar, and Xe plasmas. At that time, the gas type was switched without turning off the plasma. The plasma oxidation conditions are the same in all cases.
[0064]
FIG. 11 is a graph showing the measurement results of the withstand voltage. 11A, 11B, and 11C, respectively, after performing surface cleaning by low energy ion irradiation for 5 minutes using He, Ar, and Xe plasmas, a gate insulating film is formed, and then He is further added. This sample was subjected to post irradiation by low energy ion irradiation for 5 minutes using Ar, Xe plasma. In FIG. 11, the horizontal axis indicates the withstand voltage, and the vertical axis indicates the frequency of the element from which each withstand voltage is obtained. For example, a bar graph with a horizontal axis of 10 MV / cm is the frequency of occurrence of elements having a withstand voltage in the range of 9.5 to 10.4 MV / cm.
[0065]
From the figure, it can be seen that the distribution variation is the smallest and the withstand voltage is large when Xe plasma is used. This is because Xe ions do not create defects inside the substrate and can efficiently supply energy only to the surface, so that the substrate surface before oxidation can be cleaned most without introducing defects, and damage can be caused by post irradiation. This is because the gate oxide film can be made dense without introduction.
[0066]
It goes without saying that the same effect can be obtained even if the present invention is applied to a plasma apparatus using different plasma sources or different plasma oxidation conditions.
[0067]
Example 4
In this example, a case where the present invention is applied to a plasma process in which the surface of the substrate is oxynitrided at a low temperature using a radial line slot antenna plasma process apparatus is shown.
[0068]
Since the plasma processing apparatus using the radial line slot antenna used in this example is the same as that of the third embodiment, a description thereof will be omitted. In the same manner as in Example 3, a case will be described in which a Si wafer is used as the substrate, and the surface of the Si wafer is directly oxynitrided with O ₂ and N ₂ to form a gate oxynitride film.
[0069]
FIG. 12 is a schematic view showing a cross-sectional view of the element prepared in this example and a measurement system for the dielectric breakdown injection charge amount of the element. In FIG. 12, the element whose dielectric breakdown injection charge is measured is composed of an object 7001 made of an n-type Si wafer, a field oxide film 7002, a gate oxynitride film 7003, and a gate electrode 7004. Reference numeral 7005 is a probe used for measuring the dielectric breakdown injection charge amount, 7006 is a voltmeter, 7007 is a constant current source, and 7008 is an ammeter. The formation of the element shown in FIG. 12 and the measurement of the dielectric breakdown injection charge amount were performed according to the following procedure.
[0070]
(1) A field oxide film 7002 (thickness: 800 nm) made of SiO _{2 is} deposited on an n-type Si wafer 7001 by a thermal oxidation method [(H ₂ + O ₂ ) gas, H ₂ = 1 l / min, O ₂ = 1 l / min, the temperature of the object to be processed = 1000 ° C.], a part of the field oxide film 7002 was wet-etched to expose the surface of the n-type Si wafer 7001.
[0071]
(2) Only the exposed surface of the n-type Si wafer 7001 is directly oxynitrided using the plasma processing apparatus according to the present invention, and the gate insulating film 7003 made of SiO _x N _y (area = 1.0 × 10 ^{−). 4} cm ² , thickness = 5.6 nm). The film formation conditions at that time are initially performed for 15 minutes at a gas species of Ar / He / O ₂ , a gas pressure of 30 mTorr, a partial pressure ratio of Ar: He: O ₂ = 68%: 30%: 2%, and a microwave power of 700 W. The remaining 5 minutes are the gas species Ar / He / N ₂ , the partial pressure ratio Ar: He: N ₂ = 68%: 30%: 2%, and the microwave power 700 W. The object to be processed was kept in an electrically floating state, and the temperature of the object to be processed was 430 ° C.
[0072]
(3) A gate electrode 7004 (thickness = 1000 nm) made of Al was formed on the field oxide film 7002 and the gate nitride film 7003 by vapor deposition.
[0073]
(4) The probe 7005 is brought into contact with the gate electrode 7004, and a constant current is supplied from the constant current source 7007 through the gate electrode 7004 so that the current density is 100 mA / cm ^2. And the time for the dielectric breakdown of the gate oxynitride film 7003 was measured. The current density value multiplied by this time is the dielectric breakdown injection charge amount.
[0074]
FIG. 13 is a graph showing the measurement results of the dielectric breakdown injection charge amount. In FIG. 13, the horizontal axis represents the injected charge amount, and the vertical axis represents the cumulative frequency of the element from which each injected charge amount was obtained. The plasma oxide film shown in Example 3 is compared with the plasma oxynitride film of this example. It can be seen that a high average charge injection amount can be obtained by using the plasma oxynitride film. This is because by performing nitridation after the oxide film is formed, a small amount of nitrogen is mixed into the gate insulating film, thereby improving the characteristics.
[0075]
【The invention's effect】
According to the present invention, it is possible to provide a plasma processing method capable of dramatically reducing defects introduced due to ion irradiation in a substrate, or a film and a substrate newly deposited / formed on the substrate. it can.
[Brief description of the drawings]
FIG. 1 is a graph showing etching depth with respect to secondary ion intensity.
FIG. 2 is a schematic view showing an example of a plasma apparatus according to the present invention.
FIG. 3 shows an impurity profile in Si when Xe is used as a dilution gas.
FIG. 4 is a schematic view showing a cross-sectional view of an element manufactured in this example together with a measurement system for the withstand voltage of the element.
FIG. 5 is a schematic view of a plasma apparatus.
FIG. 6 is a graph showing measurement results of dielectric strength voltage when Ta is used as a gate electrode.
FIG. 7 is a schematic view showing a cross-sectional view of the device prepared in Example 2 together with a measurement system for the dielectric breakdown injection charge amount of the device.
FIG. 8 is a graph showing measurement results of dielectric breakdown injection charge amount.
FIG. 9 is a schematic view of a plasma apparatus used in a silicon direct oxidation experiment.
10 is a schematic view showing a cross-sectional view of the element manufactured in Example 3 together with a measurement system for the withstand voltage of the element. FIG.
FIG. 11 is a graph showing measurement results of dielectric strength voltage.
12 is a schematic view showing a cross-sectional view of an element prepared in Example 4 together with a measurement system for a dielectric breakdown injection charge amount of the element. FIG.
FIG. 13 is a graph showing measurement results of dielectric breakdown injection charge amount.
[Explanation of symbols]
206 vacuum vessel,
207 Electrode I,
208 substrates,
209 Focus ring,
210 shower plate,
211 electrode II,
212 gas inlet,
213 means for applying a magnetic field,
214 vacuum pump,
215 matching circuit I,
216 high frequency power supply I,
217 matching circuit II,
218 High-frequency power supply II,
4001 substrate,
4002 Field oxide film,
4003 Gate oxide film,
4004 Gate electrode,
4005 The probe used to measure the withstand voltage,
4006 Voltmeter,
4007 voltage applying means,
4008 ammeter,
401 vacuum vessel,
402 electrode I,
403 Electrode II,
404 Ta target,
405 silicon wafer,
406 matching circuit I,
412 matching circuit II,
408 high frequency power supply I,
413 high frequency power supply II,
5004 Gate electrode,
5005 probe,
5007 constant current source,
5010 Al electrode,
901 vacuum vessel,
902 Source gas inlet,
903 vacuum pump,
904 dielectric plate,
905 antenna,
908 substrate,
909 reflector,
6001 substrate,
6002 Field oxide film,
6003 Gate oxide film,
6004 gate electrode,
6005 probe,
6006 Voltmeter,
6007 voltage applying means,
6008 Ammeter.

Claims (6)

  A semiconductor manufacturing method characterized in that, when etching is performed using plasma, a gas containing Ar is switched to a gas containing Xe during the process.   2. The semiconductor manufacturing method according to claim 1, wherein the etching is etching of an interlayer insulating film.   A semiconductor manufacturing method characterized in that, when a film is formed using plasma, a gas containing Xe is switched to a gas containing Ar during the process.   4. The semiconductor manufacturing method according to claim 3, wherein the film formation is an electrode film formation on an insulating film.   The semiconductor manufacturing method according to claim 4, wherein the film formation is film formation of a gate electrode on a gate insulating film.   6. The semiconductor manufacturing method according to claim 3, wherein the film formation is sputter film formation.

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