JPH06275536A - Formation of metallic film - Google Patents

Abstract

PURPOSE:To form a metallic film having a uniform quality and uniform thickness on the vapor growth surface of a wafer while the generation of particles is prevented by forming the metallic film on the vapor growth surface after forming an oxide film on the rear surface of the wafer opposite to the vapor growth surface. CONSTITUTION:After forming a uniform SiO2 film 15 having a thickness of about 200Angstrom on the rear surface 13 of a sample, a W film 17 is formed on the vapor growth surface 12 of the sample. When the film 17 is formed in such a way, it becomes unnecessary to seal the periphery of the sample and the temperature drop of the sample can be prevented, since the formation of the film 13 on the rear surface 13 can be prevented by the SiO2 film 15 even when a mixed gas infiltrates to the rear surface 13. Therefore, the temperature of the vapor growth surface 12 can be maintained in a uniform state. In addition, the coating can be made uniform and the W film 17 formed on the vapor growth surface 12 can have a uniform quality and uniform thickness. Moreover, since the formation of the W film 17 on the rear surface 13 can be prevented, the stripping off of the film 17 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal film, and more particularly to a method for forming a metal film which can be used in a low pressure CVD process of, for example, tungsten (hereinafter referred to as W).

[0002]

2. Description of the Related Art Conventionally, one of the LSI manufacturing processes is a process of burying metal mainly in contact holes or through holes that connect upper and lower wirings. At this time, for example, W is often used as the metal because of its good burying property. In such a W CVD process, WF is used.
A method of forming a W film by a reaction represented by the following reaction formula using the reduction reaction of ₆ is used.

2WF ₆ + 3SiH ₄ → 2W + 3SiF ₄ + 6H ₂ WF ₆ + 3H ₂ → W + 6HF 2WF ₆ + 3Si → 2W + 3SiF ₄ Normally, in this method, 300 ° C. to 8 ° C. on the vapor phase growth surface of the wafer.
At a temperature of 00 ° C., W having a good filling property is vapor-deposited by a low pressure CVD method to form a W film. FIG. 5 is a schematic sectional view showing a conventional wafer on which a W film is formed, and 40 in the figure shows the wafer. Si on one surface of the Si substrate 11
The O ₂ film 35 is formed, the aluminum wiring 34 is formed on the SiO ₂ film 35, the SiO ₂ film 38 is formed on the aluminum wiring 34, and W is formed in the contact hole 36 formed in the SiO ₂ film 38. It is embedded and covered with a W film 37 whose surface is flattened.

By the way, the back surface 33 of the wafer 40 immediately before the W CVD process is performed is made of SiO ₂ which is a natural oxide film.
If the film is thin, or if Si on the back surface 33
The O ₂ film is etched by a plurality of HF cleaning treatments performed up to the W CVD process, and the single crystal Si (0
01) The surface is exposed. Generally, W is very easy to grow on a conductor film and a semiconductor film such as TiN, polycrystalline Si and single crystal Si. On the other hand, Si
It is extremely difficult to grow on an insulating film such as an O ₂ film.

In the conventional W film forming method,
Although the wafer 40 is fixed to the CVD apparatus by the pressure fixing method, it cannot be strongly pressed in order to avoid damaging the wafer 40. Therefore, a slight gap is formed between the periphery of the wafer 40 and the device.

Therefore, in such a state, CVD of W is performed.
When the process is performed, the mixed gas flows into the back surface 33 from the gap around the wafer 40, and unnecessary W is added to the edge portion of the back surface 33.
A film is easily formed. Since this W film is extremely thin and sparse, it is easy to peel off, and the peeled W film becomes particles, which causes contamination of the wafer 40, the apparatus, and the like.

Therefore, in order to solve such a problem,
For example, as shown in FIG. 6, the heater chuck face 3
By covering the periphery of the wafer 50 on 1 with the seal ring 41, it is possible to prevent the mixed gas from entering the back surface 43, prevent the W film from being formed on the back surface 43, and prevent the generation of particles due to the peeling of the W film. Method (Japanese Patent Laid-Open No. 3-6
No. 4480) has been proposed.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method disclosed in Japanese Patent No. 4480, when the temperature of the seal ring 41 is lower than the temperature of the wafer 50, the seal ring 41 radiates heat from the wafer 50, and the gas of the wafer 50 near the contact region between the wafer 50 and the seal ring 41 is removed. This lowers the temperature of the phase growth surface 42. As a result, the coating speed decreases, the amount of vapor deposited material decreases, and it becomes difficult to form the W film having uniform film quality and film thickness. Therefore, in order to obtain uniformity in the film quality and film thickness of the W film, it is necessary to maintain temperature equilibrium between the wafer 50 and the seal ring 41.

However, it is difficult to maintain the temperature equilibrium between the wafer 50 and the seal ring 41 because of the difference in the material between them. Therefore, the formation of the W film on the back surface 43 is prevented, and the W film is prevented. There is a problem that it is impossible to form a W film having uniform film quality and film thickness while preventing peeling of the film.

The present invention has been made in view of the above problems. By preventing the formation of a metal film on the back surface, the metal thin film is prevented from peeling off, and particles are prevented from forming on the vapor phase growth surface. An object of the present invention is to provide a metal film forming method capable of forming a metal film having uniform film quality and film thickness.

[0011]

In order to achieve the above-mentioned object, a method for forming a metal film according to the present invention comprises forming an oxide film on the back surface of a vapor phase growth surface of a wafer and then forming the oxide film on the vapor phase growth surface. The feature is that a metal film is formed.

[0012]

In general, metal such as W used for wiring is T
It has a property that it is very easy to grow on a conductor film and a semiconductor film such as iN, polycrystalline Si and single crystal Si, and is very difficult to grow on an insulating film such as a SiO ₂ film.

Utilizing this property, before the W CVD process is performed, a thin SiO ₂ film of about 200 Å is formed on the back surface of the wafer.
By forming the film, the W film is prevented from being formed on the back surface in the W CVD process.

On the back side, the thin SiO of about 200 Å
_As a method of forming the _two films, for example, in the initial stage of the LSI manufacturing process, the vapor phase growth surface is covered with a SiN film which is an antioxidant film, and then only the back surface is heated to about 2000Å by thermal oxidation or steam oxidation. There is a method of forming the above-mentioned SiO ₂ film that is sufficiently thick. Then, the SiO ₂ film is scraped by a plurality of cleaning treatments with HF performed until the W CVD process is performed, and the back surface is thin and uniform with a thickness of about 200Å.
An O ₂ film is formed.

As another method, at the early stage of the LSI manufacturing process, the vapor phase growth surface is formed of an anti-oxidation film S.
There is a method of covering with an iN film and forming a thin uniform SiO ₂ film having a thickness of about 200 Å only on the back surface immediately before performing the W CVD process.

By thus forming the thin SiO ₂ film having a thickness of about 200 Å on the back surface and then performing the W CVD process on the vapor phase growth surface, even if the mixed gas enters the back surface, The SiO ₂ film on the back surface prevents the formation of the W film on the back surface.
This eliminates the need to cover the periphery of the wafer with a seal ring, prevents the temperature of the wafer from lowering, makes the temperature on the vapor phase growth surface uniform, and enables uniform coating. It becomes possible to form a metal film having uniform film quality and film thickness on the entire surface.

Moreover, by preventing the formation of the metal film on the back surface, the peeling of the metal thin film does not occur, the generation of particles is prevented, and the particles are prevented from contaminating the wafer or the device. It becomes possible to do.

[0018]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of the method for forming a metal film according to the present invention will be described below with reference to the drawings. In this example, a W film is used as the metal film. 1A to 1D are schematic cross-sectional views showing samples A to D on which a W film is formed.

First, four samples A to D which are different in the state of the vapor phase growth surface and which have been subjected to the following processing are prepared.

A A single crystal Si substrate 11 was subjected to wet cleaning with HF for 2 minutes to remove a natural oxide film (FIG. 1 (a)).

B single crystal Si substrate 11 vapor phase growth surface 12
And SiH ₄ (250 sccm) and N ₂ (5
(00 sccm) in a mixed gas atmosphere at a temperature of 620 ° C. and a pressure of 0.3 Torr.
A polycrystalline Si film 14 having a thickness of 4000 Å is formed by the method (FIG. 1 (b)).

The C single crystal Si substrate 11 is subjected to a heat treatment at 950 ° C. for about 30 minutes in a mixed atmosphere of H ₂ and O ₂ , and a 2000 Å SiO ₂ film 1 is formed on the vapor phase growth surface 12 and the back surface 13.
5 is formed. Furthermore, SiH ₄ (250 sccm) and N ₂ (500 sccm) are formed on the vapor-phase growth surface 12 and the back surface 13.
In a mixed gas atmosphere with a pressure of 0.3 at a temperature of 620 ° C.
40 by the thermal reduced pressure CVD method under the conditions of Torr.
A polycrystalline Si film 14 of 00Å is formed. After that, only the vapor phase growth surface 12 is covered with a resist film (not shown) of 1.2 μm, the polycrystal Si film 14 on the back surface is removed using hydrofluoric nitric acid (HF + HNO ₃ ), and finally at a temperature of 150 ° C. H ₂ S
The resist film was removed using O ₄ (Fig. 1
(C)).

D on a single crystal Si substrate 11 in an O ₂ atmosphere,
A heat treatment is performed at a temperature of 950 ° C. for about 30 minutes to form a 200 Å SiO ₂ film 15 on the vapor phase growth surface 12 and the back surface 13. Next, Ti was sputtered while flowing N ₂ gas to form a TiN film 16 of 1000 Å only on the vapor phase growth surface 12 (FIG. 1 (d)).

[0024]

[Table 1]

Next, on each of the vapor phase growth surfaces 12 of Samples A to D, the vapor phase growth surface and the back surface of which are as shown in Table 1,
In three different mixed gas atmospheres shown in Table 2, a W film is formed in three stages by a low pressure CVD method under the conditions of a temperature of 450 ° C. and an atmospheric pressure of 45 Torr.

[0026]

[Table 2]

First, in the first stage, Si, which has a good reducing property for W, is used.
A mixed gas containing H ₄ is used, and the formation and seeding of the W film are assumed. Next, in the second stage, the step portion is assumed to be embedded. Finally, in the third step, the uniformity of the film thickness and film quality of the W film is supposed to be improved. In this way, the W film is formed on the vapor phase growth surface 12 of each of the samples A to D.

2 (a) to 2 (d) show that W is formed on the vapor phase growth surface 12.
It is a typical sectional view showing each of samples A-D in which film 17 was formed.

In the embodiment, a low pressure CVD apparatus 21 having a plurality of chambers as shown in FIG. 3 is used in order to improve the throughput. In the low pressure CVD apparatus 21, a load lock chamber 23 is arranged between two cassette chambers 22 in which a cassette 22 a is arranged, and the load lock chamber 23 and the transport chamber 24 are connected by a buffer station 25. A robot arm 29a is provided in the load lock chamber 23, and a robot arm 29b is provided in the transport chamber 24. A blanket tungsten chamber 26 is connected to one side surface of the transport chamber 24 via a valve 27, and a tungsten silicide chamber 28 is connected to the other side surface of the transport chamber 24 via a valve 27.

The blanket tungsten chamber 26 and the tungsten silicide chamber 28 are two independent process chambers.

When using the low pressure CVD apparatus 21,
For example, the sample A in the cassette 22a is a robot arm 29.
mounted on a, pulled out from the two cassettes 22a,
It is placed in the buffer station 25 in the load lock chamber 23, then placed on the robot arm 29b, and transferred to the designated process chamber. The sample A placed in the process chamber is pressed against the heater chuck face 31 by a pressing and fixing method with three-point support using three clamp pins 30 made of alumina having a width of 1 to 2 mm as shown in FIG. The process is carried out by heating to about 480 ° C. During this time, the sample A is conveyed in a vacuum from the cassette 22a face down.

Table 3 shows the W film 17 on the back surface 13 of each of the samples A to D in which the W film 17 is formed on the vapor growth surface 12.
The results of visual inspection for the presence or absence of peeling are shown.

[0033]

[Table 3]

As is clear from the results shown in Table 3, in the samples A and B according to the comparative example in which the SiO ₂ film 15 was not formed on the back surface 13, the W film 17 was peeled off, 13 in sample C and sample D according to the embodiment which has been formed a SiO ₂ film 15, not caused the peeling of the W film 17, SiO ₂ which has been formed on the back surface 13
It was confirmed that the film 15 prevented the peeling of the W film 17 on the back surface 13.

As described above in detail, in the metal film forming method according to the embodiment, the back surface 13 of the sample has a thickness of 200Å.
Since the W film 17 is formed on the vapor-phase growth surface 12 of the sample after the SiO ₂ film 15 having a uniform degree is formed, even if the mixed gas enters the back surface 13, the SiO ₂ film 15 prevents the back surface 1 from forming.
The formation of the W film 17 in 3 is prevented. Therefore, it is not necessary to cover the periphery of the sample with the seal ring, and the temperature of the sample can be prevented from lowering. Therefore, the temperature on the vapor phase growth surface 12 can be made uniform, the coating can be made uniform, and the W film 17 having a uniform film quality and film thickness can be formed on the vapor phase growth surface 12.

Moreover, since the formation of the W film 17 on the back surface 13 is prevented, the peeling of the W film 17 can be prevented,
It is possible to prevent the generation of particles, and it is possible to prevent contamination of a sample, an apparatus, or the like due to the particles.

The SiO ₂ formed on the back surface 13
The film 15 may be removed after forming the W film 17. To remove the SiO ₂ film 15 on the back surface 13, first, W CVD
After performing the process, the W film 17 on the vapor phase growth surface 12 is 1.2 μm thick.
m resist film and then SiO ₂ film 15 on the back surface 13
Using NH ₄ F, etching rate of about 1000Å / mi
Over-etching of about 50% or more is performed with n, and finally the resist film is removed using H ₂ SO ₄ at a temperature of 150 ° C.

In the above embodiment, the case where W is used as the metal film has been described as an example, but the present invention can be similarly applied to the case where other metal such as Al or Cu is used as the metal film. .

[0039]

As described in detail above, in the method for forming a metal film according to the present invention, an oxide film is formed on the back surface of the vapor phase growth surface of a wafer, and then the metal film is formed on the vapor phase growth surface. Therefore, even if the mixed gas wraps around the back surface, the oxide film can prevent the metal film from being formed on the back surface. Therefore, it is not necessary to cover the periphery of the wafer with a seal ring, the temperature of the vapor phase growth surface can be made uniform, and the metal film having uniform film quality and film thickness is formed on the vapor phase growth surface. can do.

Moreover, it is possible to prevent the formation of the metal film on the back surface, prevent the peeling of the metal thin film, prevent the generation of particles, and contaminate the wafer, the device, etc. by the particles. Can be prevented.

Therefore, it is possible to improve the filling characteristics of the contact holes and the through holes and the flatness of the surface, and at the same time, it is possible to prevent contamination of the manufactured semiconductor device.

[Brief description of drawings]

1A to 1D are schematic sectional views showing samples A to D used in an example of a method for forming a metal film according to the present invention.

2A to 2D are schematic cross-sectional views showing Samples A to D according to examples in which a W film is formed on each vapor phase growth surface.

FIG. 3 is a reduced pressure C used in a reduced pressure CVD method according to an embodiment.
It is a schematic plan view showing a VD device.

FIG. 4 is a side view showing a method of fixing a sample in a low pressure CVD apparatus according to an example.

FIG. 5 is a schematic cross-sectional view showing a wafer on which a W film is formed by a conventional metal film forming method.

FIG. 6 is a side view showing a method of fixing a wafer in another conventional method of forming a metal film.

[Explanation of symbols]

11 single crystal Si substrate (wafer) 12 vapor phase growth surface 13 back surface 15 SiO ₂ film (oxide film) 17 W film (metal film)

Claims (1)

[Claims] 1. A method for forming a metal film, comprising forming an oxide film on the back surface of a vapor growth surface of a wafer, and then forming a metal film on the vapor growth surface.