Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-02-01
2004-04-20
Coleman, W. David (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S240000, C438S765000, C438S776000, C438S784000
Reexamination Certificate
active
06723595
ABSTRACT:
This application claims the benefit of Korean Patent Applications No. 2001-5043 filed on Feb. 2, 2001, which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for performing Chemical Vapor Deposition (CVD), and more particularly to Atomic Layer Deposition (AID) Processes.
2. Discussion of the Related Art
In the field of thin film technology requirements for thinner deposition layers, better uniformity over increasingly larger area substrates, larger production yields, and higher productivity have been driving forces behind emerging technologies developed by equipment manufactures for coating substrates in the manufacturing of various semiconductor devices.
Electric devices are recently highly integrated to have smaller size and light weight because of semiconductor devices. Specifically, the manufacture of Ultra Large Scale Integration is possible due to the improved thin film deposition technologies manufacturing the semiconductor devices.
Namely, process control and uniform film deposition achieved in the production of a microprocessor can be achieved. These same factors in combination with new materials also dictate higher packing densities for memories that are available on a single chip or device. As these devices become smaller, the need for greater uniformity and process control regarding layer thickness rises dramatically.
Various technologies well known in the art exist for applying thin films to substrates or other substrates in manufacturing steps for integrated circuits (ICs). Among the more established technologies available for applying thin films, Chemical Vapor Deposition (CVD) is an often-used and commercialized process. Atomic Layer Deposition (ALD), a variant of CVD, is a relatively new technology now emerging as a potentially superior method for achieving uniformity, excellent step coverage, and transparency to substrate size. ALD, however, exhibits a generally lower deposition rate than CVD.
CVD is flux-dependent application requiring specific and uniform substrate temperature and precursors (chemical species) to be in a state of uniformity in the process chamber in order to produce a desired layer of uniform thickness on a substrate surface. These requirements becomes more critical as substrate size increases, creating a need for more complexity in chamber design and gas flow technique to maintain adequate uniformity.
In the CVD method alluded above, deposition rates of thin films and characteristics of deposited thin films depend on circumstances of the process chamber, such as chamber temperature and pressure, accompanying precursor's flow rate. Another problem in CVD coating, wherein reactants and the products of reaction coexist in a close proximity to the deposition surface, is the probability of inclusion of reaction products and other contaminants in each deposited layer. Also reactant utilization efficiency is low in CVD, and is adversely affected by decreasing chamber pressure. Still further, highly reactive precursor molecules contribute to homogeneous gas phase reactions that can produce unwanted particles which are detrimental to film quality. Therefore, Low Pressure Chemical Vapor Deposition (LPCVD) by which step coverage and uniform thickness of thin film are improved is now in the spotlight in forming thin films on a substrate surface. However, when using LPCVD, the deposition rates decrease, thereby attempting to introduce reaction gases having higher partial pressures. This also causes the problems that gas reactions occur in an undesired position of reaction chamber, so the possibility of contaminants in the deposited layer increases.
On account of above-mentioned problems, Atomic Layer Deposition (ALD) has been researched and developed. Although a slower process than CVD and although the similarity to CVD in using precursor reactions, ALD demonstrates a remarkable ability to maintain ultra-uniform thin deposition layers over complex topology. This is at least partially because ALD is not flux dependent as described earlier with regards to CVD. This flux-independent nature of ALD allows processing at lower temperatures than with conventional CVD rocesses.
ALD processes proceed by chemisorption at the deposition surface of the substrate. The technology of ALD is based on concepts of Atomic Layer Epitaxy (ALE) developed in the late 1970s or early 1980s, for example, U.S. Pat. No. 4,058,430, for growing of polycrystalline and amorphous films of ZnS and dielectric oxides for electroluminescent display devices. The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD appropriate reactive precursors are alternately pulsed into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas purge. Each precursor injection provides a new atomic layer additive to previous deposited layers to form a uniform layer of solid film. The cycle is repeated to form the desired film thickness.
A good reference work in the field of Atomic Layer Epitaxy, which provides a discussion of the underlying concepts incorporated in ALD, is Chapter 14, written by Tuomo Suntola, of the Handbook of Crystal Growth, Vol. 3, edited by D. T. J. Hurle, .COPYRGT. 1994 by Elsevier Science B. V. The Chapter title is “Atomic Layer Epitaxy”. This reference is incorporated herein by reference as background information.
To further illustrate the general concepts of ALD, an ALD process for forming a film of materials A and B, as elemental materials, will be explained hereinafter. A solid layer of element A is formed over the initial substrate surface, and then a first purge is processed to form a single atomic layer of element A. Over the A layer, a layer of element B is applied, and then, a second purge is performed. Therefore, the layers are provided on the substrate surface by alternatively pulsing a first precursor gas A and a second precursor gas B into the region of the surface, resulting in providing the AB solid material.
Meanwhile, gaseous reactants and their bonding energy are dependant on a substrate and a material which are under the deposited thin films. When forming a single-crystalline layer on a surface of single-crystalline silicon substrate, there are a lot of active portions which are distributed uniformly on that silicon substrate surface and on which gaseous reactants are deposited. By way of applying a thermal energy to the gaseous reactants with maintaining the substrate at a high temperature, gaseous reactants are uniformly deposited and decomposed in the surface of substrate, and thus, silicon atoms are rearranged and grow to a single-crystalline thin film in accordance with the single-crystalline surface of the substrate. At this time, the physically deposited gaseous reactants exist on the chemically deposited silicon layer provided on the substrate surface, and thus such gaseous reactants act as impurities and contaminants that decrease purity of deposited layer. Therefore, a purge process proceeds after such a depositing process. Namely, the substrate heated with the aid of a suitable heating source is subjected to the gaseous reactants, and then purged using an inert gas. Therefore, the chemically deposited reactants are left on the substrate, whereas the physically deposited reactants are removed from the substrate, resulting in forming a single atomic silicon layer on the single-crystalline silicon substrate.
This type of procedure is also disclosed in U.S. Pat. No. 4,389,973, for example. According to that patent, the wafer is sequentially subjected to a plurality of gaseous reactants in order to form thin films thereon. During the deposition processes, the gas phase diffusion barrier is used as a carrier gas in order to prevent reactions between source gases, or the carrier gas is used to remove the residual gases after injecting each source gas.
U.S. Pat. No. 4,767,494, as another example, discloses the compound semico
Brewster William M.
Coleman W. David
Duane Morris LLP
Jusung Engineering Co. Ltd.
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