Semiconductor device with self-aligned contact and manufacturing method thereof

[0002] The present invention relates to high integration of a semiconductor device, and more particularly, to a semiconductor device manufactured in a simplified process including a self-aligned contact process and a method of manufacturing the semiconductor device.

[0003] Recently, there has been a remarkable progress in integration technology of a semiconductor integrated circuit. The high integration of a semiconductor integrated circuit is generally attained if a micro line, space, and contact pattern are realized by improving a lithographic resolution.

[0004] However, alignment technique between layers has been less improved in comparison with resolution technique in lithography. In these circumstances, if alignment allowance is ensured, an entire area size inevitably increases. This is a big problem preventing high integration of the circuit.

[0005] In an attempt to overcome the increase in area size, a method has been employed in which a contact is formed in a self-alignment manner to the gate.

[0006] For example, manufacturing steps of a semiconductor device conventionally formed by such a method are shown in FIGS. 1A to 1F.

[0007] In FIG. 1A, a device isolating region 4 is formed in the surface portion of a silicon substrate 2 and a well 2a, which has an opposite conductive type to that of the substrate 2. An n-diffusion layer 6 is formed in the surface portion of the silicon substrate 2. A p-diffusion layer 8 is formed in a surface portion of the well 2a. A gate electrode 12 is formed on the silicon substrate 2 and well 2avia a gate oxide film 10. A reference numeral 14 indicates a cap layer formed of a silicon nitride (SiN) film. Furthermore, a silicon nitride film 16 is formed on the silicon substrate 2. Note that a gate side wall 18 is formed on both sides of the gate electrode 12.

[0008] As shown in FIG. 1B, the silicon nitride film 16 is removed from the surface of the silicon substrate in each of the regions with and without the well 2aby RIE (reactive ion etching), and thereafter, impurity ions are implanted into the silicon substrate 2 and the well 2a. In this manner, N⁺ diffusion layers 20, 22 and a P⁺ diffusion layer 24 serving as a source/drain are formed. Thereafter, an interlayer film 26 is deposited over an entire surface of the silicon substrate 2.

[0009] Subsequently, as shown in FIG. 1C, a resist 28 is formed on the interlayer film 26. However, the resist 28 is not formed on a contact formation region to the source/drain of the substrate 2. Then, etching is selectively performed to the resultant structure under such a condition that the silicon nitride film 14 is not etched, as shown in FIG. 1D, using the resist 28 as a mask. As a result, a contact hole 30 is formed. Accordingly, a contact (to the gate electrode) can be formed even if an alignment allowance is not taken to the gate.

[0010] As shown in FIG. 1E, a resist 32 is deposited in the contact hole 30 and on the interlayer film 26 excluding the portion in which a contact (to the gate) is to be formed in a later step. Thereafter, a contact hole 34 is formed on the gate using the resist 32 as a mask.

[0011] Thereafter, as shown in FIG. 1F, metal wiring layers 36, 38 are formed in each of contact holes 30, 34 and on the interlayer film 26.

[0012] However, the semiconductor formation method mentioned above requires two contact hole formation steps opposite to each other, that is, the step of forming a contact hole by etching the nitride film formed on the gate (corresponding to FIG. 1E) and a step of forming a contact hole without etching the nitride film formed on the gate (corresponding to FIG. 1D). Since two steps are required for the contact hole formation, the number of processing steps increases.

[0013] An object of the present invention is to provide a semiconductor device and a manufacturing method thereof capable of forming a semiconductor device, which requires a single contact hole formation step, even if a self aligned contact is included in the device.

[0014] More specifically, the semiconductor device of the present invention comprises

[0015] a gate electrode formed above a semiconductor substrate;

[0016] a cap layer having a first contact hole, formed on the gate electrode in a self alignment manner to the gate electrode;

[0017] an interlayer film deposited above the semiconductor substrate and the cap layer, and having a second contact hole formed on the first contact hole; and

[0018] a wiring layer formed in the first and second contact holes,

[0019] wherein the first contact hole and second contact hole are formed by using mutually different masks.

[0020] The method of manufacturing a semiconductor device according to the present invention comprises

[0021] a first step of processing a laminate structure having a gate insulating film, a gate electrode and a cap layer formed on a substrate, into a gate form in order to form a first conductive-type MIS transistor and a second conductive type MIS transistor;

[0022] a second step of etching an entire surface of an insulating film which coats the first conductive type MIS transistor region and a cap layer formed on gate contact portions of the first and second conductive type MIS transistors to substantially expose a substrate surface of the first conductive type MIS transistor and at the same time, to remove a part of the cap layer from the gate contact portions of the first and second conductive type MIS transistors and then, implanting a first conductive type impurity; and

[0023] a third step of etching an entire surface of an insulating film which coats the second conductive type MIS transistor region and a cap layer formed on the gate contact portions of the first and second conductive type MIS transistors to substantially expose a substrate surface of the second conductive type MIS transistor and at the same time, to remove remainders of the cap layer on the gate contact portion of the first conductive type MIS transistor and the cap layer on the gate contact portion of the second conductive type MIS transistor, and then, implanting a second conductive type impurity.

[0024] Furthermore, the method of manufacturing a semiconductor device according to the present invention comprises

[0025] a first step of processing a laminate structure having a gate insulating film, a gate electrode, and a cap layer formed on a substrate into a gate form, in order to form a first conductive type MIS transistor and a second conductive type MIS transistor;

[0026] a second step of implanting a first conductive type impurity and a second conductive type impurity into the first conductive type MIS transistor region and the second conductive type MIS transistor region, respectively;

[0027] a third step of depositing an insulating layer over an entire surface of the first conductive type MIS transistor region and the second conductive type MIS transistor region;

[0028] a fourth step of removing the insulating layer between adjacent gates in a part of an MIS transistor formation region to thereby substantially expose a substrate surface;

[0029] a fifth step of selectively forming a plug contact between the adjacent gates;

[0030] a sixth step of etching an entire surface of an insulating film which coats the first conductive type MIS transistor region and the cap layer formed on gate contact portions of the first and second conductive type MIS transistors to substantially expose a substrate surface of the first conductive type MIS transistor and at the same time, to remove a part of the cap layer on the gate contact portions of the first and second conductive type MIS transistors, and then, implanting a first conductive type impurity;

[0031] a seventh step of etching an entire surface of an insulating film which coats the second conductive type MIS transistor region and the cap layer formed on the gate contact portions of the first and second conductive MIS transistors to substantially expose a substrate surface of the second conductive type MIS transistor and at the same time, to remove remainders of the cap layer on the gate contact portion of the first conductive type MIS transistor and the cap layer on the gate contact portion of the second conductive type MIS transistor, and then, implanting a second conductive type impurity;

[0032] an eighth step of forming an interlayer film, which is different from the insulating film, above the substrate; and

[0033] a ninth step of forming a contact hole by selectively etching the interlayer film, the contact hole extending to a source/drain of the first conductive type MIS transistor, a source/drain of the second conductive type MIS transistor and the gate contact portions.

[0034] In the present invention, when resist masks for the N-type impurity implantation and P-type impurity implantation are formed, a pattern is formed so as to remove the contact portion above the gate. By virtue of this, an integrated circuit having a self-aligned contact can be formed by a single contact hole formation step.

[0035] Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

[0036] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

[0037] FIGS. 1A to 1F are cross-sectional views of a conventional semiconductor device, showing manufacturing steps;

[0038] FIG. 2A is a cross-sectional view of a semiconductor device according to Embodiment 1 of the present invention, in which the diameter of a contact hole portion in the interlayer film is larger than that of the contact hole portion in contact with the gate;

[0039] FIG. 2B is a cross-sectional view of a semiconductor device according to Embodiment 1 of the present invention, in which the diameter of a contact hole portion in the interlayer film is smaller than that of the contact hole portion in contact with the gate;

[0040] FIGS. 3A to 3F are cross-sectional views of a semiconductor device according to Embodiment 1 of the present invention, showing manufacturing steps;

[0041] FIGS. 4A to 4L are cross-sectional views of a semiconductor device according to Embodiment 2 of the present invention, showing manufacturing steps which is the same as in Embodiment 1 except that a plug is previously formed in a micro-patterned portion; and

[0042] FIGS. 5A to 5G are cross-sectional views of a semiconductor device according to Embodiment 3 of the present invention, showing manufacturing steps which is the same as in Embodiment 1 except that a thin silicon nitride film is deposited before an entire contact hole is etched.

[0043] Now, embodiments of the present invention will be explained with reference to the accompanying drawings.

[0044] First, Embodiment 1 of the present invention will be explained referring to FIGS. 2 and 3. In the semiconductor device according to Embodiment 1, a memory cell region of DRAM and a peripheral circuit region having an N-MOSFET and a p-MOSFET are formed on a single semiconductor substrate.

[0045] FIGS. 2A and 2B are cross-sectional views of the semiconductor device according to Embodiment 1 of the present invention. In these cases, the diameter (first diameter) of the contact hole portion in contact with the gate differs from the diameter (second diameter) of the contact hole portion in a SiO₂interlayer film. More specifically, the second diameter is larger than the first diameter in the case of FIG. 2A. Conversely, the second diameter is smaller than the first diameter in the case of FIG. 2B.

[0046] FIGS. 3A to 3F are cross sectional views of the semiconductor device according to Embodiment 1, showing manufacturing process thereof.

[0047] In FIG. 3A, an n-well 52ais formed on a p-type silicon (Si) substrate 52 in a lithographic step. Thereafter, a device isolating region 54 is formed in the surface of the p-type silicon substrate 52 and between an n-channel MOS transistor of the memory cell region 42 and an N-channel MOS transistor 44aof the peripheral circuit region 44, and between an N-channel MOS transistor 44aand a p-channel MOS transistor 44bof the peripheral circuit region 44.

[0048] Subsequently, a gate insulating film 56, a polysilicon layer (gate electrode) 58, and a silicon nitride film (cap layer) 60 are stacked one upon the other on the surface portion of the silicon substrate 52. The resultant structure is subjected to ion implantation and thermal treatment, thereby forming n, p, and n type source/drain diffusion regions (shallow diffusion layers) 62, 64, 66 in the surface of the silicon substrate 52. Furthermore, a silicon nitride film 68 is deposited in such a way that the space between the gates may not be filled with the silicon nitride film 68. Note that a gate side wall 70 is formed on both sides of the gate electrode 58.

[0049] As shown in FIG. 3B, using a resist 72 as a mask, the silicon nitride film 68 is selectively etched off from the P-channel MOS transistor 44bof the peripheral circuit region 44 by reactive ion etching (RIE). Thereafter, a P⁺ layer 74 serving as a source/drain is formed by ion implantation.

[0050] Note that the resist 72 is formed so as to have a contact pattern 76 for etching away a silicon nitride film 60 not only from the P-channel MOS transistor 44bbut also from a part of the gate of the N-channel MOS transistor 44ain the peripheral circuit region 44. The contact pattern 76 is formed so that the underlying silicon nitride film 60 may be etched away.

[0051] On the other hand, the silicon nitride film 60 formed on the gate of the P-channel MOS transistor 44bis completely exposed. Since no contact pattern is formed, the entire surface of the silicon nitride film 60 is uniformly etched away.

[0052] In FIG. 3C, the silicon nitride film 68 formed on the memory cell region 42 and the N-channel MOS transistor 44aof the peripheral circuit region 44 is etched away by RIE using a resist 84 as a mask. Thereafter, n-type impurity ions are implanted into the substrate surface to form N⁺ layers 78 and 80 serving as a source/drain.

[0053] In this case, a contact pattern 82 is formed on the gate of the P-channel MOS transistor 44b. The contact pattern 82 is formed in such a way that the underlying silicon nitride film 60 may be etched away by using the resist 84 as a mask. On the other hand, the silicon nitride film 60 is uniformly etched off from the gate of the N-channel MOS transistor 44a.

[0054] In the N-channel MOS transistor 44aand the P-channel MOS transistor 44bof the peripheral circuit region 44, contact holes are formed by etching the contact portions 60aand 60bon the gate twice in the aforementioned steps. As a result, the gate polysilicon layer 58 is exposed therein. Note that the silicon substrate 52 is also exposed by etching the silicon nitride film 68.

[0055] Next, the P⁺ layer 74 and the N⁺ layers 78, 80 (serving as a source/drain) formed on the afore-mentioned step are activated by applying heat treatment to them.

[0056] Then, as shown in FIG. 3D, after a SiO₂interlayer film 86, which has an etching selective ratio between the silicon nitride film (cap layer) 60 and the gate side wall 70, is deposited, a resist 88 is formed on the film 86 except a contact-hole formation portion. Thereafter, as shown in FIG. 3E, contact holes 90a, 90b, 90c, 90d, 90eare patterned by selectively etching the interlayer film 86.

[0057] In this case, the contact holes 90a, 90c, 90eon the P⁺ layer 74 and the N⁺ layers 78, 80 (serving as a source/drain) are formed in a self-alignment manner to the gates. Whereas, in the contact holes 90b, 90dformed on the gates, the silicon nitride film 60 is not present. As a result, contact portions 60a, 60bin contact with the gate polysilicon layer 58 are formed.

[0058] As shown in FIG. 3F, a wiring layer 92 is formed in the formed contact holes 90ato 90eand on the interlayer film 86.

[0059] As described, according to the method of Embodiment 1, it is possible to form an integrated circuit including a self-aligned contact (SAC) structure without increasing the number of lithographic steps.

[0060] Now, Embodiment 2 of the present invention will be explained.

[0061] FIGS. 4A to 4L are cross-sectional views of a semiconductor device according to Embodiment 2, showing manufacturing steps thereof. Embodiment 2 is the same as Embodiment 1 except that a plug is formed on a micro patterning portion in advance. Like reference numerals are used in FIGS. 4A to 4L to designate like structural elements corresponding to those in FIGS. 3A to 3F and any further explanation is omitted.

[0062] In FIG. 4A, a device isolating region 54 is formed in a surface of a substrate 52. Subsequently, a gate insulating film 56, a polysilicon layer 58, and a silicon nitride film 60 are stacked one upon the other on the silicon substrate 52. Then, ion implantation and heat treatment are applied to the resultant structure, to form source/drain diffusion regions 62, 64, 66 on the surface of the silicon substrate 52. A silicon nitride film 68 is formed on the source/drain diffusion regions 62, 64, 66 in such a way that a space between gates may not be filled with the film 68.

[0063] As shown in FIG. 4B, for example, a SiO₂insulating layer 100 is deposited over the entire surface so as to fill the space between the gates. Then, lithography is applied to the resultant structure in such a way that a portion except the memory cell region may be covered with a resist mask 102, as shown in FIG. 4C.

[0064] Subsequently, the exposed insulating layer 100 and silicon nitride film 68 in the gate portion of the memory cell region are subsequently etched away. Furthermore, the resist mask 102 is removed and then an N-type polysilicon 104 is deposited over the entire surface doped with impurities, as shown in FIG. 4D.

[0065] The N-type polysilicon 104 is etched back. In this manner, the N-type polysilicon 104 is selectively left in the space between the gates of the memory cell region, as shown in FIG. 4E. As a result, a plug 106 is formed. Thereafter, the memory cell region including the space between gates is covered with the resist mask 108 and then the insulating layer 100 of the peripheral circuit region is removed.

[0066] Thereafter, as shown in FIG. 4F, the resist mask is removed. Subsequently, a silicon nitride film is formed over the entire surface of the semiconductor device. In this way, the semiconductor device having a plug in a part of the space between side walls of the adjacent gates.

[0067] In the semiconductor device manufactured in the steps of FIGS. 4A to 4F, the plug 106 is formed in the space between the side walls of adjacent gates in the micro-patterned memory cell region, as shown in FIG. 4G. The silicon nitride film 68′ is formed on the plug 106.

[0068] As shown in FIG. 4H, after the silicon nitride film 68 is removed by RIE from the p-channel MOS transistor in the peripheral circuit region, a P⁺ layer 74 serving as a source/drain is formed by ion implantation. In this case, the resist 72 having a contact pattern 76 is formed on the gate of the N-channel MOS transistor in the peripheral circuit region. Thereafter, the underlying silicon nitride film 60 at the contact pattern 76 is etched away. Whereas, the silicon nitride film 60 on the gate of the P-channel MOS transistor is completely exposed and therefore no contact pattern is formed. Hence the silicon nitride film 60 is uniformly etched away.

[0069] Then, as shown in FIG. 4I, the silicon nitride films 68, 68′ on N-channel MOS transistors of the memory cell region and the peripheral circuit region are etched off by RIE using a resist 84 as a mask. Subsequently, n-type impurity ions are implanted to form an N⁺ layer 80.

[0070] In this case, a contact pattern 82 is formed on the gate of the P-channel MOS transistor so that the underlying silicon nitride film 60 at the contact pattern 82 can be etched away. The silicon nitride film 60 on the gate of N-channel MOS transistors in the memory cell region and the peripheral circuit region is uniformly etched away.

[0071] By the steps mentioned above, the contact portions 60a, 60bformed on the gates of the N-channel MOS transistor and the P-channel MOS transistor are etched twice. As a result, a contact hole is formed in which the gate polysilicon layer 58 is exposed. At the same time, the silicon substrate 52 is also exposed by etching the silicon nitride film 68 during the etching step. In addition, the plug 106 is exposed in the memory cell region by etching the silicon nitride film 68′.

[0072] The P⁺ layer 74 and the N⁺ layer 80 (serving as a source/drain) formed in the steps mentioned above are activated by applying a heat treatment to them.

[0073] After a SiO₂interlayer film 86 is deposited, the resist 88 is formed in a portion except a contact hole formation portion, as shown in FIG. 4J. Subsequently, contact holes 90a′, 90b, 90b, 90d, 90eare patterned, as shown in FIG. 4K, by selectively etching the interlayer film 86.

[0074] In this case, the contact holes 90a′, 90c, 90eformed respectively on the plug 106, the P⁺ layer 74 and the N⁺ layer 80 are formed in a self-alignment manner to the gates. Whereas, in the contact holes 90b, 90dformed on the gates, a contact with the gate polysilicon layer 58 can be obtained through the contact regions 60a, 60bin which no silicon nitride film 60 is present.

[0075] As shown in FIG. 4L, a wiring layer 92 is formed in the formed contact holes 90a′ and 90bto 90eand on the interlayer film 86.

[0076] In this way, a plug contact may be formed before a deep diffusion layer having an LDD structure is formed by implantation in a portion having a micro patterned pitch between adjacent gates.

[0077] Now, Embodiment 3 will be explained.

[0078] FIGS. 5A to 5G are cross-sectional views of a semiconductor device, showing a manufacturing process which is the same as in Embodiment 1 except that a thin silicon nitride film is deposited before an entire contact hole is etched.

[0079] FIGS. 5A to 5C are the same as FIGS. 3A to 3C regarding Embodiment 1, detailed explanation is omitted.

[0080] After the contact portions 60a, 60bare formed by the process of FIGS. 5A to 5C, a thin silicon nitride film 108 is formed on the surface of the substrate 52, as shown in FIG. 5D.

[0081] As shown in FIG. 5E, after a SiO₂interlayer film 86 is deposited on the thin silicon nitride film 108 and the silicon nitride film 60, a resist 88 is formed on the portion excluding a contact hole formation portion. Then, as shown in FIG. 5F, the contact holes 90ato 90eare patterned and the interlayer film 86 is selectively etched by RIE. In this time, a thin silicon nitride film 108, which is deposited on the P⁺ layer 74, and N⁺ layers 78, 80 (serving as a source/drain) within the contact holes 90ato 90eand on the contact portions 60a, 60bto the gate, is also removed.

[0082] In this case, the contact holes 90a, 90c, 90eformed on the P⁺ layer 74 and the N⁺ layers 78, 80 (serving as a source/drain), are formed in a self-alignment manner to the gates. Whereas, in the contact holes 90b, 90dformed on the gates, contact to a gate polysilicon layer 58 is obtained through contact regions 60a, 60bin which no silicon nitride film 60 is present.

[0083] Subsequently, a wiring layer 92 is formed in the formed contact holes 90ato 90eand on the interlayer film 86, as shown in FIG. 5G.

[0084] According to the method of Embodiment 3, since the thin silicon nitride film and the STI portion serving as the element isolation region have etching selective ratios, respectively, it is possible to prevent an STI portion from being etched during the etching of the contact portion. As a result, the reliability of the process is improved when contact is formed in a self-alignment manner.

[0085] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.