US-12622234-B2 - Selective in-situ carbon-based mask protection

Abstract

A method of etching an underlying layer includes performing a pretreatment step, a reaction step, and an etch step. The pretreatment step includes exposing surfaces of a patterned carbon-containing layer to oxygen to form C—O bonds at the surfaces with or without using plasma. The reaction step includes exposing the C—O bonds to an oxygen-reactive precursor to selectively form a mask protection layer on the surfaces of the patterned carbon-containing layer. The etch step is performed after the pretreatment step, and includes flowing an etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask. Any of the pretreatment step, the reaction step, and the etch step may be performed consecutively, concurrently, or repeated as a cycle.

Inventors

• Yu-Hao Tsai
• Du Zhang
• Mingmei Wang
• Maju TOMURA
• Ryo Matsubara
• Yoshihide Kihara

Assignees

• TOKYO ELECTRON LIMITED

Dates

Publication Date

20260505

Application Date

20240326

Claims (20)

1. 1 . A method of etching an underlying layer, the method comprising: performing a pretreatment step comprising exposing surfaces of a patterned carbon-containing layer to an oxygen-containing gas to form C—O bonds at the surfaces, the patterned carbon-containing layer having openings exposing the underlying layer; performing a reaction step comprising exposing the C—O bonds to an oxygen-reactive precursor to selectively form a mask protection layer on the surfaces of the patterned carbon-containing layer; and performing an etch step after the pretreatment step, the etch step comprising flowing an etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask.
2. 2 . The method of claim 1 , wherein the pretreatment step and the reaction step are performed concurrently.
3. 3 . The method of claim 1 , wherein the reaction step is performed after the pretreatment step, and wherein the etch step is performed after the reaction step.
4. 4 . The method of claim 3 , wherein the reaction step is performed immediately after the pretreatment step without purging the oxygen-containing gas.
5. 5 . The method of claim 3 , further comprising: performing a cycle after performing the etch step, the cycle comprising repeatedly performing the reaction step and the etch step to form additional mask protection layers and continue etching the underlying layer, respectively.
6. 6 . The method of claim 5 , wherein performing the reaction step during the cycle comprises forming the additional mask protection layers without flowing oxygen.
7. 7 . The method of claim 1 , wherein the reaction step and the etch step at least partially overlap.
8. 8 . The method of claim 1 , wherein no plasma is excited during the pretreatment step.
9. 9 . The method of claim 1 , wherein: the etch step further comprises applying etch source power to excite the plasma from the etchant gas; and the pretreatment step further comprises exciting plasma from the oxygen-containing gas by applying pretreatment source power lower than the etch source power.
10. 10 . The method of claim 1 , wherein the oxygen-reactive precursor is a tungsten-containing gas, and wherein a bulk of the mask protection layer is pure tungsten.
11. 11 . The method of claim 1 , further comprising: performing a cycle comprising repeatedly performing the pretreatment step, the reaction step, and the etch step.
12. 12 . A method of etching an underlying layer, the method comprising: performing a pretreatment step comprising exposing surfaces of a patterned carbon-containing layer to oxygen to form C—O bonds at the surfaces, the patterned carbon-containing layer having openings exposing the underlying layer; and performing an etch step after the pretreatment step, the etch step comprising concurrently flowing a gas mixture comprising an oxygen-containing gas, an oxygen-reactive precursor, and an etchant gas, selectively forming a mask protection layer using the oxygen-reactive precursor on the surfaces of the patterned carbon-containing layer, and exciting plasma from the gas mixture to etch the underlying layer using the patterned carbon-containing layer as an etch mask.
13. 13 . The method of claim 12 , wherein all carbon-containing compounds in the gas mixture are saturated compounds.
14. 14 . The method of claim 12 , wherein no plasma is excited during the pretreatment step.
15. 15 . The method of claim 12 , further comprising: performing a cycle comprising repeatedly performing the pretreatment step and the etch step.
16. 16 . A plasma etching system comprising: a chamber configured to contain plasma; a substrate support disposed in the chamber and configured to support a substrate comprising a patterned carbon-containing layer having openings exposing an underlying layer; an oxygen source fluidically coupled to the chamber and configured to supply an oxygen-containing gas through one or more valves; a precursor source fluidically coupled to the chamber and configured to supply an oxygen-reactive precursor through the one or more valves; an etchant source fluidically coupled to the chamber and configured to supply an etchant gas through the one or more valves; and a controller operationally coupled to the one or more valves, the controller comprising a processor and a non-transitory computer-readable medium storing a program including instructions that, when executed by the processor, perform a method comprising cyclically performing the following steps in situ within the chamber performing a pretreatment step comprising exposing surfaces of the patterned carbon-containing layer to the oxygen-containing gas to form C—O bonds at the surfaces, performing a reaction step comprising exposing the C—O bonds to the oxygen-reactive precursor to selectively form a mask protection layer on the surfaces of the patterned carbon-containing layer, and performing an etch step after the pretreatment step, the etch step comprising flowing the etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask.
17. 17 . The plasma etching system of claim 16 , wherein the reaction step and the etch step at least partially overlap.
18. 18 . The plasma etching system of claim 17 , wherein the etch step further comprises continuing to expose the surfaces of the patterned carbon-containing layer to the oxygen-containing gas.
19. 19 . The plasma etching system of claim 16 , wherein the pretreatment step and the reaction step are performed concurrently.
20. 20 . The plasma etching system of claim 16 , wherein the reaction step is performed after the pretreatment step, and wherein the etch step is performed after the reaction step.

Description

TECHNICAL FIELD The present invention relates generally to etching processes, and, in particular embodiments, to systems and methods for protecting a patterned carbon-containing layer used as an etch mask during an etching process. BACKGROUND Microelectronic device fabrication typically involves a series of manufacturing techniques that include formation, patterning, and removal of a number of layers of material on a substrate. Etch masks may be formed (e.g., deposited, grown, patterned) to protect regions of the substrate and allow for pattern transfer via etching. Wet or dry etching processes may be used, with plasma etching processes being an example of a dry etching process. Etching processes that etch dielectric materials are often used to create electrical (e.g., conductive) connections between and within layers. Etching processes are used in a variety of semiconductor processing areas such as in memory manufacture. One category of etching processes is high aspect ratio (HAR) etching, which includes processes such as high aspect ratio contact (HARC) etches for contact formation. Obtaining a high aspect ratio during etching is important for a variety of semiconductor processes such as during NAND formation (e.g., 3D-NAND), NOR gate formation, and others. One way that manufacturers are using HAR etching processes to increase the number of transistors and other semiconductor devices per unit area, is utilizing the vertical dimension (3D). For example, in a 3D NAND memory array, charge trapping flash transistors are stacked vertically one on top of another on the sidewalls in high aspect ratio openings. In DRAM memory arrays, to increase capacitance, high aspect ratio DRAM trench capacitor openings are etched deeper and deeper into the semiconductor substrate. Through silicon vias (TSV) for stacking integrated circuit chips are fabricated by etching high aspect ratio holes completely through substrates. The overall yield of the fabrication process is affected by both the quality of the features formed during etching processes (the etch profile) and the uniformity of the process across the substrate. Mask loss (due to the mask material being etched away during the etching process) can degrade the etch profile and decrease uniformity, both of which lower the yield of acceptable devices during the fabrication. Mask loss may be especially pronounced when employing high bias power, such as during a HAR etch, which may be used for important fabrication steps like HARC etches. Further, selectivity between the mask and feature sidewalls may also be important, such as to avoid profile problems like bowing. One conventional method of combatting mask loss is to use a different material as the bulk material of the mask, but this can be more complicated and/or more expensive. Another conventional method is to increase the mask thickness, but this can have negative impacts on the patterning capabilities of the mask itself as well as the attainable aspect ratio and critical dimension (CD) for the etched features. Carbon deposition during the etching process can also afford some mask protection, the carbon is deposited on all surfaces (i.e., non-selectively) including the material being etched and therefore can work against the etching process even as it may protect the mask to some extent. Therefore, improved etching methods that can selectively form mask protection layers on etch masks to improving selectivity may be desirable. SUMMARY In accordance with an embodiment of the invention, a method of etching an underlying layer includes performing a pretreatment step, a reaction step, and an etch step. The pretreatment step includes exposing surfaces of a patterned carbon-containing layer to an oxygen-containing gas to form C—O bonds at the surfaces. The patterned carbon-containing layer has openings exposing the underlying layer. The reaction step includes exposing the C—O bonds to an oxygen-reactive precursor to selectively form a mask protection layer on the surfaces of the patterned carbon-containing layer. The etch step is performed after the pretreatment step, and includes flowing an etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask. In accordance with another embodiment of the invention, a method of etching an underlying layer includes performing a pretreatment step, a reaction step, and an etch step. The pretreatment step includes exposing surfaces of a patterned carbon-containing layer to oxygen to form C—O bonds at the surfaces. The patterned carbon-containing layer has openings exposing the underlying layer. The etch step is performed after the pretreatment step and includes concurrently flowing a gas mixture that includes an oxygen-containing gas, an oxygen-reactive precursor, and an etchant gas, selectively forming a mask protection layer on the surfaces of the patterned carbon-containing layer using the oxygen-reactiv