JPH05102083A - Method and apparatus for dry etching - Google Patents

Abstract

PURPOSE:To suppress the microloading effect due to etching and eliminate the irradiation damages by applying a cluster of ionized atoms on the object to be processed. CONSTITUTION:The pressure difference of the insides of vacuum container 1 and reservoir 4 is set to 10<-4>-10<-5>Torr. After the container is evacuated sufficiently, reactive gas is introduced into the reservoir 3 to a pressure of several Torr. The diameter of nozzle 5 is set to around 1mm and the pressure inside the vacuum container is kept at 10<-4>Torr. The reactive gas passing through the nozzle 5 is cooled to form clusters. At that time the clusters ionized by electron beam are accelerated the voltage impressed between an electrode 7 and the reservoir 4, and are applied on the surface of a wafer 3 thereafter. Thus, there is no fear of irradiation damages even when the accelerated voltage is 1keV.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method and an apparatus therefor.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic sectional view of a dry etching apparatus which has been widely used in the conventional fine processing of semiconductor device manufacturing processes. In FIG. 4, a high frequency power 111 is applied to the cathode 102, and a plasma 104 is generated in the reaction vessel 101 into which the reaction gas is introduced. A wafer 103 is placed on the cathode 102, and reactive ions 1 are generated from the plasma by the self-bias induced on the surface of the anode 102 (wafer 103).
05 is accelerated, and the impact on the wafer 103 causes the etching reaction to proceed. This self-bias voltage changes according to individual conditions such as gas and RF power, the shape of the electrode, the electrode area ratio of the cathode and the anode, but in a practical device configuration, the acceleration is usually about 100 eV to 500 eV. A voltage will be induced.

It is well known that the so-called reactive ion etching apparatus having such a structure has made a great contribution to the fine processing of semiconductors. However, miniaturization has progressed remarkably, and even with such an excellent apparatus, there are the following problems in future device fabrication.

First, one of the problems is the problem of irradiation damage. In the processing of the gate portion which is the active portion of the MOS device, or in the processing of the portion which is electrically connected to the gate electrode, impact of high energy ions causes various damages. For example, the metal on the inner wall of the reaction vessel is released into the gas phase by the sputtering action, and it is injected into the gate portion. As a result, a new impurity rank is formed, and the operating characteristics of the device change.

During the etching, the wafer is in a floating state because it is not DC-electrically connected to anything. Therefore, the electrons, ions, or secondary electrons emitted from the plasma accumulate charges on the gate electrode, and when the charges are remarkable, the gate insulating film is destroyed. In recent years, in order to obtain a large capacitance with a small area, this insulating film also uses an extremely thin one (for example, a SiO ₂ film of 50 Å may be destroyed even when a potential of about 5 V is applied). It has been done and is easily destroyed. All of these arise from the principle of this system in which etching is advanced by irradiating charged particles, and are inevitable in principle.

Such charging of electric charges may cause an abnormal etching shape in addition to the above. That is,
As shown in the schematic cross-sectional view of the pattern of FIG. 5, the end pattern 119 of the densely-existing portion 117 of the pattern, which is adjacent to the less-existing portion 118 of the pattern, has a tapered sidewall (in the lower portion, In some cases, the pattern width becomes wider) or in an inverse taper shape (the pattern width becomes narrower toward the bottom). It is considered that this is because, as shown in FIG. 6, the individual patterns are charged, the potential becomes positive with respect to the substrate, and the trajectory of the incident ions is bent. This charging phenomenon is not yet well understood and cannot be easily solved by the current technology. Another problem is a phenomenon called the microloading effect.

FIG. 7 shows a schematic sectional view when the thick film 122 to be etched is etched. The base substrate is omitted. When the etching rate was examined by changing the interval of the mask 121, the following results were obtained. For example,
It can be seen that when the film 122 of polycrystalline silicon or the like is etched with a chlorine or fluorine-based gas, the etching rate becomes lower as the groove width becomes narrower. This is called the microloading effect, which is a big problem when etching fine grooves.

[0008] The cause of the microloading effect is not simple because it involves a plurality of elements. It is considered that the main reason for this is that the smaller the width is, the smaller the incident amount of ions that promote etching per unit area becomes. In plasma, the ions mainly performed random motion due to thermal motion and gradual motion due to weak electric field. Generally, it is said that ions are accelerated by a bias voltage in the sheath and vertically incident on the wafer. However, in reality, many ions strike the wafer with an oblique component. Therefore, the narrower the opening width of the pattern,
The deeper the groove is, the smaller the amount of ions reaching the bottom, which is the etching surface. Further, the neutral active species (mainly halogen elements dissociated in plasma) which are etching species are supplied from the plasma to the wafer only by diffusion and thermal motion. Therefore, the incident angle dispersion on the wafer is large and narrow, and the deeper the groove is, the smaller the supply amount is, and the etching rate is reduced.

Attempts have also been made to reduce the microloading effect by aligning the directionality of ions by lowering the pressure. However, as the pressure is lowered, the plasma density is lowered and the etching rate is lowered, and the ion energy is increased. As a result, irradiation damage is increased or the selection ratio is decreased, which is not a fundamental solution.

[0010]

As described above, in the conventional dry etching method and apparatus, the so-called microloading effect in which the etching rate changes depending on the pattern width is likely to occur. Further, irradiation damage due to impact of high energy particles and abnormal pattern shape due to electrification of the substrate are likely to occur, which is a problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dry etching method in which the microloading effect is eliminated, irradiation damage is small, and a good etching shape can be obtained. Another object of the present invention is to provide a dry etching apparatus used for implementing the dry etching method. [Constitution of Invention]

[0012]

In order to solve such a problem, the present invention provides a step of forming a cluster-like atomic population by blowing a gas containing a reactive element from a high pressure region to a low pressure region, There is provided a dry etching method comprising a step of ionizing the formed cluster-like atomic population, and a step of irradiating the object with the ionized cluster-like atomic population to selectively etch the object.

Further, according to the present invention, the gas containing the reactive element is blown out from the high pressure region to the low pressure region,
Forming a cluster-like atomic population, ionizing the formed cluster-like atomic population, applying an alternating electric field or an alternating magnetic field, or both to the ionized cluster-like atomic population, and an ionized cluster-like Provided is a dry etching method including a step of selectively etching a target object by irradiating the target object with a group of atoms.

Further, according to the present invention, a reaction vessel, a gas reservoir which is maintained at a pressure higher than that of the reaction vessel, and which contains a gas containing a reactive element, and an outlet of the gas reservoir, which is provided inside the reaction vessel from the gas reservoir. A gas is blown into the nozzle to generate a cluster-like atomic population composed of atoms of the gas, a means for ionizing the cluster-like atomic population, and the ionized cluster-like atomic population is drawn out and housed in a reaction vessel. A dry etching apparatus comprising: an accelerating unit for irradiating an object to be processed.

Furthermore, the present invention is provided with a reaction vessel, a gas reservoir which is maintained at a pressure higher than that of the reaction vessel and which contains a gas containing a reactive element, and an outlet of the gas reservoir,
A gas is blown from a gas reservoir into a reaction container to generate a cluster-like atomic population composed of atoms of the gas, a means for ionizing the cluster, and an alternating electric field or an alternating current to the ionized cluster-like atomic population. A dry etching apparatus comprising: a means for applying a magnetic field or both; and an accelerating means for drawing out an ionized cluster-like atomic population and irradiating the object to be processed housed in a reaction container. provide.

Here, the step of selectively etching the object to be processed includes the step of selectively etching a predetermined region on the surface of the object to be processed, or selectively etching the material to be etched with respect to the underlying material. It means a step of etching.

As described above, the method and apparatus of the present invention charge clusters of loosely bound 10-several thousands of reactive atoms (cluster) to form a cluster ion beam which can be extracted with a low acceleration energy. It is transported with little dispersion and is vertically irradiated for etching.

The reactive element used in the present invention includes:
Mention may be made of halogen, oxygen, hydrogen and nitrogen. In addition, multiple heterogeneous elements are used as reactive elements, and multiple cluster-like atomic populations are generated, and these are simultaneously and individually
Alternatively, the object to be processed can be irradiated alternately with a constant cycle. In this case, the composition ratio of the different elements can be set arbitrarily. It is preferable that the substrate has a temperature control function for controlling the chemical reaction on the surface of the object to be processed.

[0019]

The cluster ion beam technology applied to the present invention has been developed for the purpose of being used for film forming technology. Therefore, its generation and control technology itself has already been established to some extent (Reference: Takagi, Applied Physics Vo1.55 No.8
P.746 (1986)), the present invention is the first to be applied to etching technology.

According to the present invention, by using the cluster ion beam which is vertically irradiated, it is possible to supply the required etching gas into the fine groove all the time, regardless of the groove width. is there. Therefore, it becomes possible to process all patterns to the same etching rate and shape.

In a cluster ion beam, since many lumps of atoms are charged to a valence of one or several, the amount of charges applied to the substrate is substantially small relative to the number of supplied atoms, and the substrate itself is charged. Hateful. Therefore, an abnormal etching shape, which is considered to be caused by bending of incident ions due to the charging of the insulating mask material or the film to be etched, does not occur.

Further, for the same reason, even if the beam is accelerated to several kilovolts to irradiate the substrate, the energy of each atom is extremely low and irradiation damage is reduced. Since the beam can be accelerated at such a high voltage, it is possible to vertically irradiate the wafer with a beam with small dispersion and good directionality. Therefore, regardless of the groove width, atoms can be supplied to the surface where etching proceeds at the same density. In addition, since the acceleration is high and the mass is large, it is difficult to receive the action of charging the substrate (even if the substrate is charged). Furthermore, even if a relatively low pressure is used for high-precision processing, a large amount of etching species can be supplied to the etching surface, which enables high-speed etching.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram schematically showing an etching apparatus according to an embodiment of the present invention. In FIG. 1, a susceptor 2 is arranged in a vacuum container 1, and a wafer 3 is placed thereon. A gas reservoir 4 for introducing a reactive gas used for etching is provided above the vacuum container 1, and a gas is blown to the outlet of the gas reservoir 4.
A nozzle plate 5 having a large number of nozzles for forming clusters is attached. Below the nozzle plate 5, a hot filament electron gun 6 as an electron supply source for ionizing the clusters and an electrode 7 for accelerating the ionized clusters are arranged. Reference numerals 8 and 9 indicate a gas supply system, and 10 indicates a direction in which the gas is evacuated. Bias power is applied to the susceptor 2 by a power supply system 11, and the substrate temperature is controlled through a pipe 12 connected to a temperature control device. Next, an actual etching procedure by the above-described etching apparatus will be described.

The wafer 3 is transferred onto the susceptor 2 in the vacuum container 1 by a load lock mechanism (not shown). In the present invention, the load lock mechanism is indispensable because the process can be performed in a high vacuum. In order to efficiently form the clusters by utilizing the adiabatic expansion of the gas, the pressure difference (pressure ratio) between the vacuum container 1 and the reservoir 4 is set to 10 ⁻⁴ −1.
It must be 0 ^-5 Torr. On the other hand, etching is
The mean free path of the gas is sufficiently long, and it is preferable to carry out at 10 ⁻⁴ Torr level or less. Therefore, after thoroughly evacuating the container,
A reactive gas such as chlorine (C12) for several T is stored in the reservoir 3.
Introduce up to orr pressure.

The nozzle 5 has a diameter of about 1 mm, and the inside of the vacuum chamber is evacuated to maintain the level at 10 ^-4 Torr. The reactive gas that has passed through the nozzle 5 is rapidly cooled by adiabatic expansion and clusters are formed. Since this cluster is electrically neutral, it is ionized by the electron beam emitted from the hot filament electron gun 6 here. Here, only a monovalent or divalent charge is given to one cluster composed of thousands of atoms, and therefore, the charge per atom is substantially very small.

The ionized clusters are accelerated by the voltage applied between the electrode 7 and the reservoir 4, pass through the mesh-shaped electrode 7, and are irradiated on the surface of the wafer 3. The accelerating voltage of ions is in the range of about 100 eV to several KeV, depending on the individual process and the material to be etched.
It can be selected appropriately.

In the cluster thus accelerated, even if the acceleration voltage is 1 KeV, if the group of 1000 atoms, the substantial acceleration voltage of each atom is 1 eV, and there is no concern about irradiation damage. Not an extremely low value. Therefore, the beam can be irradiated with high acceleration without worrying about damage, and the directionality of the cluster beam can be controlled extremely well. That is, a constant amount of etching species (clusters) can be supplied to the etching surface regardless of the width of the groove, and the microloading effect disappears.

Further, although etching is performed under a relatively low pressure, a large amount of etching species are supplied to the etching surface, so that high speed etching is possible. FIG. 2 shows the results of actually examining the etching depth with respect to the groove width when a silicon substrate having a mask such as SiO ₂ formed on the surface thereof was etched using chlorine gas. RIE used for comparison
Was a generally used parallel plate type, and was carried out under a chlorine gas pressure of 2 mTorr. The cluster beam was performed in the apparatus of FIG. 1 under a gas pressure of 0.1 mTorr. Here, the beam irradiation was performed on the entire surface of the substrate. The etching depth on the Y-axis is 1 for a sufficiently wide groove.
Is standardized for each case.

As is apparent from FIG. 2, in the ordinary RIE, the etching depth sharply decreases with the groove width of 0.5 μm or less, but the decrease is small in the cluster beam. As a result of evaluation of the etching shape, it was found that tapering of the pattern, which is considered to be caused by charging, was not observed at all. Also, in the evaluation of irradiation damage, in the prototype device,
Although many metal parts were exposed, reduction of metal contamination was not achieved, but for electrical damage such as dielectric breakdown and transistor threshold change, the reference (etching only with neutral active species) was downed. As with the flow etching device, no damage was observed. Next, another embodiment of the present invention will be described.

In FIG. 1, reference numeral 13 is a gas introduction port for introducing another gas 9 without passing through the nozzle.
By introducing another gas 9 from this gas inlet 13, for example, neutral etching species in the gas phase or etching products are scavenged (excluded) to prevent isotropic etching or to generate etching. It is possible to prevent reattachment of an object. Specifically, when chlorine gas is used as a reaction gas and etching is performed, hydrogen or a gas containing hydrogen is introduced from the gas introduction port 13 so that non-clustering occurs or the cluster beam decomposes after impact on the substrate. The generated chlorine atoms can prevent isotropic etching. By providing a means for activating the gas before the gas introduction port 13, the above-mentioned action can be further promoted.

As a method of fixing the substrate 3 on the susceptor 2, an electrostatic chuck is effective from the viewpoint of temperature control. However, when applying a direct current to the substrate, it is necessary to use a mechanical chuck. FIG. 3 is a diagram showing an etching apparatus according to still another embodiment of the present invention.

In the etching apparatus shown in FIG. 3, the reservoir 4 has a structure that is longer than the diameter of the wafer in the direction perpendicular to the plane of the drawing, and forms a band-shaped cluster beam. The formed clusters enter the electron cloud 14 for ionization. The electrons of the electron cloud 14 are extracted from the plasma 20 by the electron source 6. In this case, the energy of electrons is set to around 100 eV, which has a high ionization efficiency.

The ionized clusters pass through the mesh-shaped extraction electrodes 7 and enter between the deflection electrodes 15. here,
The band-shaped cluster beam is scanned left and right on the paper surface by the alternating electric field E formed by the deflection electrode 15. Reference numeral 23 schematically shows the locus of a certain cluster beam. Further, the deflecting electrode 15 can be made to act as a mass filter by applying an alternating magnetic field 22 that is orthogonal to the electric field 16. That is, wafer 3
It is possible to appropriately select the mass of the clusters to be irradiated on the substrate, and it is possible to control the etching species such as removing clusters having a small number of particles.

The deflected beam is accelerated by the accelerating electrodes 17 and 18 in the direction perpendicular to the surface of the wafer 3 and is irradiated on the wafer 3. Here, the accelerating electrode 17 has the same potential as the extraction electrode 7, and is 100% with respect to the reservoir 4 and the electrode 14 of the electron source.
The acceleration is set to about V. In addition, the deflection electrode 1
When an alternating potential swinging around the potential of the extraction electrode 7 is applied to the electrode 5, the interaction between the electrodes is reduced and the turbulence of the beam is reduced. A voltage of minus several hundred to several thousand V is applied to the accelerating electrode 18 with respect to the accelerating electrode 17, and a cluster beam having a small angular dispersion and good directivity is applied to the wafer 3.
Supply to.

As described above, in the etching method of the present invention, since the acceleration of the cluster beam is high and the charge per atom of the cluster is small, the wafer 3 is less charged and the beam is not easily affected. In addition, the low-speed electron source 19 and the wafer 3
It is possible to give an electron to. Further, in the etching of the conductive film, the shape and etching characteristics can be controlled by applying a DC voltage to the wafer 3.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications can be made. For example, in the above embodiments, the irradiation of the cluster-ion beam was performed on the entire surface of the substrate on which the mask was formed, but it is also possible to perform the selective irradiation without using the mask. Further, in the device according to the above embodiment,
The reservoir, nozzle, extraction electrode, and wafer are arranged in a straight line from top to bottom, but in consideration of contamination from the nozzle and electrode, the part above the extraction electrode may be arranged on the side surface of the vacuum container. it can. Also, the material of each part must be selected in consideration of the material to be etched so as not to contaminate metal or organic matter. Also, near the nozzle, the gas adiabatically expands, cools and clusters,
The temperature of the nozzle plate gradually decreases. This causes the process to change over time. Therefore, a mechanism for controlling the temperature by a heater or the like may be attached to the nozzle plate. It is also preferable to control the temperature of the entire reaction container.

Further, the nozzle has a plurality of kinds of gases,
A plurality of nozzles may be prepared for each, and each gas may be independently introduced into the reaction vessel to form a cluster. A plurality of different gases may be emitted from the nozzle in a pulsed manner, and a means for synchronizing or asynchronizing the cycle may be provided. It is also possible to install a piezo valve composed of a piezoelectric element in the nozzle and install a mechanism that repeats opening and closing at high speed. Furthermore, it is possible to provide a means for irradiating the substrate to be etched with a low-speed electron beam or a means for forming plasma near the substrate to be etched.

[0039]

As described above, according to the method of the present invention, since the charge per atom is small and a highly accelerated cluster ion beam is irradiated for etching, etching of a fine pattern is performed by a microloading effect. Without, it is possible to do with a good etching profile. Also, irradiation damage caused by the high energy beam,
Machining can be performed without causing abnormal pattern shape due to charge-up. Further, since the processing can be performed in a low vacuum, the indercut caused by the neutral active atoms does not occur.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an etching apparatus used in an embodiment of the present invention.

FIG. 2 shows the relationship between the etching groove width and the etching depth in the etching method according to the embodiment of the present invention,
The characteristic view shown in comparison with E.

FIG. 3 is a diagram schematically showing an etching apparatus used in another embodiment of the present invention.

FIG. 4 is a diagram schematically showing a conventional etching apparatus.

FIG. 5 is a diagram for explaining a problem of a conventional etching method.

FIG. 6 is a diagram for explaining a problem of a conventional etching method.

FIG. 7 is a diagram for explaining a problem of a conventional etching method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Susceptor, 3 ... Wafer, 4 ... Gas reservoir, 5 ... Nozzle plate, 6 ... Hot filament electron gun, 7
… Electrodes, 8, 9… Gas supply system.

Claims (4)

[Claims] 1. A step of forming a cluster-like atomic population by blowing a gas containing a reactive element from a high-pressure area to a low-pressure area, a step of ionizing the formed cluster-like atomic population, and an ionized cluster. Etching method comprising the step of selectively etching the object to be processed by irradiating the object to be processed with a group of atomic atoms. 2. A step of forming a cluster-like atomic population by blowing out a gas containing a reactive element from a high-pressure area to a low-pressure area, a step of ionizing the formed cluster-like atomic population, an ionized cluster-like The method comprises the steps of applying an alternating electric field, an alternating magnetic field, or both to the atomic group, and selectively etching the object by irradiating the object with the ionized cluster-like atomic group. Dry etching method. 3. A reaction vessel, a gas reservoir that is maintained at a higher pressure than that of the reaction vessel and contains a gas containing a reactive element, and an outlet of the gas reservoir that is provided to discharge gas from the gas reservoir into the reaction vessel. A nozzle for generating a cluster-like atomic population composed of the atoms of the gas, a means for ionizing the cluster-like atomic population, and an object to be treated contained in the reaction container for drawing out the ionized cluster-like atomic population. A dry etching apparatus comprising: an accelerating means for irradiating the surface of the dry etching apparatus. 4. A reaction vessel, a gas reservoir that is maintained at a pressure higher than that of the reaction vessel and that contains a gas containing a reactive element, and an outlet of the gas reservoir that is provided at the outlet of the gas reservoir to supply gas into the reaction vessel. Blow-off, a nozzle for generating a cluster-like atomic population composed of atoms of the gas, a means for ionizing the cluster-like atomic population, an alternating electric field or an alternating magnetic field, or both, to the ionized cluster-like atomic population. A dry etching apparatus comprising: an applying unit; and an accelerating unit for extracting an ionized cluster-shaped atomic population and irradiating the object to be processed housed in a reaction container.