Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-03-28
2003-11-04
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492100, C250S492220, C250S397000, C250S398000, C250S305000, C250S306000, C250S302000, C250S308000, C250S309000, C250S310000, C250S556000, C382S145000, C356S237100, C356S237200, C356S237300, C356S237400, C356S237500, C356S370000, C355S054000, C355S078000
Reexamination Certificate
active
06642529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the manufacture of reticles used in fabricating semiconductor devices. More particularly, the present invention relates to determining the accuracy of the reticle formation and a method for determining distortions in the patterning of the reticle such that the method enables a user to decide whether or not the reticle should be used to form patterns on films deposited over semiconductor wafers.
2. Description of the Related Art
Today's semiconductor devices are continually being pushed to meet stricter demands. As devices using this technology inundate the marketplace, consumers place higher demands on the devices. These demands include smaller, more compact devices with greater functionality.
Semiconductor devices employ various circuitry in a chip to perform user specified functions. As is well known, the circuitry consists of various metallization lines, dielectric layers and other components interconnected throughout the entire chip. The metallization lines and dielectric layers are formed by first depositing a metal layer or a dielectric layer onto a semiconductor wafer. The metallization lines and dielectric layers are deposited on the semiconductor wafer by spin coating, chemical vapor deposition, deposition and other standard techniques of applying films onto wafers. After deposition, the film must be patterned to form a metallization layer or other component on the semiconductor wafer.
Now making reference to
FIG. 1
, a photoresist layer
104
is applied by spin coating photoresist over a deposited layer
101
. Once the photoresist layer
104
is spin coated onto a wafer
102
, the wafer
102
is patterned. The wafer
102
is placed into a stepper that contains a reticle
100
which has a proper pattern
100
a
for the deposited layer
101
. The stepper machine transfers the image of the reticle
100
onto the semiconductor wafer
102
by passing a light source
103
through the reticle
100
. The reticle
100
acts as a filter and only allows a certain pattern of light from the light source
103
to pass through and onto the photoresist layer
104
of the wafer
102
. The pattern of the light passing through the reticle
100
is the pattern for a feature to be formed on the deposited layer
101
of the semiconductor wafer
102
. The light
103
passing through the reticle
100
and onto the photoresist layer
104
will react with the photoresist layer
104
. The reaction will affect the solubility of the exposed portions of the photoresist layer
104
when the photoresist layer
104
is immersed in a solvent. For example, if the photoresist is positive, it will become more soluble as it is exposed to the light. Therefore, photoresist
104
a
will become soluble when it is subjected to an immersion process (not shown), leaving the pattern defined by photoresist
104
b
. If the photoresist is negative, the photoresist will become more insoluble as it is exposed to the light. For example, the photoresist
104
b
will dissolve and the photoresist
104
a
will remain after the photoresist
104
subjected to an immersion process (not shown).
The pattern for the reticle which is used to pattern the film is first designed in an integrated computer design (IC) using a computer aided design program. After the design is made, the features of the design which are to be formed on the wafer must be transferred to the reticle. For example, what will define a metallization line in the digital IC design will be transferred to the reticle in order for it to be imaged onto the photoresist
104
of the semiconductor wafer. The reticle is a glass plate which will be placed into the stepper. Chromium is deposited on top of the glass plate by any standard technique. A photoresist layer is then spin coated over the chromium layer. Once the photoresist is deposited over the chromium layer, the photoresist is patterned with either a laser tool or using an electron beam direct write exposure technique. After the image is formed on the reticle, the reticle is ready to pattern films on semiconductor wafers.
However, in most cases, the image that appears on the reticle will not be the same image that is in the computer digital IC layout. For example, a rounding effect may occur at sharp edges, such as those edges used to define a square feature on the reticle. The square feature will have rounded edges approximating parabolas instead of edges approximating the corners of the square. This effect occurs due to well known proximity effects and because features of the digital IC design are being designed at such a small scale that it is difficult to reproduce the same digital image on the reticle.
In order to avoid these problems, designers typically employ serifs at the edges of a feature in the digital IC design which is transferred to the reticle. For example, serifs would be placed in the corners of the aforementioned square to compensate for the rounding effect which takes place in the corners of the square. The serif increases the amount of area in each of the corners to compensate for anticipated losses. Thus, the area created by the serifs will compensate for the loss of area due to the rounding of the edges within a square feature not containing the serifs.
Nonetheless, the use of serifs in the prior art creates problems because many changes may be required to get proper image formation on a wafer. With the current available methods, a user is unable to determine how all the changes (e.g., proximity effects) will change the original digital IC design after it is transposed onto a reticle and finally onto the film of a semiconductor wafer. Furthermore, the prior art checks on reticles only involved checking proximity effects due to close line separations, while no checks can be made to determine problems with the overall image, such as corners. As a consequence, the image formed on the reticle may not function as originally intended because the image has experienced too many distorting changes which are not appreciated until the reticle transfers the patterns to photoresist.
Typically, even before a reticle will be used to form patterns on the film, a determination must be made as to the quality of the reticle (e.g., how planar is the glass, imperfections on the surface of the reticle and concavities which render the reticle impractical for use). This determination is usually done by placing test patterns on the reticle and then ascertaining how closely the design on the reticle conforms to the design in the digital IC layout.
However, as mentioned above, the quality of the reticle can only be tested by placing the reticle with the test pattern into the stepper and forming patterns on a film of the wafer itself. This greatly slows down the process time since this requires a user to wait until the photoresist develops before one may determine the accuracy of the photoresist image. Also, a user is precluded from making a series of reticles without worrying about whether or not the reticles form the desired images on the films. Instead, after one reticle is made, a user must use-the developed photoresist layer to determine the reticle's accuracy. Furthermore, as is well known in the art, there is a general push to generate reticles more quickly in order to facilitate the manufacture of semiconductor wafers.
As a result, the current methods of checking reticles is time consuming and expensive. A user must actually place the reticle into the stepper and print the reticle image with photolithography before a determination can be made as to the quality of the reticle. Also, the time of using the stepper, developing the photoresist and using the wafer increase the cost of ascertaining the quality of a reticle.
In view of the foregoing, there is a need for a method of determining the accuracy of a particular reticle which avoids the problems of the prior art. This new method should facilitate checking reticles in a time efficient and cost efficient manner.
SUMMARY OF THE INVENTION
Broadly speaking, the p
Sethi Satyendra S.
Subramanya Sudhir G.
Takemoto Clifford
Lee John R.
Vanore David A.
Zawilski Peter
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