RTP Chamber Research Articles

A Study on Chamber Contamination Control of Rapid Thermal Nitridation Process By Applying Quartz Liner

To improve the characteristics of barrier wall in DRAM plug contact via, the rapid thermal nitridation(RTN) process has been widely used via rapid thermal process chamber. With combination of high temperature heat, process gas such as NH3 and wafer being processed, the Ammonium Chloride(NH4Cl) is generated as a byproduct of this process and chamber is contaminated by NH4Cl depositing on the reflector. This contaminant diffracts the thermal energy which comes into pyrometers and degrades process quality. To prevent this chamber contamination from the byproduct such as NH4Cl, the transparent quartz liner on reflector plate is adopted. In this study, the influence of quartz liner on reflector plate, the improvement of chamber contamination and pyrometer sensitivity were investigated. In RTN process, TiSix or CoSix is formed in Si contract area as an ohmic contact and improves the adhesion with tungsten by transducing Ti to TiN.[1] Eq.1 shows how Ammonium Chloride (NH4Cl(s)) is generated during RTN process as a byproduct. NH4Cl sublimes at 337.6°C and the reflector plate increases no more than 225.3°C at 1000°C, 90sec process condition. Therefore NH4Cl is deposited on the chamber wall as well as reflector plate. Fig.1 shows the diagram of NH4Cl deposition on reflector plate as a contaminant. This contaminant diffracts the thermal energy which comes into pyrometers and degrades the silicide uniformity. In Fig.2, device “A” at target temperature has more uniform shape than device “B” which has been processed in lower temperature than target of “A”. Fig.3 shows transparent quartz in RTP chamber to prevent reflector plate from the contaminant. Fig.4 shows presence of quartz liner has very stable halogen lamps power dissipation than without quartz. Fig.5 shows temperature error against target value with quartz liner is much lower than without quartz. In this paper, the influence of quartz liner on reflector plate, the improvement of chamber contamination and pyrometer sensitivity were investigated. From experimental result, presence of quartz liner protects reflector plate from contamination and keeps power dissipation of halogen lamps in stable. As a result, it means that more accurate heat control is possible in RTN process which could affect the quality of plug contacts of semiconductor device. Reference [1] ] Zhao Wenbin, Chen Haifeng, XiaoZhiqiang, Li leilei, Yu Zongguang, Journal of Semiconductors (2009) 056001 Figure 1

Nitrided Gate Oxide Formed by Rapid Thermal Processing for 4H-SiC MOSFETs

Rapid Thermal Processing has been evaluated as an alternative to the conventional furnace process for gate oxide formation of SiC MOSFETs. We show that the growth of the SiO2 films in a RTP chamber is orders of magnitude faster than in a conventional furnace. As well as being fast, this innovative oxidation method produces a significant improvement of MOSFET performances. Indeed, we demonstrate that combining the beneficial effect of in-situ surface preparation by H2 anneal with the one of N2O oxidation, the channel mobility increases and the electrical stability with respect to constant bias stress at low-field is improved.

Modeling and control of distributed thermal systems

This paper investigates the application of model-based control design techniques to distributed temperature control systems. Multivariable controllers are an essential part of modern-day rapid processing (RTP) systems. We consider all aspects of the control problem beginning with a physics-based model and concluding with implementation of a real-time embedded controller. The system used as an example throughout is an RTP chamber widely used in semiconductor wafer processing. With its exceptionally stringent performance requirements (low nonuniformity of wafer temperature, high temperature ramp rates), RTP temperature control is a challenging distributed temperature control problem. Additionally, it is important in the semiconductor industry because of the progressively smaller thermal budget resulting from ever decreasing integrated circuit dimensions. Despite our emphasis on faster cold wall single-wafer processing RTP chambers, the approach described here for solving distributed temperature control problems is equally applicable to slower distributed systems, such as hot-wall batch-processing furnaces. For the physical model, finite volume techniques are used to develop high-fidelity heat transfer models that may be used for both control design and optimal chamber design. Model-order reduction techniques are employed to reduce these models to lower orders for control system design. In particular, principal orthogonal decomposition techniques have been used to derive low order models. Techniques such as linear quadratic Gaussian H/sub 2//H/sub /spl infin// methods are employed for feedback control design. While the methods are illustrated here using a generic RTP system, they have been successfully implemented on commercial RTP chambers.

An Interactive System for Wafer Emissivity Estimation as Determined in an RTP Chamber

ABSTRACTWe demonstrate an interactive software system in which the emissivity of wafers can be estimated in situ using different models. The system allows the data taker to introduce a choice of design parameters necessary for the control of temperature uniformity. The objective of the interactive system is to obtain a better estimation of the wavelength dependent emissivity by using existing data such as integrated emissivity, for example, as input information. Results for some of the models are presented and compared to show differences in the models chosen. The principle advantage offered by the system are the likely prospects of a realistic improvement and confident assessment for real time temperature measurement and control in an RTP environment.

Estimation of Emissivity of a Wafer in an RTP Chamber by a Dynamic Observer

AbstractA method of estimation of wavelength-dependent emissivity of silicon wafers using thermocouple measurements is presented here. A dynamic observer and a persistent excitation of the lamps are required for convergence of the observer's estimates to the actual values of parameters for emissivity approximation. A TI designed RTP equipment and adaptive close-loop temperature control have been used to generate the required persistent excitation. Theory of emissivity estimation by this method has been developed and illustrated by experiment with this 3- zone RTP system.

Emissivity Independent Process Control in a Short Wavelength ARC Lamp RTP Chamber

AbstractTwo dimensional temperature measurements of patterned wafers are presented. The measurements are made using a commercially available CCD camera operating at λ=900nm, yielding a spatial resolution of 1 pixel per mm2 and a relative accuracy of ±0.25 °C. The emissivity is determined using a reflectivity measurement made possible by the unique properties of a short wavelength arc lamp RTP chamber. The use of this measurement system for closed loop control is discussed and the application to maintaining accurate time temperature profiles independent of emissivity is described.

Tisi2 Characterization of CVD-Titanium and RTP on a Cluster Platform–an Initial Investigation

AbstractThe silicidation of chemical vapor deposited (CVD) titanium has been investigated utilizing the Materials Research Corporation (MRC) PHOENIX™ cluster-tool platform which incorporated an AST elektronik GmbH cluster RTP chamber. This initial investigation focuses on C49 and C54 TiSi2 phase formation on bare silicon wafers. Equipment description, process results, comparison to classical PVD Ti silicide processing and future investigations will be presented.

Modeling of three-dimensional effects on temperature uniformity in rapid thermal processing of eight inch wafers

A three-dimensional steady-state model of the industry-standard AG Associates 4108 Heatpulse Rapid Thermal Processing system has been developed for the study of thermal uniformity across 8 inch wafers. The model combines radiation energy transfer among all solid surfaces in the chamber with energy transfer among the chamber materials and to the process ambient. Surfaces included are those of the tungsten filaments of the lamps, the silicon wafer, the polysilicon annular thermal guard ring, the quartz process tube, and the gold reflectors which surround the lamps and process tube. These surfaces are divided into approximately 4800 individual surface elements for the radiation transfer allowing very accurate thermal analysis. The model has previously been shown to provide very good agreement with experiment for temperature distributions across an 8 inch wafer. The model is presently used to make quantitative examinations of asymmetric effects occurring in a RTP chamber which cannot be examined by 2-dimensional models. Situations examined include the effect of nonuniform lamp power distributions. Also examined is tilting of the wafer with respect to the flow tube and reflective chamber.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Combined Simulation and Measurement Study of Temperature Uniformity in Rapid Thermal Processing

ABSTRACTModeling and simulation of rapid thermal processing has been studied extensively in the past. This work presents the results of a combined simulation and measurement study of a commercial multilamp RTP chamber. The simulations were used to estimate the contributions of different geometrical, material, process, and physical effects on temperature uniformity. The physical effects considered in the simulations included radiation, thermal conduction, transient effects during ramp up and cool down and the effects of patterns on the wafer surface. The effects were corroborated by direct temperature measurements using thermocouple embedded wafers, and the results were used to reliably calculate stress effects. The stress distributions were determined analytically in cases without surface films on the wafer. In the case of wafers with surface films, stress distributions were calculated based on thermal strains. This study allows us to concentrate efforts on increasing temperature uniformity to those areas where the greatest benefits in terms of yield and film uniformity can be obtained.

Pyrometric Emissivity Measurements and Compensation in an RTP Chamber

ABSTRACTThe emissivity effects and compensation schemes encountered in pyrometric temperature measurements in RTP systems are described in this paper. The emissivity effects include substrate roughness, layered films, substrate temperature, and chamber reflectivity. Compensation techniques are derived based on the emissivity effects, and include reference thermocouples and reflectance-based measurements. Compensated emissivity results in wafer-to-wafer temperature variations of less than ± 6 C, compared to as much as ± 100 C for uncompensated emissivity. A new model for emissivity analysis at temperatures larger than 700 C is also described.