Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Multiple layers
Reexamination Certificate
2002-05-20
2004-11-02
Lund, Jeffrie R. (Department: 1763)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Multiple layers
C438S761000, C438S762000, C427S255700, C117S088000, C117S098000, C117S200000, C118S715000, C118S725000, C118S730000
Reexamination Certificate
active
06812157
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thin film deposition at a single atomic layer precision for manufacturing of semiconductor devices. More particularly, this invention describes a variety of apparatus configurations to enable atomic layer chemical vapor deposition of thin films of various materials on the surface substrate.
BACKGROUND OF THE INVENTION
The manufacturing of advanced integrated circuits (ICs) the microelectronic industry is accomplished through numerous and repetitive steps of deposition, patterning and etching of thin films on the surface of a silicon wafer. An extremely complex, monolithic and three dimensional structure with complex topography of variety of thin film materials such as semiconductors, insulators and metals is generated in a typical IC fabrication process. The present trend in the ICs, which is going to continue in the foreseeable future, is to increase the wafer size and decrease the critical device dimensions. As an example, the silicon wafer size has progressed in recent years from 150 mm to 200 mm and now to 300 mm and the next wafer size of 400 mm is on the horizon. Simultaneously, the critical device dimension has decreased from 0.35 micron to 0.25 micron to 0.18 micron. Research and development for the future device dimension devices at 0.13 and next to 0.10-micron technologies is being conducted by several leading IC manufacturers. Such steps are necessary to increase the device speed, sophistication, capability and yield. These trends in the IC production technology have placed extremely stringent and divergent demands on the performance of semiconductor manufacturing equipment that deposit, pattern or etch progressively smaller device structures on the surface of a silicon wafer. This in turn translates into extremely precise control of the critical process parameters such as film thickness, morphology, and conformal step coverage over complex topography and uniformity over an increasingly large area wafer surface.
Various well-developed and established technologies for thin film deposition are being practiced in the IC industry at present, the most prominent being chemical vapor deposition (CVVD) and physical vapor deposition (PVD). Both of these techniques, however, are flux dependent. This means that the number of gaseous species impinging per unit area of the wafer surface must be constant. In a conventional CVD process, the gas mixture is sprayed evenly from a larger diameter showerhead, with hundreds of pinholes in it, facing directly opposite the wafer. With increasing wafer diameter, this entails an even larger showerhead with larger number of pinholes with a strict condition that each pinhole must receive equal amount of gas all the time. An even worse situation is encountered when two or more gases, that are spontaneously reactive towards each other, are required to deposit a thin film. In such a case, the operation of a CVD reactor to deposit large area thin films becomes an extremely difficult task.
Moreover, temperature uniformity of the deposition surface plays an extremely crucial role in affecting the rate of film deposition. This factor being rather crucial in CVD as compared to PVD. In a practical example, the wafer temperature must be maintained at +/−1 degree C. at 500 degree C. This leads to complex and expensive heater designs and temperature control hardware and ultimately to added cost and complexity. The average rate of film deposition in CVD mode can be tailored over a wide range. The rate of deposition may be as high as 1000 A/min to as low as 100 A/min. However, yet another fundamental shortcoming of CVD being a dynamic process (and PVD also) is extremely low degree of film uniformity below a certain minimum value of thickness, typically below 200 Å (Angstrom). With complex device topography, this limitation is exacerbated to bring highly non-uniform film deposition.
The PVD process requires a high vacuum apparatus to throw vaporized material in cluster form towards the surface of the wafer. This leads to poor control on film deposition rate, expensive apparatus, and also limitations on the type of materials to be deposited. Also, the PVD being a line of sight process is much less amenable to achieve conformal film deposition over a complex topography. Such fundamental attributes of these prevalent film deposition technologies place severe constraints on the equipment performance, their scale-up and result in to deficiencies in process control that are being increasingly and rapidly felt as the rapid progress towards smaller device dimensions and larger wafer diameter continues.
A variant of CVD called rapid thermal CVD (RTCVD) is being employed recently to achieve precise control on film deposition rate. In a typical RTCVD process, the wafer is rapidly heated or cooled by radiation from switching on and off a large bank of high power lamps to the desired reaction temperature. Simultaneously, the wafer is exposed to reactive gases. The optimum temperature thus achieved for desired time duration acts like a reaction switch. Further process control can be achieved by simultaneously switching the gas flow towards the wafer. This technique, though rapidly emerging, has some serious drawbacks. First, rapid heating and cooling may lead to wafer warping, slip and undesirable film stress. Second, RTCVD is invariably susceptible to complexities arising from undesirable deposition on windows, optical properties of chamber materials, expensive and complex hardware for optics and radiation control. Also required is the chamber construction material that can withstand rapid and repeated thermal shocks under high vacuum.
Atomic layer chemical vapor deposition (ALCVD or merely ALD) is a simple variant of CVD. It was invented in Finland in late 70's to deposit thin and uniform films of compound semiconductors, such as zinc sulfide. There are several attributes of ALD that make it an extremely attractive and highly desirable technique for its application to microelectronic industry. ALD is a flux independent technique and it is based on the principle of self-limiting surface reaction. It is also relatively temperature insensitive. In a typical ALD sequence two highly reactive gases react to form a solid film and a gaseous reaction by-product is formed. It is carried out in discrete steps as follows.
FIG. 1
is a schematic of a conventional ALD process cycle with two inert gas pulses and two reactive gas pulses. First a reactive gas (A) is pulsed over the wafer
10
. The gas molecules saturate the wafer
10
surface by chemically reacting with it to conform to the contours of the surface. This process is called chemisorption. Next an inert gas (P) pulse is sent over the surface that sweeps away excess number of gas molecules that are loosely attached (physiosorbed) to the surface and thus a monolayer of highly reactive species is formed on the wafer
10
surface. Next the second reactive gas (B) is pulsed over the wafer
10
surface. This reacts rapidly with the monolayer of first gas already adsorbed and a desired film is formed with the elimination of the gaseous by-product. Again an inert gas pulse (P) is introduced that sweeps away by-product and an excess of the second type of reactive gas. The wafer
10
surface is thus covered by a monolayer of desired film (AB) that is as thin as a single atomic layer. The surface is left in a reactive state for the complete sequence to start over. The desired film is thickness is built by repeating the complete reaction sequence described above for definite number of times.
There are numerous practical advantages that ALD can offer over the state-of-the-art techniques such as CVD and RTCVD. Being a flux independent techniques ALD is transparent to the wafer size. It means in an ALD reactor a 300 mm wafer can be coated as simply and as precisely as a 150 mm wafer. ALD also considerably simplifies the reactor design. Also being a chemically driven process, it is much less temperature sensitive. ALD usually offers a temperature window that ca
Lund Jeffrie R.
Sawyer Law Group LLP
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