JP3629179B2 - Manufacturing method of semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to formation of a trench.
[0002]
[Prior art]
In order to obtain a large capacity with a small area in a semiconductor memory device or the like, a trench capacitor is used. For this reason, formation of a deep trench is required.
[0003]
Such a deep trench is usually formed by an etching process. As a hard mask in this etching, a conventional TEOS (tetraethoxysiane, Si (0C ₂ H ₅ ) 4) is decomposed by a low pressure CVD (LP-CVD) method. The resulting CVD SiO2 film is frequently used.
[0004]
However, this film has a problem that it is difficult to remove with good uniformity when peeling off by dry etching or the like after trench formation. For this reason, there is a problem that a step is formed on the silicon oxide film after the dry etching for removing the CVD SiO ₂ film is performed, and this step affects a subsequent process. In the case of TEOS, there is also a problem that the CVD SiO ₂ film cannot be removed immediately after etching for trench formation.
[0005]
On the other hand, doped oxides such as BSG, BPSG, and PSG are examples of materials that have been handled in the same manner as such CVD-SiO ₂ insulating film materials. These BSG, BPSG, and PSG have an advantage that the etching rate at the time of wet etching is higher than that of, for example, a TEOS film, and when used as a hard mask, peeling when it becomes unnecessary can be easily performed.
[0006]
FIG. 13 is a cross-sectional view for each process in the case where a trench is formed using BSG as a doped oxide.
[0007]
First, the BSG film 12 is formed on the silicon semiconductor substrate 11 by the CVD method or the like. Further, a resist 13 is applied on the BSG film by a spin coat method or the like (FIG. 13A).
[0008]
Next, exposure and development are performed using an exposure mask corresponding to a desired pattern, and the resist 13 is patterned (FIG. 13B).
[0009]
Next, the BSG film 12 is etched using the patterned resist 13 ′ as an etching mask (FIG. 13C).
[0010]
Subsequently, the resist 13 ′ is peeled off, and the silicon 11 is etched using the etched BSG film 12 ′ as a hard mask to form a deep trench (FIG. 13D).
[0011]
Then, after forming the trench, the BSG film 12 ′ is removed.
[0012]
[Problems to be solved by the invention]
However, BSG, BPSG, when using a doped oxide such as PSG as a hard mask material, as compared with the case of using other CVD Si0 ₂ film as a hard mask material, a problem tends to occur a change in the etching shape is there.
[0013]
This is because BSG, BPSG, and PSG have the property of easily absorbing moisture, so that when the etching process is performed, the moisture contained in the BSG, BPSG, and PSG films is released into the chamber atmosphere during the process, It is considered that the etching characteristics change due to this influence.
[0014]
Since the amount of moisture absorption of BSG, BPSG, and PSG depends on the leaving atmosphere of the sample, it is inevitable that the processing characteristics vary slightly due to the difference in the leaving state.
[0015]
Therefore, when using BSG, BPSG, the PSG film has a problem that changes forced the etching conditions for the case of Si0 ₂ film.
[0016]
The present invention has been made to solve such problems, and it is possible to improve the characteristics during etching without impairing the original characteristics of doped oxide films such as BSG, BPSG, and PSG. It is a daily matter to provide a method for manufacturing a semiconductor device.
[0017]
[Means for Solving the Problems]
A method for manufacturing a semiconductor device according to the present invention includes:
Forming a doped oxide film as a hard mask material on the silicon substrate to be etched;
Applying a resist on the doped oxide film;
Patterning the resist, and etching the doped oxide film using the patterned resist as an etching mask to obtain a patterned hard mask;
Removing the resist;
Performing a baking treatment in an atmosphere at 100 to 550 ° C. to remove moisture contained in the doped oxide film;
And etching the substrate using the patterned hard mask to form a recess.
In this case, a protective cap layer may be further formed on the doped oxide layer, and a resist may be applied on the protective cap layer.
[0018]
In addition, another method for manufacturing a semiconductor device according to the present invention includes:
Forming a doped oxide film forming a first layer of an interlayer insulating film on a silicon substrate;
Forming a silicon oxide film forming a second layer of an interlayer insulating film on the doped oxide film;
Patterning the doped oxide layer and the silicon oxide film to form a contact hole so that the silicon substrate is exposed;
Performing a baking process in an atmosphere of 100 to 550 ° C. to remove moisture contained in the doped oxide film exposed in the contact hole;
And a step of embedding a contact material in the contact hole.
[0019]
As described above, according to the present invention, since the baking process is performed in the atmosphere of 100 to 550 ° C. after the patterning of the doped oxide film, the moisture is removed from the highly hygroscopic doped oxide film. Does not cause deterioration of characteristics.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a cross-sectional view showing a processing process for forming a deep trench according to the present invention.
[0022]
The sample used here is obtained by forming a thermal oxide film (8 nm), a SiN film (200 nm), and a BSG (700 nm) on the silicon substrate 1. However, in FIG. 1, the thermal oxide film and the SiN film are omitted.
[0023]
First, the silicon semiconductor substrate 1 is thermally oxidized in an oxidizing atmosphere to form a thermal oxide film with a thickness of 8 nm on the surface thereof. A silicon nitride film is formed with a thickness of 200 nm. Subsequently, a BSG film 2 is formed thereon by a CVD method or the like. Further, a resist 3 is applied on the BSG film by a spin coat method or the like (FIG. 1A).
[0024]
Next, exposure and development are performed using an exposure mask corresponding to a desired pattern to pattern the resist (FIG. 1B).
[0025]
Next, the BSG film 2 is etched using the patterned resist 3 ′ as an etching mask to obtain a pattern as a hard mask (FIG. 1C).
[0026]
Subsequently, the resist is peeled off, and a baking process is performed on the patterned BSG film 2 ′ (FIG. 1D). In this baking process, O ₂ gas was flowed at a flow rate of 300 sccm and a pressure of 30 Pa, the temperature of the plate on which the wafer was placed was set to 250 ° C., and the process was performed for 300 seconds. By this baking process, the moisture 4 contained in the BSG film 2 ′ is removed.
[0027]
Then, the silicon substrate 1 is etched using the BSG film 2 ′ after baking as a hard mask to form a deep trench (FIG. 1E). This BSG film is removed after trench formation.
[0028]
As described above, the baking process is performed after the etching of the BSG film.
[0029]
This baking temperature was determined as follows.
[0030]
The upper graph in FIG. 2 shows the temperature in the case where no baking is performed, and the lower graph in FIG. 2 shows the temperature in both cases where the BSG film is baked at 250 ° C. for 5 minutes in an N ₂ gas flow atmosphere. It is a graph which shows the analysis result of desorption gas when raising. The gas focused here is water with m / z = 18.
[0031]
From this graph, it can be seen that by performing baking, the amount of released water is effectively suppressed particularly in the temperature range of 100 to 300 ° C., and is reduced even in the temperature range of 300 to 550 ° C.
[0032]
Thus, the moisture release from the BSG is in the range of 100 to 550 ° C. Therefore, the baking of the BSG does not cause oxidation of each material, does not cause deterioration of the BSG, and does not cause deterioration of the BSG. It can be seen that it is effective to perform at a temperature as high as possible while satisfying the condition that the temperature is higher than the above temperature.
[0033]
Next, the effect of applying the present invention will be described.
[0034]
FIG. 4 to FIG. 8 are graphs showing the results of experiments conducted on those with and without baking after etching of the BSG film. In each graph, for each item date, the case where the mask material at the time of etching is BSG and the case of TEOS are compared. As described below, the etching characteristics were remarkably improved by applying the present invention. In each figure, data is taken at the wafer center (center), 10 mm from the wafer edge, and 25 mm.
[0035]
FIG. 3 is a diagram for explaining the contents of each dimension item used in FIGS. As shown in FIG. 3A, etching is performed in a state where a patterned BSG film 2 ′ as a hard mask is formed on the silicon substrate 1 before the trench etching, and the trench 5 as shown in FIG. The specifications are defined for what was obtained.
[0036]
That is, the DT depth shown in FIG. 4 is the distance from the interface between the silicon substrate and the BSG to the bottom of the trench, the DT bottom diameter shown in FIG. 5 is the diameter at a position 0.5 μm above the bottom of the trench, and FIG. Is the ratio of the etching rate of Si to the mask material (BSG or TEOS), the upper taper shown in FIG. 7 is the slope angle at the upper part of the trench, and the lower taper shown in FIG. 8 is the slope angle at the lower part of the trench. .
[0037]
From these graphs, there is no difference in etching characteristics between when the TEOS film is baked and when the baking is not performed, whereas when the BSG film is baked, it is not performed. Etching characteristics are different, and when baked, it shows the same characteristics as the TEOS film, but when baked, it deteriorates in several days. I understand.
[0038]
That is, in the graph showing the DT bottom diameter (FIG. 5), the selection ratio (FIG. 6), and the lower taper angle (FIG. 8), the value is small only when there is no BSG. These causes are considered as follows. At the time of etching, the BSG film, which is a mask material, is also slightly removed. At this time, moisture contained in the BSG is released from the etched BSG film into the chamber atmosphere.
[0039]
In addition, since the wafer surface temperature rises to about 150 ° C. when the wafer is exposed to electric discharge, moisture in the BSG film is also released into the chamber atmosphere.
[0040]
In this way, moisture is released into the chamber atmosphere, so that oxygen is supplied from water molecules. Therefore, the release of moisture from the BSG film has the same effect as when oxygen is added to the etching gas.
[0041]
The taper angle control of the trench etching shape is usually adjusted by increasing or decreasing the amount of oxygen added. This is due to the mechanism by which the tapered shape is formed. That is, SiBr ₄ is mainly produced as a reaction product during etching. At this time, when oxygen is added, SiBr ₄ generated as a reaction product and oxygen are combined to form SiBr _x O _y (x and y are arbitrary numbers). Since SiBr _x O _y has a lower vapor pressure than SiBr, it is deposited on the wafer surface during etching. As a result, deposits are deposited on the side walls of the trench, and the etching shape is tapered.
[0042]
Here, if the amount of oxygen added during etching is increased, the proportion of SiBr ₄ bonded to oxygen also increases, and the amount of SiBr _x O _y increases. As a result, deposition on the trench sidewall during etching also increases, resulting in a shape with a more tapered angle.
[0043]
For the above reasons, when oxygen is added to the etching gas, the taper angle becomes gentler as the amount of added oxygen is increased.
[0044]
Next, consider the case where moisture (H ₂ O) is added. In this case, oxygen contains oxygen atoms, and when SiBr ₄ is present, SiBr ₄ is oxidized to generate SiBr _x O _y as in the case of adding oxygen.
[0045]
As a result, when moisture is added, the same effect as when oxygen is added is generated, and the etching shape becomes an etching shape with a gentler angle.
[0046]
If the BSG is not baked, a relatively large amount of water is present in the BSG, so that the wafer temperature rises during the etching process as described above, and is included when the BSG itself is etched. Moisture is released along with the etching. As a result, the moisture concentration in the etching gas atmosphere is relatively increased, and the same effect as when oxygen or water is added is produced. In this way, the etching shape is tapered, and the diameter at the bottom of the trench is reduced.
[0047]
In the description so far, it has been described that a large amount of SiBr _x O _y is generated due to the release of moisture from the BSG and the amount of deposition increases, so that the etching shape becomes a tapered shape.
[0048]
In the following description, the case where the etching shape has a taper shape, and the etching is further advanced with respect to the shape narrowed at the bottom of the trench will be described. In this case, a different phenomenon will occur.
[0049]
That is, the etching reaction occurs at the bottom of the trench, but the reaction area decreases when the diameter of the bottom of the trench is reduced. Therefore, the amount of SiBr ₄ generated by the etching reaction is reduced as compared with the case where the trench diameter is large.
[0050]
At this stage, since the amount of SiBr ₄ itself that is the source of SiBr _x O _y is reduced, the effect of reducing the amount of deposits is produced. The deposition on the wafer surface also had the effect of suppressing the etching of the BSG, which is the mask material, and collapsed, but this effect diminished as the deposition decreased, resulting in the BSG being the mask material. As a result, the amount of collapse increases.
[0051]
According to the results of this experiment, when trench etching was performed to the end, the effect of increasing the deposition due to the increase in moisture and becoming a taper shape appeared at the beginning of etching, and the generation amount of reaction products decreased in the second half of etching. Therefore, the deposition is reduced, and as a result, the effect of increasing the collapse amount of the BSG of the mask appears.
[0052]
With respect to the trench depth (FIG. 4) and the upper taper (FIG. 7), which are other etching characteristics, even when BSG is used, if it is baked, what is the etching characteristic when TEOS is used? It can be seen that there is no difference. It has been confirmed that the etching rate of the BSG film by the NH ₄ F + HF + H ₂ 0 treatment after the trench formation is maintained at a high etching rate equivalent to the case where no baking is performed. In this respect, as described above, TEOS has a problem that peeling after trench formation is difficult.
[0053]
As described above, by performing the baking process on the BSG film, the etching characteristics can be improved as compared with the case where the baking process is not performed, and high etching at the time of the chemical treatment, which is a characteristic of the BSG film. It was confirmed that the speed could be maintained.
[0054]
In the case of the TEOS film as a comparative example, there is no difference in the etching characteristics due to the difference in the presence or absence of the baking, so that the etching characteristics change due to the BSG film. This proves that this occurs because the BSG film described above has a characteristic that it easily absorbs moisture.
[0055]
In the above-described embodiments, the case of the BSG film as the hard mask material has been described. However, it is confirmed that the bake effect is also observed in the case of BPSG and PSG, which are highly hygroscopic doped oxides like BSG. Has been. This is considered to be due to the high hygroscopicity of BPSG and PSG as well as BSG.
[0056]
In addition, the effect of the baking of the present invention is that it is daily to desorb the moisture absorbed by the BSG, so the time from the baking of the BSG film to the etching process is important. It is. In some experiments, if the treatment is within 13 days after baking, the etching characteristics are not affected. However, the standing time after baking is hygroscopic depending on the film quality of BSG. Since it can be considered that the value of the value changes significantly, it is not possible to uniquely determine the leaving time after baking. It is necessary to confirm the environmental conditions and film quality and conduct experiments to determine the allowable standing time.
[0057]
Although the case where a deep trench is formed has been taken up in the above embodiment, the present invention can be applied to other processes including processing of BSG, BPSG, PSG and the like.
[0058]
Further, for example, the present invention can be applied to a case where BSG is used as a hard mask material when etching a shallow trench.
[0059]
FIGS. 9A to 9C and FIGS. 10A and 10B are cross-sectional views showing the steps in the case of forming element isolation by shallow trenches.
[0060]
First, the surface of the silicon substrate 21 is oxidized in an oxidizing atmosphere to form a 6 nm thick thermal oxide film 22, on which a silicon nitride film 23 is 150 nm, a BSG film 24 is 500 nm, and a non-doped TEOS film 25 is 20 nm thick. Then, a laminated film is formed, and a resist 26 is applied thereon (FIG. 9A), and the applied resist 26 is patterned (FIG. 9B). Using this patterned resist 26 'as a mask, the non-doped TEOS film 25, BSG film 24, silicon nitride film 23, and thermal oxide film 22 are etched (FIG. 9C). Thereafter, the resist on the wafer surface is peeled off by discharge in an oxygen atmosphere to obtain the state shown in FIG. The silicon substrate is etched using the patterned non-doped TEOS film 25 'and BSG film 24' as a mask to form a shallow trench 26 (FIG. 10B).
[0061]
FIG. 11 is a graph showing the results of comparing the STI taper angles for those with and without BSG baking before silicon etching for shallow trench formation.
[0062]
Note that etching of silicon was performed using Cl ₂ / O ₂ gas. The etching conditions were a pressure of 40 mTorr, an RF power of 500 W, a gas flow rate of Cl ₂ = 100 sccm, and O ₂ = 20 sccm.
[0063]
As is apparent from FIG. 11, the taper angle is 86 ° for those that are baked after silicon etching, whereas the taper angle is about 82 ° for those that are not baked.
[0064]
This is because SiCl ₄ generated as a reaction product of the etching reaction at the time of etching is combined with O to form SiCl _x O _{y having} a low vapor pressure, which is deposited and forms a taper in the etched shape, but is not baked. In this case, moisture in the BSG was generated during the etching of the silicon, and the taper angle became steeper because of the same effect as supplying excess oxygen.
[0065]
Note that the present embodiment is different from the first embodiment in that a non-doped TEOS film is formed on the surface of the BSG. However, the BSG surface is exposed after the BSG processing, and the BSG in this portion absorbs moisture.
[0066]
Thereby, when the BSG is baked, the moisture in the BSG is removed, but when the BSG is not baked, the etching is performed with the moisture in the BSG remaining. It is thought that it had influenced.
[0067]
As described above, even when another film is present on the BSG surface, it is possible to obtain the effect of baking BSG when the process including exposing the BSG surface is included.
[0068]
In general, a thin film such as a thin non-doped CVD SiO ₂ film is deposited on the surface of the BSG, BPSG, or PSG film to prevent moisture absorption. However, the surface or cross-section of the BSG, BPSG, When PSG is exposed, moisture is absorbed from the portion, and the etching characteristics are also changed. Therefore, the etching characteristics are improved by baking.
[0069]
Next, a case where BPSG is used as a part of the interlayer insulating film will be described.
[0070]
FIGS. 12A and 12B are cross-sectional views according to processes showing such an embodiment. First, a BPSG film 32 and a TEOS film 33 are sequentially stacked on a silicon substrate 31 to form contact holes. When the TEOS and BPSG films are etched using a resist (not shown) having a corresponding pattern, the side surfaces of the BPSG film 32 are exposed (FIG. 12A). In this state, the BPSG film is baked at a temperature of 250 ° C., and then tungsten 34, which is a metal serving as a contact wiring material, is buried in the contact hole (FIG. 12B).
[0071]
As a result of evaluating the reliability of the contact wiring created in this way, it was confirmed that the reliability of the wiring was improved when baking was performed before embedding the wiring material, compared with the case where it was not performed. .
[0072]
This is because, when not baked, moisture contained in BPSG gradually diffuses and reacts with tungsten, which is a wiring material, to produce tungsten oxide, so that the buried tungsten does not function as a wiring material. It is considered a thing.
[0073]
On the other hand, when the baking process is performed before embedding the wiring material, the moisture in the BPSG is removed, so that there is no diffusion of the moisture from the BPSG in the subsequent test, thereby improving the reliability of the wiring. It is thought that sex was maintained.
[0074]
As described above, other films are formed on the surface, but when BSG, BPSG and PSG are exposed, they are deposited on the surface of BSG, BPSG and PSG to prevent moisture absorption even when there is no exposure. Since the effect of the thin film may be insufficient, the baking process according to the present invention is effective.
[0075]
Further, the basic conditions are not limited to the conditions shown in the above embodiment, but can be changed within a range not departing from the gist of the present invention, such as other gas, mixed gas, processing temperature, processing time, and processing pressure. is there.
[0076]
As described above, according to the present invention, the BSG, BPSG, and PSG films before processing such as etching are baked in an atmosphere at 100 to 550 ° C., thereby suppressing the shape change during etching due to moisture absorption. be able to.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for each process showing an embodiment of a method for manufacturing a semiconductor device according to the present invention.
FIG. 2 is a graph showing the selection of the baking temperature that characterizes the present invention.
FIG. 3 is a cross-sectional view showing a shape after etching, which is an item for confirming the effect of application of the present invention.
FIG. 4 is a graph showing the influence of the root on the trench depth.
FIG. 5 is a graph showing the influence of the root on the bottom diameter of a trench.
FIG. 6 is a graph showing the influence of baking on the selectivity, which is the ratio of the etching rate of silicon to the mask material.
FIG. 7 is a graph showing the effect of bake on the upper taper of the trench.
FIG. 8 is a graph showing the influence of bake on the lower taper of the trench.
FIG. 9 is a cross-sectional view by process showing a first half of a process in the case of forming element isolation by a shallow trench.
FIG. 10 is a sectional view by process showing the latter half of the process in the case of forming element isolation by a shallow trench.
FIG. 11 is a graph showing the results of comparing the STI taper angles for those with and without BSG bake before silicon etching for shallow trench formation.
FIG. 12 is a cross-sectional view for each process when BPSG is used as a part of an interlayer insulating film.
FIG. 13 is a cross-sectional view showing a process of forming a trench using a conventional BSG film as a hard mask.
[Explanation of symbols]
1, 11, 21, 31 Silicon substrate 2, 12, 24 BSG film 3, 13 Resist 4 Moisture 5 Trench 22 Thermal oxide film 23 Silicon nitride film 25, 33 TEOS film 26 Shallow trench 32 BPSG film

Claims (11)

Forming a doped oxide film as a hard mask material on the silicon substrate to be etched;
Applying a resist on the doped oxide film;
Patterning the resist, and etching the doped oxide film using the patterned resist as an etching mask to obtain a patterned hard mask;
Removing the resist;
Performing a baking treatment in an atmosphere at 100 to 550 ° C. to remove moisture contained in the doped oxide film;
Etching the substrate using the patterned hard mask to form a recess;
A method of manufacturing a semiconductor device including: Forming a doped oxide film as a hard mask material on the silicon substrate to be etched;
Forming a protective cap layer on the doped oxide layer;
Applying a resist on the protective cap layer;
Patterning the resist, and etching the protective cap layer and the doped oxide film using the patterned resist as an etching mask to obtain a patterned hard mask;
Removing the resist;
Performing a baking treatment in an atmosphere at 100 to 550 ° C. to remove moisture contained in the doped oxide film;
Etching the substrate using the patterned hard mask to form a recess;
A method of manufacturing a semiconductor device including: 3. The method for manufacturing a semiconductor device according to claim 2, wherein the protective cap layer is a non-doped TEOS layer. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the recess is a trench. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the doped oxide is BSG or BPSG. 3. The manufacturing method according to claim 1, wherein the baking process is performed in an oxygen atmosphere. Forming a doped oxide film forming a first layer of an interlayer insulating film on a silicon substrate; forming a silicon oxide film forming a second layer of an interlayer insulating film on the doped oxide film;
Patterning the doped oxide layer and the silicon oxide film to form a contact hole so that the silicon substrate is exposed;
Performing a baking process in an atmosphere of 100 to 550 ° C. to remove moisture contained in the doped oxide film exposed in the contact hole;
Embedding contact material in the contact hole;
A method for manufacturing a semiconductor device comprising: 8. The method of manufacturing a semiconductor device according to claim 7, wherein the doped oxide film is BPSG. 8. The method of manufacturing a semiconductor device according to claim 7, wherein the silicon oxide film is obtained by thermally decomposing TEOS. 8. The manufacturing method according to claim 7, wherein the baking process is performed in an oxygen atmosphere. 8. The manufacturing method according to claim 7, wherein tungsten is embedded as the contact material.

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