Semiconductor Memory Device Having an Aluminum-Based Metallization Film and a Refractory Metal Silicide-Based Metallization Film

The present invention generally relates to a semiconductor memory device having an aluminum-based metallization film and a refractory metal silicide-based metallization film.

Generally, in a conventional field effect transistor, source and drain regions are formed by a self-alignment process in which a gate electrode is used as a mask film. Therefore, such a gate electrode is formed by using polysilicon having a high heat-resistant property. Polysilicon has a disadvantage in that it's value of electrical resistance is higher than that of an alloy of aluminum-silicon, which is used for forming source and drain electrodes. As in a case of a dynamic random access memory (DRAM) device where a gate electrode of a polysilicon film is used as a word line, a metallization film of an aluminum-silicon alloy is formed on an insulating film positioned in a vicinity of a top surface of the DRAM device, and is connected to the gate electrode of the word line at a suitable position. That is, the aluminum-silicon metallization film is used for improving conductivity of the gate electrode. However, an aluminum-silicon alloy has a disadvantage that heat-resistance is low.

It is also known to use, as a metallization film, a polycide film which is a stacked layer consisting of a polysilicon film and a refractory metal silicide film. Compared with an aluminum-silicon metallization film, a polycide film has a disadvantage of high electric resistance and has advantages of high heat-resistance and high resistance to electromigration and stress-migration.

As can be seen from the aforementioned explanation, metallization materials have both advantages and disadvantages.

Recently, a size of a semiconductor chip of the DRAM device is limited in view of a size of a package which accommodates the semiconductor chip. For example, a standard package has a width (a short side) of approximately 7.5 (mm) (300 (mil)). Therefore, a semiconductor chip is necessarily of a rectangular shape. As a result, in a case where sense amplifiers, bit drivers and column decoders are arranged along the short side of the chip, a bit line pitch which defines a distance between centers of neighboring bit lines, must be necessarily reduced, compared with a word line pitch which defines a distance between centers of neighboring word lines arranged in a direction of a long side of the chip. On the other hand, in a case where a row driver and a row decoder (word decoder) are arranged in the short-side direction of the chip, the word line pitch must be made smaller than the bit line pitch. Therefore, it is required to provide a metallization structure suitable to the rectangular semiconductor chip.

It is therefore a general object of the present invention to provide a novel and useful semiconductor memory device having an aluminum-based metallization film and a refractory metal silicide-based metallization film which can meet the above requirement.

A more specific object of the present invention is to provide a semiconductor memory device in which one of the bit and word lines which has a relatively narrow line pitch is formed by a refractory metal silicide-based metallization film, and the other line which has a relatively wide line pitch is formed by an aluminum-based metallization film. With the above metallization structures, advantageous properties of the refractory metal silicide-based metallization and the aluminum-based metallization can be greatly utilized. A semiconductor memory device having the above-mentioned metallization structure has, an the whole, good conductivity, high heat-resistance and high electromigration and stress-migration resistance. Additionally, the production process can be simplified.

The above objects of the present invention are achieved by a semiconductor memory device which includes a semiconductor substrate; a first insulation film having a contact hole; a plurality of gate electrodes provided so as to be surrounded by the first insulation film; a storage capacitor layer including a pair of electrodes, one of the pair of electrodes being in contact with the semiconductor substrate through the contact hole; an interlayer insulation film formed on the storage capacitor layer; a plurality of bit lines formed on the interlayer insulation film and arranged with a first pitch defining a distance between neighboring bit lines; a second insulation film formed on the bit lines; and a plurality of word lines formed on the second insulation film and arranged with a second pitch defining a distance between neighboring word lines. One of the bit and word lines which has a relatively wide pitch comprises an aluminum-based metallization film, and the other line which has a relatively narrow pitch comprises a refractory metal silicide-based metallization film.

The above objects of the present invention are also be achieved by a semiconductor memory device comprising a semiconductor substrate; a first insulation film having a contact hole; a plurality of gate electrodes provided so as to be surrounded by the first insulation film and arranged with a first pitch defining a distance between neighboring gate electrodes; a storage capacitor layer including a pair of electrodes, one of the pair of electrodes being in contact with the semiconductor substrate through the contact hole; an interlayer insulation film formed so as to cover the storage capacitor layer; and a plurality of bit lines formed on the interlayer insulation film and arranged with a second pitch defining a distance between neighboring bit lines. Each of the gate electrodes comprises a refractory metal silicide-based metallization film, and each of the bit lines comprises an aluminum-based metallization film.

Other objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.

FIG. 1 is a plan view of an essential portion of a semiconductor memory device of a preferred embodiment of the present invention;

FIG. 2 is a cross sectional view taken along a line II--II shown in FIG. 1;

FIG. 3 is a plan view of a chip of the semiconductor memory device; and

FIG. 4 is a cross sectional view of another preferred embodiment of the present invention.

The present invention is based on the following viewpoints in order to obtain metallizations suitable for the aforementioned semiconductor chip in which it is necessary to reduce the line pitch in the short side of the semiconductor chip. Since polysilicon has high resistance, polysilicon is suitable neither for a word line metallization film which contributes to enhancing conductivity of the gate electrodes, nor for a bit line. An aluminum-based metallization such as pure aluminum and an alloy of aluminum and silicon has poor heat-resistant properties and poor electromigration and stress-migration resistance. On the other hand, the aluminum-based metallization has greatly low resistance, and is always employed in a peripheral circuit portion of the DRAM device such as a decoder circuit, a sense amplifier and a logic circuit. From the above reasons, it is advantageous to using the aluminum-based metallization provided in a memory cell portion of the DRAM device from the viewpoint of improvement in performance and manufacturing process.

It is noted that a metallization pattern of an electrode or wiring interconnection decreases in cross section as the width thereof decreases. As a result, the current density of current which flows through the metallization pattern increases, which shortens a lifetime of the device. It is noted that the lifetime depends exponentially on the current density. A reduction of the life time due to electromigration and stress-migration is different depending on material. The lifetime of a refractory metal silicide metallization film is much longer than that of the aluminum-based metallization.

From the aforementioned viewpoints, in the present invention, one of the bit and word lines which has a relatively narrow line pitch is formed by a refractory metal silicide-based metallization, and the other line which has a relatively wide line pitch is formed by an aluminum-based metallization. With the above metallization structures, advantageous properties of the refractory metal silicide-based metallization and the aluminum-based metallization can be greatly utilized. A semiconductor memory device having the above-mentioned metallization structure has good conductivity, high heat-resistance and high electromigration and stress-migration resistance.

A description is given of a preferred embodiment of the present invention with reference to FIGS. 1 and 2. FIG. 1 is a plan view of an essential portion of a semiconductor memory device of the preferred embodiment, and FIG. 2 is a cross sectional view taken along a line II--II of FIG. 1.

Referring to FIGS. 1 and 2, a field insulation film 12 of a silicon dioxide film is formed on a main surface of a p-type silicon substrate 11 by selective thermal oxidation. A gate insulation film 13 is formed on the surface of the silicon substrate 11 by thermal oxidation. A polysilicon film is formed by chemical vapor deposition and is then patterned by the conventional photolithography technology. Thereby gate electrodes (word lines) of polysilicon films 14.sub.1, 14.sub.2, 14.sub.3 are formed as shown in FIG. 2. Thereafter, n.sup.+ -type regions 15.sub.1 and 16.sub.1 are formed by doping the silicon substrate 11 with arsenic (As) ions by a conventional self-alignment process. The region 15.sub.1 is a source region, or a bit line contact region, and the region 16.sub.1 is a drain region, or a contact region to a storage capacitor electrode. An interlayer insulation film 17 is formed on the entire surface by chemical vapor deposition. Contact holes are formed in the interlayer insulation film 17 by anisotropic etching. Then a polysilicon film 20 is formed by chemical vapor deposition and is then patterned by the conventional photolithography technology. Thereby a storage electrode 18.sub.1 is formed so as to be in contact with the n.sup.+ -type drain region 16.sub.1. The storage electrodes 18.sub.1 are then subjected to thermal oxidation to form a dielectric film (not shown) around the storage electrodes 18.sub.1. An opposed electrode (called a cell plate) 19.sub.1 is formed by depositing a polysilicon film and patterning the deposited polysilicon film. The opposed electrode 19.sub.1 is the other electrode out of the paired electrodes of the memory cell capacitor. An interlayer insulation film 20 is deposited to the entire surface. A contact hole to the source region 15.sub.1 is formed in the interlayer insulation film 20 and the gate insulation film by anisotropic etching. A polysilicon film 21.sub.1 formed on the entire surface by chemical vapor deposition. Subsequently, a tungsten silicide film 22.sub.1 is formed on the polysilicon film 21.sub.1 by sputtering. The polysilicon film 21.sub.1 and the tungsten silicide film 22.sub.1 are subjected to a patterning process based on the conventional photolithography technology. Thereby, bit lines 30.sub.1 and 30.sub.2 each consisting of the patterned polysilicon film 21.sub.1 and tungsten silicide film 22.sub.1 are formed. Then a passivation film 23 of a phosphosilicate glass (PSG) film is formed. Then an aluminum-based metallization film such as a pure aluminum film and an alloy film of aluminum and silicon is formed on the phosphosilicate glass film 23, and is then patterned. Thereby word lines 24.sub.1, 24.sub.2 and 24.sub.3 are formed. The word lines 24.sub.1, 24.sub.2 and 24.sub.3 are connected to related gate electrodes 14.sub.1, 14.sub.2 and 14.sub.3, and contribute to improving conductivity of the gate electrodes 14.sub.1, 14.sub.2 and 14.sub.3. In FIG. 1, MC indicates a memory cell portion which amounts to 2 bits.

As can be seen from FIG. 1, the memory cell portion MC has a rectangular shape and has long sides along which the bit lines 30.sub.1 and 30.sub.2 extend, and short sides along which the word lines 24.sub.1 and 24.sub.2 extend. The rectangular shape of the memory cell portion MC is necessarily determined depending on a shape of the semiconductor chip on which the memory cell portion MC is formed. That is, the shape of the chip has a rectangular shape, and therefore has long sides along which the bit lines 30.sub.1 and 30.sub.2 extend, and short sides along which the word lines 24.sub.1 and 24.sub.2 extend.

FIG. 3 is a schematic plan view of the semiconductor chip of the DRAM device. The chip comprises four identical blocks 100, 200, 300 and 400, and another block 500. Each of the blocks 100, 200, 300 and 400 includes two memory cell arrays 110 and 111, two sense amplifiers 112 and 113, two column decoders 114 and 115, and two row decoders 116 and 117. The block 500 is a logic circuit. Each of the memory cell arrays 110 and 111 has a plurality of memory cells which are arranged in the form of a matrix. Pads 120 are provided on the chip along short sides of the chip.

As shown in FIGS. 1 and 3, the sense amplifiers 112 and 113 are arranged in the short-side (width) direction of the chip, it is required to set a bit line pitch (P1) of the bit lines 30.sub.1 and 30.sub.2 narrower than a word line pitch (P2) of the word lines 24.sub.1 and 24.sub.2. As described previously, electromigration and stress-migration increase as the width of the metallization becomes narrow. From this reason, the bit lines 30.sub.1 and 30.sub.2 are constituted by polycide films, each of which consists of sequentially stacked polysilicon and tungsten silicide films, as described before. On the other hand, the word line pitch P2 of the word lines 24.sub.1 and 24.sub.2 can be wider than the bit line pitch P1. Therefore, electromigration and stress-migration occur less in the word lines 24.sub.1 and 24.sub.2 than in the bit lines 30.sub.1 and 30.sub.2. From the above reason, the word lines 24.sub.1 and 24.sub.2 are constituted by aluminum-based metallization films, as described before. With this metallization structure, good conductivity of the word lines 24.sub.1 and 24.sub.2 can be obtained.

The aforementioned structure provided by the present invention is advantageous particularly to DRAM devices. This is because DRAM devices are based on changing up/discharging operations with respect to memory cell capacitors. On the other hand, in SRAM devices, EPROM devices and mask ROM devices, a current is passed through a bit line, and a high-speed operation is particularly required. From these viewpoints, aluminum-based metallization films are generally used for forming bit lines.

A description is given of another preferred embodiment of the present invention with reference to FIG. 4. In FIG. 4, those parts which are the same as those in the previous figures are given the same reference numerals.

An essential feature of the embodiment of FIG. 4 is that gate electrodes 44.sub.1, 44.sub.2, . . . are constituted by polycide films, and bit lines 22.sub.1A, . . . are constituted by aluminum-silicon alloy films. The gate electrode 44.sub.1 consists of a patterned polysilicon film 44.sub.1A and a patterned tungsten silicide film 44.sub.1B. In the embodiment of FIG. 4, row decoders (not shown) are arranged in the short-side direction of the chip, and sense amplifiers (not shown) are arranged in the long side direction thereof. Therefore, the pitch P2 of the neighboring gate electrodes (or word lines) must be smaller than that (P1) of the neighboring bit lines. It is noted that since the conductivity of the polycide gates electrodes 44.sub.1, 44.sub.2, . . . is better than that of a polysilicon film, the gate electrodes 44.sub.1, 44.sub.2, . . . can be used as word lines by themselves. In other words, additional word lines such as the word lines 24.sub.1 and 24.sub.2 are not necessary to obtain satisfactory conductivity of word lines.

In the above embodiments, the tungsten silicide films 22.sub.1, 44.sub.1B and 44.sub.2B can be substituted with molybdenum silicide, tantalum silcide or titanium silicide films.

The present invention is not limited to the aforementioned embodiments, and variations and modifications may be made without departing from the scope of the present invention.