JP3584544B2 - Method for manufacturing semiconductor device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device having a narrow groove or trench in a substrate.
[0002]
[Prior art]
2. Description of the Related Art In the manufacture of semiconductor devices, it is known to form narrow grooves (hereinafter, referred to as trenches) on a semiconductor substrate, for example, a silicon substrate by using RIE (reactive ion etching). By forming this trench in a silicon substrate, it is used for improving the degree of integration of an integrated circuit element or a vertical power MOSFET used for the input / output section of various information processing devices, and for improving the performance of the element. You. The size of the trench formed on the silicon substrate by the RIE is about 0.5 to 3 μm in width and about several to several tens of μm at present, and a relatively fine trench is obtained. .
[0003]
However, when a trench is formed by RIE, a layer contaminated with heavy metal or a damaged layer such as crystal disorder or surface roughness having a thickness of several tens of nm is often formed on the formed sidewall of the trench. As a method for removing the heavy metal contamination layer and the damaged layer, wet or dry chemical etching may be used in combination with the trench forming step. However, when a normal chemical etching treatment is used in combination, subtle variations occur in the treatment conditions, which may make it impossible to uniformly remove the damaged layer or further promote surface roughness.
[0004]
Therefore, in order to recover the above-described surface roughness and remove the damaged layer, it is now common practice to thermally oxidize the trench surface at a high temperature to form an oxide film. However, it is known that in the method of oxidizing the surface of the trench to form an oxide film, a very large stress acts on the corner and the bottom of the trench, and dislocation is generated on the corner and the bottom of the trench due to this stress. For example, a crystal defect may be generated due to the above. However, once a crystal defect such as a dislocation is introduced into a semiconductor substrate, it is impossible to remove the crystal defect in a subsequent process. Therefore, from the viewpoint of preventing deterioration of element characteristics in a semiconductor device having a trench, it is required to reduce stress at corners and bottoms of the trench so that crystal defects are never introduced.
[0005]
On the other hand, as the miniaturization progresses, the semiconductor device manufacturing process temperature tends to decrease, and the same applies to the trench oxide film forming step. Since the influence of the generated stress on the substrate is smaller when the oxidation temperature at the time of forming the oxide film is higher, the stress generated in the oxidation process of the trench tends to further increase as the oxide film formation temperature of the trench decreases. . Therefore, it is difficult to prevent generation of crystal defects such as dislocations, and it is strongly required to solve this problem.
[0006]
[Problems to be solved by the invention]
As described above, it is difficult to prevent crystal defects such as dislocations formed near the surface of the trench by the conventional technology, and there is no method of manufacturing a semiconductor device that can easily and effectively remove the crystal defects. For this reason, the semiconductor device using the trench side wall as an active region of the device has been adversely affected by a decrease in carrier mobility and lifetime. Therefore, in principle, the trench formed for the purpose of improving the device characteristics and greatly improving the device cost due to high integration, etc., has a sufficient role due to the above-mentioned technical problems in the oxidation process. There is a problem that does not play.
[0007]
Further, since the trench is formed in the silicon substrate by reactive ion etching (RIE) or the like, the bottom or corner of the formed trench becomes acute, and an oxide film having a sufficient thickness can be formed on the bottom or corner. However, there is a problem that the dielectric breakdown voltage of the oxide film formed in this region is low. To solve this, it is necessary to form a thicker oxide film than usual.On the other hand, when the thickness of the oxide film is increased, crystal defects such as dislocations are likely to be formed. There was a problem that it was significantly reduced.
[0008]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method capable of easily and effectively preventing the occurrence of crystal defects formed near the surface of a trench and manufacturing a highly reliable semiconductor device. It is an object.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following features.
[0010]
The present invention is a method for forming an oxide film on a surface of a trench formed in a semiconductor substrate, wherein, during the formation of the oxide film, a temperature of forming the oxide film with respect to the semiconductor substrate on which the trench is formed. As described above, the heat treatment is performed in a non-oxidizing gas. That is, the formation of the oxide film includes an oxidation step of the surface of the trench, the heat treatment step after the oxidation step, and the oxidation step again after the heat treatment step.
[0011]
The present invention may further include a step of removing the oxide film, and a step of newly forming a second oxide film on the surface of the trench after removing the oxide film.
[0012]
Heat treatment performed in the previous SL nonoxidizing gas in is characterized in that the treatment temperature is 950 ° C. or higher.
[0013]
In addition, the non-oxidizing gas is one or a mixture of hydrogen, nitrogen, argon, helium, xenon, and krypton.
[0014]
Further, the oxygen concentration in the trench formation region of the semiconductor substrate is set to 1.5 × 10 ¹⁸ cm ⁻³ or less.
[0015]
[Action and effect]
In the oxidation step of oxidizing the surface of the trench at a high temperature to form an oxide film, extremely large stress acts on the corners and the bottom of the trench because, when silicon is oxidized from the surface, the volume is about 2. It is believed that this is due to doubling. Due to this increase in volume, tensile and compressive stresses are generated at the corners and the bottom of the trench during oxidation.
[0016]
However, the tensile and compressive stresses change depending on the viscosity coefficient of the oxide film. The higher the temperature, the lower the viscosity coefficient, and the faster the relaxation of the generated stress. If the temperature is lower than 950 ° C., the relaxation of the stress is small because the oxide film behaves almost as an elastic body. Therefore, in order to utilize the effect of lowering the viscosity coefficient of the oxide film, the temperature may be set to 950 ° C. or higher. Therefore, the present invention utilizes the property that the viscosity coefficient of the oxide film decreases when the temperature is equal to or higher than the predetermined temperature (950 ° C.).
[0017]
In the present invention, when the situation in which a strong tensile and compressive stresses in the oxidation initial trenches occurs, i.e. an oxide layer formed Applications in the heat treatment in a non-oxidizing gaseous argon or the like to the semiconductor substrate performed. Thus, the stress is relaxed by lowering the viscosity coefficient of the oxide film so that the critical stress for generating crystal defects such as dislocation during formation of the oxide film is prevented. Therefore, generation of crystal defects around the trench can be easily and effectively suppressed.
[0018]
Similar effects can be obtained by using any one of hydrogen, nitrogen, helium, xenon, and krypton or a mixed gas thereof in addition to argon as the non-oxidizing gas.
[0019]
In the present invention , first, in order to suppress the introduction of crystal defects, the same heat treatment as described above is performed so as not to reach the limit stress at which crystal defects such as dislocations occur during oxidation of the trench surface, An oxide film (first oxide film) is formed. Then, the curvature of the bottom and the corner of the trench is increased by the first oxide film forming step. Next, the first oxide film is removed, and a second oxide film is newly formed on the surface of the trench. Since the curvature of the corners and the bottom of the trench is large, the thickness of the second oxide film formed in this region is prevented from being reduced, and a good withstand voltage can be obtained also in the region.
[0020]
Note that, in the present invention, the oxygen concentration in the semiconductor region where the trench is formed is set lower than 1.5 × 10 ¹⁸ cm ⁻³ . This is because if the oxygen concentration in the trench formation region or the element formation region in the semiconductor substrate is high, oxygen diffuses and aggregates during various processes, and crystal defects such as dislocation due to stress are likely to occur. It is a thing which paid attention to. As described above, in the present invention, by setting the oxygen concentration to be lower than 1.5 × 10 ¹⁸ cm ⁻³ , the generation of crystal defects due to the diffusion and aggregation of oxygen contained in the semiconductor substrate in the subsequent heat treatment step Can be suppressed.
[0021]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
Example 1
FIG. 1 is a view showing a trench forming step and an oxide film forming step in the present embodiment, and FIG. 2 is a view showing time and temperature conditions in a trench oxidizing step and a heat treatment step.
[0023]
First, as shown in FIG. 1A, after an oxide film 12 having a thickness of about 500 nm is formed on a silicon substrate 10, the surface of the oxide film 12 is covered with a resist 14 except where trenches are to be formed.
[0024]
Next, as shown in FIG. 1B, the oxide film 12 in a region not covered with the resist 14 is etched using RIE (reactive ion etching) with the resist 14 as a mask, and then the resist 14 is removed. I do.
[0025]
After removing the resist, the silicon substrate 10 is etched from the opening of the oxide film 12 using a gas mainly composed of HBr to form a trench 20 having a depth of about 4 μm as shown in FIG. Further, the oxide film 12 on the silicon substrate 10 is removed using a dilute hydrofluoric acid solution, and the exposed surface of the silicon substrate 10 is etched with a fluorine-based gas to about 20 to 40 nm.
[0026]
After the surface of the silicon substrate 10 is etched, the silicon substrate 10 is sufficiently washed, and the silicon substrate 10 is humidified and oxidized at a temperature of 1000 ° C., specifically, oxidized in a pyrogenic atmosphere. Thus, an oxide film 16 is formed on the surface (side wall, bottom, and corner) of the trench 20 and the surface of the silicon substrate 10 as shown in FIG.
[0027]
The step of forming the oxide film 16 will be specifically described below with reference to FIG.
[0028]
First, the temperature is increased at a rate of 2 ° C./min from 800 ° C. to 1000 ° C., and the temperature is maintained at 1000 ° C. for about 5 minutes. Then, the silicon substrate 10 is subjected to pyrogenic oxidation for about 15 minutes.
[0029]
Subsequently, heat treatment is performed at 1000 ° C. for about 10 minutes in an argon atmosphere using argon as a non-oxidizing gas, and then oxidation is performed again for about 45 minutes under the same conditions, that is, 1000 ° C. (pyrogenic oxidation: H 2 (Oxidation in an H2O atmosphere obtained by burning gas and O2 gas inside the reaction tube).
[0030]
After a lapse of 45 minutes, heat treatment is again performed at 1000 ° C. for 10 to 15 minutes in an argon atmosphere, and then the temperature is lowered from 1000 ° C. to 800 ° C. at 2 ° C./min.
[0031]
By performing the oxidation for a total of 60 minutes, the oxide film 16 having a thickness of about 350 nm or more could be formed.
[0032]
FIG. 3A is a schematic diagram of a cross section of the trench portion of the present embodiment manufactured as described above. FIG. 3B is a schematic view of a cross section of a trench portion obtained by oxidizing a trench by a conventional method. Note that the silicon substrate 10 in FIG. 3 has an oxygen concentration of 1.5 × 10 ¹⁸ cm ⁻³ or less, and in FIG. 3A, a non-oxidizing gas such as argon and nitrogen is used in the heat treatment. A mixed gas was used.
[0033]
In FIG. 3B, the trench 20 is formed by RIE. After the trench 20 is formed, the silicon substrate 10 is simply subjected to pyrogenic oxidation for 60 minutes without performing a heat treatment in a non-oxidizing gas to form the trench 20. Oxide film 30 is formed on the surface of silicon substrate 10 and the surface of silicon substrate 10. According to FIG. 3B, a large number of crystal defects 32 are generated at the bottom, corner, and periphery of the trench 20.
[0034]
On the other hand, when heat treatment is performed in a non-oxidizing gas during or immediately after oxidation as in the present embodiment, as shown in FIG. 3A, the region where the trench 20 is formed in the silicon substrate 10 is formed. No generation of crystal defects such as dislocations due to oxidation is observed in the periphery. Therefore, it is clear that the occurrence of crystal defects is sufficiently suppressed by performing the heat treatment in the oxidation step. This is because, during or immediately after oxidation where strong tensile and compressive stress is generated, by performing a heat treatment in the non-oxidizing gas, the viscosity coefficient of the oxide film is reduced and the stress is relaxed. The relaxation of the stress prevents the occurrence of crystal defects by reaching the critical stress for crystal defect generation.
[0035]
Further, according to the method of the present embodiment, not only the occurrence of crystal defects is suppressed, but also a damage layer such as crystal disorder and surface roughness having a thickness of several tens nm which is generated on the trench side wall at the time of trench formation is reduced. nm or less. As a result, the surface mobility of the trench side wall can be made comparable to that of a conventional semiconductor device having a planar structure. In addition, since the occurrence of crystal defects is sufficiently suppressed, even if a pn junction of the semiconductor element is formed on the side wall of the trench, it is possible to reduce the leak current by one digit or more compared to the conventional case. This is because the crystal defects in this region of the silicon substrate 10 are small, and the recombination current in the depletion layer of the semiconductor element is reduced.
[0036]
Even when the thickness of the oxide film 16 is set to a value other than 350 nm in this embodiment, it is possible to sufficiently suppress generation of crystal defects by performing a heat treatment in a non-oxidizing gas during and immediately after the oxidation step. did it.
[0037]
The heat treatment in a non-oxidizing gas is higher effect can be obtained by carrying out during oxide film formation step in and both immediately as shown in this embodiment, Saishi necessarily during the formation process is not limited thereto line to give a heat-treated Te.
[0038]
Further, a bipolar transistor which was electrically isolated from other regions was manufactured by using the trench formed by the manufacturing method of this embodiment as an element isolation, and a highly reliable transistor without variation in current amplification factor was obtained. Was done. That is, by using the trench formed by the method of this embodiment for element isolation, a semiconductor element having excellent characteristics can be manufactured.
[0039]
Further, in this embodiment, as the silicon substrate 10, an MCZ (Magnetic-field-applied Czochralski) substrate whose oxygen concentration in the substrate is about 1.7 × 10 ¹⁷ cm ⁻³ is used. An epitaxial substrate in which a silicon crystal is epitaxially grown to a predetermined thickness, and an FZ (Floating Zone) substrate are also applicable. Further, the silicon substrate is subjected to a heat treatment at a high temperature, a low temperature and a high temperature, for example, a silicon substrate 10 is subjected to a hydrogen heat treatment to form a denuded layer (a defect-free layer) with a thickness of more than ten μm near the surface. A similar effect was observed. In the case of a CZ substrate having an oxygen concentration of about 1.5 × 10 ¹⁸ cm ⁻³ or more, generation of crystal defects such as dislocations could not be sufficiently suppressed, although it depends on the thermal history.
[0040]
Further, when the oxidation temperature is set to 950 ° C. or more, an effect other than the pyrogenic method for forming an oxide film, such as a dry oxidation method, is effective.
[0041]
Further, as the atmosphere in the heat treatment, in addition to argon, use of a non-oxidizing gas such as nitrogen, hydrogen, helium, krypton, or xenon, or a mixed gas of these gases was also effective.
[0042]
Example 2
Another embodiment of the present invention will be described below with reference to FIGS. The same parts as those in the drawings already described are denoted by the same reference numerals and description thereof will be omitted.
[0043]
First, as in the first embodiment, an oxide film 12 having a thickness of about 500 nm is formed on a silicon substrate 10, and then the oxide film 12 is partially etched by RIE using a resist as a mask to form a window for forming a trench. Open. Next, the resist is removed, the silicon substrate 10 is washed, and a trench 20 having a depth of about 3 μm is formed as shown in FIG. After that, the oxide film 12 is removed, and the silicon substrate 10 is sufficiently washed.
[0044]
Next, an oxide film 16 is formed as a first oxide film at a temperature of about 1000 ° C. by using a pyrogenic oxidation method, as shown in FIG.
[0045]
This oxidizing step is the same as that of the first embodiment. As shown in FIG. 2, first, the temperature is raised from 800 ° C. to 1000 ° C. at a rate of 2 ° C./min. I do. Next, heat treatment is performed at 1000 ° C. in an argon atmosphere for about 10 minutes, and then oxidation is performed for about 45 minutes, and subsequently heat treatment is performed at 1000 ° C. for 10 to 15 minutes in an argon atmosphere, and the temperature is increased to 1000 ° C. at a rate of 2 ° C./min. To 800 ° C. Then, an oxide film 16 of about 350 nm is formed on the surface of the trench 20 and the silicon substrate 10.
[0046]
By oxidizing the trench 20 as described above, the curvature of the concave and convex portions (bottom and corner) of the trench side wall increases. This is considered to be because the stress generated at the bottom and the corner of the trench 20 is reduced by the oxidation treatment as in the present embodiment, and the diffusion of the oxidized species in the oxide film 16 into the substrate is not restricted.
[0047]
Next, the formed oxide film 16 is removed, and oxidation is performed at a temperature of 950 ° C. for 30 minutes in a dry oxygen atmosphere. Thereby, as shown in FIG. 4C, an oxide film 18 of about 50 nm is formed on the surface of the trench 20 and the silicon substrate 10 as a second oxide film.
[0048]
In order to evaluate the oxide film 18 formed as described above, polycrystalline silicon was buried in the oxide film 18 in the trench 20 and the dielectric breakdown voltage of the oxide film 18 was measured. As a result, the dielectric breakdown voltage of the conventional trench oxide film was about 5 to 6 M / V, whereas the dielectric breakdown voltage of the oxide film 18 of this embodiment was improved to about 8 to 9 M / V. Although the dielectric breakdown voltage of the oxide film 18 is slightly lower than the intrinsic withstand voltage of the normal oxide film by more than 10%, the dielectric breakdown voltage is improved to such an extent that no trouble occurs in manufacturing a semiconductor device.
[0049]
The reason why the breakdown voltage is improved is that the trench 20 is oxidized to form the oxide film 16, the curvature of the bottom and the corner of the trench 20 is increased, and then the new insulating film 18 is added to the trench 20. This is because the oxide film 18 does not become thin at the bottom and the corner of the trench 20. This is because the heat treatment is performed as described above when forming the oxide film 16 to suppress the occurrence of crystal defects.
[0050]
In the present embodiment, the irregularities on the surface of the trench side wall after the formation of the oxide film 18 could be made 2 nm or less, and the surface mobility was almost the same as that of the semiconductor element having the planar structure.
[0051]
The silicon substrate 10 used in this embodiment is a substrate formed by an epitaxial method. However, the present invention is not limited to this. Similar to the first embodiment, a silicon substrate having a ten-odd μm denuded layer formed on its surface by a hydrogen heat treatment, or a CZ substrate having an oxygen concentration lower than 1.5 × 10 ¹⁸ cm ^−3. A similar effect was observed even when an FZ substrate or an MCZ substrate was used. However, in the case of a CZ substrate having an oxygen concentration of about 1.5 × 10 ¹⁸ cm ⁻³ or more, generation of crystal defects could not be sufficiently suppressed as in Example 1.
[0052]
Further, the oxidation temperature in forming the oxide film 16 may be 950 ° C. or higher. For example, there is an effect even if the oxide film 16 is formed by a dry oxidation method or a dry oxidation method to which hydrochloric acid is added.
[0053]
Further, as in the case of Example 1, other than nitrogen, the heat treatment atmosphere was effective even with nitrogen, hydrogen, helium, xenon, krypton, or a mixed gas thereof.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a trench forming step and a subsequent oxidizing step in a manufacturing process of a semiconductor device according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between time and temperature in an oxidation step and a heat treatment step after a trench forming step in Examples 1 and 2 of the present invention.
FIG. 3 is a schematic cross-sectional view after forming an oxide film of a trench portion manufactured by the method of Example 1 of the present invention and a conventional method.
FIG. 4 is a view illustrating a trench forming step and a subsequent oxidation step in the manufacturing process of the semiconductor device according to the second embodiment of the present invention.
[Explanation of symbols]
10 silicon substrate, 12, 16, 18 oxide film, 14 resist, 20 trench.

Claims (7)

A method of forming an oxide film on a surface of a trench formed in a semiconductor substrate,
During the formation of the oxide film, a heat treatment is performed on the semiconductor substrate on which the trench is formed at a temperature equal to or higher than the formation temperature of the oxide film and in a non-oxidizing gas ,
The formation of the oxide film includes:
Oxidizing the surface of the trench,
A step of the heat treatment after the oxidation step;
The oxidation step again after the heat treatment step;
A method for manufacturing a semiconductor device, comprising: A method of forming an oxide film on a surface of a trench formed in a semiconductor substrate,
During the formation of the oxide film, a heat treatment is performed on the semiconductor substrate on which the trench is formed at a temperature equal to or higher than the formation temperature of the oxide film and in a non-oxidizing gas,
The formation of the oxide film includes:
Oxidizing the surface of the trench,
A step of the heat treatment after the oxidation step;
A second oxidation step after the heat treatment step,
A second heat treatment step after the second oxidation step;
A method for manufacturing a semiconductor device, comprising: In claim 1 Symbol placement methods, further
A step of etching a surface of the semiconductor substrate with a fluorine-based gas before forming the oxide film . The method according to any one of claims 1 and 2,
The method of manufacturing a semiconductor device, wherein the temperature of the heat treatment performed in the non-oxidizing gas is 950 ° C. or higher . The method according to any one of claims 1 and 2 ,
The method of manufacturing a semiconductor device according to claim 1, wherein the non-oxidizing gas is one or a mixture of hydrogen, nitrogen, argon, helium, xenon, and krypton . The method according to any one of claims 1 and 2,
A method for manufacturing a semiconductor device, wherein an oxygen concentration in a trench formation region of the semiconductor substrate is 1.5 × 10 ¹⁸ cm ⁻³ or less . In claim 1 Symbol placement methods, further
Removing the oxide film;
Forming a new second oxide film on the surface of the trench after removing the oxide film;
A method for manufacturing a semiconductor device, comprising:

Images