Abstract:
The semiconductor device of the present invention comprises a semiconductor substrate; and a conductive element formed on the semiconductor substrate and capable of being opened when a predetermined current flows, wherein the conductive element turns plurality of times.

Description:
[0001]    This application is based on Japanese patent applications No. 2003-183369 and No. 2004-168131, the content of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device, and more particularly to a semiconductor device including a fuse. 
         [0004]    2. Description of the Related Art 
         [0005]    When a semiconductor device includes fuses, it is possible to adjust the resistance value by opening some of the fuses, or alternating a defective element to a functional element by opening one of the fuses connected to the defective element. This method of alternating the defective element to the functional element is applied to a semiconductor device having redundancy. Conventionally, it is common to open the fuses by laser irradiation. However, there are some problems in opening the fuses by the laser irradiation. 
         [0006]    Firstly, in order to avoid damage to elements other than the fuse when the fuse is opened, the portion to be opened in the fuse has to be placed with a predetermined space from the elements. Thus, the size of the semiconductor device is increased. 
         [0007]    In addition, in order to form a fuse to be opened by the laser irradiation, additional photolithography processes are necessary. Usually, an insulating layer is formed on a fuse. Thus, an additional step to adjust the thickness of the insulating layer to form an opening above the fuse for laser irradiation is necessary. In addition, when the semiconductor device including a fuse is examined, the following three steps are necessary. Firstly, electrical properties of the device are examined, then, the fuse is opened, and finally, electrical properties are examined again. Thus the manufacturing processes for the semiconductor device are increased and makes the cost of manufacturing the semiconductor device is greater. 
         [0008]    In order to solve the problem caused by the laser irradiation, there have been attempts to open the fuses by current flow. For example, Japanese patent application No. 2002-197884 discloses a fuse that is opened by current flow. In this application, a part of the fuse is made narrow, or the fuse includes an angled portion to promote blowout of the fuse. 
       SUMMARY OF THE INVENTION 
       [0009]    However, the inventor of the present invention found that the fuse disclosed in the above application still has a problem in that a large amount of current or voltage is required to open the fuse. 
         [0010]    The present invention has been conceived in view of the foregoing situation, with the object of providing a semiconductor device including a fuse which needs less current or voltage to be opened compared with a conventional fuse. 
         [0011]    According to the present invention, there is provided a semiconductor device comprising: a semiconductor substrate; and a conductive element formed on the semiconductor substrate and capable of being opened when a predetermined current flows, wherein the conductive element turns plurality of times. 
         [0012]    Here, “a conductive element capable of being opened when a predetermined current flows” is a fuse. The word “turn” or the word “turning” means that at which the conductive line rotates more than 90 degrees. 
         [0013]    As the conductive element turns plurality of times, the conductive element can be formed such that the center portion of the conductive element is surrounded by the rest portions of the conductive element. With this structure, the center portion of the conductive element is heated by the rest portions thereof. Thus, the center portion of the conductive element can be kept relatively high temperature so that the conductive element is easily opened when a predetermined current flows therethrough. 
         [0014]    The conductive element may include a first one way linear portion which extends in a first direction, an another way linear portion which extends in a second direction which is substantially opposite direction to the first direction, and a second one way linear portion which extends in the first direction. The first one way linear portion, the another way linear portion, and the second one way linear portion may be positioned parallel to each other and electrically connected with each other. 
         [0015]    With this structure, either one of the first one way linear portion, the another way linear portion, and the second one way linear portion is placed to be surrounded by the other portions. Thus, the portion surrounded by the other portions can be kept relatively high temperature. Therefore, the conductive element is easily opened when a predetermined current flows therethrough. 
         [0016]    The conductive element may include a first one way linear portion which extends in a first direction, a another way linear portion which extends in a second direction which is substantially opposite direction to the first direction, an second one way linear portion which extends in the first direction, a first connecting portion which connects one of the edges of the first one way linear portion and one of the edges of the another way linear portion, and a second connecting portion which connects the other of the edges of the another way linear portion and one of the edges of the second one way linear portion. The first one way linear portion, the another way linear portion, the second one way linear portion, the first connecting portion, and the second connecting portion may be electrically connected with each other. 
         [0017]    The conductive element may include a plurality of first linear portions positioned parallel to each other and each of which extends in a first direction, and a plurality of second linear portions positioned parallel to each other and each of which extends in a second direction which is different from the first direction. The plurality of first linear portions and the plurality of second linear portions may be placed such that at least one of the plurality of first linear portions or at least one of the plurality of second linear portions is surrounded at four sides by the rest of the plurality of first linear portions and the plurality of second linear portions. 
         [0018]    With this structure, the linear portion which is surrounded by the other linear portions at four sides can be kept relatively high temperature. Thus, the conductive element is easily opened at the linear portion which is surrounded by the other linear portions when a predetermined current flows therethrough. 
         [0019]    The plurality of first linear portions and the plurality of second linear portions may be placed such that the current respectively flow toward different directions in the first linear portions adjacent to each other, and the current respectively flow toward different directions in the second linear portions adjacent to each other, when the current flows from one of the edges of the conductive element to the other edge of the conductive element. 
         [0020]    With this structure, magnetic field generation is avoided even when the current flows through the conductive element. 
         [0021]    The conductive element may include a plurality of first linear portions positioned parallel to each other and each of which extends in a first direction, a plurality of second linear portions positioned parallel to each other and each of which extends in a second direction which is different from the first direction, a current input terminal, and a current output terminal electrically connected with the current input terminal. The plurality of first linear portions and the plurality of second linear portions may be placed such that the current respectively flow toward different directions in the first linear portions adjacent to each other, and the current respectively flow toward different directions in the second linear portions adjacent to each other, when the current flows from the current input terminal to the current output terminal. 
         [0022]    With this structure, magnetic field generation is avoided even when the current flows through the conductive element. 
         [0023]    The conductive element may include a narrow portion which is formed to have narrower width than those of the rest of portions of the conductive element. 
         [0024]    With this structure, the conductive element is easily opened at the narrow portion when the current flows therethrough. 
         [0025]    The conductive element may include a broad portion which is formed to have wider width than those of the rest of portions of the conductive element. 
         [0026]    As the broad portion enables electro migration of the conductive element to become large, the conductive element is easily opened at the place between the broad portion and a current output terminal. 
         [0027]    The conductive element may further include a current input terminal and a current output terminal, the broad portion may be formed between the current input terminal and the turned portion. The broad portion may be formed in the vicinity of the turned portion of the conductive element. 
         [0028]    As the electro migrations of the conductive element at the corner is small, the conductive element is easily opened at the place between the broad portion and the turned portion. 
         [0029]    The broad portion may be formed in the vicinity of the current input terminal. As described above, the conductive element turns plurality of times, and the broad portion placed in the vicinity of the conductive element is kept at relatively high temperature. Thus, with the electro migration of the broad portion and the conductive element, the conductive element is easily opened in the vicinity of the broad portion. 
         [0030]    The broad portion may be formed substantially in the center of the conductive element. 
         [0031]    As described above, the conductive element turns plurality of times, and the center portion of the conductive element is kept at relatively high temperature. Thus, the conductive element is easily opened at the center portion thereof when the current flows therethrough. In addition, by forming the broad portion in the center of the conductive element, the conductive element is more easily opened by the current. 
         [0032]    According to the present invention, there is provided a semiconductor device comprising: a semiconductor substrate; and a conductive element formed on the semiconductor substrate and capable of being opened when a predetermined current flows, wherein the conductive element is formed to have a corner and includes a broad portion which is formed to have wider width than those of the rest of portions of the conductive element. 
         [0033]    As the broad portion enables electro migration of the conductive element to become large, the conductive element is easily opened at the place between the broad portion and a current output terminal. In addition, the electro migrations of the conductive element at the corner is small. Therefore, the conductive element formed as above is easily opened at the place between the broad portion and the corner by the current. 
         [0034]    The conductive element may further include a current input terminal and a current output terminal, the broad portion may be formed between the current input terminal and the corner. The broad portion may be formed in the vicinity of the corner of the conductive element. 
         [0035]    The broad portion may be formed substantially in the center of the conductive element. 
         [0036]    The semiconductor device may further include a second conductive formed to surround the conductive element, wherein the conductive element and the second conductive element may be insulated from each other. 
         [0037]    With this structure, the heat generated at the conductive portion when the current flows therethrough is reflected by the second conductive element and remains inside the second conductive element. Thus, the conductive element is more easily opened. 
         [0038]    The second conductive element may include a via conductive element which is formed at the side of the conductive element. 
         [0039]    The second conductive element may include a conductive plate which is formed above or below the conductive element. 
         [0040]    The conductive element may be constituted of a material mainly including copper, a poly-silicon including impurities, SiGe (silicon germanium), or silicide. 
         [0041]    The semiconductor device may further include a transistor formed on the semiconductor substrate. The current supplied to the conductive element is controlled by switching on and off the transistor. The transistor may be MOSFET. 
         [0042]    It is to be noted that any arbitrary combination of the above-described structural components and expressions whether directed to a method, an apparatus, or a system and so forth are all effective and are encompassed by the present embodiments. 
         [0043]    Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  shows a plan view of a fuse of a first embodiment according to the present invention. 
           [0045]      FIGS. 2A and 2B  show a fuse which turns once. 
           [0046]      FIG. 3  shows a plan view of a fuse in a second embodiment according to the present invention. 
           [0047]      FIG. 4  shows the relationship between the number of the turnings in each of the fuses and the voltage necessary to open each of the fuses. 
           [0048]      FIG. 5  shows the relationship between the number of turnings in each of the fuses and current necessary to open each of the fuses. 
           [0049]      FIG. 6  is a plan view showing the fuse in a third embodiment according to the present invention. 
           [0050]      FIG. 7  is a cross sectional view along the I-I line shown in  FIG. 6 . 
           [0051]      FIG. 8  is a plan view showing the fuse in the fourth embodiment according to the present invention. 
           [0052]      FIG. 9  is a cross sectional view along the J-J line shown in  FIG. 8 . 
           [0053]      FIG. 10  shows an example of a fuse according to the present invention. 
           [0054]      FIG. 11  shows an alternative example of fuse shown in  FIG. 1 . 
           [0055]      FIG. 12  shows another alternative example of fuse shown in  FIG. 1 . 
           [0056]      FIG. 13  shows an alternative example of fuse shown in  FIG. 3 . 
           [0057]      FIG. 14  shows a plan view of a fuse in a embodiment according to the present invention. 
           [0058]      FIGS. 15A and 153  are diagrams showing how fuse is opened in the embodiment according to the present invention. 
           [0059]      FIG. 16  shows an alternative example of the fuse the embodiment according to the present invention. 
           [0060]      FIGS. 17A and 17B  show an alternative example of the fuse in the embodiment according to the present invention. 
           [0061]      FIG. 18  shows another alternative example of the fuse in the embodiment according to the present invention. 
           [0062]      FIG. 19  shows another alternative example of the fuse in the embodiment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    The invention will now be described based on preferred embodiments which are not intended to limit the scope of the present invention but to exemplify the invention. All of the features and the combinations thereof described in the embodiments are not necessarily essential to the invention. 
         [0064]      FIG. 10  shows an example of a fuse according to the present invention. The fuse  440  includes a conductive line  441 , and a current input terminal  101  and a current output terminal  102  formed at the both ends of the conductive line  441 . In this example, the conductive line  441  of the fuse  440  is constituted of a plurality of linear portions and angled connecting portions each of which connect adjacent linear portions to each other. 
         [0065]    The fuse  440  turns a plurality of times. In this specification, the word “turn” or the word “turning” means that at which the conductive line rotates more than 90 degrees. In this example shown in  FIG. 10 , the conductive line  441  rotates 90 degree at a corner between one of the linear portions and one of the angled portion, and rotates again at a next corner between the angled portion and one of the linear portions. Thus, the turning includes two corners in this example. 
         [0066]    Therefore, some of the linear portions placed at a center of the plurality of linear portions are kept at a relatively high temperature as they are heated by other linear portions surrounding them. Thus, the conductive line  441  of the fuse  440  has a temperature profile as shown in  FIG. 10 . Therefore, there is concern that the fuse  440  could be easily opened at the center of the conductive line  441 . 
         [0067]    The embodiments of the present invention will be explained in the following. 
         [0068]      FIG. 1  shows a plan view of a fuse of a first embodiment according to the present invention. In this embodiment, the fuse  100  turns twice. 
         [0069]    The fuse  100  is formed on an insulating layer formed on a semiconductor substrate, for example. In this case, the insulating layer includes any layers formed at any level on the semiconductor substrate. The insulating layer may include an insulating layer which isolates elements, an insulating inter layer, or an interlayer insulating layer which is formed at the bottom of a trench. 
         [0070]    The fuse  100  includes a current input terminal  101  and a current output terminal  102  at its ends. The fuse  100  further includes a first one way linear portion  103 , a first other way linear portion  104 , and a second one way linear portion  113  between the current input terminal  101  and the current output terminal  102 . The fuse  100  further includes a first angled connecting portion  106  which connects the first one way linear portion  103  and the first other way linear portion  104 , and a second angled connecting portion  107  which connects the first other way linear portion  104  and the second one way linear portion  113 . 
         [0071]    The fuse  100  has a first turning including a first corner between the first one way linear portion  103  and the first angled connecting portion  106 , and a second corner between the first angled connecting portion  106  and the first other way linear portion  104 , and a second turning including a third corner between the first other way linear portion  104  and the second angled connecting portion  107 , and a fourth corner between the second angled connecting portion  107  and the second one way linear portion  113 . 
         [0072]    In fuse  100  formed as above, when a certain current flows from the current input terminal  101  to the current output terminal  102 , heat is generated at shaded portions  108  which are formed outside of the fuse  100  and are added to heat generated at shaded portions  109  which are formed inside of the fuse  100 . The shaded portions  108  and the shaded portions  109  may be an insulating layer and may be constituted of insulating materials, for example. Thus, the first other way linear portion  104  placed between the shaded portions  109  is heated by the shaded portions  109  and is easily opened. Therefore, the fuse  100  is easily cut. The fuse may be constituted of a material mainly including copper, a poly-silicon including impurities, SiGe (silicon germanium), or silicide. 
         [0073]      FIG. 11  shows an alternative example of the fuse  100  shown in  FIG. 1 . The fuse  100  shown in  FIG. 11  rotates substantially perpendicular at each of the corners. The fuse  100  may rotate more than 90 degrees at each of the corners, a point A or a point B, as shown in the drawing. The fuse  100 , in this case, has a first one way linear portion  432 , a first other way linear portion  434 , and a second one way linear portion  436 . The first one way linear portion  432  and the first other way linear portion  434  form an acute angle less than 90 degrees. The first other way linear portion  434  and the second one way linear portion  436  form an acute angle less than 90 degrees. With this structure shown in  FIG. 11 , the first other way linear portion  434  placed in the middle of the linear portions  432  and  436  is heated by those linear portions  432  and  436 . Thus, the first other way linear portion  434  is easily opened by current. 
         [0074]      FIG. 12  shows another alternative example of the fuse  100  shown in  FIG. 1 . 
         [0075]    As the current input terminal  101  and the current output terminal  102  are formed to have large areas, there is a concern that a large amount of heat radiation will occur in the fuse near the connecting point of the terminals  101  and  102 . Therefore, the effect of the introduction of a plurality of turnings on the ease with which the fuse is opened will be reduced. The fuse shown in  FIG. 12  has a structure such that the turnings of the fuse are placed far from the terminals  101  and  102 . Thus, heat does not radiate away from the turnings of the fuse in this example. Therefore, the fuse  100  is easily opened by current. 
         [0076]      FIGS. 2A and 23  respectively show a fuse which turns once. 
         [0077]      FIG. 2A  shows a plan view of a fuse  200  which is a single unit of the fuse  100  shown in  FIG. 1 . The fuse  200  includes a current input terminal  201  and a current output terminal  202  at its ends. The fuse  200  further includes a one way linear portion  203 , an other way linear portion  204 , and an angled connecting portion  206  which connects the one way linear portion  203  and the other way linear portion  204 . 
         [0078]      FIG. 2B  shows an alternative example of the fuse  200  shown in  FIG. 2A . The fuse  210  may further include oblique connecting portions  256  placed between the one way linear portion  203  and the angled connecting portion  206 , and between the angled connecting portion  206  and the other way linear portion  204 . With this structure, the current is efficiently supplied to the place at which fuse  210  is to be opened. 
         [0079]    The fuse of the embodiments according to the present invention may include the units shown in  FIGS. 2A and 2B . 
         [0080]      FIG. 3  shows a plan view of a fuse of a second embodiment according to the present invention. In this embodiment, the fuse  300  turns four times. 
         [0081]    The fuse  300  is formed on an insulating layer formed on a semiconductor substrate, for example. The fuse  300  includes a current input terminal  301  and a current output terminal  302  at its ends. The fuse  300  further includes a first one way linear portion  303 , a first other way linear portion  304 , a second one way linear portion  313 , a second other way linear portion  314 , and a third one way linear portion  323  between the current input terminal  301  and the current output terminal  302 . The fuse  300  further includes a first angled connecting portion  306  which connects the first one way linear portion  303  and the first other way linear portion  304 , a second angled connecting portion  307  which connects the first other way linear portion  304  and the second one way linear portion  313 , a third angled connecting portion  316  which connects the second one way linear portion  313  and the second other way linear portion  314 , and a fourth angled connecting portion  317  which connects the second other way linear portion  314  and the third one way linear portion  323 . 
         [0082]    In the fuse  300  formed as above, when a certain current flows from the current input terminal  301  to the current output terminal  302 , heats generated at shaded portions  308  which are formed outside of the fuse  300  are added to heat generated at shaded portions  309  which are formed inside of the fuse  300 . Thus, the three linear portions placed at the center of the fuse  300 , the first other way linear portion  304 , the second one way linear portion  313 , and the second other way linear portion  314 , are easily opened. Logically, of these three linear portions, the second one way linear portion  313  which is placed at the center of the other linear portions is most easily opened. In this embodiment, fuse  300  is easily opened with the heat distributions generated at the periphery of the fuse  300 . 
         [0083]      FIG. 13  shows an alternative example of the fuse  300 . The fuse  300  shown in  FIG. 13  turns six times. 
         [0084]    The fuse  300  includes a current input terminal  301  and a current output terminal  302  at its ends. The fuse  300  further includes a first one way linear portion  402 , a first other way linear portion  406 , a second one way linear portion  410 , a second other way linear portion  414 , a third one way linear portion  416 , a third other way linear portion  420 , and a fourth one way linear portion  424  between the current input terminal  301  and the current output terminal  302 . The fuse  300  further includes a first angled connecting portion  404  which connects the first one way linear portion  402  and the first other way linear portion  406 , a second angled connecting portion  408  which connects the first other way linear portion  406  and the second one way linear portion  410 , a third angled connecting portion  412  which connects the second one way linear portion  410  and the second other way linear portion  414 , a fourth angled connecting portion  415  which connects the second other way linear portion  414  and the third one way linear portion  416 , a fifth angled connecting portion  418  which connects the third one way linear portion  416  and the third other way linear portion  420 , and a sixth angled connecting portion  422  which connects the third other way linear portion  420  and the fourth one way linear portion  424 . 
         [0085]    With the above structure, the second other way linear portion  414  is easily opened. As the second other way linear portion  414  is surrounded at four sides by the linear portions and angled connecting portions, the second other way linear portion  414  is kept at relatively high temperature and the fuse is easily opened at its center. 
         [0086]    In addition, the linear portions (or angled connecting portions) of the fuse  300  are preferably designed to be placed such that when the current flows from the current input terminal  301  to the current output terminal  302 , the current flows in opposite directions in the linear portions adjacent to each other. 
         [0087]    In  FIG. 13 , for example, when the current flows from the current input terminal  301  to the current output terminal  302 , the current flows from right to left in the first one way linear portion  402 . On the other hand, at the same time in  FIG. 13 , the current flows from left to right in the third other way linear portion  420  which is adjacent to the first one way linear portion  402 . 
         [0088]    Likewise, in  FIG. 13 , when the current flows from the current input terminal  301  to the current output terminal  302 , the current flows from bottom to top in the first angled connecting portion  404 . On the other hand, at the same time in  FIG. 13 , the current flows from top to bottom in the fifth angled connecting portion  418  which is adjacent to the first angled connecting portion  404 . 
         [0089]    With this structure, magnetic field generation is avoided even when the current flows through the fuse  300 . 
         [0090]    As described above, the fuse in the embodiments according to the present invention includes at least a linear portion which is surrounded by other linear portions. With this structure, the linear portion surrounded by other linear portions is kept at a relatively high temperature such that the linear portion is easily opened by the current. 
         [0091]      FIGS. 4 and 5  show the relationships between the number of the turnings in each of the fuses and voltage or current necessary to open each of the fuses. Here, each of the conductive lines formed between the current input terminal and the current output terminal of each of the fuses has same length. The number “0 (zero)” in the horizontal axis means that the current input terminal and the current output terminal of a fuse are placed on a line and connected via a linear conductive line. The values on the vertical axis shown in  FIG. 4  indicate the voltage supplied between the current input terminal and the current output terminal that is necessary to open each of the fuses. The values on the vertical axis shown in  FIG. 5  indicate the current supplied between the current input terminal and the current output terminal that is necessary to open each of the fuses. 
         [0092]    As shown in  FIGS. 4 and 5 , as the number of the turnings in a fuse increase, the voltage or the current necessary to open the fuse decreases. When the number of the turnings increases further, the decrease in the voltage value or the current value approaches a limit. 
         [0093]    As described above, according to the first embodiment and the second embodiment of the present invention, it is possible to reduce the voltage or current that must be supplied to the fuse in order to open the fuse. 
         [0094]      FIGS. 6 and 7  show a fuse of a third embodiment according to the present invention.  FIG. 6  is a plan view showing the fuse of this embodiment.  FIG. 7  is a cross sectional view on the I-I line shown in  FIG. 6 . In this embodiment, the fuse is covered with a conductive portion other than that of the conductive lines of the fuse itself. 
         [0095]    Now, referring to  FIGS. 6 and 7 , the structure of the fuse  600  will be explained. 
         [0096]    The fuse  600  is formed in a second insulating layer  654  which is formed on a first insulating layer  652  formed on a semiconductor substrate  651 . Here, to simplify the explanation, the second insulating layer  654  is shown as a single layer. Actually, the second insulating layer  654  is constituted of a plurality of insulating layers. The fuse  600  is covered with a bottom plate  653 , a top plate  660 , and vias  656  and  659  at its bottom, top, and sides respectively. The vias  656  and  659  are formed to fill the via holes  655  and  658 , respectively. The vias  656  and  659  are connected with each other through a pad terminal  657  which is formed simultaneously with the fuse  600 . The vias  656  and  659  may be not necessarily connected though the pad terminal  657  as long as the vias  656  and  659  are formed to function as a wall to prevent the conductive materials diffusing from the fuse  600  and affecting other devices when the fuse  600  is opened. 
         [0097]    The fuse  600  is opened when a certain current flows from the current input terminal  601  to the current output terminal  602 . The fuse  600  includes a first one way linear portion  603  which is connected to the current input terminal  601 , a first other way linear portion  604 , and a first angled connecting portion  606  which connects the first one way linear portion  603  and the first other way linear portion  604 . The fuse  600  further includes a fifth one way linear portion  643  which is connected to the current output terminal  602 , a fourth other way linear portion  634 , and a eighth angled connecting portion  647  which connects the fifth one way linear portion  643  and the fourth other way linear portion  634 . Logically, the third one way linear portion  623  at the center of the nine linear portions of the fuse  600  is most easily opened. 
         [0098]    With the heat distributions generated at the periphery of the fuse  600 , the fuse  600  is easily opened. In addition, in this embodiment, the conductive materials which diffuses from the fuse  600  when the fuse  600  is opened are blocked by the bottom plate  653 , the top plate  660 , and the vias  656  and  659  in such a way that they do not have an effect on other devices. Furthermore, by covering the fuse  600  with conductive materials other than the materials constituting the fuse  600 , such as the bottom plate  653 , the top plate  660 , and the vias  656  and  659 , the heat generated at the fuse  600  when the current flows therethrough is reflected by these conductive materials and remains inside those conductive materials. Thus, the fuse  600  is more easily opened. 
         [0099]    Although it is disclosed in this embodiment that four sides of the fuse  600  are covered with the conductive materials, the present invention is not limited to this example. For example, only the upper and lower of the fuse  600  may be covered with the conductive materials, or only the left side and right side of the fuse  600  may be covered with the conductive materials. 
         [0100]      FIGS. 8 and 9  show a fuse of a fourth embodiment according to the present invention.  FIG. 8  is a plan view showing the fuse of this embodiment.  FIG. 9  is a cross sectional view on the J-J line shown in  FIG. 8 . As in the fuse of the third embodiment, the fuse in this embodiment is covered at top, lower, and sides with a conductive portion other than the conductive lines of the fuse itself. In addition, the fuse of this embodiment includes a narrow portion. 
         [0101]    As shown in  FIG. 8 , the third one way linear portion  623 , which is placed at a center of the nine linear portions that constitute the fuse  610 , includes a narrow linear portion  683 . 
         [0102]    Due to this narrow linear portion  683 , the fuse  610  can be opened with lower current or voltage than is necessary for the fuse  600  of the third embodiment. 
         [0103]      FIG. 14  shows a plan view of a fuse of a fifth embodiment according to the present invention. In this embodiment, the fuse  442  basically has a same structure as that of the fuse  300  shown in  FIG. 3  of the second embodiment, and turns four times. The fuse  442  includes a conductive line  443  including a plurality of linear lines and a plurality of angled connecting portions, a current input terminal  301  and a current output terminal  302  formed at the ends of the conductive line  443 . The fuse  442  further includes a broad portion  444  formed on the linear portion which is placed at the center of the plurality of linear portions. The broad portion  444  is formed to have a wider width than those of the linear portions. This broad portion  444  enables electro migration of the conductive materials constituting the fuse  442  to become large. Thus, the fuse  442  is easily opened at a point between the broad portion  444  and one of the turnings near the broad portion  444 . 
         [0104]      FIGS. 15A and 15B  are diagrams showing how the fuse  442  is opened in this embodiment. As shown in  FIG. 15A , the second one way linear portion  313  and the third angled connecting portion  316  are at right angles. Thus, the electro migrations of the conductive materials constituting the fuse  442  at the connecting point C of portions  313  and  316  are small. On the other hand, the electro migrations of the conductive materials constituting the fuse  442  in the broad portion  444  are large because the width of broad portion  444  is wider than the rest of the fuse  442 . Due to these electro migrations of the conductive materials, the second one way linear portion  313  is easily opened as shown in  FIG. 15B . 
         [0105]      FIGS. 16 ,  17 A and  17 B show alternative examples of the fuse of the present embodiment. 
         [0106]    As shown in  FIG. 16 , the fuse includes the broad portion  444  between the current input terminal  301  and the corner D joining linear portion  452  at a right angle. Due to the broad portion  444 , the linear portion  452  is easily opened at a place between the corner D and the broad portion  444 . 
         [0107]    As shown in  FIG. 17A , the fuse may include a first one way linear portion  456 , a first angled connecting portion  458 , and a first other way linear portion  460  between the current input terminal  301  and the current output terminal  302 , in addition to terminals  301  and  302 . The fuse may further include the broad portion  444  between the current input terminal  301  and the corner E at which first one way linear portion  456  is connected to the first angled connecting portion  458 . With the broad portion  444 , the first one way linear portion  456  is easily opened at a place between the broad portion  444  and the corner E as shown in  FIG. 17B . 
         [0108]      FIG. 18  shows another alternative example of the fuse of the present embodiment. Here, the fuse  470  turns six times. 
         [0109]    The fuse  470  includes a current input terminal  301  and a current output terminal  302  at its ends. The fuse  470  further includes a first one way linear portion  402 , a first other way linear portion  406 , a second one way linear portion  410 , a second other way linear portion  414 , a third one way linear portion  416 , a third other way linear portion  420 , and a fourth one way linear portion  424  between the current input terminal  301  and the current output terminal  302 . The fuse  470  further includes a first angled connecting portion  404  which connects the first one way linear portion  402  and the first other way linear portion  406 , a second angled connecting portion  408  which connects the first other way linear portion  406  and the second one way linear portion  410 , a third angled connecting portion  412  which connects the second one way linear portion  410  and the second other way linear portion  414 , a fourth angled connecting portion  415  which connects the second other way linear portion  414  and the third one way linear portion  416 , a fifth angled connecting portion  418  which connects the third one way linear portion  416  and the third other way linear portion  420 , and a sixth angled connecting portion  422  which connects the third other way linear portion  420  and the fourth one way linear portion  424 . 
         [0110]    The fuse  470  further includes the broad portion  444  formed on the second other way linear portion  414  which is placed at the center of the plurality of linear portions of the fuse  470 . 
         [0111]    With this structure, the second other way linear portion  414  is easily opened at a place between the broad portion  444  and the corner between the second other way linear portion  414  and the fourth angled connecting portion  415 . As described above, due to the broad portion to the fuse, the electro migration of the conductive material at the broad portion is large and the fuse is easily opened. On the other hand, a concern remains that the amount of heat generated in the fuse will be radiated by the broad portion and the fuse will not be easily opened. However, with the structures shown in  FIGS. 14 and 18 , the broad portion is formed at the center of the fuse, and thus, the broad portion is kept at a relatively high temperature by heat from the remaining portions of the fuse that surround the broad portion. Therefore, the fuse is easily opened by taking advantage of the electro migration of the conductive material without being affected by radiant heat loss. In particular, in the fuse shown in  FIG. 18 , the broad portion  444  is kept at higher temperature because it is surrounded at four sides by the linear portions and angled connecting portions. Thus, the fuse  470  is more easily opened. 
         [0112]    The fuse of the present invention may include a structure such shown in  FIG. 19 . As described above, due to the broad portion to the fuse, the electro migration of the conductive material at the broad portion is large and the fuse is easily opened. On the other hand, a concern remains that the amount of heat generated in the fuse will be radiated by the broad portion and the fuse will not be easily opened. However, with the structure shown in  FIG. 19 , the conductive element turns plurality of times, and the broad portion  444  placed in the vicinity of the conductive element is kept at relatively high temperature. Thus, with the electro migration of the broad portion  444  and the conductive element, the conductive element is easily opened in the vicinity of the broad portion  444 . 
         [0113]    Although the above embodiments describe the conductive materials constituting the fuse as being formed on a plane which is parallel to the semiconductor substrate, the present invention is not limited to these embodiments. For example, the one way linear portions and the other way linear portions may be formed as vias which are perpendicular to the semiconductor substrate and formed to break through the insulating layer. In this case, the angled connecting portions which connect one of the one way linear portions and the next other way linear portions may be formed on a plane which is parallel to the semiconductor substrate. In this example, the current input terminal and the current output terminal of the fuse may be simultaneously formed with the angled connecting portions. Here, both of the current input terminal and the current output terminal may be formed above or below the insulating layer, or either the current input terminal or the current output terminal may be formed above the insulating layer and the other terminal may be formed below of the insulating layer. 
         [0114]    Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may further be made by those skilled in the art without departing from the scope of the present invention which is defined by the appended claims.