Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-11-16
2002-03-19
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S328000, C430S330000
Reexamination Certificate
active
06358672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device fabrication, and more particularly, a semiconductor device fabrication system and a method of forming a semiconductor device pattern using the same for providing a desired size of a semiconductor device pattern through the irradiation of Ultra Violet (UV) light on a photoresist pattern, and then, performing a flow process, and a photoresist for manufacturing semiconductor devices thereby.
2. Description of the Related Art
Generally, a semiconductor device is manufactured by an array of processes such as deposition, photolithography, etching, and ion-implantation, etc.
That is, a pattern of the semiconductor device is formed by depositing a polycrystalline film, an oxide film, a nitride film, and a metal film, etc. on a semiconductor wafer, and carrying out a photolithography process, an etching process, and an ion-implantation process, etc. thereon. The photolithography process has a significance in the semiconductor device fabrication process, in which a predetermined pattern for semiconductor device integrated circuits is formed on the wafer using a Photo Mask.
The photolithography process is used in various semiconductor device fabrication processes for 16M DRAM, 64M DRAM, and further 256M DRAM and 1G DRAM or higher according to the light source used in an exposure processing step. Currently used light sources for the photolithography process are g-line(436 nm), i-line(365 nm), DUV(248 nm) and KrF laser(193 nm), etc.
Photoresist used in the photolithography process is made of highly polymerized photo-sensitive substance solubility of which is changed by the chemical reaction with light.
That is, light is projected on the photo mask having micro-circuits preformed, and the photoresist substance of the light-incident portion is changed into more fusible substance or more infusible substance compared with the photoresist substance of the light-nonincident portion. Then, it is developed with an appropriate developer thereby forming positive or negative type photoresist pattern. The photoresist pattern made as above functions as a mask in the following processes after the photolithography process, such as etching and ion-implantation processes, etc.
The types of the photoresist are divided according to the exposure light source such as g-line, i-line, and DUV. However, the above photoresist generally has a difficulty in forming a photoresist pattern having a size shorter than the wavelength of the exposure light source.
Currently, the resolution of a contact hole pattern in the photolithography process is lower than that of a line & space pattern so that the pattern uniformity over all of the wafer surface is not good.
Therefore, there is a demand for new technology to allow the formation of the contact hole pattern having a size of 0.20 &mgr;m or less which is required for the highly-integrated semiconductor devices over 64M DRAM in order to overcome the limit resolution of the photoresist.
Currently, the method for forming the contact hole having a smaller size than the wavelength of the exposure light source is as follows.
First, as flow process method for a photoresist pattern, a normal photoresist pattern of contact holes having a size bigger than wanted is formed using a normal chromium (Cr) mask, and then, heat over the softening point of the photoresist is applied on the photoresist pattern so as to occur the softening of the highly polymerized photoresist and reduce its viscosity and flow it. As a result, the size of the photoresist pattern is reduced.
Second, as a modified exposure method, exposed portion and non-exposed portion are clearly defined by exposing using a modified illumination and a Phase Shift Mask (PSM). As a result, a photoresist pattern has a smaller size of contact hole than using a normal light and a photo mask.
The flow method by i-line photoresist including novolak resin, photo active compound (PAC), solvent and additives uses the speed difference due to the increase of thermal properties attributable to the pyrolysis of the PAC by heat and the Cross-Linking reaction of the resin and the PAC, and the photoresist pattern flow phenomenon by the decrease of the viscosity by heat.
The flow of the i-line photoresist proceeds with the Cross-Linking reaction, and the flow phenomenon is properly controlled by the Cross-Linking reaction. That is, because the flow phenomenon of the i-line photoresist gradually proceeds with the temperature changes, it is little affected by the temperature changes of the process and the facilities.
In case of the i-line photoresist, 0.25 &mgr;m of pattern can be obtained by the flow method. By applying a modified light and the PSM on the i-line photoresist, 0.28 &mgr;m of pattern can be achieved.
FIG. 1
shows the conventional pattern formation method for semiconductor devices, and in other words, shows a processing sequence of the contact hole formation method using the i-line photoresist.
Referring to
FIG. 1
, first, as step of coating a wafer with photoresist (S
2
), with the i-line photoresist is coated on the wafer having Hexamethyldisilazane (HMDS) pre-deposited thereon. Then, as step of soft-baking the photoresist (S
4
) on the wafer, the solvent included in the photoresist is removed by the soft bake so that the adhesiveness of the photoresist is improved, and the coating state of the photoresist on the wafer with a certain thickness is maintained. After the soft bake, as step of exposing after aligning a photo mask on the photoresist (S
6
), a wafer having the i-line photoresist thereon is moved to an i-line stepper, and the PSM having a fine pattern formed thereon is aligned over the wafer.
Then, the wafer having the photoresist thereon and the PSM aligned with the wafer is irradiated with an i-line light source so as to carry out the exposure. Then, as step of Post Exposure Bake (PEB) for the exposed wafer (S
8
), the wafer passing through the exposure is baked at a proper temperature so as to remove the wave pattern produced by standing wave phenomenon which occurs on the photoresist pattern during the reinforcement interference and the destruction interference by the incident light and the reflection light of the exposure light source, and improve the photoresist pattern profile, and further, improve the resolution of the photoresist pattern. Next, as step of the formation of the photoresist pattern by developing and cleaning the wafer passing through the PEB (S
10
), the wafer with the PEB completed is moved to a developing unit, a developer is supplied on the photoresist on the wafer so as to form a photoresist pattern, and the development by-products are removed using a cleaning solution.
Then, as step of hard bake for the developed wafer (S
12
), the photoresist pattern with the development completed is dried, and hardened so as to harden the photoresist pattern.
Then, as step of flow bake after the hard bake (S
14
), heat is applied on the photoresist pattern at a temperature over the softening point of the photoresist so as to reduce the softening and the viscosity of the highly-polymerized photoresist, and make the photoresist pattern flow thereby reducing the pattern size. However, in case of carrying out the flow method using the i-line photoresist and the PSM by a modified light, the photoresist pattern having 0.18 &mgr;m of resolution can be formed, but the thermal properties of the pattern of highly-polymerized photoresist becomes nonuniform because part of the non-exposure portion is exposed nonuniformly. That is, during the exposure for the photoresist pattern formation, the exposed amount on the Cell portion of high-density pattern and the Peri portion of low-density pattern, non-exposure portion respectively is nonuniform. As a result, the nonuniformity of the exposed amount results in a flow rate difference in the hardness by heat, and so, a Bulk effect of the distortion of the contact hole pattern occurs in the interface of the Cell portion and the Peripheral portion.
In the meantime,
Choi Kwang-seok
Chung Hoe-sik
Ha Hun-hwan
Jeoung Gyu-chan
Jung Jin-hang
Baxter Janet
Gilmore Barbara
Samsung Electronics Co,. Ltd.
Volentine & Francos, PLLC
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