Patent Publication Number: US-7718345-B2

Title: Composite photoresist structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/465,811, filed Aug. 20, 2006, which itself is a continuation of U.S. application Ser. No. 10/708,983, filed Apr. 5, 2004. Additionally, application Ser. No. 10/708,983 is itself a divisional of U.S. application Ser. No. 10/063,307, filed Apr. 10, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photoresist structure, and more particularly, to a photoresist structure suitable for sub-micron pattern transfers in semiconductor processes. 
     2. Description of the Prior Art 
     Generally, integrated circuit production relies on the use of photolithographic processes and etching processes to define various electrical elements and interconnecting structures on microelectronic devices. With the coming of a generation of Ultra Large Scale Integrated (ULSI) Circuits, the integration of semiconductor devices has gotten larger and larger. G-line (436 nm) and I-line (365 nm) wavelengths of light have been widely used in photolithography processes. However, in order to achieve smaller dimensions of resolution, wavelengths of light used for photolithography processes have been reduced into deep UV regions of 248 nm and 193 nm. Nevertheless, the shorter the wavelengths of light are, the thinner the photoresist layers are. The thin photoresist layers might not be thick enough for blocking the etching processes in the following fabrication. As a result, for a photolithography process utilizing short wavelengths of light, it is necessary to look for a photoresist structure suitable for lithography processes and etching processes. 
     Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram of a prior art photoresist structure. As shown in  FIG. 1 , a semiconductor wafer  10  comprises a substrate  12 , an anti-reflection layer  14 , and a photoresist layer  16 . Because wavelengths of light used for exposure processes are related to the depth of focus (DOF), a required thickness of the photoresist layer  16  depends on the wavelengths of light. Accordingly, the thickness of the photoresist layer  16  has to be thin enough so that the molecules in the surface of the photoresist layer have approximately the same focus as the molecules in the bottom of the photoresist layer. However, the photoresist layer  16  is used to be a hard mask on the substrate  12  in the following etching processes. For this reason, the thin photoresist layers might not be thick enough for blocking the following etching processes. 
     Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram of another prior art photoresist structure used to overcome the above-mentioned problem. As shown in  FIG. 2 , a semiconductor wafer  20  comprises a substrate  22 , a silicon oxynitride layer  24 , an anti-reflection layer  26 , and a photoresist layer  28 . Therein the silicon oxynitride layer  24  serves as a hard mask so that the photoresist layer  28  together with the silicon oxynitride layer  24  can block the etching processes in the following fabrication. After the predetermined pattern of the mask is transferred onto the substrate  22 , the silicon oxynitride layer  24 , the anti-reflection layer  26 , and the photoresist layer  28  are removed. However, the silicon oxynitride layer  24  is not easy to etch away. Thus, the process of removing the silicon oxynitride layer  24  usually causes damage to the surface of the substrate  22 . 
     In addition, methods used to overcome the above-mentioned problem further include bi-layer photoresist technology (U.S. Pat. No. 6,323,287) and top surface image (TSI) technology (U.S. Pat. No. 6,296,989). However, both of the two methods require new photoresist materials. For example, the photoresist layer used in the TSI technology comprises silicon-containing materials. Providing new photoresist materials will increase production costs and increase complexity and difficulty of processes. As a result, it is necessary to look for a photoresist structure suitable for sub-micron pattern transfers in photolithography processes and etching processes. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the claimed invention to provide a composite photoresist structure so as to solve the above-mentioned problem. 
     According to the claimed invention, a composite photoresist structure includes a first organic layer disposed over a substrate to be etched, a sacrificial layer disposed on the first organic layer, and a second organic layer disposed on the sacrificial layer. The thickness of the first organic layer and the thickness of the second organic layer are both larger than the thickness of the sacrificial layer. 
     It is an advantage over the prior art that the claimed invention provides a composite photoresist structure including a first organic layer, an inorganic sacrificial layer, and a second organic layer. The first and second organic layers are both thicker than the sacrificial layer. Furthermore, a thickness of the second organic layer can be adjusted according to wavelengths of light sources used in exposure processes. Simultaneously, by adjusting thicknesses of the sacrificial layer and the first organic layer, the composite photoresist structure is thick enough to block following etching processes. Thus, the claimed photoresist structure is suitable for sub-micron pattern transfers in semiconductor processes. In addition, the first organic layer is regarded as a hard mask and it is easily removed by use of plasma. It is a further advantage that removing the first organic layer will not damage the substrate. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a prior art photoresist structure. 
         FIG. 2  is a schematic diagram of another prior art photoresist structure. 
         FIG. 3  is a schematic diagram of a composite photoresist structure according to the present invention. 
         FIG. 4A  to  FIG. 4F  are schematic diagrams illustrating an etching process utilizing the composite photoresist structure. 
         FIG. 5  is a schematic diagram of a composite photoresist structure according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram of a composite photoresist structure according to the preferred embodiment of the present invention. As shown in  FIG. 3 , a composite photoresist structure  30  comprises a first organic layer  30   a , a sacrificial layer  30   b  located on the first organic layer  30   a , and a second organic layer  30   c  located on the sacrificial layer  30   b . The first organic layer  30   a  and the second organic layer  30   c  both comprise organic materials. The sacrificial layer  30   b  comprises inorganic materials. In addition, the thickness of the first organic layer  30   a  and the thickness of the second organic layer  30   c  are both larger than the thickness of the sacrificial layer  30   b . Furthermore, the thickness of the first organic layer  30   a  is also larger than the thickness of the second organic layer  30   c.    
     In particular, the first organic layer  30   a  is made of low dielectric organic materials, such as SiLK™. Additionally, the first organic layer  30   a  is also made of spin-on glass (SOG). Consequently, it is easy to remove the first organic layer  30   a  by means of plasma, which includes oxygen (O 2 ), nitrogen (N 2 ), hydrogen (H 2 ), argon (Ar), C x F y , C x H y F z , or helium (He) plasma. The sacrificial layer  30   b  is made of inorganic anti-reflection materials such as silicon oxynitride (SiON) and silicon nitride (SiN). In addition, the sacrificial layer  30   b  is also made of materials used for conventional hard masks, such as silicon nitride and silicon oxide. Moreover, the second organic layer  30   c  is made of organic photoresist materials that include positive photoresist materials and negative photoresist materials. Furthermore, the second organic layer  30   c  is made of organic materials suitable for utilizing in the e-beam lithography process. Noticeably, the composite photoresist structure  30  is suitable for any photolithography processes in the semiconductor fabrication. It should be known by one skilled in the art that a thickness of each of the first organic layer  30   a , the sacrificial layer  30   b , and the second organic layer  30   c  could be adjusted according to requirements of processes. 
     Please refer to  FIG. 4A  to  FIG. 4F .  FIG. 4A  to  FIG. 4F  are schematic diagrams illustrating an etching process utilizing the composite photoresist structure  30 . As shown in  FIG. 4A , a semiconductor wafer  40  comprises a substrate  42  and the composite photoresist structure  30  formed on the substrate  42 . The substrate  42  is a silicon substrate, a metal substrate or a dielectric layer, which has a planar and smooth surface. Firstly, as shown in  FIG. 4B  and  FIG. 4C , an exposure process and a development process are performed to transfer a predetermined pattern onto the second organic layer  30   c . Then, using the second organic layer  30   c  as an etching mask, a dry etching process is performed on the sacrificial layer  30   b  in order to transfer the predetermined pattern in the second organic layer  30   c  onto the sacrificial layer  30   b . Besides, in another embodiment of the present invention, the predetermined pattern can be formed in the second organic layer by utilizing the e-beam lithography process. 
     As shown in  FIG. 4D  to  FIG. 4F , utilizing the sacrificial layer  30   b  to be an etching mask, an anisotropic etching process is performed to transfer the predetermined pattern onto the first organic layer  30   a . Then, using the sacrificial layer  30   b  and the first organic layer  30   a  as an etching mask, an etching process is performed to transfer the predetermined pattern in the first organic layer  30   a  onto the substrate  42 . While etching the substrate  42 , the sacrificial layer  30   b  is removed concurrently. After transferring the predetermined pattern onto the substrate  42 , the first organic layer  30   a  is subsequently removed. Up to now, the predetermined pattern on the mask is thoroughly transferred onto the substrate  42 . The first organic layer  30   a  is regarded as a hard mask, and its thickness can be adjusted in order to block subsequent etching processes. Thus, the composite photoresist structure  30  can be used in a photolithography process utilizing light sources with wavelengths shorter than 248 nm in deep UV regions. Furthermore, conventional hard masks are generally made out of silicon nitride or silicon oxide, which are not easy to etch away. Hence, an acidic trough is required to remove the conventional hard masks. Conversely, it is easy to remove the first organic layer  30   a  through use of plasma. Furthermore, removing the first organic layer  30   a  will not damage the substrate  42 . 
     Please refer to  FIG. 5 .  FIG. 5  is a schematic diagram of a composite photoresist structure according to another embodiment of the present invention. As shown in  FIG. 5 , a composite photoresist structure  50  comprises a first organic layer  50   a , a sacrificial layer  50   b  located on the first organic layer  50   a , an anti-reflection layer  50   c  located on the sacrificial layer  50   b , and a second organic layer  50   d  located on the anti-reflection layer  50   c . The first organic layer  50   a  is made of low dielectric organic materials. In addition, the first organic layer  50   a  can be made of spin-on glass (SOG). It is easy to remove the first organic layer  50   a  by use of plasma. The sacrificial layer  50   b  is made of materials used for hard masks such as silicon nitride and silicon oxide. The anti-reflection layer  50   c  is made of organic materials used for organic bottom anti-reflection coating such as polyimide and the like. Additionally, the anti-reflection layer  50   c  can also be made of inorganic materials used for inorganic bottom anti-reflection coating such as silicon oxynitride (SiON). The anti-reflection layer  50   c  can prevent incident light from reflecting from the substrate to the composite photoresist structure  50 . Thus, due to the anti-reflection layer  50   c , forming a standing wave in the second organic layer  50   d  is avoided. The second organic layer  50   d  is made of organic photoresist materials that comprise positive photoresist materials and negative photoresist materials. As mentioned above, the composite photoresist structure  50  can be utilized in any photolithography processes. It should be known by one skilled in the art that a thickness of each of the first organic layer  50   a , the sacrificial layer  50   b , the anti-reflection layer  50   c , and the second organic layer  50   d  could be adjusted according to requirements of processes. However, in this embodiment, the first and second organic layers  50   a ,  50   d  are both thicker than the sacrificial layer  50   b , while the sacrificial layer  50   b  is thicker than the anti-reflection layer  50   c . In addition, the first organic layer  50   a  is thicker than the second organic layer  50   d.    
     In comparison with the prior art, the present invention provides a composite photoresist structure including a first organic layer, an inorganic sacrificial layer, and a second organic layer. A thickness of the second organic layer could be adjusted according to wavelengths of light sources used in exposure processes. Simultaneously, by adjusting thicknesses of the sacrificial layer and the first organic layer, the composite photoresist structure is thick enough to block ensuing etching processes. Thus, the claimed photoresist structure is suitable for sub-micron pattern transfers in semiconductor processes. As a result, the predetermined pattern of the mask can be accurately transferred onto the semiconductor wafer, and a critical dimension (CD) is therefore controlled well. In addition, the first organic layer is regarded as a hard mask and it is easily removed through use of plasma. It is also an advantage that removing the first organic layer will not damage the substrate. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.