JPH04286356A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor device which is provided with a capacitor suitable for the memory cell of a DRAM (dynamic random access memory), enhanced in surface area by making its surface rugged, and hardly deteriorating in dielectric breakdown strength even if a dielectric film of high dielectric constant is used. CONSTITUTION:The method includes a first process where a first electrode layer 12 whose surface is rugged is formed, a second process where a high dielectric film 14 high in dielectric constant is provided onto the surface of the first electrode layer 12, and a third process where an insulating film 16 is formed oxidizing or nitriding a part near an interface between the high dielectric film 14 and the first electrode layer 12 through a heat treatment carried out in an oxidizing atmosphere or a nitriding atmosphere.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to semiconductor devices, particularly DRA
The present invention relates to a semiconductor device having a capacitor suitable for use in an M (dynamic random access memory) memory cell, and a method for manufacturing the same.

0002

2. Description of the Related Art A capacitor constituting a memory cell of a DRAM has a structure in which a dielectric film is sandwiched between a lower electrode and an upper electrode. In conventional DRAMs, a silicon oxide film is used as a dielectric film. As the degree of integration of DRAMs increases, the thickness of silicon oxide films is becoming thinner and thinner, and in order to ensure capacitor capacity by thinning silicon oxide films, we are reaching the limits of thinning in terms of reliability. It's approaching.

Therefore, in order to increase the capacitance of a capacitor, methods have been considered such as increasing the area by making the surface of the lower electrode uneven, and using a high dielectric film having a higher dielectric constant than a silicon oxide film as the dielectric film. ing.

0004

[Problems to be Solved by the Invention] However, in the method of increasing the area by making the surface of the lower electrode uneven, when a silicon oxide film is formed on the uneven surface, stress is concentrated at the acute corners as shown in FIG. As a result, the silicon oxide film that grows becomes thinner, and dielectric breakdown occurs at these acute corners, resulting in a decrease in dielectric strength.

[0005] In the method of using a high dielectric film with a high dielectric constant, it is difficult to make the film thin because the high dielectric material originally has a large leakage current and a low withstand voltage, and it is difficult to form a capacitor with a large capacitance. The problem was that it was difficult to An object of the present invention is to provide a semiconductor device having a capacitor whose dielectric strength does not deteriorate even when the surface is made uneven to increase the area and a high dielectric constant film is used, and a method for manufacturing the same. It is in.

[0006]

[Means for Solving the Problems] The principle of the present invention will be explained using FIGS. 1 and 2. A lower electrode layer 12 is formed on a silicon substrate 10, and the surface of the lower electrode layer 12 is made uneven to increase its area. After the high dielectric constant film 14 with a high dielectric constant is formed on the lower electrode layer 12, when heat treatment is performed in an oxidizing atmosphere or a nitriding atmosphere, the vicinity of the interface between the lower electrode layer 12 and the high dielectric constant film 14 is oxidized (interfacial oxidation). or nitrided (interfacial nitrided), as shown in FIG. 1(a), the lower electrode layer 1
An insulating film 16 is formed between the high dielectric constant film 14 and the high dielectric constant film 14 . The high dielectric film 14 relieves stress at the acute angle portion, and an insulating film 16 with a uniform thickness is formed.

[0007] In order to reliably relieve the stress at the acute angle portion, it is desirable that the high dielectric constant film 14 be thicker than the insulating film 16. Furthermore, even if the film thickness of the high dielectric constant film 14 formed on the uneven lower electrode layer 12 becomes thinner at the acute corner portions, it becomes thinner at the acute corner portions when heat treated in an oxidizing atmosphere or a nitriding atmosphere. As shown in FIG. 1(b), many oxidizing or nitriding species pass through the high dielectric constant film 14, which has become easier for seeds to pass through due to stress, and act on the interface. The insulating film 16 becomes thicker at the thin acute corner portions of the dielectric film 14, and the portions with low dielectric strength are naturally repaired.

Furthermore, as shown in FIG. 2, instead of heat treatment in an oxidizing atmosphere or nitriding atmosphere, an oxide film is formed between the lower electrode layer 12 and the high dielectric constant film 14 by performing a heat treatment in an oxidizing atmosphere to oxidize the interface. After forming the lower electrode layer 12 and the oxide film 16a, heat treatment is performed in a nitriding atmosphere to nitride the interface.
A nitride film 16b may be formed in between. Note that, conversely, interfacial oxidation may be performed after interfacial nitridation.

[0009]

[Operation] According to the present invention, as described above, the first
After forming a high dielectric film with a high dielectric constant on the electrode layer, heat treatment is performed in an oxidizing atmosphere or a nitriding atmosphere to oxidize or nitride the vicinity of the interface between the high dielectric film and the first electrode layer to form an insulator. Since a film is formed, the stress at the acute angle portions of the unevenness is relaxed, and even if a high dielectric film with a high dielectric constant is used, the dielectric breakdown voltage does not deteriorate.

0010

Embodiment A method of manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to a capacitor of a DRAM memory cell. first,
A nitride film (not shown) is formed in the element region of the silicon substrate 20, and field oxidation is performed to form a field oxide film 22. Subsequently, the nitride film is removed to expose the surface of the silicon substrate 20 in the element region (FIG. 3(a)).

Next, a gate oxide film 24 is formed, and polycrystalline silicon is deposited by the usual CVD method and patterned to form a gate electrode 26 which is a word line. Next, using the gate electrode 26 as a mask, the silicon substrate 2 is
As ions are implanted into the 0 surface to form impurity regions 28 and 30. Subsequently, after forming the BPSG film 32,
Annealing is performed at 0° C. to melt and planarize the BPSG film 32 and to activate the impurity regions 28 and 30. Subsequently, a contact hole to the impurity region 30 is opened in the BPSG film 32.

[0012] Next, silane (SiH4) was applied for 200 sc at a pressure of 0.1 to 0.2 Torr and a temperature of 570°C.
The BPSG film 32 was deposited under low pressure CVD conditions at a flow rate of cm.
When polycrystalline silicon is deposited thereon, a polycrystalline silicon electrode layer (storage electrode layer) 34 having an uneven surface is formed. If the entire film thickness of the polycrystalline silicon electrode layer 34 is 300 nm, irregularities of about 100 nm are formed on the surface. This nearly doubles the surface area of the formed capacitor.

Next, by plasma CVD using tetraethoxy tantalum as a source gas, a film having a high dielectric constant (relative dielectric constant = 20
) A high dielectric constant film 36 is formed by growing tantalum oxide (Ta2O5) to a thickness of 3 nm. Subsequently, the polycrystalline silicon electrode layer 34 and the high dielectric constant film 36 are patterned (FIG. 3(b)).
).

Next, in a dry oxygen atmosphere, the temperature is about 900°C.
By heat treatment, a silicon oxide film 38 of approximately 1 nm thick is formed at the interface between the polycrystalline silicon electrode layer 34 and the high dielectric constant film 36.
grows (interfacial oxidation). The relative dielectric constant of tantalum oxide forming the high dielectric film 36 is about five times that of the silicon oxide film 38 (=4), so the 3 nm thick high dielectric film 36 and the 1 nm thick silicon oxide film The dielectric film on which 38 is laminated has a thickness of approximately 1.6 nm (=3 [nm]/5+1 [nm]
This corresponds to a silicon oxide film with a thickness of 0.6 [nm] + 1 [nm]). Note that heat treatment for interfacial oxidation can be performed by RTA (Rapid Thermal Treatment) using light (laser, ultraviolet rays, infrared rays, etc.) even if heated in an electric furnace.
Al Aneal) may be used, or heat treatment using plasma may be used. In particular, if optical heating is used, the high dielectric constant film 36 has a large refractive index and serves as an antireflection film, so only the interface is heated intensively.
This is advantageous for interfacial nitriding and interfacial oxidation.

Subsequently, an upper electrode layer 40 made of tungsten or titanium nitride is formed by CVD. Subsequently, after depositing an interlayer insulating film 42 on the entire surface, a bit contact is opened, a bit line 44 made of aluminum or silicide is formed (FIG. 3(c)), and finally a cover film (not shown) is deposited. do. The present invention is not limited to the above embodiments, and various modifications are possible.

For example, in the above embodiment, the polycrystalline silicon electrode layer 34 and the high dielectric constant film 36 are heated in an oxidizing atmosphere.
The interface was oxidized (interfacial oxidation), but the interface was nitrided in a nitriding atmosphere, and the polycrystalline silicon electrode layer 34 and the high dielectric constant film 36
A silicon nitride film may be formed in between. It is advantageous to use N2H4 hydrazine as the nitriding atmosphere since it has excellent reactivity and permeability. Moreover, since it has excellent reactivity, nitriding can be performed at a low temperature of 800 to 900°C.

Furthermore, when heat-treating the interface between the polycrystalline silicon electrode layer 34 and the high dielectric constant film 36, the interface is first heat-treated in an oxidizing atmosphere (interfacial oxidation), and then heat-treated in a nitriding atmosphere (interfacial nitridation). It's okay. Conversely, interfacial oxidation may be performed after interfacial nitridation. Furthermore, although tantalum oxide was used as the high dielectric film in the above embodiment, zirconium (Zr
), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), etc. Group 3A, group 4A, or group 5A oxides (ZrO2, TiO2, HfO2, V2O
5, Nb2O5, etc.).

[0018]

As described above, according to the present invention, a high dielectric constant film having a high dielectric constant is formed on a first electrode layer having an uneven surface, and then heat-treated in an oxidizing atmosphere or a nitriding atmosphere. Since an insulating film is formed by oxidizing or nitriding the vicinity of the interface between the high dielectric film and the first electrode layer, stress is relaxed at the acute corners of the unevenness, and a high dielectric film with a high dielectric constant is used. The dielectric strength voltage is high, and the dielectric strength voltage does not deteriorate even when
Moreover, a capacitor with an increased opposing area can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a diagram of the principle of the present invention.

FIG. 3 is a process cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a cross-sectional shape of a silicon oxide film formed on an uneven surface.

[Explanation of symbols]

10...Silicon substrate 12...Lower electrode layer 14...High dielectric film 16...Insulating film 16a...Oxide film 16b...Nitride film 20...Silicon substrate 22...Field oxide film 24...Gate oxide film 26...Gate electrode 28, 30... impurity region 32...BPSG film 34...Polycrystalline silicon electrode layer 36...High dielectric film 38...Silicon oxide film 40... Upper electrode layer 42...Interlayer insulation film 44...Bit line

Claims (6)

[Claims] 1. A first electrode layer having an uneven surface; an insulating film formed on the first electrode layer; a high dielectric constant film having a high dielectric constant formed on the insulating screen; A semiconductor device comprising a second electrode layer formed on a dielectric film. 2. The semiconductor device according to claim 1,
A semiconductor device characterized in that the thickness of the high dielectric constant film is thicker than the thickness of the insulating film. 3. The semiconductor device according to claim 1, wherein the first electrode layer contains silicon, the insulating film is a silicon oxide film or a silicon nitride film, and the high dielectric constant film is a group 3A film. , 4A group, or 5A group element oxide. 4. A step of forming a first electrode layer having an uneven surface, a step of forming a high dielectric constant film having a high dielectric constant on the first electrode layer, and a heat treatment in an oxidizing atmosphere or a nitriding atmosphere. A method of manufacturing a semiconductor device, comprising the step of oxidizing or nitriding the vicinity of the interface between the high dielectric constant film and the first electrode layer to form an insulating film. 5. The method of manufacturing a semiconductor device according to claim 4, wherein the heat treatment is performed so that the thickness of the insulating film becomes thinner than the thickness of the high dielectric constant film. 6. The method of manufacturing a semiconductor device according to claim 4, wherein the first electrode layer contains silicon, and the insulating film formed by heat treatment is a silicon oxide film or a silicon nitride film. , the high dielectric constant film is 3A
1. A method for manufacturing a semiconductor device, comprising an oxide of an element of Group 4A or Group 5A.