Patent Publication Number: US-2003232283-A1

Title: Method for forming a photoresist pattern on a semiconductor substrate

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to semiconductor technology, and more particularly to a method for forming a photoresist pattern on a semiconductor substrate in lithography.  
       [0003] 2. Description of the Related Art  
       [0004] In semiconductor processing, lithography is frequently used for reproducing circuits and structures on a semiconductor substrate. As a first step in lithography, a photoresist layer is formed on a semiconductor substrate such that an image can be projected and developed on the substrate.  
       [0005] The photoresist material is a liquid that is coated in a very thin layer on top of the semiconductor substrate by a spin coating apparatus, and then baking is performed to cure the photoresist material by hot plates. In order to prevent the standing wave effect and the photoresist material poison issue, a top anti-reflection layer (ARL) is frequently deposited on the photoresist layer for defining a specific feature of the circuit. FIGS. 1 a  to  1   c  are cross-section illustrating a conventional method for forming a photoresist pattern on a semiconductor substrate.  
       [0006] In FIG. 1 a,  a substrate  10  such as a semiconductor substrate is provided. A photoresist material (not shown) is coated on the substrate  10  by a spin coating apparatus, and then a first baking  11  is performed to form a photoresist layer  12  by hot plates (not shown).  
       [0007] In FIG. 1 b,  after the substrate  10  covered by a photoresist layer  12  is cooled to room temperature, another photoresist material such as an anti-reflection material is coated on the photoresist layer  12 . Also, a second baking  13  is performed again to form an ARL  14  by hot plates. The anti-reflection layer  14  is a top ARL to prevent the standing wave effect and the photoresist layer  12  poison issue.  
       [0008] In FIG. 1 c,  lithography is performed to the photoresist layer  12  and the top ARL  14  to remove the top ARL  14  and to form a photoresist pattern  12  on the substrate  10 .  
       [0009] In the conventional method, however, baking is performed twice to cure the photoresist material and anti-reflection material, respectively, to form the photoresist layer  12  and the top ARL  14 . That is, many hot plates are required and the lithography steps are increased for the layers  12 ,  14 . As a result, the manufacturing cost is increased and the throughput is reduced.  
       SUMMARY OF THE INVENTION  
       [0010] It is therefore an object of the present invention to provide a method for forming photoresist layers on a substrate without baking twice to reduce the manufacturing cost.  
       [0011] Another object of the present invention is to provide a method for defining a photoresist pattern on a substrate to increase throughput by simplifying the steps of lithography are.  
       [0012] According to an aspect of the invention, there is provided a method for forming photoresist layers on a substrate, which includes the steps of: coating a first photoresist material on the substrate; coating a second photoresist material on the first photoresist material before baking the first photoresist material; and baking the substrate to simultaneously form a first photoresist layer and a second photoresist layer over the first photoresist layer. The method further includes a step of cooling the substrate to room temperature after the baking step.  
       [0013] According to another aspect of the invention, there is provided a method for forming a photoresist pattern on a substrate, which includes the steps of: coating a photoresist material on the substrate; coating an anti-reflection material on the photoresist material before baking the photoresist material; baking the substrate to simultaneously form a photoresist layer and an anti-reflection layer over the photoresist layer; performing an exposure on the anti-reflection layer and the photoresist layer by a patterning mask; and performing a development on the anti-reflection layer and the photoresist layer to form a photoresist pattern on the substrate. The method further includes a step of cooling the substrate to room temperature after the baking step. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
     [0015]FIGS. 1 a  to  1   c  are sectional diagrams showing a method for forming a photoresist pattern on a semiconductor substrate according to the prior art.  
     [0016]FIGS. 2 a  to  2   c  are sectional diagrams showing a method for forming a photoresist pattern on a semiconductor substrate according to the present invention.  
     [0017]FIG. 3 a  is a trend chart showing the relationship between the yield (%) and lot number (#) according to the present invention.  
     [0018]FIG. 3 b  is a trend chart showing the relationship between the yield (%) and lot number (#) according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0019]FIGS. 2 a  to  2   c  are sectional diagrams showing a method for forming a photoresist pattern on a semiconductor substrate according to the present invention.  
     [0020] In FIG. 2 a,  a substrate  20  is provided. The substrate  20  is understood to possibly include a semiconductor wafer, active and passive devices formed within the wafer. Herein, a smooth substrate  20  is shown to simplify the diagram. A layer to be defined  22  is formed on the substrate  20  by deposition. The layer to be defined  22  can be a conductive layer such as a polysilicon layer, or a dielectric layer such as a silicon oxide layer. Thereafter, a first photoresist material (not shown) is coated on the substrate  20  by a spin coating apparatus (not shown), and a second photoresist material (not shown) is coated on the first photoresist material by a spin coating apparatus before the first photoresist material is baked. In the present invention, for example, the first photoresist material can be a chemical amplified resist (CAR) material and the second photoresist material can be an organic anti-reflection material.  
     [0021] Next, hot plates (not shown) are used to bake  21  the substrate  20  to simultaneously form a photoresist layer  24  and a top ARL  26  over the photoresist layer  24 . In the present invention, the baking  21  is performed at 100˜140° C. for 50˜80 seconds.  
     [0022] In FIG. 2 b,  after the substrate  20  covered by the layers  26 ,  24  is cooled to room temperature, an exposure  23  is performed on the layers  26 ,  24  using a patterned mask  28 . Subsequently, a development is performed on the layers  26 ,  24  to remove the top ARL  26  and to form a photoresist pattern  24  on the substrate  20 , as shown in FIG. 2 c.    
     [0023]FIGS. 3 a  and  3   b  are trend charts showing the relationship between the yield (%) and lot number (#) according to the present invention and the prior art, respectively. As shown in FIGS. 3 a  and  3   b,  while the present invention uses one baking, the average yield (about 60%) is higher than that (about 52%) of the prior art.  
     [0024] Therefore, compared with the conventional method for forming a photoresist pattern on a substrate, the present invention just uses one baking to cure the photoresist material. It is an advantage to reduce the manufacturing cost by reducing the numbers of hot plates. Moreover, the steps of lithography are simplified to increase the throughput.  
     [0025] Finally, while the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.