JPS6141144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a solid-state device in which a photoconductive film is provided on a large number of bit addressing MOS transistors built into a silicon substrate, and this photoconductive film is connected to the source electrodes of the MOS transistors. The present invention relates to a method of manufacturing an imaging device.

Numerous bit address MOS transistors,
A fixed imaging device in which a photodiode, a shift register element, and the like are fabricated on a single silicon substrate is usually constructed as shown in FIG. Here, 1 is a horizontal shift register consisting of a large number of MOS transistors or charge transfer elements, 2 is a similar vertical shift register, 3a, 3b, ... are MOS transistors for column addresses, and 4a, 4b, ... are MOSs for bit addresses. Transistor, 5a, 5
b... are photodiodes formed in the source electrodes of MOS transistors 4a, 4b..., 6 is a load resistor, 7 is a bias power supply, 8a, 8b... are row address lines made of polysilicon, etc., 9
a, 9b, . . . are column address lines made of aluminum or polysilicon, and 10 is a video signal output terminal. The horizontal and vertical shift registers 1 and 2 are driven by two-phase clock pulses C _px and C _py and shift pulses S _pX and S _py .

On the other hand, in a solid-state imaging device equipped with a photoconductive film, a photoconductive film is used in place of the photodiodes 5a, 5b, . . . . In this case, for bit address
The MOS transistor and the photoconductive film connected to its source region are configured in the relationship shown in Figure 2, where 11 is a P (or N) conductivity type silicon substrate, and 12 is a silicon substrate that insulates a large number of MOS transistors from each other. Field oxide film for isolation, 13 is N
(or P) conductivity type source region, 14 is an N (or P) conductivity type drain region, 15 is a gate oxide film, 16 is a gate electrode made of polysilicon,
17 is a first interlayer insulating film formed by CVD method or the like; 18a and 18b are drain and source electrodes made of aluminum (containing silicon) or molybdenum; 19 is a second interlayer insulating film;
0 indicates a photoconductive film, 21 indicates a photoconductive film connecting electrode that is in ohmic contact with the source electrode 18b and extends onto the insulating film 19, and 22 indicates a transparent electrode.

Such a device is usually manufactured by the following steps. First, a silicon oxide film is uniformly formed on a silicon substrate by thermal oxidation. Then, M.O.S.
A region where a transistor is to be formed is covered with a silicon nitride film, and a heat treatment for selective oxidation is performed to increase the thickness of the silicon oxide film other than directly under the silicon nitride film. Next, by sequentially removing the silicon nitride film and the silicon oxide film immediately below, the field oxide film 1 is removed.
2 is completed. Next, a thin silicon oxide film for the gate oxide film 15 and a polysilicon film for the gate electrode 16 are sequentially formed, and then the portions other than the gate region are removed by etching. Next, the drain region 14 and the source region 13 are formed by thermal diffusion or ion implantation, and a silicon oxide film for the first interlayer insulating film 17 is formed and holes are formed therein, and the drain electrode 18a and the source electrode 18b are Formed by beam evaporation or sputtering. After this, the electrode 18a,
Heat treatment is performed for 30 to 60 minutes at a temperature of about 430° C. in a hydrogen atmosphere to also alloy the substrate 18b and the substrate 11. Next, a silicon oxide film for the second interlayer insulating film 19 is formed to a thickness of about 1 μm by the CVD method, and a hole is made in this film 19 to form a photoconductive film connecting electrode 21 made of a molybdenum-niobium alloy or the like. form. Next, after heat treatment is performed again at a temperature of approximately 430° C., a photoconductive film 20 is formed by vapor deposition, and heat treatment is performed at approximately 500° C. in vacuum. Then, a transparent electrode 22 is formed on the photoconductive film 20.

Such a solid-state imaging device with a photoconductive film exhibits good characteristics in terms of photosensitivity, afterimage, blooming, etc. However, the threshold voltage of the MOS integrated circuit as the base of the photoconductive film 20 is determined by the manufacturing process of the device. There were problems that could easily change during the process.

The threshold voltage changes depending on various factors, one of which is the dangling bond generated between the silicon substrate 11 and the gate oxide film 15.
This dangling bond is generated when the silicon substrate 11 is oxidized at high temperature, and when it becomes an interface state, the threshold voltage changes. The dangling bonds can be eliminated by performing the heat treatment in the hydrogen atmosphere described above, but since hydrogen bonded to silicon is unstable, the subsequent heat treatment, that is, the second interlayer Hydrogen desorption occurs during the step of forming the insulating film 19 by the CVD method (reaction temperature is about 400° C.), especially the step of heat-treating the crystalline photoconductive film 20 at about 500° C. in vacuum, changing the threshold voltage. let

Furthermore, when forming the drain electrode 18a and the source electrode 18b from silicon-containing aluminum, for example, structural defects may occur in the silicon substrate 11 due to soft X-rays generated during electron beam evaporation or ultraviolet rays generated during sputtering. , this also causes a change in the threshold voltage.
Therefore, the drain electrode 18a and the silicon substrate 11
Heat treatment is performed at around 430°C in a hydrogen atmosphere for 30 to 60 minutes to form an alloy with the metal. However, next, a second interlayer insulating film 19 with a thickness of about 1 μm was formed.
During the formation process using the CVD method (reaction temperature is about 400° C.), as the alloying progresses further, the drain electrode 18a moves slightly, causing a crack in the second interlayer insulating film 19. .

The present invention is characterized in that the effect of the first heat treatment performed to eliminate structural defects generated in the silicon substrate 11 and the occurrence of the cracks are largely influenced by the processing temperature of the subsequent heat treatment, that is, If heat treatment is performed at a high temperature other than in a hydrogen atmosphere after the first heat treatment in a hydrogen atmosphere, hydrogen desorption occurs and the effect of eliminating structural defects cannot be obtained satisfactorily, and furthermore, the interlayer insulating film 19 is cracked. This was done with a focus on the fact that it is more likely to occur.

According to the method for manufacturing a solid-state imaging device of the present invention, the processing temperature of the first heat treatment in a hydrogen atmosphere, which is performed after forming the drain electrode 18a and the source electrode 18b, is set at 450°C to 550°C, which is slightly higher than the conventional temperature. At the same time, the processing temperature of the second heat treatment in a hydrogen atmosphere performed after forming the photoconductive film connecting electrode 21 is set to a value at least 5° C. lower than the processing temperature of the first heat treatment. Set.

Next, examples of the present invention will be shown. However, the steps up to forming the drain electrode 18a and the source electrode 18b are the same as the conventional steps described above, so a description thereof will be omitted. After forming the electrodes 18a and 18b, the silicon substrate 11 is heated at 450°C to 550°C, preferably in a hydrogen atmosphere for 30 minutes or more.
A first heat treatment is performed at a temperature of 470°C to 500°C. Next, a second interlayer insulating film 19 made of silicon oxide with a thickness of 0.5 μm to 1.0 μm is deposited using the CVD method (reaction temperature is approximately 400 μm).
After that, a photoconductive film connecting electrode 21 made of Mo--Nb alloy, Zr, etc. is formed by electron beam evaporation or sputtering. Even at this stage, structural defects occur on the surface portion of the silicon substrate 11 due to soft X-rays or ultraviolet rays, so a second heat treatment is then performed in a hydrogen atmosphere to replenish the desorbed hydrogen. However, this second heat treatment is performed at a temperature that is at least 5 degrees Celsius lower than the first heat treatment temperature (420 degrees Celsius to 545 degrees Celsius).
℃).

Since the first heat treatment temperature is set high, the alloying is almost completed by this heat treatment, and the alloying between the drain electrode 18a and the silicon substrate 11 hardly progresses when the second interlayer insulating film 19 is formed. This prevents cracks from occurring in the second interlayer insulating film 19. In addition, the silicon substrate 11
Structural defects occurring on the surface of the substrate are almost completely eliminated by replenishing hydrogen through the second heat treatment. In addition,
When the first heat treatment is set at 500°C, the second heat treatment can be set at 470°C. How much to lower the temperature is also related to the length of the first heat treatment time; if the first heat treatment time is 60 minutes,
A good guideline is to lower the temperature by 5°C to 20°C for 30 minutes. Further, the second heat treatment time may also be approximately 30 minutes to 60 minutes.

After performing the second heat treatment, a photoconductive film 20 and a transparent electrode 22 are formed. The photoconductive film 20 has, for example, Zn--Se as the first layer, (ZnTe) _1-y
(In ₂ Te ₃ ) In the case of a four-layer structure in which _y is the second layer, CdTe is the third layer, and ZnSe is the fourth layer, the silicon substrate 11 is kept at a temperature of about 250°C and the first layer has a thickness of about 0.2μ. Next, the silicon substrate 11 is kept at about 180°C, and the second layer is about 1μ thick, and the third layer is about 0.5μ thick.
Each layer is deposited to a thickness of . Then, the fourth layer is deposited to a thickness of about 0.2 μm while keeping the silicon substrate 11 at a temperature of about 250° C. After this, heat treatment was performed at about 500° C. in vacuum for several minutes, but the hydrogen desorption caused by this heating hardly caused any changes in the threshold voltage or interface state density. especially,
By selecting the temperature of the final vacuum heat treatment to be 470° C. or lower, no fluctuation is observed and no cracks occur in the second interlayer insulating film, making it possible to obtain a good solid-state imaging device. Ta.

Although the above has been described as an example using a crystalline photoconductive film, it can also be applied to a solid-state imaging device equipped with an amorphous photoconductive film, especially when high-temperature heat treatment is required in the device sealing or packing process. It has excellent effects when applied to things that require

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a general circuit configuration of a solid-state imaging device, and FIG. 2 is an enlarged sectional view of a main part of the solid-state imaging device with a photoconductive film. 11...Silicon substrate, 13...Source region,
14... Drain region, 17... First interlayer insulating film, 18a... Drain electrode, 18b... Source electrode, 19... Second interlayer insulating film, 20... Photoconductive film, 21... Photoconductive Electrode for membrane connection.

Claims (1)

[Claims] 1 After forming a drain region and a source region of a MOS transistor on a silicon substrate, a first interlayer insulating film is formed, and then a drain electrode in ohmic contact with the drain region and a source electrode in ohmic contact with the source region are formed in the silicon substrate. Formed on an insulating film and heated at 450℃ to 550℃ in a hydrogen atmosphere
After performing a first heat treatment at a temperature of After that, a second heat treatment is performed in a hydrogen atmosphere at a temperature at least 5° C. lower than the first heat treatment, and then a photoconductive film is formed on the photoconductive film connecting electrode. 1. A method for manufacturing a solid-state imaging device, comprising heating the solid-state imaging device.