JPH0794680A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE:To improve contact with a substrate without sacrifice of oxygen barrier properties while preventing production of hillock in the formation of a conductive oxide electrode. CONSTITUTION:When a two layer electrode of ruthenium oxide (RuO2) 5/ Ruthenium(Ru) 4 is formed as the lower electrode of a capacitor on a semiconductor substrate using a dielectric oxide film 6, a first layer 4 of Ru is grown under the conditions that 300Angstrom <d<500Angstrom and 300 deg.C<Ts<450 deg.C where (d) is the film thickness and Ts is the substrate temperature whereas a second layer 5 of RuO2 is grown under the conditions that 1000Angstrom <d<3000Angstrom and 350 deg.C<Ts< 700 deg.C. A conductive oxide 5 is also grown as the lower electrode of the capacitor under a lowest crystal growth temperature or at a highest growth rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a two-layer film of a conductive oxide such as ruthenium oxide (RuO ₂ ) and ruthenium (Ru) as a lower electrode of a capacitor. Regarding

Along with the high integration and miniaturization of DRAMs, oxide dielectrics having a high dielectric constant have been studied as dielectric films for capacitors. At this time, a conductive oxide is often used as the lower electrode of the capacitor.

[0003]

2. Description of the Related Art In a current DRAM having a memory cell composed of one transistor / one capacitor, the lower electrode of the capacitor must be connected to the source / drain of the transistor. Therefore, the lower electrode is silicon (Si)
It is composed of a diffusion layer provided on the substrate or a metal film formed on a silicon substrate.

When an oxide dielectric film is formed by using silicon as an electrode, a silicon dioxide (SiO ₂ ) film is formed on the interface and the effective dielectric constant is lowered. When forming a metal electrode on silicon, a composite electrode of platinum (Pt) / tantalum (Ta) has been studied, but when an oxide dielectric film is formed on it, platinum permeates oxygen. As a result, tantalum is actually oxidized and it becomes impossible to make contact with the silicon substrate.

For this reason, conductive oxide electrodes having excellent oxygen barrier properties have been investigated. The RuO ₂ / Ru two-layer structure electrode as a conductive oxide electrode has the RuO ₂ layer as an effective oxygen barrier, and the underlying Ru layer functions as an oxygen barrier layer layer when forming the RuO ₂ layer. .

[0006]

When an electrode having a two-layer structure of RuO ₂ / Ru is formed on a silicon substrate, first, a Ru layer formed by silicidation of Ru formed directly on silicon and
The unevenness of the RuO ₂ layer becomes a problem. Also, depending on the film thickness of each layer, hillocks (protrusions) are generated in the RuO ₂ layer due to strain due to stress. It was also found that there is a critical film thickness for the barrier property against oxygen in the RuO ₂ layer.

In addition, the conductive oxide generally used as the lower electrode easily forms columnar crystals, which causes a problem that oxygen is allowed to pass through the crystal grain boundaries. The present invention does not impair the oxygen barrier property in forming an oxide conductive electrode, for example, an electrode having a two-layer structure of RuO ₂ / Ru,
Moreover, the purpose is to prevent the generation of hillocks on the electrodes.

[0008]

[Means for Solving the Problems] 1)
When forming a ruthenium oxide (RuO ₂ ) / ruthenium (Ru) two-layer structure electrode as the lower electrode of a capacitor using an oxide dielectric film on a semiconductor substrate, the growth conditions for the first Ru film are The film thickness d is 300Å <d <500Å, the substrate temperature T _S is 300 ° C. <T _S <450 ° C., and the second layer of RuO ₂
As a film growth condition, a film thickness d is set to 1000Å <d <3000Å and a substrate temperature T _{S is set} to 350 ° C. <T _S <700 ° C., or 2) an oxide dielectric film on a semiconductor substrate. This can be achieved by a method of manufacturing a semiconductor device in which a conductive oxide is grown as the lower electrode of a capacitor using GaN at the lowest temperature or the highest growth rate that allows crystal growth.

[0009]

The present inventor has experimentally confirmed the following range as the growth conditions of RuO ₂ / Ru that does not impair the oxygen barrier property and does not cause hillocks in the formation of a RuO ₂ / Ru two-layer structure electrode. (1) As the growth condition of the first Ru layer, the film thickness d is 300Å
<D <500Å, growth temperature (substrate temperature) T _S is 300 ° C
<T _S <450 ° C. (2) As the growth condition of the _second RuO ₂ layer, the film thickness d is 1000
Å <d <3000Å, growth temperature (substrate temperature) T _S of 350
℃ <T _S <700 ℃.

The RuO ₂ / Ru two-layer structure electrode grown under these conditions can suppress formation of hillocks on the surface of RuO ₂ and undulation of the surface, and has excellent oxygen (O ₂ ) barrier property. Can be formed (see FIG. 2).

Further, in general, when the oxide conductive electrode is grown, it is grown at the minimum crystal growth temperature or is grown at a high speed in order to suppress the growth of the columnar crystals. next,
Experimental results will explain how disadvantages occur when the above limit is exceeded. In contrast to (1), 300Å> d: In the region below the limit value indicating the oxygen barrier effect of the Ru film, the Si surface is oxidized in this case.

D> 500Å: hillock formation occurs due to stress. 300 ° C.> T _S : Crystallinity deteriorates. T _S > 450 ° C .: Hillock is formed. In contrast to (2), 1000Å> d: The barrier property against oxygen is not sufficient, and a large amount of oxygen leaks to the underlying Ru film.

D> 3000Å: hillock formation occurs due to stress. 350 ° C.> T _S : The crystallinity is poor, and when a high dielectric film is formed on top, it reacts with it.

T _S > 700 ° C .: RuO ₂ decomposition occurs. In addition, columnar crystals are formed.

[0015]

1 (A) to 1 (D) are sectional views for explaining an embodiment of the present invention. In FIG. 1 (A), the substrate 1 a silicon dioxide (SiO ₂₎ as an interlayer insulating film on the film 2 is formed, opening in the SiO ₂ film 2 of the lower electrode forming portions, here with a deposition and etchback poly Embed the silicon film 3.

Then, the Ru layer 4 is formed on the polysilicon film 3 by the reactive sputtering method at a substrate temperature of 400 ° C. and a thickness of 300 Å.
Then, the RuO ₂ layer 5 was grown to 1500 Å at a substrate temperature of 500 ° C.
grown. After that, the RuO ₂ / Ru film is patterned to form the lower electrode.

Here, the Ru layer 4 is formed to prevent the oxidation of the silicon surface, and the RuO ₂ layer 5 functions as an electrode. In FIG. 1 (B), a strontium titanate (SrTiO ₃ ) film 6 is formed as an oxide dielectric film on the substrate by magnetron sputtering to cover the lower electrode.

In FIG. 1C, the side wall 7 made of a SiO ₂ film by vapor phase growth (CVD) growth is formed on the side surface of the SrTiO ₃ film 6 by using deposition and anisotropic etching. In FIG. 1 (D), a platinum film 8 is formed as an upper electrode on the SrTiO ₃ film 6.

FIG. 2 is a diagram (1) showing the effect of the present invention.
The figure shows the analysis results by Auger electron spectroscopy. The vertical axis represents the atomic concentration AC (%), and the horizontal axis represents the elapsed time (minutes) when sputtering was performed from the surface of the RuO ₂ / Ru two-layer structure.
The sample used is the RuO ₂ / Ru two-layer structure electrode prepared under the above-mentioned growth conditions, which is annealed at 700 ° C. in the atmosphere.

From these results, it is shown that RuO ₂ , Ru and Si are sequentially formed on the surface, and that SiO ₂ is not formed on the Si surface. Therefore, it shows that the oxygen barrier property is good.

Next, Auger electrons RuO ₂ / Ru film grain size 100Å grown in RuO ₂ / Ru film and RuO ₂ Growth temperature 350 ° C. the crystal grain size 500Å grown at a growth temperature 750 ° C. of RuO ₂ The result of the spectroscopy is shown in FIG.

FIGS. 3A and 3B are diagrams showing the effect of the present invention (2)
Is. In Fig. 3 (A) with a crystal grain size of 500Å, the oxide electrode Ru
The metal Ru film of the barrier layer formed under the O ₂ film is oxidized. Therefore, it reacts with Si under the Ru film to form SiO ₂ . On the other hand, in Fig. 3 (B) with a crystal grain size of 100Å, it can be seen that the metal Ru film of the barrier layer formed below the RuO ₂ film of the oxide electrode is not oxidized.

An example of the minimum temperature or the maximum growth rate at which crystal growth is possible in order to suppress the growth of the columnar crystals when the oxide conductive electrode is grown is as follows. Conductive oxide minimum growth temperature Maximum growth rate (growth temperature at this time) (℃) (Å / min) (℃) RuO ₂ 350 1000 500 In the example, the RuO ₂ film was used as the oxide conductive electrode. Also, with respect to ReO ₂ , IrO ₂ , OsO _2, etc. of the same kind, the same effect as that of the embodiment is obtained by growing these crystals at the minimum growth temperature or the maximum growth rate.

[0024]

EFFECTS OF THE INVENTION Oxide conductive electrodes such as RuO ₂ / Ru 2
According to the present invention, in the formation of a layered electrode, the underlying silicon is not oxidized, so that the barrier property against oxygen generated when the oxide dielectric is formed on the electrode is not impaired. Therefore, the contact with the underlying silicon was improved. Moreover, it was possible to prevent the occurrence of hillocks on the electrodes.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating an embodiment of the present invention.

FIG. 2 is a diagram showing the effect of the present invention (1)

FIG. 3 is a diagram showing the effect of the present invention (2)

[Explanation of symbols]

1 Si substrate as semiconductor substrate 2 SiO ₂ film 3 Polysilicon film 4 Metal Ru film 5 RuO ₂ layer as conductive oxide film 6 SrTiO ₃ film as oxide dielectric film 7 Sidewall made of SiO ₂ film 8 Pt as upper electrode film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/314 M 7352-4M 21/3205 21/8242 27/108 H01L 21/88 M 7210-4M 27/10 325 J

Claims (2)

[Claims] 1. When forming an electrode having a two-layer structure of ruthenium oxide (RuO ₂ ) / ruthenium (Ru) as a lower electrode of a capacitor using an oxide dielectric film on a semiconductor substrate,
The film thickness d is set to 300 Å <d <5 as the growth condition of the Ru film of the second layer.
And the substrate temperature T _S is 300 ° C. <T _S <450 ° C.
As the growth condition of the second layer of RuO ₂ film, the film thickness d is 1000Å <
d <3000Å, substrate temperature T _S is 350 ° C <T _S <700 ° C
A method of manufacturing a semiconductor device, comprising: 2. A semiconductor device, wherein a conductive oxide is grown as a lower electrode of a capacitor using an oxide dielectric film on a semiconductor substrate at a minimum temperature or a maximum growth rate capable of crystal growth. Production method.