BACKGROUND OF THE INVENTION 0001 1. Field of the Invention 0002 This invention relates to a method for filling of a shallow trench isolation, more particularly, to a method of gap filling shallow trench isolation with ozone (O3)-tetraethoxysilane (TEOS) in the fabrication of integrated circuits. 0003 2. Description of the Prior Art 0004 Shallow trench isolation (STI) has been gaining popularity for quarter-micron technology and beyond to replace the traditional localized oxidization of silicon (LOCOS) isolation process. However, as the design rule continues to shrink, gap filling of the smaller trench becomes a great challenge. Currently, both ozone-TEOS and high density plasma chemical vapor deposited (HDPCVD) oxide are being studied extensively for STI gap filling. For the ozone-TEOS approach, surface sensitivity of sub-atmospheric chemical vapor deposited (SACVD) ozone-TEOS oxide on thermal oxide is the most critical issue. An underlayer of thermal oxide is desired for good sidewall isolation. However, the surface sensitivity of ozone-TEOS deposition over thermal oxide results in a degradation of the ozone-TEOS deposition rate and wet etch rate. Therefore, a suitable interface must be formed over thermal oxide before ozone-TEOS is deposited. 0005 Referring to FIG. 1, there is shown a substrate which comprises a semiconductor substrate 10, a pad oxide layer 12 and the first silicon nitride layer 14. The material of the semiconductor substrate 10 is monocrystalline silicon. Shallow trench isolation regions are to be formed in the semiconductor substrate to isolate active areas of the integrated circuit device from one another. A layer of pad oxide layer 12 is grown on the surface of the semiconductor substrate 10. Then the first silicon nitride layer 14 is deposited over the pad oxide layer. We usually use silicon dioxide to be the material of the pad oxide layer 12. 0006 Referring to FIG. 2, a shallow trench is etched into the substrate using conventional photolithography and etching techniques. The shallow trenches 16 may be as small as 0.35 microns in width and are etched to a depth of between about 3000 and 5000 angstroms. A thermal oxide layer 17 is grown on the sidewalls of the trench 16 to a thickness of about 350 angstroms, as depicted in FIG. 3. This thermal oxide provides a good sidewall isolation. Then the trenches are to be filled with a dielectric material. The trenches will be filled with ozone-TEOS. First, an underlayer is to be deposited within the trenches to eliminate surface sensitivity and to eliminate the deleterious effects of the thermal oxide underlayer on ozone-TEOS deposition and wet etch rates. 0007 Referring to FIG. 4, the second silicon nitride layer 18 is deposited on the thermal oxide layer 17 and the first silicon nitride layer 14. A layer of plasma-enhanced silane oxide SiH4 18 is deposited by plasma enhanced chemical vapor deposition (PECVD) over the surface of the substrate and within the trenches 16. Then nitrogen is implanted to the plasma-enhanced silane oxide layer by using plasma treatment and the plasma-enhanced silane oxide become the second silicon nitride layer 18. The second silicon nitride layer 18 can eliminate surface sensitivity and to eliminate the deleterious effects of the thermal oxide underlayer on ozone-TEOS deposition and wet etch rates. 0008 Referring to FIG. 5, the ozone-TEOS layer 22 is deposited on the second silicon nitride layer 18 and is filled of the trench 16 by using the subatmospheric chemical vapor deposition method. Referring to FIG. 6, we remove the second silicon nitride 18 layer which is on both sides of the trench 16 and over deposition in ozone-TEOS 22 by using a polishing way. At present, the polishing way is chemical mechanical polishing (CMP). When we polish to the first silicon nitride, we stop the chemical mechanical polishing process and end the gap filling of shallow trench isolation process. 0009 Referring to FIG. 7, when the ozone-TEOS layer 22 is deposited on the second silicon nitride layer 18 and is filled of the trench 16 by using the subatmospheric chemical vapor deposition method, the deposition velocity of ozone-TEOS in the first surface 24, the second surface 26 and the third surface 28 are the same. This condition can easily make that when ozone-TEOS which is deposited on the second surface 26 of the trench, and ozone-TEOS which is deposited on the third surface 28 of the trench are contact with each other and ozone-TEOS which is deposited on the first surface of the trench still not reach this contact point. The vapor of ozone-TEOS will not enter into the trench and will not be deposited on the first surface 24 of the trench continuously. The void defects 19 will be produced inside the ozone-TEOS layer 22 in the trench 16 and will be found hardly. The void defects 19 inside the trench 16 will make the semiconductor elements occur in leak of an electric current in the proceeding process. Especially when the volume of the semiconductor element is reduced and the size of the trench 16 is following more and more small, the void defects 19 will be produced more easily by using traditional method to fill of the shallow trench isolation. Therefore, we must use the present invention to reduce the probability of producing the void defects inside the trench. The bottom of the trench 16 is the first surface 24 of the trench and the sidewalls of the trench 16 comprises the second surface 26 and the third surface 28 of the trench 16.

SUMMARY OF THE INVENTION 0010 In accordance with the above-mentioned invention backgrounds, the void defects are produced inside the filled layer of the trench more easily by using traditional method. The main objective of the invention is to provide a method for filling the shallow trench isolation by ozone-TEOS and preventing the void defects to be produced inside the ozone-TEOS layer in the integrated circuit process. 0011 The second objective of this invention is to prevent the void defects to be produced inside the shallow trench isolation and increase the velocity of the process by using different reaction rate in silicon to ozone-TEOS and silicon nitride to ozone-TEOS. 0012 The third objective of this invention is to improve the structure strength of the deposited ozone-TEOS layer by using the second silicon nitride layer which is deposited on the thermal oxide layer. 0013 The fourth objective of this invention is to prevent the void defects which are produced inside the filled layer of the trench to decrease the volume of the semiconductor elements successfully and increase the density of the elements in the semiconductor. 0014 The further objective of this invention is to reduce the probability of leaking the electric current in the semiconductor element and to increase the qualities of the semiconductor elements by avoiding the void defects being produced inside the filled layer of the trench. 0015 In according to the foregoing objectives, the present invention provides a method for using ozone-TEOS to be the material to fill of the trench and to avoid the void defects being produced inside the filled layer of the trench by using different reaction rate in silicon to ozone-TEOS and silicon nitride to ozone-TEOS. The void defects will affect the semiconductor elements to occur leaking the electric current. This method can increase the qualities of the semiconductor elements and decrease the volume of the semiconductor elements successfully to increase the density of the elements in the semiconductor. The method can also increase the process velocity of filling of the shallow trench isolation.

BRIEF DESCRIPTION OF THE DRAWINGS 0016 In the accompanying drawing forming a material part of this description, there is shown: 0017 FIG. 1 is a cross-section representation of a substrate; 0018 FIG. 2 is a cross-section representation of forming a trench in the substrate; 0019 FIG. 3 is a cross-section representation of forming a thermal oxide layer on the surface of the trench; 0020 FIG. 4 is a cross-section representation of depositing the second silicon nitride layer on the thermal oxide layer which is on the surface of the trench and the first silicon nitride layer which is formed on the substrate. 0021 FIG. 5 is a cross-section representation of depositing the ozone-TEOS layer on the second silicon nitride layer, filling the trench, and producing the void defects inside the trench. 0022 FIG. 6 is a representation of substrate after using the chemical mechanical polishing method to remove the over deposited ozone-TEOS. 0023 FIG. 7 is a representation of producing the void defects inside the filled trench by using the traditional method. 0024 FIG. 8 is a cross-section representation of a substrate; 0025 FIG. 9 is a cross-section representation of forming a trench in the substrate; 0026 FIG. 10 is a cross-section representation of forming a thermal oxide layer on the surface of the trench; 0027 FIG. 11 is a cross-section representation of depositing the second silicon nitride layer on the thermal oxide layer which is on the surface of the trench and the first silicon nitride layer which is formed on the substrate. 0028 FIG. 12 is a cross-section representation of removing the second silicon nitride layer and the thermal oxide layer which are on the first surface of the trench by using anisotropic etching method. 0029 FIG. 13 is a cross-section representation of depositing the ozone-TEOS layer on the second silicon nitride layer and filling the trench. 0030 FIG. 14 is a representation of substrate after using the chemical mechanical polishing method to remove the over deposited ozone-TEOS. 0031 FIG. 15 is a representation of using the method of the present invention for filling of the shallow trench isolation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 0032 The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 0033 Referring to FIG. 8, there is shown a substrate which comprises a semiconductor substrate 100, a pad oxide layer 120 and the first silicon nitride layer 140. The material of the semiconductor substrate 100 is monocrystalline silicon. Shallow trench isolation regions are to be formed in the substrate to isolate active areas of the integrated circuit device from one another. A layer of pad oxide layer 120 is grown on the surface of the semiconductor substrate 100 and the material of the pad oxide layer is silicon dioxide in usual. The thickness of the pad oxide layer is about 100 to 120 angstroms and the thickness of the pad oxide layer is about 110 angstroms at present. Then the first silicon nitride layer 140 is deposited over the pad oxide layer 120. The thickness of the first silicon nitride layer 140 is about 1300 to 1700 angstroms and the thickness of the silicon nitride layer 140 is about 1500 angstroms at present. 0034 Referring to FIG. 9, a shallow trench is etched into the substrate using conventional photolithography and etching techniques. The shallow trenches 160 may be as small as 0.10 to 0.24 microns in width and are etched to a depth of between about 3000 and 4000 angstroms. A thermal oxide layer 170 is grown on the sidewalls of the trench 160 to a thickness of about 150 to 210 angstroms, as depicted in FIG. 10. This thermal oxide layer 170 provides a good sidewall isolation. Then the trench 160 is to be filled with a dielectric material. The trench 160 will be filled with ozone-TEOS. First, an underlayer is to be deposited within the trenches to eliminate surface sensitivity and to eliminate the deleterious effects of the thermal oxide underlayer on ozone-TEOS deposition and wet etch rates. 0035 Referring to FIG. 11, the second silicon nitride layer 180 is deposited on the thermal oxide layer 17 and the first silicon nitride layer 140. A layer of plasma-enhanced silane oxide SiH4 180 is deposited by plasma enhanced chemical vapor deposition (PECVD) over the surface of the substrate and within the trenches 160. Then nitrogen is implanted to the plasma-enhanced silane oxide layer by using plasma treatment and the plasma-enhanced silane oxide become the second silicon nitride layer 180. The second silicon nitride layer 180 can eliminate surface sensitivity and to eliminate the deleterious effects of the thermal oxide underlayer on ozone-TEOS deposition and wet etch rates. The thickness of the second silicon nitride layer 180 is about 90 to 150 angstroms. 0036 Referring to FIG. 12, we use the anisotropic etching method to remove the thermal oxide layer 170 and the second silicon nitride layer 180 from the first surface 240 of the trench 160, and to make the semiconductor substrate 100 be shown on the first surface 240 of the trench 160. The bottom of the trench 160 is the first surface 240 of the trench and the sidewalls of the trench 160 comprises the second surface 260 and the third surface 280 of the trench 160. At present, we use reactive ion etching method to be the anisotropic etching method. Referring to FIG. 13, the ozone-TEOS layer 220 is deposited on the second silicon nitride layer 180 and is filled of the trench 160 by using the subatmospheric chemical vapor deposition method. Referring to FIG. 14, the ozone-TEOS 220 which is over deposition is removed by using a polishing way. At present, the polishing way is chemical mechanical polishing (CMP). When we polish to the first silicon nitride layer, we stop the chemical mechanical polishing process and end the gap filling of shallow trench isolation process. 0037 After finishing the deposition ozone-TEOS process and before proceeding chemical mechanical polishing process, we form an oxide layer on the contacting surface between the ozone-TEOS layer and the semiconductor substrate to increase the structure strength of the ozone-TEOS layer on the first surface of the trench and to remove the impurities which are in the contacting surface between the ozone-TEOS layer and the semiconductor substrate. If the oxide layer is formed on the contacting surface, the thickness of the oxide layer is about 90 to 110 angstroms. 0038 In the traditional technologies, we can find that the ozone-TEOS reaction selective ratio of silicon to silicon nitride is about 1:5. In other words, the velocity of depositing ozone-TEOS on the silicon material is five times than the velocity of depositing ozone-TEOS on the silicon nitride material. We can use this technology to solve the void defects produced inside the filled material of the trench when we deposit the ozone-TEOS layer. 0039 When we use the traditional technology to fill of shallow trench isolation by using ozone-TEOS, the deposition velocity of ozone-TEOS in the first surface 24, the second surface 26 and the third surface 28 of the trench are the same because the material in the first surface, the second surface, and the third surface of the trench is silicon nitride. 0040 Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims. This condition can easily make that when ozone-TEOS which is deposited on the second surface of the trench, and ozone-TEOS which is deposited on the third surface 28 of the trench are contact with each other and ozone-TEOS which is deposited on the first surface of the trench still not reach this contact point. The vapor of ozone-TEOS will not enter into the trench and will not be deposited on the first surface 24 of the trench continuously. The void defects 19 will be produced inside the ozone-TEOS layer 22 in the trench 16 and will be found hardly. Referring to the FIG. 15, the present invention removes the second silicon nitride layer and the thermal oxide layer from the first surface of the trench, and show the semiconductor substrate on the first surface of the trench by using the anisotropic etching method before depositing the ozone-TEOS layer. The anisotropic etching method is the reactive ion etching method at present. When we start to deposit the ozone-TEOS layer, the velocity of depositing the ozone-TEOS layer on the first surface of the trench is five times than the velocity of depositing the ozone-TEOS layer on the second surface of the trench by using the velocity of depositing the ozone-TEOS layer on the semiconductor substrate to be five times than the velocity of depositing the ozone-TEOS layer on the silicon nitride layer. The velocity of depositing the ozone-TEOS layer on the second surface of the trench and the velocity of depositing the ozone-TEOS layer on the third surface of the trench are the same. This condition makes the way of filling trench from the bottom to the top of the trench. This filling way can avoid the void defects to be produced when ozone-TEOS which is deposited on the second surface of the trench, and ozone-TEOS which is deposited on the third surface 28 of the trench are contact with each other and ozone-TEOS which is deposited on the first surface of the trench still not reach this contact point. After finishing the gap filling of shallow trench isolation process, the void defects, which are not found easily inside the shallow trench isolation layer, will make the semiconductor elements to occur the leaking electric current conditions. When the volume of the semiconductor elements are decreased, the void defects are produced more easily inside the complete filled trench by using traditional technology to fill of the shallow trench isolation layer. Therefore, we must use the method of the present invention to increase the qualities of the semiconductor elements and to increase the density of elements on the semiconductor. 0041 In accordance with the present invention, we use the difference between the velocity of depositing the ozone-TEOS layer on the silicon layer and the velocity of depositing the ozone-TEOS layer on the silicon nitride layer to remove the second silicon nitride layer and the thermal oxide layer from the first surface of the trench and to show the semiconductor substrate on the first surface of the trench by using anisotropic etching method before depositing the ozone-TEOS layer in the gap filling of shallow trench isolation process. The velocity of depositing the ozone-TEOS layer on the first surface of the trench is higher than the velocity of depositing the ozone-TEOS layer on the second or the third surface of the trench is higher in the depositing ozone-TEOS process. The way of filling trench is from the bottom to the top of the trench and can avoid the void defects, which are produced inside the filled layer and are found hardly to affect the qualities of the semiconductor elements, after finishing the filling process. The present invention can also make the volume of the semiconductor elements be decreased successfully and increase the density of elements in the semiconductor. 0042 Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.