JP4456412B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus used for etching an interlayer insulating film (mainly containing silicon oxide as a main component) in a manufacturing process of a semiconductor device, particularly an etching process.

  In the semiconductor device manufacturing process, the wafer diameter (12 inches) is approaching, and in semiconductor process equipment, especially dry etching equipment using plasma, how can surface treatment be uniformly performed? It is extremely important in terms of both etching characteristics and throughput. As an indispensable element for uniform etching, uniform supply of radical and ion flux to the wafer can be mentioned.

Conventional oxide film etching apparatuses can be roughly divided into two systems according to plasma density. One is a low medium density plasma type represented by a parallel plate type, and the other is a high density plasma type represented by an ECR (electron cyclotron resonance) type. In either case, a mixed system of a chlorofluorocarbon gas typified by C ₄ F ₈ and a rare gas typified by Ar is used as the plasma gas. In the case of a parallel plate type, in order to uniformly supply radical and ion fluxes to the wafer in a narrow electrode structure with an electrode interval of 10 to 20 mm, a gas introduction path is provided in the upper electrode, and gas can be uniformly supplied from the electrode surface. The shower plate structure is adopted. The uniformity of plasma can be ensured even in a narrow electrode structure because there is basically no magnetic field. On the other hand, in the case of the ECR type, as in the case of the parallel plate type, the gas supply is provided with a shower plate directly under the electromagnetic wave introduction window so that the radical flux can be uniformly incident on the wafer. However, with regard to the uniformity of the plasma, the uniformity is achieved by diffusing the plasma to some extent in consideration of the fact that the plasma is constrained by the applied magnetic field.
An etching apparatus is disclosed in, for example, Patent Document 1.

JP 09-321031 A

By the way, as described above, there are two types of oxide film etching apparatuses using plasma, a low medium density plasma type typified by a parallel plate type and a high density plasma type typified by an ECR type. As the wafer diameter of 12-inch and larger wafers and semiconductor elements become finer, research and development of an etching apparatus equipped with a new plasma source is actively pursued with the aim of further highly accurate oxide film etching. The band ECR plasma type is one of them. Using a UHF band electromagnetic wave of 300 MHz to 1 GHz as a plasma excitation frequency, and actively using electron cyclotron resonance with a magnetic field applied by a magnetic field applying means provided outside the etching chamber, a medium density of 10 ¹¹ cm ⁻³ In addition, it is possible to realize plasma with a low electron temperature in which the diffusion region is 1 to 2.5 eV. This UHF band ECR plasma type etching apparatus is disclosed in, for example, Patent Document 1.

In this apparatus, electromagnetic waves are introduced by a microstrip antenna (hereinafter referred to as MSA) having a three-layer structure of a ground potential conductor, a dielectric, and a conductor plate via a coaxial line. The distance between the sample to be processed and the MSA facing it is 50 mm to 100 mm. Therefore, for example, fluorine radicals dissociated and generated in a mixed gas plasma of Ar and C ₄ F ₈ are consumed on the wafer surface and the MSA surface in the wafer central region, but in the wafer peripheral region, Since the consumption effect is small, the radical concentration increases, and for example, the etching rate of a silicon nitride film used as a stopper layer during self-alignment contact processing increases, and the selectivity to the nitride film in the peripheral region decreases.

  The present invention has been made in view of the above-mentioned problems of the UHF band ECR type etching apparatus, and the etching of the silicon oxide film is performed at a level of 0.2 micrometers or less in response to an increase in wafer diameter of 12 inches or more. However, by providing an etching apparatus that can perform uniform processing and high-selection processing within the wafer surface by performing uniform, high-precision and high-speed processing, and by uniformly and reducing the etching rate of the silicon nitride film. is there.

  In order to achieve the above object, according to the present invention, a plasma processing apparatus having the following configuration is provided.

  The plasma processing apparatus according to the present invention includes a vacuum vessel evacuated by a vacuum evacuation unit, a gas introduction unit for introducing a source gas into the vacuum vessel, and a unit for placing a sample to be processed in the vacuum vessel. And a means for introducing high-frequency power into the vacuum vessel, the raw material gas introduced into the vacuum vessel by the gas introduction means is converted into plasma with the high-frequency power, and the plasma of the sample to be processed is obtained by the plasma. A plasma processing apparatus for performing surface treatment is characterized in that active species control means for controlling active species generated in the plasma is provided around the workpiece sample setting means. Thus, by providing means for controlling the active species generated in the plasma around the workpiece (wafer), the distribution of the active species incident on the wafer can be efficiently controlled. The plasma processing apparatus can further be provided with means for applying a high frequency bias power to the sample to be processed. Thereby, the incidence of ions on the workpiece (wafer) can be promoted, and the surface treatment efficiency can be increased.

  The plasma processing apparatus according to the present invention includes a vacuum vessel that is evacuated by a vacuum evacuation unit, a gas introduction unit for introducing a source gas into the vacuum vessel, and a sample to be processed in the vacuum vessel. The raw material introduced into the vacuum vessel by the gas introducing means, and a sampled means for processing and electromagnetic wave introducing means for introducing an electromagnetic wave having a frequency of 300 MHz to 1 GHz into the vacuum vessel In a plasma processing apparatus for converting a gas into a plasma with the introduced electromagnetic wave and performing a surface treatment of the sample to be processed with the plasma, an annular member is disposed around the sample setting means, and a high frequency bias is applied to the annular member. It is characterized in that a means for applying electric power is further provided. With this configuration, when the concentration of fluorine radicals dissociated and generated in the plasma is low in the central portion of the sample (wafer) to be processed and high in the peripheral portion, high-frequency bias power is applied to the annular member (for example, made of silicon). By applying and promoting the incidence of ions on the annular member, the amount of fluorocarbon-based deposition film on the annular member is suppressed, and the surface reaction on the antenna and wafer surface is realized in a pseudo manner. It is possible to consume fluorine radicals around the wafer and reduce the nitride film etching rate. The electromagnetic wave introducing means can include an electromagnetic wave radiation antenna having a three-layer structure of a conductor plate, a dielectric, and a ground potential conductor. Further, the plasma processing apparatus can be further provided with means for applying a high-frequency bias power to the sample to be processed.

  The plasma processing apparatus according to the present invention further includes means for adjusting the temperature of the surface of the annular member. According to this configuration, when the concentration of fluorine radicals dissociated and generated in the plasma is low in the central portion of the wafer and high in the peripheral portion, the surface temperature of the annular member is adjusted to thereby adjust the fluorocarbon to the annular member. It is possible to suppress the deposition amount of the system deposition film, consume fluorine radicals in the wafer peripheral region, and reduce the nitride film etching rate.

  Furthermore, the plasma processing apparatus according to the present invention can include both means for applying a high frequency bias power to the annular member and means for adjusting the surface temperature of the annular member. According to this configuration, by applying the high-frequency bias power, the incidence of ions to the annular member is promoted, and the surface temperature of the annular member is adjusted, whereby the fluorocarbon-based deposition film on the annular member is adjusted. By effectively suppressing the deposition amount of fluorine and effectively consuming fluorine radicals at the periphery of the wafer, the etching rate of the nitride film at the periphery of the wafer can be reduced, and surface treatment with good uniformity can be achieved.

  Furthermore, the plasma processing apparatus according to the present invention can be configured to distribute the high-frequency bias power applied to the sample to be processed and apply the distributed high-frequency bias power to the annular member. According to this configuration, the high-frequency power applied to the annular member can be supplied by the same power source as the high-frequency power applied to the sample to be processed, which can contribute to reduction of the device installation area and cost reduction of the device.

  In the plasma processing apparatus according to the present invention, the surface temperature adjusting means of the annular member can be a temperature adjusting means using at least one heat source of a heater, a lamp, and a heat medium. According to such a configuration, the temperature of the entire surface of the annular member can be adjusted efficiently and uniformly by using a combination of the plurality of heat sources as appropriate.

  The plasma processing apparatus according to the present invention is characterized in that the surface of the annular member has irregularities. According to this configuration, the effective surface area of the annular member can be increased by the uneven structure, and active species can be controlled efficiently.

  Further, the plasma processing apparatus according to the present invention monitors the distribution state of active species in the plasma, and applies the high-frequency bias power applied to the annular member according to the distribution state of the active species or the annular member. Means may be provided for feedback control of the surface temperature. According to this configuration, during the surface treatment of the sample to be processed (wafer), the variation of the active species concentration distribution accompanying the variation of the plasma, particularly the variation of the fluorine radical concentration distribution, is monitored and applied to the annular member. By applying feedback control to the high-frequency bias power and the surface temperature of the annular member, stable and uniform surface treatment can always be performed.

  The annular member in the plasma processing apparatus according to the present invention can be made of a material mainly composed of silicon, silicon carbide, carbon, silicon nitride film, aluminum, stainless steel, silicon oxide, and aluminum oxide. According to this configuration, by appropriately changing the material of the annular member, the fluorine radical consumption efficiency can be improved and the uniformity of the nitride film etching rate can be realized.

  In the plasma processing apparatus according to the present invention, the annular member preferably has a width in the range of 5 mm to 200 mm and a height in the range of 0 mm to 90 mm. According to this configuration, active species can be controlled efficiently even when the processing conditions are changed by changing the width and height of the annular member within the above range.

  According to the present invention, the radical distribution non-uniformity has been a problem in the UHF band ECR type etching apparatus having the MSA structure and the distance between the MSA and the lower electrode as the workpiece setting means being 50 mm to 100 mm. The non-uniformity in the sample surface of the etching rate of the sample to be processed due to the property is greatly reduced, which can greatly contribute to the improvement of the processing yield.

  From the above, for example, in the etching process of a silicon oxide film using a fluorocarbon gas, even when a large-diameter wafer of 12 inches or more is used, ultra-precision processing of 0.2 micrometers or less is highly uniform and highly accurate. It can be realized by satisfying the requirements at the same time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of a plasma processing apparatus (etching apparatus) according to one embodiment of the present invention. In the present embodiment, an air-core coil 2 is installed around the vacuum vessel 1. The raw material gas is introduced into the vacuum vessel 1 from the gas introduction pipe 3, and the electromagnetic wave from the UHF power source 5 of 500 MHz is supplied to the electromagnetic wave radiation antenna (disk-shaped conductor plate) 14 through the coaxial line 4. ECR plasma is generated in the vacuum vessel 1 by interaction with the magnetic field applied by the air-core coil 2. A lower electrode 6 is provided in the vacuum container 1, and a sample (wafer) 7 to be processed is placed thereon. An 800 KHz high frequency bias power supply 8 is connected to the lower electrode 6 via a blocking capacitor 9, whereby ions in the plasma are transferred to the wafer by a high frequency bias voltage (Vpp) of about 1 kV to 2 kV applied to the wafer 7. 7 Etching is performed by drawing the surface. In the present embodiment, a mixed gas of C ₄ F ₈ and Ar is introduced into the vacuum container 1 as the source gas, and the vacuum container 1 is provided by a conductance valve 11 provided between the vacuum exhaust system 10 and the vacuum container 1. The internal pressure was adjusted to 5 to 20 mTorr, and the silicon oxide film on the surface of the wafer 7 was etched.

  Next, the electromagnetic wave supply system will be described in detail. A 500 MHz electromagnetic wave generated by the UHF power source 5 is transmitted through a coaxial line 4 to a microlayer having a three-layer structure comprising an aluminum disk-shaped conductor plate 14 provided on a ground potential conductor plate 12 via a dielectric 13. Supplied to a strip type electromagnetic radiation antenna. Here, by setting the diameter of the disk-shaped conductor plate 14 to a certain characteristic length, an excitation mode is formed at the interface between the disk-shaped conductor plate 14 and the dielectric 13. In this embodiment, a disc-shaped conductor plate having a diameter of about 25 cm 2 capable of exciting in the TM01 mode is used. In the microstrip antenna (MSA) having a three-layer structure consisting of the ground potential conductor plate 12 / dielectric material 13 / disk-shaped conductor plate 14, the impedance from the feeding point depends on the position of the feeding point to the disk-shaped conductor plate 14. Change. The value is generally from 0 to about 300 Ω from the center position of the conductor plate to the peripheral edge of the conductor plate. Therefore, in order to achieve impedance matching and transmit electromagnetic waves to the back surface of the conductor plate 14 with high efficiency to maintain the generation of plasma, as shown in FIG. 1, it is concentric with an eccentric point avoiding the center point of the conductor plate 14. Power is supplied and high axial symmetry and radiation efficiency are achieved. Although not shown in the figure, the electromagnetic wave transmission line from the coaxial line 4 is divided into two lines, one of which is a line longer than the other by a quarter wavelength, It is possible to supply power to two points. By shifting the lengths of the two transmission lines by a quarter wavelength in this way, the phases of the supplied electromagnetic waves can be shifted by 90 degrees from each other, and a rotating electric field is synthesized on the disk-shaped conductor plate 14, Circularly polarized waves can be excited. This improves the axial symmetry of the radiated electric field and the efficiency of conversion of electromagnetic waves into electron kinetic energy by electron cyclotron resonance.

  Next, a source gas introduction system will be described. The source gas is introduced from the back surface of the ground potential conductor plate 12 through the gas introduction pipe 3. When the TM01 mode is excited, there are circular electric field nodes at positions shifted from the center point of the disk-shaped conductor plate 14. Therefore, as shown in FIG. 1, the local discharge can be prevented by introducing the gas from the position where the electric field intensity is minimum. Further, the disk-shaped conductor plate 14 is provided with an internal space for accommodating the introduced gas, and the introduced gas is introduced from at least 10 or more micro holes provided on the surface (lower surface) of the disk-shaped conductor plate 14. The structure allows uniform dispersion in the vacuum vessel 1. Further, a silicon disk 15 having gas passage holes is fixed to the surface (lower surface) of the disk-shaped conductor plate 14 at positions corresponding to the above-described minute holes. The structure is such that fluorine radicals that cause a reduction in the etching selectivity between the mask and the silicon nitride film and the silicon oxide film can be consumed. Furthermore, a heat medium adjusted to an appropriate temperature by a temperature adjusting means (not shown) can be introduced into the disk-shaped conductor plate 14 via an appropriate heat medium introduction pipe. The surface of the silicon disk 15 can be adjusted to a desired temperature.

  A chuck portion 16 for holding a sample to be processed (semiconductor wafer) 7 is provided at the center of the upper surface of the lower electrode 6 serving as a sample setting means. For example, an electrostatic chuck is used as the chuck mechanism. This electrostatic chuck has a structure in which a conductive thin film such as a copper thin film is sandwiched between two ceramic thin films such as aluminum nitride on the upper surface holding the wafer 7, and a voltage supply lead to the conductive thin film The wire is connected to a DC voltage source through a low-frequency pass filter composed of a coil or the like. The chuck mechanism for the wafer 7 may be a mechanical chuck that is mechanically clamped by a clamp member. Further, the chuck portion 16 is provided with a heat transfer gas supply hole (not shown). By supplying a gas having a good heat transfer property such as helium gas to the heat transfer gas supply hole, a sample to be processed (wafer) is provided. ) Heat conduction efficiency from 7 to the lower electrode 6 can be improved.

An annular member (hereinafter referred to as a focus ring) 17 is arranged on the outer periphery of the sample (wafer) 7 placed on the lower electrode 6. The focus ring 17 is made of a conductor or an insulator, and is provided with high-frequency bias power supply means (consisting of a high-frequency bias power supply 8 ′ and a blocking capacitor 9 ′). It has the function of making the radical concentration distribution in the plasma uniform. Although not shown, the high frequency bias power applied to the electrostatic chuck 16 of the lower electrode 6 can be divided using a capacitor and supplied to the focus ring. In this case, since the power split ratio is determined by the ratio between the sheath capacity of the front surface of the wafer 7 and the capacity of the capacitor, in order to change the high-frequency bias power applied to the focus ring 17, the power split ratio described above is used. It is better to leave the capacitor with a variable capacitance. FIG. 2 shows the radial distribution from the wafer center of the fluorine radical concentration in the generated plasma. The plasma gas was Ar400 sccm with C ₄ F ₈ added at 20 sccm, and the pressure was adjusted to 20 mTorr to generate plasma. When the focus ring 17 is not used, the fluorine radical flux at the wafer center is about 1. 1 × 10 ¹⁶ cm ⁻² , whereas about 8 inches around the 8-inch wafer. The value is about 3 times as large as 0 × 10 ¹⁶ cm ⁻² . On the other hand, when a high frequency bias power of 300 W is applied to a silicon focus ring having an outer diameter of 300 mm and an inner diameter of 205 mm to operate the ion acceleration voltage at 400 V, the fluorine radical flux is 1. 0 × 10 ¹⁶ cm ⁻² , 1. 1 × 10 ¹⁶ cm ⁻² , the uniformity is greatly improved. When the focus ring 17 is not used, the fluorine radicals dissociated and generated in the plasma increases at the wafer peripheral portion with a lot of space and decreases at the wafer central portion, but the focus ring 17 is installed, By promoting the incidence of ions on the focus ring, the silicon and fluorine radicals that react on the surface of the focus ring react with, for example, silicon tetrafluoride, so that the fluorine radical concentration is around the wafer. This is because it decreases in part.

  FIG. 3 is a graph showing the relationship between the difference in the etching rate of the silicon nitride film within the 8-inch wafer surface and the acceleration voltage of ions to the focus ring. As the accelerating voltage of ions to the focus ring is increased, the difference in the etching rate of the silicon nitride film within the wafer surface decreases. When there was no focus ring, the etching rate difference in the wafer surface of the silicon nitride film was 23 nm, but when the focus ring was installed and the acceleration voltage of ions was increased to 400 V, the etching rate difference became 5 nm. It can be seen that the uniformity of the etching rate is improved. However, this relationship differs depending on processing conditions such as plasma gas, UHF power, gas pressure, and the material of the focus ring. Therefore, in order to obtain the desired uniformity of the etching process of the silicon nitride film, information on the processing conditions, the acceleration voltage of ions to the focus ring and the focus ring material is obtained in advance by processing a dummy wafer or by computer simulation. It is desirable to know and change the above processing conditions and the like as appropriate.

  Returning to FIG. 1, a high frequency bias of, for example, 800 kHz can be applied to the electrostatic chuck portion 16 on the lower electrode 6 via a blocking capacitor 9 and an impedance matching device not shown. At the time of processing, plasma is generated by the interaction between the electromagnetic wave radiated from the MSA and the magnetic field applied by the air-core coil 2, and high frequency bias power is applied to the electrostatic chuck unit 16, so that generated ions in the plasma are processed. Etching is performed by accelerating the sample 7.

  FIG. 4 shows an embodiment in which the same effect as described above is provided by adjusting the temperature of the surface of the focus ring 17 instead of applying high-frequency bias power to the focus ring 17. A heat medium introducing pipe 18 for introducing a heat medium whose temperature is appropriately adjusted is installed on the back surface of the focus ring 17 to adjust the temperature of the surface of the focus ring 17. By adjusting the surface temperature, deposition of a deposited film on the surface of the focus ring 17 can be suppressed, consumption of fluorine radicals in the peripheral area of the wafer can be promoted, and a nitride film etching rate around the wafer can be reduced.

  Further, although not shown, a configuration in which high-frequency bias power applying means for the focus ring 17 and surface temperature adjusting means for the focus ring 17 are provided together may be employed. With this configuration, in addition to the above-described high-frequency bias power application effect, the effect of adjusting the surface temperature can be obtained, and a stable etching process can be realized.

  In addition to the configuration of FIG. 1, the function of monitoring the radical concentration distribution in the plasma is added to FIG. 5 to feed back the high frequency bias power to the focus ring 17 and the surface temperature adjustment of the focus ring 17. This is an example. For example, if the uniformity of the distribution of fluorine radicals in the radial direction of the sample decreases due to plasma fluctuations or the like during processing of the sample 7 to be processed, the radical concentration difference between the central part and the peripheral part of the sample 7 The acceleration voltage of ions is controlled by applying high-frequency bias power that is detected by the distribution monitoring means and matches the detected concentration difference to the focus ring 17. In the case of the present embodiment, as a radical distribution monitoring means, a method of measuring light emission from radicals is adopted. Light emitted from the vicinity of the wafer surface is introduced into the spectroscope 20 through the optical system 19 and detected by the photomultiplier tube 21, and this detection signal is taken into the personal computer 22 and processed to obtain the radical concentration distribution. Measurement is performed, and application of high-frequency bias power to the focus ring 17 is controlled so that the density distribution is uniform. As a result, as shown in FIG. 3, the difference in the etching rate of the nitride film in the wafer surface depends on the acceleration voltage of ions to the focus ring 17, so that it is necessary to determine the conditions beforehand using a dummy wafer. In addition, it becomes possible to perform a stable etching process with high accuracy even against subtle fluctuations in conditions during the process.

1 is a schematic configuration diagram of a plasma processing apparatus (dry etching apparatus) according to an embodiment of the present invention. FIG. 2 is a diagram showing a concentration distribution of fluorine radicals in a sample (wafer) 7 surface when a high frequency bias power is applied to the focus ring 17 in the apparatus shown in FIG. 1. The figure which shows the relationship between the difference of the nitride film etching rate in the sample (wafer) 7 surface, and the acceleration voltage of the ion to the focus ring 17. FIG. The schematic block diagram of the plasma processing apparatus (dry etching apparatus) which becomes another one Example of this invention. The schematic block diagram of the plasma processing apparatus (dry etching apparatus) which becomes another one Example of this invention.

Explanation of symbols

1: vacuum vessel, 2: air core coil, 3: gas introduction tube, 4: coaxial line, 5: 500 MHz power supply, 6: lower electrode, 7: semiconductor wafer, 8: high frequency bias power supply, 8 ′: high frequency bias power supply, 9 : Blocking capacitor, 9 ': Blocking capacitor, 10: Vacuum exhaust system, 11: Conductance valve, 12: Earth potential conductor, 13: Dielectric, 14: Disc-shaped conductor plate, 15: Silicon disc, 16: Sample chuck Part: 17: focus ring, 18: heat medium introduction tube, 19: optical system, 20: spectroscope, 21: photomultiplier tube, 22: personal computer.

Claims (4)

A vacuum vessel being evacuated by evacuation means;
Gas introduction means for introducing a source gas into the vacuum vessel;
A lower electrode for placing a sample to be processed in the vacuum vessel;
In a plasma processing apparatus provided with means for introducing high-frequency electromagnetic waves and converting the introduced source gas into plasma,
An annular member is arranged on the outer peripheral side of the position where the sample to be processed of the lower electrode is placed,
A high-frequency bias power source for applying a high-frequency bias power to the workpiece is attached,
The high-frequency bias power is divided, the divided high-frequency bias power is applied to the annular member together with the workpiece, and the high-frequency bias power applied to the annular member is determined in advance. Means for controlling the concentration of active species generated in the plasma around the annular member and the sample to be processed , according to processing conditions of the processed sample and information on the material of the annular member Is attached,
The plasma processing apparatus, wherein the annular member is made of a material mainly composed of silicon, silicon carbide, carbon, silicon nitride film, aluminum, stainless steel, silicon oxide, or aluminum oxide. The plasma processing apparatus according to claim 1,
The plasma processing apparatus according to claim 1, wherein the means for dividing the high-frequency bias power uses a capacitor and divides the high-frequency bias power according to a capacitance ratio of the capacitor. The plasma processing apparatus according to claim 2, wherein
A plasma processing apparatus, wherein the power dividing capacitor has a variable capacity. The plasma processing apparatus according to claim 1,
A plasma processing apparatus, further comprising means for monitoring a distribution state of active species in the plasma and adjusting a high-frequency bias power applied to the annular member according to a fluctuation amount thereof.

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