Abstract:
A method of fabricating thin film transistor. A thin oxide layer is formed as a protection layer for a thin film transistor. Since the oxide layer does not affect the fabrication process of a barrier layer, the thin oxide layer can be formed as the protection layer to protect the thin-film resist layer formed subsequently from being damaged by ions produced during dry etching process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a thin film resistor of an interconnect by dual damascene. 
     2. Description of the Related Art 
     Dual damascene is a technique which fabricates planar and vertical interconnects at the same time. An insulation layer is formed on a substrate. After planarization, the pattern of conductive wires and contact window is transferred. The insulation layer is then etched to form a trench for the planar interconnects, and a contact window for vertical interconnects. A metal layer is formed to fill the trench and the contact window to form the conductive wires and the contact at the same time. The interconnection is thus achieved. Silicon has a certain solid solubility for metal at a high temperature. While a high temperature process is performed, a mutual diffusion occurs between silicon atoms and metal atoms to cause spikings. The spikings are often too long to cause a short circuit by piercing through the silicon. The short circuit affects the performance of devices greatly, and sometimes even causes a device failure. Therefore, a barrier layer is formed between a metal layer and a silicon layer to avoid the spiking effect, as well as to enhance the adhesion between silicon and metal. 
     A resistor is a component commonly used in both memory and logic circuit. The resistance of a resistor is a function of both the length and cross sectional surface area, that is, R=ρ L/A , wherein, ρ is the resistivity, L is the length through which current flowing, and A is the cross sectional surface area which current flowing through. 
     A resistor in an integrated circuit is typically formed by lightly doping a polysilicon region. Strips of polysilicon with various length and cross sections are formed as resistors with different resistance. Alternatively, resistors with various different resistance may also be formed by high resistant conductor and low resistant conductor. Typically, the low resistant conductor is formed by doped polysilicon, while the high resistant conductor is formed undoped polysilicon. As the integration of a semiconductor device is increased, the quality demand of material for forming the semiconductor device is raised. For example, to obtain a device with a reduced surface or volume, a resistor with a sufficiently high resistance has to be formed with a restricted dimension. However, the resistance per unit area and length of material such as polysilicon is limited, and thus, causes the difficulty for the fabrication of device with a high integration. 
     To increase the resistance per unit of a resistor, material such as chromium silicide (Cr x Si y ) has been used to fabricate resistant layer to replace the doped or undoped polysilicon. 
     FIG. 1A to FIG. 1C shows a fabrication method for forming a thin film resistor. 
     In FIG. 1A, a substrate  100  is provided. A borophosphosilicate glass (BPSG) layer  102  is formed on the substrate  100 . A thin film resistant layer  104  is formed on the BPSG layer  102 . Using sputtering, a metal layer made of aluminum or alloy of aluminum/silicon/copper (Al/Si/Cu)  106  is formed on the BPSG layer  104  to protect the thin film resistant layer  104  from being etched in a subsequent dry etching process. 
     In FIG. 1B, the metal layer  106  is patterned, and the remaining metal layer  106   a  is formed as an etching mask for defining the underlying thin film resistant layer  104 . The defined thin film resistant layer is denoted as  104   a . The BPSG layer  102  is defined by dry etching to form a contact window  110  penetrating through the resultant BPSG layer  102   a . A conductive layer  112  is formed over the substrate  100  and to fill the contact window  110 . 
     In FIG. 1C, the conductive layer  112  is patterned as a conductive layer  11   2   a  of a conductive wire for interconnection  112   a . The metal layer  106   a  is stripped to expose the thin film resistant layer  104   a . After the formation of the thin film resistant layer  104   a , an electric characteristic test is typically performed. A laser cutting machine is often used to cut the thin film resistant  104   a  into a thin film resistor with a required resistance. Therefore, the requirement of the circuit design can be more precisely achieved. 
     However, in the conventional method, an aluminum contained metal layer  106  is formed as a protection layer as the thin film resistant layer  104   a . While a barrier layer is formed by material containing titanium, the aluminum in the protection layer will react with titanium. As a consequence, the protection layer cannot effectively protect the thin film resistant layer  104   a . A conformal barrier for improving the adhesion between a contact window and a contact plug and to avoid the spike effect can not be formed in the contact window. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a protection layer to protect a thin film resistant layer. In addition, the protection layer is not affected or damaged by the formation of a barrier layer. 
     To achieve the above-mentioned objects and advantages, a method of fabricating a thin film resistor is provided. A substrate having an insulating layer thereon is provided. The thin film resistor is formed to cover a part of the insulating layer. An oxide layer is formed on the thin film resistant layer and the insulation layer. The oxide layer and the insulating layer are patterned to form a contact window to expose a part of the substrate. A conformal barrier layer is formed to cover the oxide layer and the contact window surface. A part of the barrier layer and a part of the oxide layer are removed to expose the thin film resistor and a part of the insulating layer. A contact is formed to fill the contact window and a conductive pattern is formed on a part of the thin film resistor. 
     In the invention, a thin oxide layer is formed as a protection layer to protect the thin film resistor from being etched by ions during the subsequent dry etching process. Furthermore, a barrier layer is formed to enhance the adhesion between the contact and the contact window, so as to prevent the spiking effect without damaging the protecting layer. 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A to FIG. 1C show a conventional method of fabricating a thin film resistor; 
     FIG. 2A to FIG. 2F show a method of fabricating a thin film resistor in a preferred embodiment according to the invention; and 
     FIG. 3A to FIG. 3F are top views of FIG. 2A to FIG. 2F, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2A to FIG. 2F are cross sectional views showing a method of fabricating a thin film resistor, while FIG. 3A to FIG. 3F are top views of FIG. 2A to FIG. 2F, respectively. 
     Referring to both FIG.  2 A and FIG. 3A, a substrate  200  is provided. The substrate may comprise semiconductor devices or circuits (not shown). An insulating layer  202 , for example, a BPSG layer, is formed on the substrate  200 . A thin film resistor  204  (a patterned thin film resistant layer), for example, a chromium silicide formed by sputtering, is formed on the insulating layer  202 . A thin oxide layer  206  is formed, for example, by chemical vapor deposition (CVD), on and conformal to the insulating layer  202 . The thin oxide layer  206  is formed as a protecting layer to prevent the thin film resistor  204  from being damaged by ions during a subsequent dry etching process. 
     Referring to both FIG.  2 B and FIG. 3B, the thin oxide layer  206  and the insulating layer  202  are patterned, for example, by photolithography and etching. A contact window  208  exposing a part of the substrate  200  is thus formed and penetrating resultant thin oxide layer  206   a  and the resultant insulating layer  202   a . A conformal barrier layer  210 , for example, a metal layer such as a titanium contained metal layer formed by sputtering, is formed on the thin oxide layer  206   a  and the surface of the contact window  208 . The temperature of the substrate  200  is raised up to about 700° C., for example, by rapid thermal process (RTP). A chemical reaction thus occurs at the interface between the metal layer  210  and the contact window  208 . That is, the metal contained in the barrier layer  210  is reacted with silicon contained in the substrate  200  exposed by the contact window  208  to form a metal silicide layer (not shown), for example, a titanium silicide layer (TiSi x ). By the formation of this metal silicide layer, the adhesion of the contact window for a metal plug is improved, and the spiking effect is eliminated. 
     Referring to both FIG.  2 C and FIG. 3C, portions of the barrier layer  210  and the thin oxide layer  206   a  are further removed, for example, by wet etching, to expose a part of the insulating layer  202   a  and to define a resistor region  212 . 
     Referring to both FIG.  2 D and FIG. 3D, the part of the barrier layer  210  and the thin oxide layer  206   a  over the thin film resistor  204  are removed to expose the thin film resistor  204 . 
     Referring to both FIG.  2 E and FIG. 3E, a conductive layer is formed on the insulation layer  202   a  to cover the thin film resistor  204  and the remaining barrier layer  210 , so as to fill the contact window  208 . A contact, for example, a plug or a via, is thus formed to couple with the substrate  200 . The conductive layer is patterned to form a conductive layer  214   a  covering the barrier layer  210 , and a conductive layer, that is, the contact  214   b  covering the thin film resistor  204 . The conductive layers  214   a  and  214   b  are the pattern for interconnects as specifically required. According to the requirement of circuit, the covering areas of the conductive layers  214   a  and  214   b  are different. 
     Referring to both FIGS. 2F and 3F, the conductive layer  214   b  is further defined to expose a part of the thin film resistant layer  204  and to form the resultant conductive wires  214   c  and  214   d . In this example, the conductive wires  214   c ,  214   d  and the thin film resistant layer  204  are connected in series. 
     In this invention, a thin oxide layer is formed as a protecting layer to prevent the thin film resistant layer from being damaged by ions during a subsequent dry etching process. The titanium contained metal layer used in the conventional is replaced by the thin oxide layer in this embodiment. Therefore, the adhesion between a contact plug and the contact window is improved, and the spiking effect caused by the formation of the barrier layer in the prior technique is eliminated. 
     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.