JPS6258675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to amorphous hydrogenated silicon photoconductive films.

CVD is a method for creating amorphous hydrogenated silicon.
method, plasma CVD method, reactive sputtering method, ion plating method, etc. Amorphous hydrogenated silicon is formed by reactions involving chemically active hydrogen. For this reason, substrates that react with hydrogen, such as transparent electrodes, are often damaged, resulting in the generation of many interface states, as well as pinholes, peeling, and surface depressions.
Damage during the initial stage of film formation greatly affects the properties of the film formed later. Films near the substrate surface that contain less hydrogen are less affected by the substrate.
However, amorphous hydrogenated silicon has good properties such as photoconductivity when a certain amount of hydrogen enters the film.

The relationship between hydrogen pressure, substrate temperature, and characteristics during the production of amorphous hydrogenated silicon will be explained using a reactive sputtering method as an example. Using a magnetron type sputtering device, amorphous silicon hydride is formed on I _{o 2} O ₃ on a glass substrate using an Ar pressure of 5×10 ^-3 Torr and a discharge power of 200 W using a Si polycrystal as a target. Substrate temperature T _s and hydrogen partial pressure P _H at this time
FIG. 1 shows how pinholes occur due to _{No. 2} . It can be seen that the higher the substrate temperature T _s , the fewer pinholes occur. As the substrate temperature T _s increases, the amount of hydrogen in the amorphous hydrogenated silicon decreases. Furthermore, as the hydrogen partial pressure increases, pinholes are more likely to occur.

From the above, the higher the substrate temperature _Ts , the
It can also be seen that the smaller the hydrogen partial pressure P _H2 is, the less pinholes occur. This shows that the smaller the amount of hydrogen in the film, the fewer pinholes will occur.

The amorphous hydrogenated silicon photoconductive film of the present invention has the above-mentioned two points: the amorphous hydrogenated silicon cannot obtain good photoconductive properties unless it contains a certain amount of hydrogen; This was done taking into consideration that the smaller the number, the fewer film defects such as pinholes will occur. That is, the amorphous hydrogenated silicon of the present invention is formed on the first amorphous hydrogenated silicon by reducing the hydrogen content of the first amorphous hydrogenated silicon on the substrate side, which greatly affects film defects. The hydrogen content is lower than that of the second amorphous hydrogenated silicon.

The band states of an image pickup tube target constructed using an amorphous hydrogenated silicon photoconductive film in an embodiment of the present invention are shown in FIGS. 2a and 2b. Figure 2a shows the case where the hydrogen concentration of amorphous hydrogenated silicon increases stepwise at a thickness D from the transparent electrode 1 on the substrate, and Figure 2b shows the hydrogen concentration of amorphous hydrogenated silicon. A band diagram is shown in which the value linearly increases as the distance from the transparent electrode 1 increases. In these figures, the solid line shows a band diagram when a positive voltage is applied to the transparent electrode 1, and the dotted line shows a band diagram when no voltage is applied to the transparent electrode 1. Figure 2a
In this case, by providing a second amorphous silicon hydride 3 with a higher hydrogen concentration than the amorphous silicon hydride 2 with a lower hydrogen concentration, the injection of electrons from the electrode 4 is blocked and a good result is obtained. It becomes a photoconductive film with special characteristics.

In addition, in the case of FIG. 2b, amorphous hydrogenated silicon 5
Since the amount of hydrogen in the photoconductive film is linearly increased, the band gap gradually increases, and the electrons and holes excited in the photoconductive film by light are easily separated by the internal electric field, resulting in good photoconductivity. Show characteristics.

As described above, amorphous silicon hydride is formed in advance with a hydrogen concentration that does not generate pinholes, and then amorphous silicon with a desired amount of hydrogen is formed on the amorphous silicon hydride photoconductive film, which results in fewer pinholes. Moreover, an image pickup tube target with excellent photoconductive properties can be obtained.

By providing a layer 3 with a high hydrogen concentration on the surface side as shown in FIG. 2a, injection of carriers from the electrode 4 on the opposite side to the transparent electrode 1 can be prevented and dark current can be reduced. Furthermore, as shown in FIG. 2b, by increasing the hydrogen concentration within the photoconductive film as it moves away from the transparent electrode 1, an internal electric field is created within the photoconductive film, which improves the separation of excited electrons and holes. Improves conductive properties.

Examples of the present invention will be described in more detail below.

Example 1 As shown in FIG. 3, a transparent electrode I _o2 O 3 32 on a glass substrate 31 is placed on a transparent electrode I o2 O ₃ on a glass substrate 31 using a magnetron sputtering device at a substrate temperature of 200°C and an argon pressure P _Ar =5×10 ^-3 Torr.
Under the condition of discharge power 200W, hydrogen partial pressure P _H2 = 2×
After forming the photoconductive film 33 with a relatively low hydrogen concentration at 10 ^-3 Torr for 10 minutes, the hydrogen partial pressure P _H2 =8×
When 10 ^-3 Torr was introduced and a photoconductive film 34 having a relatively high hydrogen concentration was formed for 60 minutes, a good photoconductive film with a thickness of 1 μm without pinholes was obtained.

Example 2 Similarly, as shown in FIG. 3, a transparent electrode SnO ₂ 32 was formed on a glass substrate 31 using a magnetron sputtering device.
Above is the substrate temperature and 250℃, P _Ar = 3 × 10 ^-3 Torr, P _H
After forming amorphous silicon hydride 33 for 70 minutes under conditions of ₂ = 1 × 10 ^-3 Torr and discharge power of 300 W, the substrate temperature
Membrane 34 with high hydrogen concentration for 10 minutes after being lowered to 200℃
form. Finally, an electrode Sb ₂ S ₃ 35 is formed to form an image pickup tube target. The voltage-current characteristics when voltage is applied with the transparent electrode 32 positive are shown in the fourth graph.
As shown in the figure. As is clear from the figure, in the image pickup tube target of Example 2, the photocurrent changes only slightly compared to the conventional image pickup tube target, but in the case of this example with the light guide film 34 having a high hydrogen concentration, the dark current changes. , the dark current is reduced compared to the case without it.

Example 3 In this example, a photoconductive film having a bandgap that changes in an inclined manner is produced by plasma CVD.
That is, after the reactor is evacuated, a mixed gas of SiH ₄ and H ₂ is introduced to bring the pressure to 1 Torr. Here P _siH
4 /(P _siH4 +P _H2 )0.1 and a discharge power of 5 W to form a film of amorphous silicon hydride. At this time, as shown in Figure 5, a comparison was made between the case where film formation was performed using program A shown by the solid line, which lowers the substrate temperature from a high temperature, and the case where film formation was performed using program B, which gradually increases the substrate temperature. . When the substrate temperature was gradually increased, the hydrogen concentration in the photoconductive film became smaller toward the substrate, and hydrogen was removed from the deposited film, resulting in many pinholes. However, by lowering the substrate temperature and gradually increasing the hydrogen concentration in the photoconductive film in the direction of the film thickness, a pinhole-free film with a high quality inclined bandgap was obtained.

Note that, as in Example 2, the photoconductive film 33 with a low hydrogen concentration is doped with an impurity, for example, phosphorus P.
When formed into a layer, the effect of preventing film defects from occurring is even greater.

As explained above, the amorphous hydrogenated silicon photoconductive film of the present invention can prevent film defects such as pinholes and exhibits good photoconductive properties, making it ideal for forming image pickup tube targets. be.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between hydrogen pressure, substrate temperature, and the degree of pinhole generation in an amorphous hydrogenated silicon photoconductive film, and FIG. A diagram showing energy bands of a photoconductive film, FIG. 3 is a cross-sectional view of an image pickup tube target using an amorphous hydrogenated silicon photoconductive film in an embodiment of the present invention, and FIG. 4 is a diagram showing an image pickup in an embodiment of the present invention. FIG. 5 is a diagram showing the voltage-current characteristics of the tube target, and is a diagram showing a method of changing the hydrogen concentration of the photoconductive film depending on the substrate temperature. 31... Glass substrate, 1, 32... Transparent electrode, 2,
33... Photoconductive film with low hydrogen concentration, 3, 34... Photoconductive film with high hydrogen concentration, 4... Electrode.

Claims (1)

[Scope of Claims] 1. A first amorphous silicon hydride formed on a transparent electrode on a substrate and in contact with the transparent electrode, and a first amorphous silicon hydride formed on the first amorphous silicon hydride. and a second amorphous silicon hydride having a higher hydrogen concentration than the first amorphous silicon hydride. 2. The amorphous hydrogenated silicon photoconductive film according to claim 1, wherein the hydrogen concentration of the amorphous hydrogenated silicon film increases linearly along the thickness direction.