Dry ashing by secondary excitation

An ashing process and device forms radicals of an ashing gas through a secondary reaction. A plasma is generated from a first gas, which is diffused through a first gas distribution plate (GDP). The plasma is diffused through a second GDP and a second gas is supplied below the second GDP. The first gas reacts with the second gas to energize the second gas. The energized second gas is used in ashing a resist layer from a substrate.

BACKGROUND

With the increasing down-scaling of semiconductor devices, various processing techniques (e.g., photolithography) are adapted to allow for the manufacture of devices with increasingly smaller dimensions. For example, as the density of gates increases, the manufacturing processes of various features in the device (e.g., overlying interconnect features) are adapted to be compatible with the down-scaling of device features as a whole. Oxygen plasma etching (or ashing) can be used for removal of resist materials used in a photolithography process, however, such processes may undesirably erode underlying structures.

DETAILED DESCRIPTION

The fabrication of various solid state devices uses planar substrates, such as semiconductor wafers, on which integrated circuits are fabricated. Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include patterning of the semiconductor wafer or depositing and patterning various layers on the semiconductor wafer. Patterning of these elements is performed by formation of a photoresist or other masking layers, patterning the photoresist or other masking layers by using standard lithographic or photolithographic techniques, and etching the underlying material exposed by the pattern, thereby etching the underlying wafer or layers in the pattern of the masked pattern on the substrate. The mask is then removed or stripped from the substrate to expose the top surface of the patterned layer.

Embodiments provide a stripping device and method which strips a resist layer through an ashing process using an etching or ashing gas which is excited through a secondary reaction. The resist layer, for example, may be a photoresist or bottom anti-reflective coating (B ARC) layer which is stripped after a photolithography process. Embodiments are able to strip the resist layer with reduced damage or no damage to the underlying structures in the process. Resist layers may be stripped by a dry ashing process where the layer is decomposed, for example by oxidation or similar process, in a stripping or etching chamber. Even though an ashing gas may be selective to the material of the resist layer to generally exclude exposed materials underlying the resist layer, high-energy radicals of the ashing gas may cause decomposition of underlying structures. Embodiments use a secondary reaction to excite the ashing gas, thereby reducing or preventing high energy radicals of the ashing gas from forming. As such, the underlying structures are eroded less or not at all when the resist layer is stripped.

In a typical ashing process, for example, a wafer may be subjected to a high density plasma source and gas to deliver radicals for ashing. However, the process of producing the high density plasma in the presence of an ashing gas produces ions, ultraviolet (UV) radiation, low energy radicals, and high energy radicals which may undesirably attack the underlying substrate or layers, thereby causing material loss of these layers. Material loss is undesirable because it may affect yield of valid devices from the wafer. Moreover material loss may be better or worse in different areas of the wafer, for which compensation may be difficult, and for which differences in material loss across the wafer may be magnified as subsequent layers are applied and patterned.

Another problem with material loss may occur when a resist layer may need to be reworked prior to etching the underlying layers. For example, a resist layer may be patterned and then the pattern analyzed for pattern accuracy or defects. If the resist layer needs to be removed and reworked, the removal process may cause undesirable premature patterning due to material loss in the underlying layers.

Because embodiments use an ashing gas which is excited to form radicals of the ashing gas through a secondary reaction, high energy radicals of the ashing gas are not formed. As such, because primarily only lower energy radicals of the ashing gas are formed, the underlying layers below the resist are not eroded when the resist layer is stripped by the ashing process.

After patterning a target layer and removing the pattern mask by ashing, subsequent processing steps are then performed, including depositing and patterning subsequent layers and so forth. This process is used to cumulatively apply multiple electrically conductive layers and insulating layers on the wafer and pattern the layers to form circuits. The final yield of functional circuits on the wafer depends on proper application of each layer during the process steps.

FIG. 1illustrates an ashing chamber10in accordance with some embodiments. Chamber10includes an upper area20where plasma is generated in plasma region22. A gas (referred to as Gas A) is supplied by gas supply12through a gas line14and out one or more gas supply nozzles16into the upper area20. A plasma is created in the chamber by a plasma source18which produces a plasma of Gas A. Gas A may include an inert non-ashing gas having multiple excitation states, such as argon (Ar), helium (He), krypton (Kr), xenon (Xe), or radon (Rn), other gases having multiple excitation states, such as nitrogen molecules (N2), or combinations thereof.

Chamber10also includes a middle area40. The upper area20and middle area40are separated by a gas distribution plate (GDP)30. GDP30is retained in a holder32and has multiple through-holes34from top to bottom to provide plasma products produced in the plasma region22to a low ion region42in the middle area40. GDP30is described in greater detail below. GDP30functions to distribute plasma products according to the placement of through-holes34. The sizes and disposition of through-holes34are selected to distribute plasma products to the low ion region42, according to a desired distribution. Ions are not desired. As such, GDP30is grounded and will neutralize some of the ions as they strike GDP30. GDP30may also absorb or neutralize some of the energy of the radicals and reduce UV radiation passing to the middle area40. Through-holes34of GDP30allow radicals and may allow some of the plasma, ions, and UV radiation to pass through through-holes34into low ion region42. In some embodiments, about 10% to 30% of the radicals, plasma, ions, and UV radiation will pass through to low ion region42, depending on the design of GDP30. In some embodiments less than 10% or more than 30% of the plasma, ions, and UV radiation may pass through to low ion region42. As such, GDP30reduces the number of ions and UV radiation in low ion region42.

Chamber10also includes a lower area70. The middle area40and lower area70are separated by another GDP, GDP50. GDP50is retained in a GDP holder52and has multiple through-holes54from top to bottom to distribute radicals from the low ion region42to a substrate processing region72. GDP50also has multiple small holes56interspersed throughout the bottom of GDP50. Holes56distribute a second gas (referred to as Gas B) to the substrate processing region72. GDP50is described in greater detail below in conjunction withFIGS. 4 through 11b.

The distance d1is the distance between GDP30and GDP50, and is also understood as being the height of the middle area40. The distance d1may be configurable by moving GDP30or GDP50up or down in chamber10prior to processing. In some embodiments, distance d1may be between about 2 cm and 6 cm, such as about 4 cm. Other distances may be used. The distance d1may be selected depending on the composition chosen for Gas A and Gas B.

In some embodiments, through-holes34of GDP30and through-holes54of GDP50may be aligned, while in other embodiments, GDP50may be placed without regard to GDP30, so that the through-holes34may or may not be are aligned to or overlapping with through-holes54.

Gas B is provided by a gas source60by a gas line62. Gas B enters through side channels in GDP50, which are routed to holes56. In some embodiments, GDP holder52may incorporate a gas channel64which provides Gas B to the side channels of GDP50. In some embodiments, Gas B may be routed directly to GDP50, which may have channels and to distribute Gas B to holes56. Gas B may include any suitable ashing gas different from Gas A, such as oxygen (O2), nitrogen (N2), hydrogen (H2), nitrogen trifluoride (NF3), tetrafluoromethane (CF4), another fluorocarbon, a hydrofluorocarbon (CxHyFz), or combinations thereof.

GDP50functions to distribute plasma products from the low ion region42according to the placement of through-holes54. GDP50is grounded and will neutralize some of the ions as they strike GDP50. GDP50may also absorb some of the energy of the radicals and UV radiation passing to the lower area70. Through-holes54of GDP50allow radicals and may allow some of the plasma, ions, and UV radiation to pass through through-holes54into substrate processing region72. In some embodiments, about 10% to 20% of the radicals, plasma, ions, and UV radiation from low ion region42will pass through to substrate processing region72, depending on the design of GDP50and alignment of through-holes54of GDP50to through-holes34of GDP30. In some embodiments, more than 20% or less than about 10% of the ions and UV radiation from low ion region42will pass through to substrate processing region72. As such, GDP50further reduces the number of ions and UV radiation in substrate processing region72.

In operation of chamber10, Gas B enters substrate processing region72in an unenergized state and collides with energized radicals of Gas A entering substrate processing region72from low ion region42. Gas B species are therefore indirectly energized by way of the Gas A radicals. This process is described in greater detail below in conjunction withFIG. 12.

Still referring toFIG. 1, at the bottom of lower area70is a pedestal80which retains a substrate90. In some embodiments pedestal80is movable by arm82, which may move the substrate up or down. Pedestal80is housed within chamber side members84. In some embodiments, pedestal80may include temperature control features to heat or cool the pedestal. In some embodiments, pedestal80may be maintained between about 100° C. to about 300° C., such as about 250° C., during processing. Other temperatures may be used as appropriate. The distance d2is the distance between pedestal80and GDP50and may be changed by moving pedestal80up or down. In some embodiments, distance d2may be between about 2 cm and 10 cm, such as about 6 cm. Other distances may be used. Moving pedestal80closer to GDP50will provide faster, more aggressive ashing, while moving pedestal80further from GDP50will provide slower, less aggressive ashing. In some embodiments, chamber10may be configured to move the pedestal80during processing, for example, so that substrate90is closer to GDP50at the start of processing and moves away from GDP50during processing.

Chamber10may include additional components necessary for operation, such as an exhaust, vacuum pump, inductors, coils, and so forth which would be understood by a person of ordinary skill in the art.

FIGS. 2athrough 3cillustrate various embodiments and views of GDP30, in accordance with some embodiments. GDP30may be comprised of any suitable material. In some embodiments, GDP30is comprised of a conductive material, such as aluminum, and has a thickness between about 5 mm and 20 mm, such as about 6.4 mm. Other thicknesses may be used. In some embodiments, GDP30may have a circular shape in top-down view and have a diameter between about 280 mm and 320 mm, such as about 300 mm. Other shapes and dimensions may be used for GDP30.

FIG. 2aillustrates a cross-section of GDP30where through-holes34of GDP30are dispersed in a regular pattern and have a standard size. The cross-section ofFIG. 2acan be taken along a line A-A, for example, inFIG. 3a. The pitch p1between holes may be between about 5 mm and 30 mm, such as about 10 mm. Other values for the pitch p1may be used. The value of pitch p1may vary depending on the cross-section taken. The width w1of each hole may be between about 1 mm and about 10 mm, such as about 3 mm. Other widths of the through-holes may be used. Although through-holes34are illustrated as being cylindrical, in some embodiments, through-holes34may be funnel shaped, such as illustrated below with respect to through-holes54ofFIG. 8. Through-holes34, such as discussed below with respect toFIGS. 2band 2c, may also be funnel shaped in some embodiments.

FIG. 3aillustrates a top-down view of GDP30, in accordance with some embodiments. As illustrated inFIG. 3a, a pattern of through-holes34is shown. Other patterns may be used, such as circular patterns.

FIG. 2billustrates a cross-section of GDP30where through-holes34of GDP30are dispersed in a combination of patterns of through-holes34having multiple sizes. The cross-section ofFIG. 2bcan be taken along a line B-B, for example, inFIG. 3b. The pitch p2between a through-hole34aof one pattern to a through-hole34bof another pattern may be between about 3 mm and 15 mm, such as about 10 mm. The pitch p3between a through-hole34bto a through-hole34amay be between about 15 mm and 80 mm, such as about 40 mm. Other values for pitch p2and pitch p3may be used. The value of pitch p2and the value of pitch p3may vary depending on the cross-section taken. The width w2of each through-hole34ain a first pattern may be between about 1 mm and about 10 mm, such as about 3 mm. The width w3of each through-hole34bin a second pattern may be between about 1 mm and about 10 mm, such as about 3 mm. Other widths of the through-holes may be used. In some embodiments, additional patterns of through-holes34may be used on conjunction with the patterns of through-holes34aand through-holes34b. In some embodiments, some patterns may be used in certain parts of GDP30, while in other parts of GDP30, other patterns may be used. For example, a pattern or set of patterns of through-holes34toward the outer edge of GDP30may be different from the pattern or set of patterns of through-holes34used toward the inner portion of GDP30

FIG. 3billustrates a top-down view of GDP30ofFIG. 2b, in accordance with some embodiments. As illustrated inFIG. 3b, a pattern of through-holes34ais shown and another pattern of through-holes34bis shown as being interspersed with the pattern of through-holes34a. Other patterns may be used, such as circular patterns.

FIG. 2cillustrates a cross-section of GDP30where through-holes34of GDP30are dispersed randomly. Through-holes34may also have multiple sizes or the same size. The cross-section ofFIG. 2ccan be taken along a line C-C, for example, inFIG. 3c. The pitch p4between one through-hole34to another, for example, through-hole34cto34b, may be between about 3 mm and 15 mm, such as about 10 mm. The pitches between through-holes34will range from one hole to another due to the random distribution of through-holes34. In some embodiments, multiple sizes of through-holes34may have different widths. For example, the width w4aof a small sized through-hole34amay be between about 1 mm and about 10 mm, such as about 3 mm. The width w4bof a medium sized through-hole34bmay be between about 1 mm and about 10 mm, such as about 4 mm. The width w4cof a large sized through-hole34cmay be between about 1 mm and about 10 mm, such as about 5 mm. Other widths may be used for the through-holes34.

FIG. 3cillustrates a top-down view of GDP30ofFIG. 2c, in accordance with some embodiments. As illustrated inFIG. 3c, a random distribution of through-holes34is shown in various sizes, including small sized through-hole34a, medium sized through-hole34b, and large sized through-hole34c. More or fewer different sizes may be used for through-holes34. For example, in some embodiments, all of small sized through-holes34aare the same width, all of medium sized through-holes34bare the same width, and all of large sized through-holes34care the same width. In some embodiments, each of the small sized through-holes34amay have varying widths within a range, each of the medium sized through-holes34bmay have varying widths within another range, and each of the large sized through-holes34cmay have varying widths within yet another range. In some embodiments, the sizes of all through-holes34may be the same.

In some embodiments, the GDP30may have through-holes34selected and distributed based on a combination of the through-holes34described above in conjunction withFIG. 2athrough 3c. Although the through-holes34are illustrated as being perpendicular to the top or bottom surface of GDP30, it should be understood that through-holes34may also not be perpendicular to the top or bottom surface of GDP30, in accordance with some embodiments.

FIGS. 4 through 9illustrate various embodiments and views of GDP50, in accordance with some embodiments. GDP50may be comprised of any suitable material. In some embodiments, GDP50is comprised of a conductive material, such as aluminum, and has a thickness between about 10 mm and 30 mm, such as about 15 mm. Other thicknesses may be used. In some embodiments, GDP50may have a circular shape in top-down view and have a diameter between about 280 mm and 320 mm, such as about 300 mm. Other shapes and dimensions may be used for GDP50.

FIG. 4is an illustration of a bottom-up view of GDP50, in accordance with some embodiments. In some embodiments, holes56may be distributed substantially uniformly on the bottom of GDP50. Through-holes54may be interspersed among holes56. It should be understood that, although the holes56and through-holes54are illustrated as being in a pattern, any suitable distribution of holes56and through-holes54may be used, including a distribution similar to the through-holes34, described above with respect toFIGS. 2athrough 3c. Distributions of through-holes54and holes56may be selected based on the composition of Gas A and composition of Gas B.

FIG. 5throughFIG. 8illustrate cross-sections ofFIG. 4, where the top of GDP50is oriented to the top of each figure.FIG. 5illustrates a cross-section ofFIG. 4taken along the line D-D, through-holes56. A channel58is oriented lengthwise above holes56and provides a route for Gas B to travel through to be distributed to each of holes56. Gas B will generally travel from the outside edges of GDP50toward the center of GDP50. The pitch p5between holes56may be between about 1 mm and 10 mm, such as about 2 mm. Other values for the pitch p5may be used. The value of pitch p6may vary depending on the cross-section taken. The width w5of each of holes56may be between about 0.1 mm and about 1 mm, such as about 0.2 mm. Other widths of holes56may be used. The height h5of channel58may be between about 0.5 mm and about 1 mm, such as about 0.6 mm. Other heights of channel58may be used.

FIG. 6illustrates a cross-section ofFIG. 4taken along the line E-E, through through-holes54, in accordance with some embodiments. The pitch p6between through-holes54may be between about 5 mm and 30 mm, such as about 10 mm. Other values for the pitch p6may be used. The value of pitch p6may vary depending on the cross-section taken. The width w6of each of through-holes54may be between about 1 mm and about 10 mm, such as about 3 mm. Other values for the widths w6of through-holes54may be used.

FIG. 7illustrates a combined view of the cross-section ofFIG. 5and the cross-section ofFIG. 6, in accordance with some embodiments, with the cross-section ofFIG. 5shown in dashed lines.

FIG. 8illustrates a cross-section ofFIG. 4taken along the line E-E, through through-holes54, in accordance with some embodiments.FIG. 8illustrates that through-holes54may be funnel shaped. The pitch p7at the top of through-holes54may be between about 5 mm and 30 mm, such as about 10 mm. Other values for the pitch p7may be used. The value of pitch p7may vary depending on the cross-section taken. The width w7tat the top of each of through-holes54may be between about 1 mm and about 10 mm, such as about 3 mm. The width w7bat the bottom of each of through-holes54may be between about 0.25 mm and about 2.5 mm, such as about 0.75 mm. Other values for the width w7tand width w7bof through-holes54may be used. Although the through-holes54are illustrated as being perpendicular to the top or bottom surface of GDP50(for example, inFIGS. 5 through 7), it should be understood that through-holes54may also not be perpendicular to the top or bottom surface of GDP50, in accordance with some embodiments.

FIG. 9is an illustration of a top-down view of GDP50, in accordance with some embodiments. Through-holes54are illustrated. Channels58are shown in phantom by dashed lines. Although channels58are illustrated as extending from one side of GDP50to the other in parallel lines, it should be understood that other arrangements of channels58may be used. In some embodiments, for example, channels58may have a grid pattern. In some embodiments, channels58of GDP50may interface with gas channels64of GDP holder52.

FIG. 10illustrates a top down view of GDP holder52, in accordance with some embodiments. In some embodiments, GDP holder52may have an integrated gas channel64(shown in phantom by dashed lines). Gas channel64may be provided to supply gas (i.e., Gas B) to the edges of GDP50to channels58of GDP50. A gas channel feed66may be provided to supply gas to gas channel64. In some embodiments, gas channel64may be omitted and gas channel feed66may be provided to supply gas directly to channel feed59a(seeFIGS. 11aand 11b). In some embodiments, multiple gas channel feeds66may be provided around the periphery of GDP holder52.

FIGS. 11aand 11billustrate views of GDP50, in accordance with some embodiments. In some embodiments, channels58are enclosed on the edges of GDP50and GDP50has an integrated channel feed59which may interface with gas channel feed66to provide gas to channels58and, in turn, to holes56. As illustrated inFIG. 11a, in some embodiments, an inlet for channel feed59amay be located in line with channel58and gas may be provided to channel feed59aby gas channel feed66in GDP holder52(seeFIG. 10). In some embodiments, an inlet for channel feed59bmay be located in other areas of GDP50. In some embodiments, the inlet for channel feed59bmay be coupled directly to a gas feed and not provided through GDP holder52.

Turning now toFIG. 12,FIG. 12illustrates a close-up view of the secondary excitation of Gas B, in accordance with some embodiments. Gas A is directly excited by the energization from generating a plasma of Gas A. The energy of Gas A is reduced through GDP30(not shown) into low ion region42. Radicals of Gas A, illustrated as A*, are in low ion region42. The energy of Gas A is further reduced through GDP50into substrate processing region72. As illustrated inFIG. 12, Gas B enters substrate processing region72in an unenergized state from holes56. Energized radicals of Gas A entering substrate processing region72from low ion region42through through-holes54collide with Gas B molecules near the bottom of GDP50. During this collision, energized radicals of Gas A transfer their energy to Gas B in a Penning Ionization to create radicals of Gas B. The Penning Ionization can be described by the following chain reaction.
A*+B→B++e−+A(eq.1)
B++e−+A+B→B*+A(eq.2)

In the reaction, radicals of Gas A (A*) collide with neutral molecules of Gas B (B), thereby forming cations of Gas B (B+), free electrons (e−), and neutral Gas A molecules (A), represented by equation 1 (eq. 1). Then in a further spontaneous reaction represented by equation 2 (eq. 2), the cations of Gas B (Bk) combine with neutral molecules of Gas B (B) and free electrons (e−) to form radicals of Gas B (B*). Because the excitation state of Gas A is higher than the excitation state of Gas B, radicals of Gas B (B*) form, while Gas A remains as neutral molecules (A). Moreover, the radicals of Gas B cannot have a higher excitation state than the radicals of Gas A. Therefore, high energy radicals (e.g., having an energy greater than or equal to 10 eV) of Gas B are prevented from being formed, and only lower energy radicals (e.g., having an energy less than or equal to about 5 eV) of Gas B are formed. In addition to radicals of Gas B, UV radiation and ions may also be generated.

Referring now toFIG. 13,FIG. 13illustrates a flow diagram of a method200of dry ashing by secondary excitation is illustrated, in accordance with some embodiments. At step210, a plasma is generated with a first gas, such as Gas A, in an ashing or etching chamber, such as chamber10ofFIG. 1. In some embodiments, Gas A may be a non-ashing or non-etching gas, such as an inert gas. In some embodiments, Gas A may be an ashing or etching gas having multiple excitation states, such as N2. Effluents of the generated plasma may include ions, radicals of species of Gas A in multiple excitation states, and UV radiation. At step220, effluents of the plasma of Gas A are diffused through a first grounded GDP, such as GDP30, thereby affecting the effluents of the plasma of Gas A. For example, the number of ions and amount of UV radiation will be reduced after diffusion through the first GDP, such as described above with respect toFIG. 1. Radicals of Gas A in multiple excitation states also diffuse through the first GDP, which may reduce the energy level of the radicals of Gas A and which may neutralize some of the radicals.

At step230, the remaining effluents of the plasma of Gas A diffuse through a second GDP, such as GDP50, thereby further affecting of the remaining effluents of the plasma of Gas A. UV radiation and ions of Gas A may be drastically reduced with between about 1% and about 6% of the total effluents of the plasma of Gas A diffusing through the second GDP. Radicals of Gas A in multiple excitation states also diffuse through the second GDP, which may further reduce the energy level of the radicals of Gas A and which may further neutralize some of the radicals.

At step240, an unenergized species of a second gas, such as Gas B, is provided out of holes at the bottom of the second GDP. Radicals of Gas A diffusing through the second GDP collide with the unenergized Gas B species and a Penning Ionization causes the energy of the radicals of Gas A to transfer to the Gas B species, thereby forming radicals of the Gas B species. Gas B may include any suitable ashing or etching gas different from Gas A, such as oxygen (O2), nitrogen (N2), hydrogen (H2), nitrogen trifluoride (NF3), tetrafluoromethane (CF4), another fluorocarbon, a hydrofluorocarbon (CxHyFz), or combinations thereof. Other suitable ashing or etching gases may be used. Because radicals of Gas B are formed in a secondary reaction, the radicals have a lower energy than if the plasma had been created with Gas B directly, and the energy levels of the radicals are limited by the energy levels of the radicals of Gas A. As such, primarily only lower energy radicals of Gas B are formed. In some embodiments, depending on the species of the selected gasses, some high energy radicals of Gas B may also be formed, however, the number of high energy radicals of Gas B formed is less than would be if the plasma was formed from Gas B directly.

At step250, a substrate, such as substrate90, is exposed to the radicals of Gas B. A resist material, such as a photoresist layer or BARC layer may be disposed on the substrate and the radicals of Gas B combine with the resist material to decompose the material. Optionally, the substrate may be moved closer to or further from the second GDP to control the intensity of the decomposition. Optionally, the temperature of the substrate may be controlled by heating/cooling elements in a pedestal on which the substrate is retained during the ashing process. In some embodiments, the substrate may be exposed to the radicals of Gas B for about 30 seconds to about 300 seconds. In some embodiments, the substrate may be exposed for less time than 30 seconds or more time than 300 seconds. Due to the highly selective ashing resulting from the secondary excitation of the ashing gas, Gas B, the substrate may be exposed to Gas B without regard to exposure time, without suffering unwanted decomposition of underlying materials.

Accordingly, the method200decomposes the resist layer in a selective manner, thereby ashing or etching the resist layer without damaging the underlying structures to prevent unwanted loss of materials of the underlying structures. While certain embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.

FIGS. 14 through 17illustrate cross-sectional views of intermediate stages of a photolithography technique used to in the formation of features in a target layer102on a semiconductor device100, in accordance with some embodiments. Although a description of the formation of mandrels124(seeFIG. 17) are described below, it should be understood that the techniques described below may be used to form other types of pattern layers.

The target layer102is a layer in which a plurality of patterns is to be formed in accordance with embodiments of the present disclosure. In some embodiments, semiconductor device100is processed as part of a larger wafer. In such embodiments, after various features of the semiconductor device100is formed (e.g., active devices, interconnect structures, and the like), a singulation process may be applied to scribe line regions of the wafer in order to separate individual semiconductor dies from the wafer (also referred to as singulation).

In some embodiments, the target layer102is an inter-metal dielectric (IMD) layer. In such embodiments, the target layer102comprises a low-k dielectric material having a dielectric constant (k value) lower than 3.8, lower than about 3.0, or lower than about 2.5, for example. In alternative embodiments, target layer102is an IMD layer comprising high-k dielectric material having a k value higher than 3.8. Openings may be patterned in the target layer102with the embodiment processes, and conductive lines and/or vias may be formed in the openings as described below.

In some embodiments, the target layer102is a semiconductor substrate. The semiconductor substrate may be formed of a semiconductor material such as silicon, silicon germanium, or the like. In some embodiments, the semiconductor substrate is a crystalline semiconductor substrate such as a crystalline silicon substrate, a crystalline silicon carbon substrate, a crystalline silicon germanium substrate, a III-V compound semiconductor substrate, or the like. The semiconductor substrate may be patterned with an embodiment process, and subsequent process steps may be used to form shallow trench isolation (STI) regions in the substrate. Semiconductor fins may protrude from between the formed STI regions. Source/drain regions may be formed in the semiconductor fins, and gate dielectric and electrode layers may be formed over channels regions of the fins, thereby forming semiconductor devices such as fin field effect transistors (finFETs).

In some embodiments, the target layer102is a conductive layer, such as, a metal layer or a polysilicon layer, which is blanket deposited. Embodiment patterning processes may be applied to the target layer102in order to pattern semiconductor gates and/or dummy gates of finFETS. By using embodiment processes to pattern a conductive target layer102, spacing between adjacent gates may be reduced and gate density may be increased.

InFIG. 14, a film stack including the target layer102is formed in semiconductor device100. In some embodiments, the target layer102may be formed over a semiconductor substrate104. The semiconductor substrate104may be formed of a semiconductor material such as silicon, doped or undoped, or an active layer of a semiconductor-on-insulator (SOI) substrate. The semiconductor substrate104may include other semiconductor materials, such as germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. Other substrates, such as multi-layered or gradient substrates, may also be used. Devices (not illustrated), such as transistors, diodes, capacitors, resistors, etc., may be formed in and/or on an active surface of semiconductor substrate104. In other embodiments where the target layer102is a semiconductor substrate used to form finFETs, the semiconductor substrate104may be omitted.

AlthoughFIG. 14illustrates target layer102being in physical contact with semiconductor substrate104, any number of intervening layers may be disposed between target layer102and semiconductor substrate104. Such intervening layers may include an inter-layer dielectric (ILD) layer comprising a low-k dielectric and having contact plugs formed therein, other IMD layers having conductive lines and/or vias formed therein, one or more intermediary layers (e.g., etch stop layers, adhesion layers, etc.), combinations thereof, and the like. For example, an optional etch stop layer (not illustrated) may be disposed directly under the target layer102. The etch stop layer and may act as a stop for an etching process subsequently performed on the target layer102. The material and process used to form the etch stop layer may depend on the material of the target layer102. In some embodiments, the etch stop layer may be formed of silicon nitride, SiON, SiCON, SiC, SiOC, SiCxNy, SiOx, other dielectrics, combinations thereof, or the like, and may be formed by plasma enhanced chemical vapor deposition (PECVD), low pressure CVD (LPCVD), physical vapor deposition (PVD), or the like.

The film stack further includes an anti-reflective coating (ARC)106formed over the target layer102. The ARC106aids in the exposure and focus of overlying photoresist layers (discussed below) during patterning of the photoresist layers. In some embodiments, the ARC106may be formed from SiON, silicon carbide, materials doped with oxygen (O) and nitrogen (N), or the like. In some embodiments, the ARC106is substantially free from nitrogen, and may be formed from an oxide. In such embodiments, the ARC106may be also referred to as a nitrogen-free ARC (NFARC). The ARC106may be formed by Plasma Enhance Chemical Vapor Deposition (PECVD), High-Density Plasma (HDP) deposition, or the like.

The film stack further includes a hard mask layer108formed over the ARC106and the target layer102. The hard mask layer108may be formed of a material that comprises a metal (e.g., titanium nitride, titanium, tantalum nitride, tantalum, a metal-doped carbide (e.g., tungsten carbide), or the like) and/or a metalloid (e.g., silicon nitride, boron nitride, silicon carbide, or the like), and may be formed by PVD, Radio Frequency PVD (RFPVD), Atomic Layer Deposition (ALD), or the like. In subsequent processing steps, a pattern is formed on the hard mask layer108using an embodiment patterning process. The hard mask layer108is then used as an etching mask for etching the target layer102, where the pattern of the hard mask layer108is transferred to the target layer102.

The film stack further includes a dielectric layer110formed over the hard mask layer108. The dielectric layer110may be formed from a silicon oxide, such as borophosphosilicate tetraethylortho silicate (BPTEOS) or undoped tetraethylorthosilicate (TEOS) oxide, and may be formed by CVD, ALD, spin-on coating, or the like. In some embodiments, the dielectric layer110acts as an etch stop layer for patterning subsequently formed mandrels and/or spacers (e.g., mandrels124, seeFIG. 17). In some embodiments, the dielectric layer110also acts as an anti-reflective coating.

The film stack further includes a mandrel layer112formed over the first dielectric hard mask layer108. Mandrel layer112may be formed of a semiconductor such as amorphous silicon, polysilicon, silicon nitride, silicon oxide, or another material that has a high etching selectivity with the underlying layer, e.g., with the dielectric layer110.

A tri-layer photoresist120is formed on the film stack over the mandrel layer112. The tri-layer photoresist120includes a bottom layer114, a middle layer116over the bottom layer114, and an upper layer118over the middle layer116. The bottom layer114and upper layer118may be formed of photoresists (e.g., photosensitive materials), which include organic materials. In some embodiments, the bottom layer114may also be a bottom anti-reflective coating (BARC) layer. The middle layer116may comprise an inorganic material, which may be a nitride (such as silicon nitride), an oxynitride (such as silicon oxynitride), an oxide (such as silicon oxide), or the like. The middle layer116has a high etching selectivity relative to the upper layer118and the bottom layer114. The various layers of the tri-layer photoresist120may be blanket deposited sequentially using, for example, spin-on processes. Although a tri-layer photoresist120is discussed herein, in other embodiments, the photoresist120may be a monolayer or a bilayer (e.g., comprising only the bottom layer114and the upper layer118without the middle layer116) photoresist. The type of photoresist used (e.g., monolayer, bilayer, or tri-layer) may depend on the photolithography process used to pattern the mandrel layer112. For example, in advanced extreme ultraviolet (EUV) lithography processes, a monolayer or bilayer photoresist120may be used.

In some embodiments, the upper layer118is patterned using a photolithographic process. The pattern of the upper layer118may be evaluated for accuracy. If the pattern of the upper layer118is determined to be faulty, the upper layer118may be removed by an ashing technique, such as the method200of ashing using an ashing or etching chamber such as chamber10, described above. The upper layer118of the tri-layer may be reapplied and re-patterned. In embodiments using a monolayer or bilayer photoresist, the topmost layer may be removed, reapplied, and re-patterned without damaging the underlying resist layers or underlying target layers.

Subsequently, when the upper layer118is evaluated as non-faulty, the upper layer118is used as an etching mask for patterning of the middle layer116(seeFIG. 15). The middle layer116is then used as an etching mask for patterning of the bottom layer114, and the bottom layer114is then used to pattern the mandrel layer112(seeFIGS. 16 and 17). It has been observed that by using a tri-layer photoresist (e.g., tri-layer photoresist120) to etch a target layer (e.g., mandrel layer112), improved definition in fine-pitched patterns can be achieved in the target layer (e.g., mandrel layer112).

The upper layer118is patterned using any suitable photolithography process to form openings122therein. As an example of patterning openings122in the upper layer118, a photomask (not shown) may be disposed over the upper layer118. The upper layer118may then be exposed to a radiation beam including an ultraviolet (UV) or an excimer laser such as a 248 nm beam from a Krypton Fluoride (KrF) excimer laser, a 193 nm beam from an Argon Fluoride (ArF) excimer laser, or a 157 nm beam from a F2excimer laser, or the like while the photomask masks areas of the upper layer118. Exposure of the top photoresist layer may be performed using an immersion lithography system to increase resolution and decrease the minimum achievable pitch. A bake or cure operation may be performed to harden the upper layer118, and a developer may be used to remove either the exposed or unexposed portions of the upper layer118depending on whether a positive or negative resist is used. The openings122may have strip shapes in a plan view (not illustrated). The pitch P14of the openings122may be the minimum pitch achievable using photolithographic processes alone. For example, in some embodiments, the pitch P14of the openings122is about 80 nm. Other pitches P14of the openings122are also contemplated.

After the patterning of the upper layer118, the pattern of the upper layer118is transferred to the middle layer116in an etching process. The etching process is anisotropic, so that the openings122in the upper layer118are extended through the middle layer116and have about the same sizes in the middle layer116as they do in the upper layer118. The resulting structure is illustrated inFIG. 15.

Optionally, a trimming process (not illustrated) may be performed to increase the size of the openings122in the middle layer116. In an embodiment, the trimming process is an anisotropic plasma etch process with process gases including O2, CO2, N2/H2, H2, the like, a combination thereof, or any other gases suitable for trimming the middle layer116. The trimming may increase the width W14of the openings122and decrease the width W15of the portions of the middle layer116between the openings122. The trimming process may be performed in order to achieve a desired ratio of the width W14to the width W15so that subsequently defined lines are uniformly spaced. In other embodiments, the middle layer116is initially patterned to have a desired ratio of the width W14to the width W15and the trimming process may be omitted.

InFIG. 16, an etching process is performed to transfer the pattern of the middle layer116to the bottom layer114, thereby extending the openings122through the bottom layer114. The etching process of the bottom layer114is anisotropic, so that the openings122in the middle layer116are extended through the bottom layer114and have about the same sizes in the middle layer116as they do in the bottom layer114. As part of etching the bottom layer114, the upper layer118(seeFIGS. 15 and 15) may be consumed.

InFIG. 17, the pattern of the bottom layer114(seeFIG. 16) is transferred to the mandrel layer112using an etching process. The etching process of the mandrel layer112is anisotropic, so that the openings122in the bottom layer114are extended through the mandrel layer112and have about the same sizes in the mandrel layer112as they do in the bottom layer114. Thus, mandrels124are defined from remaining portions of the mandrel layer112(e.g., portions of mandrel layer112between openings122). The mandrels124have a pitch P14(see alsoFIG. 14). In some embodiments, pitch P14is a minimum pitch achievable using photolithographic processes. During etching the mandrel layer112, the middle layer116is consumed, and bottom layer114may be at least partially consumed.

In embodiments when the bottom layer114is not completely consumed while etching the mandrel layer112, an ashing process, such as the ashing or etching method200described above, may be performed to remove remaining residue of the bottom layer114.

Embodiments provide an ashing process and device which forms radicals of an ashing gas through a secondary reaction, thereby preventing or reducing high energy radicals of an ashing gas. Whereas a typical ashing process to remove a resist layer may damage underlying layers of a resist layer by the presence of high energy radicals of an ashing gas, embodiments provide an ashing process in which an ashing gas is excited in a secondary reaction. Thus, high energy radicals of the ashing gas which may damage underlying structures are prevented from being formed.

One embodiment is a method, including generating a first plasma from a first gas. The first plasma is diffused, in a wafer processing chamber, through a first gas distribution plate (GDP), forming a first low energy region. The first plasma is diffused from the first low energy region through a second GDP, forming a substrate processing region. A second gas is supplied in the substrate processing region, where the first plasma energizes the second gas to form radicals of the second gas, where the radicals of the second gas strip a layer from a substrate.

Another embodiment is a method including generating a plasma from a first gas. The method also includes passing, in a wafer processing chamber, a first percentage of the plasma through a first gas distribution plate (GDP). The method further includes passing a second percentage of the first percentage of the plasma through a second GDP into a first area of the wafer processing chamber. A second gas is supplied to the first area of the wafer processing chamber, where radicals of the first gas from the second percentage collide with the second gas to energize the second gas. A wafer is exposed to the energized second gas.

Another embodiment is a chamber, including a plasma source generator, a first gas source, a first gas distribution plate (GDP), a second gas source, a second GDP, and a pedestal. The first GDP is disposed between the plasma source generator and the second GDP. The second GDP is disposed between the first GDP and the pedestal.