JPH01253271A - Semiconductor element - Google Patents

Abstract

PURPOSE:To build a breakdown resistant structure characterized by absence of dispersion of leak currents by a method wherein microcrystals Si:H, produced by plasma CVD and equipped with resistance highly stable and reproducible at low temperatures, are used as a field plate resistance film. CONSTITUTION:A reaction vessel 12 is evacuated by an evacuating system 13 and then an H2-containing film forming gas is introduced into the reaction vessel 12 through a gas supply system 14. After this, power is applied across a cathode electrode 15 and anode electrode 16 from an RF power source 17, which results in the generation of plasma across the two electrodes 15 and 16 and in the formation of an amorphous silicon film on a substrate on the heated anode electrode 16. In this process, the Si:H film growth rate is set at 0.1-0.5Angstrom /sec for the formation of a microcrystal Si:H film constructed of approximately 100Angstrom diameter crystal grains. For a decreased film growth rate, percentage of H2 is to be raised in the film forming gas.

Description

[Detailed description of the invention] [Industrial application field] The present invention is applied to bipolar transistors, power MO3FETs,
The present invention also relates to the breakdown voltage structure of semiconductor devices that require high breakdown voltage, such as insulated gate bipolar transistors.

[Conventional technology]

Guard rings, field plates, etc. are used as the breakdown voltage structure of the above-mentioned high breakdown voltage semiconductor devices, but because they require less area and can provide stable breakdown voltage,
Field plates are increasingly being used. Next, the field plate provided in these high voltage semiconductor devices and its operation will be explained with reference to FIG.

FIG. 3 is a partial cross-sectional view of a high-voltage semiconductor element, showing an N-semiconductor substrate 1. P'' region 2. Insulating film 3. Low resistance film such as conductive metal 4. Resistive film of field plate 5. Negative electrode 6. Its terminal 7. Positive electrode 8. This is the part representing 9 and its terminal 10. 3, when a positive voltage is applied between electrode 6 and electrode 9, the PN junction between P″ region 2 and N− substrate 1 becomes reverse biased, and the depletion layer becomes N−.
It spreads toward the substrate 1 side and is electrically insulated. At this time, the equipotential surface of the depletion layer becomes, for example, as shown by the dashed-dotted line 11 in FIG. Since the electrode 8 is at the same potential as the electrode 9, a voltage is also applied between the electrode 6 and the electrode 8. In this state,
If resistive n*5 is not formed, P″
The breakdown voltage between region 2 and N-substrate 1 is determined by the size of the curvature of the impurity diffusion depth of P region 2, and the PN in the plane
The value is usually much smaller than that in the case of bonding. This is because the electric field concentrates on the curvature of PJTI region 2. Figure 4 shows a diagram showing the breakdown voltage calculated from the magnitude of the curvature and the length of the depletion layer. This is a diagram showing the relationship when the vertical axis is the ratio of the curve ml diameter r4 and the length W,4 of the depletion layer, and the breakdown voltage in the case of a planar junction is set to 1. teeth,
It can be seen that even under normal conditions, the withstand voltage is less than half that of planar bonding.

Unlike the insulating film 3, the resistive film 5 shown in FIG. This is intended to bring the breakdown voltage closer to that of a planar junction by reducing the concentration of electric field on the curved portion of the junction. That is, the voltage of the film 5, which is a resistor, is applied to the surface of the N-substrate 1 directly under the resistive film 5 through the insulating film 3, and the voltage distribution is from the negative electrode 6 to the positive electrode 8. The voltage increases linearly, and N-substrate 1
The depletion layer is expanded near the surface of P″ region 2 and N−
Since the junction between the substrates l is greater than or equal to 0, which is closer to that in the case of planar bonding, in order to bring the withstand voltage of such an element closer to the withstand voltage in the case of planar bonding, the distance between the negative electrode 6 and the positive electrode 8 is It turns out that you can make it larger. As the resistive film 5 of this field plate, an amorphous silicon film or a polycrystalline silicon film, which is usually formed by vapor deposition or the like, is used.

[Problem to be solved by the invention]

As described above, providing a resistive film is an effective means for semiconductor devices that require high breakdown voltage, but when using amorphous silicon for the resistive film, vapor deposition methods do not allow sufficient control of the resistance value. It is difficult to form a resistive film with good reproducibility. This resistance value determines the leakage current of the semiconductor element, so if a variation occurs in the resistance value, the leakage current will also vary accordingly, causing deterioration of the element characteristics. On the other hand, when a polycrystalline silicon film is used as the resistive film, the film is formed at a high temperature of around 400'C, and since the resistive film is usually deposited after forming the metal electrode, high-temperature treatment is required. This causes deterioration of the film quality of the metal electrode.

The present invention has been made in view of the above points, and its purpose is to provide a semiconductor element having a field plate resistive film that can be formed at a relatively low film formation temperature and has a highly stable resistance value. It's about doing.

[Means to solve the problem]

In order to solve the above problems, the semiconductor device of the present invention uses microcrystalline Si:H, which can obtain stable resistance values with good reproducibility at low temperatures by the plasma C, VD method, as the resistive film of the field plate. be.

(Function) The resistive film of the present invention is formed at a temperature of up to about 300°C, and variations in film thickness and specific resistance can be controlled with good reproducibility within ±10%, and impurities can be introduced. As a result, a wide range of resistance values from 10 9 to 1 O −1 Ω·cm can be obtained, making it suitable for use as a field plate, and a semiconductor element having a breakdown voltage structure with stable leakage current can be obtained.

〔Example〕

The present invention will be explained below based on examples.

As mentioned above, the resistive film used in the present invention is made of microcrystalline Si.
:H, and can be formed using, for example, a plasma CVD thin film production apparatus used in the production of solar cells. FIG. 1 shows a cross-sectional view of the main parts of the apparatus configuration, and the main parts are the reaction vessel 12. Exhaust system 13 to evacuate this to vacuum. Gas supply system that supplies film-forming gas】4. Cup 0-Code Electric 1415. Anode electrode 16
．． RF power source 17 connected to cathode electrode 15. Anode electrode 16 Semiconductor plate 1 located above and forming a resistive film
8. It consists of a heater 19 located below the anode electrode 16 and heating the semiconductor board 18 and a heater power source 20. Note that the device manufacturing process up to the formation of the resistive film will be omitted, and here it will simply be treated as one day of manufacturing a semiconductor board.

Microcrystal S using this device! Since the method for forming a :H resistive film is almost the same as that for forming an amorphous silicon film for a solar cell, an outline of the procedure for forming a normal amorphous silicon film will first be described. First, reaction vessel I2
is evacuated by the vacuum evacuation system 13 until the degree of vacuum is approximately several m Torr or less, and then a film forming gas such as 5iHa containing Ht is supplied into the reaction vessel 12 from the gas supply system 14.
Part of the reaction vessel 12 is evacuated using a vacuum evacuation system 13 to maintain the pressure inside the reaction vessel 12 at about I Torr. Thereafter, power is supplied from the RF power source 17 to the cathode electrode 15 and the anode electrode 16, and plasma is generated during the rain amount i 15.16. At this time, an amorphous silicon film is formed by the plasma generated between the picture electrodes 15 and 16 on, for example, a substrate (not shown here) on the anode electrode 16 which is heated to about 200°C by the heater 19 by the electric current [20]. can be formed.

The above process is the same when forming a microcrystalline Si:H film, but the difference from when forming an amorphous silicon film is the growth rate of the film. That is, the growth rate of a normal amorphous silicon film is 1 to 4 people/see, whereas when forming a microcrystalline Si 2H film, the growth rate is slowed to <Lo, 1 to 0.5 It should be about 1 person/sec. In this way, Si with almost 100 grains:
A H film can be grown. To reduce the film growth rate, H! in the film forming gas of S f Ha and Hz is required. In other words, to increase the flow rate of H2.

Figure 2 shows the relationship between the temperature of the semiconductor substrate 18 forming the resistive film (hereinafter referred to as the film forming temperature) and the growth rate of the Si:H film when the ratio of the 5tHn:Hz film forming gas is changed. FIG. The curve (a) in Figure 2 is S i H4:
Hz = 1: 41 curve (b) is S i Ha:
H2=1:9. Curve (c) is 5IHa:Hz=1:
14. As shown in Figure 2, H2
By increasing the amount of 2it, the film growth rate decreases,
In curve (c), a microcrystalline St 2 :H film can be obtained. In addition, since the film growth rate does not change much depending on the film formation temperature, microcrystalline Si:
It is possible to grow H films. This microcrystalline SL
:When forming an H film as a resistive film, if the film is grown without introducing impurities, it will be N-type with a resistivity of 1O''Ω・
However, if impurities such as boron are added to the
If it is introduced from the gas supply system 14 in the figure, a film with even higher resistance can be obtained, and similarly, by introducing pH, etc. during film formation, a film with lower resistance can be obtained. As described above, the microcrystalline S1:H film as a resistive film in the present invention has a flow rate of H,
By introducing impurities, it is easy to control the resistance value over a wide range of 10'' to 1O-1 Ω·cm.

Furthermore, the microcrystalline Si:H film obtained in this way has a variation of ±1 in film thickness and resistivity even for large areas.
It has excellent reproducibility of within 0%.

〔Effect of the invention] Bipolar transistor, power MOS FET.

Conventionally, amorphous silicon films or polycrystalline silicon films made by vapor deposition have been used as resistive films for field plates in high-voltage semiconductor devices such as insulated gate bipolar transistors, but these have been difficult to control the resistance value and reproducibility. inferior to
In addition, high-temperature treatment was required, so that satisfactory results could not be obtained, whereas in the present invention, as described in the examples,
Using a plasma CVD thin film manufacturing device, the amount of Hz a in the SiH4:Hz film forming gas was increased to reduce the film forming rate, and a microcrystalline St:H film was formed at a low temperature while impurities were introduced. The resistance value can be controlled over a wide range, and the microcrystalline St:H film, which has a stable resistance value and good reproducibility, is used as a resistive film suitable for the field plate, resulting in stable characteristics with no variation in leakage current. A great effect can be obtained in that a semiconductor element having a high breakdown voltage structure can be constructed.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main parts of the apparatus for forming microcrystalline Si:HWJ in the present invention, Fig. 2 is a diagram showing the relationship between film formation temperature and film growth rate using H2 flow rate as a parameter, and Fig. 3 4 is a partial cross-sectional view of a semiconductor element including a field plate, and FIG. 4 is a diagram showing the relationship between the breakdown voltage and the ratio of the radius of curvature of a PN junction having curvature to the length of the depletion layer. ■... N-semiconductor substrate, 2... P' region 3.
...Insulating film, 5...Resistive film, 6...Negative side electrode, 8
, 9... Positive side electrode, 11... Equipotential surface during bias, 12... Reaction vessel, 13... Vacuum exhaust system, 14...
...Gas supply system, 15...Power node y 1 Figure, temperature (C) 2 Figure

Claims (1)

[Claims] 1) An insulator provided on the surface of the semiconductor substrate having a second conductivity type region in a first conductivity type semiconductor substrate, and in which a depletion layer is expanded by applying a reverse bias to the semiconductor substrate and the second conductivity type region. A semiconductor element in which a voltage is applied by a resistive film through a film, the resistive film being a microcrystal S.
A semiconductor device characterized by using an i:H film.