BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating a “bird's beak” which is grown at the edge of a silicon nitride layer;
FIG. 2
a to 2f are cross-sectional views illustrating a STI structure formed by one conventional STI process;
FIG. 3
a to 3e are cross-sectional views illustrating a STI structure formed by another conventional STI process;
FIG. 4
a to 4i are cross-sectional views illustrating a STI structure formed by a STI process according to the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
According to a particular embodiment of the present invention, there is provided a method for forming a trench isolation structure, comprising the steps of:
Sequentially forming a pad oxide layer and an etch barrier layer on a semiconductor substrate, and sequentially defining the etch barrier layer, the pad oxide layer, and the substrate to form a trench;
Forming a liner oxide layer on the inner surface of the trench;
Forming a isolation oxide layer which fills up the trench and covers the sidewall of the pad oxide layer and the etch barrier layer;
Performing a planarization process on the isolation oxide layer until the etch barrier layer has been exposed;
Sequentially removing the etch barrier layer and the pad oxide layer on the substrate; after both of the etch barrier layer and the pad oxide layer have been removed, a recess may be formed on the sidewall of the trench; for filling the recess on the sidewall of the trench, the method further comprises the following steps of:
Forming a spin-on-glass layer on the substrate and the isolation oxide layer such that the recess on the sidewall of the trench is filled with the spin-on-glass, and performing an annealing process on the spin-on-glass layer;
Thereafter, performing the process of removing the spin-on-glass layer until both of the substrate and the isolation oxide layer have been exposed; the process of removing the spin-on-glass layer comprises the two steps of: first, removing a portion of the spin-on-glass layer by a dry etching process such that the thickness of the remaining spin-on-glass layer is in the range of 100 Å to 200 Å; second, performing a wet etching process to remove the remaining spin-on-glass layer until both of the substrate and the isolation oxide layer have been exposed.
The particular embodiment of the present invention will now be described in detail with reference to the accompanying drawings.
First, as shown in FIG. 4a, a pad oxide layer 410 and an etch barrier layer 420 are formed on a substrate 400. Thereafter, A photoresist layer is sprayed on the etch barrier layer 420, and the opening of the photoresist layer is formed by using an exposure process and a developing process, etc. The region on the substrate 400 corresponding to the position of the opening of the photoresist layer is an isolation region, and the rest region on the substrate is an active region. Using the photoresist layer as a mask, the etch barrier layer 420 and the pad oxide layer 410 are etched by an anisotropic etching process until the region on the substrate 400 where an isolation trench will be formed has been exposed. Finally, the photoresist layer on the etch barrier layer 420 is removed.
The substrate 400 is made of silicon or silicon-on-insulator. The pad oxide layer 410 may be made of silicon oxide, etc., and is typically formed by a thermal oxidation process. The pad oxide layer 410 can also be made of silicon oxynitride, and is typically formed by a low-pressure chemical vapor deposition process or a plasma enhanced chemical vapor deposition process. The etch barrier layer 420 is made of silicon nitride, for example, and is typically deposited on the pad oxide layer 410 by a chemical vapor deposition process.
As shown in FIG. 4b, the substrate 400 is etched to a predetermined depth using the etch barrier layer 420 as a mask, thus forming a trench 430. The substrate 400 may be etched by an anisotropic etching process, such as a reactive ion etching (RIR) process. Typically, the depth of the trench 430 is in the range of 0.1 μm to 1.5 μm.
As shown in FIG. 4c, a liner oxide layer 440 is formed on the inner surface of the trench 430. The liner oxide layer 440 may be made of silicon oxide, etc., and may be formed by a thermal oxidation process.
As shown in FIG. 4d, the trench 430 is filled with an insulation material, thus forming an isolation oxide layer 450. The isolation oxide layer 450 may be silicon oxide, etc. The trench 430 is filled up with the insulation material, which also covers the entirety of the pad oxide layer 410 and etch barrier layer 420, as shown in FIG. 4d. The isolation oxide layer 450 may be deposited in the trench 430 and on the etch barrier layer 420 by a chemical vapor deposition process. Preferably, this chemical vapor deposition process is a high-density plasma chemical vapor deposition (HDPCVD) process by which a silicon oxide insulation layer is deposited in the trench 430 and on the surface of the etch barrier layer 420 using O2 and silane (SiH4) as reactive gases.
Thereafter, as shown in FIG. 4e, the isolation oxide layer 450 is planarized, e.g., by a chemical mechanical polishing process until the etch barrier layer 420 has been exposed. Alternatively, the isolation oxide layer 450 is planarized by the chemical mechanical polishing process until the isolation oxide layer 450 has a relatively planar surface, the isolation oxide layer 450 is subsequently etched by an etching process until the etch barrier layer 420 has been exposed.
Finally, as shown in FIG. 4f, the etch barrier layer 420 and the pad oxide layer 410 are removed sequentially. The etch barrier layer 420 is removed e.g., by a wet etching process using a hot five-valent phosphoric acid solution. The pad oxide layer 410 is typically removed by a wet etching process, e.g., using a hydrofluoric acid solution. Since the wet etching process is isotropic, a portion of the insulation material on the sidewall of the trench 430 in contact with the semiconductor substrate may be etched when the pad oxide layer 410 is being removed by a hydrofluoric acid solution. As a result, as shown in FIG. 4f, a shallow trench isolation structure in which a recess 470 is formed on the sidewall of the trench 430 is formed.
As shown in FIG. 4g, a spin-on-glass layer 460 is formed on the substrate 400 and on the isolation oxide layer 450. The spin-on-glass layer 460 is preferably made of silicon oxide. The spin-on-glass layer 460 is formed by uniformly spreading a silicide-containing solution over the wafer by rotating the wafer, and then curing the silicide into non-crystalline silicon oxide by separating it from the solvent by heating.
In a particular embodiment of the present invention, a wafer with a structure as shown in FIG. 4f are rotated, and the methanol solution with a concentration of 15% to 25% silicon oxide is uniformly spread over the wafer. With the high speed rotation of the wafer, a silicon oxide film layer with a uniform thickness containing the solvent is formed on the surface of the wafer. Thereafter, in order to densify the spin-on-glass layer 460, an annealing process is performed at the temperature in the range of 850° C. to 1050° C. During the annealing process, methanol is vaporized, and a solid-state silicon oxide film layer with a uniform thickness is formed on the surface of the wafer. The thickness of the spin-on-glass layer would be reduced during the annealing process. According to the present invention, it is required that the thickness of the spin-on-glass layer after being annealed is in the range of 300 Å to 1000 Å. This not only ensures that the recess on the sidewall of the trench is filled up with the spin-on-glass, but also ensures that each of the substrate and the isolation oxide layer still has a relatively planar surface after the spin-on-glass layer has been removed by an etching process.
According to the present invention, the spin-on-glass layer 460 is formed by spinning coating using a liquid-state silicide solution, thus ensuring that each of the substrate 400 and the spin-on-glass layer 460 formed on the surface of the isolation oxide layer 450 still has a relatively planar surface after the recess on the sidewall of the trench 430 is filled up with the spin-on-glass.
According to the present invention, the thickness of the spin-on-glass layer 460 is in the range of 300 Å to 1000 Å, preferably, in the range of 300 Å to 500 Å. In some embodiments of the present invention, the thickness of the spin-on-glass layers are 400 Å, 600 Å, 700 Å, 800 Å, 900 Å, etc., respectively.
As shown in FIG. 4h, after the annealing process has been completed, the process of removing the spin-on-glass layer 460 is performed until both of the substrate 400 and the isolation oxide layer 450 have been exposed. According to the present invention, the process of removing the spin-on-glass layer 460 comprises the two steps of: first, removing a portion of the spin-on-glass layer 460 by a dry etching process such that the structure as shown in FIG. 4h is formed, the thickness of the remaining spin-on-glass layer 460a is in the range of 100 Å to 200 Å, thus ensuring that the surface of the substrate 400 will not be damaged during the dry etching process; second, removing the portion of the remaining spin-on-glass layer 460a that is higher than the substrate 400 by a wet etching process such that the structure as shown in FIG. 4i is formed.
The dry etching process of removing a portion of the spin-on-glass layer 460 may be a O2 plasma etching process, for example. After the dry etching process has been completed, as shown in FIG. 4h, the thickness of the remaining spin-on-glass layer 460a is in the range of 100 Å to 200 Å, in some particular embodiments of the present invention, after the dry etching process has been completed, the thickness of the remaining spin-on-glass layers are 120 Å, 140 Å, 150 Å, 180 Å, etc., respectively. Since the spin-on-glass layer 460 has a relatively planar surface before the dry etching process is performed, the remaining spin-on-glass layer 460a still has a planar surface after the dry etching process has been completed.
The process of removing the remaining spin-on-glass layer 460a may be a wet etching process which is performed on silicon oxide using a hydrofluoric acid solution, for example. After the wet etching process has been completed, as shown in FIG. 4i, the structure in which only the recess on the sidewall of the trench 430 is filled with the spin-on-glass layer 460 is formed.
After a trench isolation structure in which a recess is formed on the sidewall of a trench by a conventional process has been formed, a spin-on-glass layer is formed on the substrate and on an isolation filling layer by a spin-on-glass process. After the recess has been filled with the spin-on-glass, the spin-on-glass layer still has a relatively planar surface. Therefore, the trench isolation structure formed by the dry etch process and the wet etch process still has a planar surface. Also, the disadvantage that the recess is formed on the sidewall of the trench can thus be overcome.
The above-described method for filling recesses according to the present invention is applicable for not only the shallow trench isolation structure, but also other semiconductor structures with recesses on surfaces. That method comprises the steps of: providing a semiconductor substrate containing recesses, forming a spin-on-glass layer on the substrate such that the recesses on the substrate is filled with the spin-on-glass; and removing the spin-on-glass layer until the substrate has been exposed.
The detailed method for filling recesses according to the present invention refers to the method for filling recesses on sidewalls of trenches in the shallow trench isolation process.
While the present invention has been disclosed with respect to certain preferred embodiments, the present invention is not limited thereto. Various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Thus the protection scope of the present invention should be as defined by the claims.
Patent Application
20080081433
