JP2983243B2 - Thin film type electronic device - Google Patents

Description

The present invention relates to a thin-film laminated electronic device having a structure in which a thin film is formed on a substrate, and particularly to reducing the internal stress of the thin film. And a thin film laminated electronic device.

(Related Art) In recent years, research and development of a contact type image sensor, a solid-state imaging device, a thin film transistor, and the like using a non-single-crystal thin film such as amorphous silicon for an active layer have been advanced. Of these, contact-type image sensors and solid-state imaging devices are devices that use carriers generated by light in a non-single-crystal thin film, while thin-film transistors are devices that control the current flowing in the non-single-crystal thin film by the electric field effect. is there. In any device, it is essential to obtain a high quality non-single-crystal thin film of an active layer, typically a hydrogenated amorphous silicon film, in order to obtain good device characteristics, and in particular, the mobility of carriers in the thin film. It is important to increase

By the way, the hydrogenated amorphous silicon film has an Si—H bond and Si
Has the -H ₂ bond, electron mobility in the amorphous silicon hydride film is known to depend on the ratio of these bonds. Specifically, increase the ratio of Si-H bonds
By reducing the ratio of Si—H ₂ bonds, the electron mobility in the hydrogenated amorphous silicon film is increased.

However, increasing the proportion of Si—H bonds and decreasing the proportion of Si—H ₂ bonds generally increases the internal stress of the thin film.
That is, as shown in FIG. 9 as an example, when the electron mobility of the hydrogenated amorphous silicon film increases, the internal stress of the film naturally increases. Therefore, when a thin film having a high electron mobility is deposited to improve device characteristics, there is a disadvantage that the film is easily peeled off from the substrate.

(Problems to be Solved by the Invention) As described above, conventionally, electronic devices such as a contact type image sensor, a solid-state imaging device, and a thin film transistor using a non-single-crystal thin film such as amorphous silicon for an active layer have a high electron transfer. When a thin film is deposited to a certain degree, there is a problem that the thin film is easily peeled off due to a large inherent internal stress. As a result, in order to reduce the internal stress, a thin film having electron mobility smaller than a desired value has to be deposited, and there is a problem that good device characteristics cannot be obtained.

Note that the above problem is not limited to an electronic device using a non-single-crystal thin film, and in an electronic device having a structure in which a thin film is deposited on a substrate, the thin film may be peeled from the substrate due to internal stress of the thin film. This has been a factor in lowering the reliability of the electronic device.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a thin-film laminated electronic device that can prevent peeling of a thin film due to internal stress of a thin film deposited on a substrate and can improve device characteristics and reliability. .

In particular, the present invention relates to a contact-type image sensor, a solid-state imaging device, a thin film transistor, or the like which does not peel off even when a non-single-crystal thin film having high electron mobility is deposited, and has excellent electron and hole traveling properties. It is an object of the present invention to provide a thin-film laminated electronic device.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to provide a portion of a thin film layer in which the number of main constituent elements of a thin film in a unit volume, that is, a density is small, and a stress is applied in this portion. To absorb.

That is, the present invention provides a thin-film laminated electronic device in which a thin film of amorphous silicon or the like is formed on a substrate having a step,
A structure in which the density of the main constituent elements of the thin film is smaller than that of other parts is arranged in the thickness direction of the thin film in a linear or planar shape having a desired width inside the thin film, and a substrate of the structure is provided. The side is not in contact with the substrate surface.

(Operation) According to the present invention, a non-single-crystal thin film made of amorphous silicon or the like having high electron mobility is formed by a film having a low density disposed inside the thin film layer, which plays a role of absorbing stress. It can be deposited without peeling. By appropriately selecting the width of the linear or planar low-density portion within a desired range, there is no problem that this portion adversely affects the device characteristics. Therefore, a thin-film laminated electronic device having excellent characteristics in which carriers such as electrons and holes can travel more easily than before can be formed without any process problems such as film peeling.

Although the operation has been mainly described above with respect to an amorphous silicon-based thin film, the present invention is not limited to this, and has a similar effect on a metal layer and further on an insulating layer such as a silicon nitride film or a silicon oxide film. Even if a thin film is formed under a condition of a large stress, it is possible to prevent the thin film from peeling off.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

First, an example in which an amorphous silicon film having a large internal stress is not peeled when formed on a glass substrate is described as a first example.
FIG. 2 and FIG. In both figures, a schematic diagram of a cross-sectional transmission electron micrograph is shown so that the magnitude of the density can be clearly seen.

In FIG. 1, after a hydrogenated amorphous silicon film 2 is deposited on a glass substrate by about 1 μm, a hydrogenated amorphous silicon film 3 having a small silicon density is formed with a desired thickness of 200 ° or less, Thereafter, a hydrogenated amorphous silicon film 4 was deposited to about 1 μm under the same conditions as the silicon film 2. Incidentally, in the actual photograph, the portion 3 in FIG. 3 is observed whitish because the density is small and electrons are easily transmitted as compared with the thin films 2 and 4.

When the amorphous silicon films 2 and 4 are continuously formed,
Since the film was formed under the condition that the internal stress was 4 × 10 ⁹ dyn / cm ² or more, peeling of the film occurred. However, in the embodiment of FIG. 1, the structure 3 having a low silicon density absorbs the stress. No peeling of the film occurred.

Here, as a method for forming the hydrogenated amorphous silicon film, a plasma CVD method of dividing a silane gas by plasma and a photo-CVD method of decomposing by light energy may be used as is well known in the art. Further, in order to form a hydrogenated amorphous silicon film having a low silicon density, for example, the formation substrate temperature T _S may be lowered to increase the amount of hydrogen contained in the thin film. In this embodiment, 2 and 4 are formed at T _S = 250 ° C., and the structure portion 3 having a low silicon density is formed at T _S = 150 ° C.

FIG. 2 shows an example in which a structure 3 of a hydrogenated amorphous silicon film having a low silicon density is formed in a plane, not obliquely to the glass substrate 1 but obliquely. In this figure, reference numeral 2 denotes a hydrogenated amorphous silicon film, and the structure 3 was intentionally formed and arranged during the deposition of 2. Although 3 is linear in the drawing, it is actually arranged in a plane. The line width of the structure portion 3 having a low silicon density is set to a desired value in the range of 10 to 200 °, but need not be constant. Further, the structure portion 3 may be constituted by two or more lines or two or more surfaces.
In order to form the structure 3 arbitrarily, the 3
This can be realized by appropriately selecting a dimensional structure.

In order to confirm that the structure portion 3 actually realizes a small silicon density, the present inventors evaluated using an energy dispersive X-ray analysis method (EDX method). An electron beam focused to a diameter of 10 ° φ was scanned in the direction of 5 to irradiate the cross section, and the characteristic X-ray dose (X-ray peak intensity) emitted from the cross section of the sample was measured. As a result, as shown in FIG. 3, it was found that the silicon density was clearly reduced in the structural part 3. Similarly, a decrease in silicon density in the structure 3 was confirmed by energy loss spectroscopy (EELS).

The effect of this embodiment is that when the structure 3 is not formed, the hydrogenated amorphous silicon film 2 is peeled off from the substrate 1. However, in this embodiment in which the structure 3 is formed, film peeling occurs. Turned out not to be.

Next, a second embodiment in which the present invention is applied to an actual electronic device will be described.

FIG. 4 is a diagram showing a cross-sectional structure of a solid-state imaging device having a structure in which a photoelectric conversion layer of a hydrogenated amorphous silicon thin film is stacked on a CCD substrate on which a scanning circuit and a collecting electrode are integrated.
In the figure, 10 is a Si substrate, 11 is a storage diode, 12 is a vertical CCD, 13 is a transfer electrode, 14 and 16 are insulating films, 15 is an extraction electrode, and 17 is a pixel electrode. A substrate is formed.

Reference numeral 21 denotes a hole blocking layer, for example, a hydrogenated amorphous carbide layer, 22 denotes a main photoconductive layer, a hydrogenated amorphous silicon film, and 23 denotes an electron blocking layer, for example, a p-type amorphous silicon carbide. The layers 21 to 23 form a hydrogenated amorphous silicon thin film based photoelectric conversion layer. The total thickness of the photoelectric conversion layer is about 1 to 2 μm. Finally, a transparent electrode 24 that can transmit light is formed. Further, in order to absorb the intrinsic internal stress of the hydrogenated amorphous silicon film 22, a planar (linear in the figure) structural portion 25 having a low silicon density is arranged in the photoelectric conversion layer.

In this embodiment, the hydrogenated amorphous silicon film 22 has an internal stress as large as 4 × 10 ⁹ dyn / cm ² or more, and also has an electron mobility.
Although a thin film having a large value of 0.45 cm ² / VS or more was used,
The film was not peeled off due to the effect of stress absorption by the structural portion 25, and a good element having high-speed optical response could be formed.

On the other hand, if the three-dimensional structure of the CCD imaging device substrate having a step on the surface due to the formation of the pixel electrode 17 is not appropriate, and if the structural portion 25 is not arranged, the same lamination can be easily performed. Was peeled off, and the device was not formed.
The structural portion 25 preferably has a line width of 200 ° or less when viewed from the cross section, and a value in the range of 20 to 100 ° is typically sufficient to obtain the effect of the present invention. Also, the structure
It is needless to say that 25 is not limited to a planar shape, and that a linear shape is also effective.

Next, in a high-sensitivity solid-state imaging device having a two-story structure in which hydrogenated amorphous silicon-based thin films are stacked as shown in FIG.
Various methods for arranging the structure portion 25 having a low silicon density in the hydrogenated amorphous silicon film will be described in detail.

The first method is to change the thickness of the pixel electrode 17. The thickness of the pixel electrode 17 is 500Å, 1000Å, and 2000 そ れ ぞ れ, respectively.
FIGS. 5 (a) to 5 (c) schematically show how to arrange the structure portions 25 having a low silicon density in the case where the above is changed.

In the case of FIG. 5 (a), the structure portion 25 having a low silicon density is hardly formed as observed by a cross-sectional TEM photograph. From FIG. 5 (b) to FIG. 5 (c), as the thickness of the pixel electrode 17 is increased, the structure portion 25 can be clearly observed. That is, in the range of this embodiment, the structure portions 25 having a lower density could be more reliably arranged as the pixel electrodes 17 were made thicker. As a result, this stacked solid-state imaging device 10
The number of chips where film peeling occurred per 0 chip was as shown in the following table.

Here, as the thickness of the pixel electrode 17 increases, the number of chips having peeled off decreases. This is because the structure part 25 having a low density is securely arranged and the internal stress of the film is absorbed by the structure part 25. Needless to say, In this example, the total thickness of the photoelectric conversion films 21, 22, and 23 made of an amorphous silicon-based thin film was 2 μm, but the hydrogenated amorphous silicon film 22 had an internal stress of 4 × 10 ⁹ dyn / cm ^2. Those having the following values were used. In this example, a low-pressure mercury lamp was used as the ultraviolet light source, and the photoelectric conversion film was formed by a mercury-sensitized CVD method using silane gas as a source gas. Similar effects can be obtained. For example, in order to obtain a hydrogenated amorphous silicon film having an internal stress of 4 × 10 ⁹ dyn / cm ² or more in a mercury-sensitized CVD method, a substrate temperature of 230
℃ and silane gas pressure of 0.2 Torr or less, furthermore, the flow rate of silane, the amount of mercury contained in silane gas,
The ultraviolet light intensity of the low-pressure mercury lamp may be set to an appropriate condition.

In this embodiment, a Ti electrode can be used as the pixel electrode 17, but in this case, a reactive ion etching (RIE) method, a wet etching method, or the like can be used as a method of patterning the Ti electrode. Desirably, the RIE method having the characteristic of anisotropic etching which is less likely to cause undercut in the Ti pixel electrode is preferable.

The following conditions can be typically used as the RIE etching conditions for the Ti electrode. Etching gas is CO 20
~ 50sccm, BCl3 ₃₀ ~ 60sccm, Cl2 ₂₀ ~ 50sccm, diluted He
Is 1000 ~ 3000sccm, and total gas pressure is 0.5 ~ 2To
rr, and the discharge power may be set in the range of 200 to 500 W. By adjusting the above etching conditions, the taper angle of the side wall of the etched Ti pixel electrode can be controlled, and the electrode end 26 where the side wall and the SiO ₂ contact each other can have a curvature.

Here, the structure portion 25 having a low silicon density is a kind of crystal defect, and the crystal defect portion 25 may be in contact with the pixel electrode 17 in some cases. In this case, the crystal defect portion between the pixel electrode 17 and the transparent electrode 24 or between the adjacent pixel electrodes 17
Leakage current would flow through 25, which is undesirable. Therefore, by forming the end portion 26 of the pixel electrode 17 with a smooth continuous curve, crystal defects do not occur from the end portion, and the above-described leak current can be prevented. As a method of forming the end portion smoothly, etching conditions for forming a pixel electrode, that is, etching conditions for wet etching or dry etching may be appropriately selected.

Another method for arranging the structure portion 25 having a low silicon density will be described. This is a method in which the hydrogenated amorphous silicon film 22 is sequentially formed by different film forming methods.

FIG. 6 shows a plasma CVD of a hydrogenated amorphous silicon film 22.
This is an example in which a lower layer portion formed by a CVD method and an upper layer portion formed by a mercury-sensitized CVD method are combined. In Figure 6, 22 ₁ hydrogenated amorphous silicon film formed by a plasma CVD method, 22 ₂ are hydrogenated amorphous silicon film formed by the mercury sensitized CVD method. In this example, the plasma
As the CVD method, a method of decomposing silane gas by high frequency discharge of 13.56 MHz and forming a film was used. Generally, the temperature of the substrate installed on the ground electrode is 200 to 300 ° C., and the high-frequency power is 5 to 10
0W, gas pressure 0.1 ~ 2Torr, introduced silane flow rate 5 ~ 100s
What is necessary is just to form a thin film as ccm.

As a mercury-sensitized CVD method, in this example, a thin film is deposited by introducing ultraviolet light from a low-pressure mercury lamp into a chamber through a quartz window into a silane gas containing a small amount of mercury and decomposing the silane gas, for example, forming As conditions, the substrate temperature is 100 to 300 ° C., the introduced silane flow rate is 5 to 200 sccm,
The gas pressure may be set at 0.05 to 2 Torr. Sixth
In the figure, 25 ₁ is small structures of silicon density disposed within the thin film 22 ₁ formed by a plasma CVD method, 25 ₂ small silicon density disposed in the thin film 22 in ₂ formed by the mercury sensitized CVD method It is a structural part. 27 indicated by the dashed line
It is hitting the thin film 22 ₁ and 22 ₂ of the boundary surfaces, not necessarily the silicon density is lower in the boundary surface. As shown in this figure, the arrangement of the structure portion 25 having a low silicon density differs from the boundary surface 27 as a boundary. The reason will be described below.

In general, according to the plasma CVD method, other ions mainly of the neutral species participate in the film formation, and a seed potential distribution occurs on the substrate. Is large, but the deposition rate is low in a direction perpendicular to the deposition direction, that is, in a direction parallel to the substrate.
Thus, small structures 25 ₁ of silicon density is disposed at an angle of more than 45 degrees with respect to the horizontal direction to the substrate. on the other hand,
The mercury-sensitized CVD method using a low-pressure mercury lamp has a feature that the film is substantially isotropic because neutral species are involved in the film formation. Thus, small structures 25 ₂ of silicon density can be arranged at a substantially 45 ° angle with respect to the horizontal plane of the substrate.

Then, a hydrogenated amorphous silicon film 22 ₂ formed by the mercury sensitized CVD method in FIG. 7 is formed on the lower layer, to form a hydrogenated amorphous silicon film 22 ₁ which is formed by a plasma CVD method on the upper layer Here is an example of the case. Based on the above principle, the manner in which the structure 25 is formed in FIG. 7 is opposite to that in FIG.

As described above, as shown in FIGS. 6 and 7, the arrangement of the structure portion having a low silicon density can be changed as desired by different film formation methods or combinations of different film formation methods. In these examples, two layers were stacked by two different film forming methods. However, the present invention is not limited to this, and two or more film forming methods, such as the above-described film forming method and ECR plasma CVD method, may be used. Even if two layers are stacked by combining magnetron sputter link method, ion plating method, ion gun CVD method, direct excitation light CVD method, etc., the arrangement of parts with low silicon density is also desired in each case. Can be changed to Further, it goes without saying that, by changing the arrangement, the manner of absorbing the internal stress in the thin film is different, and the manner of peeling the film is different.

According to the study of the present inventors, compared to the case of laminating thin films having the same internal stress, the case where the portion having a small silicon density is arranged at an angle close to 45 ° with respect to the direction horizontal to the substrate surface is better. However, the film is difficult to peel off. For example, the same 4 × 10
^When a hydrogenated amorphous silicon film having an internal stress of ⁹ dyn / cm ² was formed, peeling of the film was less likely to occur when the film was formed by mercury-sensitized CVD than by plasma CVD. In addition, a method of changing the growth rate of the thin film is also effective in changing the arrangement method of the portion having a low density or changing the density itself of the portion.

Next, a third embodiment in which the present invention is applied to a thin film transistor will be described. FIG. 8 is a cross-sectional view showing a schematic configuration of an inverted stagger type TFT, and schematically shows a cross-sectional TEM photograph as before. Gate electrode 31 on glass substrate 30
After forming an insulating film 32 such as a silicon oxide film or a silicon nitride film of about 3000 mm, a hydrogenated amorphous silicon film 33 as an active layer is formed, for example, by 500 mm, and an n ⁺ type hydrogenated non- This is a configuration in which a crystalline silicon film 34 is deposited, for example, by 500 °, and a source electrode and a drain electrode are provided on 35 and 36.

In this embodiment, in addition to this structure, a structure portion having a low silicon density indicated by reference numeral 37 in the figure is arranged in a planar shape (linear shape in the figure). The structural part 37 does not necessarily need to be arranged in all the deposition parts 32, 33, 34 and 36, and in this embodiment, it is arranged in the laminated parts 32, 33 and 34.

In this embodiment, as in the previous embodiment, the internal stress of the hydrogenated amorphous silicon film 33 is as large as 4 × 10 ⁹ dyn / cm ² or more, and the electron mobility is also as large as 0.45 cm ² / VS or more. Although a thin film having a high value was used, no peeling of the film occurred, and good device characteristics having a sufficiently large field-effect mobility could be obtained. That is, a high ON current and high-speed switching characteristics were realized. In contrast, the structure 37
It is needless to say that the film was easily peeled off when was not arranged. Of course, by disposing the structural portion 37, peeling of the insulating film 32 can be prevented.

The present invention is not limited to the embodiments described above. In the embodiment, the example in which the amorphous silicon film is used as the thin film has been described. However, the present invention is not limited thereto, and the present invention can be applied to a non-single-crystal thin film formed on a substrate. Can be applied. Further, the present invention can be applied to formation of an oxide superconductor thin film.
Further, the present invention can be applied not only to a solid-state imaging device and a thin film transistor but also to a contact image sensor, and further to an electronic device having a structure in which a thin film is deposited on a substrate having a step. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, the number of main constituent elements of a thin film in a unit volume, that is, a structure having a small density is provided inside a thin film deposited on a substrate having a step. Therefore, the stress can be absorbed by this structure. Therefore, it is possible to prevent the thin film from being peeled off due to the internal stress of the thin film deposited on the substrate, and to realize a thin film laminated electronic device capable of improving device characteristics and reliability. In particular, when applied to a solid-state imaging device, the light response characteristic can be increased in speed, and when applied to a thin film transistor, a high on-current and high-speed switching characteristic can be realized.

[Brief description of the drawings]

1 and 2 are sectional views showing the structure of a first embodiment of the present invention, FIG. 3 is a characteristic diagram showing the relationship between a scanning position and a peak intensity, and FIG. 4 is a second embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating a schematic configuration of a stacked solid-state imaging device for explaining an example, FIG. 5 is a cross-sectional view illustrating a relationship between a pixel electrode thickness and a structure forming state, and FIGS. FIG. 8 is a cross-sectional view showing an example in which a crystalline silicon film is formed in two layers, FIG. 8 is for explaining the third embodiment of the present invention, and is a cross-sectional view showing a schematic structure of a thin film transistor, and FIG. FIG. 4 is a characteristic diagram for explaining a problem and showing a relationship between an internal stress of a hydrogenated amorphous silicon film and electron mobility. 1 ... glass substrate, 2,4 ... hydrogenated amorphous silicon film, 3,25,37 ... structural part, 17 ... pixel electrode, 21,23 ... hydrogenated amorphous carbide layer, 22 ... ... hydrogenated amorphous silicon film, 24 ... transparent electrode, 26 ... electrode end, 27 ... boundary surface, 30 ... glass substrate, 31 ... gate electrode, 32 ... insulating film, 33, 34 ... ... hydrogenated amorphous silicon film.

Continuation of front page (56) References JP-A-60-206270 (JP, A) JP-A-57-159070 (JP, A) JP-A-63-115325 (JP, A) JP-A-63-224259 (JP) , A) JP-A-1-261869 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 27/14-27/148 H01L 31/04 H01L 29/786

Claims (3)

(57) [Claims] 1. A thin-film laminated electronic device comprising a non-crystalline thin film formed on a substrate having a step, wherein a thin film is provided with a structural portion in which the density of a main constituent element of the thin film is smaller than other portions. A thin-film laminated electronic device, wherein the thin-film electronic device is arranged in a thickness direction of the thin film in a linear or planar shape having a desired width, and the substrate side of the structure is not in contact with the substrate surface. 2. The thin-film laminated electronic device according to claim 1, wherein said thin film is an amorphous silicon film. 3. A step is formed on the surface of the substrate depending on the presence or absence of a conductive layer, and a structure portion having a density of the main constituent element smaller than the other is formed in a thickness direction of the thin film by a step on the surface of the substrate. The thin-film laminated electronic device according to claim 1.