Plasma ashing apparatus and endpoint detection process

Abstract

A plasma ashing apparatus for removing organic matter from a substrate including a low k dielectric, comprising a first gas source; a plasma generating component in fluid communication with the first gas source; a process chamber in fluid communication with the plasma generating component; an exhaust conduit in fluid communication with the process chamber; wherein the exhaust conduit comprises an inlet for a second gas source and an afterburner assembly coupled to the exhaust conduit, wherein the inlet is disposed intermediate to the process chamber and an afterburner assembly, and wherein the afterburner assembly comprises means for generating a plasma within the exhaust conduit with or without introduction of a gas from the second gas source; and an optical emission spectroscopy device coupled to the exhaust conduit comprising collection optics focused within a plasma discharge region of the afterburner assembly. An endpoint detection process for an oxygen free and nitrogen free plasma process comprises monitoring an optical emission signal of an afterburner excited species in an exhaust conduit of the plasma asher apparatus. The process and apparatus can be used with carbon and/or hydrogen containing low k dielectric materials.

Description

[0001] The present disclosure relates to semiconductor apparatuses and processes, and more particularly, to plasma mediated processes and plasma apparatuses suitable for ashing organic material from a substrate including a low k dielectric material.[0002] Recently, much attention has been focused on developing low k dielectric thin films for use in the next generation of microelectronics. As integrated devices become smaller, the RC-delay time of signal propagation along interconnects becomes one of the dominant factors limiting overall chip speed. With the advent of copper technology, R has been pushed to its practical lowest limit for current state of the art so attention must be focused on reducing C. One way of accomplishing this task is to reduce the average dielectric constant (k) of the thin insulating films surrounding interconnects. The dielectric constant (k) of traditional silicon dioxide insulative materials is about 3.9. Lowering the dielectric constant (k) below 3.9 wi...

AI Technical Summary

Benefits of technology

0060] The operating pressures within the process chamber 16 are preferably about 100 millitorr to about 3 torr, with about 200 millitorr to about 2 torr more preferred, and with about 500 millitorr to about 1.5 torr even more preferred. Moreover, the process chamber 16 may further include additional features depending on the application. For example, a quartz window may be installed and a UV light source may be placed in proximity to the wafer. Such a non-columnar light source may have a wavelength similar to UV excimer lasers that have been shown to enhance photoresist removal in bulk strip applications and as such, could be used in parallel with microwave plasma generated reactive gases. Moreover, pre- and post-photoresist strip exposure to the light source could also provide residue removal and implanted resist removal advantages. Overhead RF sources, optical ports, gas analyzers, additional light sources, and the like could also be used either independently, or in combination, with the process chamber 16 providing an extremely flexible process platform.

0061] Coupled to the process chamber 16 is the exhaust assembly component 18. The exhaust assembly component 18 includes an exhaust conduit 170 in fluid communication with an interior region of the process chamber 16. An inlet 172 of the exhaust conduit 170 is fluidly attached to opening 158 in the bottom plate 156 of the process chamber 16. The exhaust conduit 170 preferably has a substantially straight shape from inlet 172 to outlet 174, thereby minimizing high impact areas (e.g., sharp bends and curves in the conduit) and the propensity for buildup of photoresist material and plasma ashing byproducts at sharp bends. In a preferred embodiment, the exhaust conduit 170 is fabricated from quartz or sapphire coated quartz. A minimum diameter of the exhaust conduit 170 (and opening 156) is preferably at least about 2 inches for a 300 mm ashing apparatus (about a 1.5 inch diameter or greater is preferred for a 200 mm plasma ashing apparatus). By centrally locating the exhaust conduit 170 within the process chamber 16, flow from the plasma tube to the exhaust assembly is simplified and provides greater plasma uniformity.

Problems solved by technology

As integrated devices become smaller, the RC-delay time of signal propagation along interconnects becomes one of the dominant factors limiting overall chip speed.

The ashing step is typically followed by a wet chemical treatment to remove traces of the residue, which can cause further degradation of the low k dielectric, loss of material, and may also cause increase in the dielectric constant.

Although gas mixtures containing one or more of these sources efficiently ash photoresist from the substrate, the use of these gas sources has proven detrimental to substrates containing low k dielectrics.

The increases in dielectric constant affects, among others, interconnect capacitance, which directly impacts device performance.

Moreover, the use of oxygen-containing plasma discharges is generally less preferred for advanced device fabrication employing copper metal layers since copper metal is readily oxidized at the elevated temperatures typically employed for photoresist ashing.

Occasionally, the damage is not detected during metrology inspection of the substrate after plasma processing.

However, the damage can be readily demonstrated by a subsequent wet cleaning process, as may be typically employed after plasma ashing, wherein portions of the carbon and / or hydrogen-containing low k dielectric material are removed.

The removed portions of the dielectric material are a source of variation in the critical dimension (CD) of the feature that is frequently unacceptable and impacts overall device yield.

Moreover, even if a wet clean process is not included, the electrical and mechanical properties of the dielectric material may be changed by exposure to the oxygen-free plasma discharges thereby affecting operating performance.

However, the mechanism of removal is different for these less aggressive plasma discharges.

The buildup of these ashing materials can lead to short mean-time-between-clean (MTBC) times and frequent rebuild / replacement of vacuum hardware resulting in loss of throughput and increased costs of ownership.

Additionally, deposits of photoresist material within the process chamber that are located above the plane of the substrate can lead to particulate contamination on the substrate, thereby further affecting device yields.

An additional problem with oxygen free and nitrogen free plasma discharges is the non-uniformity of the plasma exposure.

Since these plasma discharges are less aggressive, non-uniformity is a significant issue.

However, it has been found that the less aggressive plasma discharges have fewer reactive species and the dispersal from the center point of the baffle plate to its outer edge can result in hot spots on the wafer, i.e., areas of non-uniformity.

Another problem with oxygen free and nitrogen free plasmas concerns endpoint detection.

Traditional endpoint detection methods and apparatus are not suitable for muse with these types of plasma discharges.

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