Patent Application
20150136171
The present disclosure relates to plasma ashing, and more particularly to plasma ashing including liquid or vapor injection into the plasma to create new reactive species.
The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Some integrated circuit (IC) devices require minimum substrate damage and little or no oxidation during plasma photoresist stripping processes. Some new technologies, such as high-dose, ultra-shallow junction implants for source/drain extensions, 3D integration schemes and processes involving new materials such as high K/metal gate and SiGe, pose new challenges to advanced photoresist processes. In addition, shrinking photoresist thicknesses, new photoresist materials, and the use of aggressive multi-species implant dose conditions also increase the difficulty when performing post-implant residue removal.
Oxidizing or fluorine-containing plasma strip approaches, while effective for residue removal, often cause unacceptable substrate loss and dopant bleaching. Fluorine-free, O2-forming gas (N2/H2) based downstream plasma strip processes may cause significant silicon oxidation (˜1 Å oxide growth per cleaning step) due to plasma exposure and do not offer sufficient residue removal efficacy.
Oxygen-free plasmas formed from reducing chemistries that typically employ forming gas (N2/H2), optionally with a high percentage of H2, offer low substrate oxidation. However, this approach has low resist removal rates, plasma-induced changes to the dopant distribution, and limited residue removal capability.
Plasmas with a controlled mix ratio of active oxygen (O*) and active nitrogen (N*) species, such as N2O— or NH3-based plasmas, provide excellent front end of line (FEOL) cleaning solutions. These plasmas offer acceptable resist removal rates, low Si oxidation, little impact on dopant distribution profiles and good residue removal capability. However these approaches may limit residue removal efficiency and throughput for some post implant strip or advanced integration processes.
A plasma ashing system according to the present disclosure includes a process chamber including a substrate. A carrier gas supply provides a carrier gas to the processing chamber. A plasma source is configured to create plasma to the process chamber. A liquid injection source is configured to at least one of inject a compound into the plasma or supply the compound into the plasma. The compound is normally a liquid at room temperature and at atmospheric pressure. A controller is configured to control the liquid injection source, to expose the substrate to the plasma for a predetermined period and to purge reactants from the processing chamber after the predetermined period.
A method for ashing a substrate includes arranging a substrate in a processing chamber; supplying a carrier gas to the processing chamber; creating plasma in the processing chamber; at least one of injecting a compound into the plasma and supplying the compound into the plasma, wherein the compound is normally a liquid at room temperature and at atmospheric pressure; exposing the substrate to the plasma for a predetermined period; and removing reactants from the processing chamber after the predetermined period.
Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
In the drawings, reference numbers may be reused to identify similar and/or identical elements.
The present disclosure describes systems and methods for liquid injection plasma ashing with improved resist and residue removal capability and with superior substrate loss performance for advanced dry strip applications.
Referring now to
The substrate processing system 10 may include any type of plasma asher or other system. For example, a plasma asher employing an inductively coupled plasma reactor or a downstream plasma asher may be used. Other suitable plasma ashers include, but are not limited to, electron cyclotron residence (ECR) systems, radio frequency (RF) systems, hybrid systems, or other suitable systems. In one example, the plasma asher is a downstream plasma asher, such as for example, a microwave plasma asher.
A controller 68 may sense operating parameters such as chamber pressure and temperature inside the process chamber using one or more sensors 70. A vacuum pump 74 typically draws process gases out of the process chamber 12 and maintains a suitably low pressure within the reactor by a flow restriction device, such as a restriction valve 72. The controller 68 may also control the valves and/or mass flow controllers 20 as well as other components of the system 10.
In some examples, a liquid injection system 78 injects liquid into the plasma. The liquid injection system 78 includes a liquid source 80, a shut off valve 82, and a valve 84 to control the amount of added liquid/vapor substance. A heater 86 may be provided to heat lines 88 between the liquid source 80 and the shutoff valve 82, the valve 84 and the plasma source 16 (or the process chamber 12).
The shut off valve 82 may be used to stop the liquid flow when desired and may include a remotely triggered and pneumatically or electrically controlled shut off valve. In some examples, the valve 84 may include a fine-adjustable needle valve. The liquid may include water, alcohol, hydrazine, peroxide, benzene, or other suitable liquid. While the liquid is shown being introduced at the plasma source 16, the liquid can be introduced directly into the plasma in the process chamber 12 and/or in other suitable ways.
In
One benefit of generating plasma with injected liquids is to provide novel plasma chemistries, new plasma radicals and/or novel mix ratios of plasma active species that can be helpful for one or more of the following: (1) improved resist removal capability, (2) improved substrate loss characteristics, (3) improved implant crust and residue removal capability, (4) improved Si, SiN, SiGe, oxide or metals oxidation, (5) improved dopant retention performance, etc.
In some examples, the liquid injection plasma ashing according to the present disclosure includes a mix of a carrier gas and compound that is normally (at room temperature and at atmospheric pressure) in liquid form. The compound is introduced into the plasma as a vapor or injected as a liquid. As a result of the lower pressure, higher temperature, and/or energy supplied by the plasma, the compound dissociates into new reactive species. In some examples, the carrier gas includes at least one of argon (Ar), helium (He), molecular nitrogen (N2), forming gas (FG) (such as for example, 97% N2 and 3% H2), molecular oxygen (O2), ammonia (NH3), molecular hydrogen (H2), or other carrier gas. The mix may optionally include a reactive gas. The reactive gas may include at least one of molecular oxygen (O2), molecular hydrogen (H2), ammonia (NH3), CxFy, CxHy, carbon monoxide (CO), carbon dioxide (CO2), nitrous oxide (N2O), nitrogen triflouride (NF3), or other reactive gas (where x and y are integers).
The plasma generated from this mixture produces new plasma species that are unique (in type, composition, mix ratio, abundance, etc.). The benefit of the introduction of the new species includes one or more of improved resist removal rates, reduced substrate loss, improved residue and polymer removal rates, improved dopant retention performance, and/or improved device performance or yield.
Referring now to
At 124, the mix is disassociated into one or more new reactive species (as compared to the plasma without the compound) due to the lower pressure, higher temperature and/or energy supplied by the plasma. At 132, the substrate is exposed for a predetermined period. At 136, reactants are removed from the processing chamber by purging or evacuating the chamber.
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Photoresist removal rates were measured for nitrogen and NH3/O2 (90% NH3, 10% O2) plasma, chemistries with and without added liquid or vapor injection additives of IPA and H2O2. The resist removal rate was determined with a 1.8 mm thick AZ1512 I-line photoresist and with a plasma exposure of 30 s at 275° C. wafer temp at 1 Torr and 7 slm TGF of the carrier gas. The Table I below shows the results, indicating significant response from the additives. It should be noted that a lower ash rate could potentially be of benefit for improved crust and residue removal capability.
The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.
In this application, including the definitions below, the term controller may be replaced with the term circuit. The term controller may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; memory (shared, dedicated, or group) that stores code executed by a processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.
The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared processor encompasses a single processor that executes some or all code from multiple controllers. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more controllers. The term shared memory encompasses a single memory that stores some or all code from multiple controllers. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more controllers. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage.
The apparatuses and methods described in this application may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data.
