JPH11186221A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To etch an Si oxide film with high selectivity at high speed by etching it with a reactive gas after irradiating this oxide film with X rays through a mask. SOLUTION: The manufacturing method comprises the step of forming an Si oxide film 1 on an Si substrate 2, the step of forming a photoresist film 3 having a contact etching mask by the lithography, the step of irradiating the Si oxide film 1 with X rays 4 through other than the mask of the resist film 3 to form affected parts 5, the step of etching the oxide film 1 with a reactive gas using nitrogen trifluoride to form contact holes 6 by the reactive etching using the reactive gas not contg. C, thus enabling high speed etching and improving the selectivity with the increase the etching speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for selectively etching a silicon oxide film to form a pattern.

[0002]

2. Description of the Related Art Conventionally, in a silicon oxide film etching process in a semiconductor device manufacturing process, dry etching using fluorocarbon plasma has been performed. Generally, fluorocarbon gas includes carbon tetrafluoride (CF
₄ ), methane trifluoride (CHF ₃ ) or a mixed gas thereof, or a gas obtained by mixing argon, oxygen, hydrogen, carbon monoxide, or the like with this gas has been used.

In the etching process of the silicon oxide film, it is important to obtain a selectivity with respect to a base material. Silicon is mainly present as a base material. Until now,
In dry etching of a silicon oxide film using fluorocarbon gas plasma, it is reported that a deposition film formed from carbon and fluorine is deposited on silicon and that etching is suppressed, thereby ensuring a selectivity. (Journal of Vocum S
science & Technology. A5 1
987 pp1585).

[0004] Since the fluorocarbon film is deposited on the silicon oxide film, the etching rate of the silicon oxide film also decreases. The selectivity increases because the rate of this decrease is small compared to the case of silicon, but more deposits are required to obtain a high selectivity, and as a result, when the selectivity is high, the silicon oxide film Is remarkable, and for example, it has been reported that under conditions that a selectivity of 14 is obtained in etching using C ₂ F ₆ + CH ₄ gas plasma, only an etching rate of about 400 nm / min is obtained. (Japanese Patent Laid-Open No. 61-276)
No. 34). In the etching using the fluorocarbon gas, the fluorocarbon film also deposits on the side wall of the pattern being etched, and acts as a side wall protective film, thereby affecting the etching shape. In order to perform complete anisotropic etching, it is necessary to improve the coverage of the fluorocarbon film for protecting the side wall of the pattern. When the pattern dimension becomes 0.25 μm or less and the depth becomes 1.5 μm or more in the future, the deposition of the fluorocarbon film on the pattern side wall, especially at a deep place will decrease and the coverage will be deteriorated.
There is a problem that it is difficult to control the etching shape and anisotropic etching cannot be obtained.

Further, the fluorocarbon film also deposits on the side wall of the chamber, and there is a problem that the deposited film becomes dust. From the above, it is desired to realize etching of a silicon oxide film using gas plasma containing no carbon or having a low carbon content.

However, carbon-free gas,
For example, in the etching using nitrogen trifluoride (NF ₃ ) or sulfur hexafluoride gas (SF ₆ ), the etching rate is 1 μm / min or more, but the selectivity with the underlying silicon film is only about 1. There is a problem.

Further, as another gas, bromic acid gas (HB
r) Etching of silicon oxide film by plasma has been reported (Dry Process Symposium Proceedings 19)
88 pp58). However, when using the bromic acid gas plasma, the silicon oxide film is hardly etched, and the etching rate is about 5 nm / min. Here, it is reported that the X-ray irradiation further increases the etching rate of the silicon oxide film. That is, it is described that the bond between silicon and oxygen is broken by X-ray irradiation, causing damage, and increasing the etching rate of the damaged portion. However, even when the etching rate is increased by irradiating X-rays,
There is a problem that the etching rate of the silicon oxide film is about 20 nm / min, and the selectivity to the underlying silicon film is much smaller than 1.

[0008]

In this conventional silicon oxide film etching using fluorocarbon gas plasma, a high selectivity to silicon can be obtained because a deposition gas is used. There are problems such as a decrease in controllability of etching shape and generation of dust. Further, when a fluorine-based gas containing no carbon is used, a high etching rate can be obtained, but a high selectivity with respect to the underlying silicon cannot be obtained. Further, in the etching of a silicon oxide film using a hydrobromic acid gas, the etching rate is low, and it is difficult to obtain a high selectivity with respect to the underlying silicon.

An object of the present invention is to provide a method of manufacturing a semiconductor device having a high selectivity and capable of anisotropically etching a silicon oxide film at high speed.

[0010]

A method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device in which a silicon oxide film formed on a semiconductor substrate is patterned by a dry etching method. The method is characterized in that the film is irradiated with X-rays and then etched using a reaction gas.

FIG. Japan by Sugita et al.
anse Jonrnal of Applied P
The penetration depth into the silicon oxide film when the X-ray energy reported in Physics 1991 pp 281 is changed is shown. When the X-rays of 800 eV are irradiated, it is found that almost 1 μm penetrates into the silicon oxide film. The bond energy between silicon and oxygen is 8.3 eV, and the X-rays can sufficiently cut the bond to form a damaged portion. Further, when nitrogen trifluoride or fluorine gas is introduced at the time of X-ray irradiation, fluorine is bonded to the cut dangling bond of silicon and silicon and oxygen are prevented from being recombined to form a silicon oxide film. Therefore, in the etching in the next step, the etching rate of the damaged portion formed here increases. At this time, the X-rays are almost absorbed by the silicon oxide film and do not damage the underlying silicon film. Utilizing the effect of increasing the etching rate, highly anisotropic etching is realized. That is, by irradiating X-rays through the etching mask, X-rays are radiated to the silicon oxide film only in the transmitted portions, thereby selectively forming damage in the silicon oxide film and increasing the etching rate in the portions. On the other hand, since the damage is not formed in the portion through which the X-ray is not transmitted, the etching rate does not increase. As a result, anisotropic etching is realized without using the side wall protective film.

[0012]

The damaged portion in the silicon oxide film due to X-ray irradiation is
The etching rate is higher than other parts, high-speed etching is realized, and a high selectivity with respect to the underlying silicon is obtained. Further, since the damaged portion is formed anisotropically due to the directivity of the X-ray, anisotropic etching can be realized without forming a sidewall protective film which is necessary when a gas containing carbon is used. Since this is not affected by the coverage of the deposited film, the contact size will be 0.25 in the future.
Anisotropic etching can be realized even when the depth is not more than μm and the depth is not less than 1.5 μm.

Further, since the gas plasma containing no carbon, the radical neutral beam, or the gas plasma containing a small amount of carbon is used for etching the silicon oxide film, the deposition of the fluorocarbon film on the chamber wall is suppressed. As a result, generation of dust can be suppressed, and the frequency of cleaning the etching apparatus can be significantly reduced.

[0014]

Next, the present invention will be described with reference to the drawings. FIGS. 1A to 1C are views for explaining a first embodiment of the present invention, and are cross-sectional views of a semiconductor chip shown in the order of processes when applied to forming a contact pattern of a silicon oxide film. It is.

First, as shown in FIG. 1A, a silicon oxide film 1 is formed on a silicon substrate 2 by a CVD method.
Thereafter, masks 1-2 for contact etching are used.
A photoresist film 3 having a thickness of about μm is formed by a lithography process.

Next, as shown in FIG. 1B, X-rays 4 are irradiated. The X-rays 4 pass through the portions other than the mask of the photoresist film 3 and irradiate the silicon oxide film 1. The bond between silicon and oxygen in the irradiated portion of the silicon oxide film 1 is cut, and a damaged portion 5 is formed. X-ray energy is determined by the thickness of the silicon oxide film. As shown in FIG.
In the case of μm, it is understood that X-rays of about 800 eV may be used. At this time, the penetration length of the X-rays into the silicon oxide film is about 1 μm, and damage is formed in the silicon oxide film 1 in the depth direction. Most of the X-rays 4 are absorbed by the silicon oxide film 1 and do not reach the underlying silicon, so that there is no damage.

Next, as shown in FIG. 1C, the contact hole 6 is formed by etching the silicon oxide film by a reactive ion etching method using a gas containing no carbon. Nitrogen trifluoride gas was used as the reaction gas, and the etching conditions were a gas flow rate of 880 sccm, an etching pressure of 500 mTorr, and a high frequency power of 820 W.

When X-ray irradiation is not performed under these etching conditions, the etching rate of the silicon oxide film is 400 nm.
/ Min. On the other hand, the etching rate of a damaged portion formed by X-ray irradiation is about 2 to 4 times higher than other portions. From this, high-speed etching of 1 μm / min or more is possible. In addition, the selectivity is improved about 2 to 4 times in response to the increase in the etching rate. Further, a damaged portion is formed only in a portion transmitted through the mask due to the directivity of the X-ray, so that etching with high anisotropy is realized. This does not depend on the coverage of the deposited film, which is a problem when a deposition gas is used. Therefore, when the dimension of the contact hole 6 is 0.25 μm or less and the depth is 1.5 μm or more. In this case, anisotropic etching is realized.
In addition, since a gas containing no carbon is used, there is no deposition on the chamber wall, so there is no problem such as generation of dust.

In the first embodiment, nitrogen trifluoride gas is used as the etching gas, but the same effect can be obtained by using fluorine gas or carbon tetrafluoride gas. The same effect can be obtained by using a fluorine radical neutral beam in which a grounded mesh electrode is provided between upper and lower electrodes to remove ions instead of the gas plasma ion etching.

In the second embodiment, a sample in which a silicon oxide film is formed on a substrate and a contact etching mask is formed is placed in a vacuum chamber. Thereafter, while introducing nitrogen trifluoride at a gas flow rate of 100 sccm, X-rays are irradiated from a beryllium window provided opposite to the sample. At this time, fluorine is bonded to the damaged portion, and silicon is recombined with oxygen to prevent SiO ₂ from being formed again. As a result, as compared with the case where nitrogen trifluoride is not introduced at the time of X-ray irradiation as in the first embodiment, the etching rate is 1.
Increase by about 5 times.

In the second embodiment, nitrogen trifluoride is used as the gas introduced at the time of X-ray irradiation, but the same effect can be obtained by using fluorine gas.

FIGS. 2A and 2B are cross-sectional views of a semiconductor chip for explaining a third embodiment of the present invention, in which an X-ray mask is used without using a photoresist film mask. Show the case.

First, as shown in FIG. 2A, a silicon oxide film 1 is formed on a silicon substrate 2 by a CVD method.
Next, X-rays 4 are irradiated through an X-ray mask (metal mask) 7. As the X-ray mask, a tantalum or tungsten X-ray absorber having a thickness of about 1 μm is adhered to a silicon nitride film or silicon carbide film membrane. Except for the mask, the X-ray 4 passes through and irradiates the silicon oxide film 1 to form a damaged portion 5A.

Next, as shown in FIG. 2B, etching is performed by a dry etching method under the same conditions as in the first embodiment to form a contact hole 6A. According to this method, since a pattern can be formed without using a photoresist film mask, there is an advantage that the number of steps can be reduced.

[0025]

As described above, according to the present invention,
In the etching of the silicon oxide film, high-selectivity, high-speed, high-anisotropic etching can be realized. Further, the frequency of chamber cleaning can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip for explaining a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor chip for explaining a third embodiment of the present invention.

FIG. 3 is a view showing the penetration length of X-rays into a silicon oxide film obtained from calculation results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon oxide film 2 Silicon substrate 3 Photoresist film 4 X-ray 5,5A Damaged part 6,6A Contact hole 7 X-ray mask

Claims (6)

[Claims] In a method of manufacturing a semiconductor device, in which a silicon oxide film formed on a semiconductor substrate is patterned by a dry etching method, the silicon oxide film is irradiated with X-rays through a mask and then etched using a reaction gas. A method of manufacturing a semiconductor device. 2. The method according to claim 1, wherein nitrogen trifluoride, fluorine, or carbon tetrafluoride is used as the reaction gas. 3. The method of manufacturing a semiconductor device according to claim 1, wherein a neutral beam of ions of a reactive gas or fluorine radicals is used for the dry etching. 4. The method according to claim 1, wherein the X-ray irradiation is performed in a nitrogen fluoride or fluorine atmosphere. 5. The method according to claim 1, wherein a photoresist film is used as a mask. 6. The method according to claim 1, wherein a metal mask is used as the mask.