Patent Application
20080248598
Not applicable.
The present invention relates generally to semiconductor device manufacturing and, more particularly, to a method and apparatus for determining characteristics of a stressed material using scatterometry.
The fabrication of complex integrated circuits involves the fabrication of a large number of transistor elements, which are used in logic circuits as switching devices. Generally, a plurality of process technologies are currently practiced for complex circuitry, such as microprocessors, storage chips, and the like. One process technology currently used is complimentary metal oxide silicon (CMOS) technology, which provides benefits in terms of operating speed, power consumption, and/or cost efficiency. In CMOS circuits, complementary transistors (e.g., p-channel transistors and n-channel transistors) are used for forming circuit elements, such as inverters and other logic gates to design complex circuit assemblies, such as CPUs, storage chips, and the like.
During the fabrication of complex integrated circuits using CMOS technology, millions of transistors are formed on a substrate including a crystalline semiconductor layer. A transistor includes pn-junctions that are formed by an interface of highly doped drain and source regions with an inversely doped channel region disposed between the drain region and the source regions. The conductivity of the channel region, i.e., the drive current capability of the conductive channel, is controlled by a gate electrode formed in the vicinity of the channel region and separated therefrom by a thin insulating layer. A conductive channel is formed when an appropriate control voltage is applied to the gate electrode. The conductivity of the channel region depends on the dopant concentration, the mobility of the majority charge carriers, and—for a given extension of the channel region in the transistor width direction—on the distance between the source and drain regions, which is also referred to as channel length.
Hence, the overall conductivity of the channel region substantially determines an aspect of the performance of the MOS transistors. By reducing the channel length, and accordingly, the channel resistivity, an increase in the operating speed of the integrated circuits may be achieved.
The continuing shrinkage of the transistor dimensions does raise issues that might offset some of the advantages gained by the reduced channel length. For example, highly sophisticated vertical and lateral dopant profiles may be required in the drain and source regions to provide low sheet and contact resistivity in combination with a desired channel controllability. Moreover, the gate dielectric material may also be adapted to the reduced channel length in order to maintain the required channel controllability. However, some mechanisms for obtaining a high channel controllability may also have a negative influence on the charge carrier mobility in the channel region of the transistor, thereby partially offsetting the advantages gained by the reduction of the channel length.
The continuous size reduction of the critical dimensions, i.e., the gate length of the transistors, necessitates the adaptation of current process techniques and possibly the development of new process techniques. One technique for enhancing the channel conductivity of the transistor elements involves increasing the charge carrier mobility in the channel region for a given channel length, thereby offering the potential for achieving a performance improvement that is comparable with the advance to a future technology node while avoiding or at least postponing many of the process adaptations associated with device scaling.
One efficient mechanism for increasing the charge carrier mobility is to modify the lattice structure in the channel region, for instance by creating tensile or compressive stress in the vicinity of the channel region so as to produce a corresponding strain in the channel region, which results in a modified mobility for electrons and holes, respectively. For example, creating tensile strain in the channel region for a standard crystallographic configuration of the active silicon material increases the mobility of electrons, which, in turn, may directly translate into a corresponding increase in the conductivity. On the other hand, compressive strain in the channel region may increase the mobility of holes, thereby providing the potential for enhancing the performance of p-type transistors.
The introduction of stress or strain engineering into integrated circuit fabrication is a promising approach for future device generations. Strained silicon may be considered as a “new” type of semiconductor material that enables the fabrication of fast powerful semiconductor devices without requiring expensive semiconductor materials and also allows the use of many of the well-established current manufacturing techniques.
One technique for inducing stress in the channel region involves introducing, for instance, a silicon/germanium layer next to the channel region so as to induce a compressive stress that may result in a corresponding strain. The transistor performance of p-channel transistors may be considerably enhanced by the introduction of stress-creating layers next to the channel region. For this purpose a strained silicon/germanium layer may be formed in the drain and source regions of the transistors. The compressively strained drain and source regions create uni-axial strain in the adjacent silicon channel region. When forming the Si/Ge layer, the drain and source regions of the PMOS transistors are selectively recessed, while the NMOS transistors are masked. Subsequently, the silicon/germanium layer is selectively formed by epitaxial growth. For generating a tensile strain in the silicon channel region, Si/C may be used instead of SiGe.
A gate electrode 120 may be formed above the semiconductor layer 110. The gate electrode 120 may be formed of doped polysilicon or other suitable material which is provided above the semiconductor layer 110 and is separated therefrom by a gate insulation layer 130. The first semiconductor material 110 forms a channel region 140 for a finished transistor. Sidewalls of the gate electrode 120 are provided with disposable sidewall spacers 150. The disposable sidewall spacers 150 may consist of any appropriate dielectric material, such a silicon nitride, silicon dioxide, or mixtures thereof. The disposable sidewall spacers 150 may be used as an etch and growth mask in an etch process and an epitaxial growth process for the formation of an embedded strained semiconductor region.
The semiconductor device 100 of
It should be appreciated that after the formation of the recess 160, the semiconductor device 100 may be subjected to any necessary or suitable pretreatments for preparing the device 100 for a subsequent epitaxial growth process. Thereafter, a stressed semiconductor material 170 (see
During the formation of stressed silicon structures, several parameters affect the net stress, which in turn modulates the hole or electron mobility. These parameters include the proximity of the strained material cavity to the gate electrode, the cavity depth, the stress dopant (e.g., germanium or carbon) content of the stressed film, implant conditions, etc. The control of each of these parameters may be attempted to enhance strain and thereby enhance the performance of the completed devices.
The behavior of a stressed silicon structure is strongly dependent on geometric confinement. Hence, optimization based on blanket wafer studies and metrology measurements on large pad areas is ineffective for attempting to collect data for controlling the fabrication of devices with much smaller stressed layer cavities. Spatial variations in growth rates, etch rates, etc. on a wafer (i.e., within die and/or across wafer) caused by the local pattern density differences, non-uniformity in process conditions, etc. result in variations in the final device structure. These variations are commonly referred to as loading effects. Current techniques for monitoring actual devices involves costly and time consuming cross-sectional analysis, which hinders the ability to characterize and optimize the devices for increased performance.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
One aspect of the present invention is seen in a method that includes illuminating at least a portion of a first grid including a first plurality of stressed material regions formed at least partially in a semiconducting material. Light reflected from the illuminated portion of the first grid is measured to generate a first reflection profile. A characteristic of the first plurality of stressed material regions is determined based on the first reflection profile.
Another aspect of the present invention is seen in a test structure including a first plurality of stressed material regions recessed with respect to a surface of a semiconductor layer and defining a first grid. Members of a first plurality of exposed portions of the semiconductor layer are disposed between members of the first plurality of stressed material regions.
The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
One or more specific embodiments of the present invention will be described below. It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the present invention unless explicitly indicated as being “critical” or “essential.”
The present invention will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to
The deposition tool 220 may be used to form the process layers for the gate electrode 120, the gate insulation layer 130, the sidewall spacers 150, and/or the stressed semiconductor material 170. The etch tool 230 may be employed to form the gate electrode 120, the sidewall spacers 150, and or the recesses 160. For ease of illustration and to avoid obscuring the present invention, only a portion of the processing line 200 is illustrated. An actual implementation of the processing line 200 may have additional types of tools and multiples instances of each tool type. For example, different etch tools and/or deposition tools may be used to form the process layers or features described above.
In general, the scatterometry tool 240 determines the characteristics of the recessed stressed layer of the exemplary semiconductor device 100 of
The controller 250 provides feedback to the deposition tool 220 and/or the etch tool 230 based on the measurements generated by the scatterometry tool 240. The controller 250 adjusts the operating recipe of the controlled tool 220, 230 to improve the deposition and/or etching processes for subsequently processed wafers 210 to improve the recessed stressed layer characteristics.
In the illustrated embodiment, the controller 250 is a computer programmed with software to implement the functions described. However, as will be appreciated by those of ordinary skill in the art, a hardware controller designed to implement the particular functions may also be used. Moreover, the functions performed by the controller 250, as described herein, may be performed by multiple controller devices distributed throughout a system. Additionally, the controller 250 may be a stand-alone controller, it may be integrated into a tool, such as the deposition tool 220, etch tool 230, or the scatterometry tool 240, or it may be part of a system controlling operations in an integrated circuit manufacturing facility.
Portions of the invention and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
Referring now to
The test structure of
By varying the dimensions of the test structures 300, 350, different devices sizes and/or pitches may be provided. These variations simulate different loading effects expected on the actual fabricated devices. Hence, an assortment of test structures 300, 350 may be provided to match the devices expected on the wafer 210. For example, test structures having the same Z dimensions, but different X and Y (i.e., pitch) dimensions may be provided. The test structures 300, 350 exhibit simplified topologies as compared to the topology of the actual semiconductor devices 100 (i.e., due to the absence of the gate electrode 120) to allow them to be more readily analyzed by the scatterometry tool 240.
Turning now to
The scatterometry tool 240 may use monochromatic light, white light, or some other wavelength or combinations of wavelengths, depending on the specific implementation. The angle of incidence of the light may also vary, depending on the specific implementation. The light analyzed by the scatterometry tool 240 typically includes a reflected component (i.e., incident angle equals reflected angle) and a refracted component (i.e., incident angle does not equal the reflected angle). For purposes of discussion here, the term “reflected” light is meant to encompass both components.
Variations, such as width, depth, spacing, fill height, and stress dopant concentration of the stressed material regions 320 in the grid 400 cause changes in the reflection profile (e.g., intensity vs. wavelength—tan(δ), phase vs. wavelength—cos(Ψ), where δ and Ψ are common scatterometry outputs known to those of ordinary skill in the art) measured by the scatterometry tool 240 as compared to the light scattering profile that would be present in grids 400 having reference characteristic values. Due to the variety of test structures 300, 350 provided. Various measurements may be taken to distinguish between the sources of variation. Through these comparisons, the pitch, depth, spacing, fill height, and/or stress dopant concentration of the stressed material regions 320 may be determined.
The reflection profile 500 of
The data processing unit 246 receives a reflection profile measured by the detector 244 and compares it to the reference reflection profile library 248. Each reference profile has an associated stressed layer characteristic metric related to one or more characteristics of the grid 400 (e.g., X, Y, Z, F, or C). For example, the stressed layer characteristic metric may comprise actual width, depth, spacing, fill height, and/or concentration measurements. The data processing unit 246 determines the reference reflection profile having the closest match to the measured reflection profile. Techniques for matching the measured reflection profile to the closest reference reflection profile are well known to those of ordinary skill in the art, so they are not described in greater detail herein. For example, a least squares error technique may be employed.
In another embodiment, the controller 250 or other external controller (not shown) may be adapted to compare the measured reflection profile to the reference reflection profile library 248. In such a case, the scatterometry tool 240 would output the matching reference reflection profile, and the controller 250 may link that reference reflection profile to an associated stressed layer characteristic metric.
In still another embodiment, the measured reflection profile may be compared to a target reflection profile selected from the reference reflection profile library 248 for a test structure 300 having grid 400 exhibiting known and desired characteristics (e.g., the reflection profile 500 of
After receiving the stressed layer characteristic metric from the scatterometry tool 240, the controller 250 may take a variety of autonomous actions. In one embodiment of the present invention, the controller 250 is adapted to modify the operating recipe of the deposition tool 220 and/or the etch tool 230 based on the stressed layer characteristic metric to control operations on subsequently processed wafers. The controller 250 may adjust the recipe for subsequently processed wafers to control the characteristics of the grid 400 or the stress dopant concentration. Deposition parameters such as deposition time, chamber pressure, chamber temperature, reactant gas concentration, etc., or etch recipe parameters, such as the etch time, plasma chemical compositions, RF power, gas flow, chamber temperature, chamber pressure, end-point signal, etc., may be changed to correct variations in the width, spacing, depth, fill height, or stress dopant concentration of the stressed semiconductor material 170 in the actual device corresponding to the stressed material regions 320 in the test structures 300, 350.
The controller 250 may use a control model of the deposition tool 220 or the etch tool 230 for determining its operating recipe. For example, the controller 250 may use a control model relating the stressed layer characteristic metric to a particular operating recipe parameter in the controlled tool 220, 230 to control the process to correct for variation. This correction may also result in the correction of the process as it affects the other features formed on the device. The control model may be developed empirically using commonly known linear or non-linear techniques. The control model may be a relatively simple equation based model (e.g., linear, exponential, weighted average, etc.) or a more complex model, such as a neural network model, principal component analysis (PCA) model, or a projection to latent structures (PLS) model. The specific implementation of the model may vary depending on the modeling technique selected.
Grid characteristic models may be generated by the controller 250, or alternatively, they may be generated by a different processing resource (not shown) and stored on the controller 250 after being developed. The grid characteristic models may be developed using the tools 220, 230 or using different tools (not shown) having similar operating characteristics. For purposes of illustration, it is assumed that the grid characteristic models are generated and updated by the controller 250 or other processing resource based on the actual performance of the tools 220, 230 as measured by the scatterometry tool 240. The grid characteristic models may be trained based on historical data collected from numerous processing runs of the tools 220, 230.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
