Improvements in or relating to electrodes for LSI

Abstract: In the capacitor, electrode, or wiring having alpha ray emitting source (in particular, Pt electrode), a layer (alpha ray shielding layer) (18), which has at least one type selected from the group of nickel, cobalt, copper, and tungsten, their compounds or alloys made of at least two types of them, and compounds and alloys made of them and silicon is provided. It is possible to shield off the alpha ray effectively, to suppress generation of soft errors, to enable use of Pt and other new materials in making the electrodes and wiring, and to reduce the cost of the mold resin.

Description: Detailed explanation of the invention Industrial application field This invention concerns a type of capacitor, electrode or wiring structure, and semiconductor device characterized by the fact that there is an insulating layer (in particular, a ferroelectric layer made of metal oxides). Prior art For the large-scale integrated circuit (LSI), the phenomenon in which the memory content disappears temporarily without accompanying the physical damage of the device structure is known as a soft error. The main reason for the soft error is the alpha ray generated by the minute amount of radioactive nuclear seeds contained in the material of the LSI. Among the materials that form the LSI, for silicon, oxygen, nitrogen, boron, phosphorus, arsenic, aluminum, titanium, tungsten, and copper, there are no natural radioactive isotopes, and the main sources of the alpha ray are uranium (U) and thorium (Th) contained as impurities. In order to alleviate the soft error of LSI, it is necessary to reduce the content of uranium and thorium to the ppb level in the structural materials of the LSI. On the other hand, there is still a high demand for increasing the degree of integration of the LSI. For this purpose, the oxide film-nitride film-oxide film structure (the so-called ONO structure) is adopted, and the steric structure of the cell capacitor of the dynamic random-access memory (DRAM) becomes more complicated. The reason is as follows: as the effective specific dielectric constant is selected at about 5 for the ONO structure, in order to ensure the electrical capacitance of the cell capacitor with respect to the shrinking cell area, efforts can be made only on the shape of the cell capacitor in order to guarantee the area. This, however, increases the burden on the manufacturing operation of a DRAM with respect to both technology and cost. In order to solve this problem, study is conducted using oxides with a high permittivity such as tantalum oxide (Ta 2 O 5 ), strontium titanate (SrTiO 3 ), BST (Ba x Sr (1-x) Ti O 3 ), PZT (PbZr x Ti (1-x) O 3 ), etc., as insulating materials of cell capacitor. The most significant difference between these substances and silicon oxide and nitride is that it has a higher oxidizing power for silicon. Consequently, using a silicon electrode with these new types of insulating materials and selecting a type of material with a high oxidation resistance as the electrode is possible. At present, platinum is believed to be the candidate for this purpose. However, platinum differs from the conventional elements used as the materials for LSIs in that it contains a radioactive isotope that emits alpha rays, that is, Pt 190 that can emit alpha rays with a kinetic energy of 3.18 MeV in 5.4 x 10 11 of radioactive half-life. The content of Pt 190 in platinum is 0.013%, and it is very difficult to isolate it when cost is a consideration. If the alpha ray level cannot be alleviated using certain methods, it is impossible to reduce the soft error level to the appropriate level for commercially using the platinum electrodes in manufacturing DRAMs. For example, when a 2000-Å-thick platinum film (1 Å = 0.1 nm) is formed on a silicon substrate, the dose of the alpha ray emitted from the platinum film into silicon is 0.02 photon/h·cm 2 . That is, one alpha ray photon on 10 cm 2 for 50 h. This calculated result is the number of alpha ray photons emitted from Pt into silicon. For the DRAM, the soft error should be in the range of 500-1000 FIT (failure in time, where 1 FIT means that a defect takes place in 1 device among 10 9 devices in 1 h). That is, 1000 FIT means that one soft error takes place in 1000 h for 1000 DRAMs. When the size of the DRAM's cell array portion is about 1 cm 2 , the frequency for the soft error is on the order of about 10 -6 photon/h·cm 2 . Although not every alpha ray photon can lead to a soft error, the aforementioned value of 0.02 photon/h·cm 2 (the measured value is 0.007 photon/h·cm 2 ) is still too high. On the other hand, if the amount of U, Th, and other radioactive elements in platinum can be kept to less than 10 ppb, it is acceptable to ignore the influence of the alpha ray caused by these radioactive elements. Conventional ferroelectric memory devices are known from JP-A-4 014 862 and JP-A-5 275 711, for example. Let us discuss the effect in alleviating the influence of the alpha ray generated by the platinum electrode in the conventional structure. When a ferroelectric material and platinum electrode are used corresponding to the DRAM, the COB (capacitor over bitline) structure shown in Figure 16 is adopted for the following two purposes: to ensure the area of the cell capacitor and to prevent degradation of the cell capacitor portion in the high-temperature heat treatment for forming the other portions. In this COB structure, a stack-type cell capacitor CAP is formed on the upper portion of wordline WL and bitline BL. Polysilicon (20) is used as the contact between lower (platinum) electrode (16) of cell capacitor CAP and n + -type diffusion layer (3) (source region) of silicon substrate (1). In this figure, (2) represents a field oxide film; (4) represents an n + -type diffusion layer (drain region); (5) represents a gate oxide film; (8) represents an upper or first electrode; (10) and (10') represent interlayer insulating films; (11) and (12) represent contact holes; (17) represents a dielectric material (such as PZT) film; and TR represents a transfer gate. However, for the aforementioned cell capacitor CAP, the height of polysilicon contact (20) arranged beneath lower or second (platinum) electrode (16) is at most 1 µm. By means of this silicon portion, the energy of the alpha ray generated by Pt 190 in lower electrode (16) can be reduced to only about 3 MeV. This energy is still high enough to cause a soft error. Problems to be solved by the invention The purpose of this invention is to provide a type of capacitor, electrode or wiring structure, and DRAM or other semiconductor device using them characterized by the fact that, even when platinum or some other electroconductive material is used as the electrode, etc., it is still possible to shield the alpha ray effectively in order to prevent the soft error. Means for solving the problems The above mentioned problems are solved by a device as claimed in claim 1. Further embodiments are defined in the dependent claims. In particular, this invention is effective when the capacitor insulating layer is made of tantalum oxide (Ta 2 O 5 ), strontium titanate (SrTiO 3 ), barium strontium titanate (Ba x Sr (1-x) TiO 3 : BST), or lead zirconate titanate (PbZr x Ti (1-x) O 3 : PZT); and the second electrode layer and/or the first electrode layer contains platinum. Brief description of figures Reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a schematic cross-sectional view of the capacitor in an application example of this invention. Figure 2 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 3 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 4 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 5 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 6 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 7 is a schematic cross-sectional view of the capacitor in another application example of this invention. Figure 8 is an enlarged cross-sectional view (cut along line VIII-VIII of Figure 9) illustrating the memory cell of the dynamic RAM incorporated in the capacitor with a COB structure according to this invention. Figure 9 is an enlarged plan view of the aforementioned memory cell. Figure 10 is an enlarged cross-sectional view (cut along line X-X of Figure 11) illustrating the memory cell of another dynamic RAM incorporated in the capacitor with a CUB structure according to this invention. Figure 11 is an enlarged plan view of the aforementioned memory cell. Figure 12 is a diagram illustrating data of the alpha ray stopping thickness of the various elements. Figure 13 is a diagram illustrating the data of alpha ray stopping power of the various elements. Figure 14 is an enlarged cross-sectional view of the dynamic RAM incorporated in the structure of this invention. Figure 15 is an enlarged cross-sectional view of another dynamic RAM incorporated in the structure of this invention. Figure 16 is an enlarged cross-sectional view of the memory cell of the dynamic RAM incorporated in the capacitor with a COB structure in the conventional example. Application examples In the following, this invention will be explained in more detail with reference to application examples. Figures 1-7 are diagrams schematically illustrating the various examples of the capacitor of this invention using ferroelectric film of metal oxides. In the characteristic configuration of the capacitor shown in Figure 1, platinum (Pt) is used to manufacture lower electrode (16) of ferroelectric film (17) made of tantalum oxide, strontium titanate, barium strontium titanate (BST), or lead zirconate titanate (PZT), and a conductive layer (18) made of compounds or alloys made of at least two types of the simple metals of Ni, Co, Cu, and W, and compounds or alloys made of these simple metals with silicon is arranged beneath said lower electrode (16). For example, ferroelectric film (17) may be made of a PZT film, lower electrode (16) may be made of a Pt layer, and conductive layer (18) may be made of a Ni layer. The upper electrode (8) may be made of Al or Ti. Electroconductive diffusion barrier layers (13') and (13) (such as a W layer) with small diffusion coefficients are arranged between conductive layer (18) and lower electrode layer (16) and between conductive layer (18) and hard-wire layer (3), respectively, for preventing diffusion of said Ni, etc. inside conductive layer (18), to the other portions. Hard-wire layer (3) may be made of a polysilicon layer. As shown in Figure 4, it may also be an n + -type semiconductor region (3) formed using the diffusion method on P - type silicon substrate (1) (in this case, the so-called conductive layer (18) is used as the so-called contact; (10) in the figure represents an insulating layer). Said ferroelectric film (17) may be manufactured using the conventional sol-gel method, CVD method, or the sputtering method to a thickness in the range of 0.05-10 µm. Also, the thickness of said lower electrode (16) may be in the range of 0.05-1 µm. Said conductive layer (18) has a thickness in the range of 0.9-1.3 µm; diffusion barrier layers (13') and (13) have thicknesses in the range of 0.01-1 µm; and the thickness of upper electrode (8) is in the range of 0.01-10 µm. Said layers (18), (13'), (13), (8), and (16) may be formed using the conventional sputtering method and vacuum deposition method. In the capacitor shown in Figure 1, the configuration of the diffusion barrier layer may be varied. For example, it is possible to arrange it beneath conductive layer (18) alone as shown in Figures 2 and 5, or to arrange it above conductive layer (18) alone as shown in Figures 3 and 6; also, it may not be arranged as shown in Figures 3 and 7. The aforementioned capacitor and its electrode structure of this invention explained in the above can be used preferably for the capacitor (such as a stack-type capacitor) of the memory cell of the dynamic RAM. Figures 8-11 illustrate two examples of the memory cells of the dynamic RAM. In the example illustrated in Figures 8 and 9, element regions defined by field oxide film (2) are formed on one principal surface of p - -type silicon substrate (1). Here, transfer gate TR made of MOS transistor and memory cell M-CEL made of capacitor CAP are arranged. Capacitor CAP has the same substrate structure schematically illustrated in Figure 4, and a so-called COB structure is formed on the upper portion from bitline BL connected to n + -type diffusion region (drain region) (4) through contact hole (11), and conductive layer (18) is used as a contact with respect to n + -type diffusion region (source region) (3) (where, (10) and (10') represent the interlayer conductive layers). Figures 10 and 11 illustrate examples of the so-called CUB (capacitor under bitline) structure with capacitor CAP arranged in the lower portion from bitline BL. Otherwise, this example is identical to the aforementioned example. As explained above, by using the capacitor of this invention, a Pt electrode with a high oxidation resistance is arranged in contact with ferroelectric film (17) with a high dielectric constant as lower electrode (16). Said conductive layer (18) is arranged to shield off the alpha ray. In this way, it is possible to prevent especially the phenomenon of a soft error caused by the alpha ray emitted from the Pt electrode to reach the side of the semiconductor substrate. The details for measure of an alpha ray are explained as follows. Usually, when the alpha ray emitted from Pt electrode (16) reaches the side of the semiconductor substrate, the change of cell capacitor CAP is reduced by the electrons generated by the alpha ray (more specifically, the charge stored in source region (3)), and the memory content stored in cell capacitor CAP drops to an undiscernable level. However, if there is little change in the charge of the capacitor even when the alpha ray passes through the layer, the memory is not erased. Here, the proportion of the electrons generated by the alpha ray and collected by the cell capacitor (the collection efficiency) is κ, the amount of electricity stored in the capacitor is Qs, and the absolute value of the electricity of the electrons is e. Also, the energy of the alpha ray when it is incident on the diffusion layer is Ea, and the energy needed for forming an electron/hole pair is ε pair . The condition for no erasure of the memory content of the capacitor by the alpha ray can be represented by the following formula: 0.4 (Qs/κe) ε pair > Ea In this case, suppose the sensitivity of the sense amplifier of the DRAM is designed appropriately to ensure that when about 60% of the charge in the cell capacitor is left, the memory content can be read correctly. The collection efficiency κ has a value depending on the structure, etc. However, when it is 0.1, one out of 10 electrons is collected to the cell capacitor. Then, as Qs is about 3 x 10 -14 C, e = 1.6 x 10 -19 C, and ε pair = 3.6 eV, the aforementioned condition becomes Ea < 2.7 MeV. The energy of the alpha ray generated from Pt 190 is 3.18 MeV. Under the aforementioned conditions, before the alpha ray emitted from the platinum electrode reaches the diffusion layer of the substrate silicon, it is necessary to decrease the energy to 2.7 MeV. For this purpose, an effective measure is to arrange an alpha ray shielding material in the lower portion of Pt electrode (16). Another method for preventing the alpha ray is to remove Pt 190 from the platinum. However, this is impossible in consideration of the cost of the refinement operation. In addition, although the problem can be solved if platinum is not used as the electrode, a substituting electrode is needed. This is nevertheless difficult to realize. For the alpha ray shielding materials made of the typical elements or alloys, the thicknesses needed for decreasing the energy of the alpha ray incident at an energy of 3.18 MeV to an energy of 2.7 MeV were derived using the Bethe Bloche formula (see "Butsurigaku Daijiden" [Dictionary of Physics], published by Baifukan, "Ionization loss" section), with results shown in Figure 12. As can be seen from Figure 12, the ranges of flight of alpha rays when the energy of the alpha ray becomes 2.7 MeV, that is, the thicknesses of the shielding materials, are listed in the following Tables I and II. The shielding powers of the various elements and alloys with respect to the alpha ray, that is, the alpha ray stopping powers (the energy decay rate for unit thickness), are shown in Figure 13. The data of the alpha ray stopping power for realizing the aforementioned necessary attenuation (0.48 MeV) from 3.18 MeV to 2.7 MeV are also listed in the following Tables I and II. Thickness needed for decreasing the energy of the alpha ray incident at an energy of 3.18 MeV to 2.7 MeV (µm) Silicon Aluminum Titanium Copper Cobalt Nickel Tungsten 2.16 µm 1.88 µm 1.48 µm 0.88 µm 0.87 µm 0.86 µm 1.04 µm Alpha ray stopping power (MeV/µm) 0.222 MeV/µm 0.255 MeV/µm 0.324 MeV/µm 0.545 MeV/µm 0.551 MeV/µm 0.560 MeV/µm 0.462 MeV/µm Thickness needed for decreasing the energy of the alpha ray incident at an energy of 3.18 MeV to 2.7 MeV (µm) Wsi 2 W 5 Si 3 Cu 56 Ni 45 Ni 2 Si 1.19 µm 1.06 µm 0.84 µm 0.84 µm Alpha ray stopping power (MeV/µm) 0.403 Mev/µm 0.453 Mev/µm 0.571 Mev/µm 0.571 Mev/µm From the results, in order to realize the attenuation needed for the energy of the alpha ray, the thickness for silicon, aluminum, and titanium becomes as high as that of the contact connecting the silicon substrate and platinum lower electrode. This is too high, and this is inappropriate. On the other hand, as shown in Figure 13, copper, cobalt, nickel, Cu 55 Ni 45 , and Ni 3 Si have high alpha ray stopping power in this energy region. If the height of the contact is larger than 1.1 µm, although the stopping power of tungsten, WSi 2 , or W 5 Si 3 is not as high as copper, it is possible to decrease the energy of the alpha ray emitted from platinum in the electrode to the desired level. This alpha ray stopping power is effective with respect to the alpha ray emitted from the platinum electrode, and it is also effective for the alpha ray emitted from the other sources (including the external portion of the semiconductor device). Usually, the substance with a high alpha ray stopping power has a high density and a low mean ionization energy. As the atomic number is increased, the density rises, while the mean ionization energy increases. The elements with high alpha ray stopping power include Co (atomic number 27), Ni (atomic number 28), and Cu (atomic number 29) as explained above. However, for W (atomic number 74) with a higher atomic number, the alpha ray stopping power is high when the alpha ray energy is high. In the vicinity of 3 MeV, where a problem takes place, there is a certain decrease in the alpha ray stopping power, yet it is still relatively high. For Fe (atomic number 26) as a neighbor of Co, the density is not very high, and the alpha ray stopping power is inappropriate. Based on the aforementioned data, for the structure in the application example of this invention (such as the cell in Figure 8), there is a type of film capacitor, its electrode structure or the contact structure of the silicon substrate characterized by the fact that, instead of the conventional types of contact materials, such as polysilicon, aluminum, titanium, and compounds and alloys of these elements, the material selected from alloys or compounds made of at least two of copper, cobalt, nickel, and tungsten as simple metals, or alloys or compounds made of the aforementioned simple metals and silicon, with excellent alpha ray stopping power even with a small thickness, is used as the alpha ray shielding material (said conductive layer (18)). Figure 14 is a diagram illustrating another application example of the memory cell of a dynamic RAM having alpha ray shielding material based on this invention. In this application example, the characteristic feature different from the aforementioned example (such as the example shown in Figure 8) is as follows: in the memory cell using platinum in manufacturing bitline BL, contact (28) is formed out of the same type of alpha ray shielding material as above, such as Cu, Co, Ni, W, their compounds or alloys, or their compounds or alloys with silicon. Consequently, in the configuration of this application example, the same effect as above can be realized. In addition, for bitline BL made of platinum, as it has a high electroconductivity, the operation speed can be increased, and, at the same time, the alpha ray emitted from bitline BL can be effectively shielded off by a shielding material (contact) (28). Consequently, it is possible to prevent or suppress invasion of the alpha ray into the n + -type diffusion region (4), and it is possible to reduce the occurrence of soft errors caused by bitline BL. Figure 15 is a diagram illustrating yet another application example of the memory cell of the dynamic RAM having an alpha ray shielding structure. In addition to the features in the aforementioned examples (such as the examples illustrated in Figures 8 and 14), there is the following characteristic feature: interlayer insulating film (10), (10'), or (10'') is made of the same type of material as the aforementioned alpha ray shielding material, such as Cu, Co, Ni, or W (or their compound or the compound or alloy made of these elements and silicon). This type of interlayer insulating layer can be formed easily by means of sputtering of CuO, etc. Consequently, for the configuration in this application example, the same effects of the aforementioned examples can be realized. Also, it is possible to reduce or prevent the alpha ray emitted from U, Th, or other radioactive elements, unavoidably contained in the filler (such as SiO 2 , etc.) added for adjusting the thermal expansion coefficient in mold resin (21), from invading the silicon substrate, and it is possible to reduce the soft errors by using mold resin (20). Usually, when the pretreatment of silica is performed until the content of the aforementioned radioactive elements in the mold resin becomes 10 ppb or less, the cost of the treatment becomes high. On the other hand, in this application example, although this treatment is not performed, the alpha ray shielding effect of interlayer insulating layer (10), (10'), or (10'') is able to reduce the soft errors. Consequently, the cost can be reduced. Also, the aforementioned alpha ray shielding layer can be used for all of interlayer insulating layers (10), (10'), and (10''), the effect can be displayed even when it is used in making only one of these layers. Said alpha ray shielding layers (18), (28), etc., can be made of at least two of the metals of Cu, Ni, Co, and W, their compounds or alloys, or their compounds or alloys with silicon. Also, these elements may be added with a prescribed proportion into other layers made of other elements (such as Si) to form an alpha ray shielding layer. In this case, the content added may be in the range of 40-100 mol%, preferably in the range of 70-100 mol%. In addition to the contact of the bitline explained above, the alpha ray shielding layer can also be arranged in the lower portion of the other metal wiring made of Pt to display the alpha ray stopping power. This is effective for devices other than the aforementioned dynamic RAM. In the aforementioned cell capacitor, lower electrode (16) contains Pt. When upper electrode (8) also contains Pt, or both electrodes contain Pt, the same alpha ray shielding structure as explained above can be adopted. The layered structure of the cell capacitor is not limited to that explained above. For example, in the example shown in Figure 8, diffusion barrier layers (13) and (13') are omitted, or one diffusion barrier layer (such as (13')) is omitted, while the other layer is arranged. When a diffusion layer is arranged, it is possible to form the diffusion barrier layer using Ti, W ruthenium (Ru) or their mixture. Also, it may be used as a contact. For the diffusion barrier layer, as shown in Figure 14, the same structure as above may be adopted for the bitline and wiring. In addition, it is possible to change the material of ferroelectric film (17), the layout of the cell, etc. Also, this invention can be adopted for various devices in addition to the aforementioned dynamic RAM. Effects of the invention As explained above, in this invention, for the capacitor having an alpha ray source, electrode or wiring, and a layer made of compounds or alloys made of at least two of simple metals of nickel, cobalt, copper, and tungsten, and compounds or alloys made of the aforementioned simple metals and silicon is arranged. In this way, this layer is able to shield the alpha ray effectively so that generation of the soft errors can be suppressed. Consequently, it is possible to use Pt or some other new material as the electrode or wiring, so that the cost of the mold resin can be reduced.

Claims: An electrically conductive component in an integrated circuit device having a semiconductor substrate (1), said electrically conductive component comprising: a first layer (16) of an electrically conductive metal susceptible to providing an alpha ray emission; and a second electrically conductive layer (18) having an alpha ray shielding characteristic disposed between said first electrically conductive layer (16) and the semiconductor substrate (1) of the integrated circuit, wherein the alpha ray shielding characteristic is effective to decrease the energy of the alpha ray emission from the first layer (16) of an electrically conductive metal susceptible to providing an alpha ray emission to a level no greater than substantially 2.7 MeV, said second electrically conductive layer (18) having the alpha ray shielding characteristic being made of a metal compound or metal alloy, including at least two metals selected from the group consisting of nickel, cobalt, copper and tungsten or a silicon-containing metal alloy including a metal selected from the group consisting of nickel, cobalt, copper and tungsten. The electrically conductive component described in claim 1, wherein the first layer (16) contains platinum. The electrically conductive component described in claim 1 or 2, wherein a diffusion barrier layer for preventing diffusion of the metal of the second electrically conductive layer (18) is formed between the first layer (16) and the second electrically conductive layer (18) and/or in the lower portion of the second electrically conductive layer (18). A type of capacitor having the electrically conductive component of claim 1 comprising a first electrode layer, an insulating layer formed in contact with the first electrode layer, a second electrode layer formed as the opposite layer with respect to the first electrode layer via the insulating layer, and the second conductive layer (18) being formed on the side of the second electrode layer. The capacitor described in claim 4, wherein the insulating layer is made of tantalum oxide, strontium titanate, barium strontium titanate, or lead zirconate titanate; and the second electrode layer and/or the first electrode layer contains platinum. The capacitor described in claim 4 or 5, wherein a diffusion barrier layer for preventing diffusion of the metal of the second conductive layer (18) is formed between the second electrode layer and the second conductive layer (18), and/or in the lower portion of the second conductive layer (18). A type of semiconductor device according to any one of claims 1-6.

Inventors: AOKI KATSUHIRO, FUKUDA YUKIO, NISHIMURA AKITOSHI, NUMATA KEN, AOKI, KATSUHIRO, FUKUDA,YUKIO, NISHIMURA,AKITOSHI, NUMATA, KEN
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1995
Main classification: H01L27
IPC codes: H01L21, H01L23, H01L27