JPH02174123A - Formation of film - Google Patents

Abstract

PURPOSE:To form a gate insulating film by using one kind of film formation method, whose dielectric breakdown strength is good and which has a good interface characteristic between itself and a semiconductor layer by a method wherein a flow-rate ratio of raw material gases is changed while the film is being formed. CONSTITUTION:In a silicon oxide film formed between a metal layer and a semiconductor layer by a photo-assisted CVD method used to form a film by decomposing a raw-material gas by being irradiated with light, the film of a part coming into contact with the metal layer is formed under a condition that a flow-rate ratio of a gas for silicon supply use to a gas for oxygen supply use is at 1X10<-3> or higher and 1X10<-2> or lower. In addition, the film of a part coming into contact with the semiconductor layer is formed under a condition that the flow-rate ratio is smaller than 1X10<-3>. When the flow-rate ratio of the raw-material gases is changed, it is possible to obtain an insulating film whose dielectric breakdown strength is high and whose interface with reference to a semiconductor (silicon film) is good.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a film forming method.

[Conventional technology]

In the case of a device in which a gate insulating film is formed after forming a metal electrode, such as TPT (Thin Film Tractor/Raster), the gate insulating film has a two-layer structure using two film forming methods. This is because it is difficult to sufficiently cover pinholes that tend to occur on metal and to form a good interface state with the semiconductor layer with only one insulating film formed by one film formation method. 2
As an example of a layer structure, the surface of a semiconductor layer is coated with light CV at a low temperature.
A method of covering with a 5i01 film formed in D, followed by raising the temperature and forming a further Sin film by thermal CVD at atmospheric pressure was reported by Mimura et al. ) is reported on page 290. This method requires many steps such as temperature increase, replacement of raw material gas, and change of deposition pressure settings in order to switch from optical CVD to thermal CVD. On the other hand, after forming the electrode, its surface is anodized,
Thereafter, a method of integrally forming a gate insulating film and amorphous silicon in a vacuum was reported by Nichico et al. in 1988 in the Technical Report of Television Engineering, page 7.

In this case, film formation can be done in an integrated process, but the process is not simplified because a wet process (1), which involves dipping the substrate in an aqueous solution, is added. As described above, with conventional methods, it is difficult to form a gate insulating film that has good dielectric strength and a good interface state with the semiconductor layer using one type of film formation method. Ta.

[Problem that the invention attempts to solve]

The purpose of the present invention is to solve the problems of such conventional methods.
An object of the present invention is to provide a method for forming a gate insulating film which has a good dielectric strength and can maintain a good interface state with a semiconductor layer using only one film forming method.

[Means to solve the problem]

In order to solve the above problems of the prior art, the present invention provides a silicon oxide film in which a silicon oxide film is formed between a metal layer and a semiconductor layer by photo-CVD, which is formed by decomposing a source gas by light irradiation. Among them, the portion in contact with the metal is formed under conditions such that the flow rate ratio of the silicon supply gas to the oxygen supply gas is 1 × 10 or more and 1 × 10 or less,
The portion in contact with the semiconductor layer was formed under conditions where the flow rate ratio was smaller than I×10 2 .

[Effect]

The dielectric strength characteristics, interface characteristics with semiconductors, etc. of the current visiting body vary greatly depending on the ratio of its constituent atoms.

Since this ratio strongly depends on the raw material gas mixture ratio during film formation, it is generally possible to stack a plurality of films with different properties by changing the raw material gas mixture ratio during film formation. For example, silicon supply gas such as silica/silicon, N, O,
When forming a silicon oxide film by mixing oxygen supply gas such as O, etc., a silicon-rich film is formed by increasing the ratio of silicon supply gas to oxygen supply gas. This phenomenon has been confirmed in various film forming methods using CVD such as light, and this phenomenon is particularly noticeable in photoCVD when both the silicon supply gas and the oxygen supply gas are photochemically decomposed. This is because the products of silicon supply gas being decomposed alone are directly injected into the membrane without reacting with the oxygen supply gas, or Si-
This is considered to be because the probability that the intermediate products of 0-H and S 1-0-4 are injected into the membrane becomes high. Therefore, in order to form a silicon oxide film having a stoichiometric composition, it is necessary to make the flow rate of the oxygen supply gas sufficiently larger than the flow rate of the silicon supply gas. A good interface can be formed between the thus obtained stoichiometric composition of 5iOzf'i and Si. However, the voltage resistance properties of this film have not been well known.

In this regard, the inventors have found through experiments that the film is easily formed when the flow rate ratio of the silicon supply gas is extremely high. This is thought to be because the number of molecules of silicon supply gas that can collide with one molecule of oxygen supply gas is very small, which tends to result in a rough film due to reasons such as low nucleation density at the initial stage of film formation. .

Figure 2 shows the leakage current of a silicon oxide film obtained by Ar-F laser CVD using 5itH1l as a silicon supply gas and N and O as FR element supply gases as a function of the raw material gas flow rate ratio.
That is, it is a diagram conceptually showing the experimental results of the present inventor that (silicon supply gas flow rate/oxygen supply gas flow rate) depends on K.

Region (2) is a region where increasing the flow rate K results in silicon richness and the breakdown voltage deteriorates. This is because the resistivity of the silicon oxide film gradually approaches the resistivity of silicon. On the other hand, in region (3), although a stoichiometric composition can be achieved by lowering the flow rate ratio, the film quality tends to become rough due to low nucleation density, etc., and the breakdown voltage deteriorates.

The region (2) in between these regions is a region that is a little richer in silicon than the stoichiometric Sing, and has a higher density of interface states with Si, but is a region where a cricon oxide film with excellent dielectric strength is formed. be.

In the present invention, by utilizing the effect discovered by the inventor that the dielectric strength characteristics and interface characteristics of the insulating film are changed by changing the flow rate ratio of the raw material gas, the gold metal A film, which is prone to generate pinholes, is A dense film with excellent pressure resistance characteristics is formed at the flow rate ratio in region (2), and a film with stoichiometric properties and excellent interfacial characteristics is formed at the flow rate ratio in region (2) on the part in contact with the interface with the semiconductor. Through this complex process, an insulating film having a high dielectric strength voltage and a good interface with a semiconductor (silicon film) can be obtained according to the present invention. Furthermore, in the present invention, unlike conventional methods, it is not necessary to use two or more film-forming methods, and the film can be formed by simply changing the film-forming conditions within a single device, so there is no need to transfer the substrate. It is possible to reduce costs and improve throughput.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to the formation of an inverted staggered TFT gate gate will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an apparatus for forming a gate insulating film to which the present invention is applied. Board 8 is a CV with an exhaust bonder
It is fixed in a D chamber 5, and a pattern is transferred onto a substrate 8 by light emitted from an ArF laser 1 through a pattern mask 2, a synthetic quartz lens 3, and a synthetic quartz window 4. The substrate 8 has a chromium gate electrode formed in the previous process on glass,
It is heated to an appropriate temperature by a heater or the like. The source gases Si*Hs and NtO are each supplied to the first mass 70-controller 26. Second square 70-control, 771C
Therefore, it is supplied to the CVD chamber 5. Ki at the start of deposition
dsilHaON201c to frua quantity ratio 2 x 10
-' The first mass flow controller 6, so that it is greater than or equal to 8×10 or less! :Second mass flow controller 7
Set. When the 5iOz film thickness reaches about 2000λ, the first mass 70-controller 6 is adjusted so that the flow rate ratio of 5i2H@ to N, OK becomes smaller than 2×10.
2nd cell 70 - change the setting value of controller 7,
Further film formation was continued to a thickness of 3000λ. Thereafter, an a-8i:H layer was formed in a post-process.

In the present invention, a film covering the vicinity of the electrode where pinholes tend to occur is first formed at a flow rate ratio that provides a good dielectric strength voltage, so there is no possibility of a poor withstand voltage. Further, since the portion in contact with a-si:) is formed at a flow rate ratio that provides a good composition, the interface characteristics with a-8i:H are also maintained good.

In the present invention, a gate insulating film with good dielectric strength and interface properties can be formed through vacuum simply by changing the flow rate ratio of the raw material gases, so there is no need to transfer the substrate from one device to another. Ta.

〔Effect of the invention〕

As explained above, according to the present invention, by changing the raw material gas flow rate ratio during film formation, one type of film formation method can have good dielectric strength and good interface properties with respect to the semiconductor layer. A gate insulating film having the following characteristics can be formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an apparatus to which the method of the present invention is applied;
FIG. 2 is a diagram showing the relationship between the properties of a film formed by photo-CVD and the raw material gas flow rate ratio. 1...ArF laser, 2...pattern mask, 3...-synthetic quartz lens, 4-old...synthetic quartz window, 5...CVDf bumper, 6・・・・・・
・First mass flow control o-9,7...Second
mass flow controller, 8... board. Yoshi 1 Illustration agent Patent attorney Susumu Uchihara

Claims (1)

[Claims] In a method of forming a silicon oxide film between a metal layer and a semiconductor layer by photo-CVD in which film formation is performed by decomposing a raw material gas by light irradiation, a portion of the silicon oxide film in contact with the metal layer is filled with a silicon supply gas. The flow rate ratio for the oxygen supply gas is 1 x 10^-^3 or more 1 x 10^-^
2 or less, and a portion in contact with the semiconductor layer is formed under conditions where the flow rate ratio is less than 1×10^-^3.