Methods for removing hard masks

Abstract

This invention provides compositions and methods suitable for etching, i.e., removing, amorphous carbon hard masks doped with elements such as boron, chlorine, or nitrogen. The compositions utilize concentrated sulfuric acid, water, and at least one oxidizing agent. In operation of the method, the compositions selectively remove doped hard mask layers with good selectivity, even in the presence of layers such as silicon dioxide, silicon nitride, tantalum nitride, and polycrystalline silicon.

Description

Technical Field

[0001] This invention generally relates to the field of microelectronic device manufacturing, and specifically to a method for etching—i.e. removing—a boron-doped amorphous carbon hard mask. Background Technology

[0002] Processing semiconductor and microelectronic devices involves various steps including depositing material layers and removing the material through a chemical process called "etching." Etching involves placing a thin mask layer over the deposited material layer. Openings are then formed in the mask, exposing selected portions of the substrate. The masked substrate is then brought into contact with an etchant that contacts the material of the underlying substrate through the openings in the mask and chemically degrades and removes the material to create openings (in three dimensions) within the substrate.

[0003] Many newer types of substrates, such as those used to fabricate three-dimensional memory devices, are processed to form openings with high aspect ratios, such as openings extending into the substrate to a depth significantly greater than their width dimension (e.g., diameter). As an example, vertically extending "channel holes" in 3D NAND memory devices are formed by etching vertically extending openings into a stack of multiple layers of deposited film in the depth direction. The depth of the channel hole can be twenty, forty, or fifty times larger than its diameter, or more. Forming this type of high aspect ratio feature in microelectronic devices through etching requires highly specialized, accurate, and precise etching processes.

[0004] For this type of etching step, a chemically resistant "hard mask" is placed over the top layer of a plurality of deposited films. The films, sometimes referred to as a "film stack," are functional materials for the memory device and can be layers of deposited silicon oxide, silicon nitride, polysilicon, or the like. The hard mask resists etch solutions used to chemically degrade and remove the material from the film stack to form high aspect ratio openings (e.g., vias) in the substrate.

[0005] A common type of hard mask is the amorphous carbon hard mask. This type of hard mask is deposited as a continuous layer onto a microelectronic device substrate and then etched to form openings within the hard mask. The subsequent step of etching the underlying substrate is performed by exposing the substrate with the hard mask to a gaseous chemical etchant capable of chemically degrading the materials of the film stack. The gaseous etchant passes through the openings in the hard mask to contact and etch away—i.e., remove—the substrate material to create openings in the substrate. After the substrate material has been etched away as needed, the hard mask must be removed from the substrate to allow the substrate to be further processed into a finished microelectronic device.

[0006] Creating precisely formed and well-defined substrate openings with high aspect ratios can be extremely challenging. Etching processes are often studied to improve the overall process as a component of hard masks, including compositions containing hard masks and methods for applying and removing them.

[0007] Hard masks can be composed of thick amorphous carbon films or various similar materials capable of withstanding plasma etching processes. For 3D NAND structures, amorphous carbon is an imperfect hard mask material because it is susceptible to etching when exposed to reactive plasma for the length of time required to process such structures. One method to increase the durability of such amorphous carbon films involves doping the carbon layer with etch-resistant elements such as boron, chlorine, and nitrogen. In the case of boron doping, the mask is hardened, thereby forming boron carbide and making the mask resemble a ceramic morphology and thus resistant to chemical etchants. Such masks are then finally removed using a (dry) reactive ion etching technique utilizing O2 plasma or O2 plasma combined with H2 plasma (see, for example, U.S. Patent No. 9,229,581).

[0008] However, there is a need for improved methods to remove hard masks that have been doped with etch-resistant elements such as boron. Summary of the Invention

[0009] In general, the present invention provides compositions and methods suitable for etching, i.e., removing, amorphous carbon hard masks doped with elements such as boron, chlorine, or nitrogen. The compositions utilize concentrated sulfuric acid, water, and at least one oxidizing agent. In one embodiment, the oxidizing agent is an iodine-containing oxidizing agent selected from, for example, iodates and periodic acid. The compositions may further include additional acids besides sulfuric acid. In the method of the present invention, the compositions may be applied to a mask, which is then desirably removed at high temperatures. During operation of the method, the compositions selectively remove doped hard mask layers with good selectivity, even in the presence of layers such as silicon dioxide, silicon nitride, tantalum nitride, and polycrystalline silicon.

[0010] Therefore, the performance of the method of the present invention is very suitable for applications containing 3D-NAND structures with 96 layers or more. Detailed Implementation

[0011] 1. In a first aspect, the present invention provides a method for removing an amorphous carbon hard mask from a microelectronic device, wherein the hard mask has been doped with an element selected from boron, chlorine, and nitrogen to form a doped hard mask, the method comprising contacting the microelectronic device with a composition comprising:

[0012] a. H2SO4, about 50% to about 98% by weight, based on the total weight of the composition;

[0013] b. Water; and

[0014] c. At least one oxidizing agent, from about 0.1% to about 30% by weight, based on the total weight of the composition.

[0015] In one embodiment, the element is boron.

[0016] In some embodiments, the oxidant is selected from, for example, iodates and periodic acid, nitric acid, perchloric acid and permanganate, and persulfate. In one embodiment, the oxidant is present in an amount from about 1% to about 15% by weight or from about 5% to 10% by weight. In another embodiment, the oxidant is periodic acid, and the amount of the oxidant is from about 5% to about 8%. In yet another embodiment, the oxidant is periodic acid, and the amount of the oxidant is from about 5% to about 6%.

[0017] In one embodiment, the iodine-containing oxidant is selected from H5IO6, HIO4, or a mixture thereof.

[0018] In one embodiment, the composition comprises about 65 to about 85% by weight of H2SO4.

[0019] In some embodiments, the composition further comprises an acid other than H2SO4. In some embodiments, the acid other than H2SO4 is selected from methanesulfonic acid, trifluoromethanesulfonic acid, boric acid, and phosphoric acid.

[0020] In some embodiments, the composition further comprises at least one surfactant. As used herein, the term "surfactant" refers to an organic compound that reduces the surface tension (or interfacial tension) between two liquids or between a liquid and a solid, typically an amphiphilic organic compound containing both a hydrophobic group (e.g., a hydrocarbon (e.g., an alkyl) "tail") and a hydrophilic group. Advantageously, the surfactant is thermally stable and retains its ionicity under strongly acidic conditions, such as those of the etching process of the present invention. Examples include perfluoroalkyl sulfonic acids and long-chain quaternary ammonium compounds (e.g., dodecyltrimethylammonium bisulfate). Fluorinated nonionic surfactants, such as Chemours', may also be used. FS-31 / FS-35. Nonionic, unfluorinated surfactants, such as poly(ethylene glycol)-poly(propylene glycol) copolymers (“PEG-PPG”), may also be used.

[0021] The amount of surfactant in the etching composition can be the amount that, in combination with other materials in the etching composition, will provide the desired overall performance. For example, the composition may contain a certain amount of surfactant, which, by weight of the total composition, can range from about 0.001 weight percent to about 10 weight percent, such as about 0.01 weight percent to about 0.5 weight percent, 1 weight percent, 2 weight percent, 7 weight percent, or 7 weight percent of surfactant.

[0022] The compositions of the present invention can therefore be used to etch or remove boron-, chloride-, or nitrogen-doped amorphous hard masks by applying such compositions to the surface of microelectronic devices. The sulfuric acid concentration and operating temperature can be varied and optimized depending on the thickness of the film to be removed. In one embodiment, the composition is applied at an environment of about 100°C to 170°C. In another embodiment, the composition is applied at an environment of about 140°C to 170°C.

[0023] The compositions of the present invention can be readily formulated as single-package formulations or multi-component formulations to be mixed upon or prior to use. For example, individual portions of a multi-component formulation may be mixed at the tool, in a storage tank upstream of the tool, or in a shipping package that delivers the mixed formulation directly to the tool. For instance, a single shipping package may contain at least two separate containers or pouches that can be mixed together by the user at the manufacturing plant, and the mixed formulation may be delivered directly to the tool. One of the at least two containers or pouches may contain an oxidizing agent, which may be solid, while the other of the at least two containers may contain a sulfuric acid solution. In one embodiment, one of the at least two containers or pouches contains an oxidizing agent, while the second of the at least two containers or pouches contains sulfuric acid. In another embodiment, one of the at least two containers or pouches contains an oxidizing agent, while the second of the at least two containers or pouches contains sulfuric acid and a mixture of sulfuric acid and another acid other than sulfuric acid. In each case, if water is to be added, the water may be added to one and / or two containers before leaving the manufacturer, may be added at the manufacturing plant before use, or a combination of both, as readily determined by a person skilled in the art. The shipping packaging and the inner containers or bags of said packaging must be suitable for storing and shipping the components of the composition, such as packaging provided by Advanced Technology Materials, Inc. (Danbury, Connecticut, USA).

[0024] Alternatively, the concentrate of the composition may be formulated and packaged in a container for shipment and for mixing with on-site sulfuric acid and optionally an acid other than sulfuric acid before and / or during use, wherein the method of use is described herein. For example, the concentrate may include at least one oxidizing agent, water, and wherein the concentration of the oxidizing agent, by weight of the concentrate, may range from about 0.1 wt% to about 30 wt% or from about 1 wt% to about 15 wt%. When present, the amount of sulfuric acid in the concentrate, by weight of the concentrate, may range from about 50 wt% to about 96 wt%. In a preferred embodiment, the concentrate for combination with on-site acid comprises, consists of, or is substantially composed of at least one oxidizing agent, water, and optionally at least one acid other than sulfuric acid. In another embodiment, the concentrate for combination with on-site acid comprises, consists of, or is substantially composed of at least one iodine-containing oxidizing agent, water, and at least one acid other than sulfuric acid. Those skilled in the art, knowing how much oxidant is needed in a low-pH composition and how much acid is present in the concentrate, can easily determine the ratio of the concentrate to the acid on site.

[0025] On the other hand, it relates to a kit containing one or more components in one or more containers suitable for forming compositions as described herein. Container (Advanced Technology Materials, Dampierre, Connecticut, USA). One or more containers containing components of the compositions described herein preferably include means for fluid communication of the components in the one or more containers for blending and dispensing. For example, see The container allows for the application of gas pressure to the exterior of a liner within the one or more containers, causing at least a portion of the contents of the liner to be discharged and thus enabling fluid communication for blending and dispensing. Alternatively, gas pressure can be applied to the top space of a conventional pressurized container, or a pump can be used to enable fluid communication. Additionally, the system preferably includes a dispensing port for dispensing the blended removal composition to a processing tool.

[0026] Generally chemically inert, impurity-free, flexible, and elastic polymeric film materials, such as PTFE or PTFA, are preferably used to manufacture liners for the one or more containers. The desired liner material is processed without co-extrusion or barrier layers, and without any pigments, UV inhibitors, or treatment agents that could adversely affect the purity requirements of the components to be placed in the liner. The list of desirable liner materials includes virgin polytetrafluoroethylene (PTFE), PFA, Membranes such as these. In some embodiments, the thickness of such padding material is in the range of about 5 mils (0.005 inches) to about 30 mils (0.030 inches), for example, a thickness of 20 mils (0.020 inches).

[0027] Regarding the containers for the reagent kits, the full text of the following patent and patent application disclosures is hereby incorporated by reference: U.S. Patent No. 7,188,644, entitled "Apparatus and Method for Minimizing the Generation of Particulates in Ultrapure Liquids"; U.S. Patent No. 6,698,619, entitled "Returnable and Reusable Bag-in-Drum Fluid Storage and Dispensing Container System"; and U.S. Patent Application No. 6,698,619, filed on May 9, 2008, in the name of John E. Q. Hughes, entitled "Systems and Methods for Material Blending and Dispensing". International application No. PCT / US08 / 63276 entitled “Discrimination”; and international application No. PCT / US08 / 85826 entitled “Systems and methods for delivery of fluid-contAINING process material compositions” filed on December 8, 2008, in the name of John EQ Hughes et al.

[0028] Therefore, in another aspect, the present invention provides a kit comprising one or more components a., b. and c. described above in one or more containers, adapted to form the composition of the present invention as described herein.

[0029] The invention can be further illustrated by the following examples of its preferred embodiments, but it should be understood that, unless otherwise specifically indicated, these examples are included for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] Example

[0031] Examples of formulations 1 to 3:

[0032]

[0033] *DIW = Deionized Water

[0034] *MSA = Methanesulfonic acid

[0035] *BHM = Boron Hard Mask

[0036] Example 1 below describes a general method for preparing and testing formulations of Examples 1 to 3.

[0037] Example A - Preparation of Etching Composition

[0038] A 50% by weight sample of H₅IO₆ was combined with water and methanesulfonic acid. 96% H₂SO₄ was slowly added to this mixture, with an ice-water bath used for cooling to control the exothermic reaction. The total solution weight for beaker tests was 300 g in a 250 ml three-necked glass flask. The resulting solution was heated with a heating pack while maintaining the temperature at 155 °C. Stirring was maintained at 360 rpm throughout.

[0039] Example B - Specimen Testing:

[0040] The wafer was cut into 1.5×3cm pieces. 2 Size, and via Teflon TM The test specimen is fastened to the Teflon tape. TM The sample was held in a (PTFE) sample holder. The processing time for blanket-coated wafers was 30 to 60 minutes, and for patterned wafers (50% over-etching) it was 120 minutes. After the etching process, the samples were washed with deionized water for 1 minute and dried with nitrogen. Film loss was measured using an ellipsometry, and the patterned wafers were inspected using scanning electron microscopy (SEM).

[0041] The table below compares the etching rate of the boron-doped amorphous film of the formulation in Example 3 with the etching rates of other surface compositions:

[0042] The test was conducted at 155°C for 30 minutes, while stirring at 360 rpm with a magnetic stir bar. An ellipsometry was used to measure membrane loss.

[0043]

[0044] BPSG = Borosilicate Phosphor Glass

[0045] Doped polycrystalline silicon = boron-doped polycrystalline silicon

[0046] Having thus described several illustrative embodiments of this disclosure, those skilled in the art will readily understand that other embodiments can be made and used within the scope of the appended claims. Many advantages of this disclosure as covered herein have been set forth in the foregoing description. However, it should be understood that this disclosure is illustrative in many respects only. Changes in detail may be made, particularly in terms of the shape, size, and arrangement of parts, without departing from the scope of this disclosure. Of course, the scope of this disclosure is defined by the language expressed in the appended claims.

Claims

1. A method for removing an amorphous carbon hard mask from a microelectronic device, wherein the hard mask has been doped with an element selected from boron, chlorine, and nitrogen to form a doped hard mask, the method comprising contacting the microelectronic device with a composition comprising: a. 50 to 98 percent by weight of H2SO4 based on the total weight of the composition; b. Water; and c. At least one oxidizing agent, comprising 0.1 to 30% by weight of the total weight of the composition; The composition further includes an acid other than H2SO4, wherein the acid other than H2SO4 is selected from methanesulfonic acid, trifluoromethanesulfonic acid, boric acid, and phosphoric acid.

2. The method according to claim 1, wherein the element is boron.

3. The method according to claim 1, wherein the oxidant is an iodine-containing oxidant.

4. The method according to claim 3, wherein the iodine-containing oxidant is selected from H5IO6, HIO4, or a mixture thereof.

5. The method of claim 1, wherein the oxidant is used in the range of 1 to 15% by weight.

6. The method according to claim 1, wherein the oxidant is selected from persulfate, nitric acid, perchloric acid and permanganate.

7. The method of claim 1, wherein the composition comprises 65 to 85% by weight of H2SO4.

8. The method according to claim 1, wherein the oxidant is H5IO6.

9. The method according to claim 1, wherein the composition further comprises at least one surfactant.

10. The method of claim 1, wherein the apparatus and the composition are heated to a temperature of 100°C to 170°C.

11. The method according to claim 1, wherein the element is chlorine or nitrogen.

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