JPH02137325A - Method for inactivating amorphous silicon surface - Google Patents

Abstract

PURPOSE:To stabilize the properties of a surface to be easily activated of a silicon layer by inactivating it immediately before it is coated with an insulating film on an amorphous silicon layer. CONSTITUTION:The face of an amorphous silicon layer 4 activated by etching is exposed with a plasma atmosphere containing nitrogen under reduced pressure to inactivate the activated surface. Then, a silicon nitride film is grown, for example, as an insulating film 6. This silicon nitride film is grown up to 0.5-1mum of thickness with material gas mixed with silane and ammonia by a plasma CVD method. Thus, the whole surface including the inactivated face P of a thin film diode body is covered with the film 6. The unnecessary part of the film 6 is removed, a window is opened at the top face of the body, metal such as aluminum is deposited in vacuum as a connecting film 7, and patterned in a predetermined shape by photoetching. Thus, the properties of the etched face of the amorphous silicon layer can be stabilized.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for inactivating an amorphous silicon surface, for example, an amorphous silicon used in a thin film element incorporated as a display driving element in an active matrix substrate of a display panel. This is a passivation treatment method for the side surface of a non-crystalline silicon layer, in which the amorphous silicon surface is an etched surface, and before an insulating film is coated thereon, an inactivation treatment is performed to stabilize the properties of the surface. Concerning a method of activation processing.

(Prior art) As is well known, amorphous silicon is
By the VD method, etc., it is possible to form an inexpensive semiconductor film with a thickness of less than 1,000 yen and stable properties, and solar cells and optical sensors using this film have been put into practical use. However, recently, so-called large integrated circuits have been developed that incorporate active elements such as transistors and diodes using thin films of amorphous silicon on fairly large insulating substrates, and are entering the stage of practical use. .

Examples of this are active matrix substrates for display panels and contact-type image sensors for facsimiles, both of which consist of multiple layers of amorphous silicon doped with impurities on a large substrate such as glass. A thin film is grown, and as in the case of an integrated circuit device, it is patterned into a fine pattern using a photo process to form active elements, and then interconnected using a connecting film. At this time, the photoetched surface of the amorphous silicon thin film, that is, the side surface of the amorphous silicon layer, is etched with silicon nitride or silicon oxide to avoid external influences or to insulate it from the connecting film disposed on top of it. covered with an insulating thin film such as

Hereinafter, an application example of such amorphous silicon will be briefly described using the above-mentioned active matrix substrate as an example, with reference to FIGS. 4 and subsequent figures.

FIG. 4 is an equivalent circuit diagram for four pixels of the display panel,
In this example, an amorphous silicon thin film diode 30 is used as an active element for display driving, and the active matrix substrate side in which the thin film diode 30 is incorporated is shown by a solid line, and the opposite substrate side is shown by a chain line.

On the active matrix Ml side, pixels arranged in a matrix are arranged as poles 10, and pixel electrodes 1 are arranged in the left-right direction in the figure.
0 and each pixel electrode 20 and each pixel electrode 10.
A thin film diode 30 connected between the scanning electrode 20 and the scanning electrode 20
will be provided. On the opposite substrate side, pixel types 1 are arranged in the vertical direction of the figure! A display electrode 40 facing i10 is provided.

A display panel is constructed by combining these two substrates and filling a display medium 50 such as liquid crystal in the gap between them. The thin film diode 30 transmits the display voltage on the scan electrode 20 to the pixel pole lO, and since the polarity of the display voltage is switched between positive and negative every scan period, there is a thin film diode 30P in the positive direction and a thin film diode 30n in the negative direction. It is constructed by connecting them in antiparallel.

FIG. 5 shows a state in which thin film diodes 30p and 3On are built on an active matrix substrate, and FIG. 6 shows a cross section taken along the line Y--Y. The active matrix substrate has a transparent insulating material III such as glass as shown in FIG. A scanning electrode 20 is formed.

The main body of the yI thin film diodes 30p and 3On is the sixth
As shown in the figure, an amorphous silicon semiconductor layer 4 with a pin structure and a very thin metal layer 4 sandwiching it from above and below! 3 and 5
These three layers are grown or deposited on the entire surface of an active matrix substrate and then photo-etched to form a generally rectangular pattern as shown in FIG.

In order to isolate the main body of the thin film diode, particularly the etched side surface of the semiconductor layer 4, from the outside and from the connecting film 7 provided thereon, an insulating film 6 made of silicon nitride or silicon oxide is provided on the main body. It is provided to cover the The connection film 7 made of metal such as aluminum is used to connect the Y4 film diode, and is provided so as to make conductive contact with the top surface of the main body of the thin film diode and a predetermined connection point through a window formed in the insulating film. It will be done. As can be seen from FIG. 5, the thin film diode 30P in the positive direction is provided on the scanning electrode 20 and connected to the pixel electrode IO through the connection film 7, and the thin film diode 30n in the negative direction is provided on the pixel electrode 20. lO
and is connected to the scanning electrode 20 by a connection 17.

In addition, in order to simplify the explanation above, ′gj in both the positive and negative directions
Although it is assumed that each film diode is composed of a single diode, in reality, each film diode is composed of a plurality of diodes, for example four, connected in series in order to match the display characteristics required by the display medium. It's normal.

(Problem M to be Solved by the Invention) The thin film of amorphous silicon used in the above-mentioned 1M diode, etc., can be grown to have extremely uniform characteristics by the plasma CVD method, etc., as described above.
Although the diode characteristics of the structure can originally be made uniform within extremely small variations, the characteristics may become unstable or the variations may increase after etching for patterning.

Figure 3 shows 100% of active matrix substrate fabrication.
These are the test results of the voltage and current characteristics of thin film diodes after being left for two weeks at a temperature of "C", with 40 thin film diodes each connected in series on the same substrate as test subjects, and their diode characteristics. The range of variation in is shown by the upper and lower lines of the figure, and the horizontal axis is the voltage V, and the @1 axis is the logarithm of the current ■.As can be seen from the figure, the diode current (2) is very small (the large variation seen in the range of 10-''μA or less of the current [in the figure) is due to the error of the measuring device.

Immediately after manufacturing, there was almost no variation in this characteristic, but in this test result, as shown in the figure, there was a considerable variation in the characteristic, especially in this case, the most important two to The problem is that there are variations in the voltage range of 3V.

Also, immediately after production, the current corresponds to the voltage of 2■! Although the value of was below to-'pA, 1O-4~10-Si
The level increased overall to 4, indicating that the leakage current increased. Note that no such change in properties was observed in the amorphous silicon thin film before etching, suggesting that the cause of the problem lies in the nature of the deformed surface of the etched amorphous silicon layer.

If the characteristics of the display driving elements vary in this way, the brightness of the display within the plane of the display panel will naturally become non-uniform. This test result is for 40 pixels, but the display panel contains at least tens of thousands of pixels! If the number of seriously defective pixels on the display reaches about 10, the active matrix substrate will become defective.
Unlike the case of semiconductor integrated circuits, in which a large number of circuits are fabricated on a wafer, an active matrix substrate cannot make use of only a portion of it, and must be discarded in its entirety. If the defective rate increases even slightly due to variations in the characteristics of the active matrix substrate, the manufacturing cost will increase rapidly, which has been a difficult point in rationalizing or putting the active matrix substrate into practical use.

It is an object of the present invention to solve this problem and provide a passivation treatment method capable of stabilizing the properties of the etched surface of an amorphous silicon layer.

[Means for Solving the Problems] The present invention provides an inert treatment method in which an etched surface of an amorphous silicon layer is exposed to a nitrogen-containing plasma atmosphere under reduced pressure immediately before coating an insulating film thereon. By applying the chemical treatment, the above objective was successfully achieved.

As the plasma atmosphere in the above configuration, a pure nitrogen atmosphere or a mixed gas atmosphere of nitrogen and hydrogen in which up to 2 parts of hydrogen is mixed to 1 part of nitrogen can be used.

Also, the pressure of this surrounding air may be any pressure that can maintain the plasma, but it may be 0.1 to 1↑or
The insulating film that covers the surface of the amorphous silicon layer that has undergone such passivation treatment, which is preferably around 0.4 Torr, can be heated to the same temperature without exposing the passivation process surface to the atmosphere. Any insulating film that can be grown or deposited in the facility following passivation can be used, but silicon nitride and silicon oxide films are the most preferred, with the former being the most preferred. When used as a film, it is desirable that the nitrogen concentration in the passivation film is higher than the nitrogen concentration in the silicon nitride film.

(Operation) Amorphous silicon is etched by dry etching or chemical etching using a reactive gas such as fluorine thread, but in either case, the etched surface is activated and an insulating film is coated on it. However, once activated, this surface is not necessarily stabilized and is considered to be the cause of problems such as increased leakage current. When an amorphous silicon layer is grown using a patterned mask, it can be seen that none of the above-mentioned problems occur.

The present invention has been made from this point of view, and involves exposing the surface of an amorphous silicon layer that has been activated by etching to a nitrogen-containing plasma atmosphere under reduced pressure to inactivate the activated surface. It was a success. On the activated surface of amorphous silicon, so-called dangling bonds of the outermost silicon atoms are exposed, and it is thought that atoms that tend to move depending on the situation are bonded to these. However, by performing the inactivation treatment according to the present invention, it is thought that nitrogen is bonded to the dangling bonds of silicon atoms and the surface of amorphous silicon is inactivated.In order to detect this bonded nitrogen, E.S.
Attempts have been made to perform surface microscopic analysis using the CA method, etc., but to date no success has been achieved in identifying nitrogen atoms.The presence of nitrogen on the surface of amorphous silicon is probably one atomic layer or at most several atoms. It is estimated that the amount is extremely small within the layer.

However, the effect of this passivation treatment is remarkable, and as described in the examples below, it is possible to maintain the original characteristics of the amorphous silicon layer before etching, and to suppress the leakage current to the minimum value. .

〔Example〕

Examples of the method of the present invention will be described below, taking as an example an active matrix substrate of a display panel in which a thin film diode using amorphous silicon is incorporated. FIG. 1 is a partially enlarged sectional view showing the thin film diode portion of this active matrix substrate at each of its main manufacturing steps.
FIG. 6(e) shows the completed state corresponding to the previous FIG. 6, and the same parts as in FIGS. 4 to 6 are given the same reference numerals. The explanation will be given below in the order of the steps shown in the figure.

In FIG. 1(a), the insulating substrate l is usually a transparent glass plate, on which e.g. The pixel electrode lO and the scanning electrode 2 are formed by vacuum-depositing or sputtering a transparent conductive film 2 such as TO (indinium tin oxide) to a thickness of approximately 0.1-thickness, and then photoetching it.
0 is formed in a pattern as shown in FIG. The same figure continues (
In the step b), a semiconductor yA4 made of amorphous silicon having a pln structure is sandwiched from above and below by extremely thin metal films 3 and 5 such as chromium, which are about 0.1-thick, to a thickness of about 0.5-thick. to fully grow. At this time, the metals 1, 13 and 5 are deposited by vacuum evaporation or sputtering, and the semiconductor 1!
! The amorphous silicon for I4 is conventionally grown, for example, by plasma CVD. A silicon hydrogen compound such as silane is normally used as the raw material gas for amorphous silicon by plasma CVD, and by sequentially adding diborane as a P-type impurity and phosphine as an N-type impurity, respectively. , an amorphous silicon layer having a p-1-n three-layer structure can be grown for the thin film diode in this fruitful example.

FIG. 1C shows the patterning process of the main body of the thin film diode, which is usually performed by dry etching the upper metal film 5. The semiconductor layer 4 and the lower metal film 3 are sequentially etched to form a rectangular pattern as shown in FIG. This etching has metal y! For A5 and 3, use chlorine-based reactive gas.

For the semiconductor layer 4, it is common to use a fluorine reactive gas. The etched surface E at this time is the side surface of the main body of the thin film diode, as can be seen from the figure, and is considered to be affected by fluorine or chlorine in the reaction gas during dry etching. Furthermore, after dry etching, the material is taken out of the equipment used for dry etching, so it is naturally affected by the atmosphere. The reason why the etched surface of the amorphous silicon for the semiconductor layer 4 is easily activated is
It is still unclear which of these reactive gases or the atmosphere exists.

In the process shown in FIG. 1(b), the above-mentioned etched surface E is subjected to inactivation treatment in, for example, a plasma CVD apparatus as an inactivated surface P, and the insulating film 6 is then placed on top of the etched surface without removing it from the apparatus. As an example of the conditions for the inactivation treatment, nitrogen gas is flowed at a flow rate of 380 sc/min, the pressure inside the device is maintained at 0.4 Torr, and 0.04 W/c- High-frequency power is applied at a density of . When the inactivation treatment temperature is 170 to 200''C, the treatment time is at least 20 minutes.

Desirably, the time is 30 minutes or more. There is no problem even if the flow rate of nitrogen gas mentioned above varies considerably, but the processing pressure is 0.1~
If it is outside the l Torr range, the processing effect will not be much.
As mentioned above, the best processing results can be obtained when the pressure is around 0.4 Torr.

Further, as the processing gas, a mixed gas of pure nitrogen or nitrogen and hydrogen may be used, and in this case, the flow rate of hydrogen is preferably in the range of 0 to 200%, taking that of nitrogen as 100%. Appropriate. The treatment conditions can be the same as for pure nitrogen.
In addition, when using this mixed gas, several atomic layers of fIlI! containing nitrogen as the main component are applied to the surface of the inactivated amorphous silicon. It is presumed that I is formed.

Then, following the passivation treatment in the same plasma CVD apparatus, a silicon nitride film, for example, is grown as a layer 1116. This silicon nitride film is produced using plasma C
It is grown to a thickness of 0.5 to lIIIm, preferably around 0.7m, by the VD method. As a result, the entire surface of the thin film diode main body including the passivated surface P is covered with the insulation M6 as shown in the figure.

Figure 1(e) shows the completed state, and to achieve this state,
First, the insulating WA 6 is patterned by photo-etching to remove unnecessary parts and a window is opened on the top surface of the thin-film diode main body. After that, a metal such as aluminum is vacuum-deposited as the connection film 7 and patterned by photo-etching. In the example of FIG. 0 in which patterning is performed in a desired shape, the negative direction 1M diode 30n provided on the pixel electrode 10 is connected to the scanning electrode 20 by this connection WA7.

FIG.
Comparing this with Figure 3, which shows the results of testing ll diodes in exactly the same manner as in Figure 3 above, the two show almost the same characteristics in the range of voltage 4 or higher, but the display panel display III! according to the present invention in the voltage range of 2 to 3 V, where the quantity is also important in terms of characteristics. Although the IK diode shows a slight variation near 2■, it shows voltage/current characteristics with much less variation than in Figure 3. Also, the rise of this characteristic in Figure 2 in this range is similar to the It can be seen that the slope is steeper than in the case shown in the figure, and therefore the display speed of the display panel is faster.

Furthermore, the value of the current ■ corresponding to the voltage of 2■ is between 10-S and 10-'A in the case of FIG.
” This is an improvement of more than an order of magnitude compared to the area near A.
This is thought to be the result of the present invention inactivating the etched surface of amorphous silicon and reducing its surface leakage current.In the 0 display panel, and after the display voltage is applied to the pixel electrode, this Since the voltage must be maintained, if the leakage current of the thin film diode is large, the display state of the pixel cannot be maintained sufficiently and the clarity of the display will decrease.However, with the present invention, the leakage current can be reduced as shown above. By doing so, the display clarity of the display panel can be increased.

〔Effect of the invention〕

As described above, in the method of the present invention, the etched surface of the amorphous silicon layer is exposed to a nitrogen-containing plasma atmosphere under reduced pressure to inactivate it immediately before coating the insulating film thereon. By doing so, the properties of the surface of the amorphous silicon layer that is easily activated can be stabilized over a long period of time, and variations in characteristics and surface leakage current of an active element using amorphous silicon as a semiconductor layer can be reduced. As can be seen from the examples, since the passivation treatment according to the present invention can be carried out in the same process as the coating process of the insulating film, the manufacturing cost of active elements is hardly increased by implementing the present invention. do not have.

The method of the present invention uses amorphous silicon.
It is particularly effective when applied to the production of active matrix substrates for display panels that incorporate transistors and thin film diodes, and image sensors for facsimile machines, improving the clarity of display panels and the detection sensitivity of charge storage type image sensors. , and can have a remarkable effect of increasing the manufacturing yield and reducing the cost.

[Brief explanation of the drawing]

All figures relate to the present invention, and FIG. 1 shows one example in which the inactivation treatment method for an amorphous silicon surface according to the present invention is applied to the production of an active matrix substrate of a display panel, showing the state of each main process. Fig. 2 is a characteristic line diagram showing the distribution of voltage and current characteristics of a thin film diode to which the method of the present invention is applied, and Fig. 3 is a characteristic line corresponding to Fig. 2 when the method of the present invention is not applied. 3 is an equivalent circuit diagram of the active matrix substrate in the embodiment shown in FIG. 1, FIG. 4 is a partially enlarged plan view of this active matrix substrate, and FIG. 5 is a partially enlarged sectional view thereof. In, 1: insulating substrate for near-active matrix substrate, 2: conductive film, 3: lower metal film, 4: semiconductor layer of amorphous silicon, 5: upper metal film, 6: insulating film, 7: connection Film, 10+pixel electrode, 20: Scanning electrode, 30: Thin film diode, 30
p, 30n: thin film diode in positive and negative directions, 40: display electrode, 50: display medium, E: etched surface of amorphous silicon layer, P: passivation treated surface of amorphous silicon layer. Figure 3'$1 4th Article No. 6 Procedural Amendment (70 21 Name of the invention ψtame v-/Fukun LlI + Yumika 13 7 Tsuru・Naikashodan) Name of address related to

Claims (1)

[Claims] A method for inactivating an etched surface of an amorphous silicon layer before coating with an insulating film, the method comprising exposing the treated surface to a nitrogen-containing plasma atmosphere under reduced pressure. Inactivation treatment method for