Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Light responsive structure
Reexamination Certificate
2002-02-04
2004-04-13
Niebling, John F. (Department: 2812)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Light responsive structure
Reexamination Certificate
active
06720587
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a structure evaluation method used in the management of a manufacturing process of semiconductor device elements, a method for manufacturing a semiconductor device, and a recording medium.
BACKGROUND ART
In recent years, a process of forming a thin film such as an oxide film, a nitride film, or a polysilicon film, on a substrate is often used in manufacturing semiconductor devices. In order to produce a device using these thin films as elements and obtain desirable characteristics, the thickness and the physical properties of each thin film need to fall within predetermined ranges, respectively. Typically, the physical properties and the thickness of a thin film vary depending on the conditions of the process of forming the thin film (hereinafter “thin film process”) and the time period for which the process is performed. Therefore, after a thin film process is performed, it is evaluated as to whether the formed thin film has the predetermined thickness and physical properties. In the mass production of the device, it is necessary to change the process conditions when it is found from the evaluation results that the formed thin film does not have the desirable thickness and physical properties.
In a conventional thin film process, a thin film formed in a single process is basically a substantially homogeneous film whose composition and other physical properties do not substantially vary in the depth direction. On the other hand, it is often the case that a polysilicon film to be a gate electrode is deposited on a silicon oxide film to be a gate insulating film, as in the case of the gate section of an Si-MOS transistor. In most of such cases, the composition is substantially uniform within each layer with a well-defined interface between layers.
An optical evaluation method is a technique for evaluating the thickness and composition of a single-layer film or each layer of a multi-layer film on the substrate. As examples of the optical evaluation method, a spectroscopic ellipsometry method and a spectroscopic reflectance measuring method are widely used.
The spectroscopic reflectance measuring method is an evaluation method in which a sample is irradiated with light so as to obtain, for each of the separated wavelength regions, the ratio (reflectance) between the intensity of light that is used for irradiating the sample and the intensity of light that is reflected from the sample.
The spectroscopic ellipsometry method is an evaluation technique in which a sample is irradiated with linearly-polarized light so as to obtain information on the sample from the change in the polarization of the reflected light. Where a component of the linearly-polarized light whose electric field vector is parallel to the incident plane is denoted as a p-polarization component, another component whose electric field vector is perpendicular to the incident plane is denoted as an s-polarization component, and their complex reflectances are denoted by Rp and Rs, respectively, &rgr;≡Rp/Rs is also a complex number. Therefore, &rgr; can be expressed as &rgr;≡tan &PSgr; ei &Dgr; using two real numbers &PSgr; and &Dgr;. The spectroscopic ellipsometry method is used to measure the two physical amounts &PSgr; and &Dgr; for each wavelength of light so as to obtain a spectrum.
A common nature of these optical evaluation methods is that since the phase and/or reflectance of light vary depending on the combination of the optical constants (refractive index n, extinction coefficient k) of the substance through which light passes, the measurement results include information on the optical constants of the substance. Moreover, since the light interference effects are significantly expressed in the optical information taken from the measurement object, the measurement results are often varied substantially by the thickness of the thin film, etc., whereby it is possible to obtain information on the thickness of the thin film, etc., with any of these evaluation methods.
However, the physical amount measured by the reflectance measuring method or the spectroscopic ellipsometry method (the reflectance in the case of the reflectance measuring method, and &PSgr; and &Dgr; in the case of the spectroscopic ellipsometry method) includes the influences of all substances that are present in the path of light, and those influences cannot directly be extracted as separated information.
Therefore, when the spectroscopic reflectance measuring method or the spectroscopic ellipsometry method is used to measure a sample so as to evaluate the thickness and physical properties of a thin film, it is necessary to go through a procedure of comparing the actual measurement value with the estimated value of the measurement value, as follows.
FIG. 10
is a flow chart illustrating a management procedure for a conventional sample evaluation and thin film manufacturing process.
First, in step ST
201
, a sample A that has been produced by a process P is measured by an evaluation method M so as to obtain actual measurement values of a physical amount (e.g., &Dgr;, &PSgr;).
On the other hand, a geometric model of the sample structure is set in step ST
202
, and an initial estimated value that defines the sample structure is set in step ST
203
, after which a theoretical estimated value of a physical amount measurement value is calculated in step ST
204
. Thus, in a case where an optical evaluation is used, the structure of a measurement sample (n and k profiles) is assumed, and the theoretical estimated value of the physical amount measurement value, which would be obtained if the n and k profiles were evaluated with the evaluation method M, is calculated.
Then, in step ST
205
, the actual measurement value of the physical amount and the theoretical estimated value are compared with each other. In this step, an evaluation value for evaluating the degree of difference between the actual measurement value and the theoretical estimated value is defined.
Then, in step ST
206
, it is determined whether the evaluation value is a local minimum value. If the evaluation value is not a local minimum, a new estimated value is set in step ST
207
, and then the process returns to the operation of step ST
204
to repeat the operations of steps ST
204
to ST
206
.
Then, if it is determined in the determination of step ST
206
that the evaluation value is a local minimum, the process proceeds to step ST
208
to decide on the estimated value of the sample structure, after which it is determined whether the sample structure is within an appropriate range in step ST
209
. If it is determined as a result of the determination that the sample structure is within the appropriate range, the process proceeds to step ST
210
to perform the next operation with the process conditions that have been set.
On the other hand, if it is determined as a result of the determination in step ST
209
that the sample structure is not within the appropriate range, the process proceeds to step ST
211
to determine whether the geometric model of the sample structure is appropriate. If the geometric model of the sample structure is appropriate, the process proceeds to step ST
212
to estimate the cause of the abnormal structure so as to take countermeasures such as changing the temperature, the time, the gas flow rate, etc.
If it is determined as a result of the determination in step ST
211
that the geometric model of the sample structure is not appropriate, the process proceeds to ST
213
to set a new geometric model, after which the process returns to step ST
203
to repeat the operations of step ST
203
and the subsequent steps.
As the evaluation value used in step ST
205
, a function which is normally a positive real number, which decreases as the difference between the actual measurement value and the theoretical estimated value decreases, and which becomes 0 when they are completely equal to each other, is used. Generally, it is often the case that a variance value &sgr; expressed by Expression (1) below:
&sgr;=&Sgr
Kanzawa Yoshihiko
Kubo Minoru
Nozawa Katsuya
Saitoh Tohru
McDermott & Will & Emery
Niebling John F.
Stevenson Andre′ C.
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