JPH0245714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to etching methods and etching gases, and more particularly to methods and gas mixtures for etching aluminum in a plasma environment.

In a planar plasma reactor, the material to be processed is placed between a pair of electrode plates, and high frequency power is applied to the electrode plates to ionize the reactant gas and form active species for performing the desired processing. here,
The term "active species" shall refer to ionized particles that react with and etch aluminum. Such reactors have been used, for example, to etch silicon, silicon dioxide, silicon nitride, aluminum, and other materials used in the manufacture of semiconductor devices.

Traditionally, plasma etching processes have been performed at relatively low pressures (eg, 100-600 μm Hg) in planar reactors. When high pressure is used, it is difficult to generate and sustain a stable and uniform plasma, and the photoresist coating is easily destroyed. Aluminum is generally relatively slow in such systems;
For example, it is etched at 1500 angstroms/minute. In this specification, the term aluminum refers to pure aluminum and 2%
Aluminum alloys such as silicon-containing aluminum-silicon alloys may be used.

It is an object of the present invention to provide a new and improved method and gas mixture for etching aluminum in a plasma reactor.

Another object of the present invention is to provide a method and gas having the characteristics described above that allow aluminum to be removed anisotropically and more rapidly than conventional methods without destroying the photoresist.

Another object of the invention is to provide a method and gas mixture of the above character, which uses higher pressures and higher power densities than conventional etching methods in a planar reactor.

These and other purposes may include a first etching gas mixture containing BCl ₃ and chlorine or CCl ₄ and chlorine and a second gas such as CHCl ₃ or SiCl ₄ to control the anisotropy of the etch. This is achieved according to the invention using a gas mixture comprising: The aluminum to be etched is placed between the electrodes of the reactor, a first etching gas mixture is introduced at a pressure of 20-500 μmHg, and a second gas is introduced.
It is introduced at a pressure of 20-300 μmHg. A voltage is then applied to the electrodes to ionize the gas and form active species in the region between the electrodes. To prevent destruction of the photoresist in close proximity to the aluminum, a third gas such as helium is introduced at a pressure of 0.5 to 7 torr. If the pressure of each of the three gases is lower than the lower limit of the above range, the plasma will diverge too widely, and if it is higher than the upper limit, the plasma will be narrowly restricted.

As shown in the drawing, this process
Housing 1 defining a reaction chamber 12
The reaction is carried out in a planar reactor 10 with 1. The housing is provided with a suitable entrance door (not shown) through which wafers or other material to be etched may be introduced into and removed from the chamber. The reactor also has a pair of planar electrodes 13, 14 spaced generally parallel within the chamber. In one preferred embodiment, the electrodes are disks on the order of 3.5-4.5 inches (8.9-11.4 cm) in diameter and spaced on the order of 0.5-2 inches (1.3-5.1 cm) apart. Power is applied to the electrodes by a high frequency generator 16 which is connected to the electrodes by conductors 17,18. This generator operates at a suitable frequency (e.g. 13.56MHz) and
It emits about ~500 watts of power, creating an electric field that ionizes the gas and forms a plasma in the area between the electrodes. During operation of the reactor, coolant is circulated through passages within the electrode (not shown) to maintain the temperature of the electrode at about 5 to 40°C. The upper electrode 14 is grounded to the reactor housing 11;
The lower electrode 13 is insulated from the housing.

Connected in parallel with the high frequency generator 16
A DC bias is applied to the electrodes by a DC source 19. This bias voltage, on the order of 150 volts or less, serves to make the etch more anisotropic, reduces the amount of residue left on the etched material, and completely protects the photoresist. .

A workpiece wafer 21 is placed between the electrodes, and in the illustrated embodiment this wafer is attached to the bottom surface of the upper electrode 14. The wafer is secured to the electrode by a vacuum chuck or other suitable means (not shown).

Gas is introduced into the chamber through manifold 23 and inlet line 24. The lower electrode 13 is made of a porous material through which gas diffuses into the chamber. It has been found that by introducing the gas in this manner, aluminum can be etched more quickly and uniformly than by other methods. An exhaust pump 26 is connected to exhaust port 27 to remove gas from the reactor chamber and maintain the pressure within the chamber at the desired level.

The reactant gas includes a first etching gas mixture and a second gas for controlling etching anisotropy. A third gas is included in the mixture to prevent destruction of the photoresist. As shown in the figures, gas is supplied from an etching source 31, a second gas source 32, and a third gas source 33. Distribution of gas from each gas source to the chamber is controlled by flow control valves 36-38.

In one preferred embodiment, the first etching gas is BCl ₃ with a pressure of 100-200 μmHg.
and chlorine with a pressure of 100-200 μmHg, the second gas consists of _SiCl4 with a pressure of 190-300 μmHg, and helium with a pressure of 0.7-2.5 torr to prevent destruction of the photoresist. include. The wafer to be etched is placed in a reactor chamber, the chamber is evacuated by exhaust pump 26, and gas is then introduced at the desired pressure. A DC bias and radio frequency power are then optionally applied to the electrodes to ionize the gas and form a plasma of active species in the region between the electrodes. Once the desired amount of aluminum has been removed, power to the electrodes is removed, the reactant gas is vented from the chamber, and the wafer is removed.

The relatively high pressures used in this etching process allow the use of higher power densities than previously possible in planar reactors. Therefore, aluminum can be removed faster than before. Good results were obtained using 3.5 to 4.5 inch (8.9 to 11.4 cm) electrodes with applied power of 50 to 400 watts. The aluminum removal rate is
Conventionally, the rate was only about 1,500 angstroms/min, but in the present invention, the rate is about 5,000 to 50,000 angstroms/min.

The significant increase in etching rate provided by the present invention allows wafers to be processed on individual substrates rather than in batches. For example, 1 micron of aluminum can be removed from a 3 inch (7.6 cm) wafer embossed with AZ-1350 positive photoresist in about 1 minute.

The combination of gases used in this process is important. The first gas mixture determines the etch rate, ie, the extent to which aluminum is removed. The second gas controls the anisotropy or direction of the etch and prevents undercutting of the photoresist. The third gas is a good thermal conductor and also has the function of preventing destruction of the photoresist.
An example of a preferred gas mixture is 150μmHg
_a first gas mixture consisting of BCl ₃ having a pressure of There's gas. However, other gases can also be used in this mixture. For example, a mixture of CCl ₄ and chlorine as the first etching gas and a mixture of CCl 4 and chlorine as the second gas.
CH ₃ Cl and/or CCl ₄ can be used.

The etching method and etching gas mixture of the present invention have a number of important features and advantages. By generating a stable, uniform plasma at high pressure and power levels, aluminum can be etched significantly faster than previously possible in a planar reactor. This increased speed allows wafers to be processed on individual substrates rather than in batches. The combination of high power and high pressure allows the number of energetic species to be kept to a minimum while the level of reactive species can be extremely high. Additionally, the anisotropy or directionality of the etch can be controlled to minimize hollowing out or destruction of the bottom portion of the photoresist.

From the foregoing, it is apparent that a new and improved method and gas mixture for etching aluminum in a planar reactor has been provided.
Although only certain preferred embodiments have been described in detail, it will be obvious that changes and modifications can be made without departing from the scope of the invention, as will be apparent to those skilled in the art.

[Brief explanation of the drawing]

The accompanying drawing is a schematic diagram showing an example of an apparatus for carrying out the method of the invention. Explanation of drawing numbers, 10...Flat reactor, 11...
...Housing, 12...Chamber, 13, 14
... Electrode, 16 ... High frequency generator, 19 ... DC
source, 26... exhaust pump, 31... etching gas, 32... second gas, 33... helium, 3
6, 37, 38...flow control valve.

Claims (1)

[Claims] 1. A method of etching aluminum in a reactor having a chamber and a pair of spaced apart substantially planar electrodes, the aluminum being disposed between the pair of electrodes in the reactor chamber. , a first etching gas mixture containing BCl ₃ and chlorine is introduced into the chamber at a pressure of 140-450 μmHg, and a second gas containing SiCl ₄ is introduced into the chamber at a pressure of 190-300 μmHg to effect anisotropic etching. A method for etching aluminum comprising the steps of: controlling the etching properties of the etching gas, causing the first etching gas mixture and the second gas to exist simultaneously in a chamber, and applying a voltage to the electrodes to ionize the gas and form active species between the electrodes. . 2. A gas mixture for etching aluminum in a plasma environment, comprising BCl ₃ and 70-250 μm with a pressure of 70-200 μmHg.
a first etching gas containing a mixture with chlorine having a pressure of 190-300 μmHg and a second gas containing _SiCl4 for anisotropy control of etching with a pressure of 0.7-1 torr; have,
and a third gas containing helium to completely protect the condition of the photoresist in the vicinity of the aluminum.