JPS62132337A - Detecting method for mis structure boundary level using optical capacitance method - Google Patents

Abstract

PURPOSE:To calculate a boundary level from relation of emitting monochromatic optical energy corresponding to a variation amount by altering a voltage applied to a MIS diode to hold flat band capacity of the diode at a predetermined value. CONSTITUTION:An insulator layer 2 is formed on an N-type Si substrate 3, an MIS diode in which metal I is deposited is cooled to 77 deg.K, and a positive voltage VG is applied to the metal I side. Thus, a boundary level density NSS(E) is satisfied by electrons 6. A negative voltage GG of the metal I side is applied, and monochromatic optical energy hnu is emitted by setting to a capacity Cfb' slightly smaller than a flat band capacity Cfb. The value of VG is varied to hold Cfb' during the meantime. Relationship between variation amount VG of the applied voltage and energy hnu of the emitting monochromatic light is shown by a curve A. This curve A is differentiated by the energy hnu to calculate a boundary level density NSS(E). Thus, a boundary level substantially over the entire range of a band gap Eg can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of obtaining information on interface states of an MIS structure using a photocapacitance method.

In the photocapacitance method, monochromatic light is irradiated onto a depletion layer region such as a gate junction or a Shontkey junction in a semiconductor to change the charge state of a deep level in this depletion layer region.
The depletion layer can be changed by holding the voltage applied to the junction and changing the depletion layer capacitance (constant voltage method), or by changing the voltage applied to the junction so as to keep the depletion layer capacitance constant (constant capacitance method). Among these, the objective is to obtain information regarding deep levels (level ionization energy, density, photoionization cross section, etc.), especially at the position of the edge of the depletion layer. It is known that the ionization energy of a level directly corresponds to the monochromatic light energy that causes a capacitance change, and that thermal excitation of carriers is suppressed by measurement at low temperatures, making it possible to detect levels with high sensitivity. ing. However, at the interface between the insulator layer (1 layer) and the semiconductor (S) in the MIS structure, there is a heterogeneous junction made of materials with different lattice constants, so many energy levels exist almost continuously. This is different from a pn junction or a Schottky junction because the interface is in contact with an insulator layer.

A carrier accumulation layer or an inversion layer may be formed, and further,
The phenomenon is complicated due to the presence of 8 pupils of minority carrier effects with frequency and temperature dependence, and there have been no reports yet of detection of interface states in MIS junctions using conventional photocapacitance methods.

Conventionally, as a method for detecting the interface state of an MIS structure, particularly for detecting the distribution N5s(E) of the energy E of the interface state density Nss, the electrostatic capacitance (hereinafter referred to as capacitance) C of the MIS diode at various temperatures T and The relationship between the applied voltage V (c-
The v6 characteristic was measured and the relationship between the change in flat band voltage Vra and the temperature change in Fermi level Ef was utilized.

This means that as the temperature T increases, the Fermi level EF (T) in the semiconductor moves from the band edge at low temperature (conduction band edge or valence band edge) to near the center of the band gap Eg. Taking advantage of the fact that the interface states existing below the level EJ(T) are filled with electrons, by changing the temperature T, the charge state of the interface states can be changed. - The energy distribution N5s(E) of the interface state density is determined from the change in FB in the characteristics.

At this time, the energy E of the level to be measured is made to correspond to the position of the Fermi level (T).

Calculation of energy E is indirect, fine control of temperature T is required, it is difficult to measure only interface states that exist near the band edge of a semiconductor, and it is difficult to measure deep interface states. Temperatures exceeding 300°C may be required, and depending on the type of semiconductor material, it may change in quality.Furthermore, in samples of the same conductivity type (n-type or p-type), the wood quality may vary from either band edge. There are drawbacks such as the fact that only interface levels existing within an energy range of up to half of the energy gap Eg can be detected.

The method for detecting the interface state of an MIS diode according to the present invention uses a photocapacitance method at low temperatures (for example, 7?''K), so it can be measured while suppressing thermal excitation from the interface state, and monochromatic light energy can be measured. 1ν and the energy E of the level to be measured can be obtained, and by selecting the monochromatic light energy 'nv, it is possible to detect even the deep interface level in terms of wood quality. This eliminates the drawbacks of interface level detection methods.

The present invention makes use of the features of the photocapacitance method as described above, and when the MIS diode is irradiated with monochromatic light of various energies, the flat band capacitance C (b or flat band capacitance Cfb) of the MIS diode is
The voltage applied to the MIS diode is changed so as to maintain the capacitance Cab in the vicinity of Δ
The purpose is to obtain information regarding the interface state density N5s(E) from the relationship between V& and the energy hv of the irradiated monochromatic light.

In the present invention, since the applied voltage VQ is changed so that the capacitance Hc of the MIS diode is fixed at the flat band capacitance C5b or the capacitance C4b in the vicinity thereof, the t95 layer 11! It can be approximated that rl is as small as a memory knife. Therefore, it is thought that the semiconductor side is filled with majority carriers, and the insulator layer (1 layer) and semiconductor (S)
It can be considered that only the so-called interface level, which is the level at the interface with the molecule, changes its charge state by monochromatic light irradiation.

At this time, the charge state of the level existing in the insulator layer (layer 1) may also change due to this monochromatic light irradiation, but in this case, the level of the interface level detected as an equivalent interface level may change. It shall be considered as including

In addition, in cases where a metamorphic layer is formed at the interface of the MIS diode and this metamorphic layer is larger than the bandgap Eg of the semiconductor, the interface state is not easily filled by the majority carriers of the semiconductor even if the MIS diode is brought into a flat band state. Except in some cases, a minute depletion layer is formed on the semiconductor side,
Flat band capacity Slightly smaller capacity fit than C5b
It is better to keep it in cfb'.

A detailed description will be given below with reference to the drawings.

FIG. 1 is a schematic energy band diagram of the MISa structure for explaining the method of detecting the interface level 4 of the MIS structure according to the present invention. This is the state when applying a voltage VC, (IVFBI comb/hl) whose absolute value is a little larger than the voltage V. In addition, monochromatic light with high energy is irradiated and captured in the interface level N5s (E). It also shows the state in which electrons are excited to the conduction band of the semiconductor. Figure 2 shows the relationship between the capacitance C of the MIS diode and the applied voltage (C-h characteristic), and the curves α, β, γ is the dark state, )11/l light irradiation, and cold light irradiation C-V
+, the respective applied voltage VGO corresponding to the capacitance Cfb′ which is slightly smaller than the flat band capacitance Cfb.
, Vb+, Vc, z and VbO and Vry+, VCl2
The differences aVel and aVGz are also shown at the same time.

As an example of the interface state detection method, a 5i02 thermal oxide film of about 800 layers was formed as the insulator layer 2 on an n-type Si substrate 3 with a carrier density n of about 2 x 10 cm, and AQ was vapor-deposited as the metal I. The MIS diode is shown below.

First, cool the MIS diode to 77°K, then
In order to form a sufficient accumulation layer at the interface of the MIS diode, a positive applied voltage V&=+37 is applied to the gold III side in a dark state and maintained for 1 minute. By this operation, the interface state density N
5s(E) is filled with electrons 6, which are the majority carriers of the semiconductor.

Next, while maintaining the dark state, apply a negative voltage vq=-3,2 to the metal I side.
929 is applied, flat band capacitance C4b=22pF
Set a slightly smaller capacitance @ C4b = 20.00pF. Then, through a spectroscope, the monochromatic light energy 1,,=0.38.0.38.0.40---11.1
8. Light irradiation is performed for 3 minutes at 1 and 20 ev, respectively, and the value of vq is changed so as to maintain C5b'=20.0 OpF throughout the period. A band diagram in such a state is shown in FIG.

The change in each applied voltage V+ (h) is taken as the applied voltage V, oti- corresponding to the capacitance C+b in the dark state, and ΔVIlf (h) = Vc+ (k) - Vc,
Display and measure as o. This aVe (-ν)
FIG. 3 shows an example of a characteristic curve when the relationship between E and the energy of irradiated monochromatic light = E is graphed.

In addition, since the light intensity of the irradiated light is increased, the change in the applied voltage Ve becomes sufficiently saturated after 3 minutes of irradiation with monochromatic light of each energy h, and the interface state immediately behind the AQ metal electrode I is It appears that the radiation can be sufficiently excited by scattered light within the semiconductor or reflected light from the back surface.

The interface state density N5s(E) is N5s(E) = Cot, cl Vratky)
= Coy, river msueA dE eA
Since it can be calculated as dE = group・1main−1111−(1) ・eA dE, the curve in Figure 3 can be calculated as energy E
(=h) and use equation (1) to calculate the interface state density N5s(E). Here, Cat is the oxide film capacitance, A is the junction area, and e is the charge element.

FIG. 4 shows a schematic diagram of the result of the interface state density N5s(E) calculated as described above.

Since the sample uses an n-type semiconductor, the energy E in FIG. 4 represents the energy measured from the conduction band lower end Ec toward the single valence band end Ev within the band gap Eg.

Note that the energy hv of the irradiated monochromatic light is the band gap Eg
(5,2 yen), the electrons excited from the valence band are further excited to the conduction band, so the optical emission ratios of electrons and regular bills are e, respectively. , eP', the value multiplied by the right side of equation (1) using the correction coefficient represents the interface state density N5s(E), 'e,,' = e, O
In the case of , the correction coefficient becomes the expansion.

The above is an example of a MIS diode using an n-type semiconductor as a substrate, but the same applies to a MIS diode using a p-type semiconductor. In this case, the energy E corresponding to FIG. 4 indicates the energy value of the interface level measured from the valence band edge 1=v.

Although only the method for detecting the interface state of the MIS structure has been described, the same result can be obtained even if the insulating layer (I layer) 2 is replaced with a semiconductor device with a wide band gap.
It can also be applied to the detection of heterojunction interface states between two semiconductors with different bandgaps.

As is clear from the above explanation, if the method of the present invention is used, the temperature only needs to be kept low enough to suppress the thermal excitation of electrons and holes from the interface states, and strict temperature control is not necessary. Since the photocapacitance method is used, the energy of the interface state can directly correspond to the energy of monochromatic light, and furthermore, if the temperature is so low that only the shallow impurity level of the semiconductor is barely thermally active, This method has advantages such as being able to detect interface levels over almost the entire band gap Eg regardless of the conductivity type of the semiconductor.

[Brief explanation of drawings]

Figure 1 shows the energy of a MIS diode using an n-type semiconductor 3 when a voltage V whose absolute value is slightly larger than the flat band voltage VFR is applied and monochromatic light of energy iν is irradiated. A schematic diagram of the band, Figure 2 shows the capacitance C of the MIS diode and the applied voltage Vct.
The characteristic curve (C-V5 characteristic curve) of the relationship between candy-like 8 (curve α) and the state in which two monochromatic lights with different energies 1qv+ (curve β) and hν2 (curve γ) are irradiated, respectively, are B C
A schematic diagram of the C-VrJ4 characteristic curve at Vlvt > k1/+).
1 ((in the illuminated state, flat band capacitance ii) When a voltage VG that maintains the capacitance near Cb is applied, the change from the applied voltage VGo in the dark state -Δ■6
Figure 4 is a graph showing the relationship between the energy key h of the irradiated monochromatic light and the interface level calculated using equation (1) by differentiating the characteristic curve in Figure 3 with respect to the energy band ν). It shows the density N5s(E). Metal, 2→SiO insulator layer, 3mH type semiconductor (S
i), 4m interface state, 5# positively charged interface state due to monochromatic light irradiation, 6 electrons in the conduction band, 7 = 6 shallow donors,
EC, EV# conduction band edge, valence band edge of semiconductor, respectively
E) m, EHs - total bending, Fermi level of semiconductor, capacitance of cozm insulator layer, d - width of depletion layer of semiconductor

Claims (1)

[Claims] This is a semiconductor level detection method using the photocapacitance method, in which monochromatic light of various energies is irradiated onto a diode with an MIS structure (hereinafter referred to as an MIS diode).
When the charge state of the interface state of the MIS diode is changed, the flat band capacitance C_fb of the MIS diode is maintained, or the capacitance C_ near the flat band where the depletion layer capacitance on the semiconductor side can be ignored.
fb' is maintained, the amount of change ΔV_G in the applied voltage of the MIS diode is measured, and the amount of change ΔV_G in the applied voltage is calculated.
A method for detecting an interface state in an MIS structure, characterized in that the interface state is calculated from the relationship between V_G and the corresponding irradiated monochromatic light energy hv.