JPH01231323A - Plasma etching device - Google Patents

Abstract

PURPOSE:To inhibit a chemical sidewall etching reaction by radicals, to reduce an undercut and to improve the accuracy of finishing by compressing and liquefying a refrigerant outside an etching chamber and vaporizing the refrigerant on a sample base. CONSTITUTION:The inside of an etching chamber 3 is set at the required degree of vacuum, a refrigerant under a gas-liquid mixed state is introduced into an evaporator 16 for a sample base 5, and a sample S is cooled at approximately -20 deg.C through the sample base 5. The inside of a plasma forming chamber 1 is supplied with an etching gas from a supply system 1g, and DC currents are made to flow through exciting coils 4 while microwaves are induced into the plasma forming chamber 1 through a waveguide 2 and a microwave introducing window 1c. Consequently, microwave are brought to the state of resonance in the plasma forming chamber 1 functioning as a plasma cavity resonator, decomposes the etching gas, and are resonated and excited, thus forming plasma. The surface of the sample S is not masked, only a section irradiated with ion beams is excited, and anisotropic etching progresses. Isotropic etching by radicals also progresses at that time, but the chemical reaction of the sample S is inhibited because the sample S is cooled, thus suppressing an undercut.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electron cyclotron resonance (electron cyclotron resonance) using microwaves.
Electron Cyclotron Re5ona
The present invention relates to a plasma etching apparatus that utilizes plasma generated by excitation (CE, ECR).

[Prior art]

The method of generating plasma by electron cyclotron resonance excitation using microwaves can generate highly active plasma at low gas pressure, allows for a wide range of ion energies to be selected, and allows for large ion currents to be used to control ion flow. It has advantages such as excellent directivity and uniformity, and its research and development are progressing as it is indispensable for manufacturing highly integrated semiconductor devices.

FIG. 3 is a longitudinal sectional view of a conventional plasma etching apparatus that utilizes electron cyclotron resonance using microwaves, and 31 indicates a plasma generation chamber. The plasma generation chamber 31 has a microwave introduction window 31c sealed with a quartz glass plate 31b at the center of one side wall, and a plasma extraction window 31d at a position facing the microwave introduction window 31c at the center of the other side wall. There is. One end of a waveguide 32 whose other end is connected to a high frequency oscillator (not shown) is connected to the microwave introduction window 31c, and the plasma extraction window 31d
An etching chamber 33 is disposed around the plasma generation chamber 31, and a waveguide 32 is excited concentrically with the plasma generation chamber 31 and one end of a waveguide 32 connected to the plasma generation chamber 31 so as to surround them. A coil 34 is provided.

In the etching chamber 33, a sample stage 35 on which a sample S such as a wafer is mounted is disposed facing the plasma extraction window 31d, and the sample S is detachably mounted on the front surface of the stage 35 by means such as electrostatic adsorption. It is intended to be done. A cooling water passage is buried in the sample stage 35, and a cooling water supply pipe 35a is connected to the cooling water passage. In addition, an exhaust port 3 connected to an exhaust device (not shown) is provided on the rear wall of the etching chamber 33.
3a is open. 31g is an etching gas supply system, and 31h and 31i are cooling water supply systems and drainage systems.

In such an etching apparatus, the plasma generation chamber 31. After setting the inside of the etching chamber 33 to the required degree of vacuum, one or more types of etching/notching gases are supplied from the gas supply system 31g into the plasma generation chamber 31, and a magnetic field is formed by the excitation coil 34. , microwaves are introduced into the plasma generation chamber 31, the etching gas is resonantly excited using the plasma generation chamber 31 as a cavity resonator to generate plasma, and the generated plasma is formed in the etching chamber 33 by the excitation coil 34. A diverging magnetic field whose magnetic flux density decreases toward the side is drawn into the etching chamber 33, and ions are projected around the sample S on the sample stage 35 to perform etching.

[Problem to be solved by the invention]

Normally, plasma generated by electron cyclotron resonance excitation is drawn out with a directionality that follows the lines of magnetic force of the divergent magnetic field as described above, and is influenced by the bias caused by the flow of ions, and has a low energy of about 20 to 30 eV. reaches the sample surface. Therefore, compared to conventional reactive ion etching and ion milling that use ions with an energy of several hundred eV, damage to the sample caused by ion bombardment is reduced, and since etching is performed by irradiation with low-energy ions, etching It is said that the selectivity (etching speed ratio between the etched object and other objects), which is one of the performance indicators of etching, is improved.

However, from the plasma generation chamber 31 to the etching chamber 3
Chemically active excited atoms and radicals are generated in the plasma extracted in step 3, and the chemical reaction between these radicals and the object to be etched also contributes to etching. It is known that chemical etching using radicals is isotropic, in contrast to physical etching using ions, which has directionality (anisotropy), and is closely related to the amount of undercut. .

The gas pressure for etching using ordinary electron cyclotron resonance excited plasma is 10-4-10-3 Torr,
In this range, etching by electron cyclotron resonance excited plasma usually involves a mixture of ionic anisotropic etching and radical isotropic etching.

As a result, the shape processed by etching results in a so-called undercut (approximately 0.3 μm), in which the etched object is smaller than the size of the protective mask. However, there remains a problem in terms of machining accuracy.

The present invention has been made in view of the above circumstances, and provides a plasma etching apparatus that suppresses chemical side wall etching and notching reactions caused by radicals by cooling the sample stage, reduces undercutting, and improves processing accuracy. The purpose is to provide

[Means to solve the problem]

The plasma etching apparatus of the present invention includes a plasma generation chamber for generating plasma by electron cyclotron resonance excitation, an etching chamber for etching the sample by introducing the generated plasma, and a plasma etching chamber provided within the etching chamber for etching the sample. In a plasma etching apparatus, a plasma etching apparatus is provided with a sample stage on which a refrigerant is placed, and a refrigerating means provided outside the etching chamber and equipped with a condenser for liquefying a refrigerant; In the present invention, the sample stage is forcibly cooled by the heat of vaporization caused by the evaporation of the refrigerant, and the sample stage is further provided with an evaporator for evaporating the fluid. ! The deposited sample is cooled to inhibit chemical sidewall etching reactions.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a plasma etching apparatus according to the present invention (hereinafter referred to as the present invention apparatus), in which 1 is a plasma generation chamber, 2 is a waveguide, and 3 is an etching chamber in which a sample S is etched. , 4 indicates an excitation coil.

The plasma generation chamber 1 is made of stainless steel and is formed to form a cavity resonator for microwaves.
- A microwave introduction window 1c closed by a quartz glass plate 1b is provided at the center of the side wall, and a plasma extraction window 1d is provided at the center of the other side wall at a position facing the microwave introduction window IC. One end of a waveguide 2 is connected to the microwave introduction window 1c, and an etching chamber 3 is provided facing the plasma extraction window 1d, and a plasma generation chamber 1 and a plasma generation chamber 1 are arranged around it. An excitation coil 4 is disposed concentrically over one end of the connected waveguides 2 . Also, the microwave introduction window 1 of the plasma generation chamber 1
A supply system 1g for an etching gas such as C12 gas is connected to the peripheral portion of c.

The other end of the waveguide 2 is connected to a high frequency oscillator (not shown), and microwaves emitted by the high frequency oscillator are introduced into the plasma generation chamber 1 through the microwave introduction window 1c.

The excitation coil 4 is connected to a DC power source (not shown),
By passing a direct current, a magnetic field is formed in the plasma generation chamber 1 so that plasma can be generated by introducing microwaves, and a diverging magnetic field whose magnetic flux density becomes lower toward the etching chamber 3 side is formed, thereby generating plasma. The plasma generated in chamber 1 is introduced into etching chamber 3.

The etching chamber 3 has an exhaust port 3a connected to an exhaust device (not shown) opened on a side wall that does not face the plasma extraction window 1d, and a sample stage 5 is disposed inside the etching chamber 3 facing the plasma extraction window 1d. A sample S is removably mounted on the front surface of the sample stage 5, facing the plasma extraction window 1d, by means such as electrostatic adsorption. Sample stand 5
An evaporator 17 of a heat pump type refrigerator, which is a freezing means for cooling, is integrally formed inside the interior, and one end of the evaporator 17 is provided near the sample stage 5 to squeeze out the liquid refrigerant. It is connected to one end of an expansion valve 16 that is expanded to create a gas-liquid mixed state. The other end of the expansion valve 16 is connected to one end of a liquid receiver 15 that is provided outside the etching chamber 3 and separates liquefied refrigerant and vaporized refrigerant and supplies only the liquefied refrigerant to the expansion valve 16. The other end of the liquid receiver 15 is connected to one end of a condenser 14 that liquefies the vaporized refrigerant. The other end of the condenser 14 is connected via an oil separator 13 to one end of a compressor 12 for compressing vaporized refrigerant, and the other end is connected to the other end of the evaporator 17 via a side wall of the etching chamber 3. has been done.

Others 1h and li indicate the cooling water supply system and drainage system, respectively.

Therefore, in such an apparatus of the present invention, the etching chamber 3
The sample S is mounted on the sample stage 5 in the plasma generation chamber 1. After setting the inside of the etching chamber 3 to the required degree of vacuum, the sample stage 5
A gas-liquid mixed refrigerant (for example, Freon gas) is introduced into the evaporator 16 of the sample S, and the sample S is cooled to about -20° C. via the sample stage 5. For this cooling, the compressor 12 compresses the vaporized refrigerant, the oil separator 13 removes the mixed oil, the condenser 14 liquefies the refrigerant through heat exchange, and the liquid receiver 15 liquefies the liquefied refrigerant. is separated, the refrigerant is throttled and expanded in the expansion valve 16 to form a gas-liquid mixed state, and the refrigerant is evaporated in the evaporator 17 to absorb the heat of the sample stage 5 and the sample S by the heat of vaporization. After cooling the sample S, the etching gas is supplied from the supply system 1g into the plasma generation chamber 1, and the excitation coil 4
A direct current is passed through the waveguide 2. Microwaves are introduced into the plasma generation chamber 1 through the microwave introduction window IC. The microwave introduced into the plasma generation chamber 1 resonates within the plasma generation chamber 1 which functions as a plasma cavity resonator, decomposes the etching gas, and excites it resonantly to generate plasma. Ions in the generated plasma are irradiated onto the sample stage 5 as an ion beam having directionality along the divergent magnetic field formed by the excitation coil 4. The surface of the sample S is not masked and only the portion irradiated with the ion beam is excited, and the etching gas is adsorbed to this excited portion, causing anisotropic etching to proceed due to a chemical reaction. At this time, isotropic etching by radicals also progresses, but since the sample S is cooled, the chemical reaction is suppressed, the sidewall etching reaction by radicals is suppressed, and undercutting is suppressed. Furthermore, plasma etching equipment is usually installed in a clean room, and in this embodiment, the expansion valve 16 is provided in the etching chamber 3 to prevent condensation on the piping and to prevent changes in the environment of the clean room due to condensation of water. I'm here.

〔effect〕

As detailed above, in the plasma etching apparatus according to the present invention, since the sample is forcibly cooled by the freezing means, it is possible to suppress sidewall etching caused by radicals, and to reduce undercuts. be effective.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a plasma etching apparatus according to the present invention, and FIG. 2 is a longitudinal sectional view of a conventional plasma etching apparatus.

Claims (1)

[Claims] 1. A plasma generation chamber that generates plasma by electron cyclotron resonance excitation, an etching chamber that etches a sample by introducing the generated plasma, and a plasma generating chamber that is provided within the etching chamber and on which the sample is placed. A plasma etching apparatus comprising: a sample stage provided outside the etching chamber, and comprising a compressor for compressing a refrigerant and a condenser for liquefying the refrigerant; and a freezing means provided for the sample stage and provided for the freezing means. A plasma etching apparatus comprising: an evaporator for evaporating refrigerant from the plasma etching apparatus.