JP4865951B2 - Plasma etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for etching an object to be etched such as a silicon dioxide film by using plasma of a reactive gas.
[Prior art]
In the semiconductor manufacturing technology, when wiring is formed on a semiconductor substrate such as a silicon wafer, it is generally necessary to form wiring holes such as contact holes and through holes in a silicon dioxide film formed on the substrate. In order to form wiring holes in this way, plasma etching technology that can efficiently form holes with high accuracy has been used almost recently. In this technique, a substrate is placed on a susceptor that is also disposed in a processing chamber and also serves as an electrode, and an etching gas is supplied into the processing chamber as a reaction gas, and a high-frequency voltage is applied to the susceptor, thereby generating a plasma of the reaction gas. Is generated in the processing chamber, and etching is performed by radicals, ions, and the like generated by this plasma. As the reaction gas used at this time, various gases are selected according to the material to be etched. For example, when etching a silicon dioxide film, a halogen compound gas such as CHF ₃ or CF ₄ is used. In general, these gases are rarely used alone, and are used in a state in which a reactive gas is added to an inert gas such as argon (Ar) gas as a dilution gas. In the plasma etching technique using such argon gas, process control generally adjusts the distance between the lower electrode susceptor and the upper electrode and the high-frequency bias voltage applied to the lower electrode. It is done by.
[0003]
[Problems to be solved by the invention]
However, when argon gas is used as a dilution gas, it is known that the etching rate at the center of the film to be etched is higher than that at the periphery, that is, the in-plane uniformity of the etching crate is poor. Yes. As described above, in-plane uniformity is not a problem when the substrate is small. However, as the wafer becomes larger and finer as in recent years, it becomes an important problem in terms of manufacturing yield. It has become. In addition, there is a disadvantage that it is troublesome to perform the process control with the inter-electrode distance or the high frequency bias voltage as described above.
[0004]
The present invention has been made in view of the above circumstances, and a first object thereof is to provide a plasma etching method that is easy to control the process and has excellent in-plane uniformity of etching rate.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a plasma etching method according to a first aspect of the present invention includes a processing chamber, an upper electrode, a lower portion provided opposite to the upper electrode, and an object to be etched supported thereon. An electrode, and a focus ring disposed around the supported object to be etched. The upper electrode includes an electrode plate, a support member for supporting the electrode plate in a processing chamber, and a plasma confinement device. The lower electrode has an electrostatic chuck that fixes the object to be etched on the lower electrode by adsorption ,
The shield ring and the electrode plate are formed of silicon , using a plasma etching apparatus,
A plasma of an etching gas and a dilution gas is generated by the upper electrode and the lower electrode in a processing chamber, and neutral particles are ionized by a charge exchange reaction between the ions and the neutral particles in the plasma. When the object to be etched, which is incident on the body and surrounded by the focus ring and is fixed by the electrostatic chuck, is etched, the mixing ratio of helium gas and argon gas is selected as the dilution gas, and the focus ring In the case of increasing the etching rate of the peripheral portion of a nearby object to be etched, the ratio of helium is used at a larger setting.
[0006]
The inventors of the present invention have studied the etching mechanism when a dilution gas such as argon gas is used in plasma etching, and this mechanism is based on the interaction between ions generated by the plasma and neutral particles. I found out that this has a big influence. This phenomenon is as follows. A large number of ions, neutral particles, and electrons are generated from the etching gas (reactive gas) by the plasma. The generated ions and the neutral particles collided violently in the plasma, and the ions gave charge to the neutral particles, and the ions that lost the charge became high-speed neutral particles and also received charges. Neutral particles are ionized. As a result, the ionized neutral particles are accelerated by the sheath electric field formed on the surface of the object to be etched and transported to the object to be etched. By such a reaction (charge exchange reaction), the etchant is supplied to the object to be etched at a high speed without losing the ion assist effect by the high speed neutral particles, and is etched. The probability of charge exchange collision at this time is about 50% for argon gas, but about 90% for helium, which is much larger for helium gas. As a result, by using helium gas as a dilution gas, the etching rate is increased, and a decrease in the etching rate at the periphery of the object to be etched, which is easily influenced by the external environment (for example, a shield ring), can be reduced. . For this reason, in the present invention, the etching rate can be increased as a whole, and a decrease in the etching rate in the periphery of the object to be etched can be suppressed, and the in-plane uniformity of the etching rate can be improved. In other words, by increasing the mixing ratio of helium to argon, the etching rate in the periphery of the object to be etched can be increased. This is because the mass of helium is 4, whereas the mass of argon is 40, the mass of helium is 1/10 that of argon, and the diffusion coefficient is proportional to the mass (mass number). This is because helium which is easily diffused particularly affects the diffusion around the etched body.
[0007]
In addition, by using a mixed gas of helium gas and argon gas as the dilution gas, and selecting the mixing ratio (flow rate ratio) of these gases, the process can be controlled without depending on the distance between electrodes or the high frequency bias voltage. Therefore, this control becomes easy.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a plasma etching method according to an embodiment of the present invention will be described with reference to the accompanying drawings.
First, an outline of a plasma etching apparatus that can be used in the present method will be described with reference to FIG.
An insulating support plate 3 is laid on the bottom of the grounded processing chamber 2 of the plasma apparatus 1, and a susceptor 5 is provided on the support plate 3 via a support base 4. The susceptor 5 constitutes a lower electrode, and an electrostatic chuck 11 for adsorbing and holding a substrate to be processed (an object to be etched), for example, an 8-inch wafer W, is provided on the susceptor 5. The susceptor 5 is connected to a grounded high-pass filter (HPF) 6, and is connected to a first high-frequency power source 50 for applying a high-frequency (for example, 2 MHz) bias voltage via a matching unit 51. ing. The electrostatic chuck 11 has a configuration in which the thin film electrode 12 is sandwiched between insulating films, and is connected to a DC power source 13 of 1.5 kV, for example.
[0009]
A heat exchange chamber 7 is provided inside the support 4, and the heat exchange medium circulates through the introduction pipe 8 and the discharge pipe 9, and the semiconductor wafer W can be maintained at a predetermined temperature via the susceptor 5. ing. This temperature control is improved in accuracy by providing a gas passage 14 for supplying an electric heating medium such as He gas on the back surface of the semiconductor wafer W.
[0010]
A substantially annular focus ring 16 is provided on the upper surface of the susceptor 5 so as to surround the electrostatic chuck 11. The focus ring 16 is formed of, for example, conductive silicon, and has a function of effectively making ions in plasma enter the semiconductor wafer W.
[0011]
An upper electrode 21 is supported on the upper portion of the processing chamber 2 via an insulating member 25 and a shield ring 55. The upper electrode 21 is formed of aluminum whose surface is anodized and has a gas chamber defined therein and a predetermined distance from the wafer W (in this preferred embodiment, the distance between the electrodes 5 and 21 is The electrode plate 23 having a large number of discharge holes 24 facing each other in parallel. The shield ring 55 is adapted to meet the demands of processing miniaturization, improvement of processing speed, and processing uniformity by confining plasma and making it uniform. The shield ring 55 and the front Symbol electrode plate 23 is more formed on silicon. Although such a shield ring 55 is effective in making the plasma uniform, the surface is easily eroded by the plasma and gradually becomes thinner during use, which adversely affects the in-plane uniformity of the etching rate. This has been confirmed by the present inventors. A preferred example of the shield ring is described in Japanese Patent Application No. 2000-279453. In the etching method of the present invention, the shield ring as described in this prior application can be used.
[0012]
The electrode support 22 is formed with a gas inlet 26 communicating with the gas chamber and connected to one end of a gas supply pipe 27. The gas supply rod 27 is provided with a valve 28 and a mass flow controller 29, and the other end thereof is connected to a processing gas supply source 30. The processing gas supply source 30 includes a reaction gas supply source that supplies an etching gas (reaction gas) such as a fluorocarbon gas (CxFy, for example, C4F8 gas) or a hydrofluorocarbon gas (CpHqFr), and a helium gas supply source that supplies a dilution gas. In addition, an argon gas supply source and other necessary gas sources such as an oxygen gas source are provided, and the supply flow rate of gas from these gas sources can be adjusted.
[0013]
An exhaust pipe 31 leading to the exhaust device 35 is connected to the lower portion of the processing chamber 2. The exhaust device 35 includes a vacuum pump such as a turbo molecular pump, and the inside of the processing chamber 2 can be reduced to an arbitrary pressure of, for example, 10 mTorr to 1000 mTorr. A gate valve 32 is provided on the side wall of the processing chamber 2 so that a semiconductor wafer can be taken in and out of the processing chamber.
[0014]
The upper electrode 21 is connected to a second high-frequency power source 40 through a power feed rod 33 and a matching unit 41 and is also connected to a low-pass filter (LPF) 42.
[0015]
Next, using the etching apparatus configured as described above, a semiconductor wafer, more precisely, a plasma etching method of a silicon dioxide film formed on the upper surface of the semiconductor wafer, and an etching obtained by actually carrying out this method The measurement data regarding the in- film uniformity of the rate will be described.
[0016]
The flow rate of the gas supplied from the processing gas supply source 30 and the exhaust of the exhaust device 35 so that the inside of the processing chamber 2 becomes 20 mTorr while the semiconductor wafer W is attracted to the electrostatic chuck 11 in the processing chamber 2. Adjusted with speed. Then, a first high frequency power was applied to the lower electrode 5 by the first high frequency power supply 50. In this embodiment, the first high-frequency power is a frequency of 2 MHz, and the power is adjusted so that the Vpp voltage is constant at 1.5 kv during processing. A second high frequency power was applied to the upper electrode 21 by the second high frequency power supply 40. This second high frequency power is 2500 W at 60 MHz. By applying high-frequency power to each electrode in this way, plasma is generated between the electrodes by the supply gas, and the silicon dioxide film is etched based on the neutral particles and ions generated by this plasma. It was.
[0017]
FIG. 2 shows the results obtained by performing such etching with different flow rates of argon gas and helium gas and measuring the in-plane uniformity of the etching rate. In this figure, the vertical axis shows the etching rate normalized with the center of the semiconductor wafer (silicon dioxide film) as 1, the horizontal axis shows the position (distance) from the center, and the line a (solid line) Shows a case where only argon gas is supplied to the processing chamber at a flow rate of 300 sccm, a line b (broken line) indicates a case where argon gas is 200 sccm and a helium gas is 100 sccm, and a line c (dotted line) indicates argon gas and helium gas. And d (one-dot broken line) are for argon gas at 100 sccm and helium gas at 200 sccm, and line e (two-dot broken line) is for only helium gas at 300 sccm. Show.
[0018]
As can be seen from FIG. 2, in the example corresponding to the prior art using only argon gas (solid line), the etching rate is generally low, and the central part is considerably higher than the peripheral part. That is, the in-plane uniformity is deteriorated. On the other hand, in the example using helium gas (two-dot broken line), not only the etching rate is increased as a whole, but also in-plane uniformity is excellent in the range of 50 mm from the center. And in the example which used argon gas and helium gas together, the etching rate of a peripheral part becomes high as the flow rate of helium gas is increased. For this reason, by appropriately selecting the flow ratio of helium gas and argon gas, etching having desired in-plane uniformity can be performed without controlling the inter-electrode distance and the high-frequency bias voltage.
[0019]
FIG. 3 shows the same reference results as in FIG. 2 when etching is performed under other conditions. However, in this example, the flow rate ratio of the dilution gas is not changed, and the shield ring 55 with a thickness of 7 mm is new (line f) and the shield phosphorus thickness becomes 5 mm after 100 hours ( It is a measurement result with line g). Here, the processing chamber pressure is 40 mmTorr, the high frequency power applied to the lower electrode is 800 kHz, 1500 W, the high frequency power applied to the upper electrode is 27 MHz, 2200 W, the interelectrode distance is 27 mm, and C ₄ F ₈ gas is used. 20 sccm, CO ₂ gas was 40 sccm, Ar gas was 500 sccm, and O ₂ gas was 10 sccm. From this measurement result, it can be seen that when argon gas is used as the dilution gas, the etching rate at the peripheral portion of the wafer decreases as time passes, that is, as the shield ring becomes thinner. In this way, when the etching rate partially changes depending on the thickness of the shield ring, helium gas is added to the argon gas and the mixing ratio of both is changed according to the thickness of the shield ring and immediately depending on the period of use. Thus, in-plane uniformity can be controlled.
[0020]
As described above, in the plasma etching method of the present invention, helium gas alone or a helium gas with a predetermined mixing ratio and argon is used as a dilution gas for generating a charge exchange reaction by generating a plasma of a reaction gas and a dilution gas. By using the gas, the process control can be easily performed, the etching rate can be increased, and the in-plane uniformity can be improved. Further, the reduction in the in-plane uniformity of the etching rate that changes according to the use period of the shield ring can be compensated by changing the mixing ratio of helium gas and argon gas according to the use period.
[0021]
In the above embodiment, in order to carry out the plasma etching method of the present invention, a parallel plate type plasma etching apparatus is used as shown in FIG. 1, but other types well known in this field are used. The device may be used. Immediately, the present invention is not defined in the type of plasma etching apparatus. Moreover, although the case where the silicon wafer in which the silicon dioxide film was formed as an to-be-etched body was etched was demonstrated, it can be applied also to the etching of another film and another semiconductor or a board | substrate. Further, the reaction gas can be appropriately selected according to the material of the object to be etched.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an etching apparatus that can be used in a plasma etching method of the present invention.
FIG. 2 is a diagram showing the measurement results of the in-plane uniformity of the etching rate when etching is performed by the plasma etching method of the present invention and the conventional method, respectively.
FIG. 3 is a diagram showing the relationship between the in-plane uniformity of the etching rate and the shield ring.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Plasma apparatus, 2 ... Processing chamber, 5 ... Susceptor (lower electrode), 21 ... Upper polarization, 30 ... Processing gas supply source, 40 ... 2nd high frequency power supply, 50 ... 1st high frequency power supply, 55 ... Shield ring.

Claims (2)

A processing chamber, an upper electrode, a lower electrode provided opposite to the upper electrode and on which the object to be etched is supported, and a focus ring disposed around the supported object to be etched. The upper electrode includes an electrode plate, a support for supporting the electrode plate in a processing chamber, and a shield ring for confining plasma, and the lower electrode absorbs an object to be etched on the lower electrode. Having an electrostatic chuck to fix,
The shield ring and the electrode plate are formed of silicon, using a plasma etching apparatus,
A plasma of an etching gas and a dilution gas is generated by the upper electrode and the lower electrode in a processing chamber, and neutral particles are ionized by a charge exchange reaction between the ions and the neutral particles in the plasma. When the object to be etched, which is incident on the body and surrounded by the focus ring and is fixed by the electrostatic chuck, is etched, the mixing ratio of helium gas and argon gas is selected as the dilution gas, and the focus ring plasma etch in g wherein the use a larger set the proportion of helium in the case of increasing the etching rate of the peripheral portion of the near object to be etched. A processing chamber, an upper electrode, a lower electrode provided opposite to the upper electrode and on which the object to be etched is supported, and a focus ring disposed around the supported object to be etched. The upper electrode includes an electrode plate, a support for supporting the electrode plate in a processing chamber, and a shield ring provided around the electrode plate for confining plasma. An electrostatic chuck for fixing the object to be etched on the electrode by adsorption;
The shield ring and the electrode plates, that is formed by silicon, using up plasma etching apparatus,
A plasma of an etching gas and a dilution gas is generated between the upper electrode and the lower electrode in a state of being confined by the shield ring and the focus ring in the processing chamber, and ions and neutral particles in the plasma are generated. Used as the dilution gas according to the state of use of the shield ring in order to enhance the uniformity of plasma when etching the object to be etched by ionizing neutral particles by the charge exchange reaction and entering the object to be etched. plasma etch in g wherein the use by changing the mixing ratio of helium gas and argon gas.

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