JPH02215128A - Formation of insulating film on semiconductor crystal substrate - Google Patents

Abstract

PURPOSE:To form an insulating film having excellent breakdown strength at the temperature not exceeding 150 deg.C with less variation with time in the film quality by a method wherein N radical produced in a different chamber is led in a reaction chamber together with PH3 so as to form a PxNy film. CONSTITUTION:An InP substrate 3 is mounted on a susceptor 4; a reaction chamber 2 is exhausted down to 10<-3>Torr; and the substrate 3 is heated at 100 deg.C. Specified amount of N2 and PH3 are led in from gas leading-in pipes 5, 7. Next, a producer 1 is actuated; N radical is led in fro another pipe 6 for reaction to PH3 so as to form a PN film 9 on the substrate 3. This film 9 in the thickness of 50nm, resistivity of 10<14>OMEGA.cm and having breakdown strength of 6X10<6>V/cm can be used as a gate insulating film of a FET. Furthermore, this insulating film 9 is hardly subjected to any variation with time in the film quantity due to moisture absorption.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for forming an insulating film on a semiconductor crystal substrate, and in particular to a method for forming an insulating film on a semiconductor crystal substrate. In particular, the present invention relates to a method of forming an insulating film suitable for use as a gate insulating film of a high frequency, high output insulated gate field effect transistor using InP.

(Prior art) InP has a higher electron saturation speed than GaAs, which is currently the mainstream material for microwave semiconductor devices.
It also has the property of high thermal conductivity, so
It is attracting attention as a material for semiconductor devices, which is expected to have higher frequency operation than GaAs.

With InP, it is difficult to form a good Schottky junction with low reverse leakage current as with GaAs.
The structure of an element using InP is an insulated gate field effect transistor (hereinafter referred to as 15FET) whose gate is a metal/insulator/semiconductor (hereinafter referred to as MIS) structure.
) has been mainly developed.

One of the biggest problems in putting InP Nl5FET into practical use is the occurrence of so-called current drift, in which the drain current fluctuates over time. Although there are currently many unknowns about the causes of current drift, the electron concentration in the operating channel changes over time due to charging and discharging of electrons to the interface level existing in the insulating film/InP (hereinafter abbreviated as IS interface). It is thought that one of the main causes is the fluctuation with the Therefore, reducing the interface state density at the IS interface as much as possible is a necessary condition for reducing current drift.

For this purpose, various insulating films such as In, Oa films, anodic oxide films,
Silicon dioxide (SiO□) film, silicon nitride film (Si)N4)
Attempts have been made to form .

However, in group ■-■ compound semiconductors such as InP, the vapor pressure of group ■ elements is generally high, so
If an insulating film is deposited at a temperature above this temperature, phosphorus (P), a group III element, will dissociate and defects will occur on the InP surface (IS interface), which will lead to the creation of a high density of interface states. . Therefore, in order to form a good IS interface, it is considered necessary to form an insulating film at as low a temperature as possible.
Deposition temperature 2 using methods such as D method and plasma CVD method
Attempts have been made to form an insulating film at a temperature of 50 to 300°C. In fact, Sin, formed by these methods, 5
Relatively good interfacial properties have been reported for iaN4 films and the like. Furthermore, recently, phosphorus has been more actively introduced into the deposition atmosphere, and insulating films such as phosphorus-doped 5in2 films (hereinafter referred to as PSG films) and phosphorous nitride films containing phosphorus as a constituent element of the film have been deposited. It was found that this is effective in preventing the dissociation of phosphorus from the InP substrate surface, and it also has good interface properties with an interface state density of 1×10″L cm−2·ev−1 or less. It has been reported.

However, insulating films formed by these low-temperature deposition methods have problems with electrical properties such as electrical resistance and dielectric strength of the film, and the InP substrate surface is damaged by the plasma and light energy used to lower the temperature. There was a problem in that the damage caused caused new interface states to be generated.

In addition, low temperature deposited films, particularly the improved phosphorous-containing insulating films described above, have had reliability problems in that the properties of the film change over time due to hygroscopicity.

In this way, there is a trade-off between lowering the deposition temperature, which is aimed at improving the InP MIS interface properties, and the properties of the deposited insulating film itself, especially the reliability-related properties such as hygroscopicity. The elements were strong.

Therefore, phosphorus nitride film and PSG film have excellent interface properties.
For insulating films containing phosphorus, such as films, the lower limit of the practical film formation temperature, that is, the lowest temperature at which a film can be formed without any problems in hygroscopicity is 150 to 200°C.
It was about.

According to experiments conducted by the present inventors, for example, even in an InP MISFET using the PSG film as a gate insulating film, the drain current fluctuated by about 10% in 30 minutes. In an InP MISFET using a SiO□ film that is not doped with phosphorus, a current fluctuation of approximately 50 to 100% was observed.Although the amount of drift is significantly reduced, the improvement effect is still insufficient. I had to say. For this reason, the actual situation is that it is not possible to manufacture InP MISFETs that can be put to practical use.

(Problem to be solved by the invention) As mentioned above, by conventional deposition methods.

When attempting to lower the insulating film deposition temperature in order to form an IS interface with low interface state density and good characteristics, problems such as a decrease in reliability due to hygroscopicity were encountered. For this reason, a deposition method capable of realizing a MISFET with good characteristics without causing current drift and forming an insulating film with excellent reliability has not been found.

The present invention has been made to solve the above-mentioned problems.
It is an object of the present invention to provide a method for forming an insulating film suitable for use in a gate insulating film of a 15FET using P.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention excites nitrogen gas in a chamber different from the reaction chamber in which the insulating film is formed, and generates nitrogen radicals together with phosphine (PH3). At least phosphorus (P) introduced into the reaction chamber and installed in the reaction chamber.
Phosphorous nitride (PN) in a semiconductor crystal substrate containing as a constituent element
In the process of forming an insulating film, the temperature of the semiconductor crystal substrate is maintained at 150° C. or less during deposition, and the semiconductor crystal substrate is made of InP.

(Function) As a result of various studies and experiments conducted by the present inventor, the present invention has been developed by generating nitrogen radicals in a chamber different from the reaction chamber in which the insulating film is deposited, so that the surface of the semiconductor crystal substrate is directly exposed to the radicals. By introducing the nitrogen radicals generated here together with PH and gas into the reaction vessel to form a phosphorous nitride film (PH film), the substrate temperature during deposition can be lowered to a level lower than that of the conventional one. This was made based on the discovery that it was possible to form a phosphorous nitride film that had good dielectric strength even at temperatures below 150° C., which was the lower limit of 150° C., and that did not change its quality over time due to hygroscopicity. By forming a phosphorus nitride insulating film using the deposition method of the present invention, a good IS interface with significantly reduced interface state density can be formed.

Note that the above-mentioned phosphorus nitride (PN) is a general term that includes compounds generally deviating from the stoichiometric composition represented by the chemical formula PxNy (X and y are integers).

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an insulating film forming apparatus.

The main parts are: microwave excitation radical generator 1° reaction chamber 2*InP substrate 3. and a susceptor 4 that holds the InP substrate 3.

A radical generating section in the radical generator 1 is spatially separated from the reaction chamber 2. Further, a heater is embedded in the susceptor 4, so that the InP substrate 3 held therein can be heated to a desired temperature. Further, a gas exhaust port 8 is provided below the reaction chamber 2, and the end thereof is connected to an exhaust pump (not shown), and the inside of the reaction chamber 2 is 1O-3To.
The structure is such that it is possible to create a reduced pressure state of about rr.

The process of forming a PH film on an InP substrate using an apparatus having such a configuration will be described below. First, InP
The substrate 3 is placed on the susceptor 4, and the reaction chamber 2 is discharged from the discharge port 8.
Evacuate the inside to about 10'''' Torr.

Next, the heater embedded in the susceptor 4 is energized to heat the InP substrate 3 to a predetermined temperature, for example, 100°C.

When the substrate temperature reaches a steady value, a predetermined amount of nitrogen and PH are introduced into the reaction chamber 2 through the introduction pipes 5 and 7, and the radical generator 1 is activated to generate nitrogen radicals. These nitrogen radicals are introduced into the reaction chamber 2 through the tube 6, react with phosphorus (P) supplied from PR, and are deposited on the PNNO3InP substrate 3.

The resistivity and dielectric breakdown field strength of the PH film formed in this way are each 1×1014Ω when the film thickness is 50n.
・c+a, 6X10″V/ci+.This is M
It can be put to practical use as a gate insulating film for ISFET. Furthermore, no change in membrane quality over time due to hygroscopicity was observed in this PH membrane.

In the above example, the case where the deposition temperature was 100°C was explained, but if the method described in the example is used, a PH film with good moisture absorption properties can be deposited even if the deposition temperature is room temperature. Yes, there is such a l5FE! τ
When depositing a gate insulating film of
There is no need to be particular about 0° C., and therefore, the present invention is not restricted to deposition conditions such as temperature and flow rate during deposition.

When we fabricated an InP MISFHT using the film formed by the method of the present invention as a gate insulating film and measured the drain current drift, we found that the amount of drift was extremely small, within 3%, as shown by the solid line in Figure 2. Ta. Furthermore, the second
The figure shows the time change in drain current when 5V is applied between the source and drain and the gate bias voltage is changed stepwise from Ov to -4V at time (t) = O.
It is shown normalized by the initial value of the drain current.

In order to clarify the effects of the present invention, Figure 2 shows the results of creating an InP MISFET with the same structure and using a PSG film deposited at 250°C as the gate insulating film, and measuring the drift under the same bias conditions. are also shown by broken lines.

In the PSG film, a drift of 9% occurs in 30 minutes,
In using a gate insulating film deposited by the method according to the present invention
It can be seen that the current drift is significantly reduced in the P MISFET.

〔Effect of the invention〕

As described above, according to the present invention, the conventional 150 to 200
The deposition temperature of PN, whose practical lower limit was 150 °C, was
Because it can be lowered to room temperature below ℃ without any hygroscopic problems,
The interface state density at the MIS interface is significantly reduced, and when the insulating film made by this method is applied to the gate insulating film for 15FtET, the amount of drift of the drain current can also be significantly reduced compared to the conventional method.

In this text, the present invention has been described with reference to an embodiment in which the semiconductor crystal substrate 3 is InP, but excellent effects can be obtained even when the present invention is applied to a semiconductor containing phosphorus such as GaP.

[Brief Description of the Drawings] Fig. 1 is a schematic diagram showing an apparatus for forming an insulating film according to the present invention, and Fig. 2 is a MISFET using an insulating film formed by the method of the present invention as a gate insulating film. FIG. 3 is a diagram showing the results of comparison with a gate insulating film formed by a conventional method regarding the time change in drain current of the gate insulating film. l Radical generation fence reaction chamber InP substrate (semiconductor crystal substrate) Susceptor 7---1---Gas introduction pipe

Claims (2)

[Claims] (1) When forming an insulating film of phosphorus nitride on a semiconductor crystal substrate containing phosphorus as a constituent element, the semiconductor crystal substrate containing phosphorus is placed in a reaction chamber, and the semiconductor crystal substrate is heated to 150°C.
The nitrogen radicals generated by exciting nitrogen in a chamber different from the reaction chamber are introduced into the reaction chamber together with phosphine to form an insulating film on the semiconductor crystal substrate. How to form a film. (2) A method for forming an insulating film on a semiconductor crystal substrate according to claim 1, characterized in that the constituent element is phosphorus and the semiconductor crystal substrate is made of InP.