Abstract:
An apparatus (and method for operating the same) which allows etching different substrate etch areas of a substrate having different pattern densities at essentially the same etch rate. The apparatus includes (a) a chamber; (b) an anode and a cathode in the chamber; and (c) a bias power system coupled to the cathode, wherein the cathode includes multiple cathode segments. The operation method includes the steps of: (i) placing a substrate to be etched between the anode and cathode, wherein the substrate includes N substrate etch areas, and the N substrate etch areas are directly above the N cathode segments; (ii) determining N bias powers which, when being applied to the N cathode segments during an etching of the substrate, will result in essentially a same etch rate for the N substrate etch areas; and (iii) using the bias power system to apply the N bias powers the N cathode segments.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to etching tools for semiconductor and photomask fabrication, and more specifically, to etching tools for dry etching.  
         [0003]     2. Related Art  
         [0004]     A conventional fabrication process usually involves the step of dry etching a top surface of a substrate (e.g., a wafer or a photomask). Typically, first, a photoresist layer or any useful masking layer can be applied to the substrate. Then, the mask layer can be patterned using a photolithography process so that only areas of substrate that need to be etched are exposed from underneath the masking layer. The other areas of the substrate that need to be kept intact are covered by the patterned masking layer. Next, the substrate (with the patterned masking layer on top) can be placed on the cathode of an etching chamber. A radio frequency (RF, typically at a frequency of 0.1 MHz to 2.5 GHz) electrical power generator can be applied to the anode of the chamber so as to generate a plasma in the chamber. As a result, etchants generated within the plasma chemically react with the exposed material of the substrate surface to create a volatile product that can easily be removed by the etch system. Thus the pattern of the patterned masking layer is transferred to the substrate surface. Additional RF electrical energy may be coupled into the cathode to both increase the rate of etch processing and to provide directionality to the reactive species generated within the plasma.  
         [0005]     However, different substrate areas facing the anode may be etched at different etch rates and with different profiles because these different substrate areas may have different pattern densities. The pattern density of a substrate can be defined as the percentage of the exposed-to-atmosphere surface of the substrate. For example, assume a 1 cm 2  substrate consists of 0.4 cm 2  being covered by the patterned mask layer and 0.6 cm 2  being exposed to the atmosphere. As the result, the pattern density of the substrate to be etched is 60%. If a substrate consists of a first substrate etch area with a higher pattern density than a second substrate etch area, then the first substrate etch area consumes etchants at a higher rate than the second substrate etch area. As a result, fewer etchants are available for further etching in the first substrate etch area than in the second substrate etch area. Therefore, the etch rate (and other properties such as feature profile) of the first substrate etch area is less than the etch rate of the second substrate etch area.  
         [0006]     As a result, there is a need for a new apparatus (and method for operating the same) which allows etching different substrate etch areas having different pattern densities at essentially the same etch rate.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides an apparatus, comprising (a) a chamber; (b) an anode and a cathode positioned in the chamber; and (c) a bias power system coupled to the cathode, wherein the cathode comprises N cathode segments electrically insulated from each other, N being an integer greater than 1, and wherein the bias power system is configured to apply N bias powers one-to-one to the N cathode segments.  
         [0008]     The present invention also provides an apparatus operating method, comprising the steps of (a) providing (i) a chamber, (ii) an anode and a cathode positioned in the chamber, and (iii) a bias power system coupled to the cathode, wherein the cathode comprises N cathode segments electrically insulated from each other, N being an integer greater than 1; (b) placing a substrate to be etched between the anode and the cathode, wherein the structure comprises N substrate etch areas facing the anode, and wherein the N substrate etch areas are directly above the N cathode segments in a reference direction and match in size and shape with the N cathode segments, wherein the reference direction is essentially perpendicular to a surface of the anode facing the cathode; (c) determining N bias powers which, when being applied one-to-one to the N cathode segments during an etching of the substrate, will result in essentially a same etch rate for the N substrate etch areas; and (d) using the bias power system to apply the N bias powers one-to-one to the N cathode segments during the etching of the substrate.  
         [0009]     The present invention also provides an apparatus operating method, comprising the steps of (a) providing (i) a chamber, (ii) an anode and a cathode positioned in the chamber, and (iii) a bias power system coupled to the cathode, wherein the cathode comprises N cathode segments electrically insulated from each other, N being an integer greater than 1; (b) placing a substrate to be etched between the anode and the cathode, wherein the substrate comprises N substrate etch areas facing the anode, and wherein the N substrate etch areas are directly above the N cathode segments in a reference direction and match in size and shape with the N cathode segments, wherein the reference direction is essentially perpendicular to a surface of the anode facing the cathode; (c) applying a plasma generation power to the anode sufficiently to generate a plasma in the chamber; and (d) applying N bias powers one-to-one to the N cathode segments  
         [0010]     The present invention also provides a new apparatus (and method for operating the same) which allows etching different substrate etch areas having different pattern densities at essentially the same etch rate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates an apparatus, in accordance with embodiments of the present invention.  
         [0012]      FIG. 2  illustrates a plasma generation power system of the apparatus of  FIG. 1 , in accordance with embodiments of the present invention.  
         [0013]      FIGS. 3A-3E  illustrate different embodiments of a cathode of the apparatus of  FIG. 1 .  
         [0014]      FIGS. 4A-4B  illustrate different embodiments of a bias power system of the apparatus of  FIG. 1 .  
         [0015]      FIG. 5  illustrates a bias power subsystem that can be used in the embodiments of  FIGS. 4A-4B , in accordance with embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  illustrates an apparatus  100 , in accordance with embodiments of the present invention. Illustratively, the apparatus  100  can comprise a chamber  110 , an anode  120  and a cathode  130  in the chamber  110 . The chamber  110  can include a gas inlet  112  and a gas outlet  114 . The gas inlet  112  can be used to receive gas species into the chamber  110 . The gas outlet  114  can be used to lead gases out of the chamber  110 . The depiction and location of gas inlet  112  and outlet  114  is purely representational in  FIG. 1 . An actual inlet and outlet may consist of a plurality of actual openings. Additionally, it is well known to one skilled in the arts that the location of the inlet and outlet can be placed at different locations within the chamber to modify the efficiency of gas flow within the chamber and consequently the gas&#39;s influence on a substrate placed within the chamber.  
         [0017]     The anode  120  can be coupled to a plasma generation power system  140 . In one embodiment, the plasma generation power system  140  can be configured to generate a plasma generation power (e.g., a radio frequency voltage) to the anode  120  so as to create a plasma from the gas species in the chamber  110 . The plasma contains etchants necessary for substrate etching.  
         [0018]     The cathode  130  can comprise N cathode segments (not shown, but details of these cathode segments will be described below) matching in size and shape with N substrate etch areas (facing the anode  120 ) of a substrate  160  placed on the cathode  130 , wherein N is an integer greater than one. The N cathode segments can be electrically insulated from each other. The cathode  130  can be coupled to a bias power system  150  which, during the etching of the substrate  160 , can be configured to generate N bias powers (e.g., each can be a radio frequency voltage) to the N cathode segments of the cathode  130 . By adjusting a bias power to a cathode segment, the bias power system  150  can adjust the energy of the ions bombarding the substrate etch area of the substrate  160  directly above the cathode segment. As a result, by adjusting the bias power to the cathode segment, the bias power system  150  can adjust the etch rate for the substrate etch area directly above the cathode segment.  
         [0019]     In one embodiment, the N bias powers can be individually assigned by prior assumptions or by theoretical calculations such that when the N bias powers are applied one-to-one to the N cathode segments during the dry etching of the substrate  160 , the N substrate etch areas experience essentially the same etch rate.  
         [0020]     In another embodiment, the N bias powers can be individually assigned by using a “design of experiments” methodology or a simpler trial-and-error methodology. More specifically, multiple substrates (not shown) identical to the substrate  160  can be etched one after another using essentially the same etching settings (i.e. pressure, etchants, gas flow rate, etc.) while individually varying the N bias powers. The resultant substrates after etching can be examined to determine the etch rate uniformity across the substrate. Then the N bias powers can be individually adjusted until the N substrate etch areas experience essentially the same etch rate. In other words, the results of the etching of a substrate can be used to determine new bias powers for etching the next substrate, and so on until the etch result is satisfactory (i.e., essentially the same etch rate for all the N substrate etch areas).  
         [0021]     Alternatively, the N bias powers can be individually determined by using a database containing correlations between bias powers, pattern densities, and etch rates. In one embodiment, the database is built from empirical data. More specifically, experiments (i.e., etching) can be carried out in a predetermined etch setting (i.e., gas flow rate, etchants, pressures, etc.) for different pattern densities and different applied bias powers, and the resulting etch rates can be recorded and entered into the database. To achieve essentially the same etch rate for all N substrate etch areas with N given pattern densities in the predetermined etch setting, the N bias powers can be individually determined using the database.  
         [0022]      FIG. 2  illustrates one embodiment of the plasma generation power system  140  of the apparatus  100  of  FIG. 1 , in accordance with embodiments of the present invention. Illustratively, the plasma generation power system  140  can comprise (i) an RF (radio frequency) power source  142 , a matching network  144  coupled to the RF power source  142 , and, for a capacitively-coupled plasma source, a blocking capacitor  146  coupling the matching network  144  to the anode  120 . For inductively-coupled plasma sources, blocking capacitor  146  is optional. The RF power source  142  produces an electrical voltage of the desired frequency. The matching network  144  matches the variable impedance of the plasma to the desired fixed impedance of the RF power source  142  so as to maximize the transfer of electrical power from RF power source  142  into the chamber  110 . Blocking capacitor  146  serves to prevent the flow of direct current (DC) power from RF power source  142  into chamber  110 , only allowing the passage of alternating current (AC) power.  
         [0023]      FIGS. 3A-3E  illustrate different embodiments  130   a,    130   b,    130   c,    130   d,  and  130   e,  respectively, of the cathode  130  of  FIG. 1 . More specifically,  FIG. 3A  shows a top-down view of the cathode  130   a.  The cathode  130   a  can have the circular shape and can comprise three cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 . In one embodiment, the cathode segments  130   a   1 ,  130   a   2 , and  130   a   3  can be electrically insulated from each other. In general, there can be N (N being an integer greater than one) concentric cathode segments having ring form as in  FIG. 3A .  
         [0024]      FIG. 3B  shows a top-down view of the cathode  130   b.  The cathode  130   b  can have the rectangular shape and can comprise four (or any integer number greater than one) cathode segments  130   b   1 ,  130   b   2 ,  130   b   3 , and  130   b   4 . The cathode segments  130   b   1 ,  130   b   2 ,  130   b   3 , and  130   b   4  can be electrically insulated from each other.  
         [0025]      FIG. 3C  shows a top-down view of the cathode  130   c.  The cathode  130   b  can have the rectangular shape and can comprise  12  (or any integer number multiple of 4 and at least 4) cathode segments of trapezoidal and triangular shapes. The cathode segments of the cathode  130   c  can be electrically insulated from each other.  
         [0026]      FIG. 3D  shows a top-down view of the cathode  130   d.  The cathode  130   d  can have the rectangular shape and can comprise cathode segments arranged in 4 rows and 4 columns (i.e., 16 cathode segments in total). In general, the number of rows and the number of columns can be any positive integer (but can not be 1 simultaneously) and do not have to be the same. The cathode segments of the cathode  130   d  can be electrically insulated from each other.  
         [0027]      FIG. 3E  shows a top-down view of the cathode  130   e.  The cathode  130   e  can have the circular shape and can comprise cathode segments arranged in 7 rows and 7 columns (i.e., 49 cathode segments in total). In general, the number of rows and the number of columns can be any positive integer (but can not be 1 simultaneously) and do not have to be the same. The cathode segments of the cathode  130   e  can be electrically insulated from each other.  
         [0028]     In general, the cathode  130  of  FIG. 1  can have any shape and can comprise any number (more specifically, any integer greater than 1) of cathode segments. Each of the cathode segments can have any size and shape.  
         [0029]      FIGS. 4A-4B  illustrate two different embodiments  150   a  and  150   b,  respectively, of the bias power system  150  of  FIG. 1 . More specifically, with reference to  FIG. 4A , assume the cathode embodiment  130   a  of  FIG. 3A  is used as the cathode  130  of  FIG. 1  (in  FIG. 4A , a cross-section view of the cathode  130   a  is shown). Because the cathode  130   a  has three cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 , the bias power system  150   a  can comprise the same number of (i.e., three) independent bias power subsystems  150   a   1 ,  150   a   2 , and  150   a   3  coupled one-to-one to the cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 , respectively. The three bias power subsystems  150   a   1 ,  150   a   2 , and  150   a   3  can be configured to generate three independent bias powers (e.g., radio frequency voltages) one-to-one to the three cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 , respectively.  
         [0030]     In general, if the cathode  130  of  FIG. 1  has M cathode segments (M being an integer greater than 1), then M bias power subsystems similar to the bias power subsystems  150   a   1 ,  150   a   2 , and  150   a   3  of can be used to generate M independent bias powers one-to-one to the M cathode segments.  
         [0031]     With reference to  FIG. 4B , assume the cathode embodiment  130   a  of  FIG. 3A  is again used as the cathode  130  of  FIG. 1  (in  FIG. 4B , a cross-section view of the cathode  130   a  is shown). In one embodiment, the bias power system  150   b  can comprise a bias power subsystem  150   b′  and an impedance dividing circuit  152  coupling the bias power subsystem  150   b′  to the cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 . The bias power subsystem  150   b′  can be configured to generate a total bias power to the impedance dividing circuit  152 . In response to receiving the total bias power from the bias power subsystem  150   b′,  the impedance dividing circuit  152  can be configured to generate three different bias powers one-to-one to the three cathode segments  130   a   1 ,  130   a   2 , and  130   a   3 . The simplest example of an impedance divider circuit is a voltage divider circuit. In this case, an input voltage is put through two resistors (fixed or variable) in series. The output voltage is taken off between the two resistors. In general, a series of M voltage dividers may be constructed to drive M cathode segments. By applying the same input voltage to each of the M voltage dividers, the output to each of the M cathode segments can be individually adjusted.  
         [0032]      FIG. 5  illustrates a bias power subsystem  500  that can be used as the bias power subsystems  150   a   1 ,  150   a   2 , and  150   a   3  of  FIG. 4A  and the bias power subsystems  150   b′  of  FIG. 4B . In one embodiment, the bias power subsystem  500  can comprise (i) an RF power source  502 , a matching network  504  coupled to the RF power source  502 , and, for a capacitively-coupled plasma source, a blocking capacitor  506  coupling the matching network  504  either to the cathode  130   a  of  FIG. 4A  or to the impedance dividing circuit  152  of  FIG. 4B . Generator  502  produces an electrical voltage at the desired frequency. Matching network  504  matches the variable impedance of the plasma across the substrate  160  ( FIG. 1 ) to the desired fixed impedance of generator  502  so as to maximize the transfer of electrical power from generator  502  into substrate  160  ( FIG. 1 ). Blocking capacitor  506  serves to prevent the flow of direct current (DC) power from generator  502  into substrate  160  and chamber  110  ( FIG. 1 ), only allowing the passage of alternating current (AC) power. Modulation of the output of generator  502  produces a modulation in the bias voltage on substrate  160  ( FIG. 1 ).  
         [0033]     In summary, with reference to  FIG. 1 , by using the N-segment cathode  130 , N bias powers can be individually determined such that when these N bias powers are applied to the N cathode segments (not shown), the N substrate etch areas of the substrate  160  directly above the N cathode segments experience essentially the same etch rate. The N bias powers can be individually determined by trials and errors, or alternatively, by using a database built through experiments.  
         [0034]     In a similar manner, the present invention can be used to etch a variety of substrates  160  ( FIG. 1 ). For example, the present invention can be used to etch a wafer or a photomask.  
         [0035]     While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.