A silicon nitride etching method

Abstract

The present invention discloses a silicon nitride etching method. A passivation gas plasma is generated by using an RF power supply to attach a passivation layer on the surface of a silicon nitride film, and the passivation layer is formed in the protrusions and grooves on the surface of the silicon nitride film; the RF power supply is adjusted to generate a clean gas plasma, and the passivation layer on the side wall of the groove on the surface of the silicon nitride film is retained, so that the clean gas plasma removes the residue on the surface of the silicon nitride film in the vertical direction; the etching gas is introduced, and the process parameters are adjusted to etch the surface of the silicon nitride film. The present invention realizes C 4 F 6 The application in silicon nitride etching, and through the optimization of process parameters such as RF power, ICP power, gas type, gas ratio and etching pressure, overcomes the etching problems such as low etching rate and over-etching of the underlying material in the traditional hard mask etching process, can effectively reduce the Si etching rate while improving the Si 3 N 4 Etching rate.

Description

Technical Field

[0001] The invention belongs to an etching treatment method in the technical field of semiconductor processing, and specifically relates to a silicon nitride etching method. Background Art

[0002] As the technology nodes of integrated circuits continue to advance, the precision requirements for manufacturing processes are becoming more stringent. Among them, the etching process, as one of the key steps in the manufacturing process, is more challenging. For process nodes below 55nm, the photolithography process usually requires the use of thinner photoresists to achieve higher photolithography accuracy. However, thin photoresists are difficult to use as etching masks. In order to improve the etching effect of the underlying material, it is usually necessary to deposit thin film materials such as Si3N4 as hard masks to replace traditional photoresist masks. The main difficulties of hard mask etching include:

[0003] The pattern transfer accuracy of the traditional process is poor. Since the pattern transfer etching of the hard mask easily causes the lateral etching of the photoresist, the hard mask pattern size drifts.

[0004] Impurity contamination problem in traditional processes. Due to the additional pattern transfer process, impurities and dirt may easily appear in device grooves and other locations, causing device failure.

[0005] The photoresist / silicon nitride selectivity ratio of the conventional etching process is low, which may easily lead to the hard mask not being etched through after the photoresist is etched.

[0006] The silicon nitride / silicon selectivity of the conventional process is relatively low, and the underlying material (such as Si, SiO2, etc.) is easily overetched during the etching of the hard mask. Summary of the invention

[0007] To solve the above problems, the present invention provides a three-step silicon nitride etching process, which improves the pattern transfer accuracy, the lower layer material selectivity, the dielectric layer etching rate, and the photoresist selectivity through passivation, cleaning and new electron gas etching, and effectively avoids device failure due to impurity contamination.

[0008] The technical solution adopted by the present invention is:

[0009] S1, passivation step: in an etcher, a passivation gas plasma is generated by the RF power supply of the etcher to attach a passivation layer to the surface of the silicon nitride film, and the passivation layer is formed in the protrusions and grooves on the surface of the silicon nitride film;

[0010] S2, cleaning step: in the etcher, adjusting the RF power supply of the etcher to generate a cleaning gas plasma, retaining the passivation layer on the side wall of the groove on the surface of the silicon nitride film, and allowing the cleaning gas plasma to remove the residues on the surface of the silicon nitride film in the vertical direction;

[0011] S3, formal etching step: introducing etching gas and adjusting process parameters to etch the surface of the silicon nitride film.

[0012] The silicon nitride film comprises a photoresist, a silicon nitride layer and a silicon substrate from top to bottom.

[0013] Before step S1, an etcher with ICP-RF dual power supplies is used to pre-etch the silicon nitride film with the photoresist as a mask to form protrusions and grooves on the surface of the silicon nitride film.

[0014] The passivation gas is C4F6, the cleaning gas is a mixed gas of O2 and Ar, and the etching gas is a mixed gas of C4F6, CHF3 and SF6.

[0015] In the passivation step of S1, 50 sccm of C4F6 is introduced, the chamber pressure of the etcher is adjusted so that the ambient pressure is 40-80 mtorr, the ICP power is 900-1100 W, the RF power is 10-35 W, the temperature of the silicon nitride film is maintained at 5-40° C., and the passivation time is 10 s.

[0016] In this step, the C4F6 with chain-like molecular structure is rapidly decomposed to form passivation free radicals, which are rapidly attached to form a passivation film. At the same time, the film formed by the chain-like molecular structure is more easily removed by chemical etching, which is beneficial to the vertical surface cleaning in the S2 cleaning step.

[0017] In the cleaning step of S2, a mixed gas of 45 sccm O2 and 10 sccm Ar is introduced, the chamber pressure of the etcher is adjusted so that the ambient pressure is 3-10 mtorr, the ICP power supply is 1000-1500 W, the RF power supply is 65 W, and the temperature of the silicon nitride film is maintained at 5-40° C. for 25 seconds.

[0018] Using a 1200W ICP power supply at 8mtorr to ionize O2 can produce a large number of O radicals. At the same time, the 65W bias and 8mtorr gas pressure can produce a large vertical physical bombardment effect, avoiding chemical etching and removal of the sidewall passivation film, which is beneficial to the accuracy of pattern transfer.

[0019] In the etching step S3, a mixed gas of 10 sccm C4F6, 15 sccm CHF3 and 5 sccm SF6 is introduced, the chamber pressure of the etcher is adjusted so that the ambient pressure is 15-30 mtorr, the ICP power supply is 1000-1500 W, the RF power supply is 40-60 W, and the temperature of the silicon nitride film is maintained at 5-40° C. This step increases the RF voltage, which is conducive to anisotropic etching.

[0020] The present invention realizes the application of a new environmentally friendly electronic gas C4F6 in silicon nitride etching. The present invention invents a three-step etching method, which overcomes the problems of low selectivity and lateral etching in the traditional silicon nitride etching process, improves the pattern transfer accuracy, the lower material selectivity, the dielectric layer etching rate, and the photoresist selectivity, and effectively avoids device failure due to impurity contamination.

[0021] Different from the prior art, the present invention adds a pre-passivation step and pre-passivates C4F6 as a passivation gas to protect the sidewalls of the device structure, which effectively reduces lateral side erosion and improves the accuracy of pattern transfer.

[0022] Different from the prior art, the present invention adds a vertical cleaning step, which can effectively remove residual impurities in the device grooves and effectively avoid device failure due to impurity contamination.

[0023] Different from the prior art, the present invention uses C4F6 as silicon nitride etching, which can effectively reduce the etching rate of photoresist and underlying Si while increasing the Si3N4 etching rate. The photoresist / silicon nitride selectivity and silicon nitride / silicon selectivity are significantly improved, which can effectively improve the etching efficiency while avoiding over-etching of the underlying material.

[0024] The present invention realizes the application of C4F6 in silicon nitride etching for the first time, and overcomes the etching problems such as low etching rate and over-etching of underlying materials in traditional hard mask etching processes by optimizing process parameters such as RF power, ICP power, gas type, gas ratio and etching pressure.

[0025] The etching method of the present invention can effectively reduce the Si etching rate while increasing the Si3N4 etching rate, and its selection is significantly improved compared with the traditional etching process.

[0026] The present invention adopts a high dielectric layer to silicon selectivity ratio when etching contact holes and through holes, thereby avoiding etching of underlying materials.

[0027] The beneficial effects of the present invention are:

[0028] The present invention invents a three-step etching method, which overcomes the problems of low selectivity and lateral etching in the traditional silicon nitride etching process, improves the pattern transfer accuracy, the lower material selectivity, the dielectric layer etching rate, and the photoresist selectivity, and effectively avoids device failure due to impurity contamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A silicon nitride etching flow chart provided according to the present invention;

[0030] Figure 2 A schematic diagram of the cross-sectional structure of a photoresist / silicon nitride hard mask / silicon substrate sample according to an embodiment of the present invention;

[0031] Figure 3 A schematic diagram of the cross-sectional structure of a sample after the passivation step S1 in the silicon nitride etching method provided in an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of a cross-sectional structure of a substrate after etching step S2 in the silicon nitride etching method provided in an embodiment of the present invention;

[0033] Figure 5 A schematic diagram of the cross-sectional structure of a substrate after the cleaning step S3 in the silicon nitride etching method provided in an embodiment of the present invention;

[0034] Figure 6 Electron scanning microscope images of the cross-section of the samples with different etching methods (left: the etching method of the present invention, etching from top to bottom for 60, 90, and 120 seconds respectively; right: the traditional process, etching from top to bottom for 60, 90, and 120 seconds respectively);

[0035] Table 1 Etching data results of different etching methods. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The traditional silicon nitride etching process usually performs one-step etching by alternately introducing etching gases such as CHF3 and SF6 into the chamber, and obtains suitable conditions after multiple process adjustments. However, this method has a relatively low etching selectivity for silicon, which not only leads to problems such as a small etching window, but also easily causes problems such as poor pattern transfer accuracy, impurity contamination, and low photoresist / silicon nitride selectivity, resulting in the hard mask not being etched through after the photoresist is etched. Especially when etching contact holes and through holes, a high dielectric layer selectivity for silicon is very important to avoid etching the underlying material.

[0038] To avoid the above problems, the three-step silicon nitride etching process performed in the embodiment of the present invention is as follows: Figure 1 shown.

[0039] In this embodiment, 300 nm SiN was deposited on a silicon substrate using a plasma enhanced chemical vapor deposition device (PECVD), and 5350 photoresist was used to perform photolithography patterning on the SiN. The sample preparation process is as follows: Figure 2 shown.

[0040] S1. Place silicon nitride on a silicon substrate, place a photoresist with a microstructure pattern on the surface of the silicon nitride, and use an etcher with an ICP-RF dual power supply to pre-etch the silicon nitride film with the photoresist as a mask to form protrusions and grooves on the surface of the silicon nitride film.

[0041] S2: During the passivation step, 50 sccm C4F6 is introduced.

[0042] C4F6 is used as the passivation gas, not only because the chain-like molecular structure of C4F6 can quickly decompose to form passivation free radicals, and quickly adhere to form a passivation film. At the same time, the film formed by this chain-like molecular structure is easier to be chemically etched and removed, which is conducive to the S2 cleaning step. In addition, C4F6 has a very low greenhouse effect. Compared with C4F8 etching gas, it can reduce the volume fraction of greenhouse gas perfluorinated compounds (PFCs) by 82% in the exhaust gas, and has good environmental friendliness.

[0043] During this step, the chamber pressure of the etcher is adjusted so that the ambient pressure is 40-80 mtorr. The pressure of this step is higher than the pressure set in the pre-cleaning step, so that the (CF)2 radicals can fully react to form a passivation film.

[0044] Then start the ICP power supply of 900-1100W to fully ionize the C4F6 passivation gas. According to the material of the carrier and the structure of the etched sample device, adjust the RF power supply to 10-35W. In this embodiment, an aluminum sheet is used as the carrier, and adjusting the RF power supply to 15W can generate 48V DC-bias, so that the CF free radicals can be stably attached to the surface of the substrate to form a passivation film.

[0045] In addition, the temperature of the silicon nitride film is maintained at 5-40°C. Too high a temperature will cause the product to volatilize and fail, which is not conducive to the adhesion of the passivation film. Since the easily broken molecular structure of C4F6 can quickly generate a metastable film, it only needs to be passivated for 10 seconds. Figure 3 Schematic diagram of the cross-sectional structure of the sample after the passivation step S1.

[0046] S3, in the cleaning step, 45sccm O2 and 10sccm Ar are introduced, wherein O2 as the main cleaning gas can be ionized at low pressure to produce etching of the passivation film perpendicular to the sample, while avoiding the peeling of the sidewall passivation film. Ar as an auxiliary gas not only improves the degree of O2 ionization, but also provides a certain amount of physical etching, which can bombard the residual etching products at the bottom of the deep groove, further optimizing the etching roughness.

[0047] When performing step S2, the optimal chamber pressure is adjusted between 3-10 mtorr according to the chamber environment of different equipment, which can facilitate the discharge of etching products and the removal of products at the bottom of deep grooves, avoiding the removal of the passivation film on the side wall of the photoresist pattern and affecting the pattern transfer accuracy.

[0048] After the pressure is adjusted, turn on the ICP power supply of 1000-1500W to ensure that O2 is fully ionized. At the same time, according to the different carrier materials and the structure of the etched sample device, adjust the RF power supply to 65W to make the lower electrode produce a small amount of self-bias voltage to ensure that the oxygen plasma is chemically etched in an infiltration manner.

[0049] In this embodiment, an aluminum sheet is used as a carrier. By adjusting the RF power supply to 65W, a 195V DC-bias can be generated, which can effectively remove the etching products at the bottom of the groove while avoiding excessive physical bombardment etching. Depending on the etching depth of the sample and the equipment chamber environment, the cleaning time can be controlled within 5-30s. Figure 4 Schematic diagram of the cross-sectional structure of the sample after the cleaning step S3.

[0050] S4, in the etching step, 10 sccm C4F6, 15 sccm CHF3, and 5 sccm SF6 are introduced.

[0051] All three gases contain F, which can generate extremely high concentration F-containing plasma after ionization, providing efficient chemical etching. Among them, C4F6 has a higher C / F ratio. When properly proportioned, it can not only effectively increase the etching rate of SiN, but also slow down the etching of photoresists with CH structures. During this step, the chamber pressure of the etcher needs to be adjusted so that the ambient pressure is 15-30mtorr to ensure that the etching gas is normally ignited and ionized to form a high-density F-containing plasma with good etching rate and uniformity.

[0052] After the pressure adjustment is completed, the equipment turns on the ICP power supply of 1100-1300W to fully ionize the etching gas. According to the material of the carrier and the structure of the etched sample device, the RF power supply is adjusted to 40-60W. In this embodiment, an aluminum sheet is used as the carrier, and the RF power supply is adjusted to 55W to generate 473V DC-bias, so that the plasma in the cavity moves vertically to the sample surface. Through directional physical impact, the vertical surface of the sample can be effectively etched without damaging the side wall passivation film.

[0053] In addition, the substrate temperature is adjusted to 5-40°C to avoid rapid lateral etching. The etching step has a relatively obvious thermal reaction formation, and the back helium leak rate is controlled. The experiment uses 10Torr back helium, and its leak rate is controlled to be less than 3sccm. The specific etching time can be adjusted according to the etching rate and SiN film thickness. In this embodiment, the etching rate reaches 214nm / min, and 300nm SiN is etched after 1.5min etching. Figure 5 It is a schematic diagram of the cross-sectional structure of the sample after etching step S3.

[0054] Figure 6 Table 1 and Table 2 are the electron scanning microscope images of the sample cross-sections of different etching methods and the etching measurement data table respectively.

[0055] Table 1 Etching data results of different etching methods

[0056]

[0057] pass Figure 6As shown in Table 1, the etching method of the present invention can effectively reduce the Si etching rate while increasing the Si3N4 etching rate, and the SiN / Si selectivity ratio is increased from 0.143 to 1.57, which can effectively prevent the lower Si from being overetched. The photoresist / SiN selectivity ratio is reduced from 0.35 to 0.14, which can effectively improve the photoresist scale resistance.

[0058] It can be seen from the implementation that the three-step silicon nitride etching process of the present invention improves the pattern transfer accuracy, the lower layer material selectivity, the dielectric layer etching rate, and the photoresist selectivity through passivation, cleaning and new electron gas etching, and effectively avoids device failure due to impurity contamination.

Claims

1. A silicon nitride etching method, characterized in that Methods include: S1, passivation step: in an etcher, a passivation gas plasma is generated by using an RF power supply to attach a passivation layer to the surface of the silicon nitride film, and the passivation layer is formed in the protrusions and grooves on the surface of the silicon nitride film; S2, cleaning step: in the etcher, adjusting the RF power supply to generate a cleaning gas plasma, retaining the passivation layer on the sidewall of the groove on the surface of the silicon nitride film, and allowing the cleaning gas plasma to remove the residues on the surface of the silicon nitride film in the vertical direction; S3, etching step: introducing etching gas and adjusting process parameters to etch the surface of the silicon nitride film; The passivation gas is C4F6, the cleaning gas is a mixed gas of O2 and Ar, and the etching gas is a mixed gas of C4F6, CHF3 and SF6.

2. A silicon nitride etching method according to claim 1, characterized in that: The silicon nitride film comprises a photoresist, a silicon nitride layer and a silicon substrate from top to bottom.

3. A silicon nitride etching method according to claim 1, characterized in that: Before step S1, an etcher with ICP-RF dual power supplies is used to pre-etch the silicon nitride film with the photoresist as a mask to form protrusions and grooves on the surface of the silicon nitride film.

4. A silicon nitride etching method according to claim 1, characterized in that: In the passivation step of S1, 50 sccm of C4F6 is introduced, the ambient pressure is adjusted to 40-80 mtorr, the ICP power is 900-1100 W, the RF power is 10-35 W, the temperature of the silicon nitride film is maintained at 5-40° C., and the passivation time is 10 s.

5. A silicon nitride etching method according to claim 1, characterized in that: In the cleaning step of S2, a mixed gas of 45 sccm O2 and 10 sccm Ar is introduced, the ambient pressure is adjusted to 3-10 mtorr, the ICP power supply is 1000-1500 W, the RF power supply is 65 W, and the temperature of the silicon nitride film is maintained at 5-40° C. for 25 seconds.

6. A silicon nitride etching method according to claim 1, characterized in that: In the etching step of S3, a mixed gas of 10 sccm C4F6, 15 sccm CHF3 and 5 sccm SF6 is introduced, the ambient pressure is adjusted to 15-30 mtorr, the ICP power supply is 1000-1500 W, the RF power supply is 40-60 W, and the temperature of the silicon nitride film is maintained at 5-40°C.

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