TECHNICAL FIELD

The present invention relates to a resist underlayer film forming composition for forming a flattened film on a stepped substrate, and a method for producing a laminated substrate that is flattened using a resist underlayer film formed from the composition.

BACKGROUND ART

In production of a semiconductor device, microprocessing has been conventionally carried out through lithography using a photoresist composition. The microprocessing is a processing method in which a thin film is formed from the photoresist composition on a substrate to be processed such as a silicon wafer, irradiated with active light such as ultraviolet light through a mask pattern including a pattern of the semiconductor device, and developed to obtain a photoresist pattern, and the substrate to be processed such as a silicon wafer is etched using the obtained photoresist pattern as a protective film. In recent years, an increase in degree of integration of semiconductor devices has advanced. As active light, an ArF excimer laser (193 nm) is used instead of a KrF excimer laser (248 nm), and thus, active light with shorter wavelength is more widely used. With the trend toward shorter wavelength, influences of diffuse reflection of active light from a substrate and standing wave have become a major issue. Therefore, an anti-reflective coating provided between a photoresist and a substrate to be processed has been widely used. For further microprocessing, a lithography technique using extreme ultraviolet light (EUV, 13.5 nm) or an electron beam (EB) as active light has also been developed. In EUV lithography and EB lithography, diffuse reflection from a substrate and standing wave do not generally occur, and thus a specific anti-reflective coating is not required. However, a resist underlayer film is widely beginning to be investigated as an auxiliary film for improving resolution and adhesion of a resist pattern.

With a shorter wavelength of exposure light, the depth of focus decreases. Accordingly, it is important that the flattening properties of a film to be formed on a substrate are improved to form a desired resist pattern with precision. For production of a semiconductor device with a fine design rule, a resist underlayer film that can be formed as a flat coating film having no steps on a substrate is required.

For example, a resist underlayer film forming composition containing a crosslinkable compound having a C2-10alkoxymethyl group or a C1-10alkyl group is disclosed (see Patent Document 1). Patent Document 1 describes that during applying the composition to a substrate having a hole pattern, the embeddability is good.

A phenylnaphthylamine novolac resin is used (see Patent Document 2).

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: International publication WO 2014/208542

Patent Document 2: International publication WO 2013/047516

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In order to prevent mixing of a resist underlayer film forming composition during laminating a photoresist composition or a resist underlayer film different from a resist underlayer film formed from the resist underlayer film forming composition, a self-crosslinkable moiety is introduced into a polymer resin that is a main component of the resist underlayer film forming composition, or a crosslinker, a crosslinking catalyst, or the like is appropriately added to the resist underlayer film forming composition, and the resist underlayer film forming composition is baked at high temperature to thermally cure a coating film. Thus, the photoresist composition and the different resist underlayer film can be laminated without mixing. Such a thermosetting resist underlayer film forming composition contains a polymer having a thermal crosslinking forming functional group such as a hydroxyl group, a crosslinker, and an acid catalyst (acid generator). Therefore, when a pattern (e.g., hole and trench structures) formed on a substrate is filled with the resist underlayer film forming composition, a crosslinking reaction is promoted due to baking, and thus the viscosity increases. Accordingly, the filling properties of the pattern are deteriorated, and thus the flattening properties after formation of a film tend to decrease.

An object of the present invention is to enhance the thermal reflow properties of a polymer and thus improve the filling properties of a pattern during baking. To enhance the thermal reflow properties of a polymer, a substituent capable of decreasing the glass transition temperature of the polymer, such as an alkyl group, is introduced into the polymer. Thus, the present invention provides a resist underlayer film forming composition that sufficiently expresses a decrease in viscosity before initiation of crosslinking reaction during baking, and forms a coating film having high flattening properties on a substrate.

Additionally, the present invention provides a resist underlayer film forming composition for forming a resist underlayer film further having heat resistance.

Means for Solving the Problems

A first aspect of the present invention is a resist underlayer film forming composition comprising a polymer having a unit structure of Formula (1):


(wherein R1is an organic group having at least two amines and at least three C6-40aromatic rings, R2and R3are each a hydrogen atom, a C1-10alkyl group, a C6-40aryl group, a heterocyclic group, or a combination thereof, and the alkyl group, the aryl group, and the heterocyclic group are optionally substituted with a halogen group, a nitro group, an amino group, a formyl group, an alkoxy group, or a hydroxy group, or R2and R3optionally form a ring together).

A second aspect of the present invention is the resist underlayer film forming composition according to the first aspect, wherein R′ is a divalent organic group derived from a compound of Formula (2):


(wherein Ar1, Ar2, and Ar3are each a benzene ring or a naphthalene ring, R6, R7, and R8are each a substituent, and are selected from the group consisting of a halogen group, a nitro group, an amino group, a hydroxy group, a C1-10alkyl group, a C2-10alkenyl group, a C6-40aryl group, and a combination thereof, the alkyl group, the alkenyl group, and the aryl group optionally contain an ether bond, a ketone bond, or an ester bond, R4and R5are each selected from the group consisting of a hydrogen atom, a C1-10alkyl group, a C2-10alkenyl group, a C6-40aryl group, and a combination thereof, the alkyl group, the alkenyl group, and the aryl group optionally contain an ether bond, a ketone bond, or an ester bond, and n1, n2, and n3 are each an integer of 0 to the maximum number of substitutions possible for each of substituents R6, R7, and R8on the rings of Ar1, Ar2, and Ar3, respectively).

A third aspect of the present invention is the resist underlayer film forming composition according to the first aspect, wherein R1is a divalent organic group derived from N,N′-diphenyl-1,4-phenylenediamine.

A fourth aspect of the present invention is the resist underlayer film forming composition according to any one of the first to third aspects, wherein R3is a hydrogen atom, R2is an aryl group selected from the group consisting of a phenyl group, a naphthyl group, an anthryl group, and a pyrenyl group, and the aryl group is optionally substituted with a halogen group, a nitro group, an amino group, a C1-10alkyl group, a C1-10alkoxy group, a C6-40aryl group, a formyl group, a carboxyl group, or a hydroxy group.

A fifth aspect of the present invention is the resist underlayer film forming composition according to any one of the first to third aspects, wherein R3is a hydrogen atom, R2is a phenyl group, and the phenyl group is optionally substituted with a halogen group, a nitro group, an amino group, a C1-10alkyl group, a C1-10alkoxy group, a C6-40aryl group, a formyl group, a carboxyl group, or a hydroxy group.

A sixth aspect of the present invention is the resist underlayer film forming composition according to the first aspect, wherein the unit structure of Formula (1) is a unit structure of Formula (1-1):


(wherein R2and R3are each a hydrogen atom, a C1-10alkyl group, a C6-40aryl group, a heterocyclic group, or a combination thereof, and the alkyl group, the aryl group, and the heterocyclic group are optionally substituted with a halogen group, a nitro group, an amino group, a formyl group, an alkoxy group, or a hydroxy group, or R2and R3optionally form a ring together).

A seventh aspect of the present invention is the resist underlayer film forming composition according to any one of the first to sixth aspects, further comprising a crosslinker.

An eighth aspect of the present invention is the resist underlayer film forming composition according to any one of the first to seventh aspects, further comprising an acid and/or an acid generator.

A ninth aspect of the present invention is a resist underlayer film comprising a cured film of the resist underlayer film forming composition according to any one of the first to eighth aspects.

A tenth aspect is a method for producing a semiconductor device comprising steps of forming an underlayer film on a semiconductor substrate from the resist underlayer film forming composition according to any one of the first to eighth aspects, forming a resist film on the underlayer film, irradiating the resist film with light or an electron beam and developing the resist film to form a resist pattern, etching the underlayer film through the formed resist pattern, and processing the semiconductor substrate through the patterned underlayer film.

An eleventh aspect of the present invention is a method for producing a semiconductor device comprising steps of forming an underlayer film on a semiconductor substrate from the resist underlayer film forming composition according to any one of the first to eighth aspects, forming a hard mask on the underlayer forming a resist film on the hard mask, irradiating the resist film with light or an electron beam and developing the resist film to form a resist pattern, etching the hard mask through the formed resist pattern, etching the underlayer film through the patterned hard mask, and processing the semiconductor substrate through the patterned underlayer film.

Effects of the Invention

When the resist underlayer film forming composition of the present invention is applied to a substrate and baked, a pattern formed on the substrate is filled with the resist underlayer film forming composition by thermal reflow of a polymer. For example, when an alkyl group that generally decreases the glass transition temperature (Tg) of a polymer is added to a main resin skeleton in the resist underlayer film forming composition, the thermal reflow properties can be enhanced, and the filling properties of the pattern can be improved.

The inventors of the present invention have found that novolac resins obtained by a reaction of a compound having at least two amines and at least three C6-40aromatic rings with an aldehyde or a ketone has excellent properties of flattening a pattern. When the novolac resins include the alkyl group and another substituent in combination, a resist underlayer film having flattening properties and heat resistance can be obtained.

Therefore, from the resist underlayer film forming composition of the present invention, a flat film can be formed regardless of an open area (unpatterned area) or a pattern area of DENSE (dense) and ISO (coarse) patterns on the substrate. This satisfies both the filling properties of the pattern and the flattening properties after filling. The resist underlayer film forming composition allows an excellent flattened film to be formed.

A silicon hard mask layer may be formed as an upper layer of the resist underlayer film by a vapor deposition method, and thus the resist underlayer film is required to have heat resistance that is sufficiently resistant to heat during vapor deposition. Through a transferred pattern of the resist underlayer film, a substrate below the resist underlayer film is processed, and thus the resist underlayer film is required to have etching resistance.

The present invention can provide a material having properties achieving a good balance among heat resistance, flattening properties, and etching resistance of the resist underlayer film obtained from the resist underlayer film forming composition of the present invention.

