JP2000340551A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve characteristics of a doped oxide film at etching treatment without deteriorating them by etching the doped oxide film to form a patterned hard mask and subjecting the hard mask to baking, and then etching a substrate to form a recessed section. SOLUTION: A BSG film 2, which is a doped oxide film, is etched with a patterned resist 3' as a mask for obtaining a patterned hard mask. Next, the resist is removed, and then the patterned BSG film 2' is baked. For the baking treatment, oxygen gas is supplied, and the treatment is conducted, for example, for 300 sec. with the temperature of a plate to mount a wafer at, for example, 250 deg.C. The water content in the BSG film 2' is removed by the baking treatment. Thereafter, a silicon substrate 1 is etched with the baked BSG film 2' as a hard mask to form a deep trench.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a trench.

[0002]

2. Description of the Related Art A trench capacitor is used in a semiconductor memory device or the like in order to obtain a large capacitance in a small area, and therefore a deep trench must be formed.

[0003] Such a deep trench is usually formed by an etching step, and a conventional TEOS (tetraethyloxy) is used as a hard mask in this etching.
low-pressure CVD si1ane, Si a _{(0C 2 H} 5) 4)
CVD SiO obtained by decomposition by (LP-CVD) method
Two films are frequently used.

However, this film has a problem that it is difficult to remove the film with good uniformity when the film is peeled off by dry etching or the like after the trench is formed. For this reason, CVD
After the dry etching for removing the SiO ₂ film is performed, a step is formed on the silicon oxide film, and there is a problem that the step affects a subsequent process. In the case of TEOS, CVD is performed immediately after etching for forming a trench.
There is also a problem that the SiO ₂ film cannot be removed.

On the other hand, BSG as such materials that have been treated like CVD-SiO ₂ based dielectric materials, BPS
There are doped oxides such as G and PSG. These B
SG, BPSG, and PSG have the advantage that the etching rate during wet etching is higher than that of a TEOS film, for example, and when used as a hard mask, they can be easily peeled off when they are no longer needed.

FIG. 13 is a sectional view showing a process in the case where a trench is formed by using BSG as a doped oxide.

First, a BS is placed on a silicon semiconductor substrate 11.
The G film 12 is formed by a CVD method or the like. Furthermore this BS
A resist 13 is applied on the G film by spin coating or the like (FIG. 13A).

Next, exposure and development are performed using an exposure mask corresponding to a desired pattern to pattern the resist 13 (FIG. 13B).

Next, the patterned resist 1
The BSG film 12 is etched using 3 'as an etching mask (FIG. 13C).

Subsequently, the resist 13 'is stripped, and the silicon 11 is etched using the etched BSG film 12' as a hard mask to form a deep trench (FIG. 1).
3 (d)).

After the formation of the trench, the BSG film 12 'is removed.

[0012]

SUMMARY OF THE INVENTION However, BS
When a doped oxide such as G, BPSG, PSG or the like is used as a hard mask material, there is a problem that a change in an etching shape is more likely to occur as compared with a case where another CVD SiO ₂ film is used as a hard mask material.

This is because BSG, BPSG, and PSG have a property of easily absorbing moisture, so that when the etching process is performed, the moisture contained in the BSG, BPSG, and PSG films enters the chamber atmosphere during the process. It is considered that the etching characteristics are changed by this effect.

The amount of moisture absorbed by the BSG, BPSG, and PSG depends on the atmosphere in which the sample is left.
It is unavoidable that the processing characteristics are delicately changed and varied due to a difference in the state of being left.

[0015] Therefore, in the case of using BSG, BPSG, the PSG film has a problem that changes forced the etching conditions for the case of Si0 ₂ film.

The present invention has been made to solve such a problem, and aims to improve the characteristics at the time of an etching process without impairing the intrinsic characteristics of a doped oxide film such as BSG, BPSG, and PSG. It is an object of the present invention to provide a method for manufacturing a semiconductor device capable of performing such a method.

[0017]

A method of manufacturing a semiconductor device according to the present invention comprises the steps of forming a doped oxide film as a hard mask material on a silicon substrate to be etched, and forming a resist on the doped oxide film. Applying a resist, patterning the resist, etching the doped oxide film using the patterned resist as an etching mask to obtain a patterned hard mask, removing the resist, and baking. Performing a treatment to remove moisture contained in the doped oxide film; and etching the substrate using the patterned hard mask to form a concave portion. is there.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming a doped oxide film as a hard mask material on a silicon substrate to be etched; and forming a protective cap layer on the doped oxide layer. Forming a, a step of applying a resist on the protective cap layer, patterning the resist,
Using the patterned resist as an etching mask, etching the protective cap layer and the doped oxide film to obtain a patterned hard mask; removing the resist; and performing a bake process to perform the doped oxide. A step of removing moisture contained in the film; and a step of etching the substrate using the patterned hard mask to form a concave portion.

As described above, according to the present invention, since the baking treatment is performed after the patterning of the doped oxide film, the moisture is removed from the highly hygroscopic doped oxide film, and the characteristics do not deteriorate during etching. .

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing steps of a process for forming a deep trench according to the present invention.

The samples used here are a thermal oxide film (8 nm), a SiN film (200 nm) on a silicon substrate 1,
BSG (700 nm) is formed. However,
In FIG. 1, the thermal oxide film and the SiN film are omitted.

First, the silicon semiconductor substrate 1 is thermally oxidized in an oxidizing atmosphere to form a thermal oxide film on the surface thereof.
It is formed with a thickness of nm. 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 spin coating or the like (FIG. 1A).

Next, exposure and development are performed using an exposure mask corresponding to a desired pattern to pattern the resist (FIG. 1B).

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. 1).
(C)).

Subsequently, the resist is stripped, and a baking process is performed on the patterned BSG film 2 '(FIG. 1).
(D)). As this baking treatment, O ₂ gas is supplied at a flow rate of 3
The flow was performed at a flow rate of 00 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 processing was performed for 300 seconds. By this baking process, the water 4 contained in the BSG film 2 'is removed.

Then, the silicon substrate 1 is etched using the BSG film 2 'after the baking as a hard mask to form a deep trench (FIG. 1E). This BS
The G film is removed after the formation of the trench.

As described above, it is a feature of the present invention that the baking treatment is performed after the etching of the BSG film.

This baking temperature was determined as follows.

In the case without the upper graph of baking 2, in an atmosphere lower graph of Figure 2 is flushed with N ₂ gas, 250
It is a graph which shows the analysis result of the desorbed gas at the time of raising temperature both in the case where baking processing was performed on the BSG film at 5 degreeC for 5 minutes. The gas of interest here is m / z
= 18.

From this graph, it can be seen that by performing the 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.

Thus, the water release from BSG is 10
Therefore, the baking of BSG satisfies the conditions of not causing oxidation of each material, not deteriorating BSG, and being higher than the temperature at the time of etching. It can be seen that it is effective to perform the process at as high a temperature as possible.

Next, effects of the present invention will be described.

FIGS. 4 to 8 are graphs showing the results of experiments performed on the BSG film after etching and after the BSG film was etched. In each graph, for each item date, the case where the mask material at the time of etching is BSG and the case where TEOS is used are compared. As described below, a remarkable improvement in etching characteristics was observed by applying the present invention. In each drawing, data is taken at the center of the wafer, at a position 10 mm from the edge of the wafer, and at a position 25 mm from the edge of the wafer.

FIG. 3 is a diagram for explaining the contents of each dimension item date 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 the obtained items.

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, and the DT bottom diameter shown in FIG.
The diameter at μm, the selectivity shown in FIG. 6 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 top of the trench, and the lower taper shown in FIG. The taper is the slope angle at the bottom of the trench.

From these graphs, it is found that there is no difference in the etching characteristics between the case where the TEOS film is subjected to the baking and the case where the baking is not carried out. The etching characteristics differed when not performed, and when the baking was performed, the characteristics were equivalent to those of the TEOS film. On the other hand, when the baking was not performed, the characteristics deteriorated in several days. It turns out that there is.

That is, in the graph showing the DT bottom diameter (FIG. 5), the selectivity (FIG. 6), and the lower taper angle (FIG. 8), the value is small only when there is no backing with BSG. These causes are considered as follows. At the time of etching, the BSG film, which is a mask material, is slightly removed. At this time, moisture contained in the BSG is released from the BSG film into the chamber atmosphere.

Further, since the wafer surface temperature rises to about 150 ° C. by exposing the wafer to electric discharge, the water in the BSG film is also released to the chamber atmosphere.

As the water is released into the chamber atmosphere in this manner, oxygen is supplied from the water molecules. Therefore, the release of moisture from the BSG film has the same effect as when oxygen is added to the etching gas.

The control of the taper angle of the etching shape of the trench is usually controlled by increasing or decreasing the amount of oxygen to be added. This is due to the mechanism by which the tapered shape is formed. That is, S is mainly used as a reaction product during etching.
iBr ₄ results. At this time, when oxygen is added, SiBr ₄ generated as a reaction product is combined with oxygen to form SiB 4.
r _x O _y (x and y are arbitrary numbers). SiBr _x
O _y is lower vapor pressure than SiBr, it is deposited on the wafer surface during etching. As a result, the deposit is deposited on the trench side walls, and the etched shape is tapered.

[0042] Here, when'll increase the amount of oxygen added during the etching, also increases the rate of SiBr ₄ is bonded to oxygen, the amount of SiBr _x O _y increases. As a result,
Deposition on the trench sidewall during etching also increases, resulting in a more tapered angled shape.

For the above reasons, when oxygen is added to the etching gas, the shape becomes such that the taper angle becomes gentler as the amount of oxygen added increases.

Next, the case where water (H ₂ O) is added will be considered. In this case, the water contains oxygen atoms and S
When iBr ₄ is present, as in the case where oxygen is added,
SiBr ₄ is oxidized to generate SiBr _x O _y .

As a result, when water is added, the same effect as in the case where oxygen is added is produced, and the etching shape becomes a more gentle etching shape.

When baking was not performed on the BSG, a relatively large amount of water was present in the BSG.
When the BSG itself is etched, the moisture contained therein is released with the etching. As a result, the water concentration in the etching gas atmosphere is relatively increased, and the same effect as when oxygen or water is added occurs. In this manner, the etched shape has a tapered shape, and the diameter at the trench bottom is reduced.

In the above description, it has been explained that a large amount of SiBr _x O _y is generated due to the release of moisture from BSG, and the amount of deposition increases, so that the etched shape has a tapered shape.

In the following description, a case will be described in which the etched shape has a tapered shape, and etching is further performed on a thinned shape at the trench bottom.
In this case, a different phenomenon occurs.

That is, although the etching reaction occurs at the bottom of the trench, the reaction area decreases when the diameter of the bottom of the trench becomes small and small. Therefore, the amount of SiBr ₄ generated by the etching reaction decreases as compared with the case where the trench diameter is large.

[0050] At this stage, the amount of SiBr ₄ itself to be under SiBr _x O _y is reduced, the effect of the amount of deposits is reduced occurs. Deposition on the wafer surface
It also had the effect of preventing the mask material BSG from being etched and collapsing, but this effect was weakened by the decrease in deposition, resulting in an increase in the amount of collapse of the mask material BSG. Becomes

According to the results of this experiment, when trench etching is performed to the end, the effect of increasing the deposition due to an increase in moisture and forming a tapered shape appears at the beginning of the etching, and the amount of reaction products generated decreases in the latter half of the etching. Has reduced the deposition and consequently the BSG of the mask
The effect of increasing the amount of collapse has appeared.

For the other etching characteristics, trench depth (FIG. 4) and upper taper (FIG. 7), BSG
Even when using, the TEOS
It can be seen that there is no difference between the etching characteristics and the etching characteristics in the case of using. Note that NH ₄ F + HF +
The etching rate of the BSG film by H 2 ₀ processing, be higher etch rates of comparable if not subjected to base one click is maintained has been confirmed. In this regard, as described above, TEOS has a problem that peeling after formation of the trench is difficult.

As described above, by performing the baking process on the BSG film, the case where the baking process is not performed is improved.
It has been confirmed that the etching characteristics can be improved and a high etching rate at the time of chemical treatment, which is a feature of the BSG film, can be maintained.

In the case of the TEOS film as a comparative example, since there is no difference in the etching characteristics due to the difference in the presence or absence of the base, the etching characteristics change because of the BSG film. This means that the above-mentioned BS
This proves that the G film is generated due to the property of easily absorbing moisture.

In the above-mentioned embodiment, the case where the BSG film is used as the hard mask material has been described, but BPSG and PS which are doped oxides having high hygroscopicity like BSG are used.
In the case of G, it has been confirmed that the effect of the background is observed. This also applies to BPSG and PSG.
This is considered to be due to high hygroscopicity as in BSG.

Further, the effect of the present invention is that it is daily to desorb moisture absorbed by BSG.
The time from the backing of the BSG film to the etching is important. In one experiment, it was found that the etching characteristics were not affected if the treatment was performed within 13 days after the baking. Since it is conceivable that the temperature changes greatly, it is not possible to uniquely determine the leaving time after the baking. It is necessary to confirm the environmental conditions and film quality and to conduct an experiment to determine the allowable leaving time.

In the above embodiment, the case where a deep trench is formed has been described.
The present invention can be applied to other processes including processing such as G and PSG.

Further, for example, the present invention can be applied to a case where BSG is used as a hard mask material at the time of etching a shallow trench.

FIGS. 9A to 9C and FIG. 10A
4B is a sectional view illustrating a step in a case where element isolation is performed using a shallow trench; FIG.

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, a BSG film 24, and a non-doped TEOS film 25 are deposited. A laminated film having a thickness of 20 nm is formed, a resist 26 is applied thereon (FIG. 9A), and the applied resist 26 is patterned (FIG. 9B). This patterned resist
Non-doped TEOS film 25, BS using 26 'as a mask
The G film 24, the silicon nitride film 23, and the thermal oxide film 22 are etched (FIG. 9C). Thereafter, the resist on the wafer surface was peeled off by discharging in an oxygen atmosphere, and FIG.
The state of (a) is obtained. Using the patterned non-doped TEOS film 25 'and BSG film 24' as a mask, the silicon substrate is etched to form a shallow trench 26 (FIG. 10B).

FIG. 11 is a graph showing the result of comparing the STI taper angle between the case where BSG was baked before the silicon etching for forming a shallow trench and the case where BSG was not baked.

The etching of silicon is performed by Cl ₂ / O
_This was performed using _two gases. Etching condition is pressure 40m
Torr, RF power 500 W, gas flow rate Cl ₂ = 10
0 sccm and O ₂ = 20 sccm.

As is clear from FIG. 11, the tape baked after silicon etching has a taper angle of 86 °, while the tape baked without silicon has a taper angle of 8 °.
It is about 2 °.

[0064] This low SiCl _x O _y next reaction SiCl ₄ generated as a product of binding to the vapor pressure and O of etching reaction in the etching, contrast is deposited to form the tapered etching shape, baked If the process was not performed, moisture in the BSG was generated during the etching of the silicon, and the same effect as when excess oxygen was supplied was obtained, so that the taper angle became steeper.

The present embodiment is different from the first embodiment in that a non-doped TEOS is formed on the surface of BSG. However, after the BSG processing, the BSG surface is exposed, and the BSG in this portion absorbs moisture.

Thus, when baking is performed on the BSG, the water in the BSG is removed, but when the baking is not performed, the etching is performed while the water in the BSG remains. It is considered that the etching characteristics were affected.

As described above, even if another film is present on the BSG surface, if the step of exposing the BSG surface is included, it is possible to obtain the effect of baking the BSG.

In general, BSG, BPS to prevent moisture absorption
Thin non-doped CVD SiO on the surface of G, PSG film
It is also possible to deposit a thin film such as _two films, but the surface or cross section is processed by BSG, BPSG,
When PSG is exposed, moisture absorption occurs from that part,
Since the etching characteristics also change, performing the baking improves the etching characteristics.

Next, a case where BPSG is used as a part of the interlayer insulating film will be described.

FIGS. 12 (a) and 12 (b) are cross-sectional views showing steps in such an embodiment.
1, a BPSG film 32 and a TEOS film 33 are sequentially laminated, and TEOS and BP are formed using a resist (not shown) in which a pattern corresponding to a contact hole is formed.
When the SG film is etched, the side surface of the BPSG film 32 is exposed (FIG. 12A). 25 in this state
A baking process is performed on the BPSG film at a temperature of 0 ° C., and then tungsten 34 which is a metal to be a contact wiring material is buried in the contact hole (FIG.
(B)).

As a result of evaluating the reliability of the contact wiring formed as described above, it was found that the reliability of the wiring was improved when baking was performed before embedding the wiring material as compared with the case where the baking was not performed. It could be confirmed.

This is because when baking is not performed, B
It is considered that the buried tungsten did not function as a wiring material because the water contained in the PSG gradually diffused and reacted with tungsten as a wiring material to generate tungsten oxide.

On the other hand, when the baking treatment is performed before the wiring material is embedded, since the moisture in the BPSG has been removed, there is no diffusion of the moisture from the BPSG even in the subsequent test. It is considered that the reliability of the wiring was maintained.

As described above, when another film is formed on the surface but BSG, BPSG, and PSG are exposed,
Even if there is no exposure, it can be used to prevent moisture absorption.
Since the effect of the thin film deposited on the surface of G, BPSG, or PSG may be insufficient, the baking treatment of the present invention is effective.

The conditions of the base are not limited to the conditions described in the above embodiment, but may be other gases, mixed gas, processing temperature, processing time, processing pressure, etc. within a range not departing from the gist of the present invention. Can be changed.

As described above, according to the present invention, by performing the baking process on the BSG, BPSG, and PSG films before the processing such as the etching, it is possible to suppress the shape change at the time of etching due to moisture absorption. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a graph showing the selection of a bake 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 applying the present invention.

FIG. 4 is a graph showing the effect of backing on trench depth.

FIG. 5 is a graph showing the effect of backing on the bottom diameter of a trench.

FIG. 6 is a graph showing the effect 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 effect of bake on the lower taper of the trench.

FIG. 9 is a sectional view showing the first half of the step of forming an element isolation by a shallow trench.

FIG. 10 is a sectional view showing the latter half of the step of forming element isolation by a shallow trench.

FIG. 11 is a graph showing the result of comparing the STI taper angle between the case where BSG was baked before silicon etching for forming a shallow trench and the case where BSG was not baked.

FIG. 12 is a cross-sectional view for each process in the case where BPSG is used as a part of an interlayer insulating film.

FIG. 13 is a cross-sectional view showing a step of forming a trench using a conventional BSG film as a hard mask.

[Description of Signs] 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)

[Claims] A step of forming a doped oxide film as a hard mask material on a silicon substrate to be etched; a step of applying a resist on the doped oxide film; and a step of patterning the resist. Using the exposed resist as an etching mask, etching the doped oxide film to obtain a patterned hard mask; removing the resist; and performing bake treatment to remove moisture contained in the doped oxide film. And forming a concave portion by etching the substrate using the patterned hard mask. 2. A step of forming a doped oxide film as a hard mask material on a silicon substrate to be etched; a step of forming a protective cap layer on the doped oxide layer; Applying a resist, patterning the resist, etching the protective cap layer and the doped oxide film using the patterned resist as an etching mask to obtain a patterned hard mask, A step of removing the moisture contained in the doped oxide film by performing a baking process; and a step of forming a recess by etching the substrate using the patterned hard mask. Device manufacturing method. 3. The method according to claim 1, wherein said protective cap layer is non-doped TEOS.
3. The method according to claim 2, wherein the semiconductor device is a layer. 4. The method according to claim 1, wherein the recess is a trench. 5. The doped oxide is BSG or B
3. The method according to claim 1, wherein the semiconductor device is a PSG. 6. The method according to claim 1, wherein the baking process is performed in an oxygen atmosphere. 7. A step of forming a doped oxide film as a first layer of an interlayer insulating film on a silicon substrate, and forming a silicon oxide film as a second layer of an interlayer insulating film on the doped oxide film. Performing a step of patterning the doped oxide layer and the silicon oxide film to form a contact hole so that the silicon substrate is exposed; and performing a bake treatment to expose the doped oxide in the contact hole. A method for manufacturing a semiconductor device, comprising: a step of removing moisture contained in a film; and a step of embedding a contact material in a contact hole. 8. The method according to claim 7, wherein the doped oxide film is BPSG. 9. The method according to claim 7, wherein said silicon oxide film is obtained by thermally decomposing TEOS. 10. The method according to claim 7, wherein said baking treatment is performed in an oxygen atmosphere. 11. The method according to claim 7, wherein tungsten is buried as said contact material.