Patent Publication Number: US-2010129735-A1

Title: Production of stamps, masks or templates for semiconductor device manufacturing

Description:
The present invention relates to a method for manufacturing a substrate for semiconductor device manufacturing and to a method for producing a set of stamps or masks, also called templates using a mastering process. 
     In a semiconductor manufacturing processes such as embossing, imprint or optical lithography, multiple patterned layers are stacked on a substrate by repeatedly applying the basic process steps. For a proper functioning of the created device accurate overlay in successive process steps is essential. This is often achieved by incorporating alignment marks in the masks or stamps used in consecutive process steps and correlating the position of the mask/stamp to similar features left on the substrate/device in previous steps. 
     For forming the structure on a stamp or a mask, equipment and processes known from the production of master discs for optical media may be used. Typically, the production of a master disc comprises the steps of cleaning a substrate, e.g. a glass substrate, and applying a layer of a radiation sensitive material to a surface of the substrate, illuminating the sensitive material on the substrate in a desired pattern by moving a focused laser spot over the substrate, and developing the layer of sensitive material. The sensitive material may be a photo-sensitive material or a phase transition layer. Writing of the information on the disc by illuminating the layer of radiation sensitive material in a predetermined pattern is usually done in a laser beam recorder. For most optical media, a spiral or concentric circles are recorded with pits and/or grooves by rotating the substrate and translating the laser spot radially relative with respect to the substrate. With the present laser beam recorders, radial positional accuracies of less than 10 nm can be achieved as well as very accurate tangential positions. 
     A method of manufacturing a stamp for use in the manufacture of small form factor (SFF) optical data storage media is known from WO 03/042985 A2 wherein on a single master plate a series of areas with spiral- or concentric-shaped information tracks is provided, with the center of each area located outside the axis of rotation of the master plate. The different areas are written one after the other on the master plate by fixing the master plate eccentrically with respect to an axis of rotation of a support structure and rotating the support structure with the attached master plate around the axis of rotation of the support structure. The stamp obtained from the thus produced master plate may be used to simultaneously produce a number of replicas corresponding to the areas on the master plate. 
     When in the production of a semiconductor device several layers subsequently have to be formed on top of each other on the same substrate, correct alignment of the different templates used for forming the structures in the different layers is very important. Therefore, a high relative positional accuracy of the structures on the different stamps or masks has to be guaranteed. 
     Further prior art is disclosed in JP-A-07 014 218, U.S. Pat. No. 6,638,692 B1, US 2006/286355 A1, EP-A-0 355 925, JP-A-04 095 243, WO 2006/045332 A and JP-A-07 320 305. 
     It is therefore an object of the invention to provide a method for manufacturing a substrate with structures in different areas thereon, with these areas having a very high relative positional accuracy, that is, the patterns in the different areas should be very good references with respect to each other. It is further an object of the invention to provide a method for manufacturing a set of stamps or masks for manufacturing semiconductor devices using the substrate. It should be possible to align the different stamps or masks with a high accuracy in subsequent process steps. 
     These objects are achieved with the features of the claims. 
     The present invention is based on the idea to write the structures in different areas of one substrate using known mastering equipment. The structures in the different areas may be structures of different stamps or masks used for manufacturing semiconductor devices. Optionally, one or more alignment marks may be formed in each of the areas at the same relative positions. The structures in the different areas arranged on one substrate are recorded in one single sweep in a laser beam recorder. This may be done by spirally moving the laser spot, or by moving the laser spot in a concentric circle and by changing the radius of the circle in a stepwise manner in order to move the laser spot over the entire substrate. Since track pitch control and rotation control are extremely good, the patterns in the different areas, preferably corresponding to the different stamps or masks, are very good references with respect to each other. For example, if the different areas are circularly arranged on the substrate, recording of all areas starts exactly at the same radius, and thus, the position of the written structures and, if applicable, the alignment marks, are determined with a very high relative position accuracy. By manufacturing a set of masks or stamps to be used in successive process steps in one run of a laser beam or e − -beam (electron beam) recorder (LBR) such as used to create masters for optical recording, a coherent mask or stamp set with very good alignment positions can be created. 
     The structures in the different areas may have any desired pattern and need not be circular structured but may have a structure in the x-y directions, for example a pattern having rows and columns. Since the structure is written according to the present invention by circularly moving the laser spot over the substrate, it may be necessary to make a coordinate transformation of the data to be written on the substrate using a software program. Furthermore, the areas may have any desired shape, for example circular or rectangular. 
     In order to prepare the templates, that is the stamps or masks, the different areas on the substrate are separated so that the templates are obtained in the form of patterned substrate elements. 
     For writing the structures in the mastering equipment, any known method may be used. Accordingly, the layer of radiation sensitive material applied to the substrate may be a photo-sensitive layer, i.e., a photoresist layer or a layer of phase transition material. In the latter case, the heat-induced phase transition is caused in the sensitive material in accordance with the structure to be formed, for example by applying laser pulses. An example for a material sensitive for phase transitions is ZnS-SiO x . 
    
    
     
       In the following, the present invention is described in more detail with reference to the drawings. 
         FIG. 1  schematically shows the arrangement of the structures of four stamps arranged on a single substrate manufactured using the method according to the invention. 
         FIG. 2  shows a SEM micrograph of a structure with a detail of the mask and the marker. 
     
    
    
       FIG. 1  illustrates an exemplary arrangement of four separate areas  2   a  to  2   d  on a substrate, each comprising the pattern of a stamp to be manufactured. The patterns in the different areas  2   a  to  2   d  may be the same or may be different. The substrate  1  used according to the invention may be a standard substrate, for example a glass substrate as used when producing a master for the CD or DVD production. As shown in  FIG. 1 , in each of the four areas  2   a  to  2   d,  an alignment mark  3   a  to  3   d  is written. Preferably, however, more than one alignment mark is written in each area in order to improve the accuracy when aligning the different stamps in the imprint lithography process. 
     It is preferred according to the present invention that the relative positions of the different areas  2   a  to  2   d  are positioned such that the respective structures in each area  2   a  to  2   d  have the same distance from the center  4  of the substrate, e.g., are positioned symmetrically with respect to the center  4  of the substrate  1 , as shown in  FIG. 1 . Thus, the four areas  2   a  to  2   d  are preferably arranged on a circle on the substrate  1 . With this particular arrangement, it can be achieved that writing the different areas  2   a  to  2   d  starts at the same track  5  with the same distance r from the center  4  of the substrate  1  when the information is written on the substrate  1  in the laser beam recorder. This is because the information is written by circularly moving the laser spot over the substrate  1 , for example by rotating the substrate  1  around the center  4  in the laser beam recorder. Furthermore, the alignment marks  3   a  to  3   d  written in each one of the areas  2   a  to  2   d  are arranged at the same relative positions in each of the areas  2   a  to  2   d,  and, as can be seen from  FIG. 1 , are also symmetrical with respect to the center  4  of the substrate  1 . Consequently, also the boundaries of the alignment marks  3   a  to  3   d  are written starting at the same track when writing the structure on the substrate so that the relative position of the alignment marks  3   a  to  3   d  on the manufactured stamps are determined with a very high positional accuracy. 
       FIG. 2  shows a scanning electron microscopy (SEM) micrograph of a pattern produced using the method of the present invention. Specifically,  FIG. 2  shows a corner of a rectangular structure  10  and an alignment mark  20 . The alignment mark  20  in the form of an alignment cross is positioned close to the corner of the rectangular pattern  10 .