JP2009147055A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device for removing a thick hard mask in a short time suppressing an influence given to a structure under the hard mask. <P>SOLUTION: The method of manufacturing a semiconductor device includes the steps of depositing a first nitride film on a substrate, removing the first nitride film on the semiconductor substrate of a first element isolating and forming region, forming a first element isolating layer on the first element isolating and forming region, filling the first element isolating and forming region with a first oxide film for isolating the element, depositing a second nitride film, depositing a stopper film composed of a-Si, poly-Si, a-SiGe, or poly-SiGe on the second nitride film, depositing a mask material on the stopper film, removing the mask material on the semiconductor substrate of a second element isolating and forming region, forming a second element isolating layer at a level deeper than the level of the first element isolating layer, removing the mask material using the stopper film as a stopper, and removing the stopper film and the first and second nitride films leaving the first oxide film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device.

  In the pixel region of the image sensor, it is necessary to form a deep element separation in order to reliably separate the pixels of each color. Usually, in order to form deep element isolation in a semiconductor substrate, an impurity for element isolation is ion-implanted into the semiconductor substrate with high implantation energy (deep ion implantation). In the deep ion implantation, it is necessary to cover the pixel formation region with a thick hard mask so that the element isolation impurity is not implanted into the pixel formation region. When removing the hard mask, a protective film for protecting the underlying structure from being etched is required as an etching stopper. In general, a resist is used as a hard mask for ion implantation, and a silicon oxide film is used as an etching stopper. In some cases, a silicon oxide film is used as the hard mask and a silicon nitride film is used as the etching stopper. However, when the silicon oxide film as the hard mask is removed, the exposed portion of the silicon nitride film as the etching stopper is also removed little by little. Therefore, if the hard mask is very thick, the etching stopper must also be formed very thick.

If the silicon nitride film as an etching stopper is very thick, the time for etching the silicon nitride film becomes long, and the productivity becomes very poor. Furthermore, if the etching time is long, it is necessary to lengthen the over-etching time, so that the underlying structure of the etching stopper that should be protected may be scraped.
JP 2006-216616 A

  Provided is a semiconductor device manufacturing method capable of removing a thick hard mask in a short time while suppressing an influence on a structure under the hard mask.

  In a method for manufacturing a semiconductor device according to an embodiment of the present invention, a first film including at least a silicon oxide film or a silicon nitride film is formed over a semiconductor substrate, and silicon or germanium is formed on the first film. Forming a stopper film made of a semiconductor containing, forming a mask material of a material different from the stopper film on the stopper film, etching a part of the mask material, and etching the mask material into the etched region. Impurities are introduced downward, the mask material is removed using the stopper film as a stopper, and the stopper film is removed using the first film as a stopper.

  In a method for manufacturing a semiconductor device according to an embodiment of the present invention, a first silicon nitride film is deposited above a semiconductor substrate, and the first silicon on the semiconductor substrate in a first element isolation formation region is formed. The first element isolation layer is formed by removing the nitride film and introducing an impurity for element isolation into the semiconductor substrate in the first element isolation formation region using the first silicon nitride film as a mask. Then, a first silicon oxide film for element isolation is filled above the semiconductor substrate in the first element isolation formation region, and a second is formed on the first silicon oxide film and the first silicon nitride film. A silicon nitride film is deposited, a stopper film made of a semiconductor containing silicon or germanium is deposited on the second silicon nitride film, and a mask material made of a material different from the stopper film is deposited on the stopper film Depositing and removing the mask material on the semiconductor substrate in the second element isolation formation region, and using the mask material as a mask, impurities for element isolation are used in the semiconductor in the second element isolation formation region. A second element isolation layer is formed at a position deeper from the surface of the silicon substrate than the first element isolation layer by introducing into the substrate, the mask material is removed using the stopper film as a stopper, and the first element isolation layer is removed. The stopper film is removed using the second silicon nitride film as a stopper, and the first and second silicon nitride films are removed while the first silicon oxide film remains.

  The method of manufacturing a semiconductor device according to the present invention can remove a thick hard mask in a short time while suppressing the influence on the structure under the hard mask.

  Embodiments according to the present invention will be described below with reference to the drawings. This embodiment does not limit the present invention.

(First embodiment)
1 to 6 are sectional views showing a method for manufacturing a semiconductor device according to the first embodiment of the invention. First, the silicon substrate 10 is prepared. A thin silicon oxide film 12 that protects the surface of the silicon substrate 10 is formed on the silicon substrate 10. The thickness of the silicon oxide film 12 is about 2 nm, for example. Further, a first silicon nitride film 20 is deposited on the silicon oxide film 12. The thickness of the first silicon nitride film 20 is 120 nm, for example. The silicon nitride film 20 is used as a mask for forming the first element isolation layer 30 and the silicon oxide film 40 in the pixel region.

  The silicon nitride film 20 is also used as a mask for forming a trench for STI (Sallow Trench Isolation) in a logic circuit region (not shown) around the pixel region. However, the process for forming the logic circuit region is omitted here.

  Next, in order to process the first silicon nitride film 20, a photoresist 22 is applied on the first silicon nitride film 20, and the photoresist 22 in the first region R1 is removed. Thereby, the cross-sectional structure shown in FIG. 1 is obtained. The first region R1 is a region where a first element isolation layer is formed.

  Further, the first silicon nitride film 20 is etched by RIE (Reactive Ion Etching) using the photoresist 22 as a mask. Thereby, as shown in FIG. 2, the silicon nitride film 20 in the first region R1 is removed. Next, using the first silicon nitride film 20 as a mask, ions used for element isolation are ion-implanted into the silicon substrate 10 in the first region R1. The impurity implanted at this time is an impurity having a conductivity type opposite to that of the silicon substrate 10. For example, when the silicon substrate 10 is P-type, this impurity is an N-type impurity such as phosphorus or arsenic. For example, when the silicon substrate 10 is N-type, this impurity is a P-type impurity such as boron. By heat-treating the silicon substrate 10, the first element isolation layer 30 shown in FIG. 2 is formed immediately below the surface of the silicon substrate 10. The first element isolation layer 30 functions as element isolation in the vicinity of the surface of the silicon substrate 10. Note that a silicon oxide film 15 for protecting the silicon substrate 10 is preferably formed on the silicon substrate 10 in the first region R1 during ion implantation.

  Next, a silicon oxide film 40 is deposited on the silicon substrate 10 and the first silicon nitride film 20 by using an HDP (High Density Plasma) method. Using a CMP (Chemical Mechanical Polishing) method, the silicon oxide film 40 is polished until the first silicon nitride film 20 is exposed. As a result, as shown in FIG. 3, the silicon oxide film 40 is filled only on the silicon substrate 10 in the first region R1. The silicon oxide film 40 and the first element isolation layer 30 are used for element isolation in the surface region of the silicon substrate 10. At this time, the silicon oxide film 40 is also filled in the STI trench in the logic circuit region.

  Next, a second silicon nitride film 50 is deposited on the first silicon nitride film 20 and the silicon oxide film 40. The thickness of the second silicon nitride film 50 is, for example, 30 nm. The silicon nitride film 50 is deposited to protect the underlying structure or the bevel (not shown) of the silicon substrate 10. Next, a stopper film 60 is deposited on the second silicon nitride film 50. The film thickness of the stopper film 60 is, for example, 185 nm. The stopper film 60 is formed of a silicon layer, a germanium layer, a silicon germanium layer, an impurity doped silicon layer, an impurity doped germanium layer, or an impurity doped silicon germanium layer (for example, amorphous silicon, polysilicon, amorphous silicon germanium, or polysilicon germanium, Alternatively, any of these elements is formed using phosphorus, arsenic, boron, antimony, carbon, or an element (a film containing an impurity such as hydrogen, nitrogen, oxygen, or chlorine) included in the film formation material. Further, a mask material 70 is deposited on the stopper film 60. Since the mask material is used as a mask in the deep ion implantation shown in FIG. 5, it is formed very thick. The thickness of the mask material 70 is, for example, 4 μm (4000 nm). The mask material 70 is, for example, a silicon oxide film such as a P (Plasma) -TEOS film, a silicon nitride film, a metal such as Al, Ni, Co, Ti, or W, a metal compound such as TiN, WN, TaN, or NbN, or carbon. Or it forms with the material which has either organic films, such as a resist, as a main component. In the case of using a metal film, it is preferable to laminate a metal compound as a barrier metal in order to suppress the reaction with the stopper 60.

  Next, the mask material 70 in the second region R2 is removed using lithography and RIE. At this time, the stopper film 60 functions as an etching stopper. Further, using the mask material 70 as a mask, an impurity for element isolation is ion-implanted into the silicon substrate 10 in the second region R2. The impurity implanted at this time is an impurity having a conductivity type opposite to that of the silicon substrate 10, similarly to the impurity implanted in the first region R <b> 1. The ion implantation in the second region R <b> 2 introduces impurities into a position deeper than the first element isolation layer 30. In order to inject impurities into a deep position of the silicon substrate 10, this ion implantation is performed with an increased implantation energy. At this time, impurities must not be implanted into the active area AA where the pixels are formed. Therefore, the mask material 70 is deposited very thick. For example, the mask material 70 has a thickness of about 10 times or more that of the stopper film 60 and a thickness of about 100 times or more that of the second silicon nitride film 50.

  By heat-treating the silicon substrate 10, the second element isolation layer 80 shown in FIG. 5 is formed at a deep position in the silicon substrate 10. The second element isolation layer 80 is formed at a position deeper than the first element isolation layer 30 and functions as element isolation in the deep part of the silicon substrate 10. The first and second element isolation layers 30 and 80 both isolate elements in the silicon substrate 10 by PN junction. The silicon oxide film 40 is isolated in the vicinity of the surface of the silicon substrate 10.

  Next, the mask material 70 is removed. When the mask material 70 is a silicon oxide film such as P-TEOS, the removal liquid of the mask material 70 is performed using a hydrofluoric acid solution that does not oxidize (does not contain an oxidizing agent). When the mask material 70 is a silicon nitride film, the removal liquid of the mask material 70 may be a hydrofluoric acid solution or a hot phosphoric acid solution. Since the stopper film 60 is provided, even if the mask material 70 is a silicon nitride film, the removal liquid of the mask material 70 is preferably a hydrofluoric acid solution having an etching rate faster than that of the hot phosphoric acid solution. When the mask material 70 is a metal compound such as Al, Ni, Co, Ti, or W, or a metal compound such as TiN, WN, TaN, or NbN, the removal liquid of the mask material 70 is a solution that contains hydrofluoric acid and does not contain an oxidizing agent. (First solution), a solution containing an acid such as hydrochloric acid, phosphoric acid, nitric acid, acetic acid or sulfuric acid (second solution), a second solution and an oxidizing agent such as hydrogen peroxide, ozone, nitrate or peroxosulfate Liquid mixture (third solution, for example, hydrochloric acid / hydrogen peroxide / sulfuric acid ozone / sulfuric acid ozone / phosphoric acid / hydrogen peroxide), ammonia, TMAH or choline or the like and a mixed liquid (fourth liquid A solution such as ammonia perwater, TMAH overwater, choline perwater, or the like, or a fifth solution containing an oxidizing agent. Alternatively, the mask material 70 may be removed by ashing using a gas (first gas) made of any of oxygen, nitrogen, hydrogen, ammonia, helium, and carbon fluoride. When the mask material 70 is an organic film such as carbon or resist, the removal liquid for the mask material 70 may be either the second solution other than hydrochloric acid or the third to fifth solutions. Alternatively, the mask material 70 may be removed by ashing using the first gas. When the mask material 70 is a silicon oxide film, the removal liquid of the mask material 70 may be buffered hydrofluoric acid (mixed liquid of hydrofluoric acid and a fluorine compound such as ammonium fluoride). Since the film thickness of the mask material 70 is thick, it is preferable that the temperature of the removal liquid is high in order to shorten the removal time.

When the above removal liquid is used, the selection ratio of the mask material 70 to the stopper film 60 (amorphous silicon or the like) (the etching speed of the mask material 70 / the etching speed of the stopper film 60) is the selection ratio of the mask material 70 to the silicon nitride film. (Etching rate of mask material 70 / etching rate of silicon nitride film) or more. Accordingly, the mask material 70 is selectively removed and the stopper film 60 is hardly etched. Therefore, the stopper film 60 can protect the silicon nitride films 20 and 50, the silicon oxide film 40 and the silicon substrate 10 provided thereunder from the removal liquid of the mask material 70. Specific examples of conditions for removing the mask material 70 are as follows.
Mask material 70: P-TEOS film having a thickness of 3 to 5 μm (for example, 4 μm)
Removal liquid: 49% hydrofluoric acid solution (temperature: 50-55 ° C.) without oxidizing agent
Removal time: 30 to 90 seconds

Thereafter, the stopper film 60 is removed. Since the stopper film 60 is made of amorphous silicon or the like, it is removed with a hydrofluoric acid solution containing an oxidizing agent. Examples of the oxidizing agent include nitric acid, hydrogen peroxide, ozone, nitrate, peroxosulfate, and the like. Further, when the germanium content of the stopper film 60 is higher than the silicon content, the stopper film 60 can be removed even if it is a solution not containing hydrofluoric acid, as long as it is an arbitrary solution containing the oxidizing agent. is there. Thereby, the stopper film 60 can be selectively removed while suppressing the etching of the second silicon nitride film 50. Even when a solution containing an alkali such as ammonia, TMAH, or choline is used, the stopper film 60 can be removed while suppressing the etching of the second silicon nitride film 50. Specific examples of the removal conditions of the stopper film 60 are as follows.
Stopper film 60: amorphous silicon with a thickness of 150 to 500 nm (for example, 185 nm)
Removal solution: hydrofluoric acid solution containing about 60% nitric acid (temperature: 25-35 ° C.)
Removal time: 5 to 10 seconds

  When a single-wafer etching apparatus is used, the removal process of the mask material 70 and the removal process of the stopper film 60 can be continuously performed in the same chamber. In this case, the removal time of the mask material 70 and the stopper film 60 is shortened.

Thereafter, the first and second silicon nitride films 50 and 20 are removed. At this time, by using a hot phosphoric acid solution, the first and second silicon nitride films 50 and 20 can be selectively removed without substantially etching the silicon oxide film 40 and the silicon substrate 10. Specific examples of conditions for removing the first and second silicon nitride films 50 and 20 are as follows.
Silicon nitride film thickness: 100 nm to 200 nm (for example, 150 nm)
Removal liquid: phosphoric acid solution (temperature: 150 ° C. to 165 ° C.)
Removal time: 30-60 minutes

  In this way, the cross-sectional structure shown in FIG. 6 is obtained. The silicon oxide film 40 remains because it is not significantly affected by etching.

  As a comparative example, when there is no stopper film 60, the second silicon nitride film 50 is used as a stopper. However, the selection ratio of the mask material 70 to the silicon nitride film is smaller than the selection ratio to the stopper film 60. Usually, a silicon nitride film can be used as an etching stopper when etching a silicon oxide film. However, when the mask material 70 is very thick as in the present embodiment, the second silicon nitride film 50 exposed in the second region R2 may be etched together with the mask material 70 when the mask material 70 is removed. . If the second silicon nitride film 50 is removed, the silicon oxide film 40 is exposed. As a result, the silicon oxide film 40 as the first element isolation is removed by the removal liquid of the mask material 70.

It is conceivable that the second silicon nitride film 50 is formed thick so that the silicon oxide film 40 is not removed. For example, in the following conditions, the thickness of the second silicon nitride film 50 is required to be about 350 nm.
Mask material 70: P-TEOS with a film thickness of 4 μm
・ Removal solution: 49% fluorine solution containing no oxidizing agent (temperature: 50-55 ° C.)

  The sum of the thicknesses of the first silicon nitride film 20 and the second silicon nitride film 50 is 470 nm. In order to remove the silicon nitride film having a thickness of 470 nm with a hot phosphoric acid solution, it takes about 100 minutes including 30% overetching. Therefore, when the second silicon nitride film 50 is thickened, it takes a long time to remove the silicon nitride films 20 and 50, and the productivity is deteriorated. Further, since the over-etching becomes long, the silicon oxide film 40 is also etched to some extent (for example, about 10 nm under the above conditions).

  On the other hand, in the present embodiment, a semiconductor containing silicon or germanium is used as the stopper film 60. For example, a silicon layer, a germanium layer, a silicon germanium layer, an impurity-doped silicon layer, an impurity-doped germanium layer, or an impurity-doped silicon germanium layer (eg, an impurity-doped silicon germanium layer) , Amorphous silicon, polysilicon, amorphous silicon SiGe or poly SiGe, or any of these impurities such as phosphorus, arsenic, boron, antimony, carbon, and elements (hydrogen, nitrogen, oxygen, chlorine) contained in the film forming material Any one of the films including the first film is used as the stopper film 60. Therefore, the first and second silicon nitride films 20 and 50 covering the silicon oxide film 40 may be thin. For example, assuming that the film thickness of the first and second silicon nitride films 20 and 50 is 150 nm, the film thickness of the first and second silicon nitride films 20 and 50 is larger than that of the comparative example (470 nm). 1/3 or less. Thereby, the removal time of the first and second silicon nitride films 20 and 50 is greatly shortened.

  Since the stopper film 60 made of a semiconductor containing silicon or germanium is difficult to be etched with respect to the removal liquid of the mask material 70, the etching rate of the mask material 70 is increased by increasing the temperature and / or the concentration of the removal liquid. However, the structure under the stopper film 60 is not affected. Therefore, the silicon oxide film 40 can be left with little etching. Thereby, the removal time of the mask material 70 can be shortened.

  When the stopper film 60 is a semiconductor film containing silicon as a main component, there is an advantage that it can be easily applied to the current production line.

  When the stopper film 60 is a semiconductor film containing germanium as a main component, there are many kinds of chemicals that can remove the semiconductor film, and there is an advantage that it is easy to select a chemical having a desired selection ratio with respect to the mask material.

(Second Embodiment)
In the method for manufacturing a semiconductor device according to the second embodiment of the present invention, the second silicon nitride film 50 is not formed. The other steps according to the second embodiment may be the same as the steps according to the first embodiment. 1 to 6, the second embodiment can be easily estimated, and therefore the illustration of the second embodiment is omitted.

  Since the second silicon nitride film 50 is not formed, the time for removing the silicon nitride film with the hot phosphoric acid solution is further shortened. When the second silicon nitride film 50 is not formed, the silicon oxide film 40 is exposed when the stopper film 60 is removed. However, since the etching solution for the semiconductor film containing silicon or germanium is usually a mixed solution of concentrated nitric acid and thin diluted hydrofluoric acid as described above, the silicon oxide film 40 is not so etched. Therefore, in order to shorten the cycle time of the manufacturing process, it is preferable to omit the second silicon nitride film 50 as in the second embodiment.

  On the other hand, in the manufacturing method according to the second embodiment, the silicon oxide film 40 is slightly etched. Therefore, in order to leave the silicon oxide film 40 more appropriately, it is preferable to provide the second silicon nitride film 50 as in the first embodiment. In order to protect the peripheral portion of the silicon substrate 10, it is preferable to provide the second silicon nitride film 50.

Sectional drawing which shows the manufacturing method of the semiconductor device according to 1st Embodiment concerning this invention. Sectional drawing which shows the manufacturing method of a semiconductor device following FIG. FIG. 3 is a cross-sectional view illustrating the method for manufacturing the semiconductor device following FIG. 2. FIG. 4 is a cross-sectional view illustrating the method for manufacturing the semiconductor device following FIG. 3. FIG. 5 is a cross-sectional view illustrating the method for manufacturing the semiconductor device following FIG. 4. FIG. 6 is a cross-sectional view illustrating the method for manufacturing the semiconductor device following FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Silicon substrate 20 ... 1st silicon nitride film 30 ... 1st element isolation layer 40 ... Silicon oxide film 50 ... 2nd silicon nitride film 60 ... Stopper film 70 ... P-TEOS
80: Second element isolation layer

Claims (6)

Forming a first film including at least a silicon oxide film or a silicon nitride film on the semiconductor substrate;
Forming a stopper film made of a semiconductor containing silicon or germanium on the first film;
Forming a mask material of a material different from the stopper film on the stopper film;
Etching a portion of the mask material;
Impurities are introduced through the stopper film into the etched region of the mask material,
Removing the mask material using the stopper film as a stopper;
A method of manufacturing a semiconductor device, comprising removing the stopper film using the first film as a stopper. Depositing a first silicon nitride film over the semiconductor substrate;
Removing the first silicon nitride film on the semiconductor substrate in the first element isolation formation region;
Using the first silicon nitride film as a mask to introduce an element isolation impurity into the semiconductor substrate in the first element isolation formation region to form a first element isolation layer;
Filling a first silicon oxide film for element isolation above the semiconductor substrate in the first element isolation formation region;
Depositing a second silicon nitride film on the first silicon oxide film and the first silicon nitride film;
Depositing a stopper film made of a semiconductor containing silicon or germanium on the second silicon nitride film;
Depositing a mask material of a material different from that of the stopper film on the stopper film,
Removing the mask material on the semiconductor substrate in the second element isolation formation region;
Using the mask material as a mask, an impurity for element isolation is introduced into the semiconductor substrate in the second element isolation formation region, so that the first element isolation layer is deeper than the silicon substrate surface. 2 element isolation layers are formed,
Removing the mask material using the stopper film as a stopper;
Removing the stopper film using the second silicon nitride film as a stopper;
A method of manufacturing a semiconductor device, comprising removing the first and second silicon nitride films while leaving the first silicon oxide film remaining.   3. The mask material according to claim 1, wherein the mask material is made of a material mainly comprising at least one of a silicon nitride film, a silicon oxide film, a metal, a metal compound, carbon, or an organic film. The manufacturing method of the semiconductor device of description. For removing the mask material, when the mask material is a silicon oxide film, a first solution containing hydrofluoric acid and no oxidant is used. When the mask material is a silicon nitride film, the first solution is used. When any one of solutions containing phosphoric acid is used and the mask material is made of a metal or a metal compound, the first solution, the second solution containing any one of hydrochloric acid, phosphoric acid, nitric acid, acetic acid, and sulfuric acid, the second A third solution containing a solution of hydrogen peroxide, ozone, nitrate or peroxosulfate, one of ammonia, TMAH or choline and one of hydrogen peroxide, ozone, nitrate or peroxosulfate A fourth solution containing the oxidizing agent, a fifth solution containing the oxidizing agent, or a gas (first gas) made of any of oxygen, nitrogen, hydrogen, ammonia, helium, and carbon fluoride, The mask Using fee if consists of carbon or an organic film, the second solution other than hydrochloric acid, the said third fifth solution, or, the first gas,
For the removal of the stopper film, when the main component of the stopper film is made of silicon, either a solution containing an oxidizing agent and hydrofluoric acid, a solution containing ammonia, a solution containing TMAH, or a solution containing choline is used. 3. The method of manufacturing a semiconductor device according to claim 1, wherein when the germanium content of the stopper film is larger than the silicon content, a solution containing an oxidizing agent is used.   For removing the stopper film, a solution containing hydrofluoric acid and nitric acid, a solution containing hydrofluoric acid and hydrogen peroxide, a solution containing hydrofluoric acid and ozone, a solution containing hydrofluoric acid and nitrate, a solution containing hydrofluoric acid and peroxosulfate 3. The method of manufacturing a semiconductor device according to claim 1, wherein any one of a liquid containing ammonia, a liquid containing TMAH, or a liquid containing choline is used.   The method for manufacturing a semiconductor device according to claim 1, wherein the step of introducing the impurity is performed to isolate a pixel of an image sensor.

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