Abstract:
The invention is directed to a method for patterning a material layer. The method comprises steps of forming a mask layer on the material layer. A multiple patterning process is performed on the mask layer for transferring at least a first pattern from a first photomask through a first photoresist and a second pattern from a second photomask from a second photoresist layer into the mask layer without performing any etching process. The mask layer exposes a portion of the material layer and the mask layer is patterned at the time that the first photoresist layer and the second photoresist layer are developed respectively. An etching process is performed to pattern the material layer by using the mask layer as an etching mask.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a patterning process. More particularly, the present invention relates to a multiple patterning process. 
     2. Description of Related Art 
     In the manufacture of integrated circuit, photolithography process is used to transfer patterns from a photo mask having customized circuit patterns to thin films formed on a wafer. The image transfer process comprises steps of forming a photoresist layer on a material layer, illuminating the photoresist layer through a photomask having the customized circuit patterns, developing the photoresist layer and then etching the material layer by using the patterned photoresist layer as a mask. Hence, the image transfer process is accomplished. For a well-manufactured integrated circuit product, the image transfer process mentioned above is performed several times to transfer the circuit patterns to each non-process layers to form the electrically circuit device. 
     Conventionally, in order to increase the integration of the device elements without being limited by the resolution of the optical tool, a double patterning process is developed. In the double patterning process, a mask layer is formed on the material layer and is patterned twice with using different photomasks. On the other words, the formation of photoresist layer, the exposure-developing process and the etching process for patterning the mask layer are repeatedly in sequence to transfer two different patterns into the mask layer. Then, by using the patterned mask layer, the material layer is pattern so as to transfer the pattern on the patterned mask layer into the material layer. Thus, the pattern in the mask layer possesses smaller pitch than the patterns of the photomasks. However, in the conventional double patterning process, the etching process should be performed several times. Therefore, the process procedure is complex and the throughput is decreased. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is to provide a method for patterning a material layer capable of simplifying the process procedure. 
     The present invention also provides a method for patterning a material layer capable of decreasing the pitch of the device element. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for patterning a material layer. The method comprises steps of forming a mask layer on the material layer and forming a first photoresist layer on the mask layer. A first exposure process is performed on the first photoresist layer. A first develop process is performed to remove the exposed first photoresist layer together with a portion of the mask layer exposed by the exposed first photoresist layer to form a first pattern of a first pitch. The first photoresist layer is removed. A second photoresist layer is formed and a second exposure process is performed on the second photoresist layer. A second develop process is performed to remove the exposed second photoresist layer together with a portion of the mask layer exposed by the second photoresist layer to form a second pattern of a second pitch, wherein the second pitch is less than the first pitch. The second photoresist layer is removed and the material layer is patterned by using the second pattern as a mask. 
     According to one embodiment of the present invention, the second pattern is used to form at least one trench in the material layer. Further, the second pitch is smaller than the optical resolution during each of the first and the second exposure processes. 
     According to one embodiment of the present invention, the mask layer is made of a bottom anti-reflection coating material. Also, the bottom anti-reflection coating material is dissolved during both of the first and the second develop processed and is not dissolved during the first and the second photoresist layers are removed. 
     The invention also provides a method for patterning a material layer. The method comprises steps of forming a mask layer on the material layer and forming a first photoresist layer on the mask layer. A first exposure process is performed on the first photoresist layer and a first develop process is formed to remove the exposed first photoresist layer together with a portion of the mask layer exposed by the first photoresist layer to form a first pattern of a first pitch. The first photoresist layer is removed and the mask layer is hardened. A second photoresist layer is formed and a second exposure process is performed on the second photoresist layer. A second develop process is performed to remove the exposed second photoresist layer and the remaining second photoresist layer and the mask layer together form a second pattern of a second pitch less than the first pitch. The material layer is patterned by using the second pattern as a mask. 
     According to one embodiment of the present invention, the second pattern is used to form at least one line of the material layer. Further, the second pitch is smaller than the optical resolution during each of the first and the second exposure processes. 
     According to one embodiment of the present invention, the mask layer is made of a bottom anti-reflection coating material. Also, the bottom anti-reflection coating material is dissolved during both of the first and the second develop processed and is not dissolved during the first and the second photoresist layers are removed. 
     The invention further provides a method for patterning a material layer. The method comprises steps of forming a mask layer on the material layer. A multiple patterning process is performed on the mask layer for transferring at least a first pattern from a first photomask through a first photoresist and a second pattern from a second photomask from a second photoresist layer into the mask layer without performing any etching process. The mask layer exposes a portion of the material layer and the mask layer is patterned at the time that the first photoresist layer and the second photoresist layer are developed respectively. An etching process is performed to pattern the material layer by using the mask layer as an etching mask. 
     According to one embodiment of the present invention, the multiple patterning process further comprises steps of forming the first photoresist layer on the mask layer. The first photoresist layer is patterned by using the first photomask and developing the first photoresist layer to remove a portion of the first photoresist layer together with a portion of the mask layer exposed by the first photoresist layer. Then, the first photoresist layer is removed and a second photoresist layer is formed on the mask layer having the first pattern therein. The second photoresist layer is patterned by using the second photomask and developing the second photoresist layer to remove a portion of the second photoresist layer together with a portion of the mask layer exposed by the second photoresist layer. The second photoresist layer is removed. 
     According to one embodiment of the present invention, after the second photoresist layer is removed, the multiple patterning process further comprises steps of hardening the mask layer and forming a third photoresist layer with a third pattern on the portion of the material layer exposed by the mask layer. Thus, the third photoresist layer and the mask layer together form the etching mask. Also, a fourth pattern of the etching mask is a combination pattern of the first pattern, the second pattern and the third pattern. 
     According to one embodiment of the present invention, a fourth pattern of the etching mask is a combination pattern of the first pattern and the second pattern. Also, a pitch of the fourth pattern is smaller than the optical resolution of the multiple patterning process. 
     According to one embodiment of the present invention, the first pattern is different from the second pattern. 
     According to one embodiment of the present invention, the mask layer is made of a bottom anti-reflection coating material. Also, the bottom anti-reflection coating material is dissolved in a developer used for patterning the first photoresist layer and the second photoresist layer and is not dissolved in a stripping solvent for removing the first photoresist layer and the second photoresist layer. 
     In the present invention, the mask layer possesses the ability to be dissolved in the developer together with a portion of the photoresist layer, the process for patterning a material layer can be performed without performing the etching process more than one time. Therefore, the process procedure of the multiple patterning process is simplified and the throughput is increased. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIGS. 1A through 1F  are cross-sectional views showing a multiple patterning process for patterning a material layer according to one embodiment of the invention. 
         FIGS. 2A through 2F  are cross-sectional views showing a multiple patterning process for patterning a material layer according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A through 1F  are cross-sectional views showing a multiple patterning process for patterning a material layer according to one embodiment of the invention. As shown in  FIG. 1A , a substrate  100  having a material layer  102  formed thereon is provided. Between the substrate  100  and the material layer  102 , there are several inter-layers (not shown). For simplifying the drawings, the inter-layers are not shown in the figures. It should be noticed that the material layer  102  can be, for example but not limited to, formed of polymer, dielectric material, such as silicon oxide or silicon nitride, or other material according to the practical requirement. 
     Then, as shown in  FIG. 1A , a mask layer  104  is formed on the material layer  102 . The mask layer  104  is an anti-reflection mask layer. That is, the mask layer  104  is not only a mask layer for the later performed patterning process of the material layer but also an anti-reflection layer for the later performed photolithography process. Moreover, the mask layer  104  can be, for example but not limited to, made from developable bottom anti-reflection coating (developable BARC) material. That is, the mask layer  104  possesses the ability to be dissolved in the developer under certain operation condition. While the operation temperature is about 160˜190° C. after BARC baking, the developable BARC can be dissolved in the developer and cannot be dissolved in the stripping solvent for removing the photoresist layer. It should be noticed that the stripping solvent for removing the photoresist layer can be, for example but not limited to, formed of propylene glycol methyl ether acetate (PGMEA), ethyl lactate (EL), methyl amyl ketone (MAK), propylene glycol monomethyl ether (PGME), or other material according to the practical requirement. 
     Still referring to  FIG. 1A , a multiple patterning process is performed. In this embodiment, the multiple patterning process is represented by transferring two patterns into the mask layer  104  sequentially. However, the present invention is not limited by the number of the patterns transferred into the same mask layer. In the multiple patterning process, a first photoresist layer  106  is formed on the mask layer  104 . In this embodiment, the first photoresist layer  106  is made of a positive type photoresist. However, the present invention is not limited by the material of the first photoresist layer  106  mentioned above. A first exposure process  110  with the use of a first photomask  108  having a first pattern  108   a  is performed on the first photoresist layer  106 . Therefore, a portion of the first photoresist layer labeled as  106   a  is exposed. 
     As shown in  FIG. 1B , a first develop process is performed to remove the exposure portion of the first photoresist layer  106   a  together with a portion of the mask layer  104  exposed by the first photoresist layer  106   b  without being dissolved in a developer. That is, at the time of dissolving the exposure portion of the first photoresist layer  106   a  in the developer, the portion of the mask layer  104  right under the exposure portion of the first photoresist layer  106   a  is dissolved in the developer as well. Thus, the mask layer  104  is transformed into a preliminary pattern mask layer  104   a  exposing a portion of the material layer  102 . 
     As shown in  FIG. 1C , the first photoresist layer  106   b  is removed. Since the mask layer  104   a , the preliminary pattern mask layer  104   a , is not dissolved in the stripping solvent for removing the first photoresist layer  106   b , the preliminary pattern mask layer  104   a  remains on the material layer  102 . Then, a second photoresist layer  112  is formed on the preliminary pattern mask layer  104   a . In this embodiment, the second photoresist layer  112  is made of a positive type photoresist. However, the present invention is not limited by the material of the second photoresist layer  112  mentioned above. A second exposure process  116  with the use of a second photomask  114  having a second pattern  114   a  is performed on the second photoresist layer  112 . Therefore, a portion of the second photoresist layer labeled as  112   a  is exposed. It should be noticed that the first pattern  108   a  of the first photomask  108  is different from the second pattern  114   a  of the second photomask  114 . 
     As shown in  FIG. 1D , a second develop process is performed to remove the exposure portion of the second photoresist layer  112   a  together with a portion of the preliminary pattern mask layer  104   a  exposed by the second photoresist layer  112   b  without being dissolved in a developer. That is, at the time of dissolving the exposure portion of the second photoresist layer  112   a  in the developer, the portion of the preliminary pattern mask layer  104   a  right under the exposure portion of the second photoresist layer  112   a  is dissolved in the developer as well. Thus, the preliminary pattern mask layer  104   a  is transformed into an etching mask layer  104   b  exposing a portion of the material layer  102 . 
     As shown in  FIG. 1E , the second photoresist layer  112   b  is removed. Since the etching mask layer  104   b  is not dissolved in the stripping solvent for removing the second photoresist layer  112   b , the etching mask layer  104   b  remains on the material layer  102 . Then, an etching process is performed to pattern the material layer  102  by using the etching mask layer  104   b  as a mask. Thus, the pattern in the etching mask layer  104   b  is transferred into the material layer  102  and the material layer  102  is transformed into a patterned material layer  102   a . It should be noticed that the pattern in the etching mask layer  104   b  is a combination pattern of the first pattern  118   a  and the second pattern  114   a . Moreover, the pitch x 1  of the pattern in the etching mask layer  104   b  is smaller than the optical resolution x 2  during each of the first exposure process  110  and the second exposure process  116 . 
     As shown in  FIG. 1F , the etching mask layer  104   b  is removed. In this embodiment, the pattern in the etching mask layer  104   b  can be, for example but not limited to, a trench pattern for forming at least one trench  102   b  in the material layer  102   a.    
       FIGS. 2A through 2F  are cross-sectional views showing a multiple patterning process for patterning a material layer according to another embodiment of the invention. As shown in  FIG. 2A , a substrate  200  having a material layer  202  formed thereon is provided. Between the substrate  200  and the material layer  202 , there are several inter-layers (not shown). For simplifying the drawings, the inter-layers are not shown in the figures. It should be noticed that the material layer  202  can be, for example but not limited to, formed of polymer, dielectric material, such as silicon oxide or silicon nitride, or other material according to the practical requirement. 
     Then, as shown in  FIG. 2A , a mask layer  204  is formed on the material layer  202 . The mask layer  204  is an anti-reflection mask layer. That is, the mask layer  204  is not only a mask layer for the later performed patterning process of the material layer but also an anti-reflection layer for the later performed photolithography process. Moreover, the mask layer  204  can be, for example but not limited to, made from developable bottom anti-reflection coating (developable BARC) material. That is, the mask layer  204  possesses the ability to be dissolved in the developer under certain operation condition. While the operation temperature is about 160˜190° C. after BRAC coating, the developable BARC can be dissolved in the developer and cannot be dissolved in the stripping solvent for removing the photoresist layer. It should be noticed that the stripping solvent for removing the photoresist layer can be, for example but not limited to, formed of propylene glycol methyl ether acetate (PGMEA), ethyl lactate (EL), methyl amyl ketone (MAK), propylene glycol monomethyl ether (PGME), or other material according to the practical requirement. 
     Still referring to  FIG. 2A , a multiple patterning process is performed. In this embodiment, the multiple patterning process is represented by transferring two patterns into the mask layer  204  sequentially. However, the present invention is not limited by the number of the patterns transferred into the same mask layer. In the multiple patterning process, a first photoresist layer  206  is formed on the mask layer  204 . In this embodiment, the first photoresist layer  206  is made of a positive type photoresist. However, the present invention is not limited by the material of the first photoresist layer  206  mentioned above. A first exposure process  210  with the use of a first photomask  208  having a first pattern  208   a  is performed on the first photoresist layer  206 . Therefore, a portion of the first photoresist layer labeled as  206   a  is exposed. 
     As shown in  FIG. 2B , a first develop process is performed to remove the exposure portion of the first photoresist layer  206   a  together with a portion of the mask layer  204  exposed by the first photoresist layer  206   b  without being dissolved in a developer. That is, at the time of dissolving the exposure portion of the first photoresist layer  206   a  in the developer, the portion of the mask layer  204  right under the exposure portion of the first photoresist layer  206   a  is dissolved in the developer as well. Thus, the mask layer  204  is transformed into a preliminary pattern mask layer  204   a  exposing a portion of the material layer  202 . 
     As shown in  FIG. 2C , the first photoresist layer is removed. Since the mask layer  204   a , the preliminary pattern mask layer  204   a , is not dissolved in the stripping solvent for removing the first photoresist layer  206   b , the preliminary pattern mask layer  204   a  remains on the material layer  202 . Then, a treatment process  212  is performed to harden the preliminary pattern mask layer  204   a . The temperature of the treatment process  212 , in this embodiment, is at least about 210° C. and the treatment process  212  is performed about 60˜240 seconds for hardening the preliminary pattern mask layer  204   a  into a preliminary pattern mask layer  204   b.    
     As shown in  FIG. 2D , a second photoresist layer  214  is formed over the substrate  200 . In this embodiment, the second photoresist layer  214  is made of a positive type photoresist. However, the present invention is not limited by the material of the second photoresist layer  214  mentioned above. A second exposure process  218  with the use of a second photomask  216  having a second pattern  216   a  is performed on the second photoresist layer  214 . Therefore, a portion of the second photoresist layer labeled as  214   a  is exposed. It should be noticed that the first pattern  208   a  of the first photomask  208  is different from the second pattern  216   a  of the second photomask  216 . In this embodiment, the second pattern  216   a  is located over a portion of the material layer  202  without having the first pattern  206   b  formed thereon. 
     As shown in  FIG. 2E , a second develop process is performed to remove the exposure portion of the second photoresist layer  214   a . Since the preliminary pattern mask layer  204   b  had been harden before the second develop process is performed, the preliminary pattern mask layer  204   b  is not dissolved in the developer used in the second develop process. That is, the patterned second photoresist layer  214   b  after the second develop process is located on a portion of the material layer exposed by the preliminary pattern mask layer  204   b . Thus, the preliminary pattern mask layer  204   a  is transformed into an etching mask layer  204   b  exposing a portion of the material layer  202 . 
     As shown in  FIG. 2F , the material layer  202  is patterned by using the preliminary pattern mask layer  204   b  and the patterned second photoresist layer  214   b  as an etching mask. Therefore, the first pattern  208   a  from the first mask  208  and the second pattern  216   a  from the second mask  216  are transferred into the material layer  202 . The material layer  202  is transformed into a material layer  202   a  with a third pattern  202   b . Accordingly, the third pattern  202   b  is a combination pattern of the first pattern  208   a  and the second pattern  216   a . In this embodiment, the third pattern composed of the preliminary pattern mask layer  204   b  and the patterned second photoresist layer  214   b  can be, for example but not limited to, a line pattern for forming at least one line in the material layer  202   a . It should be noticed that since the third pattern  202   b  in the material layer  202   a  is a combination pattern of the first pattern  208   a  and the second pattern  216   a , the pitch w 1  of the third pattern  202   b  is smaller than the optical resolution w 2  during each of the first exposure process  210  and the second exposure process  218 . 
     In the present embodiment, before the patterned mask layer  204   b  is hardened, the mask layer  204  is pattern by being directly dipping into the developer once. That is, in the present embodiment of the invention, only one pattern is transferred into the mask layer before the mask layer made of the developable BARC material is hardened. However, the present invention is not limited by this embodiment. The present embodiment can be integrated with the previous embodiment. That is, before the patterned mask layer is hardened, the mask layer can be multiple patterned several times as mentioned in the previous embodiment (as shown in  FIGS. 1A through 1D ). Therefore, the pitch of the result device element can be decreased and the density of the device element is increased. 
     In the present invention, because of the use of the mask layer made of the developable BARC material, the process for patterning a material layer can be performed without performing the etching process more than one time. That is, the mask layer of the present invention possesses the ability to be dissolved in the developer while a portion of the photoresist layer is dissolved in the developer. Therefore, the process procedure of the multiple patterning process is simplified and the throughput is increased. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.