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Topic: BEOL Dielectric Etching
Meeting Date: June 12, 2008
Time: 2pm – 5pm
Agenda:
2:00 - 2:20pm Refreshments
2:20 – 2:30pm PEUG Business Meeting
- Shawming Ma, PEUG Chair
2:30 – 5:00pm Presentations:
High Frequency Capacitively Coupled Plasma for Low Ion Energy Dual Damascene Etching
- A. Marakhtanov, Alexei.Marakhtanov@lamresearch.com, E.A. Hudson, K. Takeshita,
O. Turmel, Lam Research Corp.
Abstract: Capacitively coupled discharges are widely used for semiconductor processing, especially in the area of dielectric etching. With a wide range of film materials and complex stacks including multiple mask layers, advanced dielectric etch processes require tight control of plasma parameters, such as ion flux, radical composition, and ion energy distribution (IED). This paper presents IED measurements and patterned-wafer etch results as a function of RF bias excitation frequency applied to the wafer electrode. The aim is to produce the optimal IED for etching of soft materials, such as low-k dielectrics commonly used in Dual Damascene interconnect schemes. One key challenge arises in the trench etch step, which requires a vertical etch profile in the low-k film. But the process must avoid corner faceting of any exposed via holes or of the hard mask layer which defines the initial trench pattern. Faceting would cause an increase in via or trench critical dimension, respectively. The competing requirements of vertical profile and minimal faceting define a fairly narrow range of acceptable ion energies for the process. If power is held constant, higher RF driving frequencies typically produce plasmas with higher densities and lower potentials, and enable operation at lower pressure. Both the mean ion energy and width of the IED reaching the wafer tend to decrease as the wafer bias frequency increases. For frequencies too low, the width of the IED is too large and faceting is induced by the high energy ions. For frequencies too high, the mean IED is too low to etch the low-k film with a vertical profile and acceptable rate. Results show that the necessary IED for these applications can be obtained by applying 60MHz to the wafer electrode.
In-Situ Measurement of Thermal and Physical Contributions to Plasma Etch
- G.A. Roche, KLA-Tencor, SensArray Division, Gregory.Roche@kla-tencor.com, & M.R. Tesauro, Qimonda
Abstract: Plasma etch behavior is often explained in terms of “physical” and “chemical” components: both critically related to surface temperatures generated during plasma etching. In an attempt to measure the chemical etch rate component, a specially prepared, 300mm autonomous temperature sensor wafer was used to simultaneously record dynamic surface temperature during plasma etching of photo resist coated and bare silicon surfaces. Data for N2 / H2, Ar / O2, O2 and Cl2 etching chemistries were then compared with measured resist etch rates and RF sensor wafer data. Although insulation of the temperature sensors from the plasma by the 3 micron resist coating prevented calculation of the etch rate chemical component, the capability of this methodology with resist coatings < 500nm was shown. In addition the use of both RF and temperature sensor wafers to quickly identify and correct semiconductor etch process development issues related to isotropic etch non-uniformity was shown.
Dielectric Etching using VHF Capacitively Coupled Plasmas
- Kallol Bera, Kallol_Bera@amat.com, Shahid Rauf, Ken Collins, Applied Materials, Inc.
Abstract: Capacitively coupled plasma (CCP) discharges are widely used for dielectric etching in the semiconductor industry. Operating frequencies, especially the source frequency in multi-frequency CCP systems, have generally increased in recent years to be able to generate high electron density discharges with moderate ion energy. The combination of higher driving frequencies and larger plasma size means that electromagnetic effects start to play a more important role in determining plasma behavior. Understanding the physics of VHF plasmas is therefore critical for assessing the scalability of CCPs to future generations of dielectric etching technologies. This paper uses a computational model to elucidate the physics of VHF CCP discharges. The 2-dimensional model includes the full set of Maxwell equations in their potential formulation. The equations governing the vector potential, A, are solved in the frequency domain after every cycle for multiple harmonics of the driving frequency. Current sources for the vector potential equations are computed using the plasma characteristics from the previous cycle. The coupled set of equations governing the scalar potential, ?, and drift-diffusion equations for all charged species are solved implicitly in time. Our simulations focus on a CCP discharge at high VHF, and examine the effect of VHF power and inter-electrode spacing on the plasma characteristics. It is found that the electrostatic component of the electric field peaks in the sheath region, where there is an imbalance between positive ion and electron concentrations. Electromagnetic fields are generated by current flowing through the discharge. The electromagnetic component of the electric field peaks in the center of the chamber due to the standing wave effect. The electromagnetic fields have a strong influence on charged species location and concentration at high VHF. However, besides the operating frequency, the plasma reactor design (inter-electrode spacing and electrode sizes) and operating condition (VHF power) determine the relative importance of the electromagnetic fields in plasma dynamics.
CANCELLED: Interactions of Plasma with Dielectrics during Ultra Low-k Dual Damascene Etch
- Yifeng Zhou, Yifeng_Zhou@amat.com, Kevin Zhou, Ryan Patz, Andrew Darlak, Jeremiah Pender, and Michael Armacost, Applied Materials, Inc.
Abstract: Porous ultra-low k dielectrics with k < 2.2 are being integrated into 32nm technology node and beyond. New films with higher levels of carbon doping and more porosity interact with etching plasmas differently than the older generation films (k = 2.4). Some of these differences are the result of film chemical composition. For example, same via etch process appears to be more “polymerizing” on higher carbon content film, and etch plasma regime has to be optimized to regain selectivity between ultra-low k dielectrics and photoresist. Other differences are more related to higher porosity level that is necessary to achieve lower k value, such as ultra low-k film surface roughness. The process window to achieve smooth dielectric surface becomes smaller with higher porosity films. Surface roughness can happen on both planar and vertical surfaces, and during several etch steps including resist strip, barrier film removal, and post-etch treatment. In some cases, modification to the ultra-low k film in one etch step is not observed until several steps later. Careful control of etch plasma is necessary in every step to minimize cumulative damage to ultra-low k film to prevent surface roughness.
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