JPH0878393A - Plasma etching system - Google Patents

Abstract

PURPOSE: To allow an etching deposit not to be accumulated in a light guide device by forming recessed and projecting parts on an incident surface into which a plasma is made incident, in the light guide device for guiding the plasma generating in an etching chamber. CONSTITUTION: An etching chamber 1 is provided with a gas exhaust port 6 on the left side and a sample 7 to be etched is placed on the lower electrode 3 therein. A light guide device 8 made of quartz is fitted into the right-side wall of the chamber 1. The light guide device 8 is allowed to have numbers of grooved, thin slits on the incident surface. The slit consists of projecting parts 12 and recessed parts 13 that are formed on the incident surface of the device 8. Since an etching product 15 is accumulated on the part 12, no plasma from the parts 12 is made incident. On the other hand, the product 15 is not accumulated in the part 13, any plasma can be made incident. Such an effective configuration can secure the incident area for plasma and the plasma is hardly blocked during etching operation for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching apparatus having an etching end point detector used in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art At present, dry etching technology has become a major process technology which holds one of the keys to the fine processing technology of semiconductor devices. The material to be etched is also silicon oxide (Si
In addition to insulating films such as O ₂ ) and silicon nitride (Si ₃ N ₄ ), types of wiring materials such as aluminum (Al) and molybdenum (Mo) are increasing. It is also an indispensable technique for forming a device structure such as a trench digging process in a trench structure.

The dry etching technique includes a reactive plasma etching technique which utilizes only a chemical reaction of active particles in plasma generated by applying a high frequency electric field to an etching gas. An apparatus using this technique is reactive. A plasma etching apparatus (hereinafter referred to as a plasma etching apparatus).

FIG. 6 shows a cross section of a conventional plasma etching apparatus. Reference numeral 1 is an etching chamber, 2 is an upper electrode, and 3 is a lower electrode. The high frequency power supply 4 is connected between the upper electrode 2 and the lower electrode 3, and the upper electrode 2 is grounded. Such a structure is called a cathode couple system. Upper electrode 2
Is provided with an etching gas introduction port 5, and a gas exhaust port 6 is provided on the left side of the etching chamber 1. The arrows in the drawing indicate the gas introduction direction and the gas exhaust direction. A sample 7 to be etched is placed on the lower electrode 3. A peep window 8 is fitted in the right part of the etching chamber 1.
A phototransistor 9 is installed in the vicinity of the viewing window 8 and is connected to the tester 10 by an electric wire 16.

In the etching, the etching gas is supplied to the etching chamber 1, and the upper electrode 2 is driven by a high frequency power source.
A high-frequency electric field is applied between the lower electrode 3 and the lower electrode 3 to generate ions, active atoms, or radicals of molecules, and a chemical reaction with the sample to be etched produces a substance having a higher vapor pressure. At this time, the sample to be etched is placed during plasma etching, but the potential difference between the sample to be etched and the plasma potential is small (up to several tens of V), there is almost no effect of ion bombardment, and reactive etching by radicals. Is mainly used, and isotropic etching is possible. Light due to plasma emission is generated during etching, and the plasma emission intensity, which indicates the intensity of the light, changes as the surface state of the sample to be etched changes.

As a method of grasping the etching condition inside the etching chamber 1, a method of monitoring a change in plasma emission intensity during etching, and a change of self-bias (voltage between the upper electrode 2 and the lower electrode 3) during etching are monitored. There are ways to do it. A method that is commonly used is to monitor the plasma emission intensity. This method uses a filter to select light with a wavelength at which the amount of change in the emission intensity in plasma during etching of the film to be etched and when overetching from the end point of the film to be etched is large. Monitored, in which case the light is detected by an etch endpoint detector. This etching end point detector is composed of a light guide 8, a phototransistor 9, a tester 10, and an electric wire 16. The light generated on the sample to be etched 7 is emitted from the light guide 8 to the outside of the etching chamber 1. The light is received by the phototransistor 9, converted into an electric signal, and shown by a tester 10 below. The light guide 8 is made of a material having a high transmittance such as quartz.

When the sample 7 to be etched is silicon, fluorocarbon gas (CF ₄ ) is often used as the etching gas. This fluorocarbon gas dissociates in plasma as follows to generate active F ^* radicals.

CF ₄ ← → CF ³⁺ + F ^* + e (1) This F ^* radical produces volatile silicon fluoride (SiF ₄ ) by the following chemical reaction, and etching is performed.

Si + 4F ^* → SiF ₄ ↑ (2) SiO ₂ + 4F ^* → SiF ₄ ↑ + O ₂ ↑ (3) Si ₃ N ₄ + 12F ^* → 3SiF ₄ ↑ + 2N ₂ ↑ (4) Therefore, in general, silicon Oxygen (O ₂ ) is often added to the fluorocarbon gas in order to increase the etching rate, and when oxygen is added, the amount of F ^* generated is regulated by the following equation.

CF ₄ → CF ³⁺ + F ^* + e (5) CF ³⁺ + O + e → COF ₂ + F ^* (6) The amount of F ^* can be increased by this reaction.

However, a fluorocarbon gas such as CF ₄ or COF ₂ adheres and deposits on the inner surface of the etching chamber 1 and the viewing window 8 as etching products. FIG. 7 is a perspective view of the light guide 8 after etching. Reference numeral 11 denotes a light guide entrance surface on which light is incident, and 14 is a light guide exit surface for emitting the light to the outside. 15 is an etching product. The light guide entrance surface 11 is partially exposed, but is completely covered as the etching time increases. As a result, FIG.
As shown in the figure (see the broken line), when the etching time (discharge time) becomes long, the light incident on the light guide entrance surface 11 is blocked by the etching products, and the intensity of the light entering the phototransistor 9 is increased. (Emission intensity) is significantly reduced, and changes in plasma emission intensity cannot be monitored.
Usually, the light guide 8 is completely fixed in the etching chamber 1 in order to enhance the airtightness of the etching chamber 1, and it is very difficult to replace the light guide 8 with the etching products deposited on the surface of the light guide 8. It also takes time to remove.

[0012]

As described above, in the prior art, when etching products were deposited on the light guide, plasma light did not reach the phototransistor.
As a result, the etching end point could not be detected. It is an object of the present invention to eliminate the above-mentioned drawbacks and provide a plasma etching apparatus having a light guide in which etching products are less likely to be deposited.

[0013]

In order to achieve the above object, in the first aspect of the invention, an etching chamber and a conductor for guiding plasma light generated in the etching chamber at a predetermined position are guided. The optical device and the light guide have an incident surface on which plasma light is incident and an emission surface for emitting plasma light, and in the plasma etching apparatus having a detector for detecting plasma light from the emission surface, A second aspect of the present invention provides a plasma etching apparatus characterized in that an incident surface has an uneven portion, and in the second invention, an etching chamber and plasma light generated in the etching chamber at a predetermined position are generated. And a first light guide for guiding the plasma light, the first light guide having an incident surface on which the plasma light enters and an emission surface for emitting the plasma light. In the plasma etching apparatus having a detector that knowledge, a second light guide having an uneven portion on the incident surface to provide a plasma etching apparatus characterized by being No設.

[0014]

When the plasma etching apparatus provided by the present invention is used, since the uneven surface is formed on the incident surface of the light guide, the etching product generated by the etching is deposited in the concave due to the microloading effect. It gets harder. As a result, the plasma light can be stably supplied to the detector even under the condition that the etching products are deposited.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross section of the plasma etching apparatus of the first embodiment. Reference numeral 1 is an etching chamber, 2 is an upper electrode, and 3 is a lower electrode. The high frequency power source 4 is an upper electrode 2 and a lower electrode 3.
And the upper electrode 2 is grounded. Such a structure is called a cathode couple system. The upper electrode 2 has an etching gas inlet 5 and the etching chamber 1
Gas exhaust ports 6 are respectively provided on the left side, and arrows in the drawing indicate the gas introduction direction and the gas exhaust direction. A sample 7 to be etched is placed on the lower electrode 3.
A light guide 8 made of quartz is fitted in the right part of the etching chamber 1. The light guide entrance surface 11 is provided with innumerable groove-shaped thin slits. A phototransistor 9 is installed near the light guide 8. The phototransistor 9 is connected to the tester 10 by an electric wire 16.

FIG. 2 is an enlarged perspective view showing the light guide 8 after etching. The slit is composed of a convex portion 12 and a concave portion 13 formed on the light guide entrance surface 11. Since the etching product 15 is deposited on the convex portion 12, almost no plasma light enters from the convex portion 12.

FIG. 3 is an enlarged sectional view showing the light guide 8 after etching, which is a sectional view of FIG. Since the etching product 15 is not deposited in the concave portion 13, it can be seen that the plasma light can enter. In this way, by providing the groove-shaped slit, the etching product 1 is formed in the recess 13.
The fact that 5 does not deposit is called the microloading effect. Due to this effect, the incident area of plasma light can be secured, and it becomes difficult for the plasma light to be blocked during etching for a long time. The shape of the slit for obtaining the microloading effect may be a hole shape other than the groove shape. Furthermore, the number of light guides does not necessarily have to be one,
For example, another light guide having a slit is provided on the light guide entrance surface 11
It may be placed on top. The example is shown below.

FIG. 4 is an enlarged perspective view showing the light guide after etching when the two light guides of the second embodiment are used. On the light guide entrance surface 11 of the light guide (hereinafter referred to as the first light guide) 8 having no uneven portion, the second light guide 8 is provided to protect the first light guide 8 from etching products. An optical device 17 is placed. The second light guide 17 is provided with a hole. This hole penetrates the protective plate 17, and a predetermined portion of the light guide entrance surface 11 is exposed. The etching product 15 is deposited on the second light guide 17, but hardly deposited on the light guide entrance surface 11. Therefore, it is possible to obtain the same effect as that of the first embodiment using only one light guide. Further, in the present embodiment, even if the holes of the second light guide 17 are clogged by the etching product 15,
Since the light guide 17 can be easily replaced, the etching can be immediately started. Therefore, the effect is also great in terms of throughput.

FIG. 5 shows the intensity (emission intensity) of the light incident on the phototransistor 9 with respect to the etching time (discharge time) in the first and second embodiments. The etching conditions are such that the sample to be etched 7 is made of silicon (S) in order to prevent a change in emission intensity of plasma light during etching.
The blank wafer of i) (raw wafer without patterning) was used, the sample 7 to be etched was placed on the lower electrode 3, and etching was performed using the gas in which the etching product was deposited in the etching chamber 1. At this time, the gas used was basically fluorocarbon, and the composition was CHF ₃ : C.
O = 1: 3 and the pressure was 5.3. A high frequency voltage having a frequency of 13.56 MHz and an energy density of 4.5 W / cm ² was applied between the upper electrode 2 and the lower electrode 3.

Plasma was generated under the above etching conditions, the light during etching was guided to the phototransistor 9, and the change in emission intensity was read by the tester 10.
The viewing window used at this time is shown in FIG. For comparison, a conventional viewing window shown in FIG. 7 was also used. As the viewing window of this embodiment, a slit aspect ratio (A / B) in which the dimension B is changed to a constant value of 10 and 30 and a conventional viewing window having no slit (aspect ratio ∞) are prepared. ,
It was observed how the emission intensity during discharge time changed with respect to the aspect ratio. As a result, as shown in FIG. The emission intensity characteristic shows a tendency to decrease with respect to the discharge time.

2. This attenuation tendency is the steepest in the conventional case, and in the case of the present invention, the larger the aspect ratio of the slit, the more gradual the attenuation tendency is. 3. The emission intensity shows a gradual attenuation tendency due to the slit provided in the light guide. I knew that. The reason why the emission intensity characteristic shows a tendency to decrease is
This is because the etching product adheres to the light guide entrance surface 11 and blocks the plasma light, and the reason why the attenuation tendency is alleviated by providing the slit is that the microloading effect remarkably appears under the etching conditions. This is because the deposition rate of the etching product on the recess 13 of the slit becomes gentle in inverse proportion to the aspect ratio. Further, the reason why the emission characteristics show a gradual decrease tendency is that the etching product 15 is deposited on the convex portions 12 of the slits, so that the emission intensity is temporarily decreased. Aspect ratio is 30
In this case, if the convex portion 12 is completely covered, it will be in a substantially steady state, and the emission intensity at that time is at a level that does not affect the detection of the etching end point, and is practical.

In addition to the fluorocarbon, the present invention uses an etching gas such as chlorine gas (Cl ₂ ) or boron trichloride (BCl ₃ ) and chlorine (Cl ₂ ) such that etching products are deposited in the etching chamber 1. It is also effective when a mixed gas of nitrogen and nitrogen (N ₂ ) is used.

[0023]

As described above, according to the present invention, it is possible to suppress the deposition of etching products on the light guide having the slit by the microloading effect.
As a result, it is possible to provide a plasma etching apparatus capable of detecting the etching end point even under the etching conditions in which conventional etching products are deposited.

[Brief description of drawings]

FIG. 1 is a sectional view of a plasma etching apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged perspective view of the light guide after etching according to the first embodiment of the present invention.

FIG. 3 is an enlarged sectional view of the light guide after etching according to the first embodiment of the present invention.

FIG. 4 shows 2 after etching according to the second embodiment of the present invention.
An enlarged perspective view of two light guides.

FIG. 5 is a characteristic diagram of emission intensity with respect to discharge time of the present invention and the conventional one.

FIG. 6 is a sectional view of a conventional plasma etching apparatus.

FIG. 7 is an enlarged perspective view of a conventional light guide after etching.

[Explanation of symbols]

 1 Etching Chamber 2 Upper Electrode 3 Lower Electrode 4 High Frequency Power Supply 5 Etching Gas Inlet 6 Gas Exhaust Outlet 7 Etched Sample 8 (First) Light Guide 9 Phototransistor 10 Tester 11 Light Guide Incident Surface 12 Convex 13 Concave 14 Light guide exit surface 15 Etching product 16 Electric wire 17 Second light guide

Claims (5)

[Claims] 1. An etching chamber, a light guide formed at a predetermined location of the etching chamber and for guiding plasma light generated in the etching chamber, and the light guide includes an incident surface on which plasma light is incident and a plasma. A plasma etching apparatus having an emitting surface for emitting light and having a detector for detecting plasma light from the emitting surface, wherein the incident surface has an uneven portion. . 2. An etching chamber, a first light guide which is formed at a predetermined position of the etching chamber, and which guides the plasma light generated in the etching chamber, A plasma etching apparatus having a detector for detecting the plasma light from the emission surface, the second conductor having an uneven surface on the incidence surface, the detector having an incident surface for incidence and an emission surface for emitting plasma light. A plasma etching apparatus having an optical device mounted thereon. 3. The plasma etching apparatus of claim 2, wherein the first light guide and the second light guide can be easily separated. 4. The plasma etching apparatus according to claim 1, wherein the uneven portion has any shape of a slit, a groove, and a hole. 5. The plasma etching apparatus according to claim 4, wherein the aspect ratio of the unevenness is 30 or more.