JP2889109B2 - Semiconductor device insulating film forming method and insulating film forming apparatus - 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 and an apparatus for forming an insulating film to be an interlayer insulating film or a surface protective film of a semiconductor device, and more particularly to a method for forming a flat insulating film surface irrespective of unevenness of a base. It was made.

[0002]

2. Description of the Related Art A conventional method for flattening the surface of an insulating film (for example, SiO ₂ film) serving as an interlayer insulating film or a surface protective film of a semiconductor device so as not to be affected by irregularities of the underlying layer as much as possible. The so-called SOG (Spin-on-Glass)
There is. That is, SOG means that a solution (Si (OH) ₄ ) for forming an insulating film later is dropped on a substantially central portion of the wafer, and the wafer is rotated in this state to generate a centrifugal force, so that the solution is deposited on the wafer surface. It is diffused and then heated to about 400 ° C., and is reacted in the order of Si (OH) ₄ → SiO ₂ + H ₂ O to coat the wafer surface with an SiO ₂ film. By doing so, the solution enters into the concave portions on the wafer surface while the solution does not adhere much to the convex portions on the wafer surface, so that the surface of the insulating film can be flattened regardless of the unevenness of the base. As a result, when, for example, an upper wiring is formed on the insulating film, the probability of disconnection and the like can be reduced, and the product yield and the like can be improved.

Here, Si is used as a solution for forming an insulating film.
When (OH) ₄ is used, such a solution easily reacts even at normal temperature (about 23 ° C.) to form SiO _{2 and} lose its fluidity.
It was stored refrigerated at about ℃. And this solution has a property that the viscosity increases as the temperature rises, but the viscosity is extremely low at the temperature during refrigerated storage to suppress the reaction,
Since it is difficult to form a thin film when spin coating is performed while the viscosity is extremely low, the temperature is returned to room temperature when used, and spin coating is performed after having a certain viscosity. Was.

[0004]

However, even with the conventional method as described above, it is impossible to completely flatten the surface of the insulating film. In particular, as the miniaturization progresses and the aspect ratio increases, the surface of the insulating film becomes higher. , Embedding recesses in the base,
It has become difficult to simultaneously satisfy both of the planarization of the insulating film surface.

[0005] In addition, due to the surface condition of the base, the adhesion between the insulating film applied thereon and the base film is reduced, and the interlayer insulating film is peeled off at the time of heat treatment or the like in a later step, thereby deteriorating the product yield. Was one of the causes. The present invention
It was made focusing on these various problems,
It is an object of the present invention to provide an insulating film forming method and an insulating film forming apparatus for a semiconductor device in which the surface of the insulating film can be made flatter and the effect of modifying the underlying surface can be expected.

[0006]

According to a first aspect of the present invention, there is provided a method of forming an insulating film for a semiconductor device, comprising: applying a liquid coolant to a wafer surface immediately before spin-coating an insulating film forming solution. Spin coating was performed. In the invention according to claim 2, liquid nitrogen is applied as the liquid coolant in the invention according to claim 1.

On the other hand, in order to achieve the above object, an apparatus for forming an insulating film of a semiconductor device according to a third aspect of the present invention comprises a rotation driving means for rotating a wafer in a horizontal plane, and a state in which the wafer is held by the rotation driving means. A liquid coolant dropping unit for dropping a liquid coolant on the wafer surface; and an insulating film forming solution dropping unit for dropping an insulating film forming solution on the wafer surface held by the rotation driving unit. Was.

According to a fourth aspect of the invention, in the third aspect of the invention, liquid nitrogen is applied as the liquid coolant dropped by the liquid coolant dropping means onto the wafer surface.

[0009]

According to the first aspect of the present invention, when the liquid coolant is spin-coated, a relatively large amount of the liquid coolant enters into the concave portion on the wafer surface, while the liquid coolant enters the convex portion on the wafer surface so much. No coolant remains, and the protrusions are heated by friction with air due to the rotation of the wafer as compared with the recesses. Therefore, the temperature of the wafer surface is low in the recesses and high in the protrusions.

Then, when the solution for forming an insulating film is spin-coated in such a state, for example, the above-mentioned Si (OH)
_In the case of a solution such as ₄ , since the viscosity increases as the temperature increases, the concave portion having a lower temperature has higher fluidity,
The solution flows so as to enter from the surface of the convex portion into the concave portion since the convex portion having the higher temperature has a higher viscosity. As a result, the surface of the insulating film formed later becomes flatter.

When the surface of the wafer is cooled, for example, even if the surface of the wafer is contaminated with carbon or the like and the surface state changes from hydrophilic to hydrophobic, the hydrophobic surface layer is removed by freezing and the surface of the wafer is removed. The state returns to hydrophilic. In particular, when liquid nitrogen is used as the liquid coolant as in the invention according to claim 2, since the coolant is highly stable, it does not adversely affect the solution for forming the insulating film, If the wafer surface is sufficiently cooled by nitrogen, the surface layer of the wafer is deiced and the surface state of the wafer is restored.

Here, the invention according to claim 3 and claim 4 is an invention relating to a manufacturing apparatus suitable for realizing the invention according to the manufacturing method according to claim 1 or 2. Therefore, the respective operations of the third and fourth aspects of the invention are substantially the same as those of the first and second aspects of the invention. That is, in the invention according to claim 3,
It has two types of dropping means, a liquid coolant dropping means and an insulating film forming solution dropping means. In the operation procedure of the manufacturing apparatus according to the third aspect, first, the liquid coolant is dropped on the wafer surface by the liquid coolant dropping means, and the wafer is rotated by the rotation driving means to diffuse the liquid coolant over the entire surface of the wafer. . Next, the insulating film forming solution is dropped on the upper surface by the insulating film forming solution dropping means, and the wafer is rotated by the rotation driving means to diffuse the insulating film forming solution over the entire surface of the wafer. As a result, the same operation as that of the first aspect is obtained. Further, according to the fourth aspect, the same operation as the second aspect can be obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic configuration of an SOG film forming apparatus 1 as an insulating film forming apparatus of a semiconductor device according to one embodiment of the present invention. That is, this SOG film forming apparatus 1
A wafer holder 3 for vacuum-sucking the back surface of a wafer 2 as a silicon substrate and holding the wafer horizontally, a rotatable rotating shaft 4 connected to the center of the back surface of the wafer holder 3 and extending downward, A power source 5 for applying a rotational driving force to the rotating shaft 4, a drain 6 connected to the bottom surface, a cup 6 surrounding the wafer holder 3, and a wafer 2 held on the wafer holder 3. And two nozzles 7 and 8 facing the center of the surface from above.

Here, one of the two nozzles 7, 8 is used as a solution for forming an insulating film for forming an SOG film as a solution containing a silicon compound as a main component (for example, Si (OH) _The other end (not shown) is connected to a supply source for supplying a predetermined amount of a solution Si (OH) ₄ at room temperature. The other nozzle 8 is a nozzle for dropping liquid nitrogen N ₂ as a liquid coolant onto the wafer 2, and the other end (not shown) is another supply source for supplying a predetermined amount of liquid nitrogen. It is connected to the.

The SOG film forming apparatus 1 is used as follows. That is, as shown in FIG.
A thin silicon oxide film 10 is formed on the surface, and a wiring pattern 11 made of, for example, an aluminum-based alloy, which is a lower layer wiring of a multilayer wiring structure, is formed on the silicon oxide film 10, and a thin plasma oxide film 12 is further formed thereon. The wafer 2 thus held is held on a wafer holding table 3 of the SOG film forming apparatus 1.

Next, liquid nitrogen N ₂ is dropped on the surface of the wafer 2 from the nozzle 8, and after the drop, the power source 5 is driven to rotate the wafer holding table 3, and the wafer 2 held on the wafer is held in a horizontal plane. By rotating, the liquid nitrogen dropped on the central portion of the wafer 2 is diffused outward from the central portion by the centrifugal force generated by the rotation of the wafer 2. That is, S
In the OG film forming apparatus 1, first, liquid nitrogen is spin-coated on the surface of the wafer 2.

At this time, since the viscosity of the liquid nitrogen is extremely small, the liquid nitrogen enters into the concave and convex portions formed by the wiring pattern 11 (see FIG. 2B), and the concave portion is rapidly cooled. On the other hand, the liquid nitrogen adhering to the surface of the convex portion formed by the wiring pattern 11 is blown off by friction with the atmosphere, so that the liquid nitrogen is not cooled rapidly as in the concave portion. Heated by frictional heat due to friction between

As a result, a temperature difference occurs between the concave portion and the convex portion formed by the wiring pattern 11 such that the concave portion has a lower temperature. Thereafter, the rotation of the wafer holder 3 is temporarily stopped, and the solution Si (OH) ₄ is dropped from the nozzle 7 onto the surface of the wafer 2. After the drop, the power source 5 is driven again to bring the wafer holder 3 into a rotating state. The wafer 2 held by the wafer 2 is rotated in a horizontal plane, and the solution Si (OH) ₄ dropped on the central portion of the wafer 2 is diffused outward from the central portion by the centrifugal force generated by the rotation of the wafer 2. That is, in the SOG film forming apparatus 1 of the present embodiment, the spin coating of the solution Si (OH) ₄ is performed after the spin coating of the liquid nitrogen.

Here, the surface temperature of the wafer 2 and the solution Si
As shown in FIG. 3, the viscosity of (OH) ₄ is such that the viscosity increases (that is, the fluidity decreases) as the surface temperature increases. Further, the relationship between the viscosity of the solution Si (OH) ₄ and the void (bubble) generation rate is such that the higher the viscosity, the higher the void generation rate, as shown in FIG. The void generation rate V (%) is shown in FIG.
As shown in (b), when the film thickness of the convex portion of the wiring pattern 11 is a and the film thickness of the concave portion is b, V = (1−b / a) × 100. However, the result shown in FIG.
The height h of the convex portion of the wiring pattern 11 is 1.0 μm, the width of the concave portion is 0.5 μm, and OCD-Type7 12000-T (trade name, manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used as a solution for forming an insulating film. It is the case when doing.

That is, the fluidity of the solution Si (OH) ₄ increases as the temperature decreases, and the void generation rate decreases as the fluidity of the solution increases. The reason why the rate of generation of voids is low will be described in more detail.
_At the time of spin coating ₄ , since the above-described temperature difference occurs between the irregularities of the wiring pattern 11, the Si (OH) ₄ flowing into the concave portion changes to a solid before the convex portion. Therefore, as shown in FIG. 5, the solution Si (OH) ₄ flows from the surface of the convex portion having a higher temperature into the concave portion having a lower temperature. Then, after that, it is appropriately heated in an annealing furnace to obtain Si (OH) ₄ → SiO ₂
+ H ₂ O occurs to form the SiO ₂ film, and therefore, regardless of the unevenness of the underlying wiring pattern 11, FIG.
As shown in (c), the SOG film 13 having an extremely flat surface
Is formed. On the other hand, if the inside of the recess is kept at room temperature, since the solution first dropped into the recess, the above-mentioned reaction occurs before the inside of the recess is completely filled, and a SiO ₂ film is formed. In addition, the surface of the SOG film cannot be made sufficiently flat.

As described above, in the present embodiment, the irregularities of the underlying wiring pattern 11 and the shape of the surface of the SOG film 13 can be made almost completely unrelated. Even if is large, SOG
The surface of the film 13 can be made flat. Incidentally, according to the findings of the present inventor, it is possible to embed a space of 0.20 μm or less.

Then, as shown in FIG. 2A, the thickness of the plasma oxide film 12 having insufficient step coverage is increased,
The aspect ratio of the wiring pattern 11 may be reduced. Further, the fact that the film thickness of the plasma oxide film 12 can be increased brings about an advantage that a process margin of an etch back performed later can be further widened.

Further, in this embodiment, since liquid nitrogen N ₂ having excellent stability is used, there is no particular adverse effect. Rather, the surface state of the plasma oxide film 12 is changed from hydrophilic to hydrophobic because a contaminant layer 14 (for example, a carbon-based contaminant layer that can be generated when the wafer 2 is transferred) is formed as shown in FIG. Even when the surface state is changed, there is an advantage that the surface state can be restored to the hydrophilic state without performing a special surface treatment such as O ₂ plasma irradiation or ultraviolet irradiation.

That is, the contaminant layer 14 has an extremely low temperature (-196
C.), the hydrophilic component below the contaminant layer 14 freezes when immersed in liquid nitrogen N ₂ , and the contaminant layer 14 is separated from the iced portion when the liquid nitrogen N ₂ is spin-coated. The excellent surface layer of the plasma oxide film 12 is the SOG film 13
It appears just before film formation. Thereby, the SOG film 1
The adhesive force at the interface between the film 3 and the plasma oxide film 12 is increased, and separation between these films can be prevented.

Here, in this embodiment, the wafer holder 3,
The rotating shaft 4 and the power source 5 constitute a rotation driving unit, the nozzle 8 and another supply source (not shown) constitute a liquid coolant dropping unit, and the nozzle 7 and a supply source (not shown) constitute a solution dropping unit for forming an insulating film. Be composed. In the above embodiment, the SOG film 13 as an interlayer insulating film is used.
Although the case where the present invention is applied to the process of forming the above is described, the present invention is not limited to this, and may be a process of forming an insulating film as a surface protective film.

In the above embodiment, the case where liquid nitrogen N ₂ is used as the liquid coolant has been described. However, the present invention is not limited to this. For example, liquid helium He may be applied, or liquid nitrogen may be used. N ₂ and liquid helium He may be used in combination. Further, in the above embodiment, SOG
Although an annealing furnace is used for heating immediately before the film 13 is formed, the present invention is not limited to this, and lamp heating, heater heating, microwave heating, or the like may be applied or used in combination.

[0027]

As described above, according to the first aspect of the present invention, the liquid coolant is spin-coated on the wafer surface immediately before the spin-coating of the insulating film forming solution. There is an effect that the surface can be made extremely flat and the contaminated layer can be removed without performing special surface treatment.

In particular, according to the second aspect of the present invention, since liquid nitrogen having excellent stability is used, there is no particular adverse effect, and since the temperature is extremely low, the contamination layer can be surely removed. There is. According to the third and fourth aspects of the invention, there is an effect that the invention according to the first and second aspects can be suitably implemented by first applying a liquid coolant by spin coating. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of the present invention.

FIG. 2 is a sectional view for explaining the operation of the embodiment.

FIG. 3 is a graph showing a relationship between a surface temperature of a wafer and a viscosity of a solution.

FIG. 4 is a diagram illustrating the relationship between the viscosity of a solution and the rate of occurrence of voids.

FIG. 5 is an enlarged sectional view for explaining the operation of the embodiment in detail.

FIG. 6 is an enlarged sectional view for explaining another operation of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 SOG film forming apparatus (semiconductor insulating film forming apparatus) 2 Wafer 3 Wafer holder 4 Rotating shaft 5 Power source 7, 8 Nozzle 10 Thin oxide film 11 Wiring pattern 12 Plasma oxide film 13 SOG film (insulating film) 14 Contamination layer N ₂ liquid nitrogen (liquid coolant) Si (OH) ₄ solution for forming insulating film

Claims (4)

(57) [Claims] 1. A method for forming an insulating film in a semiconductor device, comprising: applying a liquid coolant to a wafer surface immediately before spin-coating an insulating-film forming solution. 2. The method according to claim 1, wherein the liquid coolant is liquid nitrogen. 3. A rotation driving means for rotating a wafer in the horizontal plane, a liquid coolant dropping means for dropping a liquid coolant on the wafer surface held by the rotation driving means, and a rotation driving means. An insulating film forming apparatus for a semiconductor device, comprising: an insulating film forming solution dropping unit that drops an insulating film forming solution onto the wafer surface in a held state. 4. The apparatus according to claim 3, wherein said liquid coolant is liquid nitrogen.