A model for rapid thermal processing: achieving uniformity through lamp control

The rapid thermal processing (RTP) system requires critical control of temperature uniformity. For most RTP system, the structure and heating modes of heating component determined the control strategy. Major types of the heating system of nowadays RTP systems were reviewed and compared. Then a heating system for RTP was proposed to improve the uniformity of heaving emission, which includes optimally designed light path and high efficient light reflecting system. The simulating results of that were also given.

Issues of rapid thermal processing (RTP) system design and process applications are reviewed. Temperature measurement is the most important and limiting factor in current RTP systems. Problems related to the temperature measurement and control and potential solutions are discussed. Process uniformity control is another important issue in RTP system design. Reactor chamber design, selection and arrangement of heat source, as well as issues related to dislocation generation, patterned and doped wafer, and ramp-up (down) thennal cycle are considered. Experimental results (RTO, RTCVD silicon nitride and polysilicon) based on an in-house RTP system developed in our laboratory are taken as examples to demonstrate the process applications and system requirements for single wafer processing.

In this paper, a model-based control method for RTP (Rapid Thermal Processing) system is proposed. RTP system is a device used to heat semiconductor wafers uniformly. It can heat wafers rapidly and reduce the processing time. However, it is very difficult for a RTP system to achieve the extremely stringent requirement on temperature uniformity (±1[K] or less) without suitably controlling and coordinating the radiative heat flux from the halogen lamps. In this research, the location of lamps is optimized first. Then, a feedback control system is designed which provides optimal temperature control during the thermal processing. The design is carried out based on a linearized model and H2 optimal control. The effect of sensor location is also investigated. Numerous simulations show that satisfactory performances are obtained in both the tracking and the uniformity of wafer temperature.

This paper highlights the basic principles of rapid thermal processing (RTP) systems and the important areas of concern. The basic system characteristics, the fundamental physics involved, and the techniques for temperature measurement and control are extensively reviewed. We summarize the options currently available for 15 RTP equipment manufacturers and point out the latest developments in RTP system design and temperature measurement. Some novel options for temperature control (optical, fiber optical, and photoacoustic) are included.

A novel method for the estimation of the temperature distribution in a rapid thermal processing (RTP) system is developed in this paper. The proposed method uses a proper orthogonal decomposition algorithm to extract the dominant modes of the temperature distribution and a reduced-order model is obtained. Then, a reduced-order sliding-mode observer is developed to capture the dynamics of the dominant modes. The estimated dynamics of the dominant modes can be used to reconstruct the temperature distribution. It is proved that the estimation error would be drawn into a small boundary rapidly. Test results confirm the effectiveness of the proposed observer for the RTP system.

A new proprietary rapid thermal processing (RTP) method has been developed and implemented for the fast switching of a gas ambient surrounding a wafer inside a RTP furnace operated in the low pressure or atmospheric pressure regime. By controlling the gas flow pattern around a semi-conductor wafer, the effective volume of process gas interacting with the wafer has been reduced by a factor of 33. Thus, real-time gas sequencing can be realized so that multiple rapid thermal processing steps, involving dry and wet rapid thermal oxidation (RTO), rapid thermal nitridation (RTN), rapid thermal annealing (RTA) and chemical vapor deposition (CVD), can be carried out sequentially in a single RTP cycle. Experimental data from ion implant anneal and thermal oxide thin film growth will be presented to illustrate the major technical challenges and solutions associated with the integration of the new method into the Summit/spl trade/ RTP systems. Using this approach, the benefits of rapid thermal processing with high productivity and quick ambient switching is realized.

Rapid thermal processing (RTP) is an important process in the fabrication of semiconductor devices. It is difficult to achieve temperature uniformity control of the wafer in RTP since the system is a highly nonlinear process with strong spatial distribution. In this study, a transfer learning-based three-dimensional (3D) fuzzy multivariable control scheme is proposed for the temperature uniformity control of an RTP system. In difference to the traditional expert-knowledge based design, a two-level framework of transfer learning methodology is constructed to design the 3D fuzzy multivariable controller (3D FMC) with the help of a multi-output support vector regression (M-SVR). The 3D FMC defines a qualitative spatial fuzzy structure that will be transferred to the M-SVR. On the other hand, the structure parameters of the M-SVR will be learned from data and transferred to design quantitative parameters of the 3D FMC. Under the framework of transfer learning, the control laws (e.g. human control experience) hidden in spatio-temporal data can be extracted and formulated back into multi-output 3D fuzzy rules. The proposed method provides an effective integration of the spatial fuzzy inference and the transfer learning for 3D FLC design. The newly developed method is applied to the temperature uniformity control of a rapid thermal chemical vapor deposition (RTCVD) system at the set temperature 1000K, and the maximum non-uniformity along the wafer radius is close to 1K.

A simple model for the components that make up a rapid thermal processing system is given. These components are the furnace, the pyrometer used to measure temperature, and the control system that utilizes the pyrometer measurement to control the power to the lamps. The models for each of the components are integrated in a numerical code to give a computer simulation of the complete furnace operation. The simulation can be used to investigate the interaction of the furnace, temperature-sensing technique, and the control system. Therefore, the interplay of heat transfer (furnace) properties, optical (pyrometer) parameters, and control gains can be studied. The objective is to define variability in wafer temperature as process parameters change. The following three applications of the model are included: (1) a simulation of open-loop operation; (2) a simulation of the ramp up and subsequent operation with a step change in wafer optical properties; and (3) a simulation of the rapid thermal chemical vapor deposition of polysilicon on silicon oxide which demonstrates the applicability model for actual processes. A technique for correction of pyrometer output to improve temperature control is also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The design of a decentralized controller has been studied as an integral part of the development of a commercial rapid thermal processing (RTP) system for manufacturing display glass. The glass RTP system uses bulb-type tungsten-halogen lamps for heating. A highly uniform temperature distribution with a maximum temperature difference of less than 6 °C between any two points is required during glass processing, regardless of the size of the glass. In designing a decentralized controller that satisfies this requirement, the problems of optimal sensor location, lamp grouping, optimization-based controller tuning, and time-varying bias input signals were identified and solved. The performance of the controller was investigated experimentally and numerically.

Rapid thermal processing (RTP) is becoming increasingly more important in semiconductor wafer fabrication. A nonlinear physical model for a generic RTP system is described. This generic RTP system is representative of the state-of-the-art RTP systems. A low-order nonlinear model is developed. A model-based LQG controller is designed for the low-order model which successfully controls the full-order nonlinear simulation model.

We consider the recursive identification and feedback control of the rapid thermal processing (RTP) system where the asymmetry of the convective heat transfer coefficient, caused by gas flow in the chamber, is taken into consideration. The success of RTP depends on the precise control of water temperature by adjusting the strength of the heating lamps to minimize dopant redistribution as well as wafer warpage. An efficient method of recursive identification and optimal feedback control is developed by separating the radiation field from the temperature field of the wafer and converting the heat conduction equation for the wafer temperature to a reduced-order model by means of the Karhunen-Loève Galerkin procedure.

The effect of rapid thermal processing on wafer distortion and overlay accuracy in global alignment photolithography in the fabrication of 0.85 /spl mu/m CMOS Flash EPROM integrated circuits was studied. Both rapid thermal process parameters and system design (single and multi-lamp processors) were evaluated for their effect on overlay accuracy. It was found that a rapid thermal process (following contact etch and ion implantation) at set temperatures greater than or equal to 950/spl deg/C resulted in interconnect metallization-to-contact overlay errors in excess of 1.0 /spl mu/m across the wafer, which led to a 20% functional circuit yield loss. In the case of the single lamp processor, this misalignment was attributed to wafer distortion due to the temperature overshoot during the ramp step, which subsequently resulted in an across wafer temperature range of greater than 120/spl deg/C. This temperature overshoot and nonuniformity was eliminated by reducing the ramp rate below 100/spl deg/C/s. This ramp rate reduction, however, decreased the system wafer throughput, and required optimization to eliminate the overlay errors and minimize the effect on throughput. In this study, a 60/spl deg/C/s ramp rate was found to be optimum. For the multi-lamp RTP system, the metal-to-contact overlay error was not observed. This was believed to be due to the design of the heating mechanism in the multi-lamp processor, which did not produce the large wafer temperature overshoot and nonuniformity that was observed in the single lamp processor.

The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200 and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination of the Nb films from the substrates was observed.

A new method of temperature control for rapid thermal processing of silicon wafers is presented whereby in-situ wafer temperature is determined by measurement of wafer thermal expansion via a laser autofocus mechanism. Various potential error sources are considered including wafer bow, effects of wafer doping and crystal orientation. Results are provided showing that variations in crystalline orientation and dopant levels have no measurable effect on expansion of the silicon substrate, allowing a direct correlation of wafer expansion to temperature. The expansion measurement technique and implementation into a rapid thermal processing system as a temperature control is described. Preliminary data show the wafer to wafer repeatability of temperature is 1% (3-(sigma) ) using wafer expansion as the control.

Until recently, the semiconductor production wafer processed in a rapid thermal processing system was considered to be an opaque material where all of the incident irradiation is absorbed by the surface and volume absorption has no significance. Such an approach cannot explain several experimentally observed effects such as the different emissivity of doped and un-doped regions, difference in temperatures between die and its boundary, etc. This paper describes a method of solution of heat transfer in semitransparent medium. An example illustrates the impact of semitransparency on the wafer temperature distribution