JPS62131520A - Dry etching device - Google Patents

Abstract

PURPOSE:To avoid damage to semiconductor element by converting any ion as positive charged particles in gas plasma into neutral radical by a method wherein a shielding plate with passing pores of specified shape with small and compact structure is arranged between a plasma producing chamber and a reaction chamber. CONSTITUTION:A dry etching device composed of a plasma producing chamber 1, a gas leading-in port 2, waveguide 3 leading-in microwaves produces station ary microwaves in the plasma producing chamber 1. Within a reaction chamber 5, a wafer set on a wafer mounting base 6, an exhaust port 8 exhausting gas are provided while a shielding plate 9 is arranged between the reaction chamber 5 and the plasma producing chamber 1. When the shielding plate 9 composed of <-shape sheets 10 arranged mutual intervals almost equalized to the mean free stroke of molecule or ion is used, no molecule 11 or ion 11' can pass through the shielding plate 9 without colliding with said plate 9. Through these procedures, ion will collide with the shielding plate 9 more than once without fail losing the charge thereof so that the ion may be prevented from running into the reaction chamber 5 resultantly minimizing damage to element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an etching apparatus that utilizes gas plasma, and more particularly to a dry etching apparatus that uses chemical reactions based on neutral radicals (groups).

[Background of the invention]

In etching equipment using plasma, a method that mainly uses neutral radicals without using ions (positively charged particles) in the plasma is used to eliminate lattice defects caused by ion bombardment, rather than requiring dimensional accuracy in microfabrication of semiconductor devices. It is ideal for processes where damage to the elements is avoided. Specifically, it is used in the step of ashing and removing resist after etching a semiconductor element into minute dimensions.

As an example of this type of conventional equipment,
As disclosed in Japanese Patent No. 469, there is a method of transporting gas plasma from a plasma generation chamber to a reaction chamber using a long transport pipe. This is because during transport of the gas plasma, ions lose their charge due to collision with the transport pipe wall or recombination with electrons, and by the time they reach the reaction chamber, only neutral radicals with a long life (and those that have not been turned into plasma) This method takes advantage of the fact that the raw material gas is This method has the drawback that the length of the transport tube is required to be long enough for the ions to collide with the wall or to undergo group bonding with electrons to remove the stains, resulting in an increase in the size of the apparatus. Many ashing steps are included in the process of manufacturing semiconductor devices, and as the device structure becomes finer, the number of ashing steps increases, so it is strongly desired that the ashing device be as small as possible. Note that this method of lengthening the ion transport tube can only utilize neutral radicals that have a relatively long life among the many generated neutral radicals, so by bringing the plasma generation chamber and the reaction chamber closer together, it can be Efforts have been made to speed up the etching reaction by utilizing sexual radicals in the reaction.

Next, as a method to avoid damage to semiconductor elements due to ions of gas plasma generated in the plasma generation chamber,
As disclosed in Japanese Unexamined Patent Publication No. 57-76844, there is a method in which a microwave shielding metal plate is placed between a plasma generation region and a semiconductor wafer to be processed. Although this is effective in shielding ions, the conductance C (1/s) of the gas flow from the plasma generation chamber to the reaction chamber where the semiconductor wafer is placed is small, and the flow rate Q (Torr - VB
)=C×ΔP (pressure difference (Torr)), therefore, the flux of neutral radicals cannot be said to be sufficiently large, and the ashing reaction becomes insufficient or takes a long time. The same publication also mentions making holes in the shielding metal plate, but although this method is effective in improving conductance and increases the flux of neutral radicals, it is also possible to make holes that are too large. If the hole is opened, ions will pass through the hole and the ion shielding effect will be completely lost. Moreover, the publication does not disclose or specify the shape and size of the ion passage holes.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a shield plate between a plasma generation chamber and a reaction chamber, which has a small and compact structure and a passage hole of a specific shape. Provides a dry etching device that converts ions, which are positively charged particles, into neutral radicals and uses them as the main body of the reaction, prevents damage such as lattice defects caused by ion bombardment on semiconductor elements, and is fast and highly efficient. It's about doing.

[Summary of the invention]

Normally, ions, which are positively charged particles in gas plasma, are generated in a plasma generation chamber, but when they collide with a wall, they lose their charge and become neutral, becoming neutral radicals. Plasma contains positively charged ions and negatively charged electrons at approximately the same density, and many electrons whose mass is 10 times lighter than the ions tend to enter the wall where the plasma is in contact. Therefore, the wall has a property of having a negative potential with respect to the plasma.

This suppresses the incidence of stains, and as a result, the amount of positive charge and negative charge flowing into the wall becomes balanced.

When the wall is an insulator, the potential of the wall is equal to the potential of the plasma, which is usually called the 70-Ting potential! It will be lower than standing. Therefore, when positively charged ions collide with the wall, recombination with electrons on the wall surface is likely to occur.

In other words, the positive charge of ions can be removed by colliding with a wall. On the other hand, stable neutral radicals have a very low probability of becoming neutral radicals even if they collide with a wall. For example, the recombination rate of oxygen atoms on a solid surface is 10
'~1o-' (Hozumi: Low-temperature oxygen plasma and its applications, Chemistry area, Giant, 8 (1971), 713.), which is a very low value.

Based on the above-mentioned properties of ions in the gas plasma, the present inventors determined that K can shield the ions in the gas plasma and lead only a large amount of neutral radicals to the reaction chamber to cause a high-speed reaction. The conductance of the gas flow passing through the shielding plate, that is, the flow of neutral radicals, is adjusted so that the ions collide with the shielding plate at least once, and the number of times the generated neutral radicals hit the shielding plate is minimized. I learned that there is a need to increase

The inventors then determined that the size of the hole drilled in the shielding plate was d.
) and the mean free path (λ) of molecules and ions and found that when d > λ, most molecules and ions frequently collide with other molecules and ions, resulting in a so-called continuous flow. ) The number of ions that pass through without colliding with the wall can no longer be ignored, and we found that it is desirable that d be close to λ.

Furthermore, the present inventors investigated the influence of the sheath electric field on the gas plasma, and found that, for example, as a typical example, the plasma density n, = 10''cm-'.

Electron temperature T, =8. If v, Debye length λ, = α2m
, and the sheath width is several times the value of λ. This means that there is an electric field in the sheath that attracts positively charged ions to the wall.

For this reason, the ions are in a state where they are more likely to collide with the wall than if they had proceeded ignoring the sheath electric field, so it is sufficient to consider that the ions will hit the wall of the hole in the shielding plate at least once. I found that. If the size of the ion passage hole becomes smaller than the sheath width, the glowing part of the plasma will not enter the hole, but this does not necessarily mean that no ions will pass through the hole. It turned out that there is no limit.

The present invention was completed based on the above-mentioned knowledge. That is, in a dry etching device, a shielding plate having a large number of passage holes of a predetermined shape is placed between the plasma generation chamber and the reaction chamber, and the average number of molecules or ions passing through the passage holes of this shielding plate is approximately the size of the passage holes of the shielding plate. Basically, the shape is such that the molecules or ions traveling from the plasma generation chamber to the reaction chamber collide with the wall of the passage hole of the shielding plate at least once.

When the shape of the passage hole provided in the shielding plate used in the dry etching apparatus of the present invention is round, the diameter of the round hole is approximately the same as the mean free path of the molecule, and the depth of the hole is approximately the same as the mean free path of the molecule. It is preferably about 10 times the diameter of the pore.

The shape of the passage hole provided in the shielding plate used in the present invention is round,
It may be oval, rectangular, or polygonal, or it may have a slit-like opening of a predetermined length. Although the shape is not particularly specified, the diameter of the passage hole Alternatively, the width or depth of the slit-like opening may be approximately the same as the mean free path of molecules, and the depth of the passage hole or slit-like opening may be the diameter of the passage hole or the depth of the slit-like opening. I like it to be about 10 times the width or depth.

Furthermore, the shape of the shielding plate used in the present invention.

In a shielding plate having a passage hole having a dogleg-shaped cross section, the diameter, width, or depth of the dogleg-shaped passage hole is approximately equal to the mean free path of a molecule; It is desirable that the thickness of the plate is approximately 2I'2 times the diameter, width, or depth of the dogleg-shaped passage hole.

[Embodiments of the invention]

An embodiment of the present invention will be described below in more detail based on the drawings. In the figures, the same reference numerals indicate the same parts or parts having the same function.

1 and 2 are cross-sectional views showing the general structure of a dry etching apparatus using gas plasma, which is an example of the present invention. Both devices have a plasma generation chamber 1. Gas inlet 2. It has a waveguide 3 that guides microwaves for generating plasma. The dry etching device shown in FIG. 1 is a type that generates standing microwave waves in a plasma generation chamber 1, and the device shown in FIG. 2 is a type that uses ECR (electron cyclone resonance) using a coil 4. It is. However, in the present invention, the plasma generation source is not limited to microwaves.

A wafer 7 set on a wafer mounting table 6 is provided in a reaction chamber 5 of the dry etching apparatus, and gas is exhausted from an exhaust port 8. Note that a shielding plate 9 is arranged between the reaction chamber 5 and the plasma generation chamber 1.

Now the pressure inside the dry etching device is, for example, 10P,
(approximately cL1TOrr), the mean free path of the molecule is approximately α5m in the case of nitrogen molecules, and is approximately this length for other molecules of different sizes.

Therefore, as shown in Fig. 6, a plate 1° in the shape of < is
If a shielding plate 9 with a structure in which the shielding plate 9 is combined with a spacing d (d, 'λ...mean free path of molecules or ions) is used, molecules 11 or ions that pass through without colliding with it even once. 11' is clearly absent. In this case, the smaller the thickness t of the dogleg-shaped plate 10 is compared to the distance d, the larger the porosity of the shielding plate 9 becomes, so it is desirable that the passage rate of molecules and neutral radicals is high. . Also,
When the pressure falls below 1P (approximately (L 2 Torr)),
Since the mean free path of the molecule is about 5 or more, t<d
The shielding plate 9 should be made so that. With K in this way, the thickness of the shielding plate 9 will be 273 d, and d
Since it is zλ, even if the pressure is about IP, the thickness only needs to be a few degrees.The structure is extremely compact, and the ions are sure to collide with the shielding plate 9 at least once. Since the charge is lost, it is possible to prevent ions from flowing into the reaction chamber 5, and damage to the element is extremely reduced.

Next, another example of the shielding plate in the dry etching apparatus of the present invention is shown in FIG. As shown in the figure, a number of holes 13 having a diameter d are bored in a plate 12 having a thickness t. In this case, if 5 is small, molecules 11 pass through the hole without collision,
Ions 11' increase. By increasing inverse 1c 4/d, molecules 11. pass through without colliding with the wall. The number of ions 11' can be sufficiently reduced. However, t/
Unnecessarily increasing d is undesirable because the conductance of the flow of molecules or neutral radicals decreases. The course of the flow of molecules that accidentally pass through the cylindrical hole of such a shielding plate is determined numerically and by model using random numbers.
By analyzing this, an approximate solution for the molecular flow passing through a cylindrical hole is obtained using the ordinary Monte Carlo method (Monte Carlo method).
Fig. 5 shows the results of simulation using the e Carlo method. As shown in the figure, if the ratio of the hole depth (t) to the diameter (d), 4/d, exceeds 10, the probability of passing through the hole without colliding with the hole wall of the shielding plate is (4).
is less than 1 inch. Considering the presence of force in attracting ions by the sheath electric field, it can be said that the number of ions that pass through the holes in the shielding plate without colliding to lose charge is extremely small.

Furthermore, as mentioned above, when the pressure inside the dry etching device is 1P (approximately α1 Torr), the diameter of the hole in the shielding plate should be approximately α5W, so the thickness of the shielding plate is approximately 5++.
The thickness is about a++, so it can be extremely thin. In order to increase the conductance with respect to the flow of molecules or neutral radicals, it is possible to increase the conductance with respect to the flow of molecules or neutral radicals by making a large number of holes in the shielding plate.

〔Effect of the invention〕

As explained in detail above, in the gas plasma dry etching apparatus of the present invention, ions can be almost completely removed by simply using a small and compact shielding plate, compared to conventional large-scale apparatuses using long transport pipes. can be converted into neutral radicals with large flux, so for example, semiconductor L
In the resist ashing process after fine pattern processing in the SI manufacturing process, it is possible to ash at high speed without the semiconductor element suffering from lattice defects caused by ion bombardment, resulting in a highly reliable semiconductor element with excellent performance characteristics. can be produced efficiently and inexpensively, and has extremely high industrial value.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing the structure of a gas plasma dry etching apparatus used in an embodiment of the present invention, and FIGS. 3 and 4 are shielding diagrams used in a dry etching apparatus in an embodiment of the present invention. Figure 5, a cross-sectional view showing an example of the shape of the plate, shows the ratio of the depth and diameter of the hole in the shielding plate shown in Figure 4, and the probability of particles passing through the hole without colliding with the wall of the hole in the shielding plate. It is a graph showing a relationship. 1... Plasma generation chamber 2... Gas inlet 6... Waveguide 4... Coil 5... Reaction chamber 6... ...Wafer installation stand 7...ψ...t Wafer 8...Exhaust port 9...Shielding plate 10...Half plate 11...・Molecular 11...Ion 12...Plate']! Figure 11 Figure 2 Figure 30 Danhiko Figure 4 “Bu” Man! 2 jr

Claims (1)

[Claims] 1. A dry etching apparatus having a gas plasma generation chamber and a reaction chamber for etching using the gas plasma, wherein the gas plasma generation chamber and the reaction chamber are under low pressure where collisions between molecules can be ignored. A shielding plate is provided between the gas plasma generation chamber and the reaction chamber, which has a large number of passage holes having a size approximately equal to the mean free path of molecules or positively charged particles flowing from the gas plasma generation chamber to the reaction chamber. The dry etching apparatus is characterized in that the shielding plate has a shape such that the molecules or positively charged particles collide with a wall of a passage hole provided in the shielding plate at least once. 2. In the dry etching apparatus according to claim 1, the cross-sectional shape of the passage hole provided in the shielding plate is dogleg-shaped, and the diameter, width, or depth of the dogleg-shaped passage hole is approximately 2. A dry etching device characterized by a mean free path of charged particles. 3. In the dry etching apparatus according to claim 2, in the shielding plate in which the cross-sectional shape of the passage hole is dogleg-shaped, the thickness of the shielding plate is equal to the diameter or width of the dogleg-shaped passage hole, or A dry etching device characterized by being approximately 2√2 times the depth. 4. In the dry etching apparatus according to claim 1, the shape of the passage hole provided in the shielding plate is approximately round, and the diameter of the round hole is approximately equal to the mean freedom of molecules or positively charged particles. stroke, and the depth of the above-mentioned round hole is
A dry etching apparatus characterized in that the diameter of the round hole is approximately 10 times that of the above-mentioned round hole.