US-12628585-B2 - Selective atomic layer etch of Si-based materials

Abstract

A method of processing a substrate that includes: forming a photoresist layer including a metal and oxygen over a substrate including silicon; patterning the photoresist layer using an extreme ultraviolet (EUV) photolithographic process, a portion of the substrate being exposed after the patterning; and performing an atomic layer etching (ALE) process to etch the substrate selectively relative to the patterned photoresist layer.

Inventors

• Mehrdad Rostami
• Yu-Hao Tsai
• Toru HISAMATSU

Assignees

• TOKYO ELECTRON LIMITED

Dates

Publication Date

20260512

Application Date

20230731

Claims (20)

1. 1 . A method of processing a substrate, the method comprising: forming a photoresist layer comprising a metal and oxygen over a silicon substrate in a process chamber; patterning the photoresist layer using an extreme ultraviolet (EUV) photolithographic process, a portion of the silicon substrate being exposed after the patterning; and performing an atomic layer etching (ALE) process to etch the silicon substrate selectively relative to the patterned photoresist layer, wherein the ALE process comprises: flowing an inert gas into the process chamber, sequentially supplying a halogen-containing gas as pulses while flowing the inert gas in the absence of a plasma, and exposing the silicon substrate to a first plasma to remove a layer of the silicon substrate.
2. 2 . The method of claim 1 , wherein the the first plasma comprises argon (Ar), and wherein the ALE process further comprises repeating the flowing, the sequentially supplying, and the exposing.
3. 3 . The method of claim 1 , wherein the halogen-containing gas comprises CF 4 or NF 3 .
4. 4 . The method of claim 1 , wherein the ALE process further comprises exposing the silicon substrate to a second plasma comprising hydrogen prior to the exposing to the halogen-containing gas.
5. 5 . The method of claim 1 , further comprising, prior to the ALE process, exposing the silicon substrate to a fluorine-containing gas.
6. 6 . The method of claim 1 , wherein the patterned photoresist layer comprises tin oxide.
7. 7 . The method of claim 1 , further comprising, after performing the ALE process, applying a hydrogen-based plasma etching process to remove remaining metal oxides over the silicon substrate.
8. 8 . The method of claim 1 , wherein the substrate comprises silicon oxide, the method further comprising a reduction step to reduce a surface of the silicon substrate to silicon prior to the ALE process.
9. 9 . A method of processing silicon a substrate, the method comprising: performing an atomic layer etching (ALE) process to etch silicon of the silicon substrate selectively to a metal oxide disposed over the silicon substrate, the ALE process comprising: in the absence of a plasma, exposing the silicon substrate to a halogen-containing gas to form a modified surface layer comprising silicon, exposing the modified surface to a first plasma comprising argon (Ar) to etch the modified surface layer, and repeating the two exposure steps; and after performing the ALE process, applying a hydrogen-based plasma etching process to remove remaining metal oxides over the silicon substrate.
10. 10 . The method of claim 9 , wherein the metal oxide comprises tin oxide, and wherein the halogen-containing gas comprises CF 4 or NF 3 .
11. 11 . The method of claim 9 , wherein the ALE process removes the silicon at a first etch rate and the metal oxide at a second etch rate, the first etch rate being greater than the second etch rate.
12. 12 . The method of claim 9 , wherein the ALE process further comprises, prior to the exposing to the halogen-containing gas, exposing the silicon substrate to a second plasma comprising hydrogen in the plasma etch chamber.
13. 13 . The method of claim 9 , wherein the ALE process is performed in a plasma etch chamber, the ALE process further comprising, after the exposing to the first plasma, purging etch products from the plasma etch chamber.
14. 14 . The method of claim 9 , wherein the ALE process is performed using a plasma system comprising a first process section and a second process section, and wherein the exposing to the halogen-containing gas is performed in the first process section and the exposing to the first plasma in the second process section.
15. 15 . The method of claim 14 , wherein the plasma system comprises a rotating stage configured to hold the silicon substrate, the ALE process further comprising transferring the silicon substrate from the first process section to the second process section by rotating the rotating stage.
16. 16 . A method of processing a substrate, the method comprising: forming a patterned tin oxide layer over a silicon (Si) substrate in a process chamber, a portion of the Si substrate being exposed after forming the patterned tin oxide layer; cyclically exposing the Si substrate to a first plasma comprising hydrogen; flowing inert gas into the process chamber; sequentially supplying a halogen-containing gas as pulses while flowing the inert gas in the absence of a plasma, the supplying forming a modified Si surface; and etching the modified Si surface selectively to the patterned tin oxide layer by exposing the modified Si surface to a second plasma comprising argon (Ar).
17. 17 . The method of claim 16 , wherein forming the patterned tin oxide layer comprises: forming a photoresist layer over the Si substrate, the photoresist layer comprising tin and oxygen; exposing the photoresist layer to a pattern of an extreme ultraviolet (EUV) irradiation, an EUV-exposed portion of the photoresist forming tin oxide; and developing the photoresist layer to remove an unreacted portion of the photoresist layer and form the patterned tin oxide layer from the EUV-exposed portion of the photoresist.
18. 18 . The method of claim 17 , wherein the exposing to the pattern of the EUV irradiation is performed with a dose between 1 mJ/cm 2 and 30 mJ/cm 2 .
19. 19 . The method of claim 16 , wherein the patterned tin oxide layer has a pattern with a pitch size between 10 nm and 40 nm.
20. 20 . The method of claim 16 , wherein the exposing to the halogen-containing gas is performed at a temperature between 10° C. and 30° C.

Description

TECHNICAL FIELD The present invention relates generally to methods of processing a substrate, and, in particular embodiments, to selective atomic layer etch (ALE) of Si-based materials. BACKGROUND Generally, a semiconductor device, such as an integrated circuit (IC) is fabricated by sequentially depositing and patterning layers of dielectric, conductive, and semiconductor materials over a substrate to form a network of electronic components and interconnect elements (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated in a monolithic structure. Process flows used to form the constituent structures of semiconductor devices often involve depositing and removing a variety of materials while a pattern of several materials may be exposed in a surface of the working substrate. Etching is one of the key processes in such semiconductor device fabrication. In the modern semiconductor industry, etching is typically performed by wet etching using liquid etchants or dry etching such as reactive ion etching. As an IC's critical dimension and feature size has shrunk below 10 nm, the semiconductor industry requires increased precision in dimensions (e.g., linewidths, etch depth, and film thicknesses) during etching processes. For example, atomic scale controllability may be necessary, which is difficult to realize with conventional etching technology. For this reason, alternative etching techniques that meet such requirements are highly desired. SUMMARY In accordance with an embodiment of the present invention, a method of processing a substrate that includes: forming a photoresist layer including a metal and oxygen over a substrate including silicon; patterning the photoresist layer using an extreme ultraviolet (EUV) photolithographic process, a portion of the substrate being exposed after the patterning; and performing an atomic layer etching (ALE) process to etch the substrate selectively relative to the patterned photoresist layer. In accordance with an embodiment of the present invention, a method of processing a substrate that includes: performing an atomic layer etching (ALE) process to etch silicon of a substrate selectively to a metal oxide disposed over the substrate, the ALE process including in the absence of a plasma, exposing the substrate to a halogen-containing gas to form a modified surface layer including silicon, exposing the modified surface to a first plasma including argon (Ar) to etch the modified surface layer, and repeating the two exposure steps. In accordance with an embodiment of the present invention, a method of processing a substrate that includes: forming a patterned tin oxide layer over a silicon (Si) substrate, a portion of the Si substrate being exposed after forming the patterned tin oxide layer; exposing the Si substrate to a first plasma including hydrogen; forming a modified Si surface by exposing the Si substrate to a gas including CF4 or NF3 in the absence of a plasma; and etching the modified Si surface selectively to the patterned tin oxide layer by exposing the modified Si surface to a second plasma including argon (Ar). BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: FIGS. 1A-1G illustrate cross sectional views of a substrate during an example process of semiconductor fabrication comprising an atomic layer etch (ALE) process in accordance with various embodiments, wherein FIG. 1A illustrates an incoming substrate comprising a metal oxide resist (MOR) layer, FIG. 1B illustrates the substrate after an ultraviolet (UV) exposure step, FIG. 1C illustrates the substrate after a development step, and FIG. 1D illustrates the substrate after pre-ALE treatment step, FIG. 1E illustrates the substrate after a modification step of the ALE process, FIG. 1F illustrates the substrate after a removal step of the ALE process, and FIG. 1G illustrates the substrate after cyclically repeating the steps of ALE process; FIG. 2 illustrates simulated adsorption energies of fluorine-containing adsorbates (CF4 and NF3) useful in the modification step of the ALE process over two surfaces (Si and SnO2); FIGS. 3A-3C illustrate process flow diagrams of methods of the ALE process in accordance with various embodiments, wherein FIG. 3A illustrates an embodiment, FIG. 3B illustrates an alternate embodiment, and FIG. 3C illustrates yet another embodiment; FIG. 4 illustrates a cross-sectional view of a plasma system for performing the ALE process in accordance with an embodiment; and FIGS. 5A and 5B illustrate a spatially segregated plasma system for performing the ALE process in accordance with certain embodiments, wherein FIG. 5A illustrates a top view and FIG. 5B illustrates a cross-sectional view. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS This application relates to fabrication of se