KR20070050511A - Method of forming an device isolation area and method of forming an image device using the same - Google Patents

Abstract

In the method of forming the device isolation region and the method of forming the image device using the same, first, a trench is formed in the semiconductor substrate through a plasma etching process. In order to cure damage of the inner surface of the trench by the plasma, heat treatment is performed under a chamber atmosphere containing hydrogen and oxygen and the proportion of hydrogen is 5 to 60% to form a radical oxide film on the inner surface of the trench. Subsequently, an isolation region is formed by forming an isolation layer on the substrate to fill the trench. Subsequently, a transistor is formed on the active region formed of the device isolation region, and a photodiode is formed under the surface of the active region in contact with the device isolation region. At this time, the inner surface damage of the trench by the plasma etching process may be cured by injecting 5 to 60% of hydrogen gas to sufficiently form a radical oxide film on the inner surface of the trench. Therefore, the dark signal generation of the image element due to the damage inside the trench can be suppressed in advance.

Description

Method for forming an device isolation area and method of forming an image device using the same}

1 is a schematic cross-sectional view for describing an active pixel area of a conventional CMOS image sensor.

2 to 7 are schematic process cross-sectional views for describing a method of forming an isolation region according to an embodiment of the present invention.

8 through 11 are schematic cross-sectional views illustrating a method of manufacturing an image device by using the method of forming a device isolation region described with reference to FIGS. 1 through 6.

Explanation of symbols on the main parts of the drawings

200 semiconductor substrate 202 pad oxide film

204: nitride film for hard mask 206: hard mask

208: trench 210: sacrificial oxide film

212: radical oxide film 214: device isolation film

The present invention relates to a device isolation region formation method and an image element formation method using the same. More particularly, the present invention relates to a device isolation region formation method using a trench technique and an image element formation method using the same.

An image sensor is a semiconductor module that converts an optical image into an electrical signal. The image sensor is used to store, transmit, and display the image signal on a display device. There are two types of image sensors, a silicon semiconductor based solid-state imaging device (Charge Coupled Device (CCD), hereinafter referred to as 'CCD') and a complementary metal oxide semiconductor (CMOS). Classified as

The CMOS image sensor includes an active pixel area for capturing an image and a CMOS logic area for controlling an output signal of the active pixel area. The active pixel region may include a photo diode and a MOS transistor, and the CMOS logic region may include a plurality of COMS transistors.

1 is a schematic cross-sectional view for describing an active pixel area of a conventional CMOS image sensor.

Referring to FIG. 1, an active pixel region includes a unit pixel including a photo diode 106 and a transistor 104, and an isolation region 102 for electrically separating the unit pixel adjacent to the unit pixel. .

At this time, the device isolation process technology includes LOCOS (Local Oxidation of Silicon) technology or trench (Shallow Trench Isolation (STI) technology, etc., and recently occupies a small area, a trench that can secure an insulation margin by depth Use technology primarily.

In the device isolation region 102 using the trench technique, a predetermined mask is formed on the semiconductor substrate 100, and the trench is formed by an entire anisotropic etching process using the plasma as the semiconductor substrate 100 using the mask as an etching mask. Thus, it is formed by embedding a field oxide film (not shown) in the trench.

At this time, during the etching process, the surface of the silicon substrate 100 is subjected to plasma damage, such that a defect such as silicon dangling bond (Si-dangling bond) occurs on the surface of the substrate 100, A trap site is created in position A of FIG. 1 where electrons can be trapped due to the defect.

Electrons are trapped at the trap site at the A position, and then in using a CMOS image element, while the thermally excited electrons are introduced into the photodiode 106, the electrons trapped at the trap site are photodiode 106. Flows into. Thus, the influx of electrons can act as a source of generating dark defects at certain illuminances.

One object of the present invention to solve the above problems is to provide a method for forming a device isolation region having a trench surface from which trap sites are removed.

Another object of the present invention is to provide a method of forming an image device using the device isolation region forming method.

In the method of forming an isolation region according to an embodiment of the present invention for achieving the above object, a trench is formed in a substrate through a plasma etching process. In order to cure damage of the inner surface of the trench by the plasma, hydrogen (H ₂ ) and oxygen (O ₂ ), and the heat treatment in a chamber atmosphere in which the proportion of hydrogen is 5 to 60%, the inside of the trench A radical oxide film is formed on the surface. A device insulating film is formed on the substrate to fill the trench.

Forming the radical oxide film may be carried out at 5 to 10 Torr pressure and 800 to 1000 ℃ temperature. After forming the trench, a sacrificial oxide film may be formed on the inner surface of the trench, and the sacrificial oxide film and a portion of the trench inner surface may be removed.

According to the present invention as described above, when the hydrogen gas is introduced at 5 to 60% as described above, the oxygen radicals are sufficiently generated, and the oxygen radicals are deficient in the dangling bonds generated inside the trench, so that the dangling The electronic trap site due to the bond can be eliminated.

In the image forming method according to another embodiment of the present invention for achieving the above object, a trench is formed in the substrate through a plasma etching process. In order to cure damage of the inner surface of the trench by the plasma, heat treatment is performed under 5 to 60% hydrogen (H ₂ ) atmosphere to form a radical oxide film on the inner surface of the trench. A device insulating film is formed on the substrate to fill the trench. The transistor 104 is formed on an active region defined by the device insulating film. A photodiode is formed under the surface of the active region to contact the device insulating layer.

According to the present invention as described above, it is possible to remove the trap site formed in the trench surface to be used as the device isolation region by using the device isolation region formation method according to the embodiment to manufacture an image sensor. Therefore, by suppressing the trap site of the trench, the dark signal generation of the image sensor can be suppressed in advance.

Hereinafter, a method of forming an isolation region according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 to 7 are schematic process cross-sectional views for describing a method of forming an isolation region according to an embodiment of the present invention.

Referring to FIG. 2, a pad oxide film 202 and a nitride film 204 for a hard mask are formed on the semiconductor substrate 200.

The pad oxide layer 202 may be formed by a thermal oxidation process, and is formed to reduce stress generated when the nitride layer 204 is in direct contact with the semiconductor substrate 200.

The nitride layer 204 includes silicon nitride (SiN), and may be formed by a low pressure chemical vapor deposition (LPCVD) process.

In this case, an organic anti-reflection layer (ALL, not shown) may be further formed on the nitride layer 204. The organic antireflective film is provided to prevent the photoresist sidewall profile from being poor due to diffuse reflection in a subsequent photographic process.

Referring to FIG. 3, a photoresist pattern (not shown) for selectively exposing the nitride film 204 formed on the region where the trench is to be formed is formed on the nitride film 204. Subsequently, the nitride layer 204 and the pad oxide layer 202 are etched using the photoresist pattern as an etch mask to form a hard mask pattern 206.

After the hard mask pattern 206 is formed, the photoresist pattern is removed through an ashing process and a strip process.

Referring to FIG. 4, the trench 208 is formed by etching the exposed semiconductor substrate 200 by using the hard mask pattern 206 as an etching mask by a plasma etching process. In this case, the organic anti-reflection film is removed during etching of the semiconductor substrate 200.

In more detail, in the plasma etching process, an etching gas is injected into a process chamber in which the etching process is performed, DC or RF power is applied to the process chamber to form a plasma, and the etching gas particles ionized by the plasma are formed. These are methods for physically etching the semiconductor substrate 200 by colliding with the surface of the semiconductor substrate 200.

Here, the inner surface of the trench 208 is damaged by the collision of the ionized particles. In more detail, the semiconductor substrate 200 is usually made of silicon. As the ionized particles collide with the silicon, the outermost electrons of the silicon are separated and an incomplete silicon dangling bond is formed inside the trench 208. Is formed on the surface. In this case, the dangling bond site may serve as a trap site through which electrons introduced from the outside may be captured.

Referring to FIG. 5, a sacrificial oxide film 210 is formed on an inner surface of the trench 208. The sacrificial oxide film 210 may be formed by a dry deposition method using O ₂ gas, a wet deposition method using H ₂ O, a clean deposition method using O ₂ and HCl gas, and a method formed by high temperature and low pressure heat treatment. .

Subsequently, the sacrificial oxide film 210 is removed by a strip process. In this case, a portion of the inner surface of the trench 208 is removed while the sacrificial oxide film 210 is removed. As a result, the inner surface of the trench 208 changes more smoothly.

In this case, the deposition and removal process of the sacrificial oxide film 210 may be selectively performed. That is, it may be omitted in order to simplify the process.

Referring to FIG. 6, in order to cure damage of the inner surface of the trench 208 by the plasma, rapid thermal process is performed under a chamber atmosphere containing oxygen and hydrogen, and the ratio of hydrogen is 5 to 60%. RTP) to form a radical oxide film 212 on the inner surface of the trench 208.

In more detail, the reaction gas containing hydrogen and oxygen is injected into the process chamber, the pressure in the process chamber is maintained at about 5 to 10 Torr, and the temperature is maintained at about 800 to 1000 ° C. More preferably the reaction gas comprises about 10% hydrogen gas.

At this time, the proportion of the hydrogen gas accounts for about 5 to 60% of the reaction gas. When the proportion of the hydrogen gas is less than 5%, the amount of oxygen radicals formed by the oxygen gas is very insufficient to cure the inner surface of the trench 208. On the other hand, when the ratio of the hydrogen gas is 60% or more, the ratio of hydrogen gas may be greater than the ratio of oxygen necessary for healing the inner surface of the trench 208, thereby preventing surface healing itself. Here, a suitable ratio of hydrogen gas is about 10% of the reaction gas. This will be described later in detail.

Meanwhile, the process of forming the radical oxide film 212 will be described in more detail. During the heat treatment, oxygen radicals are formed in the process chamber by reaction of oxygen and hydrogen. The oxygen radicals combine with a damaged portion of the inner surface of the trench 208, that is, a silicon dangling bond, to form a thin radical oxide film 212 on the inner surface of the trench 208.

Therefore, the trap site of the electrons is eliminated by removing the dangling bond. As a result, leakage current generation of the semiconductor element to be formed later can occur.

On the other hand, the rapid heat treatment may use both a batch type (batch type) for processing a plurality of semiconductor substrates at once, and a method (single type) for processing the semiconductor substrate 200 sheet by sheet.

Subsequently, although not shown, an insulating film liner (not shown) is optionally formed on the surfaces of the radical oxide film 212 and the hard mask pattern 206 to a thickness of several hundred microseconds. The insulating film liner is formed to reduce stress in the device isolation layer embedded in the trench 208 by a subsequent process and to prevent impurity ions from penetrating into the field region.

The insulating layer liner should be formed of a material having a high etching selectivity with respect to the device isolation layer, which will be described later, under specific etching conditions. For example, the insulating film liner may be formed of silicon nitride (SiN).

Referring to FIG. 7, a gap buried such as Undoped Silicate Glass (USG), O ₃ -TEOS USG (O ₃ -TetraEthylOthoSilicate USG), or High Density Plasma (HDP) oxide layer is formed to fill the trench 208. An oxide film having excellent gap-fill) is deposited by a chemical vapor deposition process to form an isolation layer 214.

Preferably, a high density plasma oxide film is formed by generating a high density plasma using SiH ₄ , O ₂ and Ar gases as the plasma source.

Next, although not shown, the surface of the device isolation layer 214 is removed so that the surface of the hard mask pattern 206 is exposed to form an device isolation pattern (not shown) defining an active region.

Hereinafter, a method of manufacturing an image device using the device isolation region forming method will be described.

8 through 11 are schematic cross-sectional views illustrating a method of manufacturing an image device by using the method of forming a device isolation region described with reference to FIGS. 1 through 6.

Referring to FIG. 8, a semiconductor substrate 300 is prepared. In this case, the semiconductor substrate 300 has a structure in which a high concentration P-type layer (P ⁺⁺ ) doped with a P-type dopant and a P-type epitaxial layer (P-Epi) are stacked.

Subsequently, by performing the same process as described with reference to FIGS. 1 to 6 on the semiconductor substrate 300, an isolation region 302 for defining an active region and a field region is formed.

Subsequently, the surface of the device isolation layer (not shown) is etched to expose the surface of the hard mask pattern (not shown) to form a preliminary device isolation layer pattern (not shown), and the hard mask pattern is removed. The preliminary isolation pattern may be etched to the same height as the surface of the semiconductor substrate 300 to form the isolation pattern 302.

Referring to FIG. 9, a gate oxide layer 304 and a gate conductive layer 306 are sequentially formed on the semiconductor substrate 300 on which the device isolation pattern 302 is formed.

In more detail, a gate oxide film 304 is formed on the semiconductor substrate 300 by a thermal oxidation process, and then a conductive film 306 to be used as a gate electrode is formed on the gate oxide film 304. do.

The conductive layer 306 may have a stacked structure of a first layer including polysilicon and a second layer including metal. More specifically, first, a polysilicon layer doped with a high concentration of impurities is formed by a doping process such as a diffusion process, an ion implantation, or an in-situ doping process. Subsequently, a second layer such as tungsten (W), titanium (Ti), tungsten silicon (WSi), or titanium nitride (TiN) is formed on the polysilicon layer, thereby forming the conductive layer 306 in the first layer and the first layer. It can be formed in a laminated structure of two layers.

On the other hand, a unit pixel usually includes four gate electrodes, and the gate electrodes are a transfer gate, a reset gate, a selection gate, and an access gate.

In particular, a low voltage photodiode is buried in one side of the transfer gate. At this time, since the doping profile of the photodiode determines the charge transport efficiency, the transfer gate electrode is a high-energy N-type dopant ion implantation and a P-type dopant ion implantation to form a low voltage photodiode with a sufficient thickness of the transfer gate electrode Allow one side of the self to align.

Here, if the thickness of the transfer gate electrode is not sufficiently thick, the N-type dopant penetrates the transfer gate electrode during high-energy N-type dopant ion implantation, and high-energy P-type dopant ion implantation and low-energy P-type ion implantation are performed. It is impossible to self-align on one side of the transfer electrode, thereby degrading charge transport efficiency.

Referring to FIG. 10, a photoresist pattern is formed on the conductive layer 306, and the gate layer 308 is etched by etching the conductive layer 306 and the gate oxide layer 304 using the photoresist pattern as an etching mask. Form.

Subsequently, although not shown, a spacer may be formed on sidewalls of the gate electrode 308.

Referring to FIG. 11, a semiconductor substrate exposed between one side of the gate electrode 308 and one device isolation region 302 by sequentially implanting N-type and P-type dopants using the gate electrode 308 using an ion implantation mask. The photodiode 310 is formed under the surface of the 300.

In addition, a floating diffusion region 312 in which an N-type dopant is implanted is formed under the surface of the semiconductor substrate 300 exposed between the other side of the gate electrode 308 and the other device isolation region 302.

As a result, the photodiode 310 and the transistor constituting the unit pixel of the image element may be formed.

In fabricating the image device, after forming a trench (not shown) in the device isolation region 302, a trap oxide formed on the trench surface was removed by forming a radical oxide film on the trench surface. Therefore, while thermally excited electrons are introduced into the photodiode 310, movement of the electrons trapped in the trap site is suppressed, thereby preventing the dark signal of the image element occurring at a specific illuminance.

As described above, according to an embodiment of the present invention, after forming the trench for the device isolation region by plasma etching, 5 to 60% hydrogen is injected into the trench inner surface in order to heal structural damage. And reacts with the damaged regions of the oxygen radicals and the trench inner surface. Therefore, it is possible to suppress the generation of leakage current by eliminating trap sites where electrons can be trapped.

As described above, according to another embodiment of the present invention, when the image element is formed by using the device isolation region forming method according to the embodiment, the trap site of the electrons is removed, and the electron trapped by the trap site The dark signal generation of the image element can be suppressed in advance.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims (4)

Forming a trench in the substrate through a plasma etching process; In order to cure the damage of the inner surface of the trench by the plasma, heat treatment in a chamber atmosphere containing oxygen (O ₂ ) and hydrogen (H ₂ ) and the hydrogen ratio of 5 to 60%, on the inner surface of the trench Forming a radical oxide film on the substrate; And Forming a device insulating film on the substrate to fill the trench. The method of claim 1, wherein the forming of the radical oxide layer is performed at a pressure of 5 to 10 Torr and a temperature of 800 to 1000 ° C. 7. The method of claim 1, wherein after forming the trench, Forming a sacrificial oxide film on the inner surface of the trench; And And removing a portion of the sacrificial oxide layer and a trench inner surface. Forming a trench in the substrate through a plasma etching process; In order to cure the damage of the inner surface of the trench by the plasma, heat treatment in a chamber atmosphere containing oxygen (O ₂ ) and hydrogen (H ₂ ) and the hydrogen ratio of 5 to 60%, on the inner surface of the trench Forming a radical oxide film on the substrate; Forming a device insulating film on the substrate to fill the trench; Forming a transistor on an active region defined by the device insulating film; And And forming a photodiode under the surface of the active region in contact with the device insulating film.

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