Electronic industry gases, including fluorine-containing etching gases, are primarily used for dry etching. Dry etching effectively overcomes the fatal flaws of wet etching and has become the predominant method for etching devices at submicron dimensions, widely applied in the front-end processes of semiconductors or LCDs. The main types of fluorine-containing etchants include carbon tetrafluoride, nitrogen trifluoride, difluoroethane, octafluorocyclobutane, C4F6, C5F8, etc. Their specific uses and characteristics are detailed in Table 4.

  Carbon tetrafluoride, a fluorine-containing organic compound, has been used for many years to etch dielectric materials such as silicon dioxide and silicon nitride. In the dry etching of oxide films, fluorine-containing organic compounds are the primary etching gases. For example, octafluorocyclobutane ionizes into plasma and free radicals (Radical), including CF*, CF2*, CF3*, etc., under a high electric field. These radicals then react with silicon dioxide to complete the etching process, as shown in the reaction equation: CF* + SiO2 → SiF4 + CO/CO2.

  Fluorine-containing organic compounds are often used in conjunction with other inorganic gases. For instance, when fluorine-containing organic compounds are used with Ar to bombard the surface of the material being etched, the etching rate can be accelerated.

  Additionally, during the etching process, a large amount of reaction by-products, such as (C-H)n polymers, are generated due to the reaction with photoresist. Oxygen (O2) can help remove these by-products.

  In the reaction, the CF group is the most critical factor. Fluorine (F) plays the primary role in etching, but its reaction rates with oxide films (SiO2) and nitride films (Si3N4) are similar, resulting in a low etching selectivity ratio. Carbon (C), on the other hand, contributes to the formation of (C-H)n polymers, which can improve the etching selectivity ratio. However, excessive polymer formation can clog holes during the etching process, leading to etch stop and ultimately poor hole opening. Therefore, different etching processes require etchants with different F/C ratios. Auxiliary gases such as CO can be added to balance the carbon ratio, or the etching gas can be changed, such as adjusting the C/F ratio.

  By increasing the fluorine/carbon ratio in the plasma, for example, by adding oxygen, the etching rate of silicon dioxide can be increased. Conversely, if the fluorine/carbon ratio in the plasma is reduced, such as by adding hydrogen or CHF3, CH2F2, the etching rate of silicon dioxide can be decreased.

  Moreover, when the fluorine/carbon ratio falls below a critical value, plasma etching may stop and transition to a polymer deposition mode.

  In the dry etching process of silicon dioxide plasma, the most commonly used etching gases are fluorocarbon compounds and fluorinated hydrocarbons (where one or more hydrogen atoms in the hydrocarbon are replaced by fluorine atoms), such as CF4, CHF3, CH2F2, etc. The carbon in these compounds helps remove oxygen from the oxide layer (producing by-products CO and CO2). CF4 is the most widely used plasma etching gas in the microelectronics industry, offering a high etching rate but a low selectivity ratio for polysilicon. Due to its long atmospheric lifetime and high GWP, it is gradually being replaced by other gases. Sulfur hexafluoride and NF3 are also facing replacement due to their long atmospheric lifetimes and high GWP.

  CHF3 and CH2F2, in addition to being primary etchants, can also be used as auxiliary gases for other primary etchants to adjust the fluorine/carbon ratio.

  Among the fully fluorinated electronic gases, hexafluoroethane accounts for about 50% of the usage. Hexafluoroethane (FC-116) is widely used in semiconductor manufacturing processes due to its non-toxicity, odorlessness, and high stability, such as in dry etching (Dry Etch) and as a cleaning agent for chemical vapor deposition (CVD) chambers. As a dry etching agent, hexafluoroethane is used for plasma etching in integrated circuits, dissociating into highly reactive fluorine ions under RF (radio frequency), primarily for etching silicon and silicon compounds on the inner surfaces of reactors. Particularly with the advancement of semiconductor devices, the precision requirements for integrated circuits are increasing, and conventional wet etching cannot meet the high-precision fine-line etching requirements for deep submicron integrated circuits at 0.18-0.25um. Hexafluoroethane, as a dry etching agent, offers minimal lateral edge erosion, high etching rates, and high precision, making it ideal for processes requiring smaller line widths. Especially when dealing with components with apertures of 140nm or smaller, the previously used octafluorocyclobutane fails to etch effectively, whereas hexafluoroethane can create deep grooves on components as small as 110nm. Hexafluoroethane can also be used as a cleaning agent, primarily for cleaning CVD chambers in semiconductor chemical vapor deposition. In various CVD processes based on traditional silane (SiH4), hexafluoroethane as a cleaning gas offers advantages over silane, including lower emissions, higher gas utilization, higher cleaning efficiency, and higher equipment output.

  Monofluoromethane is used as a dry etching agent, primarily for plasma etching in integrated circuits, especially in HDP (high-density plasma) etching.

  Hexafluorobutadiene (C4F6) and octafluorocyclopentene (C5F8) are considered competitive as next-generation etching gases, particularly C4F6.

  The market demand for C4F6 as a semiconductor-grade fluorine gas is growing rapidly. It can replace CF4 in the dry process of KrF laser sharp etching of semiconductor capacitor patterns. C4F6 offers numerous etching advantages at the 0.13um technology level. C4F6 has a higher selectivity ratio for photoresist and silicon nitride compared to C4F8, which are two significant advantages. As device dimensions shrink to 0.13um, the critical dimension (CD) of holes is about 30% smaller than at 0.18um, requiring a higher selectivity ratio for the key film layer to expand the etching window and improve etching stability. Increasing the etching rate can reduce the time required for etching, thereby improving production efficiency. Improvements in etching uniformity and CD bias (critical dimension bias) enhance CD and device stability and reliability, leading to higher product yields.

  Additionally, environmental considerations are a crucial factor. Etching equipment and process technologies using gases with low global warming potential (GWP) and high environmental friendliness are expected to be rapidly developed. The GWP value of C4F6 is almost zero. For example, replacing C4F8 and C5F8 with C4F6 in oxide film etching processes can reduce greenhouse gas emissions. Moreover, semiconductor etching experts have provided data on perfluorocompound (PFC) usage during etching, indicating that replacing C4F8 with C4F6 in oxide etching offers comparable performance while reducing PFC emissions by 65%-82%. Experts suggest that, to date, C4F6 may be the only alternative that can provide the required etching conditions and reduce emissions.