CN109212919B

CN109212919B - Photoresist, preparation method and application thereof, and photoetching method

Info

Publication number: CN109212919B
Application number: CN201811265920.0A
Authority: CN
Inventors: 肖楠; 宋里千
Original assignee: Fujian Shuguang Semiconductor Materials Co ltd
Current assignee: Fujian Hongguang Semiconductor Materials Co., Ltd.
Priority date: 2018-10-29
Filing date: 2018-10-29
Publication date: 2022-02-08
Anticipated expiration: 2038-10-29
Also published as: CN109212919A

Abstract

The invention belongs to the field of semiconductors and integrated circuits, and discloses a photoresist, a preparation method thereof and application thereofAnd a lithographic method. The photoresist contains resin and a photoacid generator, wherein the resin is formed by copolymerizing 20-45 wt% of a unit monomer I, 35-65 wt% of a unit monomer II and 10-30 wt% of a unit monomer III, and the structures of the unit monomer I, the unit monomer II and the unit monomer III are respectively shown as a formula (1), a formula (2) and a formula (3). The photoresist provided by the invention can improve the adhesion between the photoresist and the surface of the substrate, accelerate the exposure rate of the photoresist, reduce the photoetching reaction energy, reduce the etching rate of the photoresist or reduce the probability of continuous reaction during development, realize that no cavity or gap exists between the photoresist and the surface of the substrate, the photoresist can be completely developed after the photoresist is filled to the bottom of the deep groove, and the patterned surface of the substrate is still completely covered by the photoresist.

Description

Photoresist, preparation method and application thereof, and photoetching method

Technical Field

The invention belongs to the field of semiconductors and integrated circuits, and particularly relates to a photoresist, a preparation method and application thereof, and a photoetching method.

Background

In the prior art, if the unit size storage density of the NAND flash memory is improved, the production process is required to be improved. The 3D memory cell array is now used to increase cell density and data capacity under existing process flows, while the core Size (Die Size) of the chip is hardly increased. In the new stacked architecture, pillars made of electrode material will vertically penetrate the multi-layered stacked memory elements and can share peripheral circuits.

The etching technique is used to make holes in the stack of layers (i.e. in the gate electrode and the insulating film of the multilayer) and the pillars will allow a deposition process to fill these holes, around which the gate is distributed. The pre-formed nitride film is used to retain data, distributed over the various junctions, and functions like a NAND memory cell.

The process needs to dig a deep groove with the depth of 4-6 mu m from the top layer to the bottom layer, the photoresist needs to be filled with the deep groove with the depth of 4-6 mu m at first, and the photoresist in the deep groove needs to be completely developed through photoetching exposure development. Second, photoresist that does not need to be developed on the wafer substrate surface needs to resist etching.

For such a process, the current general photoresist has three major problems. First, the poor adhesion of the photoresist to the substrate surface results in voids or gaps where the bottom of the photoresist pattern contacts the substrate surface. And secondly, after the deep groove is filled, because the light transmittance is not enough or the photo-acid reaction is not complete, the photoresist at the bottom of the deep groove cannot be fully developed, and the residual photoresist blocks etching. Thirdly, the photoresist is not enough to block the deep groove etching.

Disclosure of Invention

The invention aims to provide a novel photoresist, a preparation method and application thereof and a photoetching method.

The invention provides a photoresist, wherein the photoresist contains resin and a photoacid generator, the resin is formed by copolymerizing 20-45 wt% of a unit monomer I, 35-65 wt% of a unit monomer II and 10-30 wt% of a unit monomer III, and the structures of the unit monomer I, the unit monomer II and the unit monomer III are respectively shown as a formula (1), a formula (2) and a formula (3);

R₁and R₂Are acid-labile groups and are each independently selected from any one of the following structural formula series (4):

R₃is hydrogen or methyl; r₄Is C₅-C₁₂The structure of the cyclic alkyl is selected from any one of the following structural formula series (5):

x is hydrogen, methyl or ethyl, structural formula series (4) and structural formula series (5)

Represents a bond to oxygen in the host structure.

The unit monomer I contains polar hexafluoroalkyl groups, so that the adhesion of the photoresist and the substrate is enhanced; the unit monomer II is subjected to deprotection in the presence of a photoacid generator to be changed into p-hydroxystyrene, so that the solubility in an alkaline developing solution can be improved; the unit monomer III contains a high carbon-hydrogen ratio side group, so that the etching resistance of the photoresist is improved.

The resin is a terpolymer (namely, the resin comprises a terpolymer and a higher-order copolymer, wherein when the resin is the terpolymer, only one of the unit monomer I, the unit monomer II and the unit monomer III is adopted, and when the resin is the higher-order copolymer, at least one of the unit monomer I, the unit monomer II and the unit monomer III is adopted as two different monomers), the weight-average molecular weight is 3000-20000, and the molecular weight distribution is 1.2-2.5.

Preferably, R₁Is a cyclohexyl lactone radical, R₂Is tert-butyloxycarbonyl, R₃Is methyl, R₄Is adamantyl. Preferably, the content of the resin is 12-40 wt% and the content of the photoacid generator is 0.5-10 wt% based on the total weight of the photoresist. Preferably, the photoacid generator is an ionic photoacid generator which is an iodonium salt and/or a sulfonium salt and/or a nonionic photoacid generator selected from at least one of an organic halogen compound, diazosulfone, and an imidate.

Preferably, the photoresist further contains an additive and/or a solvent.

Preferably, the content of the resin is 14-35 wt%, the content of the photoacid generator is 0.6-6 wt%, and the total content of the additive and the solvent is 60-85 wt%, based on the total weight of the photoresist.

Preferably, the additive is selected from at least one of a leveling agent, a plasticizer, an organic base, a dissolution rate enhancer, and a photosensitizer, and the solvent is selected from at least one of cyclohexanone, diacetone alcohol, ethyl acetate, ethylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether.

The preparation method of the photoresist comprises the steps of uniformly mixing the resin, the photoacid generator and optional additives and solvents, and then sequentially filtering by using a first filter with the pore diameter of 20-50nm and a second filter with the pore diameter of 2-20nm, wherein the pore diameter of the first filter is larger than that of the second filter.

The invention also provides the application of the photoresist in photoetching.

The photoetching method provided by the invention comprises the following steps:

HMDS deposition: depositing gaseous HMDS (hexamethyldisilazane) on the surface of the wafer substrate in an HMDS chamber of a spin coater;

and (3) cooling: cooling a cold plate cavity of the spin coater to room temperature;

glue homogenizing: coating the photoresist on the surface of the wafer substrate deposited with the HMDS in the spin coater to form a photoresist layer;

baking: baking the mixture in a hot plate cavity of the spin coater at the temperature of 120-150 ℃ for 80-150 seconds;

and (3) cooling: cooling to room temperature in a cold plate cavity of the spin coater;

exposure: exposing by using a photoetching machine to copy the pattern on the mask plate onto the photoresist layer;

baking: baking the mixture in a hot plate cavity of the spin coater at 90-120 ℃ for 90-130 seconds;

and (3) developing: and completely developing and washing the exposed photoresist by using a developing machine.

Preferably, the photoresist is applied by spin coating.

Preferably, the photoresist layer has a thickness of 5 μm or more, preferably 5 to 16 μm.

Preferably, the wavelength of the exposure machine is 248 nm.

The photoresist provided by the invention is mainly characterized in that the components of the resin are changed, and the unit monomer I, the unit monomer II and the unit monomer III are matched for use, so that the adhesion between the photoresist and the surface of the substrate is improved, the exposure rate of the photoresist is accelerated, the photoetching reaction energy is reduced, the etching rate of the photoresist is reduced or the probability of continuous reaction during development is reduced, no hollow hole or gap is formed between the photoresist and the surface of the substrate, the photoresist can be completely developed after the photoresist is filled to the bottom of the deep groove, and the patterned surface of the substrate is still completely covered by the photoresist.

Drawings

FIG. 1 is a microscope photograph of corresponding patterns before and after adhesion test using the photoresist J1 obtained in example 1 and the reference photoresist DJ1 obtained in comparative example 1;

fig. 2 shows a scanning electron microscope result of the photoresist J1 after exposure and development, wherein fig. 2A and 2B show different shooting positions and shooting angles;

fig. 3 shows sem results of the photoresist J1 and the reference photoresist DJ1 after etching, where fig. 3A shows a result corresponding to the photoresist J1 and fig. 3B shows a result corresponding to the photoresist DJ 1.

Detailed Description

The following detailed description of embodiments of the invention is intended to be illustrative of the invention and is not to be construed as limiting the invention. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Example 1

This example is provided to illustrate the preparation of a terpolymerization photoresist resin as provided by the present invention.

The resin is a copolymer prepared by copolymerization of a comonomer in a solvent in the presence of a free radical initiator, wherein the comonomer comprises the following compounds in parts by weight: 28.6g of monomer I, 50.0g of monomer II and 22.4g of monomer III. The polymerization reaction formula is as follows:

the preparation method comprises the following steps: 28.6g of monomer I, 50.0g of monomer II, 22.4g of monomer III and 250g of tetrahydrofuran are added into a 500ml three-neck flask, nitrogen is introduced for ten minutes under the stirring condition, then the mixture is heated to 65 ℃ and 54.0g of azobisisobutyronitrile solution (4 g of azobisisobutyronitrile is dissolved in 50g of tetrahydrofuran) is added dropwise within 10 minutes, and after the reaction is continued for 6 hours, the reaction product is deprotected to obtain the final product, wherein the weight average molecular weight is 28200 and the molecular weight distribution is 2.1.

Example 2

The resin is a copolymer prepared by copolymerization of a comonomer in a solvent in the presence of a free radical initiator, wherein the comonomer comprises the following compounds in parts by weight: 28.5g of monomer I, 58.0g of monomer II and 13.5g of monomer III. The polymerization reaction formula is as follows:

the preparation method comprises the following steps: 28.5g of monomer I, 58.0g of monomer II, 13.5g of monomer III and 250g of tetrahydrofuran are put into a 500ml three-neck flask, nitrogen is introduced for ten minutes under the stirring condition, then the mixture is heated to 60 ℃ and 54.0g of azobisisobutyronitrile solution (4 g of azobisisobutyronitrile is dissolved in 50g of tetrahydrofuran) is added dropwise within 10 minutes, and after the reaction is continued for 20 hours, the reaction product is deprotected to obtain the final product, wherein the weight average molecular weight is 25400 and the molecular weight distribution is 1.9.

Example 3

This example is provided to illustrate the preparation of quaternary copolymeric photoresist resins provided by the present invention.

The resin is a copolymer prepared by copolymerization of a comonomer in a solvent in the presence of a free radical initiator, wherein the comonomer comprises the following compounds in parts by weight: 35.5g of monomer I, 40.0g of monomer II, and monomer III (having a structure represented by formula (3), wherein R is₃Is methyl, R₄Is composed of

X is hydrogen) 12.0g of a mono-or di-aromatic hydrocarbonA compound III (having a structure represented by the formula (3), wherein R3 is a methyl group and R₄Is composed of

X is methyl) 12.5 g. The polymerization reaction formula is as follows:

the preparation method comprises the following steps: 35.5g of monomer I, 40.0g of monomer II, 12.0g of monomer III, 12.5g of monomer III and 250g of tetrahydrofuran are added into a 500ml three-neck flask, nitrogen is introduced for ten minutes under the condition of stirring, then 54.0g of azobisisobutyronitrile solution (4 g of azobisisobutyronitrile is dissolved in 50g of tetrahydrofuran) is added dropwise within 10 minutes after heating to 70 ℃, and after further reaction for 12 hours, the reaction product is deprotected to obtain a final product, wherein the weight average molecular weight is 13300 and the molecular weight distribution is 2.5.

Example 4 to example 6: preparation of photoresists

(1) Resin composition

Examples four to six the resins synthesized in examples one to three were used, respectively.

(2) Photoacid generators

Example 4: the tri-p-trifluoromethylphenyl sulfonium salt, the coordination anion is perfluorobutyl sulfonic acid group, and the structural formula is shown as (6);

example 5: tri-p-tolyl sulfonium salt, the coordination anion is naphthalene sulfonic group, and the structural formula is shown as (7);

example 6: the coordination anion of the di-p-tert-butyl phenyl iodonium salt is trifluoromethanesulfonate, and the structural formula is shown as (8).

(3) Organic base

Example 4: triethanolamine;

example 5: tris (methoxyethyl) amine;

example 6: tripropylamine.

(4) Solvent(s)

Example 4: diacetone alcohol;

example 5: ethylene glycol monomethyl ether;

example 6: ethylene glycol monomethyl ether acetate.

(5) Preparation of photoresists

The above resin, photoacid generator, organic base and solvent were added to a clean plastic container (250 ml polypropylene plastic bottle) according to the ratio of table 1, and the plastic container was fixed on a mechanical oscillator, shaken at room temperature for 20 hours to sufficiently dissolve the components, and then sequentially filtered with a first filter having a pore size of 30nm and a second filter having a pore size of 8nm to obtain photoresists J1-J3, respectively.

TABLE 1

Item	Film-forming resin (wt%)	Photoacid generator (wt%)	Organic base (wt%)	Solvent (wt%)
					Example 4	15	0.6	0.5	83.9
Example 5	25	2	0.5	72.5
					Example 6	35	6	0.6	58.4

Comparative example 1

This comparative example serves to illustrate a reference photoresist and a method of making the same.

A photoresist was prepared as in example 1, except that the unit monomer I was replaced with the same parts by weight of unit monomer II to give reference photoresist DJ 1.

Comparative example 2

A photoresist was prepared according to the method of example 1 except that the unit monomer I was replaced with the same parts by weight of unit monomer III to give reference photoresist DJ 2.

Comparative example 3

A photoresist was prepared according to the method of example 1 except that the unit monomer III was replaced with the same parts by weight of unit monomer II to give a reference photoresist DJ 3.

Test example

(1) Adhesion:

the method comprises the following steps: on the test wafers, the photoresists J1-J3 obtained in examples 1 to 3 and the reference photoresists DJ1-DJ3 were coated, respectively, to form a resist layer having a thickness of 8 μm, after which an experimental pattern was developed by exposure under the same conditions, and a pattern photograph was taken with a microscope.

Step two: respectively sticking the surfaces of the photoetching patterns obtained in the step (1) by using 3M 610 adhesive tapes, slightly flattening the surfaces, then tearing off the surfaces, and taking a pattern picture by using a microscope.

The results show that after tearing, the patterns using reference photoresists DJ1-DJ3 all adhered away by the tape, while the patterns using photoresists J1-J3 were not adhered away. Wherein, the microscope images of the corresponding patterns of the photoresist J1 and the reference photoresist DJ1 before and after the adhesion test are shown in FIG. 1, and it can be seen from FIG. 1 that the patterns of the photoresist J1 and the reference photoresist DJ1 are intact before the tape is adhered, but the pattern of the photoresist J1 is not adhered after the tape is adhered, and the pattern of the reference photoresist DJ1 is partially adhered by the tape. Therefore, the adhesion of the photoresist J1-J3 provided by the invention to the wafer is stronger than that of the reference photoresist DJ1-DJ 3.

(2) Filling, developing and etching:

firstly, photoresist J1-J3 and reference photoresist DJ1-DJ3 with the thickness of 8um are respectively coated on a test wafer substrate graph (the depth of a groove is 6 mu m) by an ACT-8 spin coater, ASML 700D is used for exposure, an experimental graph with the critical dimension (line width) of 4 mu m is developed by ACT-8, and whether photoresist residues exist at the bottom of the groove of the substrate graph is checked by a scanning electron microscope. As a result, no resist residue was observed. The scanning electron microscope result corresponding to the photoresist J1 when inspecting the bottom of the pattern is shown in fig. 2, in which fig. 2A and 2B show different imaging positions and imaging angles. As can be seen from fig. 2, the bottom of the pattern is completely free of residual photoresist.

Step two: on the test wafer substrate pattern, 8 μm thick photoresists J1-J3 and reference photoresists DJ1-DJ3 were coated with an ACT-8 spin coater, respectively, exposed with ASML 700D, and developed with ACT-8 to obtain an experimental pattern with a critical dimension of 4 μm.

Step two: and (2) placing the test piece into a LAM EXELAN HPT etching machine for etching, wherein the process conditions are as follows: 60Mt/1000W/500W/45CF₄/180Ar/10O₂Etch for 60 seconds and examine the patterned surface with a scanning electron microscope.

The experimental results are as follows: after etching, the photoresists J1-J3 were also able to cover the pattern intact, while the reference photoresists DJ1-DJ2 were etched away. The results of the correspondence between the photoresist J1 (fig. 3A) and the reference photoresist DJ1 (fig. 3B) are shown in fig. 3, and it can be seen from fig. 3 that the photoresist J1 still covers the pattern, and the reference photoresist is etched away, so that the pattern originally covered by the photoresist can be seen.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. The photoresist is characterized by comprising resin and a photoacid generator, wherein the resin is formed by copolymerizing 20-45 wt% of a unit monomer I, 35-65 wt% of a unit monomer II and 10-30 wt% of a unit monomer III, and the structures of the unit monomer I, the unit monomer II and the unit monomer III are respectively shown as a formula (1), a formula (2) and a formula (3);

R₁and R₂Is an acid labile group, R₁Independently selected from any one of the following structural formula series (4); r₂Independently selected from any one of the following structural formula series (4-1);

x is hydrogen, methyl or ethyl, structural formula series (4), structural formula series (4-1) and structural formula series (5)

Represents a bond to oxygen in the host structure.

2. The photoresist of claim 1, wherein R is₁Is a cyclohexyl lactone group, R₂Is tert-butyloxycarbonyl, R₃Is methyl, R₄Is adamantyl.

3. The photoresist of claim 1 or 2, wherein the weight average molecular weight of the resin is 3000-20000, and the molecular weight distribution is 1.2-2.5.

4. The photoresist of claim 1 or 2, wherein the resin is present in an amount of 12 to 40 wt% and the photoacid generator is present in an amount of 0.5 to 10 wt%, based on the total weight of the photoresist.

5. The photoresist of claim 4, wherein the photoacid generator is an ionic photoacid generator and/or a nonionic photoacid generator, the ionic photoacid generator is an iodonium salt and/or a sulfonium salt, and the nonionic photoacid generator is at least one selected from the group consisting of organic halogen compounds, diazosulfones, and imidosulfonates.

6. The photoresist of claim 1 or 2, further comprising an additive and/or a solvent.

7. The photoresist of claim 6, wherein the resin is present in an amount of 14 to 35 wt%, the photoacid generator is present in an amount of 0.6 to 6 wt%, and the additive and solvent are present in an amount of 60 to 85 wt%, based on the total weight of the photoresist.

8. The photoresist of claim 6, wherein the additive is selected from at least one of a leveling agent, a plasticizer, an organic base, a dissolution rate enhancer, and a photosensitizer, and the solvent is selected from at least one of cyclohexanone, diacetone alcohol, ethyl acetate, ethylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether.

9. The method of preparing the photoresist according to any one of claims 1 to 8, comprising mixing the resin, the photoacid generator, and optionally additives and solvents uniformly, followed by filtering with a first filter having a pore size of 20 to 50nm and a second filter having a pore size of 2 to 20nm in this order, the pore size of the first filter being larger than that of the second filter.

10. Use of a photoresist according to any one of claims 1 to 8 in photolithography.

11. A lithographic method, comprising:

HMDS deposition: depositing gaseous HMDS on the surface of the wafer substrate in an HMDS cavity of a spin coater;

glue homogenizing: coating the photoresist of any one of claims 1-9 on the surface of the wafer substrate with the HMDS deposited therein in the spin coater to form a photoresist layer;

12. The lithographic method of claim 11, wherein the photoresist is applied by spin coating; the wavelength of the exposure is 248 nm.

13. The lithography method according to claim 12, wherein the thickness of said photoresist layer is 5 μm or more.

14. The lithographic method of claim 12, wherein the photoresist layer has a thickness of 5-16 μm.