JPH0460335B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor device, and particularly to a method for manufacturing a semiconductor device using a high melting point metal as an electrode.

[Background of the invention]

Conventionally, aluminum (hereinafter referred to as "Al") has been used as the material for electrodes, wiring, etc. in semiconductor devices.
low melting point metals such as molybdenum (hereinafter referred to as "Mo"), high melting point metals such as tungsten (hereinafter referred to as "W"), or polycrystalline silicon (hereinafter referred to as "polysilicone").
Semiconductor materials such as "Si" were used.
Each of these materials had advantages and disadvantages.
In other words, although Al has the advantage of having a low specific resistance of approximately 3×10 ^-6 Ω-cm, its melting point is low at 660°C, so it is difficult to introduce Al into the semiconductor manufacturing process, which normally requires a heat treatment process of about 1000°C. There were various restrictions to do so. On the other hand, polySi has the advantage of being able to withstand heat treatment at about 1000° C. and having a high affinity with silicon used as a substrate, allowing a greater degree of freedom in the manufacturing process of semiconductor devices. Furthermore, a silicon oxide film (hereinafter referred to as "SiO ₂ film") with good insulation can be easily formed on the surface of poly Si by simply heat-treating poly Si in an oxidizing atmosphere, and both poly Si and SiO ₂ films are _{2SO4 ,}
Since it can withstand acid cleaning (hereinafter simply referred to as "acid cleaning") with an appropriate mixture of solutions such as HOl, HNO ₃ , H ₂ O ₂ , etc., the surface of the element can be easily cleaned. When poly Si is used for semiconductor devices, etc., there is an advantage that the manufacturing yield of semiconductor devices is high. However, the resistivity of polySi is two to three orders of magnitude higher than that of metals, so polySi is used for electrodes, wiring, etc.
In semiconductor devices using Si, the propagation delay due to wiring resistance increases, making it difficult to achieve high integration and high speed.

On the other hand, high-melting point metals such as Mo have a high melting point of about 2600℃ and can withstand heat treatment of about 1000℃, so using Mo for electrodes, wiring, etc. can increase the degree of freedom in the manufacturing process of semiconductor devices. Since high melting point metals have low specific resistance, they are suitable for increasing the speed of semiconductor devices. For this reason, semiconductor devices including high-melting point metals have been in the spotlight. However, in the case of high-melting-point metals compared to poly-Si, a semiconductor device with a structure that has a stable and high-quality insulating layer like a silicon thermal oxide film on its surface, and a method for easily manufacturing it, have not been realized. As a result, semiconductor devices using high-melting point metals for electrodes, wiring, etc. could not become mainstream in semiconductor technology until now.

As a method for solving the above-mentioned problem, the present applicant has already applied for a method for manufacturing a semiconductor device having a structure in which a stable and high-quality insulating layer is provided on the surface of a high-melting point metal (Japanese Patent Application No. 51383/1983). That is, by sequentially laminating a high melting point metal oxide layer, a silicon layer, and a silicon oxide film on a high melting point metal layer provided on a base body, and heat-treating this base body in an atmosphere containing hydrogen,
An internal silicon oxide film is formed between the high melting point metal layer and the silicon layer.

FIG. 1 shows the steps of the above method. Fig. 1-A shows a step of forming a high melting point metal layer 4 on a substrate 1 having an insulating layer 3 formed on a substrate 2, and Fig. 1-B shows a step of forming a high melting point metal oxide layer 20. Fig. 1-C shows the process of forming the silicon layer 6, Fig. 1-D shows the process of forming the silicon oxide film 5, and Fig. 1-E shows the heat treatment process in a hydrogen atmosphere so that the high melting point metal oxide layer 20 becomes the internal silicon oxide film. This shows that the number has changed to 5. Next, changes in the structure in the above-mentioned internal silicon oxide film forming step will be explained based on the measurement results of Auger electron spectroscopy shown in FIG. Figure 2-A shows the structure before internal silicon oxide film formation, that is, the structure shown in Figure 1-D, Figure 2-B shows the structure after heat treatment in a hydrogen atmosphere (900°C, 10 minutes), and Figure 2-C shows the structure shown in Figure 1-D. The depth distribution of constituent elements from the surface toward the substrate is shown for the structure after further heat treatment (900°C, 30 minutes). The thickness of the poly Si layer is approximately 1100 Å.
The horizontal axis is the time for sputter etching the sample, which corresponds to the depth from the surface. a, b, and c are curves representing silicon, oxygen, and Mo, respectively.
Comparing Figure 2-B with Figure 2-A, the 0 signal, which had one peak at the interface between poly Si and Mo before heat treatment, now has two peaks. poly
The peak on the Si side corresponds to the internal silicon oxide film, and the remaining peaks correspond to the MoO ₂ layer. 2nd-C
In the figure, the _MoO2 layer is gone and an internal silicon oxide film is formed at the interface between the polySi layer and Mo. poly Si
Looking at the thickness of the layer, it becomes gradually thinner as it is heat treated. That is, as the heat treatment is carried out in a hydrogen atmosphere, MoO ₂ is gradually reduced and the poly
Si is gradually oxidized starting from the Mo side.

Figure 3 compares the oxidation characteristics of the internal oxidation method with those of the burning oxidation method (H ₂ :O ₂ =1:1) and the normal thermal oxidation method (hereinafter referred to as "dry oxidation method"). . ● indicates the internal oxidation method, ○ indicates the burning oxidation method, and × indicates the dry oxidation method. The oxidation temperature was 900°C in all cases, and the thickness of the polySi layer was approximately 1900 Å. The oxidation rate of the internal oxidation method is higher than the oxidation rate of the dry oxidation method, and the oxidation rate of the burning oxidation method is almost the same. In the internal oxidation method, process parameters for oxidation rate include heat treatment temperature, hydrogen partial pressure during heat treatment, polySi film thickness, etc. The thicker the poly Si layer, the more
Although the oxidation rate tends to decrease, in any case, it was considerably faster than the dry oxidation method when the thickness of the poly Si layer was in the range of 1000-3200 Å.

According to the theory of Si oxidation by BE Deal et al., there are several factors that determine the oxidation rate, such as the diffusion rate of the oxidant in the oxide film, the concentration of the oxidant on the oxide film surface, and the reaction coefficient at the interface between the oxide film and the Si. However, the difference in oxidation rate between the dry oxidation method and the burning oxidation method is mainly due to the difference in the diffusion rate of the oxidizing agent in the oxide film. Therefore, it seems that FIG. 3 shows that the oxidizing agent in the internal oxidation method is H ₂ O. In other words, it can be considered that polySi is oxidized by H ₂ O generated by the MoO ₂ reduction reaction MoO ₂ +2H ₂ →Mo+2H ₂ O. Here, the cap layer (hereinafter referred to as "cap layer") consisting of _two SiO layers formed on the surface of the silicon layer is an oxidizing agent that passes through pinholes and areas with poor crystallinity in the silicon layer.
It seems to play a role in preventing H ₂ O from escaping.

By using the above method, it is possible to selectively and easily form an internal silicon oxide film of the same quality as a normal silicon thermal oxide film only on the surface of the high melting point metal layer. In connection with this, various other effects can be obtained as follows.

(1) The internal silicon oxide film has excellent insulating properties, making it easy to manufacture semiconductor devices with good insulating properties between the high-melting point metal layer and the silicon layer.

(2) Since the internal silicon oxide film is formed evenly and uniformly without overhanging, semiconductor devices with fewer short circuits and disconnections can be manufactured with high yield.

(3) A multilayer wiring structure can be easily realized by using the internal silicon oxide film as an interlayer insulating film and using the silicon layer and high melting point metal layer as wiring.

(4) Since the internal silicon oxide film has good insulating properties even if it is thin, the thickness of the insulating layer covering the side surfaces of the step portion can be reduced, and the density of the semiconductor device can be increased.

(5) When adopting a process in which the internal silicon oxide film or high-melting point metal oxide layer is exposed to the outside once during the manufacturing process, the device can be cleaned with acid, making it easier to clean the device and improving the manufacturing yield. In addition, it is possible to reduce contamination of manufacturing equipment.

However, as a result of further investigation of the above method, the following points became clear.

If a method of oxidizing the surface of the silicon layer is used to form the SiO ₂ film in the process shown in FIG. 1-D, crater-shaped defects occur. Its size is 20 to several 100 μm in diameter, and its density is approximately
The number is 70-100 pieces/ ^cm2 . FIG. 4 shows an optical micrograph of the defect. It is thought that the crater-shaped defects occur because oxygen enters through pinholes or areas with poor crystallinity in the silicon film, generates MoO ₃ , and sublimes it.

If such a crater-shaped defect occurs, if an internal silicon oxide film is formed by heat treatment in a hydrogen atmosphere following the process shown in Figure 1-D, the crater-shaped defect will cause leakage of the internal silicon oxide film. This resulted in a drawback that lowered the yield of semiconductor devices.

[Purpose of the invention]

The present invention provides a method for manufacturing a semiconductor device in which a silicon oxide film is selectively formed only on the surface of a high melting point metal layer, in which an internal silicon oxide film is formed without inducing crater-like defects on the surface of the silicon layer. Its purpose is to improve the quality of the internal silicon oxide film.

[Summary of the invention]

In other words, the applicant believes that in order to form the cap layer under conditions in which MoO ₃ , which causes the above-mentioned crater-like defects, is not generated, the cap layer must be formed of a non-metallic compound layer that does not contain oxygen. Based on our knowledge and experience, we have made the following improvements.
A typical aspect of the method for manufacturing a semiconductor device according to the present invention includes a step of forming a high-melting point metal layer on a base consisting of a substrate provided with an insulating layer, and a step of forming a high-melting point metal oxide on the surface of the high-melting point metal layer. a step of forming a silicon layer on the high melting point metal oxide layer; a step of forming an oxygen-free nonmetallic compound layer on the silicon layer; and the high melting point metal layer.
forming an internal silicon oxide film between the high melting point metal layer and the silicon layer by heat-treating the substrate having the high melting point metal oxide layer, the silicon layer, and the nonmetallic compound layer in an atmosphere containing hydrogen; It is characterized by including.

[Embodiments of the invention]

The method for manufacturing a semiconductor device according to the present invention will be described in detail below based on examples.

FIG. 5 shows an embodiment of the present invention. A high melting point metal layer 14 is formed on a base body 11 having a structure including a single crystal silicon substrate 12 and a silicon oxide film having a thickness of, for example, 500 Å thereon as an insulating layer 13.
Obtain the structure shown in diagram A. Here, the material used for the high melting point metal layer 14 needs to be one that has low resistance, high heat resistance, and whose oxide is easily reduced by heat treatment in an atmosphere containing hydrogen. For example, there are Mo, W, Ta, Ti, etc. This embodiment will be described in detail below using Mo as an example. The high melting point metal layer 14 in FIG. 5-A is Mo with a thickness of about 3000 Å formed by sputtering.

Next, the surface of the high melting point metal layer 14 is oxidized to form a high melting point metal oxide layer 21 to obtain the structure shown in FIG. 5-B. Molybdenum dioxide (hereinafter referred to as "MoO ₂ ") and molybdenum trioxide (hereinafter referred to as "MoO ₃ ") are Mo oxides that are generally stably obtained when Mo is used as the high melting point metal layer 14.
MoO ₃ can be easily obtained by heat-treating Mo at a low temperature in an oxygen-containing atmosphere, but this MoO ₃ begins to sublimate at high temperatures of about 800°C or higher. For this reason, when MoO ₃ is used as the high melting point metal oxide layer 21, peeling of MoO ₃ may occur due to heat treatment in a later step, which is inconvenient. Therefore, the high melting point oxide layer 21 has a high melting point of about 1900°C and is stable at high temperatures.
It is necessary to use _MoO2 . In this example, a substrate with Mo was heat-treated at a temperature of 390°C for 15 minutes in an oxygen atmosphere to form MoO ₃ on the Mo, and then heat-treated at a temperature of 700°C for 30 minutes in a nitrogen atmosphere to form a layer on the Mo surface. A MoO ₂ with a thickness of about 700 Å was formed. It was confirmed by X-ray diffraction and electron diffraction that the Mo oxide obtained by this method was MoO ₂ .

Next, a silicon layer 16 is placed on the high melting point metal oxide layer.
is formed to obtain the structure shown in FIG. 5-C. In this example, polySi was formed to a thickness of 3200 Å by electron beam evaporation. Other formation methods such as CVD may be used to form the polySi used as the silicon layer, and impurities may be added at the time of formation.

Next, a cap layer 51 is formed on the silicon layer 16 to obtain the structure shown in FIG. 5-D.

Next, the structure shown in Figure 5-D is exposed to a hydrogen atmosphere or an inert gas containing hydrogen (for example, argon gas).
By heat treatment in an atmosphere, the high melting point oxide layer is reduced, and at the same time, the silicon layer 16 is oxidized from inside, that is, from the high melting point metal layer 14 side, to form an internal silicon oxide film 15 between the high melting point metal layer and the silicon layer 16. is formed to obtain the structure shown in FIG. 5-E. At this time, the internal silicon oxide film 15 is formed on the entire surface of the high melting point metal layer 14. In this example, in a hydrogen atmosphere
A heat treatment was performed at a temperature of 900° C. for 30 minutes to reduce MoO ₂ to Mo, and at the same time, an internal silicon oxide film 15 was formed. In the above example, heat treatment is performed at 900°C for 30 minutes, but the heat treatment conditions only need to be such that the silicon layer 16 is oxidized from within at the same time as the high melting point metal oxide layer is reduced. It does not matter if it is at the heat treatment temperature.

Next, specific examples of the present invention will be described. In this example, a plasma nitride film was used as the cap layer. In the process of Figure 5-C, about 1000 Å of poly
After forming the Si layer, plasma nitride film is applied to the substrate temperature:
_SiH4 diluted with 5% Ar at 350℃, gas pressure: 1.28Torr
It was formed to a thickness of about 330 Å in an atmosphere in which gas was flowed at 600 c.c./min and ammonia gas was flowed at 50 c.c./min. Next, add a further poly Si layer to improve adhesion.
After forming to a thickness of 2000 Å, 900 Å in a hydrogen atmosphere
Heat treated at a temperature of 30 minutes. FIG. 6 shows the structure of a sample having a plasma nitride cap layer subjected to heat treatment in a hydrogen atmosphere, as measured by Auger electron spectroscopy. It can be seen that an internal silicon oxide film is formed at the interface between poly Si and Mo. Therefore, by using a plasma nitride film as a cap layer, an internal silicon oxide film can be formed without generating defects on the sample surface. In this example, a plasma method was used to form the nitride film, but since it is sufficient to form the cap layer with a non-metallic compound layer in which oxygen does not exist, other methods such as CVD or direct thermal nitridation may also be used. Needless to say, it's a good thing. Furthermore, it goes without saying that a high-quality internal oxide film can be obtained by using a non-metallic compound film that does not contain oxygen in addition to the nitride film without limiting the temperature conditions during film formation. Regarding the atmosphere during the formation of the cap layer,
The present applicant has already proposed that the oxygen concentration should be 1% or less as a condition for forming only MoO ₂ without forming MoO ₃ (Japanese Patent Application No. 57-40109). Therefore, in the embodiments of the present invention, oxygen concentration conditions approximately equal to those described above are required.

Furthermore, focusing on the stress generated in the poly Si layer, if a cap layer with a thermal expansion coefficient smaller than that of poly Si (such as Si ₃ N ₄ ) is formed on the surface, the stress in the poly Si layer tends to be relaxed. This is because the coefficient of thermal expansion decreases as Mo>polySi>cap layer. Therefore, the stress relaxation effect of the cap layer works to prevent the occurrence of cracks in the polySi layer, and as a result, the oxidizing agent H ₂ O is prevented from escaping, which also causes defects. It is thought that this contributes to the fact that this is not the case.

〔Effect of the invention〕

As explained above, by using the present invention, it is possible to solve the problem of defects caused by the formation of a cap layer when an internal silicon oxide film is selectively formed only on the surface of a high melting point metal layer. Therefore, the following effects can be obtained.

(1) If the defects associated with the formation of the cap layer are eliminated, the leakage current of the internal silicon oxide film will decrease,
Since the dielectric strength increases, the film quality can be improved.

(2) Since defects associated with the formation of the cap layer are eliminated, semiconductor devices can be manufactured at a high yield.

[Brief explanation of the drawing]

Figures 1-A to 1-E are diagrams showing the steps of a method for manufacturing a semiconductor device using the internal oxidation method proposed by the applicant, and Figure 2 is a diagram showing the steps of a method for manufacturing a semiconductor device using the internal oxidation method proposed by the applicant. A diagram showing the depth distribution of constituent elements determined by Auger electron spectroscopy of a semiconductor device. Figure 3 shows the oxidation characteristics in the "internal oxidation method" and Figure 4 shows the oxidation characteristics in the manufacturing method proposed by the applicant. Optical micrograph of the surface of the manufactured semiconductor device, No. 5
Figures -A to 5-E are cross-sectional views showing each step of the manufacturing method according to the present invention, and Figure 6 is the constituent elements determined by Auger electron spectroscopy of a semiconductor device manufactured by the manufacturing method according to the present invention. FIG. 3 is a diagram showing the depth distribution of 1, 11... Base, 2, 12... Substrate, 3, 1
3... Insulating layer, 4, 14... High melting point metal layer, 5,
15... Internal silicon oxide film, 6, 16... Silicon layer, 20, 21... High melting point metal oxide layer, 5
0...Silicon oxide film, 51...Cap layer.

Claims (1)

[Claims] 1. A step of forming a high melting point metal oxide layer on the surface of the high melting point metal layer provided on the substrate, and a step of forming a silicon layer on the high melting point metal oxide layer,
a step of depositing an oxygen-free nonmetallic compound layer on the surface of the silicon layer; and the high melting point metal layer;
forming an internal silicon oxide film between the high melting point metal layer and the silicon layer by heat-treating the substrate having the high melting point metal oxide layer, the silicon layer, and the nonmetallic compound layer in an atmosphere containing hydrogen; A method for manufacturing a semiconductor device, comprising: