JPH01101632A - Method and device for dry etching of silicon nitride film - Google Patents

Abstract

PURPOSE:To increase the ratio of etching selection of a silicon nitride film to a silicon oxide film by employing an element F and the like as a gas to etch the silicon nitride film and introducing at least the element F as a radical into a vessel which houses a substrate to be processed. CONSTITUTION:In selectively etching a silicon nitride film 44 with respect to a silicon oxide film 43, a gas which involves an element F and other halogen elements is introduced into a vessel which houses therein a substrate to be processed, on the surface of which the silicon nitride film 44 and the silicon oxide film 43 are formed. Thereupon, at least the element F is excited at the other area and introduced into the vessel as active species while the substrate 41 is irradiated with a light from an excimer laser or the like. Hereby, the light excites the surface of the substrate 49 to promote the etching reaction. Thus, there are improved the etching speed of the silicon nitride film 44 and the selection ratio of the silicon nitride film to the silicon oxide film 43.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Field of Application) The present invention relates to a dry etching technique used in a semiconductor device manufacturing process, and in particular to a dry etching technique that can achieve a high selectivity for a silicon oxide film by photo-excited etching. The present invention relates to a dry etching method and dry etching apparatus for etching a silicon nitride film.

(Prior Art) Conventionally, during the semiconductor device manufacturing process, a silicon nitride film (Si3N4) was used for a silicon oxide film (SiOz).
When selectively etching >, chemical dry etching (CDE) using CF4+02 or CF4+02 +N2 mixed gas is mainly used. (S!s N4/S i 02) in this CDE
The etching speed ratio, that is, the selection rate, is at most 10 or less. In CDE, silicon is etched at high speed, so S! When removing 3N4, the silicon surface must be S! to prevent etching of the silicon surface.
A method of coating with 02 is used. In this case, S! used for coating! The thickness of 02 is determined by taking into consideration the etching speed ratio, or the uniformity within a wafer or between wafers when processing a plurality of wafers at the same time. Also, S!
It is known that when there is a step on the silicon surface coated with 02, the etching rate of S i 02 at the corner of the step is faster than at the flat area. S on a fast corner! 02
Since the etching rate is representative of the etching rate, the effective selection ratio becomes smaller.

Now, as a substrate to be processed, 3i is used as shown in Fig. 5).
A groove 52 with a high aspect ratio is formed on the surface of the substrate 51, and 3! It is assumed that the Si3N4 film 54 is coated with the Si3N4 film 53 on the flat surface. Drill S on this substrate to be processed! When CDE is used to remove the 3N+ film 54, S! The etching speed of 02 becomes faster, and as shown in Figure 5 (c), 3i is etched in that part.
02 may disappear and the underlying silicon may be etched. In fact, in a substrate to be processed that requires such corner portions, (S i 3 N4/S i 02 )
The etching selectivity ratio is about 3, and by considering the overetching time for more uniform etching, it is necessary to use a safe 5tO2 film to remove, for example, 2000 (person) S!3N4 films. Thickness is 1000
C person] is required.

Currently, in the process of making minute elements, S! 02
High-temperature processes such as film formation may disturb the profile of impurities that have already been formed, and therefore there is a need to shorten the time of low-temperature processes or high-temperature processes. However, s i 02 (CVDSj
02 etc.), the etching resistance is much worse than that of 5iOz formed by a thermal oxide film. Therefore, it cannot be used as an etching protection film. Furthermore, when forming a protective SiO2 film by thermal oxidation, there are cases where it is not possible to form a SiO2 film thick enough to have safe etching resistance due to constraints such as changes in the impurity profile as mentioned above. There is. In this case, 3i3N4
CDE cannot be used to remove the membrane.

On the other hand, S! using hot phosphoric acid solution! In the etching of 3N4, the etching speed ratio (S!3N4/S!02), that is, the selection ratio, is extremely high. However, in etching using hot phosphoric acid, the etching rate of 513N4 is extremely low, as low as several 10 (8/min), resulting in poor productivity and impractical. Furthermore, it is extremely difficult to control conditions such as the temperature of the etching solution during etching and to manage the etching solution, making it unsuitable for use in actual production.

In order to solve the above-mentioned problems of conventional dry etching of silicon nitride films with respect to silicon oxide films, the present inventors first developed an etching method and apparatus using a gas containing fluorine element and a halogen element other than fluorine element. (Japanese Patent Application No. 61-126398).

According to this method and apparatus, the etching selectivity and controllability of the silicon nitride film relative to the silicon oxide film are improved compared to the conventional method.

However, when obtaining a high selectivity, the etching rate of the silicon nitride film decreases, resulting in an increase in processing time, and the conditions for practical etching are limited.

(Problem to be solved by the invention) In this way, in conventional dry etching, in order to increase the etching rate of the silicon nitride film, the etching selectivity must be lowered. Etching has been severely limited by etching conditions such as gas flow rate and etching time. Further, although etching using a solution has a high selectivity as described above, there are problems in that the etching speed is slow, and the etching process and process control are difficult, making it impractical.

The present invention has been made in consideration of the above circumstances, and its purpose is to sufficiently increase the etching selectivity of the silicon nitride film over the silicon oxide film, and to reduce the etching rate of the silicon nitride film. It is an object of the present invention to provide a dry etching method which can perform the etching process sufficiently quickly and is suitable for selectively etching a silicon nitride film.

Another object of the present invention is to provide a dry etching apparatus for carrying out the above method.

[Structure of the invention]

(Means for solving the problems) The gist of the present invention is to use fluorine (F) as used in CDE.
In the dry etching method, which excites a gas containing an element and supplies the generated F atoms to a substrate to be processed on which a silicon nitride film and a silicon oxide film are formed for etching, a halogen gas other than the F element is used. By simultaneously exciting a gas containing the F element, or by simultaneously supplying F atoms to the substrate to be treated as a raw gas, and by irradiating the surface of the substrate to be treated with light such as an excimer laser,
The purpose of this method is to etch a silicon nitride film with a higher selectivity than the conventional etching ratio with respect to a silicon oxide film.

As described above, the inventors have found through experiments that the selection ratio is improved by adding a halogen gas other than the F element in CDE using a gas containing the F element. Although the mechanism for this is not clear, the etching rate of silicon nitride and silicon oxide films decreases by adding a halogen gas other than the F element, but the etching rate of the silicon oxide film decreases more than the etching rate of the silicon nitride film. This is due to the large rate of decrease in speed.

Furthermore, in CDE using a gas containing the F element and a halogen element other than the F element, the etching rate of the silicon nitride film was found to be significantly improved by irradiating the substrate with light.

In addition, irradiation of the substrate with light is an effective way to improve the etching speed. Although the etching rate of the 5i-N film is not accelerated for the 5i-02 film, the etching selectivity of the SiN film with respect to the Si02 film can also be improved. Also,
This separate house has been confirmed with C12°8r2 and other various halogen gases.

As a method for adding a halogen gas other than fluorine (F), it may be excited together with a gas containing the F element and introduced into the container, or it may be introduced into the container as a raw gas. Furthermore, instead of using a halogen gas other than F, a gas containing a halogen element may be used. Furthermore, instead of mixing a halogen gas other than F with the gas containing the F element, it is also possible to use a compound gas of the F element and another halogen element.

The present invention has been made with attention to these points, and uses a dry etching method for selectively etching a silicon nitride film with respect to a silicon oxide film. A gas containing the F element and other halogen elements is introduced into a container containing the processing substrate, and at least the F element is excited in a region different from the container and introduced into the container as an active species. The present invention also provides a dry etching method in which a substrate to be processed is irradiated with light.

The present invention further provides a dry etching apparatus for carrying out the method of the present invention.

That is, a first container for accommodating a substrate to be processed; a means for exciting a gas containing at least the F element in a region separate from the container and introducing active species generated in the region into the container; Halogen elements other than F element or at least F
A means for directly introducing a gas containing a halogen element other than the element into the container, a means for irradiating the substrate with light, a means for evacuating the inside of the container, and a means connected to the container via a vacuum valve. a second container, a means for evacuating the second container independently of the first container, and a means for transporting the substrate to be processed between the first and second containers. To provide a dry etching device with

(Function) According to the present invention, the etching selectivity of (Si3N4/5i02) is improved by adding a halogen other than F as a reactive gas to CDE that uses atoms as an etchant. When adding halogen gas other than F to CDE as an etchant, S!02
The etching rate decreases monotonically with the amount of halogen gas added other than F. On the other hand, the etching rate of SI3N4 increases when a small amount of halogen gas is added, but it decreases when a large amount is added. However, when adding an equal amount of halogen gas, S! Due to the large decrease in etching rate of 02, (S i 3 N4
/S 1O2) increases monotonically with the amount of halogen gas added. In other words, when trying to obtain a high selectivity, the etching speed of Si3N4 decreases and the etching time increases.

In this type of dry etching, light from an excimer laser or the like is used as S! 3N4. S! When irradiated to Oz, S!
For No. 02, since the etching gas originally containing F and halogen elements other than F has almost no chemical effect, there is almost no change in the etching rate. On the other hand, S! 3N
4, the etching gas acts chemically.

The light emitted from the excimer laser or the like excites the surface of the substrate to promote an etching reaction, and in some cases excites the etching gas to generate a large amount of etchant that contributes to etching. The excitation of the substrate surface and the generation of this etchant vary depending on the intensity or type of irradiated light.

Therefore, the etching speed of 513N4 is greatly improved by light irradiation, and S! The selection ratio with respect to 02 is also significantly improved.

(Embodiment) First, an embodiment of the apparatus of the present invention used in the dry etching method of the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram of a dry etching apparatus showing an embodiment of the apparatus of the present invention. In the figure, reference numeral 11 denotes a first vacuum container forming a reaction chamber, and a sample stage 13 holding a plurality of wafers 12 to be processed is accommodated within this container 11. A gas inlet 14 for introducing F atoms is provided on the upper wall of the container 11, and this inlet 14 is connected to a discharge tube 15 for transporting F atoms. The discharge tube 15 is coupled to an applicator 18 to which microwaves are supplied from a microwave power source 16 via a waveguide 17 . The gas (gas containing F element) introduced from the gas supply port 19 is excited by the microwave discharge, and this excitation causes active species (F radicals) of the gas to be supplied into the container 11. ing. Further, in the earthen wall of the container 11, another gas introduction port 20 is provided in addition to the gas introduction system described above. This gas introduction port 20 is for introducing a halogen gas other than F (for example, Cβ2, etc.) into the container 11. The inside of the container 11 is evacuated through a gas exhaust port 21.

Furthermore, a window 41 is provided above the container 11 to introduce light 43 from a light source 42 into the container 11, and the light 43 is irradiated onto the wafer 12 to be processed through the window 41. ing.

Further, a second vacuum container 23 is connected to the right side of the container 11 via a gate valve 22 . This container 2
3 is provided with a gas exhaust port 24, and the inside of the container 23 is evacuated independently from the container 11. On the right side of the container 23, valves 1 to 25 are provided to isolate the container 23 from the outside. Furthermore, a transport mechanism 26 for transporting the sample stage 13 is installed inside the container 23 . This transport mechanism 26 transports the sample stage 13 between the first and second containers 11.23 with the gate valve 22 open.

On the other hand, a gate valve 27 is located on the left side of the first container 11.
A third vacuum container 28 is connected to the vacuum container 28 via the spacer.

This container 28 is provided with a gas exhaust port 29, and the inside of the container 28 is evacuated independently of the container 11.

A gate valve 30 is provided on the left side of the container 28 to isolate the container 28 from the outside.
A transport mechanism 31 for transporting the sample stage 13 is installed inside. This transport mechanism 31 transports the sample stage 13 between the first and third containers 11.28 with the gate valve 27 open.

Further, a heating mechanism 32 for heating the wafer 12 to be processed inside the container 28 is provided outside the container 28 . This heating mechanism 32 can remove residual gas and the like adhering to the wafer to be processed that has been processed in the first container.

First Practical tb Example (Method) Next, a dry etching method using the above-mentioned apparatus of the present invention will be explained. Here, N is used as a gas containing F element.
A case will be described in which F3 gas is used and Cβ2 is used as a halogen gas other than F.

It is now assumed that all gate valves 22, 25, 27, and 30 are closed, and the interiors of all containers 11, 23, and 28 are evacuated. From this state, the gate valve 25 is opened to release the second container 23 to the atmosphere, and the sample stage 1 holding the plurality of wafers 12 to be processed in the container 23 is
Set. Here, the processing target wafer 12 is, for example, a substrate on which a silicon oxide film and a silicon nitride film are formed. Next, the gate valve 25 is closed to evacuate the inside of the second container 23, and then the gate valve 22 is opened. Next, the sample stage 13 is transported into the first container 11 by the transport mechanism 26, and then the gate valve 22 is closed. After this, the next wafer 12 to be processed is set in the second container in the same manner as above.

Next, NF3 gas is introduced from the gas supply port 19 and discharged by microwave discharge, and active species of F are introduced into the first container 11 via the discharge tube 15. At the same time, Clh gas is introduced into the first container 11 as raw gas through the gas inlet 20. Next, the wafer 12 to be processed is irradiated with light from the light source 42 . Then, the gas is exhausted from the gas exhaust port 21 at a constant flow rate, and the gas pressure inside the container 11 is maintained constant to perform etching of the wafer 12 to be processed.

When etching is completed, the introduction of the gas is stopped and the inside of the first container 11 is evacuated. When the inside of the first container 11 is sufficiently evacuated, the gate valve 27 is activated, and the sample stage 13 is transported into the third container 28 by the transportation mechanism 31. Next, close the goo 1 to valve 27 and set the heating number @ 3.
2, the wafer 1 to be processed is housed in the third container 28.
2 is heat-treated. As described above, by this heat treatment, residual halogen gas and the like adhering to the surface of the substrate 12 to be processed are removed and cleaned.

At this time, the next wafer 12 to be processed is transferred into the first container 11 and etched in the same manner as before.

Next, after the gate valve 30 is turned on and the third container 28 is released to the atmosphere, the sample stage 13 is taken out.

As a result, the entire etching process for the wafer 12 to be processed is completed.

By repeating the above operations, a plurality of wafers 12 to be processed can be successively etched. In this case, the first container 11 is not exposed to the atmosphere, making maintenance of the apparatus easier. That is, container 1
Since a halogen gas such as (Jh) is used in the container 1, when it is exposed to the atmosphere, the residual halogen gas reacts with moisture and the container 1
Although there is a risk that the constituent materials within the structure 1 will be corroded, such problems can be prevented.

Next, Cβ2 is introduced into the container from the gas inlet 20.
The reasons for adding halogen gases other than F will be explained. In order to understand this example, Fig. 2 shows the S! 3N4,5
The change in etching rate of iOz is shown. S!
Initially, the etching rate of 3N4 decreases due to the introduction of Cβ2.

S! The etching rate of Oz monotonically decreases due to the introduction of Cβ2. In this case, the total pressure inside the container is 0.2 (
Torr). Also, the etching speed ratio is C
It increases monotonically with the introduction of β2.

For Cβ2 flow i20 (SCCm) or more, the selection ratio is 10 or more, and for Cf: 1256 (SCCm), the selection ratio is 5.
It became about 0. In other words, by adding Cβ2, 5Is
S of Nq! It becomes possible to sufficiently increase the etching selection ratio with respect to Oz.

Next, a case where a KrF excimer laser is introduced into a container containing a wafer to be processed under the same conditions will be described. In this case, as the Cf12 rank increases, S! 3
The tendency for the etching rate and selectivity of N4 to increase was similar to that shown in FIG. 2, but the etching rate and selectivity were more than doubled.

In addition, the inlet of NF3 is shown in Figure 3 at 40 (sccm).
- shows the change in the etching rate of 3iN and Sio2 when the flow rate of Br2 as a halogen gas other than F is changed. The etching rate of SiN initially increases with the introduction of Br2, but the etching rate decreases with the introduction of a large amount of Br2. S! In 02, the etching rate monotonically decreases due to the introduction of Br2. In this case, the total pressure inside the container is maintained at 0.2 (Torr).

Furthermore, the etching speed ratio increases monotonically with the introduction of 8r2. In other words, due to the addition of Br2, the S! of SiN! It becomes possible to make the etching selectivity to 02 sufficiently large. In addition, in Br2,
When 20 (SCCm) was added, the selectivity was about 40.

Next, a case will be described in which KrF excimer laser light is introduced into a container containing sea urchins A to be treated under these same conditions. The etching rate of S.102 is that of Cβ2. B
r2 There was no change at all when any of the gases was added, but the etching rate of SiN was several tens of percent to several times higher by the irradiation with the light.

As the light used in the present invention, ultraviolet light has a remarkable etching effect, and in addition to KrF excimer laser, ArF and XeF laser light can also be used. Furthermore, although the effect of wavelength was not necessarily significant, the etching rate increased as the intensity of light increased. However, if the intensity of the light is too high, the heat of the light may cause distortion or peeling between the silicon oxide film and the silicon nitride film, making it impossible to perform good selective etching.

Therefore, the practical light intensity is 0.5Δ/crA~10
-/crA, and the effect of the present invention is particularly remarkable for 1
~5W/cffl. Also, H that includes the infrared region
A g lamp, a Xe lamp, etc. may also be used.

S! 3N4/S! The etching selection ratio of 02 is
Regardless of whether Cβ2 gas or Br2 gas is added, the amount increases as the amount added increases. When chlorine (Cβ2) gas is added, the Cβ2 flow rate is 30 (sccm) or more, and when Br2 gas is added, the flow rate is 50 (sccm).
From the above, S! As the etching rate of 02 decreases and approaches approximately O [people/min], the selectivity becomes extremely large.

In Figure 2, NF 336 (sccm), Cl1
The wafer shown in FIG. 4 was etched under the conditions of 256 sccm (sccm). This wafer to be processed is similar to that shown in FIG. 5(2). That is, a deep groove 42 with a high aspect ratio is formed on the surface of the 3i substrate 41, and the surface within this groove 42 has a thickness of 200 (person) S i
A 5f3N4 film 44 with a thickness of 1800 mm is formed on the flat surface.When this wafer to be processed was etched under the above conditions, the result was as shown in Fig. 4(c). As a result, etching of the silicon at the corner portions 45 and 46 was eliminated, and Si3N4 was successfully peeled off.

The etching processing time is, if you want to use light irradiation,
It takes about 10 minutes, whereas KrF
When etching was performed while irradiating with laser light, the processing time was approximately 5 minutes, which was approximately halved.

Thus, according to this example, in CDE using NF3, by adding (, R2 gas, S!3N4
The etching selectivity for 3i02 can be made extremely large. For this reason, thin S! S! using 02 as a protective film! 3N4 can be removed in a short time and is extremely effective in semiconductor device manufacturing programs. This is particularly effective in a process where only a thin oxide film can be formed in the trench in a sample having a trench, and then the Si3N4 film formed around the groove of the trench is peeled off. This step widens the process margin and eliminates disturbances in the impurity profile during oxide film formation. Moreover, the time required for the process is extremely shortened, and productivity is greatly improved. Furthermore, since the process itself is easy and control and management are simple, there are advantages such as high productivity.

Note that the present invention is not limited to the above-described embodiments; for example, as the gas used for etching, F
Any gas containing the element and other halogen elements may be used. That is, like FCn, FeI2゜FBr, FBr3,
A compound gas or a mixed gas of gases containing each element may be used. Further, it is better if the compound gas or mixed gas is excited in a region different from the container in which etching is performed, since damage to the wafer to be processed can be reduced.

Further, the gas containing the F element may be a mixed gas of CF4+02.

In addition, the present invention can be modified as appropriate without departing from the gist thereof.

〔Effect of the invention〕

As detailed above, according to the present invention, a gas containing F element and other halogen elements is used as a gas when etching a silicon nitride film by CDE, and a substrate to be processed is accommodated with at least F element as a radical. By introducing the silicon nitride film into the container, the etching selectivity of the silicon nitride film to the silicon oxide film can be sufficiently increased.

Moreover, the etching speed of the silicon oxide film can be made sufficiently faster than in container etching. Therefore, with respect to a substrate to be processed on which a silicon nitride film and a silicon oxide film are formed, only the silicon nitride film can be selectively etched, and the present invention can be applied to various semiconductor device manufacturing processes.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a dry etching apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing the S!
3N4 and S! A characteristic diagram showing the change in etching speed of 02, Figure 3 shows S! vs. Br2 flow rate. 3N4 and S
! FIG. 4 is a characteristic diagram showing the change in etching speed of S! FIG. 5, which is a cross-sectional view of the process when etching a 3N4 film, is a diagram for explaining the problems of the conventional method. 14.20...Gas inlet, 15...Discharge tube,
16... Microwave power supply, 17... Waveguide, 1
8... Applicator, 19... Gas supply port,
21.2/1.29...Gas exhaust port, 22.25,2
7.30...Gate valve, 23...-Second vacuum container, 26.31...Transportation mechanism, 28...Third
vacuum container, 32... heating mechanism, 41... 3i
Substrate, 42...groove, 43...S! 02 membrane, 44...S! 3N+ membrane, 45, 46...
Corner part. Agent Patent Attorney Yudo Nori Chika Mitsuyuki Matsuyama CfL2 '-7Fi"'! (SCCm) →sr
2 pieces (SCCm door - 1 ÷ Figure 3 (a) (b) Figure 4 (a) (b) Figure 5

Claims (14)

[Claims] (1) A gas containing fluorine element and other halogen elements is introduced into a container containing a substrate to be processed, and at least the fluorine element is excited in a region different from the container and introduced into the container as an active species. A method for dry etching a silicon nitride film, characterized in that the surface of the substrate to be processed is irradiated with light to selectively etch the silicon nitride film formed on the substrate to be processed with respect to the silicon oxide film. (2) A compound gas of a fluorine element and another halogen element is used as the gas, and the compound gas is excited in a region different from the container.
The method of dry etching a silicon nitride film described in . (3) As the compound gas, FCl, FCl_3, F
3. The method of dry etching a silicon nitride film according to claim 2, characterized in that Br or FBr_3 is used. (4) As the gas, a mixed gas of a gas containing the element fluorine and a halogen gas other than the fluorine element, or a gas containing at least a halogen element other than the fluorine element, is used, and this mixed gas is stored in a region different from the container. 2. The method of dry etching a silicon nitride film according to claim 1, wherein the dry etching method comprises: excitation. (5) As the gas, a gas containing elemental fluorine, a halogen gas other than elemental fluorine, or a gas containing at least an element of halogen other than elemental fluorine are used, and the gas containing the elemental fluorine is supplied in a region different from the container. 2. The method of dry etching a silicon nitride film according to claim 1, wherein an excited halogen gas other than the fluorine element or a gas containing a halogen element is directly introduced into the container. (6) The method for dry etching a silicon nitride film according to claim 4 or 5, wherein a CF_4+O_2 mixed gas or NF_3 gas is used as the gas containing the fluorine element. (7) The method for dry etching a silicon nitride film according to claim 4 or 5, wherein CL_2 gas or Br_2 gas is used as the halogen gas other than fluorine. (8) The substrate to be processed is characterized in that a groove is formed on the surface of the silicon substrate, the inner surface of the groove is coated with a thin silicon oxide film, and a silicon nitride film is further formed on the substrate surface other than the groove. A method for dry etching a silicon nitride film according to claim 1. (9) A method for dry etching a silicon nitride film according to claim 1, characterized in that fluorine atoms are first introduced into the container, and then another halogen-containing gas is introduced. (10) The method of dry etching a silicon nitride film according to claim 1, wherein the etching is performed at a gas pressure of 0.2 Torr or more. (11) Dry etching according to claim 1, wherein the light is excimer laser light such as KrF, ArF, or XeF, or light from an Hg lamp or a Xe lamp including infrared light. Method. (12) A first container for accommodating a substrate to be processed, and a means for exciting a gas containing at least the fluorine element in a region separate from the container and introducing active species generated in the region into the container. a means for directly introducing a halogen element other than the fluorine element or a gas containing at least a halogen element other than the fluorine element into the container; a means for irradiating the substrate to be treated with light; and a means for evacuating the inside of the container. a second container connected to the container via a vacuum valve; means for evacuating the second container independently of the first container; and a means for evacuating the second container independently of the first container; 1. A dry etching apparatus comprising means for transporting a substrate to be processed. (13) A plurality of the second containers are provided, and each container is connected to the first container via a vacuum valve. dry etching equipment. (14) The dry etching apparatus according to claim 12 or 13, wherein the second container is provided with means for heating the substrate to be processed.