JP3441469B2 - Substrate heat treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film element substrate used in an active matrix type liquid crystal display device, a line sensor or the like. More specifically, the present invention relates to a substrate heat treatment method using a vertical heat treatment apparatus in a manufacturing process.

[0002]

2. Description of the Related Art A substrate on which thin film elements such as thin film transistors are integrally formed (hereinafter referred to as a thin film element substrate) has been conventionally used as a constituent member of an active matrix type liquid crystal display device, a plasma display, an EL display or a line sensor. Widely used. The thin film element is formed in an integrated manner by applying an LSI manufacturing process using a thin film made of polycrystalline silicon or amorphous silicon formed on the surface of the substrate as a semiconductor active layer. The LSI manufacturing process includes high temperature heat treatment such as an impurity diffusion process, a gate insulating film forming process or an annealing process, and the substrate must have excellent heat resistance to withstand the maximum processing temperature during the manufacturing process. . This maximum processing temperature differs depending on the thin film material and the contents of the applied LSI manufacturing process. Even when a glass material is used as the substrate, an appropriate one is selected depending on the maximum processing temperature.
For example, when forming an amorphous silicon thin film transistor element, the maximum processing temperature is generally about 500 ° C.
In this case, barium borosilicate glass (for example, Corning 7059) having a strain point of about 600 ° C. is used.
The strain point is defined as the temperature at which the material has a viscosity of about 10 ^13.5 Pa · s and is a measure of heat resistance. When a transistor element is formed using a polycrystalline silicon thin film, when CVD is used as a method for forming a gate insulating film,
The maximum processing temperature reaches about 600 ° C. In this case,
Alumina borosilicate glass (eg Corning 1733) having a strain point of about 640 ° C. is used as the substrate material. When thermal oxidation is used instead of CVD as the method for forming the gate insulating film, the substrate processing temperature reaches about 1000 ° C. At this time, quartz glass having a strain point of about 1060 ° C. is used as a substrate material. In addition to this, various kinds of glass materials are used according to the maximum processing temperature in the LSI manufacturing process.

However, even if the temperature of the substrate is below the strain point, the viscosity decreases as the temperature rises. In particular, since the glass material is amorphous, its viscosity decreases almost monotonously as the temperature rises. Therefore, even if a heat treatment is applied at a temperature about 100 ° C. lower than the strain point, it has a property of being slightly deformed.

[0004]

Conventionally, a horizontal type heat treatment apparatus has been used in a semiconductor manufacturing process. The horizontal type has a structure in which a plurality of substrates or wafers to be heat-treated are placed in a furnace while leaning against a boat, and is characterized in that there is little backflow of air during wafer transfer. However, in recent years, as the diameter of wafers has increased and high integration has been demanded, high-quality processing capability has been demanded. Therefore, from the viewpoint of space saving and uniformity of heat treatment, a vertical heat treatment apparatus has become the mainstream instead of the horizontal heat treatment apparatus. This heat treatment apparatus includes, for example, a diffusion / oxidation furnace and an LP-CVD furnace. A vertical heat treatment apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 3-235329.

This vertical type has a structure in which only the end portions of the wafer are supported horizontally by a boat. Therefore, the support structure is basically susceptible to thermal deformation due to the weight of the wafer. Therefore, when the vertical heat treatment apparatus is used, there is a problem or a problem that the warp deformation of the wafer occurs due to its own weight even if the heat treatment is performed at a temperature about 100 ° C. lower than the strain point. Particularly, in the thin film element manufacturing process, a plurality of heat treatments such as an impurity diffusion step, a gate insulating film forming step by thermal oxidation, and an annealing step are repeatedly performed. 1
Even if the amount of warpage generated by one heat treatment is small, the deformation is accumulated each time the thermal history is repeated, and finally the amount of warpage becomes large. When the substrate is warped, a trouble such as a wafer transfer trouble or an exposure defect due to a stage suction failure of the exposure device occurs in a subsequent process. In addition, the stress inside the thin film increases with the deformation of the substrate, resulting in defective electrical characteristics of the thin film element. As the diameter of the wafer increases, the absolute amount of warpage increases, and various defects, failures, or defects frequently occur. At present, as the diameter of thin film element substrates is increasing, in order to avoid thermal deformation such as warpage, it is necessary to use expensive substrate materials with high strain point and excellent heat resistance, such as quartz glass, which increases manufacturing costs. Was invited. Even if quartz glass is used, thermal deformation cannot be avoided when heat treatment is performed near the strain point. Generally, the higher the heat treatment temperature, the more functionally stable thin film device can be obtained. However, in reality, there is a problem that the processing temperature cannot be set high from the viewpoint of suppressing thermal deformation.

In order to make it easier to understand the background of the present invention, a brief description will be given of the occurrence of substrate warp peculiar to a vertical heat treatment apparatus. Generally, a boat is used to hold the substrate in a horizontal posture. The boat has a plurality of columns or posts arranged upright at predetermined intervals along the outer peripheral direction of the substrate. A groove is formed on the side surface of each post, and the post is horizontally supported by engaging with the end of the substrate. However, the posts are not evenly spaced, and the spacing between adjacent posts is expanded to receive the substrate on one side. Therefore, the substrate is point-supported at its peripheral edge, but is not perfectly balanced in plan view. Thermal warpage deformation occurs due to the interaction between the geometrically unbalanced support structure and the own weight of the substrate.
There is a problem or a problem that the warp deformation is accumulated every time the heat treatment is repeated as long as the substrate holding posture in the planar direction is kept constant.

[0007]

In view of the above-mentioned problems and problems of the conventional technique, the present invention suppresses the occurrence of warpage even when heat treatment is performed near the strain point of a substrate using a vertical heat treatment apparatus. It is an object of the present invention to provide a substrate heat treatment method that can be performed. Further, it is an object of the present invention to provide a substrate heat treatment method capable of producing a thin film element substrate in a high yield by using an inexpensive substrate having ordinary heat resistance by suppressing thermal warp deformation. In order to achieve such an object, a vertical heat treatment apparatus is used which has a structure in which a boat in which a substrate made of a glass material is supported by a plurality of supporting portions and horizontally held at a predetermined pitch is inserted into a reaction tube. in the substrate heat treatment method of performing heat treatment twice or more Te, have at least one or more rows following heat treatment in a posture changed as compared to the planar direction of orientation of the first thermal treatment in the planar direction of the substrate placed in the boat, Of the substrate supported by the plurality of supports.
By changing the part between the first heat treatment and the next heat treatment,
In this way, we have taken measures to suppress the accumulation of substrate warpage .

[0008]

According to the present invention, when a vertical heat treatment apparatus equipped with a boat for supporting only the peripheral edge of a substrate at multiple points and holding it horizontally is used, the plane orientation of the substrate set on the boat is changed. Heat treatment is performed multiple times. The unevenness of the warp deformation appears different depending on the holding posture of the substrate in the plane direction.
Accumulation of thermal deformation can be prevented by changing the planar holding posture of the substrate so that different uneven shapes cancel each other out. In other words, in the present invention, the holding orientation of the substrate in the plane direction is changed so as to cancel the accumulation of the warp, and the heat treatment is performed a plurality of times so that the warp does not remain in the finished product. As a result, it is possible to effectively prevent warpage without using an expensive substrate having a high strain point and excellent heat resistance, and thus it is possible to manufacture a thin film element substrate at a low cost and a high yield.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram for explaining the basic concept of the substrate heat treatment method according to the present invention. A substantially round substrate or wafer 1 is supported at multiple points by boat posts 2 and held in a horizontal posture. Grooves are formed in the side surface of each post 2 so as to engage with the peripheral edge of the wafer 1. In order to mount the wafer 1 on the boat, the interval between the posts 2 adjacent to each other on one side is increased. Inevitably, the wafer 1 is held by the unbalanced multipoint support.

In the first heat treatment step, the orientation flat 3 of the wafer 1 is set in a boat in a plane posture in which it is positioned on the insertion direction side, and a predetermined processing is performed.

In the second heat treatment step, the orientation flat 3 of the wafer 1 is set in a boat so that the orientation flat 3 is displaced by 90 ° from the insertion direction, and the wafer 1 is heat treated.

FIG. 2 is a schematic diagram showing the state of warpage occurring in the first heat treatment step. A specific stress is applied to the wafer 1 due to the geometrical imbalance of the multi-point support by the posts 2, and the unevenness relationship of the warpage differs between the insertion direction A and the direction B orthogonal to the insertion direction A.

FIG. 3 schematically shows the above-mentioned concavo-convex state.
The warp is convex in the insertion direction A, and the warp is concave in the orthogonal direction B. Therefore, the wafer 1 as a whole exhibits so-called saddle type thermal deformation.

In the second heat treatment step, the wafer 1 is rotated by 90 ° and set in the boat. Therefore, the relationship between the A direction and the B direction is reversed from that in the first heat treatment step. In this case, the convex deformation caused by the first heat treatment step is canceled by the concave deformation caused by the second heat treatment step, and the concave warp deformation caused by the first heat treatment step is also generated by the second heat treatment step. Offset by convex warp deformation. Therefore, as a result, the wafer 1 is prevented from accumulating warp deformation and can maintain the substantially initial flat shape.

FIG. 4 is an external perspective view showing an example of a boat used for implementing the present invention. The boat 4 includes a pair of discs 5 and 6 vertically spaced apart from each other with a predetermined gap, and a plurality of posts 2 (4 in this example) connected between the discs 5 and 6.
It consists of and. As the material, for example, quartz glass having excellent heat resistance and high purity is used. Grooves are formed on the side surface of each post 2 at a predetermined pitch. The edges of the individual wafers engage with the grooves of the same level and are supported horizontally.

FIG. 5 shows a plan view of the boat shown in FIG. The plurality of posts 2 are arranged along the circumferential direction of the circular plate 5 with a predetermined interval. However, the interval between the posts that are adjacent to each other on the one direction side is enlarged, so that the wafer 1 can be mounted. The ends of the wafer 1 are point-supported by the grooves formed in the individual posts 2.

FIG. 6 shows an example of a vertical heat treatment apparatus used for carrying out the present invention. A gas supply pipe 8 is provided in a bottomed cylindrical quartz reaction pipe 7 which opens at the lower end and extends upward.
The individual wafers 1 are horizontally held on the boat 4 in a state of being separated from each other at a predetermined pitch, and are transported through the heat retaining cylinder 9. When the boat 4 is completely inserted inside, the opening of the reaction tube 7 is
It is adapted to be hermetically sealed by a cap 10 fixed to the heat insulation cylinder 9. A heater 11 is provided around the reaction tube 7 to maintain the ambient temperature at a high temperature. For example, when performing a thermal oxidation process using this heat treatment apparatus, the process gas is introduced from the gas supply pipe 8 while maintaining the inside of the reaction tube 7 at a high temperature atmosphere of, for example, 1000 ° C. and is held for a predetermined reaction time. .

Referring back to FIG. 1, a specific example of the substrate heat treatment method according to the present invention will be described in detail. In this example, the diameter is 15
A thin-film transistor element substrate was prepared by applying a normal LSI manufacturing process to a polycrystalline silicon thin film formed on a 0 mm round quartz glass wafer 1. In this production, a three-layer structure of silicon oxide / silicon nitride / silicon oxide was formed as a gate insulating film of a thin film transistor. It is a so-called ONO structure and has excellent pressure resistance. In applying the present invention, in the first heat treatment step,
A third layer of silicon oxide film was formed, and a second layer of silicon oxide was formed in the second heat treatment step.

The first heat treatment step was performed at 1000 ° C. for 60 minutes to thermally oxidize the surface of the polycrystalline silicon thin film. Then, silicon nitride is used as the second layer of the gate insulating film by LP-C.
Deposited by VD.

In the subsequent second heat treatment step, the surface of silicon nitride was thermally oxidized at 1000 ° C. for 60 minutes. At this time, the quartz glass wafer 1 was rotated by 90 ° from the time of the first heat treatment step, and the orientation flat 3 was installed in the boat from the insertion direction to the side. All the other steps such as the impurity diffusion step and the gate electrode forming step were performed at a processing temperature of 1000 ° C. or lower to finally prepare a thin film transistor element substrate.

The amount of warpage of the thin film element substrate prepared for the evaluation of the present invention was measured. As shown in FIG. 7, the difference in height when a span of 130 mm was scanned by the stylus method was evaluated as the amount of warpage. According to the measurement results, before the first heat treatment step, some initial unevenness was present on the substrate surface, and the orientation flat parallel direction (direction A shown in FIG. 2) and the orientation flat vertical direction (direction B shown in FIG. 2) were both about 1. The amount of warpage was 12 μm. After the first heat treatment step, a warp of about 40 μm occurred in the concave shape in the parallel orientation direction, and a warp of about 10 μm occurred in the convex shape in the vertical direction of the orientation flat. After the second heat treatment step, the concave warp is 3 in the parallel direction to the orientation flat.
While decreasing to about 0 μm, a convex warp occurred on the contrary in the vertical direction of the orientation flat by about 30 μm. In this case, the Vth characteristic of the thin film transistor element produced without any transport trouble during the process is about 1 V within the same wafer surface.
The variation was within the range, and no defective electric characteristics of the element occurred.

On the other hand, as a comparative example, a thin film element substrate was prepared by forming a gate insulating film having a three-layer structure while maintaining the same plane holding posture in both the first heat treatment step and the second heat treatment step. The other processing conditions are the same as those of the above-described specific example. The warp of the quartz glass wafer was about the same as in the above-described specific example until after the first heat treatment step, but after the second heat treatment step, a concave warp of about 80 μm occurred in the orientation flat parallel direction, and the orientation flat vertical direction. With respect to the above, a convex warpage of about 20 μm occurred. Further, the amount of warp varies greatly depending on the individual wafer. After the second heat treatment step, due to the variation in the amount of warpage of the quartz glass wafer, a transport trouble occurs at a rate of about 1 in 10, and the Vth characteristics of the thin film transistor produced also vary by about 3 V within the same wafer surface. Occurred.

As still another specific example, a polycrystalline silicon thin film transistor having a gate insulating film composed of a silicon oxide single layer was prepared using a round quartz glass wafer.
In the first heat treatment step, the surface of the polycrystalline silicon thin film was thermally oxidized at 1000 ° C. for 60 minutes to form a gate insulating film. Then, impurities were implanted through the gate insulating film to form source and drain regions. Subsequently, in the second heat treatment step, annealing was performed at 1000 ° C. for 30 minutes to activate the implanted impurities. At this time, the plane holding posture of the wafer was rotated by 90 ° from the time of the first heat treatment step, and the orientation flat was set on the boat by 90 ° laterally from the insertion direction. All other steps were performed at less than 1000 ° C. to form a polycrystalline silicon thin film transistor having a silicon oxide film single layer as a gate structure.

Before the first heat treatment step, the quartz glass wafer had a slight amount of unevenness as expected, and the amount of warpage was about 12 μm in both the parallel and parallel orientation directions. After the first heat treatment step, a concave warp was generated in the direction parallel to the orientation flat by about 40 μm, and a convex warp was generated by about 10 μm in the direction perpendicular to the orientation flat. After the second heat treatment step, the concave warp was reduced to about 30 μm in the parallel orientation direction, and conversely, the convex warpage was generated about 30 μm in the vertical orientation direction. In this case, there was no transport trouble in the process, the Vth characteristics of the formed thin film transistor were within a variation of about 1 V within the same wafer surface, and no defective element characteristics occurred.

Further, as a comparative example, in the second heat treatment step as well, the heat treatment was carried out while maintaining the same substrate plane direction holding posture as in the first heat treatment step, and a polycrystalline silicon thin film transistor substrate was prepared in the same manner as the above-mentioned specific example. . The warp of the quartz glass wafer was the same as that of the above-described specific example until after the first heat treatment step, but after the second heat treatment step, a concave warp of about 80 μm occurred in the parallel orientation direction of the orientation flat, In the direction, a convex warp of about 20 μm occurred. In addition, the amount of warp varies greatly among individual wafers. After the second heat treatment step, a transportation trouble occurred at a rate of about 1 in 10 due to the variation in the amount of warpage of the quartz glass wafer, and the Vth characteristics of the thin film transistors produced also varied by about 3 V within the same wafer surface. .

In each of the above-mentioned specific examples, the plane holding posture of the substrate is changed by 90 ° between the first heat treatment step and the second heat treatment step, but the present invention is not limited to this. Other angles may be used instead. In particular, when the heat treatment process is performed three times or more or when there is a marked difference in the heat treatment times, the optimum wafer installation direction differs according to the actual conditions. It is preferable to experimentally set the direction in which the offset or compensation of the warpage occurring in each heat treatment step is most effectively achieved.

Further, although a round substrate or wafer is used in the above-mentioned specific example, the present invention is not limited to this, and for example, a square quartz glass wafer is used as a driving substrate of an active matrix type liquid crystal display device. Can be used. In the case of a rectangular substrate, a boat structure supporting multiple points at its four corners is also conceivable. However, in this case, the warp is accumulated even if the installation direction of the substrate is rotated. Therefore, as shown in FIG. 8, in order to obtain a compensating effect for the warp of the rectangular substrate, it is preferable to use a boat that holds the rectangular substrate with a biased multi-point support structure. As shown in the drawing, each post 2 of the boat is unevenly distributed above the rectangular wafer 1.

Although the quartz glass wafer is used as the thin film element substrate in the above-mentioned specific examples, the present invention is not limited to this, and various kinds of glass materials may be used depending on the heat treatment temperature applied during the process. it can. Further, it is apparent that the heat treatment of not only glass materials but also other insulating substrates such as ceramics and metal substrates is effective in suppressing thermal warp deformation due to its own weight that occurs when a vertical heat treatment apparatus is used.

Although a polycrystalline silicon thin film transistor element is formed in the above-mentioned specific example, the present invention is not limited to this, and an element made of a semiconductor thin film such as amorphous silicon or CdSe, an MIM element, a plasma display or an EL display. It is useful when forming any of the thin film elements used for a line sensor and the like.

[0030]

As described above, according to the present invention, when a so-called vertical heat treatment is carried out in a state where only the peripheral edges of the substrate are supported at multiple points and held horizontally, the substrate installed on the boat is The heat treatment is performed multiple times by changing the plane direction. For this reason, when unevenness of thermal warp deformation occurs differently depending on the plane direction of the substrate, the unevenness direction of warp is reversed between heat treatments, so that they are offset or compensated for each other and thermal deformation does not accumulate. That is, according to the present invention, it is possible to prevent the accumulation of warpage even when the heat treatment is performed a plurality of times, and it is possible to avoid the thermal deformation of the substrate as a whole process. As a result, it is possible to prevent warpage without using an expensive substrate having a high strain point and excellent heat resistance, and thus it is possible to produce a thin film element substrate with high yield and low cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the basic concept of a substrate heat treatment method according to the present invention.

FIG. 2 is a schematic diagram for explaining a warp occurrence state of a substrate.

FIG. 3 is a schematic diagram showing a warp generation direction of the substrate.

FIG. 4 is an external perspective view of a boat used for implementing the present invention.

FIG. 5 is a plan view of the boat.

FIG. 6 is a schematic view showing an example of a vertical heat treatment apparatus used for carrying out the present invention.

FIG. 7 is a principle diagram showing a method for measuring the amount of warpage of a substrate.

FIG. 8 is a plan view showing another boat structure used for implementing the present invention.

[Explanation of symbols]

1 wafer 2 posts 3 Orifla 4 boats 7 Reaction tube 8 gas introduction pipes 11 heater

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 29/786 (56) Reference JP-A-53-101976 (JP, A) JP-A-4-120723 (JP, A)

Claims (2)

(57) [Claims] 1. A plurality of supporting parts are substrates made of a glass material.
In a substrate heat treatment method in which a vertical heat treatment apparatus for performing heat treatment by inserting a boat supported by the above and held horizontally at a predetermined pitch into a reaction tube is performed at least twice, a substrate installed in the boat faces and posture have an at least once rows following heat treatment was changed compared to the planar direction during the first heat treatment planar direction of, once the site of the substrate which is supported by the supporting portion of the plurality of
By changing between the eye heat treatment and the next heat treatment,
A substrate heat treatment method characterized by suppressing the accumulation of warpage . 2. A substrate made of a glass material is provided with a plurality of supporting portions.
In a method for manufacturing a drive substrate for a liquid crystal display device, wherein a vertical heat treatment apparatus for performing heat treatment by inserting a boat which is supported by the above and is horizontally held at a predetermined pitch into the reaction tube is heat treated at least twice. the plane orientation of the substrate placed in the boat position in at least one or more rows that have the following heat treatment was changed compared to the planar direction during the first heat treatment, the substrate supported by the support portions of the plurality of Part once
By changing between the eye heat treatment and the next heat treatment,
A method for manufacturing a drive substrate for a liquid crystal display device, which is characterized by suppressing the accumulation of warpage .