JP2002252213A - Plasma etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma etching method in which process control is facilitated and etching rate is highly uniform over the surface to be etched. SOLUTION: Plasma of the etching gas and a dilution gas is generated between an upper electrode 21 and a lower electrode 5, an electric charge exchanging reaction between ions and neutral particles ionizes neutral particles, and the ionized particles are injected to a semiconductor wafer W to etch the wafer. Then, in response to the using situation of a shield ring 55 located around the upper electrode for improving uniformity of the plasma, the mixing ratio of a helium gas to an argon gas, where the gases are used as the dilution gases, is changed to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for etching an object to be etched such as a silicon dioxide film using a plasma of a reactive gas.

[0002]

2. Description of the Related Art In semiconductor manufacturing technology, when wiring is formed on a semiconductor substrate such as a silicon wafer, wiring holes such as contact holes and through holes are generally formed in a silicon dioxide film formed on the substrate. There is a need to. As described above, in order to form the wiring holes, a plasma etching technique capable of efficiently forming a highly accurate hole has been mostly used recently. In this technique, a substrate is placed on a susceptor that also serves as an electrode and is placed in a processing chamber, an etching gas is supplied into the processing chamber as a reaction gas, and a high-frequency voltage is applied to the susceptor to generate a plasma of the reaction gas. Is generated in a processing chamber, and etching is performed by radicals, ions, and the like generated by the 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 gas of a halogen compound such as CHF ₃ or CF ₄ is used. In general, these gases are rarely used alone, and are used as a diluent gas in which a reactive gas is added to an inert gas such as an argon (Ar) gas. In the plasma etching technique using such an argon gas, the process control generally involves adjusting a distance between a lower electrode, a susceptor and an upper electrode, and a high frequency bias voltage applied to the lower electrode. It is done by.

[0003]

However, when argon gas is used as a diluent gas, the etching rate of the central portion of the film to be etched is higher than that of the peripheral portion. It is known that uniformity is poor. As described above, in-plane uniformity was not a problem when the substrate was small. However, as wafers have become larger and smaller recently, they have become an important problem in terms of manufacturing yield. Has become. Further, there is a disadvantage that it is troublesome to perform the process control by the distance between the electrodes and the high frequency bias voltage as described above.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide a plasma etching method which facilitates process control and has excellent in-plane uniformity of an etching rate.

[0005]

In order to achieve the above object, a plasma etching method according to a first aspect of the present invention is to generate a plasma of an etching gas and a diluent gas, and to generate ions of the plasma by using the plasma. When the neutral particles are ionized by the charge exchange reaction with the neutral particles and incident on the target to be etched to etch the target,
It is characterized in that helium gas and argon gas are used as the dilution gas by selecting the mixing ratio thereof. In the plasma etching method according to the second aspect of the present invention, a plasma of an etching gas and a diluent gas is generated, and the neutral particles are ionized by a charge exchange reaction between the ions and the neutral particles in the plasma. When etching the body to be etched by making it incident on the body to be etched,
When the mixture ratio of helium gas and argon gas is selected as the diluent gas to increase the etching rate in the peripheral portion of the object to be etched, the ratio of helium is set to a larger value. In the plasma etching method according to the third aspect of the present invention, a plasma of an etching gas and a diluent gas is generated, and the neutral particles are ionized by a charge exchange reaction between ions and neutral particles in the plasma. When the etching target is etched by being incident on the etching target, as the diluent gas,
It is characterized in that an argon gas and a gas having a high probability of charge exchange collision in the reaction are used by selecting their mixing ratio. In the plasma etching method according to the fourth aspect of the present invention, a plasma of an etching gas and a diluent gas is generated between an upper electrode and a lower electrode, and a charge exchange reaction between ions and neutral particles in the plasma is performed. According to the use condition of the shield ring provided around the upper electrode in order to enhance the uniformity of the plasma when etching the object to be etched by ionizing the neutral particles and incident on the object to be etched, It is characterized in that the mixture ratio of helium gas and argon gas used as a gas diluting gas is changed.

The present inventors have studied the etching mechanism when a diluent gas such as argon gas is used in plasma etching, and found that the etching mechanism between the ions generated by the plasma and the neutral particles is different. It has been found that the interaction has a great effect.
This phenomenon is as follows. Many ions, neutral particles, and electrons are generated from the etching gas (reaction gas) by the plasma. Then, the generated ions and the neutral particles collide violently in the plasma, the ions pass the charge to the neutral particles, and the ions that have lost the charge become high-speed neutral particles and also get the charge. Neutral particles ionize. As a result, the ionized neutral particles are accelerated by the sheath electric field formed on the surface of the body to be etched and transported to the body to be etched. By such a reaction (charge exchange reaction), the etchant is supplied to the object to be etched at a high speed for etching without losing the ion assist effect of the high-speed neutral particles. At this time, the probability of the charge exchange collision is about 50% with argon gas, but about 90% with helium, and the helium gas is much larger. As a result, by using the helium gas as the diluent gas, the etching rate is increased, and the decrease in the etching rate in the peripheral portion of the body 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 the in-plane uniformity of the etching rate can be increased by suppressing a decrease in the etching rate in the peripheral portion of the object to be etched. That is, by increasing the mixing ratio of helium to argon, the etching rate in the peripheral portion of the object to be etched can be increased. This means that the mass of helium is 4, while the mass of argon is 40,
The mass of helium is 1/10 of that of argon, and the diffusion coefficient is proportional to the mass (mass number). Therefore, helium, which easily diffuses, particularly affects the diffusion around the etched object. is there.

Further, by using a mixed gas of helium gas and argon gas as a diluting gas and selecting a mixing ratio (flow rate ratio) of these gases, process control can be performed without depending on the distance between electrodes or a high frequency bias voltage. Therefore, this control is facilitated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plasma etching method according to an embodiment of the present invention will be described below 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 at 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 4. The susceptor 5 constitutes a lower electrode, and is provided with an electrostatic chuck 11 for holding a substrate to be processed (an object to be etched), for example, an 8-inch wafer W by suction. The susceptor 5 is connected to a grounded high-pass filter (HPF) 6, and is connected to a high frequency (for example,
First high frequency power supply 5 for applying a bias voltage of 2 MHz)
0 is connected. The electrostatic chuck 11 has a configuration in which a thin-film electrode 12 is sandwiched between insulating films.
It is connected to a 1.5 kV DC power supply 13.

A heat exchange chamber 7 is provided inside the support table 4, and a heat exchange medium circulates through an introduction pipe 8 and a discharge pipe 9, and maintains the semiconductor wafer W at a predetermined temperature via a susceptor 5. It is possible. The accuracy of the temperature control is improved 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.

On the upper surface of the susceptor 5, a substantially annular focus ring 15 is provided so as to surround the electrostatic chuck 11. This focus ring 15
Is formed of, for example, conductive silicon and has a function of effectively causing ions in plasma to be incident on the semiconductor wafer W.

An insulating member 25 is provided above the processing chamber 2.
And the upper electrode 21 via the shield ring 55
Supported. The upper electrode 21 is formed of aluminum whose surface is anodized, and has a predetermined space between the electrode support 22 having a gas chamber defined therein and the wafer W (the distance between the electrodes 5 and 21 in the preferred embodiment is 1
(Set to 7 mm) and an electrode plate 23 having a large number of discharge holes 24 facing each other in parallel. The shield ring 55 is adapted to confine plasma and achieve uniformity, thereby meeting requirements for finer processing, improved processing speed, and uniformity of processing. The resistance of the shield ring 55 is set lower than the resistance of the electrode plate 23.
And may be formed of substantially the same material. For example, silicon can be used as this material. Such a shield ring 55 is effective in making the plasma uniform, but the surface is easily eroded by the plasma and gradually becomes thinner during use, adversely affecting the in-plane uniformity of the etching rate. This has been confirmed by the present inventors. A preferred example of the shield ring is disclosed in Japanese Patent Application No. 2000-279453.
In the etching method of the present invention, it is possible to use a shield ring as described in the prior application.

A gas inlet 26 communicating with the gas chamber is formed in the electrode support 22 and is connected to one end of a gas supply pipe 27. The gas supply tube 27 is provided with a valve 28 and a mass flow controller 29,
The other end is connected to the processing gas supply source 30.
The processing gas supply source 30 supplies a fluorocarbon gas (Cx
Etching gas (reactive gas) such as Fy (for example, C4F8 gas) and hydrofluorocarbon gas (CpHqFr)
And a helium gas supply source and an argon gas supply source for supplying a diluent gas, and other necessary gas sources, for example, an oxygen gas source, and a gas supply flow rate from these gas sources. Is adjustable.

An exhaust pipe 31 leading to an exhaust device 35 is connected to a lower portion of the processing chamber 2. This exhaust device 35
Is provided with a vacuum pump such as a turbo molecular pump, and the inside of the processing chamber 2 is, for example, 10 mTorr to 1000 m
The pressure can be reduced to an arbitrary pressure of Torr. Also,
A gate valve 32 is provided on a side wall of the processing chamber 2 so that a semiconductor wafer can be taken in and out of the processing chamber.

The upper electrode 21 is connected to a second high-frequency power supply 40 via a feed rod 33 and a matching unit 41, and is also connected to a low-pass filter (LPF) 42.

Next, a method for plasma etching a semiconductor wafer, more precisely, a silicon dioxide film formed on the upper surface of a semiconductor wafer, using the etching apparatus having the above-described structure, and a method for actually performing the method are provided. In addition, measurement data regarding the uniformity of the inside of the winding of the etching rate will be described.

In a state where the semiconductor wafer W is attracted to the electrostatic chuck 11 in the processing chamber 2, the inside of the processing chamber 2 is set to 20 mTorr.
The flow rate of the gas supplied from the processing gas supply source 30 and the exhaust speed of the exhaust device 35 were adjusted so as to be r. Then, the first high frequency power was applied to the lower electrode 5 by the first high frequency power supply 50. In this embodiment, the first
Has a frequency of 2 MHz and Vp during processing.
The power was adjusted so that the p voltage was constant at 1.5 kv. The 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 manner, plasma is generated between the electrodes by a supply gas, and the silicon dioxide film is etched based on neutral particles and ions generated by the plasma. Was.

FIG. 2 shows the result of measuring the in-plane uniformity of the etching rate by changing the flow rates of the argon gas and the helium gas. In this figure, the vertical axis indicates the etching rate normalized with the center of the semiconductor wafer (silicon dioxide film) as 1, the horizontal axis indicates the position (distance) from the center, and the line a (solid line) Means that only 30 argon gas is
When supplied at a flow rate of 0 sccm, the line b (broken line) is
Argon gas 200 sccm, helium gas 100
In the case of sccm, the line c (dotted line) indicates the case where the argon gas and the helium gas are each 150 sccm, the line d (dashed line) indicates the case where the argon gas is 100 sccm and the helium gas is 200 sccm, and the line e. (Two-dot broken line) indicates the case where only helium gas is 300 sccm,
Shown respectively.

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 center is considerably higher than the periphery. . That is, the in-plane uniformity is poor. On the other hand, in the case of using helium gas (two-dot broken line), not only the overall etching rate is high, but also the in-plane uniformity is excellent within a range of 50 mm from the center. In the example in which the argon gas and the helium gas are used in combination, the etching rate in the peripheral portion increases as the flow rate of the helium gas increases.
For this reason, by appropriately selecting the flow rate ratio between the helium gas and the argon gas, etching having desired in-plane uniformity can be performed without controlling the distance between the electrodes and the high-frequency bias voltage.

FIG. 3 shows the same reference result as 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 case where the shield ring 55 having a thickness of 7 mm is new (line f) and the case where the shield ring thickness becomes 5 mm after 100 hours have elapsed ( It is a measurement result with a line g). Here, the processing chamber pressure is 4
0 mmTorr, the high frequency power applied to the lower electrode is 8
00 kHz, 1500 W, high frequency power applied to the upper electrode is 27 MHz, 2200 W, distance between electrodes is 27 m
m, C ₄ F ₈ gas is 20 sccm, and CO ₂ gas is 40 sccm.
sccm, Ar gas is 500 sccm, O ₂ gas is 10
sccm. From this measurement result, it can be seen that when argon gas is used as the diluting gas, the etching rate at the peripheral portion of the wafer decreases as time passes, that is, as the shield ring becomes thinner.
If the etching rate changes partially depending on the thickness of the shield ring, add helium gas to the argon gas and change the mixing ratio of the two according to the thickness of the shield ring and immediately, the service period. Thereby, the in-plane uniformity can be controlled.

As described above, in the plasma etching method of the present invention, helium gas alone or helium gas having a predetermined mixture ratio is used as a diluent gas for generating a plasma of a reaction gas and a diluent gas to cause a charge exchange reaction. By using a gas and an argon gas, process control can be easily performed, an etching rate can be increased, and in-plane uniformity can be improved. Further, the decrease 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 the helium gas and the argon gas according to the use period.

In the above embodiment, a parallel plate type plasma etching apparatus is used as shown in FIG. 1 in order to carry out the plasma etching method of the present invention.
Other types of devices well known in the art may be used.
Immediately, the present invention is not limited to the type of the plasma etching apparatus. Further, although a case has been described where a silicon wafer having a silicon dioxide film formed thereon as an object to be etched is etched, the present invention can be applied to etching of other coatings and other semiconductors or substrates. further,
The reaction gas can also be appropriately selected according to the material of the body to be etched.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an etching apparatus that can be used in the plasma etching method of the present invention.

FIG. 2 is a view showing a measurement result of in-plane uniformity of an etching rate when etching is performed by a plasma etching method of the present invention and a conventional method, respectively.

FIG. 3 is a diagram illustrating a relationship between an in-plane uniformity of an etching rate and a 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 ...
Second high-frequency power supply, 50... First high-frequency power supply, 55.

Continuing from the front page (72) Inventor Hiroyuki Ishihara 5-3-6 Akasaka, Minato-ku, Tokyo TBS Release Center Tokyo Electron Limited F-term (reference) 5F004 AA01 BA09 CA02 CA03 DA00 DA22 DA23 DA26 DB03

Claims (4)

[Claims] 1. A plasma of an etching gas and a diluent gas is generated, and neutral particles are ionized by a charge exchange reaction between ions and neutral particles in the plasma, and the ionized neutral particles are incident on the object to be etched. A plasma etching method wherein a mixture ratio of helium gas and argon gas is selected as the diluent gas when etching is performed. 2. A plasma of an etching gas and a diluent gas is generated, and neutral particles are ionized by a charge exchange reaction between ions and neutral particles in the plasma, and the ionized neutral particles are incident on the object to be etched. When etching, the mixture ratio of helium gas and argon gas is selected as the diluent gas, and the ratio of helium is used at a larger setting when the etching rate of the peripheral portion of the object to be etched is increased. A plasma etching method characterized by the above-mentioned. 3. A plasma of an etching gas and a diluent gas is generated, and neutral particles are ionized by a charge exchange reaction between ions and neutral particles in the plasma to be incident on the object to be etched. A plasma etching method wherein an argon gas and a gas having a high probability of charge exchange collision in the reaction are used by selecting a mixture ratio thereof as the diluent gas when etching the silicon. 4. A plasma of an etching gas and a diluent gas is generated between an upper electrode and a lower electrode, and the neutral particles are ionized by a charge exchange reaction between ions and neutral particles in the plasma. The helium gas and the argon used as the diluting gas are used depending on the use state of the shield ring provided around the upper electrode in order to enhance the uniformity of the plasma when the object to be etched is etched by being incident on the body to be etched. A plasma etching method characterized by using a gas with a different mixing ratio.