AVS2004 Session PS1+DI-FrM: High K and Difficult Materials Etch

Friday, November 19, 2004 8:20 AM in Room 213A

Friday Morning

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8:20 AM PS1+DI-FrM-1 Inductively Coupled Plasma Etching of Poly-SiC in SF6 Chemistries
S.H. Kuah, P.C. Wood (SAMCO International Inc.)
A study was made to find a low cost and robust etching solution for silicon carbide (SiC) using a commercially available inductively coupled plasma etching tool. Sulfur hexafluoride (SF6) was selected because of its high degree of F dissociation and non-hazardous nature. A parametric study of the etching characteristics of poly-SiC in inductively coupled plasma (ICP) SF6 chemistries was performed. Etch chemistry was found to greatly affect etch rate, selectivity, final surface cleanliness and smoothness. Etch rates as high as 5884 Å/min were achieved with high SiC/Cr selectivity (36) and clean, but relatively rough etched surfaces (134 Å RA) using a SF6/CF4/He gas mixture. It was found that He addition apparently increases the ionization of SF6 in the plasma and thus increases the SiC etch rate due to increases in the SF3+ and F radical concentrations1,2. The formation of pillar-like structures and side wall deposition was observed on the etched SiC surfaces under some conditions. These unwanted etch by-products exhibited a high concentration of Cr and Fluorine. However, an Ar plasma pre-clean of the the substrate, or high ICP and/or bias powers, and CF4 addition can reduce the pillars formation significantly.

1 J.D.Scofield, B.N.Ganguly, and P.Bletzinger, J.Vac.Sci.Technol. A 18, 2175 (2000).
2 Z.A.Talib and M.Saporoschenko, Int. J. Mass Spectrom. Ion Processes 116, 1(1992).

8:40 AM PS1+DI-FrM-2 A Study of Inductively Coupled Plasma Etch of GaN/InGaN Based Light Emitting Diodes
H.D. Chiang, K.C. Leou, C.H. Shen, S. Gwo (National Tsing Hua University, Taiwan); M.H. Wu (Uni Light Technology Inc., Taiwan); C.H. Tsai (National Tsing Hua University, Taiwan)
Group III-Nitride semiconductors are of considerable interest because of their potential for optoelectronic applications such as light-emitting diodes (LEDs) and laser diodes (LDs) in the visible light regions. The dry etching process is one of the critical steps in the fabrication of nitride-based LEDs. A study based on Taguchi experimental design was carried out to investigate the etch characteristics of GaN/InGaN quantum well light emitting diodes using a high density inductively coupled plasma of BCl3/Cl2-based chemistry. The process parameters studied include inductive power, bias power, BCl3/Cl2 gas ratio and chamber pressure. The etch characteristics measured were etch rate, surface roughness, side-wall angle and etch selectivity to SiO2 mask. It was found that the variations in the bias power had maximum effect on the etch rate whereas the pressure affected etch rate the least. Anisotropic profiles were generally achieved over a wide range of parameters with low substrate bias. Certain interesting phenomena such as grass and sidewall striations were observed. Nearly smooth etched surface were observed for most etch conditions. The etch mechanisms of different etch conditions on both GaN grown by MBE and MOCVD and the differences of surface roughness before and after etching will also be discussed.
9:00 AM PS1+DI-FrM-3 High-k Materials Etching
D. Wu, B. Ji, S.A. Motika, E.J. Karwacki, M.J. Plishka (Air Products and Chemicals, Inc.)
As integrated circuit (IC) device geometry shrinks, high-k materials are needed to maintain adequate breakdown voltage. Due to their high chemical inertness and extremely low volatility, removal of the high-k materials has been technically challenging. In this paper, we will present an effective plasma etching process where a mixture of BCl3 and NF3 is identified as the reactive gas. Compared to pure BCl3, the etch rate for HfO2 was doubled after adding 25% NF3 to BCl3, and the etch rate for HfSixOy was also doubled after adding 15% NF3 to BCl3. Pure BCl3 did not etch ZrO2 at a condition of 0.55 W/cm2 power density and 500 mTorr chamber pressure. But an etch rate of 6 nm/min was achieved when using a mixture of 20% NF3 in BCl3. Detailed experimental setup and data analysis will be reviewed in this paper.
9:20 AM PS1+DI-FrM-4 Ion-Enhanced Plasma Etching of Metal Oxides in Chlorine Based Plasmas
D. Ramirez, Y. Ta, J.P. Chang (University of California, Los Angeles)
The development of plasma etching chemistries is necessary to pattern new gate dielectric materials, such as hafnium based oxides, for sub-90nm complementary metal oxide semiconductor (CMOS) devices. An electron cyclotron resonance high density plasma reactor is used in this work to study the etching of metal oxides and their corresponding metals in chlorine based chemistries. The plasma density, electron temperature and gas phase species are characterized by a Langmuir probe, an optical emission spectrometer, and a quadrupole mass spectrometer. The etching of Al2O3 and HfO2 was first studied in Cl2 and BCl3 plasmas, to allow for studies of the etching of hafnium aluminate, Hf1-xAlxOy. The dominant etch products of Al and Hf metals in Cl2 and BCl3 plasmas were metal chlorides. However, the dominant etch products of Al2O3 and HfO2 in Cl2 and BCl3 plasmas were metal chlorides and metal boron-oxy-chlorides, respectively. These results allowed us to assess the effect of metal-oxygen bond strength on the surface etching reactions, as well as the oxygen removal mechanism in the etching of metal oxides. Enhanced surface chlorination of the metal oxide surfaces was observed with increasing ion energy, which demonstrates that the etching reaction is limited by the momentum transfer from the ions to the film surface. The etch rates of Al2O3 and HfO2 and their selectivities to Si were found to increase in BCl3 plasmas due to the increased oxygen removal rate. Etching of Hf1-xAlxOy will also be presented, with a focus on predicting its etch rate based on the etching of Al2O3 and HfO2 individually. Finally, the application of a generalized model, developed for the etching of ZrO2 and HfO2, to the etching of Al2O3 and Hf1-xAlxOy in chlorine based plasmas will be discussed.
9:40 AM PS1+DI-FrM-5 Investigation of Etching Properties of HfSiO and HfSiON as Gate Dielectrics
J.H. Chen, W.S. Hwang, W.J. Yoo, S.H.D. Chan (National University of Singapore)
Hf based high-K dielectrics have been studied as the alternative gate dielectric. For the high performance logic device application, HfSiON is receiving significant attention as the most promising dielectric material because of its good thermal stability, immunity to boron penetration and high carrier mobility in the channel under the gate. In advanced HfSiON films, N profile is optimized: the top HfSiON is highly nitrided to block boron penetration, but the bottom near Si substrate remains as HfSiO to maintain high carrier mobility in the channel. We investigated the etching properties of HfxSi1-xO2 (x=0, 0.3, 0.5, 0.7 and 1) and their nitrided films in ICP of Cl2/HBr/O2. Results show that etch rates of HfSiO and HfSiON increase rapidly with increasing ion energy, ion density and ratio of Cl2. Linear dependency of etch rates on the √Eion, which obeys the universal energy dependency model of ion enhanced chemical etching yields, was observed with the etch threshold energies of 30-36 eV for HfSiO with different Si% in Cl2/HBr. Etch rates of HfSiO and HfSiON are strongly dependent on the open area of the wafer because the oxygen released from these films can suppress the etching process. The addition of the small amount of O2 to Cl2/HBr plasma or increasing pressure can suppress the etching of HfSiO and HfSiON effectively. The 6nm thick HfSiO or HfSiON can be removed by a wet chemical of 1% HF (DHF) in 30s before anneal; after 700°C anneal, etch rates drop slightly but the densified HfSiO interfacial layer (IL) of ~1nm cannot be removed in DHF. By incorporating N by the plasma nitridation, this IL can be removed by DHF in 10s, and very little Si substrate recess and clean surface can be achieved. This combined approach of the plasma etching and the wet removal proved that HfSiON can be integrated into advanced CMOS processes successfully.
10:00 AM PS1+DI-FrM-6 Etching of HfO2 and HfSiOx at Elevated Temperatures
M. Hélot (CNRS, France); G. Borvon, T. Chevolleau, L. Vallier, O. Joubert (LTM-CNRS, France); P. Mangiagalli, J. Jin, Y.D. Du, M. Shen (Applied Materials)
In CMOS technology, the traditional SiO2 used as gate dielectric is being replaced by a material presenting a higher dielectric constant (so called high-K materials) for the 65 or more likely the 45 nm nodes. In the integration of such materials, the etch process is one of key issues since the volatility of etch by-products is low and the high-K/Si selectivity seems extremely difficult to achieve. This work is dedicated to the etching of HfO2 and HfSiOx, two of the most promising candidates, using an industrial inductively coupled plasma source (ICP) with a hot cathode (the temperature range of the wafer can be adjusted from 200 to 350°C). Vertical high-K profile without footing or silicon recessing have been achieved. AFM measurements of silicon surface show an acceptable substrate roughness after etch. The etch process has to be adjusted with respect to the deposition technique (CVD vs. ALD) as well the thickness of the silicon oxide buffer layer between the silicon substrate and the high-K layer. XPS analyses reveal that the selectivity is obtained thanks to the formation of a thick C and Cl overlayer on SiO2 and not on HfO2. Even for these very thin layers, the endpoint techniques such as emission spectroscopy and spectroscopic ellipsometry have to used. Finally we found that the etch process (etch rate and uniformity) depends on the walls reactor seasoning.
10:20 AM PS1+DI-FrM-7 Ion-enhanced Etching of HfO2 with Cl+, BClx+(X = 1, 2) and SiCl x+(X = 1, 2,3) Ion
K. Karahashi, N. Mise (MIRAI-ASET, Japan); T. Horikawa (MIRAI-ASRC/AIST, Japan); A. Toriumi (MIRAI-ASRC/AIST, Univ. of Tokyo, Japan)
As advanced high-k gate dielectrics are being developed to replace SiO2 in the near future generation of microelectronics devices, understanding their plasma etch characteristics becomes vital for introducing new materials into the manufacturing process. We report on the interactions of HfO2 with ionic species contained in plasma etching environments. To clarify the ion induced reactions of Cl+, BClx+(X = 1, 2) and SiClx+ (X = 1, 2,3), we employed the mass-analyzed ion beam apparatus that can irradiate a single ionic species to the sample surface under an ultra-high vacuum condition. Etching yield of SiCl3+ ion is about 2 times larger than that of Cl+ ion, and etching products are hafnium chlorides and oxygen atom. This result suggests that chlorine atoms play a key role in etching reaction, and that the chemical etching yield increases with increasing number of chlorine atoms contained in the incident ions. The kinetic energy of etching products, which were estimated by the time delay of etching products with respects to the incident ion pulses, was larger than 0.1 eV. Therefore, products are different from thermally desorbed molecules. This indicates that desorption is caused by the momentum transfer to hafnium chloride. This work was supported by NEDO.
10:40 AM PS1+DI-FrM-8 Evaluation of the Effectiveness of H2 Plasmas in Removing Boron from Si After Etching of HfO2 Films in BCl3 Plasmas
C. Wang, V.M. Donnelly (University of Houston)
Etching of high dielectric constant ("high-K") materials in BCl3-containing plasmas is challenging due in part to boron residue that deposits on the underlying Si or SiO2 surface during the over-etching period. Boron is a p-type dopant and therefore it is best if it is removed prior to subsequent processing. We have investigated the effectiveness of H2 plasmas in removing this boron-containing layer. Following etching of HfO2 or Al2O3 thin films in a high-density BCl3 plasma, including a 60s overetch period, samples were transferred under vacuum to a UHV chamber equipped with x-ray photoelectron spectroscopy (XPS). After observing B-coverages of ~1 x 1015 (equivalent of ~ 1 monolayer), the samples were transferred back to the plasma reactor for exposure to the H2 cleaning plasma, and then re-examined by XPS. Optical emission spectroscopy was used to monitor B deposition on and removal from the plasma chamber walls. B deposition on the reactor walls during BCl3 plasma exposure reached saturated coverage in ~2 min. Following this, the H2 plasma removed half of this B layer in 90s, and 90 % in 320 s. B was rapidly removed (< 5s) from the BCl3-over-etched Si surfaces provided that the walls were first cleaned in the H2 plasma, with the Si sample held in the UHV chamber during the chamber cleaning process. Conversely, it took much longer (~170s) to remove all detectable B on the sample surface if the sample and the reactor chamber walls were cleaned in the H2 plasma at the same time. Etching rates of SiO2 and Si in the H2 cleaning plasma will be reported. Mechanisms of B deposition on and removal from chamber walls and Si and SiO2 surfaces will be discussed. A less effective sequential O2/H2 plasma cleaning process will also be presented. Supported by SRC and AMD Inc.
11:00 AM PS1+DI-FrM-9 Selective Etching of HfO2 High-k Dielectric over Si in C4F8/Ar/H2 Inductively Coupled Plasmas
K. Takahashi, K. Ono, Y. Setsuhara (Kyoto University, Japan)
As integrated circuit device dimensions continue to be scaled down, increasingly strict requirements are being imposed on plasma etching technology. Regarding gate dielectrics, the technological challenge continues for growing ultrathin SiO2 films of high quality; however, the ultimate solution relies on high dielectric constant (k) materials. In integrating high-k materials into device fabrication, an understanding of the etching characteristics of the materials is required for their removal and for contact etching. This paper presents the etch rates and possible etch mechanisms for HfO2 thin films on Si substrate in inductively coupled plasmas containing mixtures of CF4/Ar/H2 and C4F8/Ar/H2, as a function of gas composition and rf bias power. In the experiments, the discharge was established at a gas pressure of 20 mTorr and an rf source power of 280 W. The gas flow rates of fluorocarbon and Ar were 2.5 and 247.5 sccm (the ratio of fluorocarbon to total was 1 %). The rate of H2 was varied between 0 and 16 sccm. As the dc selfbias voltage was maintained at the constant value of -90 V, HfO2 and Si were etched in the CF4/Ar/H2 plasma with no relation to H2 flow rate. In the C4F8/Ar/H2 plasma, however, the conditions could be found where HfO2 was etched at the rate more than 10 nm/min, and the fluorocarbon polymer deposited on Si. In this regime, it can be possible to selectively etch HfO2 over Si. The chemical composition of the polymer was carbon-rich, and the carbon content on HfO2 was not so much as on the polymer. It can be said that carbonized products may correspond to etch products for HfO2.

This work was supported by NEDO/MIRAI Project.

11:20 AM PS1+DI-FrM-10 Characterization of the Sputtering Process in an rf Plasma for the Patterning of Nonvolatile Materials
T.J. Kropewnicki, A.M. Paterson, T. Panagopoulos, J.P. Holland (Applied Materials, Inc.)
With the integration of nonvolatile materials into microelectronic devices, such as NiFe in magnetic random access memory, perovskites in ferroelectric random access memory, and HfO2 as a transistor gate dielectric, it has become necessary to develop methods of characterizing the patterning of these materials. Removal of these nonvolatile materials by sputtering with heavy ions is probably a key component of the etching mechanism. Sputtering of materials by ion bombardment has typically been characterized using high energy ion beam systems, leading to sputtering yield probabilities as a function of ion energy. Since typical commercial plasma etch reactors use rf power to energize the ion bombardment, the usefulness of these sputtering probabilities in understanding the reaction mechanism is limited by the much lower energy levels being produced by the rf sheath, and by the spread of ion bombardment energies typically produced by an rf plasma sheath. Ion energies less than 1000 eV are common in many plasma etch systems. To create a more realistic picture of the etching process, direct measurements of the actual rf waveforms occurring on the wafer are transformed using a simple plasma sheath model into ion energy distribution functions which are then used in combination with the reported sputtering yield data to predict more accurate sputter yields for these conditions. Langmuir probe measurements of ion fluxes are then used to determine the etch rates. Comparison of these predicted rates and actual measured rates will be presented as well as possible reasons for discrepancies between the two rates.
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