KR20050112115A - Method and apparatus for multilayer photoresist dry development - Google Patents

Abstract

A method for etching an organic anti- reflective coating (ARC) layer on a substrate in a plasma processing system comprising: introducing a process gas comprising ammonia (NH 3), and a passivation gas; forming a plasma from the process gas; and exposing the substrate to the plasma. The process gas can, for example, constitute NH3 and a hydrocarbon gas such as at least one of C2H4, CH4, C2H2, C 2H6, C3H4, C3H6, C 3H8, C4H6, C4H8, C 4H10, C5H8, C5H10, C 6H6, C6H10, and C6H12. Additionally, the process chemistry can further comprise the addition of helium. The present invention further presents a method for forming a bilayer mask for etching a thin film on a substrate, wherein the method comprises: forming the thin film on the substrate; forming an ARC layer on the thin film; forming a photoresist pattern on the ARC layer; and transferring the photoresist pattern to the ARC layer with an etch process using a process gas comprising ammonia (NH3), and a passivation gas.

Description

METHOD AND APPARATUS FOR MULTILAYER PHOTORESIST DRY DEVELOPMENT}

This application is directed to US Provisional Patent Application No. 60 / 458,430, filed March 31, 2003, US Provisional Application No. 60 / 484,225, filed May 5, 2003, and August 14, 2003. And non-provisional patent application No. 10 / 640,577, the entire contents of which are hereby incorporated by reference. This application is filed on December 23, 2002, co-pending, entitled "Methods and Apparatus for Double Layer Photoresist Dry Development," Application No. 60 / 435,286, the entire contents of which are incorporated herein by reference. Related to).

The present invention relates to a method and apparatus for plasma treating a substrate, and more particularly to a method for dry development of multilayer photoresists.

During semiconductor processing, a (dry) plasma etch process may be used to remove or etch material along fine lines, patterned on silicon substrates, or in vias or contacts. Can be. Plasma etching processes generally include placing an overlying patterned protective layer (eg, a photoresist layer) on a semiconductor substrate in a processing chamber. Once the substrate is placed in the chamber, the ionizable dissociation gas mixture is introduced into the chamber at a pre-specified flow rate, and the vacuum pump is throttled to obtain ambient processing pressure. Subsequently, a fraction of the gas species present is transferred via inductively or capacitively radio frequency (RF) power, or microwave power, for example using electron cyclotron resonance (ECR). When ionized by the heated electrons, a plasma is formed. In addition, the heated electrons dissociate some species of the surrounding gas species and produce reactive species (s) suitable for exposed surface etching chemistry. Once the plasma is formed, the selected surface of the substrate is etched by the plasma. This treatment is adjusted to etch various features (e.g., trenches, vias, contacts, etc.) within selected regions of the substrate to obtain suitable conditions including the desired concentration of reactants and ion populations. do. Such substrate materials which require etching include silicon dioxide (SiO ₂ ), low-k dielectric materials, poly-silicon and silicon nitride.

1A, 1B and 1C show schematic diagrams of a general procedure for pattern etching a thin film;

2 shows a simple schematic diagram of a plasma processing system according to an embodiment of the present invention;

3 shows a schematic diagram of a plasma processing system according to another embodiment of the present invention;

4 shows a schematic diagram of a plasma processing system according to another embodiment of the present invention;

5 shows a schematic diagram of a plasma processing system according to another embodiment of the present invention;

6 shows a schematic diagram of a plasma processing system according to another embodiment of the present invention;

7 illustrates a method of etching an anti-reflective coating (ARC) layer on a substrate in a plasma processing system in accordance with an embodiment of the present invention;

8 illustrates a method of forming a bilayer mask for etching a thin film on a substrate in accordance with another embodiment of the present invention;

9A and 9B show schematic diagrams of multilayer masks.

The present invention relates to a method and apparatus for plasma treating a substrate, and to a method and apparatus for multilayer photoresist dry development. The invention also relates to the multilayer mask itself.

In one aspect of the invention, a method and apparatus for etching an anti-reflective coating (ARC) layer on a substrate in a plasma processing system is described. A process gas comprising at least one gas collectively comprising ammonia (NH ₃ ) and a passivation gas is introduced. Plasma is formed from the processing gas in the plasma processing system. The substrate is exposed to the plasma.

In another aspect of the present invention, a method and apparatus for forming a bilayer mask for etching a thin film on a substrate are described. The thin film is formed on the substrate. An anti-reflective coating (ARC) layer is formed on the thin film. A photoresist pattern is formed on the ARC layer. By etching the ARC layer using a process gas comprising one or more gases collectively comprising ammonia (NH ₃ ) and a passivation gas, the photoresist pattern is transferred to the ARC layer.

In addition, a method of smoothing sidewalls in a multilayer mask on a substrate in a plasma processing system includes: introducing a processing gas comprising one or more gases collectively comprising ammonia (NH ₃ ) and a passivation gas; Forming a plasma from the processing gas in the plasma processing system; And exposing the substrate to the plasma, wherein the passivation gas facilitates the formation of a passivation film on the sidewalls of the multilayer mask, thereby smoothing the surface roughness of the sidewalls.

a few  Detailed description of the embodiments

In the material processing method, pattern etching applies a thin layer of photosensitive material, such as photoresist, to the top surface of the substrate and then pattern it to provide a mask for transferring the pattern to the underlying thin film on the substrate during etching. It comprises a step. Patterning of the photosensitive material generally involves exposing the photosensitive material through a reticle (and associated optics), for example using a microlithography system, and then using the developing solvent to irradiate the photosensitive material (positive photoresist). And non-irradiation areas (as in the case of negative resist). With a multilayer mask, the shape can be etched in the thin film. For example, as shown in FIGS. 1A-C, a bilayer 6 comprising a photosensitive layer 3 having an pattern 2 formed using conventional lithography techniques and an organic anti-reflective coating (ARC) layer 7. ) May be used as a mask for etching the thin film 4 on the substrate 5, and the mask pattern 2 in the photosensitive layer 3 may be subjected to an individual etching step prior to the main etching step of the thin film 4. Is transferred to the ARC layer 7 through.

In one embodiment, a processing gas comprising ammonia (NH ₃ ) and a passivation gas is used in a double layer photoresist dry development method. For example, the passivation gas may be C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , Hydrocarbon gas, such as one or more of C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ , C ₆ H ₁₂ , and the like.

Although the above embodiment describes the etching of the thin film 4 on the substrate 5, it can be etched in the substrate 5 itself, with or without the thin film 4.

According to one embodiment, a plasma processing chamber 10, a diagnostic system 12 coupled to the plasma processing chamber 10, and a regulator 14 coupled to the diagnostic system 12 and the plasma processing chamber 10. A plasma processing system 1 comprising a is shown in FIG. 2. The regulator 14 is disposed to etch the organic ARC layer by performing a treatment method comprising one or more of the above-identified chemicals.

In addition, the regulator 14 is arranged to receive one or more endpoint signals from the diagnostic system 12 and post-process one or more endpoint signals to accurately determine the endpoint of the process. In the embodiment being described, the plasma processing system 1 shown in FIG. 2 uses plasma for material processing. The plasma processing system 1 may comprise an etching chamber.

According to the embodiment of FIG. 3, the plasma processing system 1a comprises a plasma processing chamber 10, a substrate holder 20 on which a substrate 25 to be processed is fixed, and a vacuum pumping system 30. Can be. Substrate 25 may be, for example, a semiconductor substrate, a wafer or a liquid crystal display. The plasma processing chamber 10 is arranged to facilitate generation of plasma, for example, in the processing region 15 adjacent the surface of the substrate 25. An ionizable gas or gas mixture is introduced through a gas injection system (not shown) and the processing pressure is adjusted. For example, an adjustment mechanism (not shown) can be used to adjust the vacuum pumping system 30. Plasma may be used to make a material specific to a given material treatment and / or to assist in the removal of material from the exposed surface of the substrate 25. The plasma processing system 1a may be arranged to process a 200 mm substrate, a 300 mm substrate, or more substrates.

Substrate 25 may be attached to substrate holder 20 via, for example, an electrostatic clamping system. The substrate holder 20 also receives, for example, heat from the substrate holder 20, transfers heat to a heat exchanger system (not shown), or transfers heat from the heat exchanger system upon heating. It may further comprise a cooling system comprising a recirculating coolant stream. In addition, gas may be delivered to the rear of the substrate 25 via, for example, a backside gas system, to improve the gap-gap thermal conductance between the substrate 25 and the substrate holder 20. Can be. Such a system can be used where temperature control of the substrate at elevated or reduced temperatures is desired. For example, the back gas system may comprise a two-zone gas distribution system and may independently change the helium gas gap pressure between the center and the edge of the substrate 25. In another embodiment, a heating / cooling element, such as a resistive heating element, or a thermo-electric heater / cooler, the substrate holder 20, the chamber wall of the plasma processing chamber 10, and any in the plasma processing system 1a. It may be included in other ingredients.

In the embodiment shown in FIG. 3, the substrate holder 20 may comprise an electrode in the processing space 15 in which RF power is coupled to the processing plasma. For example, substrate holder 20 may be electrically biased at RF voltage by transferring RF power from RF generator 40 through impedance match network 50 to substrate holder 20. The RF bias can heat the electrons to form and maintain the plasma. In this arrangement, the system can operate as a reactive ion etching (RIE) reactor, with the chamber and the top gas injection electrode serving as the ground surface. Typical frequencies of RF bias can range from 0.1 MHz to 100 MHz. RF systems for plasma processing are well known to those skilled in the art.

Optionally, RF power is applied to the substrate holder electrode at multiple frequencies. The impedance match network 50 also serves to enhance the transfer of RF power to the plasma in the plasma processing chamber 10 by reducing the reflected power. Match network topologies (eg, L-type, π-type, T-type, etc.) and automatic adjustment methods are well known to those skilled in the art.

Vacuum pump system 30 includes, for example, a turbo-molecular vacuum pump (TMP) capable of pumping speeds up to 5000 liters per second (and more), and a gate valve for regulating chamber pressure. In a conventional plasma processing apparatus used for dry plasma etching, 1000 to 3000 liters TMP per second are generally used. TMPs are useful for low pressure treatments, generally below 50 mTorr. For high pressure treatment (ie, 100 mTorr or more), mechanical booster pumps and dry roughing pumps can be used. In addition, an apparatus (not shown) for monitoring chamber pressure may be coupled to the plasma processing chamber 10. As the pressure measuring device, for example, a Type 628B Baratron absolute capacitance manometer available from MKS Instruments, Inc. (Andover, MA) may be used.

The regulator 14 has a regulated voltage sufficient to deliver and activate inputs to the microprocessor, memory, and plasma processing system 1a and to monitor outputs from the plasma processing system 1a. It consists of a digital I / O port that can generate a. The regulator 14 also includes an RF generator 40, an impedance match network 50, a gas injection system (not shown), a vacuum pump system 30 and a rear gas delivery system (not shown), a substrate / substrate holder. It may be coupled to and exchange information with a temperature measurement system (not shown), and / or an electrostatic flapping system (not shown). For example, by using a program stored in a memory, the method of etching an organic ARC layer can be performed by activating an input signal to the above-described component of the plasma processing system 1a. One example of the regulator 14 is DELL PRECISION WORKSTATION 610 ^™ , available from Dell Corporation, Austin, Texas.

Diagnostic system 12 may include an optical diagnostic system (not shown). The optical diagnostic subsystem may comprise a detector such as a (silicon) photodiode or photomultiplier tube (PMT) for measuring the intensity of light emitted from the plasma. Diagnostic system 12 may further include an optical filter, such as a narrow-band interference filter. In an alternate embodiment, the diagnostic system 12 includes a line CCD (charge coupled device), a CID (charge injection device) array, and light dispersion such as a grating or prism. It may include one or more of the devices. In addition, the diagnostic system 12 may include a light spectrum such as a monochromator (eg, a grating / detector system) for measuring light at a given wavelength, or a device as described, for example, in US Pat. No. 5,888,337. And spectrometers (including, for example, rotational gratings) to measure.

The diagnostic system 12 may include a high resolution optical emission spectroscopy (OES) sensor, such as a peak sensor system or manufactured by Bery Instruments. Such OES sensors have a broad spectrum ranging from ultraviolet (UV), visible (VIS), and near infrared (NIR) light spectra. The resolution is about 1.4 Angstroms, meaning the sensor can collect 5550 wavelengths from 240 to 1000 nm. For example, the OES sensor may comprise a high sensitivity miniature fiber optic UV-VIS-NIR spectrometer in which 2048 pixel linear CCD arrays are integrated one after the other.

The spectrometer accepts light transmitted through single and bundled optical fibers, and through fixed grating, the light output signal from the optical fibers is dispersed across the line CCD array. Similar to the arrangement described above, the light passing through the optical vacuum window is focused on the input signal end of the optical fiber through the convex spherical lens. Three spectrometers, each specifically tuned for a given spectral range (UV, VIS and NIR), form a sensor for the processing chamber. Each spectrometer includes an independent A / D converter. Finally, depending on the sensor application, it is possible to record the full emission spectrum every 0.1 to 1.0 seconds.

In the embodiment shown in FIG. 4, the plasma processing system 1b may be similar to the embodiment of FIG. 2 or 3, for example, and in addition to the components described with reference to FIGS. It may further comprise a stationary or mechanical or electrical rotating magnetic field system 60 to potentially increase and / or improve plasma treatment uniformity. The regulator 14 may also be coupled to the magnetic field system 60 to adjust the rotational speed and the field strength. Design and performance of rotating magnetic fields are well known to those skilled in the art.

In the embodiment shown in FIG. 5, the plasma processing system 1c may be similar to, for example, the embodiment of FIG. 2 or FIG. 3, wherein RF power is coupled to the impedance match network 74 from the RF generator 72. It can be made by further comprising an upper electrode 70 that can be coupled through. Typical frequencies for applying RF power to the upper electrode may range from 0.1 MHz to 200 MHz. Also, a typical frequency for applying power to the lower electrode can range from 0.1 MHz to 100 MHz. The regulator 14 is also coupled to the RF generator 72 and the impedance match network 74 to regulate the application of RF power to the upper electrode 70. The design and performance of the top electrode is well known to those skilled in the art.

In the embodiment shown in FIG. 6, the plasma processing system 1d may be similar to the embodiment of FIG. 2 or 3, for example, in which RF power is applied to the impedance match network 84 via the RF generator 82. It may further comprise an induction coil 80 coupled through. RF power is inductively coupled from the induction coil 80 through the dielectric window (not shown) to the plasma processing region 15. Typical frequencies for applying RF power to the induction coil 80 may range from 10 MHz to 100 MHz. Similarly, a typical frequency for applying power to chuck electrodes may range from 0.1 MHz to 100 MHz. In addition, a slotted Faraday shield (not shown) may be used to reduce capacitive coupling between the induction coil 80 and the plasma. The regulator 14 is also coupled to the RF generator 82 and the impedance match network 84 to regulate the application of power to the induction coil 80. In an alternate embodiment, the induction coil 80 is a "spiral" coil or "pancake" coil that communicates with the plasma processing region 15 as in a transformer coupled plasma (TCP) reactor. This can be Design and performance of inductively coupled plasma (ICP) sources, or transformer coupled plasma (TCP) sources, are well known to those skilled in the art.

Optionally, the plasma can be formed using electron cyclotron resonance (ECR). In another embodiment, the plasma is formed due to launching helicon waves. In another embodiment, the plasma is formed due to propagating surface waves. Each plasma source described above is well known to those skilled in the art.

In the following, a method of etching an organic ARC layer using a plasma processing apparatus is discussed. For example, the plasma processing apparatus may comprise various elements as described in FIGS. 2-6, and combinations thereof.

In one embodiment, the method of etching the organic ARC layer is NH _3. And C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C Hydrocarbon gas such as one or more of ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H _10, and C ₆ H ₁₂ , and the like. For example, the process parameter space may include a chamber pressure of 20 to 1000 mTorr, NH ₃ process gas flow rate of 50 to 1000 sccm, hydrocarbon process gas flow rate of 5 to 100 sccm, and an upper electrode of 500 to 2000 W (e.g. 70) RF bias, and a bottom electrode (eg, element 20 of FIG. 5) RF bias of 10-500 W. In addition, the upper electrode bias frequency may be 0.1MHz to 200MHz, for example 60MHz. In addition, the lower electrode bias frequency may be 0.1MHz to 100MHz, for example 2MHz.

For example, there is a method of etching the organic ARC layer using a plasma processing apparatus as shown in FIG. However, the scope of the method discussed by this example should not be limited. Table 1 shows that chamber pressure = 100 mTorr; Upper electrode RF power = 1200 W; Bottom electrode RF power = 100 W; Process gas flow rate NH ₃ / C ₂ H ₄ = 450/50 sccm; An electrode gap of 55 mm between the bottom surface of the electrode 70 (see FIG. 5) and the top surface of the substrate 25 on the substrate holder 20; Bottom electrode temperature (eg, substrate holder 20 of FIG. 5) = 20C; Upper electrode temperature (eg, electrode 70 of FIG. 5) = 60C; Chamber wall temperature = 50C; Rear helium pressure center / edge = 10/35 Torr; And the critical dimensions of the contour etched into the organic ARC layer using an exemplary processing method with an etching time of 180 seconds.

(Photoresist-PR; Critical Dimension-CD) NH ₃ / C ₂ H ₄ center edge Residual Top PR 478 nm 493 nm Bottom CD / Bias-MC 154/6 nm 147 / -3 nm Floor CD / Bias-CA 138 / -5 nm 134 / -9 nm

 Table 1 shows the thickness of the photoresist remaining after the ARC layer etch, the top and bottom critical dimensions of the ARC shape, and the critical dimension bias (bias, CD change from top to bottom (ie negative bias reduces CD). Positive bias indicates CD increase), and the like (for both metal contact (MC) and contact (CA)). It also reports data at the center and edge. The data demonstrates that the CD and the maintenance of the potential for reducing the CD are successful.

In alternative embodiments, the treatment chemical may further comprise helium (He). The introduction of helium in the treatment can reduce the outer sidewall roughness.

In general, the design of experimental (DOE) techniques can be used to determine the etch time; However, endpoint detection can also be used to determine this. One possible method of endpoint detection is to monitor the portion of the emitted light spectrum from the plasma region that indicates when the plasma chemistry changes because the ARC layer etch is substantially nearly complete and in contact with the underlying material film. For example, the spectral portion indicative of such a change consists of a wavelength of 387.2 nm (carbon-nitrogen (CN)) and can be measured using optical emission spectroscopy (OES). After the emission level corresponding to this frequency exceeds the specified threshold (eg, substantially falls to zero or increases above a certain level), the endpoint can be considered complete. Other wavelengths that provide endpoint information are also available. In addition, the etching time can be extended to include an over-etching period, wherein the over-etching period is composed of a time fraction (ie, 1 to 100%) between the time associated with the start of the etching process and the endpoint detection.

7 shows a flowchart of a method of etching an anti-reflective coating (ARC) layer on a substrate in a plasma processing system according to an embodiment of the present invention. The procedure 400 begins at 410 introducing a process gas into a plasma processing system, which process gas comprises an ammonia (NH ₃ ) containing gas and a passivation gas. For example, the passivation gas may be C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , Hydrocarbon gas, such as one or more of C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . Optionally, the processing gas may further comprise helium (He).

At 420, the plasma is formed from the processing gas in the plasma processing system using, for example, any of the systems shown in FIGS. 2-6, or a combination thereof.

At 430, the substrate comprising the ARC layer is exposed to a plasma formed within 420. After the first period, procedure 400 ends. For example, the primary period during which the ARC layer is exposed to the plasma is generally indicated by the time required to etch the ARC layer, or the time required to transfer the photoresist pattern to the ARC layer. In general, the first period required to transfer the photoresist pattern through the thickness of the ARC layer is predetermined. Optionally, the primary period may be further increased by the secondary period or the over-etching period. As noted above, the over-etching time may comprise a time fraction, such as 1 to 100% of the primary period, which may include extending the etching past the detection of the end point. have.

8 illustrates a method of forming a bilayer mask for etching a thin film on a substrate in a plasma processing system in accordance with another embodiment of the present invention. This method is shown in flow diagram 500, beginning at 510, forming a thin film on a substrate. The thin film may comprise an oxide layer, such as silicon dioxide (SiO ₂ ), and may be formed by various processes including chemical vapor deposition (CVD).

At 520, an anti-reflective coating (ARC) layer is formed on the substrate upper thin film. The ARC layer is an organic ARC layer that is formed using conventional techniques such as, for example, spin coating systems.

At 530, a photoresist pattern is formed on the substrate top ARC layer. The photoresist film can be formed using conventional techniques such as a photoresist spin coating system. The pattern can be formed in the photoresist film by using conventional techniques such as stepping micro-lithography systems, and developing solvents.

At 540, the photoresist pattern is transferred to the ARC layer to form a bilayer mask. Pattern transfer is completed using a dry etching technique, and the etching process is performed in a plasma processing system using a processing gas containing ammonia (NH ₃ ) containing gas and a passivation gas. For example, the passivation gas may be C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ It may comprise a hydrocarbon gas, such as one or more of C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . Optionally, the processing gas as described above may further comprise helium (He). The plasma is formed from the processing gas in the plasma processing system using, for example, any of the systems shown in FIGS. 2-6, and the substrate comprising the ARC layer is exposed to the formed plasma. The primary period during which the substrate comprising the ARC layer is exposed to the plasma is generally indicated by the time required to etch the ARC layer, or the time required to transfer the photoresist pattern to the ARC layer. In general, the first period required to transfer the photoresist pattern through the thickness of the ARC layer is predetermined. In general, however, the primary period may be further increased by the secondary period or the over-etching period. As noted above, the over-etching time may comprise a time fraction, such as 1 to 100% of the primary period, which may include extending the etching past the detection of the end point. have.

9A and 9B show side and top views, respectively, of an etched multilayer mask. The shape 600 comprises a sidewall 610 through the photosensitive layer 640 and the ARC layer 650, where a surface roughness 620 is formed during etching. The passivation gas facilitates the formation of the passivation film 630 to smooth the surface roughness 620 of the etched multilayer mask; See FIG. 9B.

Although only certain embodiments of the invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within these embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are included within the scope of the present invention.

Claims (35)

Introducing a process gas comprising one or more gases collectively comprising ammonia (NH ₃ ) and a passivation gas; Forming a plasma from the processing gas in the plasma processing system; And Exposing the substrate to the plasma; A method of etching an anti-reflective coating (ARC) layer on a substrate in a plasma processing system. The method of claim 1, The passivation gas comprises a hydrocarbon gas. The method of claim 1, The passivation gas is C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . The method according to any one of claims 1 to 3, Wherein said process gas further comprises helium. The method of claim 1, Said exposure of said substrate to said plasma is performed during a first period of time. The method of claim 5, Wherein said first period of time is determined by endpoint detection. The method of claim 6, The endpoint detection comprises optical emission spectroscopy. The method of claim 5, The first period of time corresponds to a time for etching the ARC layer and is extended by a second period of time. The method of claim 8, The second period is a fraction of the first period. Forming a thin film on the substrate; Forming an anti-reflective coating (ARC) layer on the thin film; Forming a photoresist pattern on the ARC layer; And Etching the ARC layer using a processing gas comprising at least one gas collectively comprising ammonia (NH ₃ ) and a passivation gas, thereby transferring the photoresist pattern to the ARC layer, A method of forming a bilayer mask for etching a thin film on a substrate. The method of claim 10, The passivation gas comprises a hydrocarbon gas. The method of claim 10, The passivation gas is C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . The method according to any one of claims 10 to 12, Wherein said process gas further comprises helium. The method of claim 10, Wherein said etching of said substrate is performed during a first period of time. The method of claim 14, Wherein said first period of time is determined by endpoint detection. The method of claim 15, The endpoint detection comprises optical emission spectroscopy. The method of claim 14, The first period of time corresponds to a time for etching the ARC layer and is extended by a second period of time. The method of claim 17, The second period is a fraction of the first period. A plasma processing chamber for facilitating the formation of a plasma from the processing gas; A regulator coupled to the plasma processing chamber and disposed to perform a treatment with the processing gas, The processing gas is characterized in that it comprises one or more gases, including ammonia (NH ₃ ) and the passivation gas collectively, A plasma processing system for etching an anti-reflective coating (ARC) layer on a substrate. The method of claim 19, The system further comprises a diagnostic system coupled to the plasma processing chamber and coupled to the regulator. The method of claim 20, The diagnostic system is arranged to receive a signal related to light emitted from the plasma. The method of claim 19, And said passivation gas comprises a hydrocarbon gas. The method of claim 19, The passivation gas is C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . The method according to any one of claims 19, 22 or 23, And the process gas further comprises helium. The method of claim 20, Due to the regulator, the substrate is exposed to the plasma for a first period of time. The method of claim 25, And said first period of time is determined by endpoint detection determined by said diagnostic system. The method of claim 26, And wherein said diagnostic system comprises an optical emission spectroscopy device. The method of claim 25, The first period of time corresponds to a time for etching the ARC layer and is extended by a second period of time. The method of claim 28, The second period is a fraction of the first period. Introducing a process gas comprising one or more gases collectively comprising ammonia (NH ₃ ) and a passivation gas; Forming a plasma from the processing gas in the plasma processing system; And Exposing the substrate to the plasma; Wherein the passivation gas facilitates the formation of a passivation film on the sidewalls of the multilayer mask to smooth the surface roughness of the sidewalls, A method of smoothing sidewalls in a multilayer mask on a substrate in a plasma processing system. The method of claim 30, The passivation gas comprises a hydrocarbon gas. The method of claim 30, The passivation gas is C ₂ H ₄ , CH ₄ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₄ H ₆ , C ₄ H ₈ , C ₄ H ₁₀ , C ₅ H ₈ , C ₅ H ₁₀ , C ₆ H ₆ , C ₆ H ₁₀ and C ₆ H ₁₂ . The method according to any one of claims 30 to 32, Wherein said process gas further comprises helium. Anti-reflective coatings; A photosensitive layer formed on the anti-reflective coating (the photosensitive layer and the anti-reflective coating define a shape therethrough); And A double layer mask comprising a passivation layer formed on a sidewall of a shape. The method of claim 34, A mask, characterized in that the passivation layer forms smooth smooth sidewalls.