Semiconductor device manufacturing: process – Making passive device
Reexamination Certificate
2000-03-06
2004-10-05
Potter, Roy (Department: 2822)
Semiconductor device manufacturing: process
Making passive device
C257S531000, C336S223000
Reexamination Certificate
active
06800533
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and structure for creating a high Q inductor while simultaneously reducing the surface space that is consumed by such an inductor. The inductor of the invention is a spiral inductor that is positioned in a plane that is perpendicular to the plane of the substrate on which the conductor is created.
(2) Description of the Prior Art
Modern semiconductor technology requires the creation of high performance semiconductor devices that are produced at competitive prices. A direct result of these requirements is that device density and inter-device packaging density continue to increase from which directly follows the requirement that the surface area or space that is available on the surface of a semiconductor substrate is carefully allocated and maximized in its use.
While the majority of semiconductor devices relate to the field of digital data processing, electronic circuitry can nevertheless be divided into two broad fields. One field addresses digital processing while the second field addresses the manipulation of analog signals. Digital semiconductor devices have as function the manipulation or storage of digital information. The functions of analog electronic circuitry have in previous years typically been handled by separate components such as relatively large capacitors or relatively large inductors. The separate components may have been applied in combination with digital processing capabilities, whereby however a significant portion of the functional implementation has been realized by the use of for instance capacitive and inductive components in addition to and functionally collaborating with the digital components. Circuit requirements that are imposed on components that are required for analog processing have in the past limited the integration of such components into typical semiconductor integrated circuit devices.
Modern mobile communication applications center around compact high-frequency equipment. With the continued improvements in the performance characteristics of this equipment, continued emphasis will be placed on small size of the equipment, low power consumption, increased frequency applications and low noise levels. Semiconductor devices are used in the field of mobile communication for the creation of Radio Frequency (RF) amplifiers. A major component of a typical RF amplifier is a tuned circuit that contains inductive and capacitive components. The tuned circuit has as electrical characteristic that, dependent on and determined by the values of its inductive and capacitive components, can form an impedance that is frequency dependent, which enables the tuned circuit to either form a high or a low impedance for signals of a certain frequency. In this manner the tuned circuit can either reject or pass and further amplify components of an analog signal based on the frequency of that component. The tuned circuit can therefore be used as a filter to filter out or remove signals of certain frequencies or to remove noise from a circuit configuration that is aimed at manipulating analog signals. The tuned circuit can also be used to form a high electrical impedance by using the LC resonance of the circuit and to thereby counteract the effect of parasitic capacitances that are part of a circuit. The self-resonance that is caused by the parasitic capacitance between the (spiral) inductor and the underlying substrate will limit the use of the inductor at high frequencies.
One of the key components that is applied in creating high frequency analog semiconductor devices is the inductor that forms part of a LC resonance circuit. The key challenge in the creation of the inductor is to minimize the surface area that is required for the creation of the inductor while maintaining a high Q value for the inductor. Conventional inductors that are created on the surface of a substrate are of a spiral shape, whereby the spiral is created in a plane that is parallel with the plane of the surface of the substrate. Conventional methods that are used to create the inductor on the surface of a substrate suffer several limitations. Most high Q inductors form part of a hybrid device configuration or of Monolithic Microwave Integrated Circuits (MMIC's) or are created as discrete components, the creation of which is not readily integratable into a typical process of Integrated Circuit manufacturing.
By combining the creation on one semiconductor monolithic substrate of circuitry that is aimed at the function of analog data manipulation and analog data storage with the functions of digital data manipulation and digital data storage, a number of significant advantages are achieved. Such advantages include the reduction of manufacturing costs and the reduction of power consumption by the combined functions. To reach required inductive values for particular applications, inductors can be of significant physical size and can therefore require a significant surface area of the semiconductor substrate. To limit this impact of space requirement, inductors are typically formed on the surface of a substrate in a spiral form. The spiral form of the inductor however results in parasitic capacitances between the inductor wiring and the underlying substrate, due to the physical size of the inductor. These parasitic capacitances have a serious negative effect on the functionality of the created LC circuit by sharply reducing resonance frequency of the tuned circuit of the application.
Widely used in the industry to describe the applicability of a created inductor is the Quality (Q) factor of the inductor. The quality factor Q of an inductor is defined as follows: Q=Es/El wherein Es is the energy that is stored in the reactive portion of the component while El is the energy that is lost in the reactive portion of the component. The higher the quality of the component, the closer the resistive value of the component approaches zero while the Q factor of the component approaches infinity. The quality factor for components differs from the quality that is associated with filters or resonators. For components, the quality factor serves as a measure of the purity of the reactance (or the susceptance) of the component, which can be degraded due to parasitics. In an actual configuration, there are always some physical resistors that will dissipate power, thereby decreasing the power that can be recovered. The quality factor Q is dimensionless. A Q value of greater than 100 is considered very high for discrete inductors that are mounted on the surface of Printed Circuit Boards. For inductors that form part of an integrated circuit, the Q value is typically in the range between about 3 and 10.
In creating an inductor on a monolithic substrate on which additional semiconductor devices are created, the parasitic capacitances that occur as part of this creation limit to about 10 the quality factor that can be achieved for the inductor using the conventional silicon process. This limitation is, for many applications, not acceptable. Dependent on the frequency at which the LC circuit is designed to resonate, significantly larger values of quality factor, such as for instance 100 or more, must be available. Prior Art has in this been limited to creating values of higher quality factors as separate units, and in integrating these separate units with the surrounding device functions. This negates the advantages that can be obtained when using the monolithic construction of creating both the inductor and the surrounding devices on one and the same semiconductor substrate. The non-monolithic approach also has the disadvantage that additional wiring is required to interconnect the sub-components of the assembly, thereby again introducing additional parasitic capacitances and resistive losses over the interconnecting wiring network. For many of the applications of the RF amplifier, such as portable battery powered applications, power consumption is
Chew Kok Wai Johnny
Do Manh Anh
Ma Jian Guo
Tan Hai Peng
Yeo Kiat Seng
Chartered Semiconductor Manufacturing Ltd.
Pike Rosemary L. S.
Potter Roy
Saile George O.
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