Wafer Surface Temperature Research Articles

Development of Highly Sensitive and Stable SAW-based Temperature Sensor Array and its Interface Electronics for Realtime Monitoring of Wafer Surface Temperature in Plasma Chamber

Development of Highly Sensitive and Stable SAW-based Temperature Sensor Array and its Interface Electronics for Realtime Monitoring of Wafer Surface Temperature in Plasma Chamber

Sparse identification modeling and predictive control of wafer temperature in an atomic layer etching reactor

To address the escalating demand and supply constraints for semiconductor devices, manufacturing techniques such as thermal atomic layer etching (ALE) have been utilized, which require robust temperature control systems. Radiative heating with lamps is a promising method for achieving fast and precise temperature control. However, there is limited research in analyzing the dynamic control of radiative lamp heating systems. In this study, a transient, two-dimensional (2-D) radiative heating model in a cross-flow thermal ALE reactor is constructed through Ansys Fluent. A sparse identification (SINDy) modeling approach is applied to build a reduced-order dynamic model for the prediction of system states in the control system. A model predictive controller (MPC) is then developed to bring the wafer surface temperature to the target temperature while preserving the uniformity of the temperature on the wafer surface. Control is implemented by adjusting the powers of three groups of heating lamps independently. Notably, a novel feedback-based time-varying steady-state penalty approach is applied with the MPC in this study, which enables the system to reach the target temperature range within 10 s while maintaining temperature uniformity for 1000 s.

Plasma Ion Bombardment Induced Heat Flux on the Wafer Surface in Inductively Coupled Plasma Reactive Ion Etch

Plasma plays an important role in semiconductor processes. With the recent miniaturization and integration, the control of plasma became essential for success in the critical dimension of a few nanometers and etch narrow and deep holes with their high aspect ratios. Recently, the etching process has reached physical limitations due to a significant increase in wafer surface temperature under the elevated amount of RF power, affecting not only the warpage phenomenon, but also etching uniformity and etching profiles. Therefore, the plasma characteristics are identified using an invasive single Langmuir probe (SLP) for wafer temperature diagnosis. Optical data is obtained through a non-invasive optical emission spectroscopy (OES) and the plasma parameters are derived to compare and verify with the SLP. Two variables, electron temperature and electron density, are substituted for the heat flux formula to derive the heat flux according to the location. Using a wafer-type temperature sensor, the trends of the derived heat flux values towards wafer chuck were investigated. This study presents a method to calculate heat flux values in real time, anticipate wafer temperatures, and potentially illuminate existing ion heating problems.

Toward Real Time Monitoring of Wafer Temperature in Plasma Chamber Through Surface Acoustic Wave Resonator and Mu-Negative Metamaterial Antenna

Surface acoustic wave (SAW)-based temperature sensors and wireless sensing systems were developed for real-time monitoring of the wafer surface temperature in a plasma chamber. A one-port SAW resonator was used for the temperature sensor because of its unique capabilities of 3less (wireless, batteryless, and chipless (no embedded interface electronics)). Three SAW sensors with different resonant frequencies of 380, 445, 475MHz were employed to distinguish individual sensor from the whole sensor units and prevent electromagnetic (EM) interference caused by a plasma driving frequency of 15.6 MHz in the plasma reactor. The changes of the reflection peaks in the measurement system were compared in three different cases. When the SAW sensor was connected to the antenna, the reflection peak corresponding to SAW resonant frequency was clearly observed in the reflection profile. When heat was applied to the SAW sensor by shining an infrared heater, only the reflection peak corresponding to the SAW resonant frequency was largely downshifted while the background reflection profile remained the same. High sensitivity and linearity were observed from the three sensors. The sensitivity increased on the same wafer surface as the center frequency of the sensor increased. A negligible change in the sensor resonance peak was observed when a plasma radiation was continuously illuminated on the sensor surface, indicating that the fabricated sensor with a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> passivation layer protects well against energetic X-ray and EM radiations. The sensor resonance peaks were not changed by a plasma driving frequency of 15.6 MHz that was applied between top and bottom plates.

Development of a calibration system for wafer-type temperature sensor

Wafer-type temperature sensors are widely used during semiconductor fabrication as integrated monitoring sensors for the real-time monitoring of wafer surface temperature, which affects the quality and yield of semiconductor devices. In recent years, various wafer-type temperature sensors have been developed according to the process type and temperature range for monitoring the temperature distribution. However, there is little research on the calibration system to ensure the accuracy and reliability of the developed wafer-type temperature sensor. In this study, we designed a system for the calibration of wafer-type temperature sensors. With this system, the traceability of the sensor can be guaranteed by calibrating the sensing characteristics, such as area uniformity, temperature stability, and accuracy. The conventional temperature calibration bath is calibrated by placing a wafer-type temperature sensor in a liquid-controlled system to have uniform temperature. This method is difficult to apply to the field because the wafer-type temperature sensor can be contaminated by liquids and can adversely affect semiconductor processes. For this reason, we used a heating chamber similar to chemical vapor deposition equipment for a calibration system. We evaluated the properties of the calibration system including the rising time (which means the time taken to reach the target temperature) and temperature stability according to the heat capacity. Moreover, we developed a measurement method that allows for the evaluation of the temperature of the wafer-type temperature sensor within 15 min at 150 °C. The calibration system and measurement method developed in this study are expected to improve the efficiency of semiconductor fabrication processes.

Growth of InGaAs(P) in planetary metalorganic vapor phase epitaxy reactor using tertiarybutylarsine and tertiarybutylphosphine for photovoltaic applications

The effects of wafer (surface) temperature on the surface morphologies of InP, InGaAsP, and InGaAs grown in a planetary metalorganic vapor phase epitaxy (MOVPE) reactor using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as group V precursors were investigated. Compared with small horizontal reactors, InP growths require a relatively low temperature to prevent TBP predecomposition and parasitic gas-phase reactions. However, such a low temperature can prevent the surface migration of In adatoms and degrade surface morphology, especially when a substantial amount of Ga precursors is present. Hence, growths of InGaAs require a higher temperature than that of InP and InGaAsP. In this work, 1.04 eV In0.79Ga0.21As0.46P0.54 and 0.74 eV In0.53Ga0.47As single-junction cells as well as InGaAsP/InGaAs dual-junction solar cells have been successfully fabricated. The cell performances reveal that InGaAs layers grown at 590 °C exhibit great crystal quality, while 550-°C-grown InGaAsP layers contain a noticeable extent of defect density and lattice imperfection.

Study on temperature field and flow field of doped oxidized silicon wafer prepared by vertical furnace

In this paper, the temperature field and flow field of the doped oxidized silicon wafer are studied by finite element simulation. The preparation parameters are optimized. The simulation results are verified by experiments. Experiment and simulation results show that the heater on the wafer surface temperature significantly affect the homogeneity. The temperature uniformity of the wafer surface at the bottom of the reaction chamber is significantly affected by the pedestal. By using the vertical diffusion furnace to prepare the doped oxidized silicon wafer, the uniformity of the film thickness is guaranteed. Finally, high quality silicon wafers are prepared in batches.

Characterization of the Descum Process for Various Silicon Substrates Doping

The descum process is temperature-sensitive process. It has been demonstrated that the process is very sensitive to silicon substrate doping, which impacts wafer heating. A higher doping level caused much higher resist removal when the descum process was ran in a reactor that also ran dry strip processes. The higher level of resist removal was the result of higher wafer surface temperature. The likely causes for higher wafer surface temperature are lower thermal conductivity and higher emissivity of the highly doped wafer substrate.

Analysis and Modeling of Wafer Thermal Transfer in a PECVD Reactor

The temperature distribution in the reactor, especially on the surface of the wafer, is the important factors influencing the chemical reaction in CVD and PECVD process. This paper focused on a typical cylindrical PECVD reactor carrying with a wafer, and established the combination calculation model, which divided the chamber system into two calculation domains according to the rarefied degree of the gases. A one-dimensional thermal model was developed to calculate the temperature profiles in the narrow gap between the wafer and the heater, considering the heat conduction, radiation and thermal accommodation phenomenon between the gas and the surfaces in low pressure conditions; a two-dimensional axisymmetric model was applied to calculate the temperature profiles in the chamber above the wafer, considering the heat conduction, radiation and mass transfer. We verified the validity of the model through the experimental measurement in different pressure with the aluminum matrix pedestal and the one without. The experiment and numerical calculation both pointed out that there are 15~30K temperature drop in the narrow gap between the wafer and heater with the pressure of 1~10Torr at the outlet of the chamber, the mass flow of 5000sccm at the inlet, and the fixed temperature of 673K within the heater. The lower the pressure was, the greater the differences were, and it presented a negative exponential relation. In addition, this paper predicted the response of the wafer surface temperature to the change of the narrow gap height and chamber pressure via numerical calculation model. The results showed a negative linear relationship between the wafer top surface temperature and the narrow gap height. When the narrow gap height was changed in the range of 0.15~2mm and chamber pressure of 1~10Torr, the temperature of wafer will drop 0.5~5.5K.

Growth pressure dependence of optical and structural properties of a-plane InGaN/GaN multi-quantum wells on r-plane sapphire

We investigated the influence of growth pressure on the characteristics of a-plane InGaN based MQWs. Nonpolar a-plane GaN based MQW films were directly grown on r-plane sapphire by metalorganic chemical vapor deposition (MOCVD). The growth pressure for the MQWs was varied from 100 mbar to 400 mbar, while keeping other growth parameters constant. The polarity of a-plane InGaN/GaN grown on r-plane sapphire was determined by CBED (convergent-beam electron diffraction) measurements. The blue-shifted PL peak wavelength and decreased FWHM of the PL peak were observed as the growth pressure was increased from 100 mbar to 400 mbar. Meanwhile, the PL peak intensity for MQWs increased as the growth pressure increased. This result was explained by the variation of the wafer surface temperature, which was affected by the growth pressure in spite of being exposed to the same susceptor temperature. The increased growth pressure leads to increased gas conduction and, thereby, the wafer surface temperature increased. For MQWs grown at the same wafer surface temperature, the higher growth pressure led to increased In incorporation in a-plane InGaN/GaN MQWs.

Effect of additive N 2 and Ar gases on surface smoothening and fracture strength of Si wafers during high-speed chemical dry thinning

In this work, we investigated the changes in the surface roughness and fracture strength of bare or mechanically ground Si wafers caused by high-speed chemical dry etching. High-speed chemical dry thinning was achieved by injecting NO gas and additive N 2 and Ar gases directly into the reactor during the supply of F radicals from NF 3 remote plasmas. With the additional injection of N 2 and Ar gases, together with the direct-injected NO gas, the rough surfaces of the mechanically ground Si wafers could be effectively smoothened while keeping the thinning rate of Si very fast, viz. up to 18.2 μm/min. The additive N 2 gas reduced the wafer surface temperature after thinning. The fracture strength of the Si wafers thinned down to 50 μm by the chemical dry etching process was more highly increased, due to the more effective removal of the mechanical damage and stress generated during the mechanical grinding process, as compared to the other final thinning methods such as lapping or plasma etching. The results indicated that the high-speed dry chemical thinning process could be used for the ultra-thin final thinning of Si wafers for next generation three-dimensional packaging technologies.

Silicon Wafer Surface-Temperature Monitoring System for Plasma Etching Process

A thermoreflectance temperature measuring system was developed with the aim to realize monitoring of the silicon wafer surface temperature during plasma etching. The thermoreflectance detects variations in temperature through changes in optical reflectance. To overcome such difficulties as low sensitivity and limitation in installation space and position for in situ measurements, the differential thermoreflectance utilizing two orthogonal polarizations was introduced. Noise such as fluctuations in the incident beam intensity or changes of loss in the optical path would affect both polarizations equally and would not affect the measurement. The large angle of incidence of the beam allows measurement to be performed from outside the viewing ports of existing plasma etching process chambers through the gap between the plasma electrode and the silicon wafer. In this article, an off-line measurement result is presented, with results for bare wafers as well as for wafers with metal depositions. A prototype system developed for tests in plasma etching facilities in a production line is described.

Discovering Practical Use of Sensor Wafers in CCP Reactors

This paper reviews two types of sensor wafers that fit into the niche of spatially resolved in situ plasma diagnostics. The effect of both the incident power and the backside He flow on wafer surface temperature map was studied with the temperature sensor wafer. Another sensor wafer is designed to measure the distribution of displacement current passing through the wafer. Calibrated at 13.56 MHz, it is capable of working in a wider range of source frequencies which has successfully been demonstrated in CCP reactors. It was found that the particular type of plasma reactor and the process chemistry can impact the level of correlation between the sensor and the blanket etch rate uniformity data.

Temperature and RF Current Sensor Wafers for Plasma Etching

This paper reviews two types of sensor wafers that fit into the niche of spatially resolved in situ plasma diagnostics. The effect of both the incident power and the backside He flow on wafer surface temperature map was studied with the temperature sensor wafer. It was shown that the differential information related to the ion flux density distribution can be estimated in the case of two comparable recipe settings in a complementary way. Another sensor wafer is designed to measure the distribution of displacement current passing through the wafer. Calibrated at 13.56 MHz, it is capable of working in a wider range of source frequencies that has successfully been demonstrated in CCP reactors. It was found that the particular type of plasma reactor and the process chemistry selected can impact the level of correlation between the sensor and the blanket etch rate uniformity data.

Uniformity of the wafer surface temperature during MOVPE growth of GaN-based laser diode structures on GaN and sapphire substrate

Wafer bowing has a strong impact on the wavelength homogeneity of InGaN based light emitters due to the strong temperature dependence of the In incorporation. Using in-situ curvature measurements and pyrometry we have studied the impact of growth conditions on the lateral and vertical temperature distribution across the wafer and on wafer bow on sapphire and GaN substrates. From the pyrometry signal at 950 nm the temperature of the substrate holder can be deduced. Using 400 nm pyrometry the surface temperature was determined for sufficiently thick GaN layers. While total flow and satellite rotation were found to have no impact, the total pressure affects the vertical temperature profile and thus the wafer bow. However, the effect is small and can only be used for fine tuning. To compensate for the strain of the AlGaN cladding layer in laser structures precurved GaN substrates are shown to be advantageous. Photoluminescence confirmed a spatially uniform surface temperature distribution during the deposition of the InGaN quantum well active region with a peak wavelength around 500 nm and a deviation as low as 3.5 nm on flat sapphire substrates and precurved GaN substrates.

In situ Si Wafer Surface Temperature Measurement during Flash Lamp Annealing

Automatic emissivity compensating radiation thermometry based on polaradiometry was applied to in situ wafer surface temperature measurement on a flash lamp annealing prototype system. The developed temperature measurement system consists of a dual polarization radiation thermometer and a modulating reference light source, which were mounted on two opposing ports of the process chamber. The intense background radiation from the flash lamp was successfully suppressed by introducing a water flow layer beneath the flash lamp unit and measuring at the water absorption band of 1.95 µm. Millisecond heating and cooling of the wafer was measured for various operating conditions of the flash lamp and for various silicon wafers including wafers with microstructures. The peak temperature was compared with the sheet resistance after treatment and device properties after fabrication. Good correlation was confirmed between sheet resistance and measured peak temperature for various flash lamp intensities irrespective of the surface emissivity or heating conditions. Transistor threshold voltage showed similar correlation, which verifies the applicability of the developed thermometer system to in situ measurement during production.

기판 온도에 따른 Cl2/BCl3/Ar 플라즈마에서 ZrO2박막의 건식 식각

The wafer surface temperature is an important parameter in the etching process which influences the reaction probabilities of incident species, the vapor pressure of etch products, and the re-deposition of reaction products on feature surfaces. In this study, we investigated all of the effects of substrate temperature on the etch rate of <TEX>$ZrO_2$</TEX> thin film and selectivity of <TEX>$ZrO_2$</TEX> thin film over <TEX>$SiO_2$</TEX> thin film in inductively coupled plasma as functions of <TEX>$Cl_2$</TEX> addition in <TEX>$BCl_3$</TEX>/Ar plasma, RF power and dc-bias voltage based on the substrate temperature in range of <TEX>$10^{\circ}C$</TEX> to <TEX>$80^{\circ}C$</TEX>. The elements on the surface were analyzed by x-ray photoelectron spectroscopy (XPS).

Cl2/Ar 플라즈마를 이용한 Al2O3박막의 식각

In this study, adaptively coupled plasma (ACP) source was used for dry etching of <TEX>$Al_2O_3$</TEX> thin film. During the etching process, the wafer surface temperature is an important parameter to influent the etching characteristics. Therefore, the experiments were carried out in ACP to measuring the etch rate, the selectivities of <TEX>$Al_2O_3$</TEX> thin film to mask materials and the etch profile as functions of <TEX>$Cl_2$</TEX>/Ar gas ratio and substrate temperature. The highest etch rate of <TEX>$Al_2O_3$</TEX> was 65.4 nm/min at 75% of <TEX>$Cl_2/(Cl_2+Ar)$</TEX> gas mixing ratio. The etched profile was characterized using field effect scanning electron microscopy (FE-SEM). The chemical states of <TEX>$Al_2O_3$</TEX> thin film surfaces were investigated with x-ray photoelectron spectroscopy (XPS).

Temperature dependence on dry etching of Al2O3 thin films in BCl3/Cl2/Ar plasma

During the etching process, the wafer surface temperature is an important parameter which influences the reaction probabilities of incident species, the vapor pressure of etch products, and the redeposition of reaction products on feature surfaces. In this study, the authors investigated that the effect of substrate temperature on the etch rate of Al2O3 thin film and selectivity of Al2O3 thin film over hard mask material (such as SiO2) thin film in inductively coupled plasma as functions of Cl2 addition in BCl3/Ar plasma, rf power, and dc-bias voltage based on the substrate temperature in range of 10–80 °C. The elements existed on the surface were analyzed by energy dispersive x-ray and x-ray photoelectron spectroscopy.

Optimization of rapid thermal processing for uniform temperature distribution on wafer surface

An optimization of rapid thermal processing (RTP) was conducted to obtain uniform temperature distribution on a wafer surface by using linear programming and radiative heat transfer modeling. The results show that two heating lamp zones are needed to maintain uniform wafer temperature and the optimal lamp positions are unique for a given geometry and not affected by wafer temperatures. The radii of heating lamps, which were obtained by optimization, are 45 mm and 108 mm. The emissivity and temperature of the chamber wall do not significantly affect the optimal condition. With obtained optimum geometry of the RTP chamber and lamp positions, the wafer surface temperatures were calculated. The uniformity allowance of the wafer surface is less than ±1°C when the mean temperature of the wafer surface is 1000°C.