Abstract:
The present invention provides a three-dimensional memory (3D-M) system-on-a-chip (SoC). It takes full advantage of the difference in the number of interconnect levels between the embedded processor (eP) and embedded memory (eM) in an SoC chip. The un-used interconnect space on top of the eM block is converted into 3D-M. This conversion incurs minimum additional cost, but with significant benefits: 3D-M can add a large storage capacity to the SoC chip and therefore the chip becomes more powerful.

Description:
This patent application relates to a provisional patent application, “3D-Memory System-on-a-chip”, provisional patent No. 60/511,420, filed on Oct. 14, 2003. 
   BACKGROUND 
   1. Technical Field of the Invention 
   The present invention relates to the field of integrated circuits, and more particularly to three-dimensional memory system-on-a-chip (3DM-SoC). 
   2. Related Arts 
   The latest advancement of integrated circuits enables the placement of more and more functions on a single chip, thus resulting in wide adoption of system-on-a-chip (SoC). As illustrated in  FIG. 1A , an SoC chip  0 SOC typically comprises at least one embedded memory (eM) block  0 EM and at least one embedded processor (eP) block  0 EP. The eM block  0 EM provides data storage functions while the eP block  0 EP processes the internal and/or external data. The eM block  0 EM comprises RAM and/or ROM; the eP block  0 EP could comprise logic and/or analog functional blocks. 
   Because the basic building blocks of prior-art embedded memory and embedded processor are both substrate-based transistors, the eM and eP blocks can be easily integrated on a same substrate. However, it should be noted that the eM block  0 EM requires much fewer number of interconnect levels than the eP block  0 EP. For example; in the SoC chip illustrated in  FIG. 1B , the eP block  0 EP uses four levels of interconnect  1 EP-IL 1 , IL 2 , IL 3  IL 4 , while the eM block  0 EM only uses two levels of interconnect  1 EM-IL 1 , IL 2 . For damascene-based process, within the eM region, the interconnect space  1 DY are filled with dummy metals (such as  30   d ,  40   d ) and therefore, wasted. 
   On a state-of-the-art SoC, more than ˜50% of the chip area can be embedded memory. Moreover, the number of the interconnect levels  1 EM in the eM region  0 EM and the number of the interconnect levels  1 EP in the eP region  0 EP are quite different (˜3 vs.&gt;˜8). Accordingly, a large interconnect space  1 DY is wasted (&gt;˜5 interconnect levels in &gt;˜50% of chip area). To fully utilize this wasted interconnect space  1 DY, the present invention provides a three-dimensional memory (3D-M) system-on-a-chip (3DM-SoC). It takes advantage of the fact that 3D-M can be stacked on top of the substrate circuit and does not occupy substrate real estate. Instead of dummy metals, the present invention uses 3D-M to fill in the interconnect space IDY. This 3D-M provides a large storage capacity and is an ideal supplement to the substrate-based embedded memory. As a result, the 3DM-SoC will become more powerful. 
   OBJECTS AND ADVANTAGES 
   It is a principle object of the present invention to provide a system-on-a-chip with more functionality. 
   It is a further object of the present invention to provide a system-on-a-chip with minimum added manufacturing cost. 
   It is a further object of the present invention to provide a three-dimensional memory whose structure and processing steps are compatible with the conventional interconnects. 
   In accordance with these and other objects of the present invention, a three-dimensional memory system-on-a-chip (3DM-SoC) is disclosed. 
   SUMMARY OF THE INVENTION 
   The present invention provides a three-dimensional memory system-on-a-chip (3DM-SoC). It takes full advantage of the difference in the number of interconnect levels between the embedded processor (eP) and embedded memory (eM) in an SoC chip. The un-used interconnect space on top of the eM block is converted into 3D-M. This conversion incurs minimum additional cost (for certain preferred embodiments, only one additional masking step is needed for each 3D-M level), but with significant benefits: 3D-M can add a large storage capacity to the SoC chip and therefore the chip becomes more powerful. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a layout of a prior-art system-on-a-chip (SoC);  FIG. 1B  is a cross-sectional view of the prior-art SoC chip of  FIG. 1A  along the cut-line AA′. 
       FIG. 2  is a cross-sectional view of a preferred three-dimensional memory (3D-M). 
       FIG. 3  is cross-sectional view of a preferred three-dimensional memory system-on-a-chip (3DM-SoC). 
       FIG. 4  illustrates a first preferred 3D-M/interconnect in a preferred 3DM-SoC. 
     FIGS.  5 A– 5 E illustrate a preferred manufacturing process of the first preferred 3D-M/interconnect. 
       FIG. 6  illustrates a preferred electrically-programmable 3D-M level in another preferred 3DM-SoC. 
       FIGS. 7A–7C  illustrates several preferred 3D-M layers. 
       FIG. 8  illustrates a second preferred 3D-M/interconnect in yet another preferred 3DM-SoC. 
       FIGS. 9A–9C  illustrate a preferred manufacturing process of the second preferred 3D-M/interconnect. 
       FIG. 10  illustrates a third preferred 3D-M/interconnect in yet another preferred 3DM-SoC. 
       FIGS. 11A–11D  illustrate a preferred manufacturing process of the third preferred 3D-M/interconnect. 
       FIG. 12  illustrates a fourth preferred 3D-M/interconnect in yet another preferred 3DM-SoC. 
       FIGS. 13A–13D  illustrate a preferred manufacturing process of the fourth preferred 3D-M/interconnect. 
     FIGS.  14 A– 14 CB illustrates a preferred hybrid interconnect level and two preferred manufacturing processes. 
       FIG. 15  illustrates a preferred 3DM-SoC with 3D-M covering both eM and eP regions. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In a three-dimensional memory (3D-M), one or more 3D-M levels are stacked one above another. 3D-M has been disclosed in U.S. Pat. Nos. 5,835,396, 6,717,222 and others.  FIG. 2  illustrates a preferred 3D-M. In this preferred 3D-M, at least one physical memory level  100  of the 3D-M is stacked on a substrate circuit  10 . On each memory level  100 , there are a plurality of address-select lines, including word line  102   a  and bit line  108   i ,  108   j . At each intersection of word and bit lines, there is a 3D-M cell. This preferred 3D-M is a mask-programmable 3D-M: depending on the existence or absence of an insulating layer  106 , this 3D-M cell represents either logic “0” or “1”. Contact vias ( 100   av  . . . ) provide electrical connection between address-select lines ( 102   a  . . . ) and the substrate circuit. 
   Depending on its programming means, the 3D-M can be categorized into electrically programmable 3D-M (EP-3DM) and non-electrically programmable 3D-M (NEP-3DM). Examples of the EP-3DM include 3-D RAM (3D-RAM), 3-D write-once memory (a.k.a. 3-D one-time programmable, i.e. 3D-OTP), and 3-D write-many (3D-WM). A popular NEP-3DM is mask-programmable 3-D read-only memory (3D-MPROM). Details about these 3D-M&#39;s are disclosed in U.S. Pat. No. 6,717,222, “Three-Dimensional Memory”, filed on Aug. 28, 2002, by the same inventor. 
     FIG. 3  illustrates a preferred three-dimensional memory system-on-a-chip (3DM-SoC). In this preferred embodiment, the interconnect space 3DM, which was occupied by dummy metals  30   d ,  40   d  in a prior-art SoC ( FIG. 1B ), is converted into a 3D-M level. Interconnect level IL 3  becomes the bit line  30   m  and interconnect level IL 4  become the word line  40   m . Between word and bit lines, there is a 3D-M layer  36 . The 3D-M layer  36  could comprise a diode layer (including p-n diode, p-i-n diode, Schottky diode and others), or an active device. Various preferred 3D-M layers are disclosed in U.S. Pat. Nos. 5,835,396, 6,717,222 and others. 
   In this preferred embodiment, the difference in the number of interconnect levels  1 EP,  1 EM between the eP and eM regions  0 EP,  0 EM is two (2). Accordingly, one 3D-M level could be built. If this difference is six, then up to five 3D-M levels could be built, if interleaved 3D-M structure is used; or three, if separate 3D-M structure is used (referring to  FIGS. 9–10  of U.S. Pat. No. 6,717,222). 
     FIG. 4  illustrates a first preferred 3D-M/interconnect in a preferred 3DM-SoC. Here, 3D-M/interconnect refers to two adjacent interconnect levels ILa (including lower conductors  30 L,  30 M), ILb (including upper conductors  40 L,  40 M 1 ,  40 M 2 ) and their connecting means. In a 3D-M/interconnect, there are two types of connecting means between two interconnect levels ILa, ILb:
         1) in the eP region  0 EP, by a via  38  to form a conventional interconnect;   2) in the eM region  0 EM, by a 3D-M layer  36  to form a 3D-M cell (the digital information stored in the 3D-M cell is represented by, e.g. the existence or absence of the 3D-M layer  36 ).
 
In comparison, in a conventional interconnect, there is only one type of connecting means between two interconnect levels.
       
     FIGS. 5A–5E  illustrate a preferred manufacturing process of the first preferred 3D-M/interconnect. This manufacturing process is compatible with the conventional dual-damascene process, with only one additional masking step (i.e. the step illustrated in  FIG. 5B ). Accordingly, it incurs minimum additional cost to the SoC manufacturing. It comprises the following steps:
         1) forming the first interconnect level ILa, through means such as damascene ( FIG. 5A ). Numeral  31  refers to the intra-level dielectric between lower conductors  30 L,  30 M;   2) depositing and etching the 3D-M layer. After this step, a plurality of 3D-M pillars  36  are formed at the location of logic “1” cells in the eM region  0 EM ( FIG. 5B );   3) depositing, planarizing and etching back a first inter-level dielectric  33  until the 3D-M pillars  36  are exposed in the eM region  0 EM. This is followed by the deposition of a second inter-level dielectric  35  ( FIG. 5C ). The structure and composition of these two inter-level dielectrics  33 ,  35  are similar to those used in the conventional dual-damascene process;   4) etching the via pattern and trench patterns until the top surfaces of the 3D-M pillars  36  are exposed in the eM region  0 EM and the top surfaces of the lower conductor  30 L are exposed in the eP region  0 EP ( FIG. 5D ). This step is also similar to the conventional dual-damascene process;   5) filling in and planarizing the second interconnect level ILb, through means such as CMP ( FIG. 5E ). This step is same as the conventional dual-damascene process.       
     FIG. 6  is a preferred electrically-programmable 3D-M (EP-3DM) level in another preferred 3DM-SoC. In this EP-3DM, instead of selectively having 3D-M layer at the memory cell location (as is illustrated in  FIG. 4 ), there is a 3D-M layer  36 P at every memory cell location. This 3D-M layer  36 P could comprise an antifuse-diode combo, or other active devices. Details of the EP-3DM are disclosed in U.S. Pat. Nos. 5,835,396, 6,717,222 and others. 
     FIGS. 7A–7C  illustrates several preferred 3D-M layers. The preferred 3D-M layer  36  of  FIG. 7A  comprises a p-layer  36   a  and an n-layer  36   b . It could further comprise an i-layer between the p- and n-layers  36   a ,  36   b . This i-layer could be lightly-doped. The preferred 3D-M layer  36  of  FIG. 7B  further comprises a bottom buffer layer  36   d  and a top buffer layer  36   c . These buffer layers  36   c ,  36   d  comprise conductive materials, e.g. TiW, W, Cu, or heavily-doped semiconductor materials. They can be laid down at the same time with the p- and n-layers  36   a ,  36   b . The bottom buffer layer  36   d  can prevent the damage on the lower conductor  30 M from causing defects to the n-layer  36   b , and the top buffer layer  36   c  can protect the p-layer  36   a  during the etch-back of the first inter-level dielectric  33 . The preferred 3D-M layer  36 P further comprises an antifuse layer  36   e  ( FIG. 7C ). This 3D-M layer can be used in electrically-programmable 3D-M (EP-3DM). To those skilled in the art, the above disclosed 3D-M layers just represents a small number of possible 3D-M layers. Other preferred 3D-M layers are disclosed in U.S. Pat. Nos. 5,835,396, 6,717,222 and others. 
     FIG. 8  is a second preferred 3D-M/interconnect in yet another preferred 3DM-SoC. Similar to  FIG. 4 , this preferred 3D-M/interconnect is also compatible to dual-damascene process and incurs minimum additional cost to manufacturing. The only difference is that, instead of directly contacting the 3D-M layer  36 , the upper conductor  40 M 2  contacts the 3D-M layer  36  through a half-via  38 M in the eM region  0 EM. Here, half-via  38 M only extends half-way through the inter-level dielectric  33  (i.e. from the upper conductor  40 M 2  to the top of the 3D-M layer  36 ), not like the full via  38 , which extends fully through the inter-level dielectric  33  (i.e. from the upper conductor  40 L to the lower conductor  30 L). 
     FIGS. 9A–9C  illustrate a preferred manufacturing process of the second preferred 3D-M/interconnect. Similar to the manufacturing process illustrated in  FIGS. 5A–5E , a plurality of 3D-M pillars  36  are formed in the eM region  0 EM ( FIG. 9A ). For this preferred embodiment, a 3D-M pillar  36  remains at the location of every 3D-M cell. Then the first and second inter-level dielectrics  33 ,  35  are deposited and planarized. Different from that of  FIG. 5C , no 3D-M pillar  36  is exposed in the eM region  0 EM during this step. The steps in  FIGS. 9B–9C  are similar to those in  FIGS. 5D–5E , i.e. forming via and trench and filling them with upper conductor. Here, via  38 M (i.e. via in the eM region  0 EM) is referred to as a half-via, because its depth is shorter than the full via  38  (i.e. the via in the eP region  0 EP). The digital information stored in the 3D-M is represented by the existence or absence of the half-via  38 M. 
     FIG. 10  is a third preferred 3D-M/interconnect in yet another preferred 3DM-SoC. The 3D-M in this preferred 3D-M/interconnect is a self-aligned pillar-shaped 3D-M. Details about this type of the 3D-M are disclosed in the U.S. Pat. No. 6,717,222 and others. For the self-aligned pillar-shaped 3D-M, one dimension of the 3D-M layer  36  is equal to the width of the lower conductor  30 M; and the other dimension of the 3D-M layer  36  is equal to the width of the upper conductor  40 M 2 . 
     FIGS. 11A–11D  illustrate a preferred manufacturing process of the third preferred 3D-M/interconnect. It comprises the following steps:
         1) deposit the lower conductors  30 M,  30 L and the 3D-M layer  36  sequentially. Then remove the 3D-M layer  36  in the eP region  0 EP. After that, etch the 3D-M layer  36  and the lower conductors  30 M at the same time in the eM region  0 EM. This is followed by the deposition and planarization of a dielectric layer  133  ( FIG. 11A );   2) etch openings  36   o  in the eM region  0 EM and  38   o  in the eP region  0 EP ( FIG. 11B ). In this preferred embodiment, these openings are nF-opening. Details about nF-opening are disclosed in U.S. patent application Ser. Nos. 10/230,648, 10/230,610 and others;   3) form the upper conductor  140  ( FIG. 11C );   4) pattern and etch the upper conductor  140 . This step will etch through the 3D-M layer  36  until the lower conductor  30 M is exposed ( FIG. 11D ).       
     FIG. 12  is a fourth preferred 3D-M/interconnect in yet another preferred 3DM-SoC. The 3D-M in this preferred 3D-M/interconnect is a self-aligned natural-junction 3D-M. Details about this type of the 3D-M are disclosed in the U.S. Pat. No. 6,717,222 and others. The 3D-M layer  36   b  is naturally formed at the intersection of the upper conductor  40 M 2  and the lower conductor  30 M. 
     FIGS. 13A–13D  illustrate a preferred manufacturing process of the fourth preferred 3D-M/interconnect. It comprises the following steps:
         1) deposit the lower conductors  30 M,  30 L and the first half 3D-M layer  36   a . This half 3D-M layer  36   a  could be the n-layer of the 3D-M layer  36  ( FIG. 7A ). Then remove the half 3D-M layer  36   a  in the eP region  0 EP. After that, etch the half 3D-M layer  36   a  and the lower conductors at the same time in the eM region  0 EM. This is followed by deposition and planarization of a dielectric layer  133  before forming nF-openings  36   o  in the eM region  0 EM ( FIG. 13A );   2) form the second half 3D-M layer  36   b  and remove said layer in the eM region  0 EM ( FIG. 13B );   3) etch nF-openings  38   o  in the eP region  0 EP and deposit the upper conductor  140  ( FIG. 13C );   4) pattern and etch the upper conductor  140 . This step is similar to that in  FIG. 11D  ( FIG. 13D ).       
     FIG. 14A  illustrates a preferred hybrid interconnect level ILx. In a hybrid interconnect level ILx, different conductors are used in different regions, even though they are located at the same physical level. The purpose of using different conductors in different regions is to meet different requirements on conductors in these regions. For the preferred embodiment of  FIG. 14A , in the eM region  0 M, the eM conductor  30 M comprises TiSi 2  or other conductive materials, which is suitable for the 3D-M; in the eP region  0 EP, the eP conductor  30 L comprises Cu, which is suitable for the conventional interconnect. 
   FIGS.  14 BA– 14 BB illustrate a first preferred manufacturing process for the hybrid interconnect level ILx. The eP conductor  30 L is formed first, together with a covering dielectric layer  32   t . Then a spacer layer  32   s  is formed at its both edges (FIG.  14 BA). This is followed by the deposition of the eM conductor  30 M (FIG.  14 BB). After patterning the eM conductor  30 M, the preferred hybrid interconnect level ILx is formed. 
   FIGS.  14 CA– 14 CB illustrate a second preferred manufacturing process for the hybrid interconnect level ILx. This process flow is compatible with damascene process. The eP conductor  30 L is formed in a first dielectric  31  by damascene first. Then the whole wafer surface is covered with a protective dielectric  32   u  (FIG.  14 CA). After that, a trench  32 Mt is formed in the first dielectric  31  by etching through the protective dielectric  32   u  (FIG.  14 CB). After filling the trench  32 Mt with the eM conductor  30 M and the planarization step, the preferred hybrid interconnect level ILx is formed. 
     FIG. 15  illustrates a preferred 3DM-SoC with 3D-M covering both eM and eP regions. In this preferred embodiment, besides the 3D-M in the un-used interconnect space 3DMA, there is an additional full 3D-M level 3DMB. Here, full 3D-M level refers to the 3D-M level that covers almost the whole chip, e.g. at least a portion of the eP region  0 EP and at least a portion of the eM region  0 EM. It also comprises a plurality of lower address-selection lines  50 , upper address-selection lines  60  and 3D-M cells  56 . It should be apparent to those skilled in the art that there might be more than two full 3D-M levels in a 3DM-SoC. With full 3D-M level(s), 3DM-SoC can have even larger storage capacity. 
   Finally, applications of the 3DM-SoC will be discussed. The 3D-M in the 3DM-SoC can be used to publish contents. For example, it can be used to store multimedia files (e.g. audio/video files for entertainment, map images for GPS, text/sound/images for dictionary and others . . . ) It can also be used to store test file to enable 3DM-SoC self-test. The possibilities are boundless. More details about the 3DM-SoC applications can be found in U.S. Pat. No. 6,717,222. 
   While illustrative embodiments have been shown and described, it would be apparent to those skilled in the art that may more modifications than that have been mentioned above are possible without departing from the inventive concepts set forth therein. The invention, therefore, is not to be limited except in the spirit of the appended claims.