Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Grooved and refilled with deposited dielectric material
Reexamination Certificate
2000-08-14
2002-09-03
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Grooved and refilled with deposited dielectric material
Reexamination Certificate
active
06444541
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for forming lining oxide in an opening for a shallow trench isolation (STI) and more particularly, relates to a method for forming lining oxide in an opening for a shallow trench isolation incorporating a pre-annealing step for repairing structural damages incurred in the silicon substrate by a dry etching process for forming the opening.
BACKGROUND OF THE INVENTION
In recently developed semiconductor fabrication technology, shallow trench isolations have been used in high density memory and other semiconductor devices since the isolation provides simplified back-end operations such as packaging. This is in contrast to a bird's beak type LOCOS isolation which provides an uneven top surface (or topography) on a memory device and leads to poor photolithographic results due to focusing difficulties. Shallow trench isolation can be etched in the silicon between neighboring devices. It allows a device to be built closer together.
When a shallow trench isolation is used in a semiconductor device, a more planar surface on the device can be obtained due to the absence of formation of bird's beak. Based on the advantages of a tighter line definition and a greater planarity that are achieved by the shallow trench isolation, the isolation is very suitable for applications in sub-half-micron semiconductor processes.
Isolation of individual semiconductor devices without using the bird's beak can be carried out by etching shallow vertical trenches in the silicon between neighboring devices. In shallow trench isolation, trenches of about 0.3 to 0.8 micron deep are anisotropically etched into a silicon substrate by a dry etching technique. The active regions in a substrate are protected from the etch during the trench etching step. After the trenches are formed, a chemical vapor deposition oxide is deposited on the wafer surface and then planarized so that only oxide remains in the trenches with its top surface at the same level as the original silicon surface. The processing technique has the advantages of not requiring any bird's beak and that no encroachment is involved. When two devices on a substrate are separated by a trench, the electrical field lines have to travel a longer distance and change directions twice, so that the field lines are considerably weakened. Shallow trenches of submicron dimensions are therefore adequate for isolation to prevent the punch-through and latch-up phenomena.
In a conventional shallow trench isolation forming process, for which a process flow chart
10
is shown in
FIG. 1
, a dry etching is carried out by utilizing high energy ion bombardment, for instance, in a reactive ion etching process. The high energy ion bombardment, while removing the unwanted silicon layer and thus forming the opening, also damages the remaining single crystal silicon material that surrounds the trench opening. For instance, the ion bombardment causes defects in single crystals such as dislocations that result in leakage current in the device fabricated and consequently, low yield of the fabrication process.
Two alternate conventional forming processes for a shallow trench isolation are shown in FIG.
1
. In the first process, a silicon wafer is provided in step
12
, followed by the formation of a pad oxide layer in step
14
. A silicon nitride mask layer is then formed on top of the pad oxide layer in step
16
, followed by a dry etching process shown in step
18
to form the trench opening. After the formation of the trench opening, a thin layer of silicon oxide is formed in the opening, as shown in step
20
, in order to cover the corners of the opening and to facilitate the final deposition step
22
for the oxide isolation by a high density plasma chemical vapor deposition (HDP CVD) technique. In this first conventional method, no attempt is made to repair the damaged structure caused by ion bombardment in the dry etching step
18
.
In an alternate method, also shown in
FIG. 1
, after step
20
during which a lining oxide layer is formed, a post-annealing process for the lining oxide layer in a nitrogen atmosphere is conducted in step
24
. The trench opening is then filled with oxide by a HDP CVD process in step
26
. The post-annealing process, i.e. step
24
, is conducted at a temperature of about 1,100° C. in an attempt to repair the damaged crystal structure of the silicon substrate. Since the post-annealing process is conducted after the deposition of the lining oxide layer, the repair of the silicon structure under the lining oxide layer cannot be effectively carried out. Moreover, the post-annealing process requires a separate process recipe which further complicates the fabrication process.
It is therefore an object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation that does not have the drawbacks or shortcomings of the conventional forming methods.
It is another object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation that is capable of effectively repairing silicon structures damaged by a reactive ion etching process for forming the opening.
It is a further object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation by annealing the silicon structure after a dry etching process has been conducted for forming the opening prior to a lining oxide deposition process.
It is still another object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation by annealing a silicon substrate at 1,100° C. in an environment that contains oxygen for preventing the formation of silicon nitride.
It is yet another object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation by annealing the silicon substrate at a temperature of at least 1,000° C. in an environment that contains not more than 10 vol. % oxygen.
It is another further object of the present invention to provide a method for forming lining oxide in an opening for a shallow trench isolation by annealing a silicon substrate after a dry etching process prior to depositing the lining oxide layer in the trench opening.
It is still another further object of the present invention to provide a method for forming a shallow trench isolation incorporating a lining oxide layer by first dry etching a trench opening in the silicon substrate and then annealing the substrate to repair damages to the silicon structure prior to the deposition of the lining oxide layer.
It is yet another further object of the present invention to provide a method for forming a shallow trench isolation incorporating a lining oxide layer by first dry etching a trench opening and then annealing the silicon substrate at a temperature of at least 1,000° C. in an environment that contains less than 10 vol. % oxygen.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for forming lining oxide in an opening for a shallow trench isolation in a semiconductor structure and a method for forming a shallow trench isolation incorporating a lining oxide layer are provided.
In a preferred embodiment, a method for forming lining oxide in an opening for a shallow trench isolation in a semiconductor structure can be carried out by the operating steps of first providing a silicon substrate; forming a pad oxide layer on the silicon substrate; depositing a silicon nitride mask on the pad oxide layer; patterning and forming a trench opening in the silicon substrate for the shallow trench isolation; annealing the structure at a temperature of at least 1,000° C. in a furnace; and forming a lining oxide layer in the trench opening of the silicon substrate.
The method for forming lining oxide in an opening for a shallow trench isolation in a semiconductor structure may further include the step of annealing the structure in an environment that includes oxygen,
Hsieh Jang-Cheng
Huang Chin-Te
Lai Jun-Yang
Lin Chung-Te
Shieh Meng-Shiun
Blum David S
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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