JPH0823083A - Manufacture of solid-state image sensing device - Google Patents

Abstract

PURPOSE:To restrain a semiconductor substrate from warping extraordinarily and slipping off due to thermal deformation by a method wherein insertion conditions are so set as to make temperatures inside a high-temperature thermal treatment device and a thermal gradient on the surface of the substrate lower than certain values respectively when the substrate is transferred into the high-temperature thermal treatment device. CONSTITUTION:A water high-temperature thermal treatment device is composed of a tube 27 of open tube structure fitted with a gas inlet 26 and a heating heater 25. When the heater 25 is set in operation, an intra-oven soaking region 22 of constant temperature set at an actual start of a thermal treatment is present in the tube 27. As a certain thermal gradient is present at the end of the heater 25, a part of the tube 27 between the oven opening end 21 of the tube 27 and the starting end of the intra-oven soaking region 22 is designated as an oven opening-soaking region 23. The thermal deformation of a wafer is determined in size depending on the temperature of the oven opening end 21 and a temperature rise rate of the wafer in the oven opening-soaking region 23. Therefore, the temperature of the oven opening end 21 is set to a range of 450 to 520 deg.C, and a temperature rise rate of a wafer in the oven opening-soaking region 23 is set to a range of 1.5 to 3 deg.C/second.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device manufacturing method and a manufacturing apparatus therefor.

[0002]

2. Description of the Related Art In the process of manufacturing a solid-state image pickup device, an element for converting light into an electric charge or an element for converting light into an electric charge and then transferring the electric charge by using a capacitor is n-type or p-type on a semiconductor substrate.
A mold impurity is implanted, and high temperature heat treatment at 900 ° C. or higher is performed to activate it. Further, in order to form a capacitor for transferring charges, the gate oxide film is formed by holding in an oxygen atmosphere at a high temperature of 900 ° C. or higher. Further, the gate electrode is formed by using a polycrystalline silicon film.

When manufacturing a solid-state image pickup device, a high temperature heat treatment for activation is repeatedly performed after ion implantation to form a wide variety of impurity diffusion layers. When the heat treatment is repeatedly performed at a high temperature, the semiconductor substrate is exposed to a high temperature atmosphere, and thermal stress is generated to cause crystal defects inside the semiconductor substrate.

Further, in the solid-state image pickup device, when a region where the diffusion layer is depleted is irradiated with light, electrons are generated and charges are formed. Excessive current is generated and the solid-state imaging device becomes defective.

[0005]

Therefore, when a semiconductor substrate is subjected to a high temperature heat treatment, the semiconductor substrate is affected by thermal stress due to a temperature or a thermal gradient during transportation into a high temperature atmosphere, and a crystal defect such as a slip on the semiconductor substrate or a wafer is damaged. Warpage occurs.

In the method of manufacturing a solid-state image pickup device, an impurity diffusion layer is formed in a semiconductor substrate as an element for converting light into electric charges or an element for converting light into electric charges and then transferring the electric charges by using a capacitor. There is. Therefore, a process of implanting n-type or p-type impurities by using an ion implantation method and activating the impurities by high-temperature heat treatment is repeated.
Further, in order to form an array of capacitors that transfer charges, the process of oxidizing the surface of the semiconductor substrate in a high temperature oxygen atmosphere to form a gate insulating film is repeated.

Since a large number of high-temperature heat treatments are repeated in this way, the effect of thermal stress on the semiconductor substrate cannot be neglected when being conveyed to a high-temperature heat treatment apparatus. Due to this effect, a crystal defect such as a slip occurs in the semiconductor substrate, and at the same time, an abnormal warpage occurs in the entire wafer.

Further, it has been clarified that the influence of these thermal stresses is larger when the semiconductor substrate is inserted than when it is inserted, and the deterioration of the semiconductor substrate due to the thermal stress is remarkable.

The crystal defects and the warp of the wafer deteriorate the device characteristics of the solid-state image pickup device, and significantly deteriorate the yield.

Since a large thermal stress is liable to be generated at the time of insertion into the high temperature heat treatment apparatus, the take-out temperature can be made relatively higher than the charging temperature. For this reason, the current apparatus has a system in which the temperature inside the apparatus is lowered after registering a new processing condition, and therefore the mobility rate of the equipment becomes low in the current movable system.

[0011]

In order to solve the above-mentioned problems, a method of manufacturing a solid-state image pickup device according to the present invention comprises a step of implanting an impurity for photodiode or charge transfer, and implanting an impurity on a semiconductor substrate. After that, a step of thermally diffusing the impurities, a step of heating the semiconductor substrate in an oxidizing atmosphere to form a gate insulating film after the thermal diffusion, and a step of forming a gate electrode on the gate insulating film are provided. In the step of forming the film, when the semiconductor substrate is subjected to high temperature heat treatment, the semiconductor substrate is provided with a condition for introducing the semiconductor substrate into the high temperature heat treatment apparatus so that the semiconductor substrate is not strained by heat.

Further, when the semiconductor substrate is transferred to the high temperature heat treatment apparatus, the temperature at the carry-in port of the high temperature heat treatment apparatus is 450 ° C.
The temperature is within the range of 520 ° C. or lower.

Further, the temperature which rises while the semiconductor substrate is transported to the soaking zone of the high temperature heat treatment apparatus is in the range of 1.5 ° C./sec or more and 3 ° C./sec or less.

Further, while the semiconductor substrate is transported to the soaking zone of the high temperature heat treatment apparatus, the maximum temperature difference between the central portion and the peripheral portion of the semiconductor substrate is within the range of 50 ° C. to 75 ° C.
The time until thermal equilibrium is achieved in the plane of the semiconductor substrate is within the range of 10 minutes or more and 15 minutes or less.

Further, when the temperature of charging the semiconductor substrate to the high temperature heat treatment apparatus is different from the temperature of the semiconductor wafer discharge and the temperature of the semiconductor wafer is high, the semiconductor heat treatment apparatus has a function of lowering the soaking temperature of the high temperature heat treatment apparatus at the same time when the semiconductor substrate is taken out and conveyed.

Further, the insertion temperature and the insertion temperature of the semiconductor substrate to the high temperature heat treatment apparatus are different, and the insertion temperature is lower than the insertion temperature.

[0017]

When the semiconductor substrate is conveyed to the high temperature heat treatment apparatus by the means of the present invention, the temperature of the insertion condition and the thermal gradient in the plane of the wafer to be inserted are set to a certain level or less, so that the semiconductor substrate is caused by thermal strain. It is possible to suppress the occurrence of abnormal warp and slip of the.

Further, since the occurrence of thermal strain in the wafer is larger when the wafer is inserted than when it is inserted, the temperature and thermal gradient during insertion are clearly defined. Therefore, the insertion temperature can be made higher than the insertion temperature. From this, a new system that lowers the temperature of the soaking zone to the input temperature at the same time when the wafer is taken out can be operated without lowering the operating rate of the high temperature heat treatment apparatus.

Further, by defining the temperature and the temperature gradient within the plane of the wafer, it is possible to suppress the characteristic variation of the solid-state image pickup device within the plane of the wafer during the high temperature processing.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a solid-state image pickup device according to an embodiment of the present invention will be described below with reference to the drawings. FIG.
FIG. 3 is a sectional view of a general solid-state imaging device.

As shown in FIG. 1, p is formed on the silicon substrate 1.
After the well diffusion layer 7 is formed by using the type impurities, the charge transfer diffusion layer 2 for transferring the charge and the photodiode 4 for converting the incident light into the charge are connected via the element isolation portion 3.
A solid-state imaging device is one in which several thousand to several millions are arranged. Further, in order to transfer charges, a MOS capacitor is formed on the charge transfer diffusion layer 2 via a gate oxide film 5 and a polysilicon electrode 6 which is a gate electrode.

2 to 9 are process sectional views of this embodiment. First, the well forming boron 8 is implanted on the silicon substrate 1 by the ion implantation method in the order of 10 ¹¹ cm ^-2 (FIG. 2).

Thereafter, in order to diffuse the well-forming boron 8 to form the well diffusion layer 7, the well-forming boron 8 is diffused in a nitrogen atmosphere at a high temperature of 1100 ° C. or higher (FIG. 3).

Further, in order to form the charge transfer diffusion layer 2 for transferring charges, a charge transfer diffusion layer mask 9 is formed by using a resist, and an n-type impurity 10 of arsenic or phosphorus is formed by using an ion implantation method. Acceleration energy 100k
A dose of 10 ¹² cm ^-2 order is injected at about eV (FIG. 3).

Next, in order to heat and activate the n-type impurity 10 of arsenic or phosphorus, heat treatment is performed at about 900 ° C. for 30 minutes or more using a high temperature heat treatment apparatus to form the charge transfer diffusion layer 2. (Fig. 4).

Next, in order to separate the photodiode 4 and the charge transfer diffusion layer 2, an element isolation mask 9'is formed using a resist, and the element isolation boron 11 is ion-implanted by, for example, an acceleration energy of about 100 keV. , And a dose amount of 10 ¹² cm ^{-2 is} injected (FIG. 6).

Further, as in the case of forming the charge transfer diffusion layer 2, in order to activate the element isolation boron 11, a heat treatment at about 900 ° C. for 30 minutes or more is performed using a high temperature heat treatment apparatus, and the element isolation portion is formed. 3 is formed (FIG. 7).

Next, in order to form a gate oxide film 5 in order to form a MOS capacitor for transferring charges, the atmosphere of the high temperature heat treatment apparatus is set to an oxygen atmosphere to about 1
Dozens to hundreds of n by oxidizing the silicon substrate 1 at 000 ° C.
m gate oxide film 5 is formed. In addition, the gate oxide film 5
A polycrystalline silicon film is formed by a CVD method in order to form a gate electrode thereover. Further, in order to lower the specific resistance of the polycrystalline silicon film, for example, POCl ₃ gas is used to diffuse phosphorus into the polycrystalline silicon film at a high temperature of about 900 ° C. to form a polysilicon electrode 6 of, for example, ten and several Ω. (FIG. 8).

Next, in order to form the photodiode 4, for example, phosphorus is implanted by 10 ¹² cm ⁻² order by an ion implantation method, and further, in order to activate the implanted phosphorus, a high temperature heat treatment apparatus is used. For example, phosphorus is diffused into the silicon substrate 1 at a high temperature of 1000 ° C. to manufacture a solid-state imaging device (FIG. 9).

When manufacturing a solid-state image pickup device, the solid-state image pickup device is manufactured by repeating high temperature heat treatment for ion implantation and activation for ion activation, and forming a gate oxide film by repeating the same oxidation process. When the high-temperature heat treatment is repeated in this manner, a crystal defect occurs in the silicon substrate 1 due to a thermal strain due to a temperature difference at the time of charging and taking out, a change in precipitation of oxygen in the silicon substrate 1 due to the heat treatment, and a solid state. It is known that the contrast difference between the image pickup device and other image pickup elements becomes large, and it appears as a white defect on a reproduced image, resulting in a defect.

Therefore, when manufacturing a solid-state image pickup device,
It is necessary to have a condition that thermal strain becomes small when the film is conveyed to a high temperature heat treatment apparatus.

Transfer to the high temperature heat treatment apparatus includes input and output. In the case of taking out, the boat for fixing the wafer and the supporting jig for fixing the boat are in a sufficiently high temperature state, and the time until the heat capacity of the boat and the supporting jig for the boat is large is taken out. Since it is longer than the time, even if the wafer is taken out in a relatively high temperature state, the wafer is in the same situation as the gradual cooling and the thermal strain is small.

On the other hand, in the case of loading, the boat and the boat supporting jig are sufficiently cooled, the heat capacity of the wafer and the boat is large, the temperature difference in the wafer surface is large, and the thermal stress tends to be large. .

Therefore, in the present invention, the wafer loading conditions are specifically set. The apparatus configuration of the high temperature heat treatment apparatus will be described with reference to FIG. High temperature heat treatment equipment
It is composed of an open tube 27 having a gas inlet 26 and a heater 25 for heating.

In the part where the heater 25 is provided, a soaking region 22 in the furnace having a uniform temperature part which is set during the actual heat treatment.
Exists. This area 22 becomes the wafer processing area 24. Since there is a constant thermal gradient at the end of the heater 25, it is designated as the furnace end 21. Since there is a constant thermal gradient from the furnace port end 21 to the in-furnace soaking region 22, it becomes an important parameter when setting the transfer conditions, so it is defined as the furnace port to soaking region 23. .

In the method of manufacturing a solid-state image pickup device according to the present invention, the deformation of the wafer due to thermal strain and the occurrence of crystal defects in the silicon substrate 1 cause dark current defects depending on the transportation conditions to the high temperature heat treatment device. Therefore, the transport conditions of the high temperature heat treatment apparatus are set.

Since the outside of the furnace end 21 is located outside the heater 25, the temperature tends to drop sharply. Therefore, it can be ignored as a thermal strain exerted on the wafer when the solid-state imaging device is manufactured.

The temperature of the furnace end 21 is set by the set temperature of the in-furnace soaking region 22 and the distance from the furnace port to the soaking region 23. When the temperature of the furnace port end 21 exceeds 520 ° C., the temperature difference of 75 ° C. or more is generated between the central portion of the wafer and the wafer end, although the heat capacity of the boat for transferring the wafer is different, and thus the thermal strain exerted on the wafer becomes large. Therefore, a crystal defect such as a slip is induced at the wafer edge by a high temperature heat treatment process of several degrees after the pattern formation, resulting in a dark current defect of the solid-state imaging device.

However, when the temperature at the furnace end 21 becomes 450 ° C. or lower, it is necessary to make the distance from the soaking zone very long in terms of equipment. Moreover, it is necessary to lower the temperature of the soaking zone to a considerably low temperature. However, the high-temperature heat treatment apparatus takes a longer time when the temperature is lowered than when the temperature is raised, so that the operating rate of the equipment in the manufacturing process is extremely deteriorated. From the above points,
It is necessary to set the temperature of the furnace end 21 within the range of 450 ° C to 520 ° C.

Further, the thermal strain on the wafer is caused by the furnace end 21.
The temperature of the wafer, as well as the temperature at which the temperature of the wafer rises within the range of soaking 23, determines the magnitude of thermal strain on the wafer.

The rate of temperature rise from the furnace opening to the soaking region 23 is a factor in which the wafer transfer rate is dominant. When the temperature of the furnace mouth end 21 is 520 ° C., the charging speed is 10 cm / min, and when the distance between the furnace mouth and the soaking region 23 is 12 cm, the heating rate is 3 ° C./minute.
The temperature difference between the center and the edge of the wafer is 7
Over 5 ° C. Therefore, in the state where the stress of the film formed on the wafer surface after the pattern formation exists, the thermal strain and the film stress are added by the high temperature heat treatment of several degrees, and the crystal defect such as slip occurs.

However, when the wafer heating rate becomes 1.5 ° C./sec or less, it is necessary to make the transfer speed to the high temperature heat treatment apparatus very slow. Therefore, it cannot be used because the operating rate of the equipment in the manufacturing process is extremely deteriorated. From the above points, it is necessary to set the heating rate until reaching the in-furnace soaking region 22 within the range of 1.5 ° C./sec to 3 ° C./sec.

Further, when the wafer is transferred to the high temperature heat treatment apparatus, the heat capacity of the boat, the charging temperature and the charging speed of the boat have a great influence, but as a factor causing the crystal defects such as slip in the wafer, There is a temperature difference in. Further, there is an influence of the follow-up temperature rising rate in the furnace when the temperature in the furnace is lowered after the transfer. As a factor for covering the above two points, it is necessary that the temperature difference within the wafer surface is set to 75 ° C. or less and at the same time, the time for thermal equilibrium in the surface is taken for 10 minutes or more.

However, in order to reduce the temperature difference on the wafer surface during the temperature rise and the temperature decrease, the temperature of the soaking zone is set to a low temperature, the insertion speed is made slow, and the furnace port to the soaking zone are installed. It is necessary to increase the distance of the area 23. In order to ensure the throughput of a ready-made device at a certain level or higher, the temperature difference in the wafer surface must be 50 ° C. or more, and the time until the wafer surface is in thermal equilibrium must be 15 minutes or less.

From the above points, the temperature difference within the wafer surface is 50
It is necessary to set the temperature within the range of ℃ to 75 ℃, and the transfer conditions such that the time until thermal equilibrium is achieved within the wafer surface is within the range of 10 to 15 minutes.

In the present invention, there is insertion / insertion as the conveyance, but in the case of insertion / removal, quartz or ceramics having a relatively large heat capacity in the boat for fixing the wafer is used. For this reason, the wafer itself is gradually cooled due to the heat released from the quartz and the ceramics, and the thermal strain generated in the cooling of the wafer is small. From the above results, it is possible to take out at a relatively high temperature at the time of taking out, compared to the time of taking in.

Next, a method for manufacturing the solid-state image pickup device of the present invention will be described with reference to the high temperature heat treatment recipe example of FIG. 11 and the outline of the high temperature heat treatment device of FIG.

Usually, in the high temperature heat treatment, the wafer loading time 31, the high temperature heat treatment time 32, and the wafer removal time 3
It is composed of three. The set temperature at the wafer loading time 31 is set to a method having a small thermal strain in the manufacturing method of the solid-state imaging device of the present invention. When the distance from the furnace opening to the soaking region 23 is, for example, 20 cm, the setting of the soaking zone 22 in the furnace is set to about 8
If the temperature is set to 00 ° C., the temperature of the furnace end 21 becomes about 500 ° C., and if the temperature rising rate of the wafer and the thermal gradient at the time of transfer are adapted to the present invention, the transfer speed is relatively fast, about 10 cm.
Even if it is inserted at a rate of 1 / min, crystal defects such as slips due to thermal strain do not occur on the wafer due to the repeated heat treatment when manufacturing the solid-state imaging device.

When the wafer is fixed by using a ceramic wafer-fixing boat, the set temperature for the take-out time 33 is 900 ° C. because the ceramic boat has a large heat capacity.
Even when the temperature is relatively high, the in-plane temperature difference and the temperature lowering rate are within the scope of the present invention due to the heat dissipation of the boat material during taking out, and crystal defects such as slip due to thermal strain of the wafer do not occur.

In the case of manufacturing using the solid-state image pickup device manufacturing method described in the embodiment, the manufacturing device will be described with reference to FIG. 12 in order to shorten the lead time of the manufacturing device.

As described above, the set temperatures are different depending on the conditions such as the charging temperature focusing on the wafer charging time 31 and the conditions such as the discharging temperature focusing on the wafer unloading time 33.

Therefore, in order to shorten the lead time of the manufacturing apparatus, the high temperature heat treatment in the high temperature heat treatment apparatus is completed and the set temperature of the wafer take-out time 33, for example, 900.
Cool down to ℃. When the temperature reaches a preset temperature of 900 ° C., the taking out is started. Simultaneously with the start of the insertion, the heater 2 shown in FIG.
It is a device that turns off 5 and starts cooling down to an insertion set temperature of, for example, 800 ° C.

When this apparatus is used, since there is a wafer removal time 33 and a wafer cooling time 35 by the time of wafer transfer 34, the wafer of the lot to be processed next is transferred and transferred to the high temperature heat treatment apparatus. Before that, the temperature is sufficiently lowered to the set temperature at the time of loading the wafer.

By using the manufacturing apparatus as described above, the lead time of the equipment is extended because the temperature is sufficiently lowered to the wafer input temperature by the time the insertion and removal are completed and the wafer transfer is completed. At the same time, it is possible to minimize the above, and at the same time, even if the heat treatment is repeatedly performed, crystal defects such as slips do not occur on the wafer due to thermal strain.

[0055]

EFFECTS OF THE INVENTION Crystal defects such as slips due to thermal strain do not occur at the time of insertion, and characteristic deterioration of the solid-state imaging device due to crystal defects such as dark current defects and abnormal dark current defects can be significantly reduced.

Further, since the taking-out temperature has the heat capacity of the wafer fixing boat, crystal defects such as slips do not occur even if the carrying operation is carried out at a temperature relatively higher than the charging temperature, and the characteristics of the solid-state image pickup device. There is no deterioration.

When the insertion temperature and the insertion temperature are different and the insertion temperature is lower than the insertion temperature, in order to improve the operating rate of the equipment, the insertion conveyance is started and the temperature distribution in the furnace By lowering the set temperature to the temperature setting at the time of insertion,
Since the temperature is stable at the insertion set temperature during wafer transfer, it is possible to improve the facility operation rate of the high-temperature heat treatment apparatus or minimize the decrease in the operation rate.

[Brief description of drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to a method of manufacturing a solid-state imaging device according to an embodiment of the present invention.

2A to 2D are sectional views in order of the processes, for explaining one embodiment of the present invention.

3A to 3C are cross-sectional views in order of the processes, for explaining one embodiment of the present invention.

4A to 4C are cross-sectional views in order of the processes, for explaining one embodiment of the present invention.

5A to 5C are cross-sectional views in order of the processes, for explaining one embodiment of the present invention.

6A to 6C are cross-sectional views in order of the processes, for explaining one embodiment of the present invention.

7A to 7C are sectional views in order of the processes, for explaining one embodiment of the present invention.

FIG. 8 is a process order cross-sectional view for explaining an embodiment of the present invention.

9A to 9C are sectional views in order of the processes, for explaining one embodiment of the present invention.

FIG. 10 is a schematic diagram and a temperature distribution diagram of a high temperature heat treatment apparatus for explaining an embodiment of the present invention.

FIG. 11 is a diagram showing a high temperature heat treatment recipe for explaining the method for manufacturing the solid-state imaging device of the present invention.

FIG. 12 is a diagram showing a high temperature heat treatment recipe for explaining a manufacturing apparatus used in an example of the present invention.

[Explanation of symbols]

 1 Silicon Substrate 2 Charge Transfer Diffusion Layer 3 Element Separation Part 4 Photodiode 5 Gate Oxide Film 6 Polysilicon Electrode (Gate Electrode) 7 Well Diffusion Layer 8 Well Forming Boron 9 Charge Transfer Diffusion Layer Mask 9 ′ Element Separation Mask 10 n-type Impurity 11 Element Isolation Boron 21 End of Furnace 22 Soaking Area in Furnace 23 Furnace to Soaking Area 24 Wafer Processing Area 25 Heater 26 Gas Inlet 27 Tube with Open Tube Structure

Claims (6)

[Claims] 1. A step of implanting a photodiode or an impurity for charge transfer onto a semiconductor substrate, a step of implanting the impurity and then thermally diffusing the impurity, and a step of oxidizing the semiconductor substrate after the thermal diffusing. A step of forming a gate insulating film by heating in an atmosphere; and a step of forming a gate electrode on the gate insulating film, wherein in the step of forming the thermal diffusion gate insulating film, when the semiconductor substrate is heat treated, A method for manufacturing a solid-state imaging device, comprising: a condition for introducing a semiconductor substrate into a high-temperature heat treatment apparatus in which distortion due to heat does not enter. 2. The temperature of the carry-in port of the high-temperature heat treatment apparatus when the semiconductor substrate is transferred to the high-temperature heat treatment apparatus is in the range of 450 ° C. or higher and 520 ° C. or lower. A method for manufacturing the described solid-state imaging device. 3. The temperature rising while the semiconductor substrate is transported to the soaking zone of the high temperature heat treatment apparatus is in the range of 1.5 ° C./sec or more and 3 ° C./sec or less. Item 2. A method for manufacturing a solid-state imaging device according to item 1. 4. The maximum temperature difference between the central portion and the peripheral portion of the semiconductor substrate is within the range of 50 ° C. or more and 75 ° C. or less while the semiconductor substrate is being conveyed to the soaking zone of the high temperature heat treatment apparatus. 2. The method for manufacturing a solid-state imaging device according to claim 1, wherein the time until thermal equilibrium in the plane of the semiconductor substrate is within a range of 10 minutes or more and 15 minutes or less. 5. A function of lowering the set temperature of the soaking zone of the high-temperature heat treatment apparatus at the same time when the taking-out and transporting of the semiconductor substrate starts when the temperature of the high-temperature heat-treatment apparatus is different from the temperature of the high-temperature heat treatment apparatus The method for manufacturing a solid-state imaging device according to claim 1, wherein 6. The solid-state imaging device according to claim 3, wherein the insertion temperature and the insertion temperature of the semiconductor substrate into the high-temperature heat treatment apparatus are different, and the insertion temperature is lower than the insertion temperature. Production method.