JPH0516672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention provides a microcomputer,
The present invention relates to a semiconductor device having nonlinear characteristics that is applied to a solid-state display device for solidifying the display portion of a word processor or television, a message sensor, or a liquid crystal printer.

``Prior Art'' For solid-state display panels, a system in which each picture element is controlled independently is effective for large-area displays. In a panel using such active elements, amorphous silicon is used in a 1:1 connection with all pixels.
Nonlinear elements with NIN junction structures are known. However, even if this NIN junction is used, its NI
Alternatively, it is unclear how the IN junction interface is formed, and sufficient nonlinear characteristics symmetrical about the origin in the VI characteristics have not yet been obtained.

FIGS. 2A to 2D outline the operating principle of a conventionally known NIN junction type nonlinear element.

FIG. 2A shows a semiconductor 2 having an N12, I13, N14 structure. In this case, all of the N, I, and N semiconductors are silicon non-single crystal semiconductors containing hydrogen.

Its thickness is N12700Å, I134000Å, N1
It is 4700 Å. Figure 2B shows the energy band diagram when no voltage is applied between terminals 21 and 22.
Shown below. On the other hand, if a positive voltage (Va) is applied to the substrate side terminal 22 compared to the substrate side terminal 21, the energy band structure shown in FIG. 2C will be obtained. Then electron 43
flows as a forward current as the barrier 41 lowers its height to 41'.

In addition, at the NI interface 31, part of the inert phosphorus constituting the N-type semiconductor layer 21 is mixed into the I-type semiconductor 23 during film formation by plasma CVD, so the I layer near the interface becomes N. ^-Transforms into a tendency.
Therefore, the barrier caused by the application of +Va at the NI interface became sufficiently low, and as a result, current characteristics were obtained in which only a low threshold voltage of 1 to 2 V was obtained as shown in FIG. 451.

At this time, the other barriers 42, 32 (FIG. 2B) do not constitute a barrier and do not constitute a barrier to the flow of current.

Conversely, when a negative voltage -Va is applied to the terminal 22 (Fig. 2C), the barrier 42 becomes 42', and its N
Electrons 43' of the type semiconductor layer 14 flow from 42' to 13. Such a conventional plasma using only silicon
When forming by the CVD method, the silicon of the I layer 13 mixes into the N layer 14, and the vicinity of the interface of the N layer 14 tends to become N ^- , so the intermediate region 32 is wide and -Va changes. However, the height 42' of the barrier cannot be made sufficiently low. As a result, asymmetric characteristics such as those of a PIN junction diode formed with an NIN structure tend to be obtained.

``Problems to be solved by the invention'' However, when trying to use nonlinear elements, N
Even if layers I and N are gradually laminated by plasma CVD, phosphorus, which is an N-type impurity, mixes into the I-type semiconductor layer at this NI interface. Furthermore, at the IN interface, a mixed N ^- layer of an I-type semiconductor and an N-type layer is formed in the interface region. If such impurities and constituent components were mixed with each other at the interface, it was impossible to achieve symmetry in the V-I characteristics.

``Purpose of the invention'' To eliminate such asymmetric diode characteristics,
It is an object of the invention to provide symmetry with respect to the origin. In addition, by adding carbon in the I layer,
Another purpose is to control the size of the threshold.

"Means for Solving the Problem" In order to solve the problem, the present invention uses a nonlinear element made of a non-single crystal semiconductor to which hydrogen or a halogen element is added, and the I-type semiconductor and N
A large amount of carbon was added to the interface with the type semiconductor.
SiXC _1-X (0<X<1) is provided, and this barrier layer prevents the mixing of impurities and constituents during film formation. Furthermore, the present invention is characterized in that this I-type semiconductor contains Si-
The main feature is that it has a SiXC _1-X (0<X<1)-Si structure.

The nonlinear element used in the present invention has one
Rather than using a diode consisting of a PIN junction and electrodes with contacts above and below it, a pair of electrodes each have ohmic contact, but
It consists of an element with a composite diode that has reverse rectification characteristics, and a typical example is an N-type semiconductor.
A NIN structure in which an I-type (hereinafter referred to as intrinsic or substantially intrinsic) semiconductor and an N-type semiconductor are stacked, that is, an NIN structure in which an NI junction and an IN junction are electrically connected in opposite directions and are integrated as a semiconductor. Including semiconductors with junctions, their variants NN ^- N,
It is a composite diode with NP ^- N, PIP, PP ^- P or PN ^- P structure.

The threshold voltage of such a composite diode makes the diode characteristics opposite to each other, and its build-in (rise) voltage (threshold) is equal to that of the N-type semiconductor and I-type semiconductor of the NI junction or
It can be determined by the concentration of trace impurities such as phosphorus, which determines the conductivity near the NI interface, and the concentration of impurities and additives, such as carbon, which determine the energy band width. Therefore, by controlling the manufacturing process, it is possible to control the value of the threshold voltage of a desired element, the difficulty of current flow below the threshold value, and the ease of current flow above the threshold value. Furthermore, since it is a semiconductor-semiconductor junction method without using the physical properties of the insulating film-semiconductor interface, temperature treatment, B-T treatment (bias-
It has the feature of not being unstable due to temperature and temperature treatments.

Therefore, for a solid state display element, for example, a liquid crystal, the AC bias can be controlled by controlling the level of the other electrode lead of the liquid crystal, and gradation control is also possible.

"Function" By providing a sufficiently thin barrier at such an interface, that is, preferably a barrier made of SiXC _1-X (0<X<1) that allows tunneling current to flow and having a large energy band width, the N-type semiconductor and the I-type semiconductor can be separated. It is possible to prevent the junction from becoming "sluggish", which is characteristic of amorphous semiconductors, due to the flow of a large current at the interface, and it is possible to produce a highly reliable NIN junction type nonlinear semiconductor.

The present invention will be described below with reference to Examples.

Example 1 FIG. 1A shows a longitudinal cross-sectional view of an actual device structure.

In FIG. 1A, non-alkali glass 20 was used as the light-transmitting insulating substrate. A conductive film is applied to this upper surface by sputtering or electron beam evaporation.
An ITO or tin oxide film was formed to a thickness of 0.1 to 0.5 μm, and a light-shielding chromium film was similarly laminated to a thickness of 300 to 2500 Å on the top surface. Thereafter, this conductive film was patterned using a first mask, unnecessary portions were removed, and electrodes were formed.

Thereafter, a composite diode made of a non-single-crystal semiconductor doped with hydrogen or a halogen element having an NIN structure was formed on the entire surface thereof by a plasma vapor phase reaction method. That is, by subjecting the N-type semiconductor 12 to silane and subjecting it to high frequency glow discharge at 13.56 MHz, a non-single crystal semiconductor having an amorphous structure is formed on the formation surface of the substrate maintained at 200 to 250°C. Its electrical conductivity was 10 ^-5 to 10 ^-3 (Ωcm) ^-1 and the thickness was 50 to 500 Å. Further next 10 ^-6 ~
Vacuuming was carried out sufficiently to 10 ^-7 torr. moreover,
Silane (SimH _2n+2 e.g. SiH ₄ with m=1) was mixed with methisilane (SiH _o (CH ₃ ) _4-o n=1-3). That is, when n=2, H ₂ Si(CH ₃ ) ₂ /SiH ₄ =
The flow rate was set to 1/10 to 1/200, for example 1/50 (flow rate cc).
This mixed reactive gas is introduced into a plasma reactor and subjected to a plasma reaction to form a non-single crystal semiconductor 13 represented by SiXC _1-X (0<X<1) to which type I hydrogen or halogen elements have been added. To a thickness of 0.2~1μ,
For example, it is formed by laminating it on an N-type semiconductor with a thickness of 0.4 μm. Furthermore, sufficient vacuum was drawn to 10 ^-6 to 10 ^-7 torr. Again, similar N-type semiconductors 14 having an amorphous structure were laminated to a thickness of 50 to 500 Å to form an NIN junction.

Thereafter, on this upper surface, SnO ₂ or ITO as CTF was laminated to a thickness of 500 to 1500 Å, and chromium or aluminum (500 to 1500 Å) to be used as leads and electrodes were laminated by electron beam evaporation or sputtering. Furthermore, except for the area provided as the electrode 22 and composite diode 2, other parts are
A second electrode was formed by removing the film by photoetching using a photomask.

That is, in FIG. 2A, a transparent conductive film 17 on a glass substrate 20, a first electrode 21 made of a chromium electrode 11, an NIN junction type composite diode 2 made of a N12, I13, N14 semiconductor stack, a CTF1
5. It consists of a second electrode 22 made of chromium or aluminum 16. The symbol for this NIN structure is shown in Figure 2B.

FIG. 4 shows curves 52 and 52' showing the voltage-current characteristics of the semiconductor device manufactured in this example.

Furthermore _, for comparison purposes, _{a semiconductor device (H 2 Si} (CH _{3 )} ) The voltage-current characteristics (V-I characteristics) of the semiconductor device (which has the same configuration as this example except that ₂ is not added at all) are shown by curves 51 and 51'.
Shown as

From the curve 51 in this figure, it can be seen that in the conventional semiconductor device in which carbon is not added to the I layer, the threshold value is only about 1 to 2 V.

In contrast, it can be seen that the semiconductor device manufactured in this example has a threshold voltage of 10V or more.

It can also be seen that the symmetry with respect to the origin is better in curves 52 and 52', that is, in the VI characteristic of this embodiment.

In this way, when carbon is added to the I-type semiconductor layer of the semiconductor device shown in this example, the threshold voltage is higher than that of a semiconductor device with the same configuration without carbon addition, and the symmetry of the V-I characteristic is It can be seen that the results also improve.

The two points mentioned above are the remarkable effects that can be obtained experimentally when the configuration of the present invention is adopted. The operating principle and effects of the present invention will be explained using FIG. 4.

Figure 3A shows an N-type semiconductor made of amorphous silicon doped with hydrogen (thickness of 500 Å or less, preferably 100 Å or less).
200 Å), a second semiconductor I13 consisting of an intrinsic or substantially intrinsic amorphous semiconductor represented by hydrogen-doped SiXC _1-X (0<X<1); The third type has the same characteristics as a semiconductor.
This is a semiconductor 2 having a semiconductor N14 structure. Its thickness is 100 to 200 Å for N12 and 2000 to 200 for I13.
4000 Å, N14 100-200 Å. The energy band diagram when the voltage in this case is not applied to the board side terminal 22 with reference to the board side terminal 21 is shown in the third diagram.
Shown in Figure B. In this drawing, the NI interface 31,
The IN interface 32 has approximately the same curvilinearity 31 and 32.

This is explained by the VI characteristic obtained as the electrical characteristic of the semiconductor device according to the present example described above.

In the structure of the present invention, there are two IN interfaces, but if silicon is mixed into the N layer at the IN interface,
Alternatively, if phosphorus is mixed in from the N layer, it is generally impossible for similar mixing of constituent components or diffusion of impurities to occur at these two IN interfaces. For example, when a first N-type semiconductor layer, an I-type semiconductor layer, and a second N-type semiconductor layer are generally stacked in order by a vapor phase chemical reaction method,
When forming an I-type semiconductor layer after forming the first N-type semiconductor layer, the previously formed first N-type semiconductor layer is exposed to an activated reactive gas for forming the I-type semiconductor layer. The surface will be exposed. As a result, the surface of the first N-type semiconductor layer is activated by the reaction energy of the reaction gas for forming the I-type semiconductor layer,
It will react with the reactive gas for forming the I-type semiconductor layer.

As a result, the element constituting the I-type semiconductor layer, that is, silicon, is mixed near the surface of the first N-type semiconductor layer.

In addition, when forming the second N-type semiconductor layer after forming the I-type semiconductor layer, the surface of the I-type semiconductor layer will be exposed to the reactive gas for forming the second N-type semiconductor layer. Since it is activated by the reaction energy, an impurity element, such as phosphorus, added to the second N-type semiconductor layer is mixed and diffused into the vicinity of the surface of the I-type semiconductor layer.

As a result, the state of the mixture of impurities and constituent components at the two IN interfaces is different.

As described above, the reality is that the mixing of constituent components or the diffusion of impurities at the two IN interfaces is generally unbalanced.

As a result, it is natural to recognize that the mixing ratio of constituent components or the concentration of impurities imparting one conductivity type, such as phosphorus, are different in the vicinity of these two IN interfaces.

It is thought that the states of the energy band diagrams near the two IN interfaces, which have such a mixture ratio of different constituent components or a concentration of phosphorus, which is an impurity imparting one conductivity type, are different.

If the state of the energy band diagram near the two NI interfaces is different, the symmetry of the V-I characteristic of this semiconductor device with respect to the origin will collapse depending on the difference in the state of the energy band diagram near the two NI interfaces. It should be.

However, in conventional semiconductor devices in which carbon is not added to the I layer, the symmetry of the measured VI characteristics with respect to the origin is significantly disrupted. This is clear from FIG. 4, 51 and 51'.

On the other hand, it can be seen that in this example in which carbon is added to the I layer, which is the structure of the present invention, a VI characteristic with clear symmetry with respect to the origin is obtained. This is clear from FIG. 4, 52 and 52'.

Here, if we recognize that the cause of the collapse of symmetry with respect to the origin of the VI characteristic is due to the mixing of constituent components or the diffusion of impurities, then the V
It can be concluded that the good symmetry of the -I characteristic with respect to the origin is due to the absence of mixing of constituent components or diffusion of impurities.

Considering the above, the good symmetry of the V-I characteristic with respect to the origin, which is data obtained experimentally, is due to the fact that the addition of carbon prevents the mixing of impurities and constituent components. It is natural to think so.

It can be seen that by adding carbon in this manner, this example has the electrical characteristics shown in the energy band diagram of FIG. 3B.

DMS (dimethylsilane) into the I layer in this case
The addition of was kept constant within the I layer. That is, as shown in FIG. 1C, when forming the I layer, DMS/SiH ₄ =1/50.

In FIG. 3C, when a positive voltage (+Va) is applied to the substrate 22 compared to the substrate 21, the energy band structure shown in FIG. 3C is obtained. Then, the electrons 43 flow as a forward current as the barrier 41 lowers its height to 41'. Then, a curve 52 in FIG. 5 is obtained.

Conversely, when a negative voltage (-Va) is applied to the terminal 22, as shown in D, the barrier 42
2', and the electrons 4 of the N-type semiconductor layer 14
3' flows from 14 to 13, resulting in curve 52 in Figure 5.
get.

As a result, the nonlinear characteristic 5 as shown in FIG.
2,52' can be provided corresponding to FIGS. 3C and 3D.

Further, since carbon is added to the I layer, the threshold value can be made higher than 1 to 2 V, for example, 10 V or more at +Va. In addition, carbon in this I layer is SiXC _1-X
Because it combines sufficiently with silicon to form silicon carbide, it prevents silicon from mixing into the N layer at the IN interface 32, and the threshold value on the opposite direction side (-Va side) is lower at 52' than 51', and at 52 and at the origin. It can be made to have symmetry.

That is, for the NIN junction, the rise voltage (threshold voltage) 100, 100' is the height 41, 42 and width 31, 32 of the barrier in FIG.
Determined by

Example 2 In the present invention, on the I layer side in Example 1,
In order to make the NI and IN interfaces steeper, the amount of carbon added near the interfaces was increased as shown in Figure 1D. That is, in the initial step of forming the second semiconductor, the ratio of methylsilane/silane was increased, and the barrier 34 was formed to a very thin thickness of 5 to 30 Å using a plasma vapor phase method.

Curves 53 and 53' in FIG. 4 were obtained as the VI characteristics in this example.

From this curve, it can be seen that the threshold value is 10 for Example 1.
It can be seen that the curve becomes even steeper at 0,100'.

In addition, if we create barriers 34 and 35 that allow a tunnel current of 5 to 30 Å to flow through both the NI interface and the IN interface, and create the configuration shown in Figure 1E, the V-I characteristic will be shown in Figure 4. Curves 54 and 54' could be obtained.

The VI characteristic in FIG. 4 is shown on a log scale with respect to the vertical axis, corresponding to FIG. 5. Then, the first
When a high concentration of carbon is added to the interface as shown in Figures D and E to form a barrier that prevents the mixing of impurities and constituents in each layer, the threshold value increases between +Va and -Va.
In addition to having more symmetrical characteristics, the low current regions 61, 61' in FIG. 5 become flatter, and the high current regions 62, 62' diffusion current regions rise more steeply. For,
Threshold value 100 indicating the boundary between “ON” and “OFF”,
100' may be made clearer.

"Effect" As described above, the present invention adds carbon to the interface between the I layer and the N layer or in the vicinity thereof in order to construct a composite diode having symmetrical VI characteristics with a steep threshold value. This is what I did. As a result, it is possible to perform process control for characteristics that flatten the current at voltages below the threshold and sharpen the current at voltages above the threshold.

Furthermore, this nonlinear element was able to achieve a threshold value suitable for the liquid crystal and S/N ratio used in the display element to which it is applied by controlling the amount of carbon added to the I layer.

In the present invention, carbon was added within the I layer. However, instead of carbon, oxygen or nitrogen may be used. However, since these materials easily become insulators, the amount of addition thereof must be controlled more delicately, and they are more difficult to manufacture than carbon.

[Brief explanation of drawings]

FIG. 1 shows longitudinal cross-sectional views A and B of the composite diode of the present invention, and concentration distributions C and D of carbon added to the I layer.
shows. FIG. 2 shows the operating characteristics of a conventionally known NIN junction using only amorphous silicon.
Figure 3 shows NIN with carbon added in the I layer of the present invention.
The operating principle of a nonlinear element of a junction type compound diode is shown. Figures 4 and 5 show conventional characteristics 51, 51'
and characteristics 52, 52', 53, 53' of the present invention,
54, 54' are shown.

Claims (1)

[Claims] 1. In a switching element having nonlinear characteristics, the switching element includes a first non-single-crystal silicon semiconductor layer having one conductivity type, and an intrinsic or substantially intrinsic second non-single-crystal silicon semiconductor layer on the layer. a third non-single-crystal silicon semiconductor layer having the same conductivity as the first non-single-crystal silicon semiconductor layer on the layer, and the first or third semiconductor layer; A switching element characterized in that carbon is added to the interface with the second semiconductor layer or its vicinity.