HK1114409A - Method for photomask plasma etching using a protected mask - Google Patents

Description

Photomask plasma etch using protective mask

Technical Field

Embodiments of the present invention relate to a method for plasma etching chromium, and more particularly, to a method for etching chromium layer during a mask manufacturing process.

Background

In the fabrication of Integrated Circuits (ICs) or wafers, patterns representing the various layers of a wafer are created by a wafer designer. A series of reusable masks or reticles are created from these patterns to transfer the design of each wafer layer to the semiconductor substrate during the manufacturing process. The mask pattern generation system uses a precision laser or electron beam to transfer an image of each layer of the wafer design onto the opposing mask. The purpose of the mask is very similar to photographic negatives to transfer each layer of circuit pattern onto a semiconductor substrate. The layers are fabricated using a continuous process and converted into tiny transistors and electronic circuits that can contain each complete chip. Thus, defects in the mask may also be transferred to the wafer, which may adversely affect performance. Serious defects can render the mask completely useless. Typically, a set of 15 to 30 masks may be used to construct a wafer, and these masks may be reused.

The mask is typically a glass or quartz substrate with a layer of chrome on one side. The chrome layer is covered by the anti-reflection coating and the photosensitive photoresist. During the patterning process, a portion of the photoresist is exposed to ultraviolet light to write the circuit design on the mask, and the exposed portion is made soluble in a developer. The soluble portion of the photoresist is removed to create a pattern. The pattern allows the exposed underlying chrome layer to be etched. The etching process removes the chrome layer and the anti-reflective coating where the photoresist on the mask is removed, i.e., the exposed chrome layer is removed.

Another mask used for patterning is the well-known quartz phase shift mask. The quartz phase shift mask is similar to the above, but in the quartz phase shift mask, the alternating adjacent areas of the quartz region exposed by the patterned chrome layer are etched to a depth approximately equal to half the wavelength of light, which can be used to transfer circuit patterns to a substrate during fabrication. The chrome layer is removed after the quartz etch. Therefore, when light passes through the quartz phase shift mask to expose the photoresist on the substrate, the light passing through the openings in the mask and impinging on the photoresist is 180 degrees out of phase with respect to the light passing through the closely adjacent openings. Therefore, light that may be scattered at the mask edge is offset by a 180-degree phase difference caused by light scattering at the edge of the adjacent opening, thereby causing a tight distribution of light in a predetermined region of the photoresist. The tight distribution of light helps reveal features with smaller critical dimensions. Similarly, masks used in chromeless lithography can also be used to impart a pattern to a photoresist by phase shifting the light through the quartz portions of both masks, thereby improving the light distribution used to develop the photoresist pattern. The use of a molybdenum (Mo) doped patterned silicon nitride layer also allows for a phase shift of the light generated by passing through the mask such that the image light passing through the patterned portion of the mask is 180 degrees out of phase with the light passing through the quartz substrate exposed by the openings in the patterned layer.

In one etching process, such as dry etching, reactive ion etching or plasma etching, the plasma is used to enhance the chemical reaction and etch the patterned chrome layer on the mask. Unfortunately, conventional chrome etch processes often exhibit etch bias due to plasma striking the photoresist material used to pattern the chrome layer. Because the photoresist is impacted during the chrome etch process, the critical dimension of the patterned photoresist is not accurately transferred to the chrome layer. Thus, conventional chrome etch processes may not yield acceptable performance for masks having critical dimensions less than about 5 microns. This results in mask etch feature non-uniformity and thereby reduces the ability to fabricate device features with small critical dimensions using masks.

As the mask critical dimension continues to shrink, the importance of etch uniformity continues to increase. Therefore, a chrome etch process with high etch uniformity is needed.

Therefore, an improved chrome etch process is needed.

Disclosure of Invention

The invention provides a method for etching chromium. In one embodiment, a method of etching chromium comprises: providing a film stack having a chrome layer and a patterned photoresist layer in a process chamber; depositing a protective angle-shaped protective layer on the patterned photoresist layer; etching the conformal passivation layer to expose the chrome layer through the patterned photoresist layer; and etching the chromium layer.

The invention also provides a method for forming the photomask. In one embodiment, a method of forming a mask includes: patterning a mask layer on a mask layer having at least one chromium layer; depositing a conformal passivation layer on the mask layer; etching the chromium layer through the mask layer having the protective layer deposited thereon to expose the underlying layer; and removing the mask layer and the passivation layer.

Drawings

The above-recited features of the present invention are described in more detail and in more detail in the above description, taken in conjunction with the accompanying drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a schematic cross-sectional view of an etch reactor suitable for etching chromium layers in an example embodiment;

FIG. 2 is a flowchart illustrating a method of etching a chromium layer according to an embodiment;

FIGS. 3A to 3I illustrate a quartz mask fabricated by an embodiment of the chrome layer etching method of the present invention;

FIGS. 4A-4G illustrate a quartz phase shift mask fabricated by one embodiment of the chromium layer etching method of the present invention;

FIGS. 5A-5F illustrate a quartz phase shift mask fabricated by one embodiment of the chromium layer etching method of the present invention;

FIG. 6 is a schematic cross-sectional view of one embodiment of a processing system, such as a cluster tool, including the reactor of FIG. 1.

To facilitate understanding, like reference numerals are used to designate like elements that are used in different figures.

Description of the main elements

114 match network 112 plasma power source

120 gas panel 154 support system

146 controller 148 memory

152 support circuit 140 bias power source

138 lifting mechanism for 142 matching network

156 helium source 166 chuck power supply

168 heat source power supply 164 vacuum pump

110 antenna 122 substrate

116 gas inlet 124 supports the base

190 opening in chromium layer 188

170 processing system 100 process chamber

134 heating element 158 gas conduit

144 heater 182 mask adapter

320 feature 310 trench

316 width (critical dimension) 310 protection layer

418 quartz phase shift mask 430 opening

406 anti-reflection layer 404 chromium layer

432 protective layer 434 feature

502 quartz layer 554 attenuating layer

Detailed Description

FIG. 1 is a schematic cross-sectional view of an exemplary etching process chamber 100 in which the quartz etching method of the present invention may be utilized. Suitable reactors that may be used as disclosed herein include, for example, a Discrete Plasma Source (DPS)^®) II reactor, or Tetra I and Tetra II mask etching systems, all of which may be implemented in Appl located in Santa Mooney, CalifCommercially available from ied materials, Inc. The etching process chamber 100 may also be used as a process module of the processing system 170 shown in FIG. 6, such as Centura available from Applied materials^®Integrated semiconductor wafer processing system. The processing system may also include a first chamber 172 suitable for an ashing process and a second chamber 174 suitable for polymer deposition. Examples of suitable ashing and deposition chambers include AXIOM HT^TMAnd Tetra II process chambers, also available from Applied materials.

The particular embodiments of the process chamber 100 depicted herein are for illustrative purposes and are not intended to limit the scope of the present invention.

Returning to FIG. 1, the processing chamber 100 generally includes a processing chamber body 102 having a substrate pedestal 124, and a controller 146. The chamber body 102 has conductive walls 104 that support a substantially planar dielectric ceiling 108. Other embodiments of the process chamber 100 may have other types of ceilings, such as a domed ceiling. The antenna 110 is disposed on the top plate 108. The antenna 110 includes one or more selectively controllable inductive coil elements (two coaxial elements 110a and 110b are shown in fig. 1). The antenna 110 is coupled to a plasma power source 112 through a first matching network 114. The plasma power source 112 may typically generate about 3000 watts of power at a tunable frequency in the range of about 50kHz to about 13.56 MHz. In one embodiment, the plasma power source 112 provides about 100 to about 600W of inductively coupled RF power at a frequency of about 13.56 MHz.

The substrate pedestal (cathode) 124 is coupled to a bias power source 140 through a second matching network 142. The bias power 140 may provide between about 0 and about 600W at a pulse frequency of about 1 to about 10 kHz. The bias source 140 produces a pulsed RF power output. Alternatively, the biasing source 140 may generate a pulsed DC power output. The bias source 140 may also provide constant DC and/or RF power output.

In one embodiment, the bias source 140 is configured to provide RF power at a frequency of about 1 to about 10kHz with a duty cycle of about 10 to about 95 percent less than about 600W. In another embodiment, the bias source 140 is configured to provide RF power between about 20 and about 150 Watts at a frequency between about 2 to about 5kHz, with a duty cycle between about 80 to about 95 percent.

When installed as DPS^®In an embodiment of the reactor, the substrate support pedestal comprises an electrostatic chuck 160. The electrostatic chuck 160 includes at least one clamping electrode 132 and is controlled by a chuck power supply 166. In alternative embodiments, the substrate pedestal 124 may include a substrate retaining mechanism such as a susceptor clamp ring, a vacuum chuck, a mechanical chuck, or the like.

A gas panel 120 is coupled to the process chamber 100 to provide process and/or other gases into the interior of the chamber body 102. In the embodiment shown in FIG. 1, the gas panel 120 is coupled to one or more inlets 116 formed in the channel 118 of the sidewall 104 of the chamber body 102. However, the one or more inlets 116 may be located in other locations, such as on the ceiling 108 of the process chamber 100.

In one embodiment, the gas panel 120 is configured to provide fluorinated process gas through the inlet 116 into the interior of the chamber body 102. During processing, a plasma is formed from the process gases and is sustained by inductively coupled power from the plasma power source 112. The plasma may be selectively formed remotely or excited by other means. In one embodiment, the process gas provided by the gas panel 120 comprises at least one of a fluorinated gas and a carbon-containing gas. Examples of fluorinated and carbon-containing gases include trifluoromethane and carbon tetrafluoride. Other fluorinated gases may include one or more of a fluorinated dicarbon, a hexafluoro-tetracarbon, perfluoropropane, and octafluorocyclopentane.

The pressure in the process chamber 100 is controlled by a throttle valve 162 and a vacuum pump 164. The vacuum pump 164 and throttle valve 162 can maintain the chamber pressure in the range of about 1 to about 20 mtorr.

The temperature of the wall 104 can be controlled by a liquid-containing conduit (not shown) through the wall 104. The wall temperature is typically maintained at about 65 c. Typically, the chamber wall 104 is formed of a metal (e.g., aluminum, stainless steel, etc.) and is connected to an electrical ground 106. The process chamber 100 also includes conventional systems for process control, internal diagnostics, endpoint detection, and the like. Collectively, these systems are shown as support systems 154.

The mask adapter 182 is used to secure a substrate 122 (e.g., a reticle or other workpiece) to the substrate support pedestal 124. The mask adapter 182 generally has a lower portion 184 that is ground to cover the upper surface of the pedestal 124 (e.g., the electrostatic chuck 160) and an upper portion 186 that is shaped and sized to support the substrate 122. The opening 188 is generally located substantially centrally with respect to the base 124. The bonder 182 is typically formed from a single piece of material that is etch resistant and high temperature resistant, such as polyimide ceramic or quartz. Suitable mask adapters are disclosed in U.S. patent No. 6251217, published 2001, 26/1, and incorporated herein by reference. The edge ring 126 may cover and/or secure the adapter 182 to the base 124.

The lift mechanism 138 is configured to lower or raise the adapter 182 such that the substrate 122 may be placed on or off the substrate support pedestal 124. Generally, the lift mechanism 138 includes a plurality of lift pins (only one lift pin 130 is shown) that pass through respective guide holes 136.

In operation, the temperature of the substrate 122 is controlled by stabilizing the temperature of the substrate pedestal 124. In an embodiment, the substrate support pedestal 124 includes a heater 144 and may also include a heat sink 128. The heater 144 may be one or more fluid conduits having a heat exchange fluid flowing therein. In another embodiment, the heater 144 may include at least one heating element 134 regulated by a heat source power supply 168. Alternatively, a backside gas (e.g., helium (He)) from a gas source is passed through gas conduit 158 into channels formed in the pedestal surface beneath substrate 122. The backside gas facilitates heat exchange between the pedestal 124 and the substrate 122. During processing, the pedestal 124 may be heated to a steady state temperature using the embedded heater 144, which may facilitate uniform heating of the substrate 122 after combination with the helium back-end gas.

The controller 146 includes a Central Processing Unit (CPU)150, a memory 148, and support circuits 152 for the CPU 150, and facilitates control of the processing chamber 100 and the components of the etch process, as described in further detail below. The controller 146 may be any general purpose computer processor that may be used in an industrial setting to control various chambers and reprocessors. The memory 148 of the CPU 150 may be one or more readily accessible memory devices such as Random Access Memory (RAM), Read Only Memory (ROM), floppy disk, hard disk, or any other form of digital storage, whether local or remote. The support circuit 152 is coupled to the CPU 150 to support the processor. These circuits include access, power supplies, clock circuits, input/output circuits, auxiliary systems, and the like. The methods of the present invention are typically stored in a memory 148 or other computer readable medium accessible to the CPU 150 as a software routine. Alternatively, such software routines may also be stored and/or executed by a second CPU (not shown) that is remote from the hardware being controlled by CPU 150.

FIG. 2 is a flowchart illustrating a method 200 of etching a chrome layer according to an embodiment. Although the method 200 is described below with respect to a substrate for fabricating a mask, the method 200 may be used in other chrome etch applications.

The method 200, which may be stored in computer readable form in the memory 148 of the controller 146 or other storage medium, begins at step 202 where the substrate 122 having the film stack disposed thereon is disposed on the substrate pedestal 124. In one embodiment, the substrate 122 is supported in the opening 188 of the adapter 182. The film stack disposed on the substrate 122 depicted in FIG. 1 comprises an optically transmissive silicon-based material, such as quartz (i.e., silicon dioxide (Si 0)₂) Layer 192) having an opaque light-shielding chrome layer 190, a so-called mask material, formed as a patterned mask on the surface of the quartz layer 192. The chromium layer 190 may be chromium and/or chromium oxynitride. Membrane stackThe stack may also include an attenuating layer (not shown), such as molybdenum (Mo) doped silicon nitride (SiN) or molybdenum silicide (MoSi), between the quartz layer 192 and the chromium layer 190.

In step 204, a photoresist layer is patterned over the chrome layer. The photoresist layer may be patterned using any suitable method. The film stack may also be disposed in a process chamber having a patterned photoresist.

In step 206, a conformal protective layer is deposited on the patterned photoresist layer. The protective layer may be a polymer, for example a carbon polymer with hydrogen. The protective layer may be deposited to a thickness of between about 100 and about 500 angstroms, and in another embodiment, between about 150 and about 200 angstroms.

In embodiments, the protective layer may be deposited using a plasma formed from one or more fluorocarbon process gases, such as trifluoromethane and/or octafluorocyclobutane, among others. Alternatively, the plasma may contain argon gas which can improve the deposition uniformity. In one embodiment, the protective layer is deposited using a plasma power having a power between about 200 and about 500W and a bias power between about 0 and about 20W. In another embodiment, the bias power is less than about 10W. An example process gas used to form the protective layer in a plasma process may comprise about 100 seem of trifluoromethane and about 100 seem of argon and may be maintained at a chamber pressure of about 3 to about 20 mtorr for a period of time until the protective layer thickness reaches about 500 angstroms.

In step 208, the chrome layer is etched using the passivation layer and the photoresist as an etching mask. The chrome etch step 208 includes: first, the horizontal portion of the passivation layer disposed in the opening of the patterned photoresist is removed to expose some portions of the chrome layer. Because the rate of removing the vertical portions of the passivation layer disposed on the sidewalls of the patterned photoresist is very slow compared to the horizontal portions of the passivation layer, the chrome layer is etched and the passivation layer disposed on the sidewalls of the patterned photoresist substantially maintains the Critical Dimension (CD) of the opening, thereby allowing the mask CD to be accurately transferred to the opening formed in the chrome layer, which occurs in step 208.

In an exemplary etch step 208, a plasma formed from one or more fluorinated process gases is introduced into the process chamber 100 through the gas inlet 116. Examples of process gases may include carbon tetrafluoride and trifluoromethane. The process gas may further comprise an inert gas such as helium, argon, xenon, neon, and krypton.

In another embodiment, the chromium-containing substrate 122 may utilize Tetra I, Tetra II, or DPS^®II etch module and etch using carbon tetrafluoride at a flow rate of 2 to 50sccm and trifluoromethane at a flow rate of 10 to 50 sccm. Carbon tetrafluoride was provided at a flow rate of 9sccm and trifluoromethane was provided at a flow rate of 26sccm in a particular process recipe. The pressure in the process chamber is controlled to be less than about 40 mtorr, and in one embodiment, between about 1 and about 10 mtorr, such as 2 mtorr.

During the chrome etch step 208, a substrate bias power of less than about 600W is applied to the support pedestal 124 to bias the substrate 122; in a first embodiment, the bias power is less than about 100W, and in a second embodiment, the bias power is between about 30 and about 80W. In one particular process recipe, a bias power of about 65W is applied at a tunable pulse frequency of about 1 to about 10 kHz. Alternatively, the bias power may be in the form of pulses as described above.

In step 208, a plasma generated from the process gas is sustained by applying between about 300 and about 600 watts of RF power from the plasma source power 112 to the antenna 110. Although the plasma may be excited by other methods. In an embodiment, about 420W of RF power is applied to the antenna 110 at a frequency of about 13.56 MHz.

The chromium layer 190 exposed on the substrate 122 is etched until an endpoint is reached. The endpoint may be determined by time, optical interferometry, chamber gas emission spectroscopy, or other suitable methods. The etching step may be performed in situ in the processing system 170 or the process chamber 100 where the deposition step is also performed.

Another example of an etching process is described in U.S. patent application No. 10/235,223, filed on 9/4/2002, which is hereby incorporated by reference in its entirety. Other suitable metal etching processes may also be utilized.

In step 210, the photoresist and the protection layer remaining after the etch process 208 are removed. In one embodiment, an ashing process is used to remove the remaining photoresist and the passivation layer. The removal step 210 may be performed in situ in the processing system 170 or the process chamber 100, which also performs the etching step 208.

The advantages of the chrome etch process 200 over conventional etch processes include: the etch bias is reduced, thereby making the method 200 useful in etch applications that produce small critical dimensions. Furthermore, the chrome etch process 200 may more accurately transfer critical dimensions from the photoresist to openings formed in the chrome layer such that subsequent layers etched using the patterned chrome layer may exhibit well-transferred critical dimensions, and thus the process 200 may be used to fabricate masks with small line widths, such as 45 nm node applications.

FIGS. 3A-3G illustrate a film stack 300 fabricated in a quartz mask 340 using the method 200 described above_iExamples of (1). The subscript "i" is an integer representing various stages of fabrication in the film stack shown in fig. 3A-3G.

The film stack 300 depicted in FIG. 3A₁Including a quartz layer 302 having a chromium layer 304 disposed thereon. The chromium layer 304 is typically chromium and/or a chromium oxide layer as described above. Membrane stack 300₁An anti-reflective layer 306 (shown in a non-solid view) formed on the chrome layer 304 may be included. The anti-reflective layer 306 may be a thin layer of chromium oxide or other suitable material. Membrane stack 300₁Also included is a first photoresist layer 308 disposed on the chrome layer 304 or the anti-reflective layer 306, if present.

The first photoresist layer 308 is patterned and used as an etch mask for etching the chrome layer 304 to form features 320 exposing the underlying quartz layer 302, as inFIG. 3B shows a film stack 300₂。

A conformal protective layer 310 is deposited over the photoresist 308. The protective layer 310 covers the sidewalls of a feature 320 formed in the photoresist 308 and having a predetermined thickness to define a trench 310 having a width 316, which is the film stack 300 illustrated in FIG. 3C₃. The selected width 316 is a width having a predetermined critical dimension to be transferred to the chrome layer 304.

The chromium layer 304 may be etched using a plasma formed from a chlorine-containing gas (e.g., chlorine) or a fluorine-containing gas (e.g., sulfur hexafluoride or carbon tetrafluoride). The etching process is substantially anisotropic, thereby breaking through the passivation layer at the bottom of the trench 314 to expose and further etch the chrome layer without significantly changing the width 316.

As such, the critical dimension 316 is transferred to the opening 318 formed in the chrome layer 304, as in the film stack 300 shown in FIG. 3D₄。

After the openings 318 are formed in the chrome layer 304, the first photoresist layer 308 remaining may be removed, for example, by an ashing process, to produce the film stack 300₅As shown in fig. 3E. The removal process of the photoresist layer 38 may additionally remove the remaining protection layer 310 leaving the binary mask 340.

Alternatively, the film stack 300₅May be further processed to form a phase shift mask as shown in fig. 3F-3I. To form the phase shift mask, a second photoresist layer 324 is first deposited on the film stack 300₅And fills the opening 318 to form the film stack 300 as shown in fig. 3F₆. The second photoresist layer 324 is then patterned. Typically, when forming a quartz phase shift mask, the patterned second photoresist layer 324 exposes the quartz layer 302 at the bottom of the alternating openings 318, as in the film stack 300 of FIG. 3G₇。

The quartz layer 302 exposed by the patterned second layer of photoresist 324 may be etched using a plasma formed from one or more fluorinated process gases. Examples of process gases may include carbon tetrafluoride and trifluoromethane. The process gas may further comprise an inert gas such as helium, argon, xenon, neon, and krypton. During the etching of the quartz layer 302, the bias power applied to the substrate support may be in the form of pulses as described above.

The end point of the etch is selected such that the film stack 300 shown in FIG. 3H is depicted₈The depth 328 of the etched quartz trench 326 is approximately equal to the 180 degree phase shift length of a predetermined wavelength of light through the quartz layer 302, which is used in the quartz phase shift mask. Typically 193 and 124 nm. Thus, the depth 328 is typically about 172 or 240 nm, although other masks for different lithographic wavelengths may have other depths. After the quartz trench 326 is etched, the remaining second photoresist layer 324 is removed by ashing, leaving the film stack 300₉The quartz phase shift mask 330 is formed as shown in FIG. 3I.

FIGS. 4A-4G illustrate a film stack 400 fabricated in a quartz phase shift mask 418 using the method 200 described above_iExamples of (1). The subscript "i" is an integer representing various stages of fabrication in the film stack shown in fig. 4A-4G.

The film stack 400 depicted in FIG. 4A₁Including a quartz layer 404 having a chromium layer 402 disposed thereon. The chromium layer 404 is typically chromium and/or a chromium oxide layer as described above. Film stack 400₁An anti-reflective layer 406 (optional) (shown in a non-solid figure) formed over the chrome layer 404 may be included. Film stack 400₁Also included is a first photoresist layer 408 disposed on the chrome layer 404 or the anti-reflective layer 406, when present. The first photoresist layer 408 is patterned to form an opening 430 exposing the chrome layer 404, such as the film stack 400 shown in FIG. 3B₂。

A conformal protective layer 432 is deposited over the chrome layer 404 and the first photoresist layer, covering the bottom and sidewalls of the opening 430, as in the film stack 400 shown in FIG. 4C₃. The deposition method of the protective layer 432 may be related to the deposition method of the protective layer 310 described above. The thickness of the protective layer 432 is selected so as to be constantA feature 434 defined between the vertical sidewalls of the protective layer 432 has a predetermined width 436.

The passivation layer 432 and the first photoresist layer 408 are used as a mask to etch the opening 410 in the chrome layer 404 to expose the underlying quartz layer 402, as shown in the film stack 400 of FIG. 4D₄. The etching process is substantially anisotropic, thereby breaking through the passivation layer 432 at the bottom of the feature 434 to expose and further etch the chrome layer 404 without significantly changing the width 436. Thus, the critical dimension defined by the feature 410 is transferred to the opening 438 formed in the chrome layer 404. The chrome layer 404 may be etched as described above. The protective layer 432 and the first photoresist layer 408 are removed, for example, by ashing or other suitable methods, such as the film stack 400 shown in FIG. 4E₅。

The chrome layer 404 serves as an etch mask to etch the quartz layer 402, as in the film stack 400 shown in FIG. 4F₆. The quartz layer 402 is etched in the manner described above to form a trench 404 having a bottom 416. The etching of the quartz layer 404 through the opening 438 substantially transfers the width 436 onto the trench 440.

The end point of the quartz etch is selected such that the depth 414 of the bottom 416 of the etched quartz trench 440 is approximately equal to the length of the 180 degree phase shift through the quartz layer 402 for a predetermined wavelength of light used in the quartz phase shift mask as described above.

After the trench 440 is formed on the quartz layer 402, a suitable process, such as the chromium etch process described above, may be utilized to remove the chromium layer 404 that is still present, leaving the film stack 400₇To become a quartz phase shift mask 442 as shown in FIG. 4G.

FIGS. 5A-5F illustrate a film stack 500 fabricated in a chromeless lithography mask 540 using the method 200 described above_iExamples of (1). The subscript "i" is an integer representing various stages of fabrication in the film stack shown in fig. 5A-5F.

The film stack 500 depicted in FIG. 5A₁Including having a mask layer 504 disposedA quartz layer 502 thereon. The mask layer 504 includes a chrome layer 552, such as chrome and/or the chrome oxides described above, disposed on the attenuating layer 552. The attenuating layer 554 generally has a length approximately equal to a 180 degree phase shift through the quartz layer 502 for a predetermined wavelength of light that may be used in a quartz phase shift mask. Typically 193 and 248 nanometers. Therefore, the attenuating layer is typically about 50 to about 100 nm thick, although other depths are suitable for masks that may be used at different lithographic wavelengths and/or with different thinner materials.

An optional anti-reflective layer 506 (shown in non-solid form) may be formed over the mask layer 504. The first photoresist layer 508 is disposed over the mask layer 504 or the anti-reflective layer 506, when present.

The first layer of photoresist 508 is patterned and used as an etch mask to etch the mask layer 504 to form features 520, thereby exposing the underlying quartz layer 502, as in the film stack 500 illustrated in FIG. 5B₂。

A conformal protective layer 510 is deposited over the photoresist 508. The protective layer 510 covers the sidewalls of a feature 520 formed in the photoresist 508 and having a predetermined thickness to define a trench 514 having a width 516, which is the film stack 500 illustrated in FIG. 5C₃. The selected width 516 has predetermined critical dimensions (e.g., the attenuating layer 554 and the chrome layer 552) to be transferred onto the mask layer 504.

The mask layer 504 may be etched in a two-step process, in which the chrome layer 552 is etched first, followed by the attenuating layer 554. The chromium layer 552 is etched using a plasma formed from a chlorine-containing gas (e.g., chlorine) or a fluorine-containing gas (e.g., sulfur hexafluoride or carbon tetrafluoride). The etching process is substantially anisotropic, thereby breaking through the bottom 512 of the passivation layer at the bottom of the trench 514 to expose and further etch the chrome layer without significantly changing the width 516.

The attenuating layer 554 may be etched using a plasma formed from a chlorine-containing gas (e.g., chlorine) and/or a fluorine-containing gas (e.g., sulfur hexafluoride or carbon tetrafluoride). The two steps are etchedThe etch process is substantially anisotropic, thereby breaking through the passivation layer at the bottom of the trench 514 to expose and further etch the chromium layer without significantly changing the width 516. The patterned chrome layer serves as a mask for etching the attenuating layer. Thus, a critical dimension, now defined as width 516, is transferred to an opening 518 formed in the mask layer 504, which is illustrated in the film stack 500 shown in FIG. 5D₄。

Attenuating layer 554 may be formed from a composition comprising (i) one or more fluorine-containing polymerizable materials; (ii) a chlorine-containing gas; or (iii) an inert gas, is etched. The process gas may also include a polymerization limiting or inhibiting gas.

The one or more fluorine containing gases may comprise one or more fluorine containing hydrocarbons, a hydrogen free fluorine containing gas, or a combination thereof. One or more of the fluorine-containing hydrocarbon compounds may have the general formula C_XH_YF_ZWherein x is the number of carbon atoms and is an integer of 1 to 5, y is the number of hydrogen atoms and is an integer of 1 to 8, and z is the number of fluorine atoms and is an integer of 1 to 8. Examples of fluorine-containing hydrocarbon gases include trifluoromethane, monofluoromethane, difluoromethane, pentafluoroethane, difluoroethane, and combinations thereof. A fluorocarbon-containing hydrocarbon gas having 1 to 2 carbon atoms, 1 to 4 hydrogen atoms, and 1 to 5 fluorine atoms, such as trifluoromethane, may be used to etch the attenuating layer 554.

The hydrogen-free fluorine-containing gas may have 1 to 5 carbon atoms and 4 to 8 fluorine atoms. Other non-hydrogen fluorocarbon gases may include carbon tetrafluoride, hexafluoroethane, tetracarbon hexafluoride, perfluoropropane, octafluorocyclobutane, octafluorocyclopentane, and combinations thereof. Alternatively, the process gas may comprise an additional process gas, such as fluorosulfide-sulfur hexafluoride (SF)₆)。

The fluorine-containing gas may advantageously be used to form a passivating polymer deposit that is deposited on the surfaces, particularly the sidewalls, of the openings formed in the patterned photoresist material and the etched optically transmissive material. The passivated polymer deposit may avoid over-etching of the features, thereby improving the critical dimensions transferred onto attenuating layer 554. The plasma generated from the one or more fluorine containing hydrocarbon gases generates fluorine containing species that can etch the attenuating layer 554 located on the substrate 122 without the presence of an oxidizing gas.

The chlorine-containing gas is composed of chlorine (Cl)₂) Carbon tetrachloride (CCl)₄) Hydrogen chloride (HCl) and combinations thereof and to provide highly reactive radicals to etch optically transparent materials. Chlorine-containing gases provide a source of free radicals for etch capability, and hydrogen or carbon-containing chlorine-containing gases provide a source of material for forming passivating polymer deposits that improve etch bias.

The process gas may also include an inert gas that, when dissociated as part of the plasma comprising the process gas, may generate sputtered species that increase the etch rate of the features. The presence of the inert gas as part of the plasma may also enhance dissociation of the process gases. In addition, the inert gas added to the process gas forms ionized sputter species and may further sputter away any polymer deposits on the sidewalls of the features just etched, thus reducing any passivation deposits and providing a controllable etch rate. We have observed that the addition of an inert gas to the process gas improves plasma stability and etch uniformity. Examples of the inert gas include argon (Ar), helium (He), neon (Ne), xenon (Xe), krypton (Kr), and combinations thereof, with argon and helium being more commonly used.

In one example, the process gas for etching the attenuating layer 554 may include chlorine, trifluoromethane, and argon, which is an inert gas. Alternatively, the process gas may comprise one or more polymerization-limiting gases, such as oxygen, ozone, nitrogen, or combinations thereof, which may be used to control the formation and removal of passivating polymer deposits on the substrate and thus the etch rate of the process gas. The oxygen-containing gas enhances the formation of oxygen-free species that can react with other species to reduce the formation of high molecules (i.e., passivation deposits) that deposit on the etched features.For example, oxygen and some radicals- -e.g., CF- -of plasma processes₂Reaction to form volatile radicals- -e.g. COF₂It can be exhausted from the process chamber.

The total flow rate of the process gases, including the inert gas and the selective gas, is introduced at a flow rate greater than about 15sccm, such as between about 15sccm and about 200sccm, to etch a 150 mm by 150 mm sized photolithographic mask substrate in an etch chamber. A chlorine-containing gas is introduced into the process chamber at a flow rate between about 5sccm and about 100sccm to etch a 150 mm by 150 mm photolithographic photomask substrate. When the fluorine-containing gas is introduced into the processing chamber, the flow rate is between about 1sccm and about 50sccm to etch a 150 mm x 150 mm photolithographic photomask substrate. When the inert gas is introduced into the processing chamber, the flow rate is between about 0sccm and about 100sccm to etch a 150 mm x 150 mm photolithographic photomask substrate. Optionally, the polymer confinement gas is introduced into the process chamber at a flow rate between about 1sccm and about 100sccm to etch a 150 mm by 150 mm photolithographic photomask substrate. The individual flow rates and the total flow rate of the process gases may vary depending on a number of process factors, such as the size of the process chamber, the size of the substrate to be processed, and the particular etch profile desired by the operator.

Generally, the process chamber is maintained at between about 2 mTorr and about 50 mTorr. The chamber pressure may be maintained between about 3 mtorr and about 20 mtorr, such as 3 mtorr and 10 mtorr, during the processing.

After the opening 518 is formed in the chrome layer 504, an ashing process, for example, may be used to remove the first photoresist layer 508 still present, thereby leaving the film stack 500₅As shown in fig. 5E. The removal process of the photoresist layer 508 may additionally remove the remaining protection layer 510.

The chrome portion (e.g., the patterned chrome layer 552) of the mask layer 504 may be removed using any suitable process, such as dry etching as described aboveAnd (6) manufacturing. From the film stack 500₆The remaining quartz layer 502 and patterned MoSi layer 554 form a chromeless lithography mask 540, as shown in fig. 5F.

Therefore, the present invention provides a method for etching a chromium layer, which can improve the characteristics of a trench. Thus, the methods of etching chromium layers disclosed herein facilitate the fabrication of features suitable for patterning with small critical dimensions.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic spirit and scope thereof, and the scope thereof is determined by the claims that follow.

Claims (30)

1. A method of etching a chromium layer, comprising:

providing a film stack in a process chamber, wherein the film stack is provided with a chromium layer and a photoresist layer with patterns;

depositing a conformal protective layer on the patterned photoresist layer;

etching the conformal passivation layer to expose the chrome layer through the patterned photoresist layer; and

the chromium layer is etched.

2. The method of claim 1, wherein the depositing comprises:

a polymer is deposited to a thickness of between about 100 and about 500 angstroms.

3. The method of claim 2, wherein the polymer is a hydrogen-containing carbon polymer.

4. The method of claim 1, wherein the depositing further comprises:

a plasma is formed from one or more fluorocarbon process gases.

5. The method of claim 4, wherein the one or more fluorocarbon process gases is at least one of trifluoromethane or octafluorocyclobutane.

6. The method of claim 4, wherein the depositing step further comprises:

argon gas was introduced into the plasma.

7. The method of claim 1, wherein the depositing comprises:

a bias power of between about 0 and about 20 watts is applied.

8. The method of claim 1, wherein the depositing comprises:

a bias power of less than about 10 watts is applied.

9. The method of claim 7, wherein the depositing step further comprises:

introducing about 100sccm of trifluoromethane into the process chamber;

introducing about 100sccm of argon into the process chamber;

forming a plasma from the trifluoromethane and argon; and

a chamber pressure is maintained at about 3 to about 20 mtorr.

10. The method of claim 7, wherein the depositing step further comprises:

a carbon polymer is deposited to a thickness of between about 150 to about 200 angstroms.

11. The method of claim 1, wherein the etching step further comprises:

a pulsed bias power is applied.

12. The method of claim 2, wherein said depositing and said etching steps are performed in-situ in said process chamber.

13. A method of forming a mask, comprising:

patterning a mask layer on a mask layer, the mask layer comprising at least one chromium layer;

depositing a conformal passivation layer on the mask layer;

etching the chromium layer through a mask layer having the protective layer disposed thereon to expose an underlying layer; and

removing the mask layer and the passivation layer.

14. The method of claim 13, wherein the depositing comprises:

a polymer is deposited to a thickness of between about 100 and about 500 angstroms.

15. The method of claim 14, wherein the polymer is a carbon polymer having hydrogen.

16. The method of claim 13, wherein the depositing step further comprises:

a plasma is formed from at least one of trifluoromethane or octafluorocyclobutane.

17. The method of claim 16, wherein the depositing step further comprises:

argon gas was introduced into the plasma.

18. The method of claim 13, wherein the depositing comprises:

a bias power of between about 0 and about 20 watts is applied.

19. The method of claim 13, wherein the etching the chrome layer further comprises:

providing at least one fluorocarbon process gas into a process chamber; and

a plurality of power pulses of less than 600 watts is used to bias the mask layer on a substrate support in the processing chamber.

20. The method of claim 13, wherein the removing the mask layer and the protective layer is performed in situ in the process chamber, wherein the etching the chrome layer is performed simultaneously.

21. The method of claim 13, wherein the removing steps of the mask layer and the protection layer are performed in situ in the processing system having a process chamber coupled thereto.

22. The method of claim 13, further comprising:

an attenuating layer (attenuating layer) is etched using the patterned chrome layer.

23. The method of claim 22, wherein the attenuating layer comprises molybdenum.

24. The method of claim 22, further comprising:

removing the patterned chrome layer.

25. The method of claim 13, further comprising:

forming a patterned photoresist layer on the patterned chromium layer, wherein at least one first opening in the chromium layer is filled with the photoresist, and at least one second opening in the chromium layer is opened through the patterned photoresist;

etching the quartz layer through the second opening; and

removing the patterned photoresist layer.

26. A photomask formed by a method comprising:

patterning a photoresist layer on a film stack, the film stack having a chromium-containing layer;

depositing a corner protection layer on the patterned photoresist layer by using a bias voltage of less than 20W;

etching the chromium-containing layer by using the patterned photoresist layer and the protective layer as an etching mask; and

the etch mask is removed.

27. The mask of claim 26, wherein the depositing comprises:

a polymer is deposited to a thickness of between about 100 and about 500 angstroms.

28. The mask of claim 26, wherein the film stack further comprises:

a molybdenum layer patterned using the patterned chromium-containing layer as an etching mask; and wherein

At least a portion of the patterned chromium-containing layer is removed.

29. The mask of claim 26, further comprising:

a plurality of etched features in the quartz layer.

30. The mask of claim 29, wherein the etched feature in the quartz layer is formed by a process comprising:

forming a second patterned photoresist layer on the patterned chromium-containing layer, wherein at least one first opening in the chromium-containing layer is filled with the photoresist, and at least one second opening in the chromium-containing layer is opened through the second patterned photoresist;

etching the quartz layer through the second opening; and

removing the second patterned photoresist layer.