JP4651956B2 - Interlayer dielectric film dry etching method - 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 an interlayer insulating film having a low dielectric constant and having an organic buried layer when forming a dual damascene structure.

  In recent years, along with the higher integration and higher speed of LSI, the miniaturization and multilayering of wiring on a semiconductor substrate have progressed, and the number of interconnecting portions has also increased. Therefore, a dual damascene method has been developed in which a via hole and a wiring trench are formed in an interlayer insulating film, and then a metal material is embedded in the via hole and the wiring trench to simultaneously form a connection plug and a metal wiring. The dual damascene structure is formed through the following steps, for example.

  That is, a first interlayer insulating film made of Low-k material and trench etching are formed on a substrate in which a first insulating film (SiO) used as a via layer is formed on a first wiring such as Cu with a predetermined thickness. At this time, a SiN film functioning as an etch stop film is sequentially laminated. Next, a second interlayer insulating film made of a low-k material is formed on the etch stop film, a resist is applied on the second interlayer insulating film, and a resist pattern is formed by a photolithography process. Via holes are formed by reactive etching. Next, after removing and removing the resist once, a predetermined resist pattern is formed again by a photolithography process, and then a trench for wiring is formed by anisotropic etching (via first process).

  When performing highly accurate patterning in the photolithography process after forming the via hole, for example, a KrF lithography method using a KrF excimer laser having a short wavelength is used. In this KrF lithography method, the substrate reflectivity is high and halation is likely to occur. For this reason, in order to prevent substrate reflection during the photolithography process, a BARC (antireflection film) which is an organic buried layer is formed on the upper surface including the inside of the via hole formed in the interlayer insulating film by etching. (For example, refer to Patent Document 1).

  Further, the above-mentioned interlayer insulating film for LSI is a SiOCH-based or SiOC-based low dielectric constant interlayer insulating film having a low relative dielectric constant (k) (with a relative dielectric constant (k) of 3.0 or less). , Including porous materials).

In this case, for example, in order to form a trench for wiring so as not to damage the low dielectric constant interlayer insulating film, an etching gas containing a fluorocarbon gas is used, and this etching gas is introduced in a plasma atmosphere to form the interlayer insulating film. It is conceivable to perform etching together with the buried layer.
Japanese Patent Laid-Open No. 2001-176963 (for example, claim 1).

  However, when an etching gas containing a fluorocarbon gas is used, as shown in FIG. 9, when the trench b is etched into the interlayer insulating film a, the organic buried layer c is hardly etched and the etching of the trench is completed. Later, the buried layer c protrudes from the via hole d into the trench b, and a polymer residue e (generally called “fencing”) is generated around the remaining buried layer c (FIG. 9 ( b) and (c)).

  This residue is difficult to remove together with the buried layer c when the buried layer c is removed in a later process. If the residue is forcibly removed, the interlayer insulating film a itself is damaged and becomes the trench b. As a result, there is a problem that the shape of the via hole c shifts (see FIG. 9D).

  Therefore, an object of the present invention is to provide a dry etching method for an interlayer insulating film that can etch an interlayer insulating film provided with an organic buried layer so as not to generate a polymer residue.

In order to solve the above-mentioned problems, the dry etching method for an interlayer insulating film according to the present invention comprises a SiOCH or SiOC material in which an organic buried layer is provided on the upper surface including the inside of a via hole when forming a dual damascene structure. A dry etching method for an interlayer insulating film in which an interlayer insulating film is etched and wiring holes and trenches are finely processed. Nitrogen gas is a main gas, and CH ₄ , C ₂ H ₆ , C _{3 are} added to the nitrogen gas. An etching gas in which a hydrocarbon gas selected from H ₈ , C ₄ H ₁₀ , and C ₂ H ₂ is added in a range of 50% or less of the total flow rate is used in a plasma atmosphere in which this etching gas is introduced. The step of selectively etching the organic buried layer in the initial stage of etching and the etching gas introduced in the step of etching the buried layer are used as a fluorocarbon. And a step of micro-fabricating wiring holes and trenches in the interlayer insulating film in a plasma atmosphere into which the gas is included but oxygen gas is not included and the etching gas is introduced. To do.

  According to the present invention, by using an etching gas containing nitrogen atoms at the beginning of etching, the etching selectivity of the buried layer to the resist mask on the interlayer insulating film is increased, and the organic buried layer is mainly selected. Is etched away. Then, the interlayer insulating film is selectively etched by changing to an etching gas containing a fluorocarbon gas. As a result, a buried layer does not remain in the hole or trench and a polymer residue does not occur around the buried layer.

In the step of etching the buried layer, it is preferable that only nitrogen is introduced at the initial stage of etching, and a hydrocarbon gas is added as the etching of the buried layer proceeds. At this time, the hydrocarbon gas, Ru is added in an amount of less than 50% of the total flow rate of the etching gas. A hydrocarbon gas having 1 to 4 carbon atoms is used, and the hydrocarbon gas in such a case is CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C _2. Selected from among H ₂ . If the hydrocarbon gas is added in an amount exceeding 50% with respect to the total flow rate of the etching gas, the hydrocarbon gas deposition effect is strengthened, and the etching rate of the buried layer is extremely reduced. Etching cannot be accelerated. Further, when the number of carbon atoms exceeds 4, for example, C ₅ H ₁₂ , deposition due to polymerization occurs strongly, and it becomes difficult to control the deposited film thickness (protective layer thickness), which is not practical.

In the etching step of the buried layer, the etched holes, protective film on the sidewalls of the trenches are formed, the protective film, a nitrile group, an amino group, a polymer der lever containing an imino group, hole during etching The trench sidewall is prevented from being damaged.

In the present invention, in the etching process of the buried layer, the etching gas contains H ₂ , O ₂ , CO, CO ₂ It is preferable to add a gas selected from among them to promote the etching of the buried layer.

  The step of selectively etching at least the organic buried layer may be performed under an operating pressure of 2 Pa or more. When the pressure is lower than 2 Pa, the interlayer insulating film is sputtered by ionic etching, and the dimensional conversion error of the trench increases.

In the present invention, it is preferable to use an etching gas in which nitrogen gas is a main gas and fluorocarbon is added to the nitrogen gas in the step of etching the interlayer insulating film.

  As described above, the interlayer insulating film etching method of the present invention has an effect that the interlayer insulating film provided with the organic buried layer can be etched so that no polymer residue is generated.

  Referring to FIG. 1, reference numeral 1 denotes an etching apparatus for performing fine processing of a wiring trench by dry etching on an interlayer insulating film having a buried dielectric layer according to the present invention and having a low relative dielectric constant. This etching apparatus 1 is capable of etching with low temperature and high density plasma, and has a vacuum chamber 11 provided with a vacuum exhaust means 11a such as a turbo molecular pump.

  A plasma generation unit 12 formed of a dielectric cylindrical wall is provided in the upper part of the vacuum chamber 11, and a substrate electrode unit 13 is provided in the lower part of the vacuum chamber 11. Three magnetic field coils 15, 16, and 17 are provided outside the side wall (dielectric side wall) 14 of the plasma generation unit 12, and the magnetic field coils 15, 16, and 17 provide an annular magnetic neutrality within the plasma generation unit 12. A line (not shown) is formed.

  A high frequency antenna coil 18 for plasma generation is disposed between the intermediate magnetic field coil 16 and the outer side of the dielectric side wall 14, and this high frequency antenna coil 18 is connected to a first high frequency power source 19, and three magnetic field coils 15, An alternating electric field is applied along the magnetic neutral line formed by 16 and 17 to generate discharge plasma in the magnetic neutral line.

  A substrate electrode 20 on which the processing substrate S is placed is provided via an insulator 20a in the substrate electrode portion 13 so as to face the surface formed by the magnetic neutral line. The substrate electrode 20 is connected to the second high-frequency power source 22 via the capacitor 21 and becomes a floating electrode in terms of potential and has a negative bias potential. The top plate 23 of the plasma generator 12 is hermetically fixed to the upper flange of the dielectric side wall 14 and is in a floating state in potential to form a counter electrode. A gas introduction nozzle 24 for introducing an etching gas into the vacuum chamber 11 is provided on the inner surface of the top plate 23, and this gas introduction nozzle 24 is connected to a gas source via a gas flow rate control means (not shown). Has been.

  As an interlayer insulating film in which a trench is finely processed in forming a dual damascene structure by etching using the above etching apparatus, an interlayer insulating film having a relative dielectric constant (k) of 3.0 or less, for example, HSQ formed by spin coating It is a low-k material of SiOCH material such as MSQ or SiOC material formed by CVD, and may be a porous material.

  Examples of the SiOCH-based material include a trade name NCS / catalyst chemical industry, trade name LKD5109r5 / JSR, trade name HSG-7000 / Hitachi Chemical Co., trade name HOSP / Honeywell Electric Materials, trade name Nanoglass. / Honeywell Electric Materials, trade name OCD T-12 / Tokyo Ohka, trade name OCD T-32 / Tokyo Ohka, trade name IPS 2.4 / Catalyst Kasei Kogyo, trade name IPS 2.2 / Catalyst There are products made by Kasei Kogyo Co., Ltd., trade name ALCAP-S5100 / Asahi Kasei Co., Ltd. and trade name ISM / ULVAC.

  Examples of the SiOC material include trade name Aurola 2.7 / Japan ASM Co., trade name Aurola 2.4 / Japan ASM Co., trade name Orion 2.7 / TRIKON, trade name Coral / Novellf, trade name Available from Black Diamond / AMAT. Also, trade name SiLK / Dow Chemical, trade name Porous-SiLK / Dow Chemical, trade name FLARE / Honeywell Electric Materials, trade name Porous FLARE / Honeywell Electric Materials, trade name GX-3P / Honeywell An organic low dielectric constant interlayer insulating film such as that manufactured by Electric Materials may also be used.

  For example, the dual damascene structure is formed as follows. That is, with reference to FIG. 2, the interlayer insulating film (for example, SiOCH) 32 is laminated on the SiN (or SiC) film 31 that functions as an etching stop film during etching, and the interlayer insulating film 32. A predetermined resist is applied thereon, a resist mask 33 is formed by, for example, a KrF photolithography process (see FIG. 2A), a via hole 34 is formed by anisotropic etching, and the resist mask 33 is once removed and removed. (See FIG. 2 (b)).

  Then, when forming a resist mask for forming a trench for wiring in the KrF photolithography process, an organic buried layer 35 is formed on the upper surface including the inside of the via hole 34 by coating for the purpose of preventing substrate reflection. (See FIG. 2C), a resist is coated on the buried layer 35, and a resist mask 36 for forming a trench for wiring is formed by etching in a KrF photolithography process (see FIG. 2C). (Refer FIG.2 (d)).

Examples of the buried layer (BARC) 35 include amorphous carbon (α-C), SiON, and SiO ₂ . The resist material is for KrF photolithography using a KrF excimer laser, for example, TDUR-P036 / manufactured by Tokyo Ohka Kogyo Co., Ltd. In this embodiment, a resist mask is formed in the KrF photolithography process. However, an organic buried layer 35 is provided on the upper surface including the inside of the via hole 34 for the purpose of preventing substrate reflection. If so, a resist material for ArF photolithography or F ₂ photolithography process may be used.

  In the case of etching the low dielectric constant interlayer insulating film 32 having the buried layer 35 described above, in this embodiment, nitrogen gas added with a hydrocarbon gas having 1 to 4 carbon atoms is used as an etching gas. The etching gas is introduced in a plasma atmosphere to selectively etch the organic buried layer in the initial stage of etching, and the etching gas is changed to an etching gas containing a fluorocarbon gas, and the etching gas is introduced in the plasma atmosphere. Then, the wiring trench is etched in the process of finely processing the wiring trench.

  That is, referring to FIG. 2, by using the etching gas at the initial stage of etching, the etching selectivity of the buried layer 35 with respect to the resist mask 36 on the interlayer insulating film 32 is increased. The buried layer 35 is selectively etched, and the buried layer 35 is first removed (first step for digging the buried layer 35: see FIG. 2E).

  Then, by selectively etching the buried layer 35, when the upper surface of the interlayer insulating film 32 is exposed, the interlayer insulating film 32 as well as the buried layer 35 is etched at a low etching rate. In this case, carbon and nitrogen in the plasma atmosphere are combined to form a nitrile group, an amino group, an imino group on the inner side of the resist mask 36, the inner side of the etched buried layer 35, and the side wall of the etched trench 37. Then, a protective film 38 of the polymer containing is formed (second step: see FIG. 2F).

Next, as shown in FIG. 2F, after the buried layer 35 is etched in the depth direction beyond the depth of the trench 37 to be formed in the interlayer insulating film 32, the etching gas containing a fluorocarbon gas is used. When changed, the interlayer insulating film 32 is selectively etched, and the trench 37 is formed (third step: see FIG. 2G). For example, CF ₄ , C ₂ F ₆ and C ₃ F ₈ are used as the fluorocarbon gas.

  In the microfabrication process of the trench for wiring, if nitrogen is a main gas and a fluorocarbon gas is added to the main gas, for example, a porous low dielectric constant interlayer insulating film 32 containing carbon in the film is etched. In this case, since carbon is removed as -CN gas, a layer of -C-C- or Si-C- is formed, and an etch stop phenomenon or a residue is prevented.

  As a result, it is possible to prevent the buried layer 35 from protruding and remaining in the trench and causing a polymer residue around it. Further, the side wall of the trench 37 is not damaged by the formed protective film 38. Then, after the etching of the trench 37 into the interlayer insulating film 32 is completed by the etching, the buried layer 35 remaining in the via hole 34 is removed (see FIG. 2H).

  The step of selectively etching the organic buried layer 35 using an etching gas containing nitrogen atoms is performed under an operating pressure of 2 Pa or more. When the pressure is less than 2 Pa, the interlayer insulating film 32 is sputtered by ionic etching, and the dimension conversion error of the trench increases.

  On the other hand, the step of selectively etching the interlayer insulating film 32 using an etching gas containing a fluorocarbon gas is performed under an operating pressure of 1 Pa or less. When the pressure exceeds 1 Pa, the sidewall of the trench 37 is damaged.

Examples of the hydrocarbon gas added for the purpose of forming the protective film 38 by deposition while leaving the resist mask 36 are CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , and C ₂ H ₂ . The hydrocarbon gas is added in a range of 50% or less with respect to the total flow rate of the etching gas. If it exceeds 50%, the effect of depositing hydrocarbon gas becomes strong, the etching rate of the buried layer 35 extremely decreases, and the etching of the buried layer 35 cannot be promoted.

  In this embodiment, a mixed gas of nitrogen and hydrocarbon gas is used from the beginning of etching and introduced into the vacuum chamber 11, but even if only nitrogen is used as the etching gas, it is buried at the beginning of etching. Layer 35 can be selectively etched. On the other hand, the etching gas may be nitrogen at the beginning of etching, and the hydrocarbon gas may be added to nitrogen before the upper surface of the interlayer insulating film 32 is exposed.

Further, a gas that promotes the etching of the buried layer 35 may be added to the etching gas. The gas that promotes the etching of the buried layer 35 is selected from H ₂ , O ₂ , CO, and CO ₂ and is added within a range of 10% or less with respect to the total flow rate of the etching gas. If it exceeds 10%, CHx groups in the interlayer insulating film are pulled out due to the high reactivity of oxygen itself, and the interlayer insulating film (particularly, the sidewall of the hole) is damaged.

  By the way, the etching conditions such as the mixing ratio of the hydrocarbon gas are set such that, for example, the pressure in the vacuum chamber 11 at the time of etching is set to a predetermined pressure of 2 Pa or more, and the hydrocarbon gas is added to the nitrogen. It is preferable to set so that only the ion-irradiated surface of the buried layer 35 is etched while forming the protective film 38.

  In this embodiment, as shown in FIG. 2, MSQ having a relative dielectric constant (k) of 2.5 is used as the SiOCH-based material, and 800 nm is formed on the stop layer 31 of SiN formed on the processing substrate S using a spin coater. The interlayer insulating film 32 was formed with a film thickness of. Then, a resist was applied on the interlayer insulating film 32 by a spin coater, a resist mask 33 was formed by a KrF photolithography process, a via hole 34 was formed by etching, and the resist mask 33 was once removed.

  Next, after an organic buried layer 35 is formed on the upper surface including the inside of the via hole 34 by a spin coater, a resist is applied on the buried layer 35 by a spin coater, and a trench is formed by etching in a KrF photolithography process. The resist mask 36 was formed. In this case, TDUR-P036 was used as each resist mask 33, 36, and the thickness of each resist mask was 500 nm. The organic buried layer 35 is made of amorphous carbon, and the thickness of the buried layer 35 is 800 nm.

Next, the interlayer insulating film 32 covered with the resist mask 36 and provided with the buried layer 35 was etched using the etching apparatus 1 shown in FIG. The output of the high frequency power supply 19 connected to the plasma generating high frequency antenna coil 18 is set to 2.5 KW, the output of the high frequency power supply 22 connected to the substrate electrode 20 is set to 100 W, the substrate temperature is set to 10 ° C., and the pressure of the vacuum chamber 11 is set to 2.7 Pa. did. Then, a mixed gas obtained by adding CH ₄ to N ₂ is used as an etching gas, and this mixed gas is introduced into the vacuum chamber 11 at a flow rate of 200 sccm to etch the interlayer insulating film 32 covered with the buried layer 35. did.

FIG. 3 shows the etching rates of the interlayer insulating film 32, the buried layer 35, and the resist mask 36 when the ratio of CH ₄ to the total flow rate of the etching gas is changed, and the etching of the buried layer 35 with respect to the resist mask 36. The selection ratio and the etching selection ratio of the buried layer 35 with respect to the interlayer insulating film 32 are shown.

In this case, ▪ in the figure indicates the etching rate of the resist mask 36, □ indicates the etching rate of the buried layer 35, and ● indicates the interlayer insulating film 32. Further, Δ in the figure indicates the selection ratio of the buried layer 35 with respect to the resist mask 36, and ◯ indicates the selection ratio of the buried layer with respect to the interlayer insulating film 32. According to this, when the ratio of CH ₄ exceeds 50%, the etching rate of the buried layer 35 is extremely lowered, which is not suitable for the method of selectively etching the buried layer 35 first in the initial stage of etching. I understand.

FIG. 4 shows a case where N ₂ is used as an etching gas, and H ₂ or O ₂ , which is a gas for promoting the etching of the buried layer 35, is added to N ₂ at 10% with respect to the total flow rate of the etching gas. The etching rate of the buried layer 35 is shown. According to this, it can be seen that a high etching rate can be obtained by adding H ₂ or O ₂ .

  In this embodiment, as shown in FIG. 2, MSQ having a relative dielectric constant (k) of 2.5 is used as the SiOCH-based material, and 800 nm is formed on the stop layer 31 of SiN formed on the processing substrate S using a spin coater. The interlayer insulating film 32 was formed with a film thickness of. Then, a resist was applied on the interlayer insulating film 32 by a spin coater, a resist mask 33 was formed by a KrF photolithography process, a via hole 34 was formed by etching, and the resist mask 33 was once removed.

Next, a buried layer 35 was formed on the upper surface including the inside of the via hole 34 under the same conditions as in Example 1, and then a resist pattern 36 was formed. Then, using the etching apparatus 1 shown in FIG. 1, and introducing _{N 2} into first chamber 11 at a flow rate of 200 sccm, and etching under the same conditions as in Example 1, then changed to CF _4, the CF ₄ Etching was performed by introducing into the chamber 11 at a flow rate of 200 sccm. In the etching using N ₂ , the pressure in the vacuum chamber 11 was set to 2.7 Pa, and in the etching using CF ₄ , the pressure in the vacuum chamber 11 was set to 0.7 Pa.

  5 (a) and 5 (b) are SEM photographs when trench etching is performed under the above conditions (FIG. 5 (a) corresponds to FIG. 2 (f), and FIG. 5 (b) corresponds to FIG. 2 (g)). Corresponding to). According to this, in the initial stage of etching, the etching of the buried layer 35 selectively proceeds (see FIG. 5A), and when the etching gas changes, the trench etching to the interlayer insulating film 32 proceeds. (See FIG. 5B).

  In this embodiment, as shown in FIG. 2, MSQ having a relative dielectric constant (k) of 2.5 is used as the SiOCH-based material, and 800 nm is formed on the stop layer 31 of SiN formed on the processing substrate S using a spin coater. The interlayer insulating film 32 was formed with a film thickness of. Then, a resist was applied on the interlayer insulating film 32 by a spin coater, a resist mask 33 was formed by a KrF photolithography process, a via hole 34 was formed by etching, and the resist mask 33 was once removed.

Next, a buried layer 35 was formed on the upper surface including the inside of the via hole 34 under the same conditions as in Example 1, and then a resist pattern 36 was formed. Then, using the etching apparatus 1 shown in FIG. 1, a mixed gas of N ₂ and CH ₄ is first introduced into the chamber 11 at a flow rate of 200 sccm (N ₂ : CH ₄ = 150: 50). etched under the same conditions as, then changed to CF _4, etching is performed by introducing into the chamber 11 the CF ₄ at a flow rate of 200 sccm. Note that the pressure in the vacuum chamber 11 was set to 2.7 Pa during the etching using N _2, and the pressure in the vacuum chamber 11 was set to 0.7 Pa during the etching using CF ₄ .

6 (a) and 6 (b) are SEM photographs when trench etching is performed under the above conditions (FIG. 6 (a) corresponds to FIG. 2 (f), and FIG. 6 (b) corresponds to FIG. 2 (g)). Corresponding to). According to this, the etching of the buried layer 35 proceeds selectively at the initial stage of etching (see FIG. 6A), inside the resist mask 36, inside the etched buried layer 35, and for wiring. It can be seen that a protective film is formed on the sidewall of the trench. Next, when the etching gas is changed, it can be seen that the trench etching to the interlayer insulating film 32 is proceeding (see FIG. 6B).
(Comparative example)

Together as a comparative example, a CF ₄ as an etching gas, is introduced into the vacuum chamber 11 the CF ₄ at a flow rate of 200 sccm, with the buried layer 35 of the organic interlayer insulating film 32 of the above Example 1 under the same conditions And etched. In this case, the pressure of the vacuum chamber 11 was set to 0.7 Pa.

  According to this, as shown in FIG. 7, the organic buried layer 35 is hardly etched, and after the etching of the trench 37 is completed, the buried layer 35 protrudes from the via hole 34 into the trench 37 and remains. It can be seen that a polymer residue is generated around the remaining buried layer 35.

  In this embodiment, as shown in FIG. 2, MSQ having a relative dielectric constant (k) of 2.5 is used as the SiOCH-based material, and 800 nm is formed on the stop layer 31 of SiN formed on the processing substrate S using a spin coater. The interlayer insulating film 32 was formed with a film thickness of. Then, a resist was applied on the interlayer insulating film 32 by a spin coater, a resist mask 33 was formed by a KrF photolithography process, a via hole 34 was formed by etching, and the resist mask 33 was once removed.

Next, a buried layer 35 was formed on the upper surface including the inside of the via hole 34 under the same conditions as in Example 1, and then a resist pattern 36 was formed. Then, using the etching apparatus 1 shown in FIG. 1, a mixed gas of N ₂ and CH ₄ is first introduced into the chamber 11 at a flow rate of 200 sccm, etched under the same conditions as in Example 1 above, and then into CF ₄ . Then, CF ₄ was introduced into the chamber 11 at a flow rate of 200 sccm and etching was performed (third step). In the etching using N ₂ , the pressure in the vacuum chamber 11 was set to 2.7 Pa, and in the etching using CF ₄ , the pressure in the vacuum chamber 11 was set to 0.7 Pa.

FIG. 8 shows that when etching with a mixed gas of N ₂ and CH ₄ , the mixing ratio of CH ₄ to the total flow rate is 50% (N ₂ : CH ₄ = 100: 100 (sccm)) or 25% (N ₂ : CH ₄ = 150: 50 (sccm)) shows FTIR data of the protective film formed on the sidewall of the trench.

In this case, the line A in the figure, a mixed ratio of 50% CH _4, the dotted line B is an FTIR data in the case of the mixing ratio of 25% CH _4. According to this, it turns out that the polymer which is a protective film contains a nitrile group, an amino group, an imino group, etc.

The figure which shows schematically the etching apparatus which enforces the etching method of the interlayer insulation film with a low relative dielectric constant of this invention. The figure which illustrates formation of a dual damascene structure roughly. The graph which shows the etching rate and selection ratio at the time of etching an interlayer insulation film by changing the mixing ratio of etching gas. The graph which shows the change of the etching rate at the time of adding the gas which accelerates | stimulates the etching of a buried layer. (A) And (b) is the SEM photograph when the interlayer insulation film which has a buried layer is etched by the method of this invention using the etching gas which uses nitrogen as a main gas. (A) And (b) is the SEM photograph when etching the interlayer insulation film which has a buried layer by the method of this invention using the etching gas which added nitrogen gas to this as the main gas. As a comparative example, an SEM photograph when an interlayer insulating film having a buried layer is etched. FTIR data of the protective film formed on the sidewall of the trench when the interlayer insulating film having the buried layer is etched. The figure explaining roughly formation of the dual damascene structure concerning a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching apparatus 31 Stop layer 32 Low dielectric constant interlayer insulation film 34 Via hole 35 Buried layer 36 Resist mask

Claims (6)

When forming a dual damascene structure, an interlayer insulating film made of SiOCH or SiOC material with an organic buried layer provided on the upper surface including the inside of the via hole is etched to finely process wiring holes and trenches. The dry etching method of
Nitrogen gas is a main gas, and a hydrocarbon gas selected from CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , and C ₂ H _{2 is} added to this nitrogen gas at 50% of the total flow rate. A step of selectively etching an organic buried layer at the initial stage of etching in a plasma atmosphere into which the etching gas is introduced, using an etching gas added in the following range ;
The etching gas introduced in the etching process of the buried layer is changed to an etching gas containing a fluorocarbon gas but not containing an oxygen gas, and wiring is performed on the interlayer insulating film in a plasma atmosphere in which the etching gas is introduced. And a process for finely processing a hole and a trench.   2. The interlayer insulating film according to claim 1, wherein in the etching step of the buried layer, only nitrogen is introduced at an early stage of etching, and a hydrocarbon gas is added as the etching of the buried layer proceeds. Etching method. 2. A protective film is formed on sidewalls of the etched holes and trenches in the buried layer etching step, and the protective film is a polymer containing a nitrile group, an amino group, and an imino group. Alternatively, the dry etching method for an interlayer insulating film according to claim 2 . The gas for promoting the etching of the buried layer selected from H ₂ , O ₂ , CO, and CO ₂ is added to the etching gas in the etching process of the buried layer. The method for dry etching an interlayer insulating film according to any one of claims 1 to 3 . The dry etching method of the interlayer insulating film according to any one of claims 1 to 4, characterized in that an etching process of the buried layer under more working pressure 2 Pa. In the etching process of the interlayer insulating film, a nitrogen gas as a main gas, an interlayer insulation according to any one of claims 1 to 5 which comprises using an etching gas prepared by adding fluorocarbon in the nitrogen gas A dry etching method for a film.

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