JP4500029B2 - Dry etching method for low dielectric constant interlayer insulating film - Google Patents

Description

  The present invention relates to a method for dry etching an interlayer insulating film, and more particularly to a method for dry etching a low dielectric constant interlayer insulating film containing carbon.

In general, when an interlayer insulating film made of SiO ₂ is dry-etched in a plasma atmosphere to finely process fine holes for wiring (hereinafter also referred to as holes or vias) and grooves (hereinafter also referred to as trenches), CF A mixed gas containing a system (fluorocarbon-based) gas is used (see, for example, Patent Document 1). In this case, if etching is performed only with the CF-based gas, the gases decomposed and generated during the etching process are recombined, and clustering occurs in the gas phase to deposit a CF-based film. For this reason, it is considered to prevent the occurrence of clustering by using a mixed gas obtained by adding a fluorocarbon-based gas to argon as an etching gas (see, for example, Non-Patent Document 1).

By the way, with recent high integration and miniaturization of semiconductor devices, as an interlayer insulating film, for example, a SiOCH-based low dielectric constant interlayer insulating film having a low relative dielectric constant (k) (even if made of a porous material). Good) has been developed. In this case, if the low dielectric constant interlayer insulating film covered with the resist mask is etched using a mixed gas obtained by adding a fluorocarbon-based gas to argon having a low chemical reactivity, the SiOCH-based film contains carbon. Therefore, by ion bombardment when the interlayer insulating film is etched, for example, H in the film disappears, and a layer containing -C-C- or Si-C- bond is formed at the bottom of the hole or trench, and etching is performed. Stop phenomenon occurs. For this reason, etching using a mixed gas to which oxygen (O ₂ ), nitrogen (N ₂ ), or fluorine (F) is added, or a method for promoting the generation of fluorine has been proposed.
JP 11-31678 A (description of claims). W. Chen, M. Itoh, T. Hayashi and T. Uchid, J. Vac. Sci. Technol., A16 (1998) 1594

  However, if a mixed gas in which oxygen is added to argon and a fluorocarbon-based gas is used as in the above method, carbon in the film can be effectively removed and etching rate can be effectively removed in the microfabrication of the low dielectric constant interlayer insulating film. However, a large dimensional conversion error (so-called CD loss) occurs in the etching shape due to the high reactivity of oxygen itself. That is, there is a problem that the etching reaction proceeds in the side wall direction, or carbon (CHx group) in the interlayer insulating film is pulled out and the interlayer insulating film (particularly, the side walls of holes and trenches) is damaged.

  In addition, when a mixed gas in which nitrogen is added to argon and a fluorocarbon-based gas is used, fine processing of a low dielectric constant interlayer insulating film shows good performance for hole etching, but deposition of FCN polymer on the trench sidewalls There is a problem that pattern dependency becomes strong because of too much.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a dry etching method for a low dielectric constant interlayer insulating film with small CD loss, no film damage, and suppressed pattern dependency. There is to do.

In order to solve the above-described problem, the dry etching method for an interlayer insulating film according to the present invention is a method for etching an interlayer insulating film for etching a SiOCH-based or SiOC-based interlayer insulating film containing a porous material and finely processing fine holes and grooves. A dry etching method in which etching is performed by introducing a mixed gas obtained by adding NF ₃ to an inert gas and a fluorocarbon gas. The mixed gas does not contain oxygen and the addition ratio of NF ₃ is mixed. The total gas flow rate is 5 to 10%.

  The inert gas is preferably a gas selected from helium, neon, argon, krypton, and xenon.

According to the present invention, as described above, NF ₃ is added to the etching gas when etching a low dielectric constant interlayer insulating film (which may be made of a porous material) containing carbon in the film. As a result, as in the case of oxygen addition, a high etching rate can be obtained, and an etching stop phenomenon does not occur, and etching without pattern dependency becomes possible.

The ratio of NF _{3 to be} added is 10% or less, preferably 5 to 10%, based on the total mixed gas flow rate. If it exceeds 10%, the desired etching shape cannot be obtained, and the interlayer insulating film is damaged. If it is less than 5%, a stable etching rate cannot be obtained and the etching rate is too low. Etching stop phenomenon may occur.

  The low dielectric constant interlayer insulating film is preferably formed by coating or CVD.

The mixed gas does not contain O ₂ gas.

N ₂ gas is further added to the mixed gas. Thereby, fine adjustment of an etching shape is attained. The addition rate of N ₂ gas is preferably about 5 to 50% based on the mixed gas. If it is less than 5%, a stable etching rate cannot be obtained due to the minute flow rate region, and if it exceeds 50%, the deposition rate for adjusting the etching shape can be obtained because it is lower than the polymer deposition rate when not added. I can't.

  Etching is performed by introducing the mixed gas for etching under a pressure of 1.5 Pa or less, preferably 0.4 to 1.5 Pa. When the operating pressure exceeds 1.5 Pa, it is difficult to suppress radical reaction, and when it is less than 0.4 Pa, it is difficult to perform stable etching.

According to the present invention, since NF ₃ added as an etching gas is used, a high etching rate is obtained when dry etching a low dielectric constant interlayer insulating film, and the interlayer insulating film is not damaged. CD loss is small, and an effect of enabling etching with suppressed pattern dependency is achieved.

  FIG. 1 shows an etching apparatus for performing fine processing of wiring holes and trenches by dry etching an interlayer insulating film according to the present invention. The etching apparatus 1 is capable of etching with low temperature and high density plasma, and has a vacuum chamber 2 provided with a vacuum exhaust means 2a such as a turbo molecular pump. A plasma generation unit 3 formed of a dielectric cylindrical wall is provided in the upper part of the vacuum chamber 2, and a substrate electrode unit 4 is provided in the lower part. Three magnetic field coils 6, 7, and 8 are provided outside the side wall (dielectric side wall) 5 of the plasma generating unit 3, and the magnetic field coils 6, 7, and 8 provide an annular magnetic neutrality within the plasma generating unit 3. A line (not shown) is formed. A plasma generating high frequency antenna coil 9 is disposed on the outer wall of the dielectric side wall 5, and this high frequency antenna coil 9 is connected to a high frequency power source 10 and is formed by three magnetic field coils 6, 7, 8. In addition, an alternating electric field is applied along the line to generate a discharge plasma in the magnetic neutral line.

  A substrate electrode 11 on which the processing substrate S is placed is provided in the substrate electrode portion 4 so as to face the surface formed by the magnetic neutral line. This substrate electrode is installed in the vacuum chamber 2 via the insulator 11a. The substrate electrode 11 is connected to a high frequency power supply 13 through a capacitor 12 and is configured to be a floating electrode in terms of potential and to have a negative bias potential. The top plate 14 of the plasma generating unit 3 is hermetically fixed to the upper flange of the dielectric side wall 5 and forms a counter electrode in a floating state in terms of potential. A gas introduction nozzle 15 for introducing an etching gas into the vacuum chamber 2 is provided on the inner surface of the top plate 14, and this gas introduction nozzle 15 is connected to a gas source via a gas flow rate control means (not shown). Has been.

  As a low dielectric constant interlayer insulating film formed on the processing substrate S by using the etching apparatus and finely processing wiring holes and trenches, a film made of a material having a low relative dielectric constant (Low-k material) is used. Is preferred. For example, a SiOCH material that can be formed by spin coating such as HSQ or MSQ, or a SiOC material that can be formed by CVD, and a low-k material having a relative dielectric constant of about 2.0 to 3.0 Is preferably used, and this material may be a porous material.

  Examples of the SiOCH-based material include, for example, trade names LKD5109r5 / JSR, trade names HSG-7000 / Hitachi Chemical Co., trade names HOSP / Honeywell Electric Materials, trade names Nanoglass / Honeywell Electric Materials, trade names OCD T-12 / manufactured by Tokyo Ohkasha, trade name OCD T-32 / manufactured by Tokyo Ohkasha, trade name IPS 2.4 / manufactured by Catalytic Kasei Kogyo, trade name IPS 2.2 / manufactured by Catalytic Kasei Kogyo, trade name ALCAP-S 5100 / Asahi Kasei Corporation, trade name ISM / ULVAC, etc. can be used.

  Examples of the SiOC material include, for example, trade name Aurola 2.7 / manufactured by ASM Japan, trade name Aurola 2.4 / manufactured by ASM Japan, trade name Orion 2.2 / TRIKON, trade name Coral / Novellus, trade name Black Diamond / AMAT, trade name NCS: nano-clustering sillica / catalyst chemicals, etc. can be used.

  In addition to the above, examples of the material for the low dielectric constant interlayer insulating film include, for example, trade name SiLK / Dow Chemical, trade name Porous-SiLK / Dow Chemical, trade name FLARE / Honeywell Electric Materials, trade name Organic materials such as Porous FLARE / Honeywell Electric Materials and trade name GX-3P / Honeywell Electric Materials can also be used.

  After applying a resist on the interlayer insulating film, a predetermined pattern is formed by photolithography. As this resist, known ones can be used, for example, UV-II or the like can be used.

As an etching gas used in the dry etching process of the present invention, an inert gas such as argon and a fluorocarbon-based gas (C _n F _m ) are 10% or less, preferably 5 to 10% based on the total flow rate. A mixed gas added with NF ₃ at a ratio is used. The lower limit value of NF _{3 to be} added may be a value that promotes the reaction at the bottom of the hole or trench and obtains a desired stable etching rate. For example, it is 5% or more, which is a limit value that can supply a stable flow rate. It is preferable that The fluorocarbon gas may be selected from, for example, C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , and C ₅ F ₈ .

This mixed gas is introduced into the vacuum chamber under an operating pressure of 1.5 Pa or less that suppresses radical reaction, and preferably under an operating pressure of 0.4 Pa or more, which is the lower limit value of the pressure range in which etching can be performed stably. For example, even when etching a porous low dielectric constant interlayer insulating film containing carbon in the film, the reaction at the bottom of the hole or trench contains oxygen due to the reaction of the NFx particles. This is facilitated in the same manner as in the case of etching with a mixed gas, and CD loss is small and a high etching rate is obtained. In this case, the etching stop phenomenon does not occur. In addition, since NF ₃ is less reactive than oxygen atoms, it does not damage the interlayer insulating film, particularly the holes in the film and the sidewalls of the trench.

  In this example, MSQ (methylsilsesquioxane) having a relative dielectric constant (k) of 2.5 was used as the SiOCH-based material, and a low dielectric constant interlayer insulating film having a thickness of 500 nm was formed on the substrate using a spin coater. Then, a resist was applied on the low dielectric constant interlayer insulating film by a spin coater, and a predetermined pattern was formed by photolithography. In this case, UV-II was used as the resist, and the thickness of the resist layer was 500 nm.

Next, using the etching apparatus 1 shown in FIG. 1, a mixed gas composed of C ₃ F ₈ , argon and NF ₃ was introduced into the vacuum chamber 2 to etch the low dielectric constant interlayer insulating film. This mixed gas is composed of C ₃ F ₈ : 25 sccm, argon: 205 sccm, NF ₃ : 25 sccm (about 9.3%). In this case, the etching process is such that the output of the high frequency power supply 10 connected to the plasma generating high frequency antenna coil 9 is 2 kW, the output of the high frequency power supply 13 connected to the substrate electrode 11 is 100 W, the substrate temperature is 25 ° C., and the pressure in the vacuum chamber 2 Was set to 1.3 Pa.

Further, as a comparative example, a fluorocarbon-based gas (C ₃ F ₈ ) and a mixed gas in which 25 sccm of O ₂ is added to argon instead of NF ₃ , a mixed gas in which 25 sccm of N ₂ is added, and N ₂ and O ₂ A mixed gas without any addition was introduced into the vacuum chamber 2 and the low dielectric constant interlayer insulating film was etched under the same conditions as described above.

Table 1 below shows the etching rate when the above etching treatment is performed.
(Table 1)

As is apparent from Table 1, the etching rate is higher when NF _{3 is} added than when there is no additive gas and when oxygen and nitrogen are added.

2 and 3 show SEM photographs showing the state of trenches and vias obtained when etching is performed under the above conditions. 2 (a) is a mixed gas of only C ₃ F ₈ / Ar, (b) is a mixed gas of C ₃ F ₈ / Ar / O ₂ , and (c) is a mixed gas of C ₃ F ₈ / Ar / N ₂ . It is a SEM photograph which shows the state of a trench at the time of etching using each, and a via | veer. FIG. 3 is an SEM photograph showing the state of trenches and vias when etching is performed using a mixed gas of C ₃ F ₈ / Ar / NF ₃ .

As shown in FIG. 2A, when only C ₃ F ₈ / Ar is used without adding oxygen or nitrogen as an etching gas, an etching stop phenomenon occurs in both the trench and the via. In this case, a high etching rate cannot be obtained with MSQ which is a SiOCH-based material.

As shown in FIG. 2B, when C ₃ F ₈ / Ar / O ₂ is used as the etching gas, the etching shape has a very large CD loss for both the trench and the via, and the smoothness of the sidewall is lost. Yes. This oxygen will always been divided side wall protective film during etching by a due to abstraction reaction in the film carbon by originating or oxygen to proceed little by the etching reaction in the side wall direction Guessed. Therefore, in the case of the oxygen addition process, not only the problem of CD loss but also a new problem peculiar to the low dielectric constant film due to the occurrence of film damage occurs.

As shown in FIG. 2 (c), when C ₃ F ₈ / Ar / N ₂ is used as an etching gas, a side wall protective film made of FCN polymer is formed. Although the damage is suppressed, there is a problem that the etching shape shows a strong pattern dependence because the FCN polymer is deposited too much.

On the other hand, as is apparent from Table 1 and FIG. 3, in the case of the present invention etched with a mixed gas added with NF ₃ , the etching rate is higher than that of nitrogen addition and oxygen addition, and FIG. ) And (c), there is no pattern dependency of the trench and via etching shapes, and no etching stop occurs. Furthermore, the smoothness of the patterned side wall after etching is good and the CD loss is small, so that it can be seen that the side wall protective film is firmly formed as compared with the process in the case of adding oxygen. This is because the reaction of the bottom of the fine pattern which is the ion irradiation surface is promoted by the reaction of nitrogen or NFx particles due to the addition of NF ₃ , and a nitrogenated fluorocarbon polymer (FCN polymer) is formed on the side wall. It is considered that etching with less loss is realized. It can be inferred that the reason why the NF ₃ addition has less CD loss than the oxygen addition is because NFx is less reactive than the oxygen atom. That is, in the case of oxygen addition, this oxygen is combined with carbon and volatilized and removed as COx, but in the case of N, F or NFx, it is considered that it originates from once forming an FCN polymer on the surface.

  According to the present invention, as described above, in etching of trenches and vias, an etching process with very little pattern dependency and high processing accuracy can be performed without using oxygen. Moreover, since the smoothness of the side wall is maintained, the side wall protective film is also formed firmly, and the damage in etching is also suppressed.

Incidentally, in the SiO ₂ etching, when applying the NF ₃ additive process, NF ₃ from that in the process for supplying fluorine, it can be said that even different regions simple nitrogen gas addition process so far. In addition, in the case of SiO ₂ etching, the CD control can sufficiently cope with the conventional method as shown in FIGS. 2A and 2B, and conversely, the addition of NF ₃ simply lowers the etching selectivity of the resist. Therefore, a good effect as obtained by the method of the present invention cannot be obtained. Therefore, the method of the present invention is an optimum technique for etching all low-k materials having carbon in the film.

From the above, as in the present invention, the NF ₃ addition anisotropic process with a small etching pattern dependency for the purpose of the film damage reduction process in which the pressure is set to 1.5 Pa or less and the side wall attack of the particles is reduced. The use is an important key for etching a low-k film made of a SiOCH-based material such as MSQ or a SiOC-based material.

The etching method of Example 1 was repeated except that the addition ratio of NF ₃ was 5% and 7%. As a result, the same trench and via states as in Example 1 were obtained, and a higher etching rate was obtained as compared with the case where there was no additive gas and when oxygen or nitrogen was added.

In this embodiment, an etching gas obtained by adding N ₂ gas to the mixed gas used in Embodiment 1 is introduced into the vacuum chamber 2 using the etching apparatus 1 shown in FIG. The (MSQ film) was etched to finely adjust the etching shape. In this case, the etching process is such that the output of the high frequency power source 10 connected to the plasma generating high frequency antenna coil 9 is 2 kW, the output of the high frequency power source 13 connected to the substrate electrode 11 is 0 W, the substrate temperature is 25 ° C., and the pressure in the vacuum chamber 2 Was set to 1.3 Pa, and an FCN polymer was plasma-deposited on the substrate. FIG. 4 shows the relationship between the nitrogen addition rate (%) and the FCN polymer deposition rate (nm / min) with the nitrogen addition rate varied between 0 and 90%. In this case, the relationship between oxygen addition and polymer deposition rate was also investigated.

  As is apparent from FIG. 4, when nitrogen is added, the polymer deposition rate increases up to 10% addition, and when the addition amount is further increased, the deposition rate may be the same as that without addition at about 50%. I understand. If it is less than 5%, a stable etching rate cannot be obtained due to the minute flow rate region. Therefore, the deposition effect for fine adjustment of the etching shape is obtained in 5 to 50%. On the other hand, when oxygen is added, the polymer deposition rate decreases.

According to the present invention, by using a mixed gas added with NF ₃ as an etching gas, a high etching rate can be obtained and the interlayer insulating film can be damaged when dry etching the low dielectric constant interlayer insulating film. In addition, since CD loss is small and etching with reduced pattern dependency is possible, it can be effectively applied to etching of an interlayer insulating film made of a low-k material containing carbon.

The block diagram which shows roughly an example of a structure of the etching apparatus which enforces the dry etching method of this invention. Trench obtained by carrying out conventional dry etching method is a SEM photograph showing the state of the vias, (a) represents a mixed gas of _{C 3 F 8 / Ar, (} b) the _C 3 _F 8 / Ar / O ₂ is a SEM photograph showing the state of trenches and vias when etching is performed using a mixed gas of C ₃ F ₈ / Ar / N ₂ . The dry etching method of the present invention is a SEM photograph showing a trench obtained by carrying out the state of the via _{(C 3 F 8 / Ar /} NF gas mixture _3), (a) is a trench state, (b) Are SEM photographs showing the state of vias. In etching with _{N 2} gas added in accordance with the invention, a graph showing the relationship between the _{N 2} addition rate (%) and FCN polymer deposition rate (nm / min).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching apparatus 2 Vacuum chamber 3 Plasma generating part 4 Substrate electrode part S Substrate

Claims (6)

This is a dry etching method for an interlayer insulating film in which a SiOCH-based or SiOC-based interlayer insulating film containing a porous material is etched to finely process fine holes and grooves, and NF ₃ is added to an inert gas and a fluorocarbon gas. In what is etched by introducing the mixed gas
A dry etching method for an interlayer insulating film, wherein the mixed gas does not contain oxygen and the addition ratio of the NF ₃ is 5 to 10% based on the total flow rate of the mixed gas.   2. The method of dry etching an interlayer insulating film according to claim 1, wherein the inert gas is a gas selected from helium, neon, argon, krypton, and xenon.   3. The method for dry etching an interlayer insulating film according to claim 1, wherein the interlayer insulating film is formed by coating or CVD. The dry etching method of the interlayer insulating film according to any one of claims 1 to 3, characterized in that the addition of further N ₂ gas to the mixed gas. The N ₂ gas addition rate of dry etching method of the interlayer insulating film according to claim 4, wherein 5 to 50% in the mixed gas total flow rate reference. The dry etching method of the interlayer insulating film according to any one of claims 1 to 5, characterized in that etching is carried out by introducing the mixed gas under a pressure of less than 1.5 Pa.

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