JP2003332598A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device in which warp is suppressed. <P>SOLUTION: A semiconductor device composed of a semiconductor substrate and a metal film applied to at least one side thereof entirely or partially and having warp caused by a heat history during a manufacturing process is cooled and then heated thus reducing the warp. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art Since a semiconductor device having a semiconductor substrate and a metal film is manufactured by a process involving a temperature change, when the temperature is returned to room temperature, the heat of the semiconductor substrate (eg silicon substrate) and the metal film (eg silver electrode) are increased. Due to the difference in expansion coefficient,
A warping phenomenon occurs. Usually, the entire semiconductor device is warped by making the semiconductor substrate side convex by the temperature rising process. When the semiconductor substrate side is convex and warped, a space is generated between the glass and the substrate during the modularization process of mounting a flat cover glass,
There is a problem that the adhesive inserted between the glass and the substrate does not spread and bubbles are generated, and also when it is attached to the substrate for the module, there is a problem that the adhesive does not spread and bubbles are generated. Was quite necessary. Therefore, it is necessary to flatten and fix the warped semiconductor device by using a vacuuming device, a pressure bonding device, or the like. However, it is difficult to control the thin semiconductor device because cracks are generated or deformed due to partial vacuum drawing. When the substrate itself of the semiconductor device is warped like a module for fixing the semiconductor device along a curved surface, even if the semiconductor device is not warped, the same problem as described above occurs. As a method for removing such a warp, a method has been proposed in which the material is once cooled to −70 ° C. or lower and then dried and held at a normal temperature of 50 ° C. or lower (JP 2000-332274 A). As a result, the amount of warpage of the semiconductor device can be significantly reduced.

[0003]

However, according to the above-mentioned method, it has been found that depending on the manufacturing conditions, the side opposite to the direction in which it was initially warped, that is, the metal film side is made convex and warpage remains. Therefore, it has been desired to remove the remaining warp.

[0004]

Thus, according to the present invention, a semiconductor device having a semiconductor substrate and a metal film on at least one surface thereof, wholly or partially, and having a warp due to thermal history during the manufacturing process thereof. There is provided a method for manufacturing a semiconductor device, characterized in that the warp of the semiconductor device is reduced by cooling and then heating.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As a structure having a semiconductor substrate / metal film, for example, (1) a structure in which a metal film b is formed only on a part of one surface of a semiconductor substrate a (FIG. 2 (1)) (2) Structure in which the metal film b is formed on the entire surface of one surface of the semiconductor substrate a (see FIG. 2 (2)) (3) On the other surface of the semiconductor substrate a having the structure of (2) The present invention can be applied to a semiconductor device having a structure in which a metal film (c, d) is partially or entirely formed (FIG. 2 (3) -1 and (3) -2). Examples of the semiconductor substrate that can be used in the present invention include a silicon substrate, a germanium substrate, a compound substrate of GaAs, InGaAs, or the like. Furthermore, the thickness of the semiconductor substrate is preferably 50 μm or more and 200 μm or less, although it depends on the application of the semiconductor device. When the thickness is more than 200 μm, the rigidity of the substrate hardly causes warping, which is not preferable.

The metal film that can be used in the present invention is not particularly limited as long as it has a difference in coefficient of thermal expansion from the semiconductor substrate, and any kind of metal film can be used. As a specific metal film, a film made of a refractory metal such as silver, aluminum, copper, gold, zinc, tin, titanium, tungsten, tantalum, or molybdenum, a transparent conductive oxide such as ZnO, SnO ₂ , or ITO, Further, a film in which these are laminated can be given. Further, even when the semiconductor substrate has metal films on both sides, the present invention can be applied to the case where the semiconductor device is warped due to the difference in the type and area of the metal film. The method for forming the metal film is a known method, for example, a vapor deposition method,
Any method such as a sputtering method, a CVD method, or a laser deposition method may be used.

The substrate on which the metal film is formed is cooled and then heated. Warping of the semiconductor device can be reduced by passing through this cooling and heating (see FIG. 1). The cooling temperature of the substrate may be any temperature as long as it can reduce the warpage due to the thermal history during the manufacturing process of the semiconductor device. By this cooling, the warp of the substrate can be roughly removed. As a cooling method to −70 ° C. or lower, liquid nitrogen (boiling point −195.8 ° C.), liquid helium (same as −268.9 ° C.), liquid neon (same as −245.9).
℃), liquid argon (same as -185.9 ℃) and the like, a method of immersing in a gas of -70 ℃ or less, not limited to liquid,
Alternatively, a method of spraying, a method of bringing into contact with an object cooled by a solid, liquid or gas at -70 ° C or less, and the like can be mentioned. After cooling, it is preferable to dry the substrate. As a drying method, there is a method of leaving it in a drying tank purged with a gas such as dry nitrogen which is stable at room temperature and is not corrosive and is dry.

Next, the substrate is heated. By this heating, the warp of the substrate can be further removed. The heating temperature of the substrate is preferably 50 ° C. or higher. The method of the present invention can reduce the warpage by about 80% or more as compared with the method of only cooling and not heating. Therefore, it is possible to obtain a semiconductor device that is flatter than the conventional one, and also to obtain a semiconductor device having a desired curvature by adjusting the amount of warpage. Further, the method of the present invention is preferably used in a method for manufacturing a solar cell.

[0009]

The present invention will be described in detail below with reference to a PN junction type single crystal silicon solar cell as a semiconductor device. It should be noted that this embodiment does not limit the present invention. As shown in the schematic cross-sectional view of FIG. 4 (i), the solar cell 1 has a PN junction formed by thermally diffusing impurities on one surface of a semiconductor substrate (silicon substrate) 2 and a light receiving side on the surface of the silicon substrate 2. A comb-shaped front surface electrode 6 and a back surface electrode 7 made of Ag are formed on almost the entire back surface side. P in FIGS. 3 (a) to 5 (k)
The manufacturing process of an N junction type single crystal silicon solar cell is illustrated. The manufacturing process is roughly divided into five.

In the first step (impurity diffusion step), impurities are thermally diffused to form a P / N junction on the surface of the silicon substrate 2 to form an N-type impurity diffusion layer 3 (FIG. 3).
(A)). After that, the impurity diffusion layer 3 on one surface is removed by etching (FIG. 3B). Reference numeral 4 indicates a light receiving surface. The thickness of the semiconductor substrate is not particularly limited, but the thinner the semiconductor substrate, the more easily it is warped. Therefore, the effect of applying the present invention is greatly exerted when the semiconductor substrate has a thickness of 200 μm or less. In this example, a 100 μm substrate was used.

In the subsequent second step (electrode forming step), an electrode pattern 5 is formed using a photoresist on the side of the light receiving surface 4 where the impurity diffusion layer 3 remains (FIG. 3C). Silver, which is an electrode material, is partially vapor-deposited on the light-receiving surface 4 side to form a surface electrode 6 (FIG. 3D), and then the electrode pattern 5 is peeled off to remove unnecessary electrode material (FIG. 4). (E)).
Next, an electrode material is deposited on the back surface of the patterned silicon substrate 2 on almost the entire surface (FIG. 4 (f)). The surface electrode 6
After the back electrode 7 is formed, it is desirable to form the antireflection film 8 on the light receiving surface side (FIG. 4G). Finally, a cell is cut into a predetermined shape by a dicing process to manufacture a solar cell (FIG. 4 (h)). The thickness of the electrode is not particularly limited, but like the semiconductor substrate,
If the thickness changes, the change in the amount of warp also changes. In this case, it is sufficient to deal with this by changing the respective processing time / temperature settings.

In the next third step (cooling step), the warp of the solar cell is roughly removed (see also FIG. 7 below).
By immersing the warped silicon substrate 2 (FIG. 4G) in liquid nitrogen (liquid temperature −196 ° C.)
Is cooled below about -90 ° C. After cooling, this is left to stand in a drying tank purged with dry nitrogen for a corresponding period of time and dried at room temperature. In this state, the amount of warpage is greatly reduced by cooling, but this time, the warpage remains in a convex shape on the surface of the back electrode 7, resulting in large variations in the amount of warpage.

In the fourth step (heating step), the warp of the solar cell is further reduced. Hold the cell in a jig and put it in an oven at 50 ° C or higher for a considerable time until the cell body warms up. After that, when the cell is kept at room temperature, the cell again makes the light receiving surface convex and begins to warp. FIG. 6 shows an example of a graph showing the relationship between the oven temperature and the amount of warpage when a 100 μm silicon substrate is used. From this graph, it can be seen that the amount of warpage comes closest to ± 0 at a heat treatment temperature near 55 ° C., but the value at this time naturally changes because the stress state changes as the thickness of the substrate or electrode changes.

As a heating method for heating to 50 ° C. or higher, not only an oven but also an electric heating device such as a hot plate, an IR heater using electromagnetic waves, a hot bath using a liquid such as hot water, a heating device using a heating power such as a stove, etc. It is also possible to use the method. That is, -70 without damaging the solar cell
The warp can be removed as long as it can be cooled to below ℃, dried and heated to above 50 ℃, and any method can be used. The warp removal step by cooling / heating the semiconductor substrate during the manufacturing process may be any manufacturing step as long as it is from the occurrence of the warp until it is fixed to the support plate for mounting the cover glass. When accurate warpage amount control is required, it is preferable to perform it in the final step where temperature is applied or after it.

The final fifth step (cover glass mounting step)
Then, as shown in FIG. 5 (j), the solar cell 1 cut into a predetermined size is placed on the solar cell holding member 32 with the light receiving surface 4 facing upward. Next, an adhesive 10 made of silicon on one side (for example, DC93-500 manufactured by Dow Corning)
The cover glass 9 applied with the cover glass holding jig 31
Is used for vacuum adsorption. Next, the cover glass holding jig 3
1 is moved closer to the solar battery cell 1, and the vacuum state of the cover glass holding jig 31 is released immediately before the solar battery cell 1 and the cover glass 9 come into contact with each other. After that, the cover glass 9 is separated from the cover glass holding jig 31 and adhered to the light receiving surface 4 of the solar cell 1 as shown in FIG. 5 (k), and the fifth step is completed. The reference numeral 33 indicates a positioning pin.

If the warp of the solar cell 1 is not removed, a useless gap 50 is formed between the flat cover glass 49 having no warp and the cell light receiving surface 44 as shown in FIG. In order to do so, the amount of adhesive used must be increased. If the warp is removed, a small amount of adhesive can be used, it is possible to prevent air bubbles from being mixed in the adhesive 10, and to make the thickness and weight more uniform. Further, the vacuum device for the solar battery cell holding jig 32, which is attached for fixing the warped solar battery cell body 41, is unnecessary. On the other hand, when fixing the solar battery cells to the curved surface, the warp of the solar battery cells can be used. In such a case, it is possible to fix the solar cell having a desired curvature to the substrate having a certain curvature by making good use of the above cooling / heating process.

FIG. 7 shows an actual process diagram of the warp removal processing.
Shown in. As described above, in the semiconductor device manufacturing apparatus according to the present invention, the third and fourth steps for removing the warp include a holding unit for holding the semiconductor device, a cooling unit for holding the semiconductor device at -70 ° C. or below, and drying the semiconductor device at room temperature. It is composed of four parts: a drying part for heating and a heating part capable of heating to 50 ° C. or higher. Semiconductor device 5
By setting 2 in the semiconductor device transport carrier 51, it is possible to process a large amount at a time. After the dicing into a predetermined shape is completed, the semiconductor device 52 is set on the semiconductor device transport carrier 51, held in the cooling tank 54 (for example, liquid nitrogen as the cooling medium 53), and cooled to about -90 ° C. Next, it is conveyed to the drying tank 56 and sprayed with a drying gas or the like to be dried at room temperature. Further, this is put in a heating tank 57 (for example, an oven), heated and kept at 50 ° C. or higher, then kept at room temperature and cooled to room temperature. Reference numeral 55 indicates a drying unit lid.

This series of processes can be automated by controlling the processing time and the processing temperature and adding a transfer section. The physical phenomenon of this warp removal is explained as follows. Due to the difference in the coefficient of thermal expansion between the electrode and the silicon substrate, the contraction force of the electrode portion becomes larger with cooling, and a large contraction force is generated at the interface. When this semiconductor device is returned to room temperature after cooling, the contraction force is converted into an expansion force and the metal part having a large thermal expansion coefficient tends to expand more than the semiconductor part, so that stress that makes the metal part convex is applied. If this stress exceeds a certain value, the crystal structures of both the semiconductor and the metal in the vicinity of the interface cannot withstand, a partial structural transition occurs, and the amount of warpage changes. In the case where the warpage changes due to heating with the semiconductor portion being convex, it can be considered that the opposite phenomenon occurs. By properly balancing these two phenomena utilizing the temperature difference, the warp can be further reduced.

In the warp removal process involving rapid cooling such as immersion in liquid nitrogen, when the temperature is gradually returned to room temperature, stress is continuously applied and sufficient time for structural transition is given, so that the same temperature change is involved. Even in the case of, the amount of warpage changes more than before cooling. On the other hand, even when heating above normal temperature, when it is rapidly heated in an oven or the like and gradually cooled to normal temperature, the amount of warpage is the same as before heating because stress is continuously applied in the opposite direction, that is, in the convex direction on the semiconductor substrate. It changes greatly compared to.

[0020]

EFFECTS OF THE INVENTION By removing the warp by this method, a vacuum device necessary for flat fixing is not required, which facilitates modularization. In addition, since it is possible to prevent bubbles and the like from entering, the repair time is not required and the working time is greatly shortened.
Further, even when the flat cover glass without warpage or the module is mounted on the substrate, there are advantages such as saving the raw material of the adhesive, reducing the weight and thickness, and making the air bubble mixed in highly uniform. On the contrary, when the semiconductor device is fixed to the curved surface, the warp of the semiconductor device can be controlled and fixed to a desired curvature by properly utilizing the heating / cooling conditions of the warp removal process.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a change in warpage of a semiconductor device.

FIG. 2 is a structural cross-sectional view of a semiconductor device having a semiconductor substrate / metal film.

FIG. 3 is a schematic cross-sectional view of manufacturing steps of a PN junction type single crystal silicon solar cell.

FIG. 4 is a schematic cross-sectional view of manufacturing steps of a PN junction type single crystal silicon solar cell.

FIG. 5 is a schematic cross-sectional view of a manufacturing process of a PN junction type single crystal silicon solar cell.

FIG. 6 is a graph showing a relationship between a heat treatment temperature and a warp amount of a semiconductor device after cooling treatment with liquid nitrogen.

FIG. 7 is a diagram of a warp removal process according to the present invention.

FIG. 8 is a schematic cross-sectional view of a conventional solar cell having a warp after a cover glass is attached.

[Explanation of symbols]

1: Solar cell 2: Silicon substrate 3: Impurity diffusion layer 4: Light receiving surface 5: Electrode pattern 6: Surface electrode 7: Back electrode 8: Antireflection film 9, 49: Cover glass 10: Adhesive 31: Cover glass holding jig 32: Solar cell holding jig 33: Positioning pin 41: Solar cell body 44: Cell light receiving surface 50: Void 51: Semiconductor device carrier 52: Semiconductor device 53: Cooling medium 54: Cooling tank 55: Drying part lid 56: Drying tank 57: heating tank a: Semiconductor substrate b, c, d: metal film

Claims (8)

[Claims] 1. A semiconductor device having a semiconductor substrate and a metal film on all or a part of at least one surface thereof and having a warp due to thermal history during the manufacturing process of the semiconductor substrate is cooled and then heated. A method for manufacturing a semiconductor device, characterized in that the warpage of the device is reduced. 2. The manufacturing method according to claim 1, wherein the cooling is performed by holding at −70 ° C. or lower. 3. The method according to claim 1, wherein the cooling is performed using a cooling medium selected from liquid nitrogen, liquid helium, liquid argon and liquid neon. 4. The manufacturing method according to claim 1, wherein heating is performed by holding at 50 ° C. or higher. 5. The manufacturing method according to claim 1, wherein the semiconductor substrate is a silicon substrate. 6. The semiconductor substrate has a thickness of 50 μm or more and 200 μm or more.
The manufacturing method according to claim 1, which has the following thickness. 7. The manufacturing method according to claim 1, wherein the semiconductor device is a solar battery cell. 8. The manufacturing method according to claim 7, wherein the metal film contains at least Ag.