KR101107346B1 - Photoresist Forming Method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a photoresist, and in recent years, a technology for forming a thicker photoresist mask layer for etching along with a trend of gradually increasing the depth of an etching process due to the development of vertical light emitting devices and the like. In order to meet such demands, the substrate to which the photoresist is applied is inverted during the baking process, which is essentially performed during the photolithography process, in particular, during the soft baking. The present invention relates to a method of forming a photoresist in which a softened photoresist is naturally thickened downward by gravity and becomes thicker.

Photoresist, photolithography, thickness, pattern, invert

Description

Photoresist Forming Method {Method Of Fabricating Photoresist}

1 is a flow chart of a typical photolithography process.

2A to 2G are cross-sectional views for explaining the appearance of each step in a general photolithography process.

3A to 3D are cross-sectional views illustrating a preferred embodiment of the photoresist forming method of the present invention.

FIG. 4 is a view for explaining a state in which a wafer is inverted and baked in a photoresist forming process according to the present invention. FIG.

<Description of main parts of drawing>

10. Substrate 11. Device Structure

12. Initial Photoresist 12 '. Photoresist after spin coating

13. Hot Plate 14. Exposure Area

100. Substrate 110. Device Structure

120. Initial Photoresist 120 '. Photoresist after spin coating

120 ''. Photoresist after thickness 130. Hot Plate

140. Support

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a photoresist, and in order to form a thicker photoresist layer, inverting a substrate to which the photoresist is applied during soft baking during a photolithography process. The present invention relates to a photoresist forming method in which the thickness of the photoresist, which is fluidly changed by heat, extends down naturally by gravity to increase the thickness.

The photolithography process is the core of the thin film process along with the thin film deposition process. The thin film is deposited using photo development and etching techniques. (Thin Film) is a series of processes to realize a fine circuit shape.

In addition, a photoresist is mainly used as a mask material for etching such a thin film.

Meanwhile, with the recent development of vertical light emitting devices, the depth of etching processes such as isolation etching or mesa etching is gradually increasing. As a result, the thickness of the photoresist mask layer for deeply etching the thin film layer is increased. The technology to form a thick is required.

Hereinafter, a general photolithography process using a photoresist will be described in detail with reference to the drawings.

1 is a flow chart of a typical photolithography process.

As shown in the drawings, photolithography processes generally include photoresist (PR) coating, spin coating, soft baking, exposure, and post-exposure baking. ), Development, and hard baking in that order, and are usually performed several times.

In addition, the photolithography process is broadly divided into a coating step, an exposure step, and a development step.

As shown in the figure, the applying step includes a process of applying photoresist, spin coating, and soft baking.

The exposure step includes the exposure step itself, and finally the development step includes the processes of post-exposure baking, developing, and hard baking.

2A to 2G are cross-sectional views illustrating the state of each step in a general photolithography process.

2A illustrates forming a device structure 11 on the substrate 10 and applying a photoresist 12 on the device structure.

Prior to this step, it is preferable that the wafer cleaning process and the surface treatment process be preceded first.

Here, the wafer refers to the substrate on which the device structure is formed.

2B illustrates a step of applying the photoresist 12 to a uniform thickness through a spin-coating method.

This step is to rotate the wafer through a spin coating device to spread the photoresist applied on the wafer to a uniform thickness, where the injection speed of the photoresist injected onto the wafer through the rotational speed of the wafer or an injection device, The thickness of the photoresist layer may be controlled by controlling the spraying time, the spraying speed, and the like.

However, such a conventional method of adjusting the thickness of the photoresist has a problem that a bump phenomenon occurs in which the photoresist agglomerates near the edge of the wafer, thereby making it difficult to obtain a uniform photoresist thickness.

FIG. 2C illustrates a step of soft baking the photoresist 12 'layer through a hot plate 13.

The soft baking step is a step of evaporating in the previous step and applying heat to remove the remaining solvent (Solvent).

If the process is performed with a solvent in the photoresist layer, the resistance of the photoresist layer may deteriorate during the subsequent development or etching process, and the thickness may be continuously changed to maintain a constant process condition.

Here, it is important to properly control the baking temperature and time so that other components of the photoresist are not pyrolyzed and only solvent is removed.

2D illustrates a step of selectively exposing only a desired portion 14 using a mask pattern to form a pattern in the photoresist layer 12 '.

The exposure process is mainly a process of placing a mask patterned with a thin chromium (Cr) film between the wafer and the light source, whereby the light from the light source passes through only the portion without the chromium pattern to photosensitive the photoresist layer.

In general, since the exposure process is completed by exposing different positions several times, an alignment process for precisely controlling the position to be exposed must be performed in parallel.

For reference, it is common to use light having a short wavelength as a light source used in the alignment and exposure process.

FIG. 2E illustrates a post-exposure baking of the photoresist layer 12 ′ through the hot plate 13.

As described above, exposure to short wavelengths causes incident light and light reflected from the surface of the wafer to reinforce or cancel each other, resulting in an increase in the magnitude of the wave and deteriorating the pattern reproducibility between the exposed portion and the non-exposed portion. It is called a standing wave phenomenon, and this phenomenon is particularly prominent in fine patterns.

Specifically, deteriorating the reproducibility of the pattern between the exposed portion and the non-exposed portion causes a wavy pattern to be created between the exposed portion and the non-exposed portion due to the standing wave phenomenon.

However, post-exposure baking loosens the structure of the Novolak Resin in the photoresist, and diffuses and shifts the exposed PAC (Photo Active Compound) and the unexposed PAC in the photoresist to remove standing waves. .

In other words, the post-exposure bake process is performed to remove standing wave phenomena to obtain uniformity of line widths in the wafer.

2F illustrates a development step of removing the exposed portion of the photoresist layer 12 '.

The development refers to a process of melting a portion of the photoresist layer that is relatively weakly bonded through an exposure process by using a developer.

At this time, the developer is sensitive to temperature and thus affects the development speed, so strict temperature control is required.

For reference, a method of using a developer may include a spray-puddle, a poodle, a spray, a dipping method, and the like.

The Puddle method is a method of spraying or flowing a developer onto a wafer to be developed, and then stopping the wafer to develop the developer on the wafer.

The spray method is a method for developing while continuously spraying a developer, but is good for continuous processing, but a large diameter wafer has poor line width uniformity, and there are also disadvantages of consuming a developer.

The dipping method is the most efficient method, but the continuous process is impossible and the developer is consumed so much that it is used only in small scale manufacturing or research and development.

The spray-puddle method is a method of combining the poodle method and the spray method.

FIG. 2G illustrates a hard baking of the photoresist layer 12 ′ through the hot plate 13.

This step heats the photoresist to a temperature below the melting point, thereby removing moisture remaining on the wafer after development, causing thermal cross-linking of Novolak Resin molecules in the photoresist, resulting in heat resistance of the pattern and It is performed to improve the physical strength and to cure stably.

After the hard baking, a final lining operation is performed to remove foreign matters remaining on the wafer, thereby finishing one photolithography process.

The photolithography process is used not only in a vertical light emitting device but also in various fields, and a stack thickness of a photoresist commonly used as a mask material of a photolithography process is also required.

However, to date, in order to form a photoresist layer with a thickness of several micrometers (μm) or more, only a method of repeatedly applying and baking the photoresist or using a special photoresist having a very high viscosity is used.

In addition, there is a method of increasing the thickness of the photoresist by decreasing the rotational speed during spin coating, but this causes a bump phenomenon in which the photoresist aggregates near the edge of the wafer. There was.

In order to meet the recent technical requirements of forming a thick photoresist layer as described above and to solve the problems of the prior art, the present invention is a baking (essentially performed in a conventional photolithography process). During the Baking step, in particular, during the soft baking, the photoresist-coated wafer is inverted so that the photoresist, which is flexibly changed by heat, is naturally stretched downward by gravity to tension the thickness. It is an object to provide a photoresist forming method.

The photoresist forming method according to the present invention having the above object comprises the steps of applying a photoresist (Photoresist) on top of the structure for etching; Applying the photoresist to a uniform thickness; and insulating the structure to be etched and then baking to tension the photoresist.

Two important factors in improving the thickness of the photoresist layer in the method of forming a photoresist according to the present invention are the fluid properties of the photoresist, which are changed by gravity and heat, which are forces to pull down any object on Earth.

In other words, the present invention takes advantage of the phenomenon that the photoresist material, which is fluidly changed by heat, is baked down by gravity by baking the device structure on which the photoresist layer is formed upside down. And tensioning the thickness of the photoresist.

For reference, in the photolithography process, the baking process is generally performed at least once. The reason for this is that post-exposure baking or hard baking is performed depending on the type and purpose of the photoresist. ) May be omitted, but in most cases soft baking is essential.

Prior to describing a preferred embodiment of the method of forming a photoresist according to the present invention, the types of photoresists are classified according to two criteria, and the main components and characteristics of each type will be described.

First, the photoresist can be classified according to the change in dissolution properties, and can be divided into negative photoresist and positive photoresist.

First, the negative photoresist reacts with crosslinking, etc. by exposure, so that its molecular weight is greatly increased and its solubility is inferior. However, it has excellent thermal characteristics and chemical resistance. Has been used.

However, since the resolution is poor, it is not used in recent semiconductor processes.

On the other hand, positive photoresist increases the solubility by reaction such as decomposition and molecular chain cutting by exposure, and is widely used in semiconductor manufacturing process with high etching resistance and high resolution, but thermal characteristics are negative. It is inferior to the negative photoresist.

Secondly, according to the wavelength of the sensitive light, it can be divided into a near ultraviolet photoresist and a deep UV photoresist.

First of all, near-ultraviolet rays are light from 365nm to 436nm among the light emitted from ultra-high pressure mercury lamp, and the intensity of light is prominent at 365nm and 436nm wavelength, which is called G-Line and I-Line, respectively. The photoresist prepared so as to be referred to as near ultraviolet photoresist.

In addition, the far-infrared photoresist also refers to a photoresist manufactured according to this by using light having a wavelength of 254 nm among light emitted from an ultra-high pressure mercury lamp.

On the other hand, the photoresist as described above differs depending on the type of material as follows.

First, the near ultraviolet photoresist is composed of novolak resin (Novolak Resin), PAC (Photo Active Compound), solvent (Solvent), additives (dye, coating stabilizer).

The novolak resin is a polymer that forms the basic skeleton of the photoresist, and is contained in the photoresist by about 15 to 20%.

The PAC (Photo Active Compound) serves to form a pattern by reacting with light, and contains about 5 to 10% of the photoresist.

The solvent (Solvent) is a material for improving the uniformity when applied to the wafer, occupies about 70% of the photoresist, and is highly volatile and evaporates mostly during rotation or soft baking of the wafer after application.

As such, the near ultraviolet photoresist has a characteristic of inducing a difference in solubility by bringing a molecular form into the PAC compound without changing the novolak resin when exposed to the corresponding light.

On the other hand, the far ultraviolet photoresist is made of a polyhydroxy styrene (Protective Polyhydroxy Styrene), PAG (Photo-Acid Generator) protected by a hydroxyl group.

Unlike near-ultraviolet photoresist, far-ultraviolet photoresist changes the solubility difference by using Novolak Resin which is not developed in alkaline developer through Photo-Acid Generator (PAG) activated by light. There is a characteristic to cause.

Hereinafter, with reference to the drawings will be described a preferred embodiment according to the photoresist forming method of the present invention.

3A to 3D are cross-sectional views illustrating a preferred embodiment of the method of forming a photoresist of the present invention.

3A illustrates forming a device structure 110 on the substrate 100 and applying a photoresist 120 thereon.

Prior to this step, it is preferable that the wafer cleaning process and the surface treatment process be preceded first.

Here, the wafer refers to the substrate on which the device structure is formed.

The cleaning process and the surface treatment process may be referred to as preliminary preparations for removing foreign matters on the surface of the wafer before applying the photoresist and improving the adhesion of the photoresist.

3B illustrates a step of applying the applied photoresist 120 to a uniform thickness.

At this time, it is preferable to apply the photoresist to a uniform thickness through a spin coating method.

After the injection of the photoresist is finished, the rotation of the spin coating apparatus is maintained for a predetermined time, in order to evaporate a portion of the solvent (Solvent) constituting the photoresist, wherein 70 of the solvent constituting the photoresist % To 80% are usually evaporated.

3C shows a step in which the wafer on which the photoresist 120 'is formed is inverted.

In this case, the photoresist applied on the device structure and the hot plate required for the baking process may be disposed to face each other and be spaced apart from each other.

In addition, in order to position the photoresist and the hot plate so as to face each other and to be spaced apart from each other, it is preferable to use a support as shown in FIG. 4.

3D illustrates a step of baking to stretch the thickness of the photoresist 120 '.

Here, the baking is preferably carried out at a temperature of less than 100 ℃.

In addition, the stretching of the photoresist is characterized in that the gravity is applied to the photoresist that is fluidly changed during the baking (Baking).

In addition, the stretching of the thickness of the photoresist is preferably performed during soft baking during various steps of the photolithography process.

Because it can be applied to post-exposure baking or hard baking, the solvent, one of the components of the photoresist after soft baking, is mostly evaporated, This is because the photoresist is cured.

FIG. 4 is a view for explaining a state in which a wafer is inverted and baked in the process of forming a photoresist according to the present invention.

As shown in the figure, it is preferable to invert the wafer so that the thickness of the photoresist 120 ″ fluidly changed by heat can be naturally stretched down by gravity.

In addition, the support plate 140 for fixing the wafer in an inverted form is spaced apart from the top of the hot plate (130), which is made of a thermally conductive material to transfer the thermal energy of the hot plate to the back of the wafer. When configured to do so, the photoresist can be fluidized faster.

On the other hand, by changing the height of the support or by changing the gap between the photoresist and the hot plate, it is possible to control the amount of radiant energy transferred from the hot plate to the photoresist, through which the thickness of the photoresist can be adjusted.

While the configuration of the invention according to the embodiment of the present invention has been described in detail, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.

According to the photoresist forming method of the present invention, even if a multilayer photoresist or a high viscosity special photoresist is not used, the photoresist is introduced through a simple process of inverting the wafer during the baking process. There is an advantage to increase the thickness of the layer.

In addition, according to the present invention, compared with the conventional method of increasing the thickness of the photoresist layer by applying the photoresist in double or triple, there is an advantage that the process can be greatly simplified.

In addition, according to the present invention, even if the photoresist layer is applied under the spin coating conditions of the same rotation speed, there is an effect that can secure a thicker photoresist layer than in the prior art.

In addition, according to the present invention, there is an advantage that can be applied to all photoresist having fluidity regardless of positive photoresist and negative photoresist.

As a result, according to the present invention, the thickness of the photoresist mask layer can be easily stretched through a simple process, and thus, there is an advantage that the depth of the dry etching can be deepened.

Claims (5)

Applying a photoresist on top of the structure for etching; Applying the photoresist to a uniform thickness by performing a spin coating process; and Inverting the structure for etching, and then baking the sheet to tension the photoresist. delete The method of claim 1, Baking after inverting the structure for etching, And a hot plate positioned to be spaced apart from the lower portion of the structure for etching. The method of claim 1, The tension of the photoresist, The photoresist forming method, characterized in that caused by gravity acts on the photoresist that is fluidly changed during the baking. The method of claim 1, The baking (Baking), A photoresist forming method, characterized in that carried out at a temperature of less than 100 ℃.

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