Semiconductor cleaning technology

Wafer cleaning is the most commonly used in semiconductor manufacturing process typical processing steps. In the case of silicon, cleaning operation of chemical products and tools has been very mature, has many years of extensive research, and the support of important industrial equipment. So, in all the practical importance of the semiconductor silicon cleaning technology is the most mature technology. The first complete, based on the scientific sense of the cleaning program was put forward in 1970, it is specifically designed to remove the surface of Si particles, metals and organic pollutants.

Since then, the silicon cleaning technology has experienced the sustainable development of the improvements, including gas phase equivalent replacement early part in wet chemical cleaning operations. Incredibly, modern advanced Si still rely on cleaning, roughly the same set of chemical solution, but their preparation and sent to the wafer with initially proposed have changed. In addition, traditionally made the surface of the wet cleaning chemicals to choose cleaning/trimming function is now done in gas phase.

Introduce technology of semiconductor devices, a series of new materials and all kinds of plane device structure for cleaning technology presents significant challenges. Although various silicon cleaning, method is relatively mature, but they can't meet the demand of emerging . This paper briefly reviews the past development of semiconductor wafer cleaning technology.

The progress of the semiconductor cleaning technology

The first complete, based on the scientific sense of the Si surface cleaning method has been put forward in almost 40 years ago. Since then, the semiconductor cleaning method from experiment technology accumulation progress to the manufacturing yield and semiconductor industry sustainable development has the extremely important significance in science and technology.

Semiconductor cleaning technology change with time. Early focus on the big particles and metal pollutants, in fact, the semiconductor device failure is often caused by high substrate wafer in the defect density, rather than surface caused by pollution. Order of magnitude as the particles and metal pollution decreases, and the pollution control in this area is very effective, more attention is now organic pollution and surface state. As shown in figure 1, points out, use simple light cleaning method can remove organic pollution from the surface of the Si. In addition, should pay special attention to ozone dissolved in water of the gas phase in the role of organic pollution control. Another problem is the diversity of the supervision target of cleaning method, because the FEOL and BEOL cleaning requirements are different, the latter focuses on the CMP after cleaning.

 

In terms of cleaning media, wet cleaning is still the main modern advanced wafer cleaning process. Although the Si technology of cleaning chemical material and the formula of the initial RCA were similar, but the overall process of the most obvious change include: adopted a very dilute solution; To simplify the process; Widespread use of ozone water

Based on the APM (NH4OH: H2O2: H2O) chemical material still dominate position in terms of particle removal, but if there are no signs in the frequency ultrasonic strengthening, its effect is not very effective. Based on the original RCA (HPM: HCl: H2O2: H2O) formula to remove metal chemical materials are almost gave up. With much more clean resist together innovative chemistry and chemical materials is the key to success in this field. In addition, the geometry is very dense device made in pollution control and promote the development of innovative technology, for example, including supercritical CO2 (SCCO2) cleaning.

As for dry cleaning, it is used to selectively, mostly in the form of surface cleaning steps. One example is anhydrous HF (AHF)/ethanol solution process, it can effectively remove from Si surface in a variety of applications have some oxide generated or chemical. Figure 2 is a variety of surface processing operations performed in the AHF/ethanol solution process of 25 piece of wafer and 3 piece of wafer commodity diagram of the reactor. The result of the AFM in figure 3 shows that execution process did not damage the surface of the Si.

 

 

Dry wafer is any part of the wet cleaning process. Widely recognized by the wafer drying method based on the IPA make a key part of the cleaning process had great progress, these methods the Marangoni drying and its derivative method.

No matter in the batch cleaning process or on the single crystal round cleaning process, the traditional immersion cleaning still play a leading role. Cleaning process in single crystal round, this trend due to the demand of solar battery cleaning technology to strengthen. The technology, due to the number of shear processing substrate (shearnumber), can choose batch processing method. As shown in figure 2 reactor that can make the choice by gas cleaning chemical process compatible with batch processing. But at the same time, single crystal round cleaning methods (such as rotary cleaning) is advancing to the high-end applications.

The current and future challenges

To semiconductor cleaning technology can meet the new requirements, must be to adjust and modify the existing technology. With continuous narrow longitudinal size, material loss and surface roughness in the process of cleaning operation will be a field must be attention. Remove particles without material damage and graphics is the most basic requirement, therefore must be thoughtful and compromises. Physical AIDS like trillion frequency ultrasonic agitation has potential influence on structural damage and graphics to collapse, is on its improvement, in order to keep the efficiency of particle removal process at the same time not graphics integrity harmful effects. Considering the surface morphology of atomic deterioration may have fatal influence on device performance will, even if these look like DI water to clean the most benign cleaning program elements must also be reassessed.

In order to reduce some institutions collapsed the graphics device and related damage, gas phase chemistry (for example, when it comes to the front with organic solvent vapor mixture of anhydrous HF (AHF) is more and more useful.

Nonplanar sexual problems, in order to deal with the surface of a silicon wafer cleaning technology by at least three different front processing technology challenge. Of the first CMOS process. In device geometry constantly reduced, cutting-edge digital CMOS technology challenges is to keep the grid structure has enough capacity density, this is the gate length reduced hours of drive current needed to maintain a high enough. One way is to use than SiO2 dielectric constant high gate dielectric, another way is through the three dimensional structure of MOS gate to increase the gate area do not increase the unit circuit area again, another way is the combination of both.

No matter which kind of solution to become the standard, the distribution in the gate oxide cleaning before and after the RIE etching vertical "fins" in the SOI silicon (FIG. 4 a) will become important to clean up all the process elements. Figure 4 shows around the "fin" b MOSFET examples.

 

MEMS processing and put forward some different challenges. MEMS fabrication characteristics is that it contains profound corrosion fine 3 d graphics, and demand the release of the horizontal buried deep corrosion layer oxide processing technology. Using conventional wet etching and cleaning technology can't be away from this very closely geometry may etch residue, and ensure the cantilever beam and no static friction of the operation of the diaphragm. Has studied using anhydrous HF/methanol (AHF/MeOH) (figure 2) passivation oxide etching process as the feasible solutions.

Special electrical applications (such as high temperature, high power and ultra-high speed) and optical applications (such as blue light emission or UV detection there is growing demand for improve performance, this request is greatly improved many of silicon semiconductor manufacturing technology. Examples of these materials include Cr, because it has higher than the electron mobility of Si, with high k gate dielectric integration; The SiGe to channel MOSFET machining stress; And silicon carbide SiC, the band gap is very wide. In addition to the most advanced GaAs, such as GaN, InAs, InSb, ZnO, and so on some Ⅲ - Ⅴ semiconductor is becoming more and more arouse people's interest.

Surface cleaning is becoming such problems appear constantly in semiconductor processing. This is because the inferior quality of the substrate crystal (rather than its surface cleanliness) is no longer a limit related to those materials manufacturing yield the dominant factor. With the improvement of quality of all kinds of semiconductor materials base single crystal, consideration will be change, will be to give more close attention to the cleaning technology.

Semiconductor device technology rapidly expand into the mainstream silicon outside of logic and analog application areas. The display technology, solar panels and other large photovoltaic system, the surface material may include the machining of glass, ITO (indium tin oxide) or flexible plastic substrate, and so on. Even in the mainstream silicon IC and Ⅲ - Ⅴ optical applications, the semiconductor substrate also have obvious advantages, so get a follow-up study. Sapphire single crystal Al2O3), for example, is more and more importance in the semiconductor device manufacturing a substrate. All these material cleaning is of great significance.

Over the years, the development of silicon cleaning technology is the foundation of solving other semiconductor materials surface processing challenges. The emergence of various new materials will promote the development of semiconductor cleaning technology.