Metallization Method

Abstract

To provide a metallization method.SOLUTION: There is disclosed a metallization method, comprising: (a) forming an underlayer on a first surface of a substrate from an underlayer composition comprising: a first polymer comprising an acid-labile group, and a sensitizing group, wherein (i) the first polymer comprises the sensitizing group or (ii) a compound that is distinct from the first polymer comprises the sensitizing group; wherein the underlayer has a first thickness; (b) forming a photoresist layer on the underlayer from a photoresist composition comprising: a second polymer comprising an acid-labile group, and a photoacid generator; wherein the photoresist layer has a second thickness; (c) pattern-wise exposing the photoresist layer to activating radiation; and (d) developing the exposed photoresist layer with a basic developer.SELECTED DRAWING: Figure 1A-1C

Description

[Technical field]

[0001] The present disclosure relates to a patterning process for manufacturing semiconductors. In particular, the present disclosure relates to a patterning process for manufacturing semiconductors that prevents the occurrence of a tail profile in a photoresist pattern. [Background technology]

[0002] Mobile devices, devices that are part of the Internet of Things (IoT), and wearable electronics have been getting smaller, lighter, and thinner over the years, using larger amounts of memory and performing more and more computations despite their miniaturization.

[0003] The manufacturing and packaging of these electronic devices plays an important role in size reduction. For example, flip-chip packaging methods have been used to increase the density of I / O (input / output) connections between devices, especially for microprocessing units (MPUs) and dynamic random access memory (DRAM) semiconductor chips.

[0004] Metal pillar bumps, such as copper pillar bumps, are often used as flip-chip interconnects for use in electronics and optoelectronic packaging, such as flip-chip packaging of CPU and GPU integrated circuits (chips), laser diodes, and semiconductor optical amplifiers (SOAs). Metal pillar bumps provide beneficial connection resistance, high density connection, metal migration resistance, and heat dissipation properties. Metal line patterns can also be used, for example, in redistribution layers (RDLs) to provide electrical connections between two components.

[0005] Electroplating is used to manufacture metal pillar bump arrays and line patterns. After coating a photoresist layer on the copper film surface, a mask pattern is made using photolithography. Then, in the open areas of the mask pattern, metal structures are formed on the metal surface by electroplating. Then, the photoresist is removed, and the metal layer previously covered by the resist is removed by etching.

[0006] One approach for preparing plating mask patterns is the use of thick photoresist layers to address the need for thicker and narrower pattern sizes for further increases in I / O and device density. Chemically amplified photoresists may be a suitable option to achieve faster sensitivity and improved transparency desired for higher resolution patterns. Such resist compositions include a polymer with acid labile groups, a photoacid generator (PAG) and a solvent. However, when chemically amplified resists are formed on metal layers such as copper layers, tailing profile problems have been observed due to loss of photoacid present at the interface between the metal surface and the resist. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 6,057,083 [Patent Document 2] U.S. Patent No. 6,136,501 [Patent Document 3] U.S. Patent No. 8,206,886 [Patent Document 4] European Patent Application Publication No. 01008913A1 [Patent Document 5] European Patent Application Publication No. 00930542A1 [Patent Document 6] US Patent Application Publication No. 2012 / 0064456A1 [Patent Document 7] U.S. Patent No. 6,042,997 [Patent Document 8] U.S. Pat. No. 5,492,793 [Patent Document 9] U.S. Pat. No. 5,929,176 [Patent Document 10] U.S. Patent No. 6,090,526 [Patent Document 11] U.S. Patent No. 6,692,888 [Patent Document 12] U.S. Patent No. 6,680,159 [Patent Document 13] U.S. Pat. No. 5,843,624 [Patent Document 14] U.S. Patent No. 6,048,664 [Patent Document 15] U.S. Patent No. 6,048,662 [Patent Document 16] International Publication No. 0186353A1 Brochure [Patent Document 17] U.S. Patent No. 6,306,554 [Patent Document 18] U.S. Patent No. 7,244,542 [Patent Document 19] US Patent Application Publication No. 20110003250A Summary of the Invention [Problem to be solved by the invention]

[0008] The footing of the resist pattern results in an undercut profile of the plating pattern, which can promote the collapse of the plating pattern during downstream processing. Therefore, it is desirable to eliminate the footing of the photoresist pattern used as a plating mask and provide an undercut resist pattern profile to overcome the collapse of the plating pattern. [Means for solving the problem]

[0009] Provided herein is a method of metallization comprising: (a) forming an underlayer on a first surface of a substrate from an underlayer composition comprising a first polymer comprising acid labile groups and a sensitizing group, where (i) the first polymer comprises a sensitizing group or (ii) a compound different from the first polymer comprises a sensitizing group, the underlayer having a first thickness; (b) forming a photoresist layer on the underlayer from a photoresist composition comprising a second polymer comprising acid labile groups and a photoacid generator, the photoresist layer having a second thickness; and (c) forming a photoresist layer on the underlayer from a photoresist composition comprising a second polymer comprising acid labile groups and a photoacid generator. In one embodiment, a method of metallization is disclosed that includes patternwise exposing a photoresist layer to activating radiation; (d) developing the exposed photoresist layer with a basic developer, thereby removing portions of the photoresist layer and portions of the underlying layer to form a relief pattern, the relief pattern having an undercut profile in a first surface, wherein a maximum height of the undercuts in the relief pattern, measured from the first surface, is greater than the first thickness; and (e) plating a metal onto the first surface of the substrate after forming the relief pattern. [Brief description of the drawings]

[0010] [Figure 1A] 1 illustrates an exemplary embodiment of a substrate upon which a first metal layer is disposed. [Figure 1B] 1 illustrates an exemplary embodiment of deposition of an underlayer onto a first metal layer. [Figure 1C] 1 illustrates an exemplary embodiment of depositing a photoresist layer onto an underlayer and photopatterning the photoresist layer and the underlayer. [Figure 1D] 1 illustrates an exemplary embodiment of a photoresist layer and development of an underlying layer. [Figure 1E] 1D is an enlarged view of section AA of FIG. 1D. The enlarged view shows the undercutting that occurs in the photoresist layer and the underlying layers. [Figure 1F] 1 is an exemplary depiction of the deposition (by plating) of metal on a metal layer. [Figure 1G] 3 shows the plated metal structure remaining after removal of the remaining photoresist layer and underlayer. [Diagram 2-7] Tables 7 to 12 each contain data from the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As used herein, the terms "a," "an," and "the" do not denote limitations of quantity and should be construed to include both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. "Or" means "and / or" unless otherwise stated.

[0012] As used herein, "acid labile group" refers to a group in which a bond is optionally and typically cleaved by thermal treatment by the catalysis of an acid, resulting in a polar group, such as a carboxylic acid or alcohol group, formed on the polymer, and the moiety connected to the bond that is optionally and typically cleaved is detached from the polymer. Such acids are typically photogenerated acids, in which bond cleavage occurs during post-exposure bake. Suitable acid labile groups include, for example, tertiary alkyl ester groups, secondary or tertiary aryl ester groups, secondary or tertiary ester groups with a combination of alkyl and aryl groups, tertiary alkoxy groups, acetal groups, or ketal groups. Acid labile groups are also commonly referred to in the art as "acid cleavable groups", "acid cleavable protecting groups", "acid labile protecting groups", "acid leaving groups", "acid decomposable groups" and "acid sensitive groups".

[0013] Disclosed herein is a method of manufacturing a semiconductor that suppresses the occurrence of footing in the manufacturing process. As mentioned above, footing causes undercutting of the plating pattern that can promote the collapse of the plating pattern during further processing and reliability testing. Therefore, it is desirable to eliminate or remove footing of the plating pattern. The method includes forming an underlayer having a first thickness from an underlayer composition on a first surface of a substrate. A photoresist layer having a second thickness is then formed on the underlayer and then patterned by receiving activating radiation. The exposed photoresist layer is then developed with a basic developer, thereby removing a portion of the photoresist layer and a portion of the underlayer to form a relief pattern. The relief pattern has an undercut profile at the first surface. In one embodiment, the maximum height of the undercut of the relief pattern measured from the first surface is greater than the first thickness. After forming the relief pattern, a metal may be plated on the first surface of the substrate.

[0014] 1A-1G illustrate a method of forming a plating pattern on a substrate. FIG. 1A illustrates a substrate 100 on which a first metal layer 102 is disposed. FIG. 1B illustrates the coating of an underlayer 104 on the first metal layer 102. FIG. 1C illustrates the coating of a photoresist layer 106 on the underlayer 104, followed by exposure of the photoresist layer 106 and the underlayer 104 to light. FIG. 1D illustrates development of the exposed portions of the photoresist layer and the underlayer. FIG. 1E is an enlarged depiction of the dashed line portion of FIG. 1D.

[0015] FIG. 1C shows the coating of a photoresist layer 106. The photoresist layer 106 includes a photoacid generator and a second polymer containing acid labile groups. After coating the photoresist layer 106, the photoresist layer 106 and the underlayer 104 are patternwise exposed to activating radiation 108 through a photomask 110 having optically opaque and optically transparent regions. UV light having wavelengths between 10 nanometers and 400 nanometers can be used in photopatterning. The exposed portions of the photoresist layer 106 and the underlayer 104 are removed by development as seen in FIG. 1D. FIG. 1E shows an enlarged view of the dashed portion of FIG. 1D. FIG. 1E shows the thickness "h1" of the underlayer and the undercut of height "h2" in the photoresist and the underlayer. The height h2 is measured from the top surface of the first metal layer 102. The undercut height h2 is greater than the thickness h1 of the underlayer (also measured from the top surface of the first metal layer 102).

[0016] The various layers mentioned above (shown in Figures 1A to 1E) and their compositions will now be described in detail.

[0017] substrate Examples of substrates include, but are not limited to, silicon wafers, glass substrates, and plastic substrates, optionally including one or more layers or features formed thereon. A preferred substrate is a silicon wafer.

[0018] metal layer FIG. 1A shows a substrate 100 on which a first metal layer 102 is disposed. An optional second metal layer (not shown) may be disposed on the first metal layer 102. The first metal layer may be made of, for example, titanium, silver, aluminum, gold, copper or alloys thereof. In an exemplary embodiment, the first metal layer 102 comprises titanium or copper. When a second metal layer is disposed on the first metal layer, the first metal layer preferably comprises titanium. The first metal layer may be formed using known methods, for example by chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD) or physical vapor deposition (PVD) techniques, with sputtering and plating being typical. The thickness of the first metal layer 102 is typically between 10 nm and 500 nm.

[0019] The optional second metal layer comprises tantalum, titanium, copper, silver, aluminum, gold, or alloys thereof. The second metal layer is chemically distinct from the first metal layer 102. In an exemplary embodiment, the second metal layer comprises copper. The second metal layer may be disposed on the surface of the first metal layer via chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), or a combination thereof. The thickness of the second metal layer is typically between 10 nm and 500 nm.

[0020] lower layer 1B shows deposition of an underlayer 104 on the first metal layer 102. In one embodiment, the underlayer 104 is made from an underlayer composition that includes a first polymer that includes acid labile groups and sensitizing groups and a solvent. The first polymer is typically a copolymer that includes a first repeat unit that includes an acid labile group and a second repeat unit that includes a sensitizing group. The acid labile group and the sensitizing group may be present in the same repeat unit of the polymer. The underlayer composition typically does not contain a photoacid generator (PAG).

[0021] In another embodiment, the underlayer composition comprises a compound containing a sensitizing group and a first polymer comprising an acid labile group. In this embodiment, the compound comprising a sensitizing group is different from the first polymer. The compound comprising a sensitizing group can be a polymer blended with the first polymer comprising an acid labile group. In another embodiment, the compound comprising a sensitizing group does not have to be a polymer, but rather can be a small molecule. The small molecule can be, for example, in the form of a monomer or dimer, or in a non-polymeric form.

[0022] The underlayer 104 contains sensitizing groups and therefore functions as a sensitizing layer to localize or increase the photoacid concentration at the interface between the underlayer and the photoresist layer. As a result, a thick underlayer is undesirable. It is desirable to use a higher temperature to bake the underlayer compared to the temperature at which the photoresist layer is baked in order to prevent intermixing of the two layers. In one embodiment, the sensitizing groups of the underlayer composition are bound to a polymer to prevent sublimation at the higher bake temperatures.

[0023] The acid labile groups in the underlayer facilitate positive tone patterning. The underlayer typically does not include a photoacid generator. If a photoacid generator is optionally added to the underlayer composition, the thermal stability of the photoacid generator may need to be higher than the bake temperature used (to bake the underlayer) to prevent undesired thermal decomposition.

[0024] Acid labile groups are chemical moieties that undergo a deprotection reaction in the presence of acid. Deprotection of some acid labile groups used in the examples is brought about by heat. Acetal protecting groups are easily deprotected at room temperature. The first polymer of the underlayer composition undergoes a change in solubility in the developer as a result of reaction with the acid generated from the photoacid generator (contained in the photoresist composition) after soft baking, exposure to activating radiation, and post-exposure baking. This is due to photoacid-induced cleavage of the acid labile group, which causes a change in the polarity of the first polymer. The acid labile group can be selected from, for example, tertiary alkyl carbonates, tertiary alkyl esters, tertiary alkyl ethers, acetals, and ketals. Preferably, the acid labile group is an ester group that includes a tertiary acyclic alkyl carbon or a tertiary alicyclic carbon covalently bonded to the carboxyl oxygen of the ester of the first polymer. Cleavage of such acid labile groups forms a carboxylic acid group.

[0025] In one embodiment, the first polymer comprising acid labile groups has the following formula (1): [ka] In the formula, Z is selected from a hydrogen atom, a substituted or unsubstituted C1-C4 alkyl, a substituted or unsubstituted C1-C4 fluoroalkyl, or a cyano group; Z 1 is a non-hydrogen substituent that contains an acid labile group, the cleavage of which forms a carboxylic acid on the polymer.

[0026] In one embodiment, the acid labile groups that upon decomposition form carboxylic acid groups on the polymer preferably have the formula -C(O)OC(R 1 )3 or a tertiary ester group of the formula -C(O)OC(R 2 )2OR 3 where R 1 are each independently linear C 1~20 Alkyl, branched C 3~20 Alkyl, monocyclic or polycyclic C 3~20 Cycloalkyl, Linear C 2~20 Alkenyl, branched C 3~20Alkenyl, monocyclic or polycyclic C 3~20 Cycloalkenyl, monocyclic or polycyclic C 6~20 Aryl or monocyclic or polycyclic C 2~20 Heteroaryl, preferably linear C 1~6 Alkyl, branched C 3~6 Alkyl or monocyclic or polycyclic C 3~10 cycloalkyl, each of which is substituted or unsubstituted; and each R 1 optionally includes as part of its structure one or more groups selected from -O-, -C(O)-, -C(O)-O-, or -S-, and any two R 1 The groups together optionally form a ring; R 2 are independently hydrogen, fluorine, linear C 1~20 Alkyl, branched C 3~20 Alkyl, monocyclic or polycyclic C 3~20 Cycloalkyl, Linear C 2~20 Alkenyl, branched C 3~20 Alkenyl, monocyclic or polycyclic C 3~20 Cycloalkenyl, monocyclic or polycyclic C 6~20 Aryl or monocyclic or polycyclic C 2~20 Heteroaryl, preferably hydrogen, linear C 1~6 Alkyl, branched C 3~6 Alkyl or monocyclic or polycyclic C 3~10 cycloalkyl, each of which is substituted or unsubstituted; and each R 2 optionally includes as part of its structure one or more groups selected from -O-, -C(O)-, -C(O)-O- or -S-; R 2 The groups together optionally form a ring; R 3 is a linear C 1~20 Alkyl, branched C 3~20 Alkyl, monocyclic or polycyclic C 3~20 Cycloalkyl, Linear C 2~20 Alkenyl, branched C 3~20 Alkenyl, monocyclic or polycyclic C 3~20 Cycloalkenyl, monocyclic or polycyclic C 6~20 Aryl or monocyclic or polycyclic C 2~20Heteroaryl, preferably linear C 1~6 Alkyl, branched C 3~6 Alkyl or monocyclic or polycyclic C 3~10 cycloalkyl, each of which is substituted or unsubstituted; R 3 optionally includes as part of its structure one or more groups selected from -O-, -C(O)-, -C(O)-O- or -S-, and one R 2 is R 3 and optionally forming a ring together. Such monomers are typically vinyl aromatic, (meth)acrylate or norbornyl monomers.

[0027] Suitable acid labile group-containing units include, for example, acid labile (alkyl)acrylate units such as t-butyl (meth)acrylate, 1-methylcyclopentyl (meth)acrylate, 1-ethylcyclopentyl (meth)acrylate, 1-isopropylcyclopentyl (meth)acrylate, 1-propylcyclopentyl (meth)acrylate, 1-methylcyclohexyl (meth)acrylate, 1-ethylcyclohexyl (meth)acrylate, 1-isopropylcyclohexyl (meth)acrylate, 1-propylcyclohexyl (meth)acrylate, methyladamantyl (meth)acrylate, ethyladamantyl (meth)acrylate, etc., and other cyclic and acyclic (alkyl)acrylates such as alicyclic. Acetal and ketal acid labile groups can replace the hydrogen atom at the end of an alkali-soluble group such as a carboxyl group and bond to an oxygen atom. When acid is generated, the bond between the acetal or ketal group and the oxygen atom to which the acetal-type acid-dissociable dissolution inhibiting group is bonded is cleaved by the acid. Examples of such acid labile groups are described, for example, in (Patent Document 1), (Patent Document 2), and (Patent Document 3), as well as (Patent Document 4) and (Patent Document 5). Acetal and ketal groups as part of a sugar derivative structure that are cleaved to form a hydroxyl group, as described, for example, in (Patent Document 6), are also suitable.

[0028] Suitable first polymers include, for example, phenolic resins containing acid labile groups. Particularly preferred resins of this class include: (i) polymers containing polymerized units of vinylphenol and acid labile (alkyl)acrylates as described above, such as the polymers described in (US Pat. No. 5,399,623) and (US Pat. No. 5,499,633); (ii) polymers containing polymerized units of vinylphenol and optionally substituted vinylphenyl (e.g., styrene) that does not contain hydroxy or carboxy ring substituents and acid labile (alkyl)acrylates as described above, such as the polymers described in (US Pat. No. 5,499,623); (iii) polymers containing repeat units containing acetal or ketal moieties that react with photoacid and optionally aromatic repeat units such as phenyl or phenol groups, such as the polymers described in (US Pat. No. 5,499,623) and (US Pat. No. 5,499,633); and blends of (i), and / or (ii), and / or (iii). Such polymers are useful, for example, for imaging at wavelengths of 200 nm or more, such as 248 nm and 365 nm.

[0029] Suitable first polymers include those useful for imaging at certain sub-200 nm wavelengths, such as 193 nm, such as those disclosed in U.S. Patent No. 5,399,623, and U.S. Patent No. 5,499,633 and U.S. Patent No. 5,499,623. For imaging at 193 nm wavelengths, the polymer is preferably substantially free (e.g., less than 15 mole %), and preferably completely free, of phenyl, benzyl or other aromatic groups, such groups being highly absorbing of radiation.

[0030] Other suitable polymers for use in the Underlayer composition include, for example, those that contain polymerized units of non-aromatic cyclic olefins (endocyclic double bonds), such as optionally substituted norbornenes, for example, the polymers described in, for example, U.S. Patent No. 5,399,623 and U.S. Patent No. 5,399,623. Still other suitable polymers for use in the Underlayer composition include those that contain polymerized anhydride units, particularly polymerized maleic anhydride and / or itaconic anhydride units, such as those disclosed in U.S. Patent No. 5,399,623 and U.S. Patent No. 5,399,623.

[0031] First polymers containing repeat units containing heteroatoms, particularly oxygen and / or sulfur (but other than anhydrides, i.e., the units do not contain keto ring atoms), are also suitable for use in the underlayer composition. Heteroalicyclic units can be fused to the backbone of the first polymer and can include fused carbon alicyclic units, such as those provided by polymerization of norbornene groups, and / or anhydride units, such as those provided by polymerization of maleic anhydride or itaconic anhydride. Such first polymers are disclosed in U.S. Pat. No. 5,399,411 and U.S. Pat. No. 5,499,423. Other suitable heteroatom-containing polymers include polymers containing polymerized carbocyclic aryl units substituted with one or more heteroatom (e.g., oxygen or sulfur)-containing groups, such as hydroxynaphthyl groups, as disclosed in U.S. Pat. No. 5,599,423.

[0032] The first polymer may further comprise units containing a lactone moiety to control the dissolution rate of the polymer and the photoresist composition. Monomers suitable for use in the first polymer that contain a lactone moiety include, for example: [ka]

[0033] In one embodiment, the first polymer typically further comprises a unit comprising a polar group, which enhances the etch resistance of the first polymer and the photoresist composition and provides an additional means of controlling the dissolution rate of the first polymer and the photoresist composition. Monomers for forming such units include, for example: [ka]

[0034] The first polymer may contain one or more additional units of the type described above. Typically, the additional units of the first polymer contain the same or similar polymerizable groups as those used in the monomers used to form the other units of the polymer, but may contain other, different polymerizable groups in the same polymer backbone.

[0035] Exemplary first polymers include, but are not limited to, for example: [ka]

[0036] Other exemplary copolymers that can be used as the first polymer include, for example, the following: [ka] where a+b+c, d+e+f+g, and h+i equal 100 mole % based on all polymerized units present in the first polymer.

[0037] Suitable first polymers for use in the Underlayer compositions of the invention are commercially available or can be readily prepared by one of ordinary skill in the art. The first polymer is present in the Underlayer composition in an amount sufficient to render the underlying exposed coating layer developable in a suitable developer solution.

[0038] Typically, the first polymer is present in the underlayer composition in an amount of 70 to 100 weight percent based on the total solids content of the underlayer composition. w is typically less than 100,000, for example from 4000 to 100,000, more typically from 4000 to 20,000 grams per mole (g / mol), as measured by gel permeation chromatography using polystyrene standards. Blends of two or more of the above first polymers may be suitably used in the underlayer composition of the invention.

[0039] As described above, the underlayer composition includes a sensitizing group, which may be a separate chemical moiety that is not covalently or ionically bonded to the first polymer. The sensitizing group may be attached to an "another polymer" that is present in the underlayer composition but is not covalently or ionically bonded to the first polymer. This "another polymer" may be blended with the first polymer in the underlayer composition. In another embodiment, the sensitizing group is present in the underlayer composition as a "small molecule" that may not be part of a polymer, but rather is a monomer or dimer.

[0040] The sensitizing group comprises a molecule that affects the solubility of the resist when the resist is exposed to energetic radiation. In one embodiment, the sensitizing group is a polycyclic aromatic group. In one embodiment, the sensitizing group is an anthracene or an anthracene derivative group.

[0041] In one embodiment, the first polymer (for use in the underlayer) has the following formula (2): [ka] wherein L is a divalent linking group and R 5 is as defined above, and each R 4 may be independently hydrogen, halogen (F, Cl, Br, I); substituted or unsubstituted alkyl, preferably having 1 to about 12 carbon atoms; substituted or unsubstituted alkoxy, preferably having 1 to about 12 carbon atoms; substituted or unsubstituted alkenyl, preferably having 2 to about 12 carbon atoms; substituted or unsubstituted alkynyl, preferably having 2 to about 12 carbon atoms; substituted or unsubstituted alkylthio, preferably having 1 to about 12 carbon atoms; cyano; nitro; amino; hydroxyl; and m is an integer from 0 (the anthracenyl ring is completely hydrogen-substituted) to 9. In one embodiment, m is preferably 0, 1, or 2. In a preferred embodiment, in structure (2), L is an unsubstituted methylene group and m is 0.

[0042] A preferred sensitizer unit for use in the first polymer has the following structure: [ka] wherein R 5 is hydrogen or methyl.

[0043] The sensitizer is typically present in the first polymer in an amount of 1 to 40 mole percent (mol %), typically 3 to 30 mol %, more typically 6 to 20 mol %, based on the total moles of the first polymer. Typically, the sensitizer has a molecular weight of 5,000 to 15,000 g / mol.

[0044] The first polymer for use in the underlayer may also include one or more repeat units derived from a vinyl aromatic monomer, an acrylic or methacrylic aromatic monomer having a phenolic hydroxyl group. An exemplary vinyl aromatic monomer is styrene. In one embodiment, the first polymer is represented by the following formulas (4) and (5): [ka] wherein a is 1 to 5; Z 3 is hydrogen or an alkyl group having 1 to 5 carbon atoms. In a preferred embodiment, a is 1 and Z 3 is hydrogen. R5 is hydrogen or methyl. Y is a divalent linker. The vinyl aromatic monomer preferably has a hydroxyl group at the para position on the aryl ring. A preferred first polymerized unit of the first polymer is poly(p-hydroxystyrene). The repeating units of formulas (4) and (5) act as a dissolution promoter for alkaline developers.

[0045] The vinyl aromatic repeat units are present in the first polymer in an amount of from 30 to 90 mol %, typically from 40 to 80 mol %, based on the total number of repeat units in the first polymer.

[0046] In another embodiment, the first polymer may also contain a repeat unit comprising a maleimide. The maleimide may prevent intermixing of the underlayer with the photoresist layer. In one embodiment, the first polymer may contain a repeat unit obtained through the combination of a maleimide and a repeat unit of formula (3). The repeat unit has the structure of formula (6) and is obtained by a Diels-Alder reaction. [ka]

[0047] In an exemplary embodiment, the first polymer is represented by formula (7): [ka] where l, m, and n represent the molar percentage of each polymerized unit in the first polymer and sum to 100 mol%. In one embodiment, l is 40-75 mol%, m is 8-20 mol%, and n is 5-30 mol%, based on the total moles of the copolymer. The total weight average molecular weight of the polymer of formula (7) is typically 5,000-15,000 g / mol, preferably 7,500-12,500 g / mol, using polystyrene standards.

[0048] In another exemplary embodiment, the first polymer is represented by formula (8): [ka] where h, i, j, k, and l represent the molar percentage of each polymerized unit in the first polymer, totaling 100 mol%. In one embodiment, h is 10-40 mol%, i is 5-15 mol%, j is 30-60 mol%, k is 5-15 mol%, and l is 5-15 mol%, based on the total moles of the copolymer. The total weight average molecular weight of the polymer of formula (8) is typically 5,000-20,000 g / mol, preferably 8,000-15,000 g / mol, using polystyrene standards.

[0049] As noted above, in another embodiment, the Underlayer composition can include a compound containing a sensitizing group and a first polymer that includes acid labile groups, the sensitizing group being different from the first polymer.

[0050] In one embodiment, the sensitizing group can be a substituent on an "another polymer" present in the underlayer composition, which is different from the first polymer containing the acid labile group. The polymer containing the sensitizing group can be blended with the first polymer containing the acid labile group. For example, the first polymer can be blended with the "another polymer" containing the sensitizing group using a compatibilizer such as a surfactant. For example, the "another polymer" can be a polymer of formula (2) and can be blended with other exemplary polymers and copolymers shown above (containing acid labile groups but not containing sensitizing groups).

[0051] In another embodiment, the sensitizing group included in the Underlayer composition is not in the form of a polymer, but rather in the form of a small molecule (e.g., a monomer or dimer, or a non-polymerizable small molecule). Preferred small molecule sensitizing groups are carbocyclic aryl or heteroaromatic materials containing 1, 2, 3, or 4 separate or fused aromatic rings. Heteroaromatic compounds typically contain 1 to about 3 N, O, or S ring members and 6 to 18 or more total ring members. Carbocyclic aryl sensitizer compounds also typically contain 6 to 18 carbon ring atoms. Preferably, the sensitizer compounds have one or more electron donating ring substituents, typically 1, 2, 3, 4 or 5 electron donating ring substituents, such as optionally substituted alkyl, preferably having 1 to about 20 carbon atoms, optionally substituted alkoxy, preferably having 1 to about 20 carbon atoms, optionally substituted thioalkyl, preferably having 1 to about 20 carbon atoms, optionally substituted thioalkoxy, preferably having about 1 to 20 carbon atoms, hydroxy, optionally substituted thiohydroxyalkyl, preferably having 1 to about 20 carbon atoms, etc. The sensitizer compounds may also include linked separate or fused rings that are non-aromatic rings, such as rings having 3 to about 8 ring members, particularly cyclopentyl, cyclohexyl, thienyl, etc.

[0052] Some preferred sensitivity enhancing groups for use in the Underlayer composition include the following: [ka]

[0053] In one embodiment, the sensitizing group may include an anthracenyl moiety. Examples of sensitizing moieties present in the underlayer composition include anthracene, anthracenemaleimide, anthracenemethylacrylate, 9-anthrylmethylacrylate (I), 9-anthrylmethylmethacrylate (II), 1'-(9-anthryl)ethylacrylate (III), 1'-(9-anthryl)ethylmethacrylate (IV), dihydroanthracene, dibenzo(h,k)-4-oxatricyclo(5.2.2.02,6) Included are anthracenyl moieties such as undeca-8,10-diene-3,5-dione, 7-propyliso-9-oxo-10-thia-9,10-dihydroanthracen-2-yldi-p-tolylsulfonium, 7-propyliso-9-oxo-10-thia-9,10-dihydroanthracen-2-yldiphenylsulfonium, 2-(9,10-dihydro-10-oxo-9-anthracenyl)succinic anhydride, and the like, or combinations thereof.

[0054] If the sensitizing group is not part of the polymer, the first polymer contains repeat units having acid labile groups (but does not contain repeat units having sensitizing groups, since the sensitizing group is included in the Underlayer composition as a separate component). Polymers containing repeat units having acid labile groups are described in detail above and will not be described in detail here for the sake of brevity. Small molecules containing sensitizing groups may be present in an amount of 0.1 to 15 weight percent or 1 to 10 weight percent based on the weight of total solids.

[0055] The underlayer composition may include a solvent. The solvent is used to solvate the solids used in the underlayer composition and to promote the miscibility of the various components used in the composition. It will be understood that the "polymer" used in this context of the underlayer components may refer to only the polymer or copolymer disclosed herein or a combination of the polymer or copolymer with a compound containing a sensitizing group useful in the underlayer. It will be understood that the total solids include the polymer or copolymer, the compound containing a sensitizing group, the photodestructible base, the quencher, the surfactant, any optional PAGs added, and any optional additives except the solvent.

[0056] Solvents generally suitable for dissolving, dispensing and coating include anisole; alcohols such as 1-methoxy-2-propanol (also known as propylene glycol methyl ether, PGME) and 1-ethoxy-2-propanol; esters such as n-butyl acetate, 1-methoxy-2-propyl acetate (also known as propylene glycol methyl ether acetate, PGMEA), methoxyethyl propionate, ethoxyethyl propionate; ketones such as cyclohexanone, 2,6-dimethyl-4-heptanone, 2-heptanone; ethyl lactate (EL), 2-hydroxyisobutyric acid methyl ester (HBM), gamma-butyrolactone (GBL), 3-methoxypropanoic acid methyl ester, and combinations thereof.

[0057] The amount of the solvent can be, for example, 50 to 99.5% by weight, preferably 70 to 99% by weight, and more preferably 90 to 98% by weight, based on the total weight of the underlayer composition.

[0058] The underlayer composition is applied to the first metal layer 102 to form the underlayer 104. The underlayer composition is typically applied to the surface of the metal layer by spin coating, dipping, roller coating or other conventional coating techniques. Spin coating is preferred. For spin coating, the solids content of the coating solution can be adjusted to provide the desired film thickness based on the particular coating equipment utilized, the viscosity of the solution, the speed of the coating tool and the amount of time allowed for rotation. In one embodiment, the underlayer composition is applied in a single application.

[0059] The underlayer composition can then be soft baked to produce the underlayer 104, typically by heating to a temperature of 120-210° C. for 1-6 minutes. The soft bake minimizes the solvent content in the film, thereby forming a non-tacky underlayer 104 with improved adhesion to the first metal layer 102. The soft bake can be performed on a hot plate or in an oven, with a hot plate being typical.

[0060] The underlayer 104 (after soft bake) typically has a first thickness of up to 500 nanometers (nm), preferably up to 300 nm, and more preferably up to 200 nm. In one embodiment, the underlayer has a thickness of 5 to 100 nm or 10 to 50 nm. The underlayer composition is disposed on the metal layer.

[0061] Photoresist layer 1C shows a photoresist layer 106 disposed on the underlayer 104. The photoresist layer is derived from a photoresist composition that includes a photoacid generator and a second polymer that includes acid labile groups. The photoresist layer has a second thickness that is different from the first thickness of the underlayer.

[0062] A higher photoacid concentration at the substrate interface is preferred to eliminate the tailing present in the underlayer and photoresist layer. The underlayer contains sensitizing groups and no photoacid generator, so if only the photoresist layer contained a photoacid generator, the photoacid concentration would increase at the interface between the photoresist layer and the underlayer. The photoresist layer does not contain a UV sensitizer, as its presence (in the photoresist layer) would weaken the effect of the UV sensitizing groups at the interface with the underlayer.

[0063] The photoresist composition includes a second polymer that includes an acid labile group. The second polymer does not have a sensitizing group. Acid labile polymers are described above and will not be detailed again for the sake of brevity.

[0064] Typically, the second polymer is present in the photoresist composition in an amount of 70 to 99.5 weight percent based on the total solids content of the photoresist composition. w is typically less than 100,000, for example, 4,000 to 100,000, more typically 8,000 to 25,000 grams per mole (g / mol), as measured by gel permeation chromatography using polystyrene standards.

[0065] The photoresist composition includes a non-ionic photoacid generator. In one embodiment, the photoresist composition may include an ionic photoacid generator. It is desirable to use a photoacid generator that generates a photoacid by Norrish-I type cleavage. The Norrish-I type reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates. The carbonyl group accepts a photon and is excited to a photochemical singlet state. In one embodiment, the photoacid generator is represented by the formula (8): [ka] In the formula (8), R4 is a hydrogen atom, a substituted or unsubstituted linear or branched C1-C 14 R5 is an alkyl group, a substituted heterocyclic group, or a halogen atom; R5 is a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms; a halogen atom, or an aryl group having 6 to 20 unsubstituted carbon atoms.

[0066] Examples of suitable photoacid generators are N-hydroxynaphthalimide trifluoromethanesulfonate (NHNI-TF), N-hydroxynaphthalimide perfluoro-1-butanesulfonate (NHNI-PFBS), N-hydroxynaphthalimide camphor-10-sulfonate, N-hydroxynaphthalimide 2-trifluoromethylphenylsulfonate, N-hydroxy-5-norbornene-2,3-dicarboximide perfluoro-1-butanesulfonate, N-(trifluoromethylsulfonyloxy)phthalimide, N-hydroxysuccinimide perfluorobutanesulfonate or benzeneacetonitrile, 2-methyl-α-[2-[[(propylsulfonyl)oxy]imino]-3(2H)-thienylidene] (commercially available as IRGACURE PAG 103). In a preferred embodiment, the photoacid generator may be one or more of the structures of formula (9a), (9b) or (9c) shown below. [ka]

[0067] The photoacid generator is present in the photoresist composition in an amount of 0.2 to 15 wt%, more typically 0.3 to 5 wt%, and more preferably 0.5 to 2 wt%, based on the total solids content of the photoresist composition. By minimizing the loading of the photoacid generator, the UV transparency of the photoresist can also be minimized. It enhances the UV transparency of the photoresist layer. Sufficient UV radiation through the photoresist layer can then reach the UV sensitizer in the underlying layer.

[0068] The photoresist composition further comprises a solvent. The solvent used in the photoresist composition can be the same or different from that used in the underlayer. The solvents are listed above and will not be listed again for brevity. The amount of solvent can be, for example, 20 to 95% by weight, preferably 40 to 80% by weight, more preferably 50 to 70% by weight, based on the total weight of the photoresist composition.

[0069] The photoresist composition can include other optional ingredients such as one or more surface leveling agents (SLAs), adhesion promoters and / or plasticizers. If used, the SLA is preferably present in an amount of 0.001 to 0.1 wt % based on the total solids content of the photoresist composition, and the adhesion promoters and / or plasticizers are each present in an amount of 0.1 to 10 wt % based on the total solids content of the photoresist composition.

[0070] According to the patterning process, a layer of a photoresist composition is formed on a substrate. The composition can be applied to the substrate by spin coating, dipping, roller coating or other conventional coating techniques. Spin coating is preferred. For spin coating, the solids content of the coating solution can be adjusted to provide a desired film thickness based on the particular coating equipment utilized, the viscosity of the solution, the speed of the coating tool and the amount of time allowed for rotation. In one embodiment, the layer of the photoresist composition is applied in a single application.

[0071] The photoresist composition layer may then be soft baked to minimize the solvent content in the layer, thereby forming a tack-free coating and improving the adhesion of the layer to the substrate. The soft bake may be performed on a hot plate or in an oven, with a hot plate being typical.

[0072] The photoresist composition may be disposed on the underlayer after or before the soft bake of the underlayer composition. In one embodiment, it is disposed on the underlayer after the soft bake of the underlayer composition has been performed. The photoresist composition may also be soft baked at a temperature of 90-140° C. for 1-6 minutes to remove the solvent contained in the photoresist composition. The photoresist composition forms a photoresist layer after the solvent is removed. The photoresist layer has a thickness of 1-50 micrometers, preferably 2-20 micrometers. In one embodiment, the thickness ratio of the photoresist layer to the underlayer is 1000:1-20:1.

[0073] The photoresist composition layer is then patternwise exposed to activating radiation through a photomask to create a solubility difference between exposed and unexposed regions. Referring to FIG. 1C, after coating the photoresist layer 106, the photoresist layer 106 and underlayer 104 are exposed to activating radiation 108 through a photomask 110. Activating radiation sources having wavelengths between 10 and 500 nanometers can be used for photopatterning. The exposed portions of the photoresist layer 106 and underlayer 104 are developed with a suitable alkaline developer, for example, as seen in FIG. 1D.

[0074] References herein to exposing a photoresist composition layer to radiation activating for the layer indicate that the radiation can form a latent image in the layer. The photomask has optically transparent and optically opaque areas corresponding to the areas of the resist layer that are exposed and not exposed, respectively, by activating radiation. The exposure wavelength is typically less than 500 nm, such as 365 nm, 248 nm, 193 nm, or EUV wavelengths. Preferably, the exposure is with 365 nm wavelength radiation (i-line) from a mercury lamp.

[0075] After the exposure of the photoresist composition layer, a post-exposure bake (PEB) is typically performed to decompose the acid labile group by the acid generated from the PAG during the exposure process. PEB can be performed, for example, on a hot plate or in an oven. This forms a latent image defined by the boundaries between the polarity-switched and non-switched regions (corresponding to the exposed and unexposed regions, respectively).

[0076] The photoresist composition layer is then contacted with an alkaline developer to remove the exposed portions of the layer, leaving the unexposed regions forming a resist pattern. The developer is typically an aqueous alkaline developer, such as a quaternary ammonium hydroxide solution, for example a tetraalkylammonium hydroxide solution, such as 0.26 normality (N) (2.38 wt %) tetramethylammonium hydroxide (TMAH).

[0077] As can be seen in Figures 1D and 1E (which represent an enlarged view of the dashed portion of Figure 1D), the height h2 of the undercut region measured from the top surface of the metal layer 102 is greater than the thickness h1 of the underlayer. Following removal of the exposed regions, a patterned photoresist layer 106' and underlayer 104' are formed on the substrate. Removal of the exposed portions of the photoresist layer and underlayer results in openings into the first metal layer 102 into which metal features, such as lines or pillars, can be plated.

[0078] A further aspect is a process for depositing metal on the metal layer 102. FIG. 1F is an exemplary depiction of deposition (by plating) of metal on the metal layer 102. The process typically involves immersing the metal layer in a metal plating solution and electrolytically depositing metal 112 on the metal layer 102 in the exposed portions of the photoresist composition layer. The underlayer and the developed areas of the photoresist composition layer serve as a mold for metal plating. The metal can be plated, for example, by electroplating. Various types of metal plating solutions known in the art can be used. Two or more different layers of metal can also be formed, and the layers can be of the same or different metals. Preferred plating metals include, but are not limited to, copper, nickel, tin, silver, gold, and mixtures and alloys thereof. Metal plating solutions suitable for use in forming such metals are known in the art and are commercially available from DuPont Electronics & Industrial. The thickness of the plated metal layer is typically 1 to 100 micrometers, preferably 5 to 50 micrometers or 10 to 50 micrometers.

[0079] After metal plating, the remaining photoresist layer and underlayer can be removed (stripped) from the substrate, leaving behind the plated metal feature 112. Figure 1G shows the plated metal feature 112 remaining after the remaining photoresist layer and underlayer have been removed. Suitable photoresist strippers are commercially available, for example Shipley BPR™ Photostripper (DuPont Electronics & Industrial).

[0080] Areas of exposed first metal layer 102 between plated metal features 112 can be optionally removed, for example, by an etch-back process, to electrically isolate each of the plated metal features. The resulting metal features can take the form of, for example, lines or pillars. Metal features having small widths / diameters can be formed by the compositions and methods disclosed herein. Such structures find use, for example, in electrical connections in small, lightweight, and thin devices. The line width or fillet diameter can be, for example, 0.8 to 10 micrometers, preferably 1 to 3 micrometers. The height of the features depends, for example, on the thickness of the photoresist composition resin, but heights of 2 micrometers or more can be formed.

[0081] The present invention is advantageous in that the photoresist and underlayer compositions can be used to obtain metal features that have a larger cross-sectional area at the base compared to the cross-sectional area at the top of the feature. The use of the disclosed underlayer and photoresist compositions prevents the formation of undercuts at the bottom of the metal features, thereby preventing the collapse of the metal features during further processing of the semiconductor device.

[0082] The invention will now be illustrated by the following non-limiting examples. EXAMPLES

[0083] Example 1 This example details the preparation of a first polymer for use in an Underlayer composition. The Underlayer composition comprises a polymer (first polymer) derived from the following monomers: As noted above, the first polymer comprises repeat units having a sensitivity enhancing group and repeat units having an acid labile group.

[0084] ANTMI is the reaction product of 9-anthracene-methyl methacrylate (ANTMA) and maleimide (MI). HNMA is the reaction product of 6-hydroxy-2-naphthoic acid and 2-hydroxyethyl methacrylate. Both monomers can be prepared by known methods, for example, as detailed in (Patent Document 19). Other monomers can be obtained from commercial sources. For example, ANTMA (9-anthracene-methyl methacrylate, CAS: 31645-35-9) is available from Tokyo Chemical Industry Co., Ltd., TBA (tertiary butyl acrylate CAS: 1663-39-4) is available from Tokyo Chemical Industry Co., Ltd., and MI (maleimide CAS: 541-59-3) is available from Tokyo Chemical Industry Co., Ltd.

[0085] The polyhydroxystyrene (PHS) repeat units on the UL-A3 polymer are converted after polymerization from acetoxystyrene. [ka]

[0086] Three different first polymers (UL-A1, UL-A2, and UL-A3) were prepared using different combinations of the monomers listed above. The amount (mol %) of each monomer in the first polymer in the Underlayer composition is shown in Table 1 below.

[0087] [Table 1]

[0088] Example 2 This example details different underlayer compositions made from the first polymer of Example 1. Table 2 details six different underlayer compositions (UL1-UL6) in parts per hundred (phr). Note that two of the underlayer compositions (UL1 and UL6) contained a photoacid generator. The PAG used in UL1 has no UV absorbance at i-line wavelengths. It also does not contain anthracene UV sensitizing groups. The PAG is believed to act as a dissolution inhibitor / controller for the underlayer polymer. PAGP2 used in UL6 is i-line sensitive and was sensitized by anthracene.

[0089] The solids content of all compositions was 2.2 wt% except for UL4 which was 3.5 wt%. UL5 used PGMEA (propylene glycol 1-methyl ether 2-acetate CAS: 108-65-6) as the solvent. The other UL examples used ethyl lactate (CAS: 97-64-3).

[0090] [Table 2]

[0091] The structures of the photoacid generators PAGP1 and P2 are shown below. [ka]

[0092] As a comparative example, UL7 (CI1305-10) was prepared as follows: Alkali-soluble resin-A (35 parts by weight (pbw)) and its partially protected compound with DNQ (diazonaphthoquinone sulfonic acid) (65 pbw) were dissolved in 950 pbw of PGMEA (solid content = 5 wt%). [ka]

[0093] Example 3 This example details the preparation of the second polymers (polymers D, E, F, G and H) used in the photoresist compositions. Table 3 shows the amount (mol %) of the various monomers used in the preparation of the second polymers. The structures of the various monomers used in the second polymers are shown below. As detailed above, the second polymer contains repeat units with acid labile groups. The second polymer does not contain any repeat units with sensitizing groups. [ka]

[0094] [Table 3]

[0095] Example 4 This example shows a photoresist composition containing a second polymer and a photoacid generator. Table 4 shows the photoresist composition and the amount of each component in parts per 100 parts. The structures of the photoacid generators (PAG P2 and P3) and bases (base-a and base-b) are shown in Table 4 below. SLA stands for "self-leveling agent". The solvent was present at 100 parts and included 98 parts PGMEA and 2 parts gamma-butyrolactone (GBL).

[0096] [Table 4]

[0097] [ka]

[0098] Example 5 This example illustrates the formation of a first metal layer and a second metal layer on a substrate. The first layer included copper. 200 nm of copper was deposited on a silicon substrate by PVD. Prior to copper deposition, a 150 nm titanium layer was deposited on the silicon substrate for passivation and adhesion purposes. The copper-coated substrate was immersed in 10 wt% H2SO4 for 30 seconds, followed by a deionized water (DIW) rinse and drying in a nitrogen stream. A 60 second puddle of 2.38 wt% TMAH developer, followed by a spinning DIW (deionized water) rinse and drying, is used to neutralize residual acid from basic chemicals.

[0099] Example 6 This example details the process conditions for producing the underlayer and photoresist layer. The substrate was a silicon substrate having a first metal layer comprising titanium and a second metal layer comprising copper. No primer was applied to the copper surface. The underlayers (UL1-UL5) are shown in Table 5 below.

[0100] The underlayers were baked (soft baked) at 170°C, 185°C, and 200°C for 60 seconds at each temperature. The underlayers had two thicknesses, 54 nm and 110 nm. The photoresist layers were prepared from six photoresist compositions PR1 to PR6. The photoresist layers were soft baked at 135°C for 90 seconds to remove the solvent. The photoresist layers had thicknesses ranging from 8 to 7.5 micrometers.

[0101] After soft baking, the substrates were exposed by an i-line exposure tool (NSR-2005i9C, NIKON) with 0.50 NA and 0.68 PC lens settings.

[0102] Post-exposure bake is performed at 110° C. for 90 seconds. The substrate is then developed in aqueous developer, MF™ CD-26 developer (DuPont Electronics & Industrial), 2.38 wt % TMAH (Tetramethylammonium hydroxide: CAS: 75-59-2) with single puddle and static development for 80 seconds. Single puddle means that no additional fresh developer was supplied during development. And static development means that there is no agitation, such as spinning and stopping at low spin speeds.

[0103] Table 5 below shows various bilayers that were produced by the above method.

[0104] [Table 5]

[0105] Example 7 This example was carried out to determine the pattern profile obtained from the composition of Example 6. The photoresist pattern profile was evaluated at an exposure energy that produced a space width of 1.5 μm at central focus (Eop). Table 7 shown in Figure 2 shows the pattern profile of the photoresist using the present invention.

[0106] E op No footing was observed through underlayer bake temperatures of 170-200°C at 100°C (Examples 1-3). No footing profile was produced when lower exposure energies were used (Example 4). Small undercuts were observed in these examples. Using a photoresist pattern that produces an undercut profile produces a plating pattern with a footing profile. The presence of the footing profile prevents pattern collapse of the plating pattern after the photoresist is removed. The measured undercut width was 0.2-0.3 μm and the undercut height was greater than 0.4 μm. This is more than seven times thicker than the underlayer coating thickness.

[0107] Example 8 This example was conducted to demonstrate the use of an underlayer formulation without a photoacid generator. Table 8 in Figure 3 shows the pattern profiles of a number of examples with underlayer formulations that do not include a photoacid generator.

[0108] Examples 5 and 6 (Ex5 and Ex6) both used UL-A with the same ANTMA composition. UL-A1 used in UL2 contained more maleimide (MI) and ANTMI than UL-A2. By comparing the dissolution rates of UL-A1 and UL-A2 in aqueous developers, it was determined that UL-A1 gave a faster dissolution rate. It is believed that the imide structure allows for a faster dissolution rate in alkaline developers. Both Examples 5 and 6 gave small undercut profiles. By comparing the undercut width of Example 5 with 6, it can be seen that Example 5 gave a slightly shorter width. This result indicates that the mechanism of undercutting may not be dependent on dissolution rate alone. These examples do not use PAGs, so the proposed process works without PAGs in the underlayer composition. Example 7 used a film thickness larger than Example 5. Both examples (5 and 7) did not show any tailing and had a very low undercut profile. Example 8 uses another UL-A composition with a higher content of ANTMA and TBA. It showed a greater undercut height, but no hemming.

[0109] Table 9 in Figure 4 shows the pattern profiles obtained when the photoacid generator includes another first polymer and PAG. Examples 9 and 12 used styrene inert group and low leaving group compositions. Example 9 used yet another acrylic leaving group. Example 10 used a combination of acrylic and acetal leaving groups. None of the polymer examples showed tailing, but did have small undercut features. The undercut heights in these examples were more than 9 times the coating thickness of the underlying layer.

[0110] Example 12, which uses a different PAG, also did not obtain tailing.

[0111] Table 10 in Figure 5 shows the pattern profile obtained for the bilayer process by using an underlayer with an i-line sensitive PAG added to the UL at a photoresist film thickness of 7.5 μm. Example 13 showed an undercut profile. This result shows that the addition of the PAG to the underlayer does not interfere with the effect of the invention, i.e., the amount of PAG does not interfere with the UV absorbance of the sensitizer.

[0112] Example 9 This example details comparative examples (CF-1, CF-2, and CF-3) to demonstrate the difference between a bilayer process and a single layer process where the photoresist layer is the only layer on the substrate. A single layer example is shown in Table 11 of Figure 6. Although the tailing profile was reduced by adding benzotriazole, small tailing remains on the copper surface. This gives an undercut on the plating pattern that can affect the pattern collapse during further processing.

[0113] Example 10 This is a comparative example (CF-4) where the underlayer does not contain a UV sensitizer. UL-7 used a cresol novolac resin in which some of the phenolic hydroxyl groups were protected with diazonaphthoquinone, which is decomposable at i-line wavelengths. A lower bake temperature was applied than that used in UL-1 to prevent thermal decomposition of the diazonaphthoquinone. The data is shown in Table 12 (Figure 7). This gave a tailing profile on the silicon substrate, which can give the copper a larger tail.

[0114] In summary, from the previous examples, the bilayer process gives an undercut pattern profile with an undercut height greater than the thickness of the underlayer. This can be seen in several photoresist examples using various leaving groups. The undercut profile is independent of the dissolution rate of the polymer in the underlayer and the bake temperature. Undercutting occurs with or without the addition of a PAG.

[0115] It can be seen that the localization of photoacid concentration at the interface between the underlayer and the photoresist layer produces an undercut pattern profile with an undercut height greater than the thickness of the underlayer. UV sensitization to the PAG in the photoresist can occur through the use of anthracene moieties in the underlayer. By applying a post-exposure bake, the highly condensed photoacid diffuses to the top or non-exposed areas, facilitating the development of the undercut pattern profile. [Explanation of symbols]

[0116] 100 Substrates 102 First Metal Layer 104 Lower layer 104' lower layer 106 Photoresist layer 106' Photoresist layer 108 Activating radiation 110 Photomask 112 Metal Features, Metal

Claims

1. 1. A metallization method comprising the steps of: (a) forming an underlayer on a first surface of a substrate from an underlayer composition comprising a first polymer comprising an acid labile group and a sensitizing group, the sensitizing group being a polycyclic aromatic group, the first polymer comprising the sensitizing group, and the underlayer having a first thickness; (b) forming a photoresist layer on the underlayer from a photoresist composition comprising a second polymer containing acid labile groups and a photoacid generator, the photoresist layer having a second thickness; (c) patternwise exposing the photoresist layer to activating radiation; (d) developing the exposed photoresist layer with a basic developer, thereby removing portions of the photoresist layer and portions of the underlying layer to form a relief pattern, the relief pattern having an undercut profile in the first surface, wherein a maximum height of an undercut in the relief pattern, measured from the first surface, is greater than the first thickness; (e) plating a metal onto the first surface of the substrate after forming the relief pattern; The metallization method includes:

2. 2. The metallization method of claim 1 further comprising: (f) removing said photoresist and underlayer after plating said metal.

3. 2. The metallization method of claim 1, wherein said sensitizing group is an anthracene or an anthracene derivative group.

4. The metallization method of claim 1 , wherein the underlayer composition does not include a photoacid generator.

5. 2. The metallization method of claim 1, wherein said first thickness is less than or equal to 200 nm.

6. 2. The metallization method of claim 1, wherein a ratio of said first thickness to said second thickness is less than 0.

01.

7. 2. The metallization method of claim 1, wherein the acid labile groups of the first polymer and the acid labile groups of the second polymer are independently tertiary ester groups or acetal groups.

8. 10. The method of claim 1, wherein said second polymer comprises repeat units formed from vinyl aromatic monomers.

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