Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Having substrate registration feature
Reexamination Certificate
2001-03-13
2003-11-18
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Having substrate registration feature
C356S401000
Reexamination Certificate
active
06649484
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to, in a lithography process for transferring a predetermined pattern to a substrate coated with a photosensitive material through a projection optical system, an aligning method, an exposure apparatus using this aligning method, and a semiconductor device manufacturing method utilizing this exposure apparatus.
BACKGROUND OF THE INVENTION
The lithography process in the manufacture of a semiconductor device uses an exposure apparatus for transferring a circuit pattern formed on a reticle or mask (to be referred to as a reticle hereinafter) to a wafer or glass plate (to be referred to as a substrate hereinafter) coated with a photosensitive material (to be referred to as a resist hereinafter). In this exposure apparatus, it is very important to perform alignment of the reticle and substrate relative to each other, i.e., so-called alignment, at high precision.
SUMMARY OF THE INVENTION
An alignment flow in a conventional exposure apparatus will be described with reference to FIG.
7
.
First, prealignment is performed (step
71
). Then, the positions of alignment marks formed on a plurality of sample shots set in advance from all shots are sequentially measured (step
72
). The results of position measurement are statistically processed to calculate all shot arrangements (step
73
). The respective shots are exposed on the basis of the calculation results (step
74
).
In position measurement of the alignment mark, the alignment mark formed on the substrate is illuminated through or not through a projection lens, and light reflected and diffracted by the alignment mark is received by a light-receiving means through or not through a projection lens. Position information is obtained from information obtained by the light-receiving means. As the light used to illuminate the alignment mark (to be referred to as alignment light hereinafter), non-exposure light with a wavelength different from that of light used for exposure (to be referred to as exposure light hereinafter) is used because of absorption, photosensitivity, and the like of the resist applied to the substrate.
This alignment can be performed in two methods, i.e., a method that does not employ a projection lens (to be referred to as an off-axis method hereinafter) and a method that employs a projection lens (to be referred to as a TTL method hereinafter). The alignment mark can be detected in two methods, i.e., a method of forming an image of the alignment mark on an image sensing element and observing it directly (to be referred to as an image method hereinafter) and a method of using a grating-like mark as the alignment mark to detect a spatial phase (to be referred to as a phase detection method hereinafter). Each of these alignment methods has its merits and demerits, and generalization as to which method is better cannot be made.
These alignment methods will be described.
According to the off-axis method, since the alignment light does not pass through a projection lens, alignment is not adversely affected by the optical characteristics of the projection lens. Thus, the wavelength of the alignment light can be set freely, and accordingly, an optical system used for alignment (to be referred to as an alignment optical system hereinafter) can be designed freely. That is, the off-axis method can cope with various different processes.
In the off-axis method, due to the spatial design limit of the alignment optical system and projection lens, the alignment position and the exposure position are largely different from each other. After alignment is ended, the substrate stage on which the substrate is loaded is largely driven to the exposure position. At this time, if the distance between the alignment position and exposure position (to be referred to as a base line hereinafter) is always stable, no problem occurs. In fact, however, the base line changes over time and is not stable due to the influence of the ambient atmosphere of the exposure apparatus and the like. Hence, to stabilize the base line, measurement and correction must be performed at a predetermined time interval. This in turn decreases the throughput by the time spent for measurement and correction of the base line. Also, since the off-axis method is performed not through a projection lens, alignment does not follow the behavior of the projection lens.
According to the TTL method, the alignment light passes through the projection lens, which is advantageous in terms of stability of the base line and the follow-up performance to the behavior of the projection lens.
Since the projection lens is designed such that its aberration becomes optimal to the wavelength of the exposure light, the aberration with respect to alignment light with a wavelength different from that of the exposure light undesirably becomes large. For this reason, in Japanese Patent No. 2,633,028, when alignment is performed in accordance with the TTL method by using alignment light with a wavelength different from that of exposure light, a correction optical system is provided for correcting aberration produced by the projection lens, and alignment is performed through this correction optical system.
According to the image method, the alignment mark is illuminated through the alignment optical system. Light reflected by the alignment mark forms an image on the image sensing element through the alignment optical system. The position of the formed image is read to obtain position information. The alignment optical system may or may not include a projection lens, that is, it can employ the off-axis method or the TTL method.
When alignment is performed by using the TTL method and image method, the following problems arise. For example, when a KrF excimer laser beam (wavelength: 248 nm) is used as the exposure light, as the glass material that forms the projection lens is limited to quartz, fluorite, or the like due to the transmittance required and the like, the aberration of the projection lens with respect to non-exposure light becomes very large. It is difficult to design a correction optical system that corrects this large aberration, and a large numerical aperture (to be referred to as NA hereinafter) required by the alignment optical system employing the image method cannot be obtained. To remove this problem, a correction optical system may be provided in the projection lens to correct the aberration. In this case, however, the correction optical system affects not only the alignment light but also the exposure light.
In Japanese Patent Laid-Open No. 5-343291, the phase detection method is employed in place of the image method, that is, the TTL method and phase detection method are used, thereby solving the problem concerning aberration. According to this reference, as shown in
FIG. 5
, a grating-like mark
16
as an alignment mark is illuminated with alignment light
13
, and ±n-order diffracted beams
14
(n is a natural number) produced by the grating-like mark
16
are brought to interference with each other through a spatial filter
15
. The spatial phases of interference fringes
17
formed by the interference are detected, thereby performing alignment.
When the phase detection method is used in this manner, the NA required by the alignment optical system of the phase detection method can be decreased more than that in the alignment optical system of the image method. For example, assume that a KrF excimer laser beam is used as the exposure light, an HeNe laser beam (wavelength: 633 nm) is used as the alignment light, an alignment mark with a grating pitch of 10 &mgr;m is used, and only ±1-order diffracted beams are brought to interference with each other through a spatial filter to form interference fringes. If the angle at which the ±1-order diffracted beams emerge is defined as &thgr;, since sin &thgr;=0.063, the minimum necessary NA for the alignment optical system is 0.063. In practice, since the beam spot diameters of the diffracted beams must be considered, the minimum necessary NA for the alignmen
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le Thao
Nelms David
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