F. De Smedt

A Detailed Study on the Growth of Thin Oxide Layers on Silicon Using Ozonated Solutions

The oxidation of silicon using ozonated, deionized water solutions was investigated as a function of several parameters: reaction time, pH, ozone concentration, temperature, and influence of anions. The oxidation of silicon was dependent on ozone concentration especially near neutral pH. This concentration dependence disappears at concentrations greater than 15 mg/L ozone. No temperature effect was found between 20 and 50°C. Lowering the pH leads to a less pronounced concentration dependence with no specific anion effect between HCl or . The oxidation of silicon by ozonated solutions does not lead to extensive roughening of the silicon surface as shown by atomic force microscopy measurements. Various thermal oxidation models were evaluated and the Fehnler expression represents the experimental data fairly well. The overall oxidation thus follows logarithmic growth kinetics. It is proposed that ozone dissociates at the interface in a one‐step reaction forming the oxidizing species, namely, . This radical diffuses through the layer under the influence of an electric field which develops over the oxide layer. The field‐imposed drift is the limiting factor in the oxidation process. The bulk chemistry of the ozonated solutions is of no importance to the oxidation of silicon. The initial oxidation rate, defined at an oxidation time of 6 s, was dependent on the ozone concentration below 15 mg/L and leveled off above this concentration as it was limited by the field‐imposed drift of the oxidation precursor.

On the Application of a Thin Ozone Based Wet Chemical Oxide as an Interface for ALD High-k Deposition

Introduction In order to keep pace with CMOS scaling trends, alternative gate oxide materials, with a high dielectric constant, were proposed. To have a low interface trap density, good mobility [1], and good Atomic Layer Deposition (ALD) growth characteristics [2], the presence of an interfacial oxide layer is still prerequisite. Hydroxyl groups are the key players for the initiation of the ALD reaction [3]. In this work the application of downscaled ozone based wet chemical oxide as a surface pretreatment for ALD high-k deposition is examined.

The application of ozone in semiconductor cleaning processes : The solubility issue

The solubility of ozone in aqueous solutions expressed as a pseudo-Henrys law coefficient for ozone, * H T O3 , is measured over a pH range of 1 to 8, and temperature range of 15 to 45°C in the presence of several additives: HCl, HNO 3 , HAc (Ac is acetate), NaAc, and NaOH. The value of * H T O3 was found to he a function of temperature, pH, and nature of the anion. The pseudo-Henrys law coefficient is maximal at low pH and decreases with rising pH of the aqueous solution. The addition of chloride enhances the ozone decay rate and thus decreases the solubility helow pH 2 while the addition of acetic acid/acetate results in an increase of * H T O3 for pH > 3. The solubility enthalpy ΔH 0 sol for ozone is found to be equal to (-22.38 ± 0.79) kJ/mol. For applications of ozone in semiconductor cleaning processes, knowledge of the dependence of * H T O 1 on pH, temperature, gas phase concentration, and additive is important in order to achieve optimized cleaning conditions.

The increasing importance of the use of ozone in the microelectronics industry

Abstract Recently the microelectronics industry is investigating the application of ozonated solutions in the cleaning of semiconductor devices as an alternative for the frequently used H2SO4-mixtures. The use of ozone would result in more environmentally friendly and cost-saving cleaning concepts. To optimize this new wet chemical cleaning processes, fundamental understanding of the behavior of ozone in ultrapure water is required. The decomposition and the solubility of ozone in ultrapure water were investigated as a function of pH, temperature and various additives. Some applications will also be discussed, namely the oxidation of silicon and the mechanistic aspects of the removal of organic contamination.

A Wet chemical Method for the Determination of Thickness of SiO2 Layers below the Nanometer Level

A wet chemical procedure has been elaborated to measure the thickness of thin silicon dioxide layers. The procedure is based on the etching of the layer by HF and the determination of Si concentration in the microgram per liter range in the HF containing etch solutions. Two analytical techniques were optimized for this purpose: a spectrophotometric technique, the so‐called molybdenum blue method and inductively coupled plasma mass spectrometry (ICP‐MS). In the first method a detection limit of 3.3 μg/L Si could be achieved with a sensitivity of . Interference by HF up to 0.1% v/v (volume/volume %) HF could be eliminated by adding boric acid to the solution. In the second method Si was determined by ICP‐MS using the Si isotope. The detection limit in bidistilled water was 1.2 μg/L Si with a sensitivity of (5807 ± 98) cps/(μg/L Si). The presence of HF increased the background signal of Si due to the etching of the quartz plasma torch. In 0.005% v/v HF a detection limit of 5.9 μg/L Si could be achieved. For silicon dioxide layers below 1 nm, a reproducibility better than 5% was obtained.

The Impact of Traces of Hydrogen Peroxide and Phosphate on the Ozone Decomposition Rate in “Pure Water”

To obtain an idea of the magnitudes of the ozone loss rates rO3 in practical applications of ozone, an overall determination of the ozone decay profiles and rate constants was carried out in four different systems. These systems resemble different conditions for industrial application of ozone and the peroxone process, such as in the field of micro electronics, drinking water purification, disinfection, etc. Therefore, the behavior of ozone was monitored in the pH range from 4.5 to 9.0, in pure water and phosphate buffered systems in absence and presence of small amounts of hydrogen peroxide (10−7 M to 10−5 M H2O2). First the reproducibility of the ozone decay profiles was checked and from the various kinetic formalism tests, the reaction order 1.5 for the ozone decay rate has been selected. As expected, hydrogen peroxide increases the decay rates. In pure systems, added concentrations of 10−7M H2O2 already cause a remarkable acceleration of the ozone decay in the acidic and neutral pH range compared to the pure systems. However for alkaline pH conditions almost no effect of the low hydrogen peroxide concentrations was noticed. Contradictory to literature data, in the absence of hydrogen peroxide, ozone displays faster decays in the buffered systems of low ionic strength of 0.02 compared to pure water. This acceleration is more pronounced for acidic pH conditions. Low concentrations of phosphate may indeed accelerate the ozone decay in the presence of organic matter. Adding H2O2 concentrations below 10−5M to phosphate buffered solutions has a negligible effect on the ozone decay rate compared with pure water systems, except for pH 7. It appears that phosphate masks the effect of hydrogen peroxide below 10−5 M as tested here. Thus the application of AOPs by adding low concentrations of hydrogen peroxide is not well feasible in the presence of phosphate buffers in pure water systems.

Determination of Photoresist Degradation Products in O3/DI Processing

Abstract Mainly because of cost-saving and environmental concerns, ozone has been introduced as a cleaning agent in semiconductor manufacturing in recent years. This work reports the determination of the most important degradation products formed after the stripping of two different types of photoresist (PR) {1-Line and DUV resist) by ozone processing. Six low molecular weight carboxylic acids could be identified for the I-line PR, five for the DUV PR. The behavior of these degradation products under continuous ozonation as well as their stability in water was also investigated. Despite the chemical similarity of these carboxylic acids, their behavior appears to be quite different.

Materials compatibility and organic build-up during ozone-based cleaning of semiconductor devices

As integrated circuits keep on shrinking, micro-contamination needs further to be controlled, such as particles, metallic and organic species left on the wafer surface. Nowadays the use of ozonated chemistries in cleaning processes is gaining interest since the cleaning processes are urging towards more environmentally friendly processes . However the generation and transport of ozone may lead to contamination into the cleaning solutions. This work looks at some organic and inorganic species introduced in deionized water (DIW) when processing with ozone.

Photoresist Stripping by Ozone/Water Processes: Effect of Additives

Introduction In the last decade, numerous papers have been published showing the high potential of ozone/water processes in the removal of photoresist (PR) layers [1,2]. However, reaction and transport mechanisms are far from being completely understood due to a number of reasons. At first, one has the complexity of the overall heterogeneous process with three phases: a solid photoresist layer, a (essential) water film and an ozone-rich gas ambient. In this system different transport mechanisms are involved, like the ozone mass transfer from the gas phase into the water and transport of ozone through the water film towards the photoresist surface. Secondly, the complexity is due to the chemistry of ozone in water. When dissolved in water, ozone is not stable but decomposes according to a radical chain mechanism [3]. The intermediates formed in this decomposition are highly reactive radicals that are also able to degrade the resist material (indirect oxidation). Besides the water temperature and pH, the rate of ozone decomposition is also determined by the presence of certain compounds in the process water [4]. Depending on their chemical action, they can either enhance the direct oxidation of the resist material by ozone itself or the indirect oxidation by the radical intermediates. This may ultimately lead to higher strip rates and thus a lower processing time. In this work it was investigated experimentally whether higher strip rates can be obtained by spiking the process water with of a number of selected additives. The observations will be compared with our previous experimental findings and the results will generate valuable information concerning the reaction mechanisms occurring.

Advanced Oxidation Processes in the Removal of Organics From Silicon Surfaces in IC Manufacturing: Theoretical Concepts

Ozone is considered an environmentally friendly alternative for currently applied H2SO4-based mixtures in the cleaning of semiconductor devices. In order implement ozone/water cleaning processes in practical systems, functional research is needed to understand the underlying chemical processes. Related to the removal of organic contamination from silicon surface, one needs to know whether ozone or radical species are the most efficient. A kinetic modeling study is performed to solve this problem whereby the pH is varied and different additives are checked. Theoretical concepts as Dominant Oxidation Pathway (DOP) and Radical Pool (RP) will be introduced for the evaluation of the various reaction pathways.