JP2001093900A - Method for manufacturing semiconductor device - Google Patents

Abstract

[PROBLEMS] To reduce defects in an epitaxial silicon film formed at a low deposition temperature. The method includes a step of epitaxially growing a silicon film on one main surface of a single crystal silicon substrate and a step of performing a heat treatment in an oxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the epitaxial growth of silicon, and more particularly to a method of manufacturing a semiconductor device for suppressing the occurrence of defects during epitaxial growth.

[0002]

2. Description of the Related Art With the miniaturization of LSI elements, attempts have been made to expand the possibility of LSI structures by epitaxially growing silicon during the manufacturing process. Especially in the case where such an epitaxial growth layer is used as an active region of a transistor,
It is important to realize good crystallinity in the epitaxial silicon layer.

[0003] Conventionally, in epitaxial growth of silicon on a silicon substrate on which devices have not been prepared in advance, growth has been performed at a high temperature of 1000 ° C or higher in order to obtain good crystallinity. This is because the higher the growth temperature, the more easily the silicon atoms attached on the substrate surface migrate, and the more easily the attached atoms are located in a stable position, that is, in a lattice position. Is formed.

However, it is difficult to increase the growth temperature in the epitaxial growth in the middle of the device manufacturing process, which has been required in recent years, as described above. Therefore, a good crystalline epitaxial growth layer can be formed without increasing the temperature. There was a need for a way to achieve it.

[0005]

As described above, in the epitaxial growth in the middle of the device forming process,
It has been desired to realize an epitaxially grown layer having good crystallinity without increasing the deposition temperature. However, when the deposition temperature is lowered, migration is less likely to occur and defects are more likely to occur.

It is an object of the present invention to provide a method of manufacturing a semiconductor device capable of reducing defects in a silicon film formed at a low deposition temperature in epitaxial growth of a silicon film.

[0007]

Means for Solving the Problems [Configuration] The present invention is configured as follows to achieve the above object.

(1) A method of manufacturing a semiconductor device according to the present invention (claim 1) includes a step of epitaxially growing a silicon film on one main surface of a single crystal silicon substrate and a step of performing a heat treatment in an oxidizing atmosphere. It is characterized by including.

Preferred embodiments of the present invention are described below.
The epitaxial growth of the silicon film is also performed on a non-silicon material that is formed and exposed by processing the single crystal silicon substrate. A heat treatment was performed under the same conditions as the heat treatment in the oxidizing atmosphere at the deposition temperature t ° C. in the epitaxial growth of the silicon film, and the dopant concentration was 10 ¹⁹ cm.
^-3 (100) and the thickness t _h nm of the oxide film formed on a monocrystalline silicon substrate, to satisfy the relation _{log (t h) ≧ -1.2 ×} 10 -3 × t + 1.56 .

[0010] The epitaxial growth is non-selective deposition. The epitaxial growth of the silicon film is performed after forming a trench capacitor in the single crystal silicon substrate. The deposition temperature in the epitaxial growth is 1000 ° C. or less. The heat treatment conditions in the oxidizing atmosphere correspond to conditions for forming an oxide film having a thickness of 5 nm or more on a (100) single crystal silicon substrate having a dopant concentration of 10 ¹⁹ cm ⁻³ or less.

[Operation] The present invention has the following operation and effects by the above configuration.

After forming a silicon film having a high concentration of vacancies by performing epitaxial growth, it is heated in an oxidizing atmosphere and supplied with interstitial silicon into the epitaxial growth layer, thereby being bonded to the vacancies and stabilized. Since silicon atoms existing at various positions are formed and vacancies can be prevented from growing as dislocations, dislocations can be suppressed.

[0013]

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

[First Embodiment] The structure shown in FIG. 1 was formed on a silicon substrate 1 having a (100) plane orientation by a known trench capacitor forming method. Note that reference numeral 1
Is a (100) Si substrate, 2 is an oxide film, 3 is polycrystalline silicon, 4 is a color oxide film, and 5 is amorphous silicon.

FIGS. 2 (a) and 2 (b) show photographs of the sample at this time observed by a cross-sectional TEM method. In FIG. 2, a film for processing a cross-sectional TEM sample is formed on the sample shown in FIG.

This sample was treated with a dilute hydrofluoric acid solution to remove the native oxide film on the surface and the oxide film on the main surface of the substrate out of the collar oxide film, and then introduced into an epitaxial growth chamber. After performing a heat treatment at 950 ° C. in a hydrogen atmosphere to remove a thin oxide film from the substrate surface by a reduction treatment, the temperature is lowered in the atmosphere as it is, and the deposition temperature is 700 ° C. and the pressure is 0.3.
An epitaxial silicon layer having a thickness of 2 μm was deposited at Torr using SiH ₄ as a source gas.

FIGS. 3 (a) and 3 (b) show photographs of a cross-sectional TEM image of the sample after the epitaxial growth. As is apparent from FIG. 3, on the region where the single crystal silicon is exposed, the single crystal silicon grows epitaxially, and on the other hand, the polycrystalline silicon formed by crystallization of the amorphous silicon through a thermal process is embedded. It can be seen that polycrystalline silicon is growing on the region that was removed. In addition, it was found that the growth of the single crystal silicon progressed on the boundary surface between the single crystal silicon and the polycrystal silicon so as to ride on the polycrystal silicon, and finally, the entire surface was covered with the single crystal. .
This means that, even in a state other than single-crystal silicon, for example, a base having a structure in which a silicon oxide film, a silicon nitride film, or the like which is a polycrystalline silicon or amorphous insulating film is exposed, it is generally called selective epitaxial growth. In addition to such growth that only a film is formed on a silicon substrate, even when non-selective growth is performed so that silicon grows over the entire surface, growth that covers the entire surface on the underlayer with single crystal silicon is possible. It is shown that.

After the epitaxial growth, the surface irregularities were flattened by a known CMP method, and then heat treatment was performed at 1000 ° C. for 30 minutes in each of nitrogen, hydrogen, and oxygen atmospheres.

FIGS. 4 (a) and 4 (b) show the results in FIG.
FIGS. 6A and 6B show TEM photographs of cross-sectional TEM observation results of samples heat-treated in a hydrogen atmosphere, and FIGS. 6A and 6B.

As shown in FIGS. 4A and 4B, it can be seen that there is no significant difference in the crystal state in the epitaxial growth layer in the heat treatment in a nitrogen atmosphere. on the other hand,
From the observation results of the crystal state in the hydrogen atmosphere shown in FIGS. 5A and 5B, it is observed that the heat treatment in the hydrogen atmosphere results in the generation of higher-density dislocations than immediately after the epitaxial growth. I understand.

When heat treatment is performed on these samples in an oxygen atmosphere, as is clear from FIGS. 6A and 6B, not only no new dislocations occur, but also It can be seen that dislocations in the buried epitaxial growth layer immediately above the polycrystalline silicon have disappeared.

These experimental results indicate that when a silicon film epitaxially grown at a relatively low temperature is applied to a device, it is important to perform an oxidation step after the epitaxial growth.

The following experiment was conducted to clarify the relationship between the low-temperature epitaxial growth of silicon and the subsequent oxidation step. That is, a single crystal silicon substrate was treated with a dilute hydrofluoric acid solution to remove a natural oxide film on the surface, and then introduced into an epitaxial growth chamber. 900 in a hydrogen atmosphere in an epitaxial growth chamber
After a thin oxide film was removed from the substrate surface by performing a heat treatment at a temperature of 70 ° C., the temperature was lowered in the atmosphere as it was, and a 1 μm-thick epitaxial film was formed using SiH ₄ as a source gas at a deposition temperature of 700 ° C. and a pressure of 0.2 Torr. A silicon layer was deposited.

Thereafter, the substrate was once taken out of the chamber, and heat treatment was performed in various chambers in other chambers, assuming a later heating step. Here, oxygen, nitrogen, and hydrogen were used as the heat treatment atmosphere, and heat treatment was performed at 900 ° C. for 30 minutes. The pressure was set at normal pressure (760 Torr) for oxygen and nitrogen, and reduced pressure (380 Torr) for safety in the case of heat treatment in hydrogen.

The sample after the heat treatment was observed with a transmission electron microscope to examine its crystallinity. FIG.
2 shows the observed dislocation densities of the sample that was not heat-treated and the sample that was heat-treated under each condition.

As is clear from FIG. 7, the dislocation density is greatly reduced only when heat treatment is performed in an oxygen atmosphere.
This shows that performing heat treatment in an oxygen atmosphere is effective in lowering the density of dislocations. The fact that the dislocation density decreased by the heat treatment in the oxygen atmosphere and increased by the heat treatment in the hydrogen atmosphere in this way was attributed to the dislocations present in the silicon layer epitaxially grown in this experiment due to the oxidation process. Suggests that it will disappear.

It is generally known that in the oxidation step, interstitial silicon is introduced into the substrate. If vacancies are present at a high concentration in the substrate, such interstitial silicon combines with the vacancies to form silicon atoms present at stable positions. In other words, the results of this experiment show that vacancies exist at a high concentration in the epitaxial layer grown at low temperature, and that the vacancies can prevent the vacancies from growing as dislocations by performing the oxidation process. Is shown.

In the heat treatment in the oxygen atmosphere, it is considered that there is a condition necessary to reduce dislocations. Therefore, an experiment was conducted using temperature and time as parameters, and the dislocation density was similarly measured for each sample. did. As a result, as shown in FIG. 8, the conditions necessary for reducing the dislocation density differ depending on the temperature and time.

However, the results were summarized as a relationship between the dislocation density and the oxide film thickness formed on the single crystal substrate by the heat treatment in the oxygen atmosphere under each condition.
As shown in FIG. 9, it became clear that the curves were on the same curve regardless of the heat treatment temperature. Here, the horizontal axis represents the dopant concentration of 10 ¹⁹ cm by the heat treatment in oxygen.
An oxide film thickness formed on a (100) silicon substrate of ^-3 or less. As described above, the result that the amount of oxidation required to reduce the dislocation density depends only on the formed oxide film thickness without depending on the oxidation temperature was obtained. Suggests that it is due to interstitial silicon supplied into the substrate. The amount of interstitial silicon supplied into the substrate in the oxidation process is
This is because it is clear that the thickness is proportional to the thickness of the formed oxide film. It is considered that the interstitial silicon supplied into the substrate was combined with the vacancies remaining in the substrate, so that the dislocation density could be reduced.

Here, the dopant concentration is set to 10 ¹⁹ cm ^−3.
This is because the oxide film thickness formed in this concentration range hardly depends on the oxidation conditions. This indicates that what has the effect of reducing dislocations is the oxidation process itself. As is clear from FIG. 9, if the oxidation condition is such that the oxide film thickness to be formed becomes 5 nm or more, the dislocations are reduced. It was found to be effective in reducing the amount. The degree of the effect of reducing dislocations by oxidation is as follows.
Naturally, it is considered that the value changes depending on the amount of vacancies in the original epitaxial growth layer.

Thus, an experiment was conducted to examine the amount of oxidation required to reduce dislocations on some samples using the temperature during epitaxial growth as a parameter. FIG.
Shows the results. FIG. 10 shows that the dislocation density with respect to the epitaxial growth temperature t [° C.] is the lower limit of measurement, 10 ⁻⁸ c.
It is a figure which shows the oxidation amount required in order to reduce to m- ² or less. Note that in FIG. 10, when an oxidation step necessary to reduce the dislocation density to the measurement lower limit or less is performed, (100)
The vertical axis indicates the oxide film thickness (nm) formed on the Si substrate.

As shown in FIG. 10, when the epitaxial growth temperature t was high, that is, when the temperature was about 1050 ° C. or higher, defects such as dislocations were below the detection limit without performing the oxidation step. On the other hand, when the epitaxial growth temperature t is 1000 ° C. or less, the effectiveness of the oxidation step appears. Until the epitaxial growth temperature in the experiment reaches 550 ° C., the lower the temperature, the more the oxidation amount required to sufficiently reduce dislocations. It turned out that there were many. Straight 10, log (t _h) = - is represented by ^{1.2 × 10 -3 × t + 1.56} (1).

[0033] Thus, equation (1) so that the value of the left side is the right side of the value or more, that inequality _{log (t h) ≧ -1.2 ×} 10 -3 × t + 1.56 (2) so as to satisfy the if chosen the deposition temperature t and oxidized film thickness t _h it is said that the dislocation of the epitaxial layer grown at low temperature by the present invention can be effectively reduced.

This result is considered to be because the higher the epitaxial growth temperature, the easier the silicon atoms attached to the substrate surface to move around freely, and the point defects such as vacancies do not remain in the deposited layer. On the other hand, when the epitaxial growth temperature is lowered, silicon atoms become difficult to move, and defects are likely to remain in the deposited layer. As a defect at this time, it is considered that although the attached atoms are accommodated in lattice positions, silicon atoms are not necessarily completely contained in all lattice positions, and consequently, vacancies remain as a result. This state is schematically shown in FIG.

The oxidation may be carried out in an oxidizing atmosphere, such as NO gas or N ₂ O gas, instead of oxygen, or may be diluted with nitrogen, argon or the like.
In addition, the epitaxial growth of silicon is not limited to simple silicon, and even if silicon containing arsenic, phosphorus, boron, or a material containing germanium or carbon, that is, SiGe, SiC, or SiGeC,
Further, it may contain the above impurities, that is, arsenic, phosphorus, and boron.

In the above embodiment, the case of so-called vapor phase epitaxial growth in which the deposited film is already crystallized at the time of depositing the silicon film has been described. However, when the silicon film is deposited, the deposited film is in an amorphous state. The effectiveness of the present invention has been confirmed also in so-called solid phase epitaxial growth in which single crystallization is performed by the heat step.

Using disilane (Si ₂ H ₆ ) as a source gas, an amorphous silicon film was deposited to a thickness of 500 nm on a silicon substrate at 480 ° C., and the amorphous silicon was subjected to solid-phase epitaxial growth by heat treatment at 650 ° C. for 30 minutes in a nitrogen atmosphere. . Although the deposited film was almost single-crystallized by this heat treatment, it was confirmed that dislocations remained in the film.
This dislocation did not disappear even when heat treatment was further performed in nitrogen or hydrogen.
When heat treatment was performed at 0 ° C. for 30 minutes, it was found that the temperature was reduced to an undetectable level.

This means that even when a single-crystal silicon layer is formed by solid-phase epitaxial growth, a high concentration of vacancies exists in the film immediately after deposition and immediately after crystallization, and these vacancies are supplied in the oxidation step. It shows that it is important to compensate by the interstitial silicon.

In the above embodiment, the oxidation step is performed in a chamber different from the epitaxial growth step. However, the epitaxial growth step and the oxidation step are continuously performed in the same furnace or in a so-called load lock system. It may be performed in different chambers connected to each other, which can be transported without taking the sample into the atmosphere. With this method, the steps can be shortened. After the epitaxial growth or after the oxidation step, heat treatment in a hydrogen atmosphere may be performed again. By the heat treatment in the hydrogen atmosphere, the surface of the substrate can be flattened.

It should be noted that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications without departing from the gist thereof.

[0041]

As described above, according to the present invention, after a silicon film is epitaxially grown and then heated in an oxidizing atmosphere, silicon atoms which are bonded to vacancies and exist at a stable position are obtained. Once formed, the vacancies can be prevented from growing as dislocations, so that dislocations can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional TEM photograph of the sample shown in FIG. 1 observed by a cross-sectional TEM method.

FIG. 3 is a cross-sectional photograph observed by a cross-sectional TEM method after performing epitaxial growth on the sample shown in FIG. 2;

4 is a cross-sectional photograph observed by a cross-sectional TEM method after annealing the sample shown in FIG. 3 in a nitrogen atmosphere.

5 is a cross-sectional photograph observed by a cross-sectional TEM method after annealing the sample shown in FIG. 3 in a hydrogen atmosphere.

6 is a cross-sectional photograph observed by a cross-sectional TEM method after annealing the sample shown in FIG. 3 in an oxygen atmosphere.

FIG. 7 is a graph showing the dependence of the dislocation density in an epitaxial growth layer on the heat treatment atmosphere.

FIG. 8 is a graph showing the dependence of dislocation density in an epitaxial growth layer on oxidation temperature and time.

FIG. 9 is a graph showing the dependence of the dislocation density in an epitaxial growth layer on the amount of oxidation.

FIG. 10 is a diagram showing the dependency of the dislocation density in the epitaxial growth layer on the epitaxial growth temperature.

FIG. 11 is a schematic view showing that interstitial silicon is supplied into a substrate by heat treatment in an oxidizing atmosphere, and dislocations are less likely to be formed due to bonding with vacancies.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... (100) Si substrate 2 ... Oxide film 3 ... Polycrystalline silicon 4 ... Color oxide film 5 ... Amorphous silicon

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F045 AB02 AC01 AC11 AD11 AE21 AF03 BB07 BB12 DA61 DA67 DB03 HA06 HA16 HA23 5F058 BA20 BC02 BF29 BF55 BF62 BJ01 BJ06

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device, comprising: a step of epitaxially growing a silicon film on one main surface of a single crystal silicon substrate; and a step of performing a heat treatment in an oxidizing atmosphere. A step of forming a material other than single-crystal silicon exposed on a part of the single-crystal silicon substrate; a step of epitaxially growing a silicon film on one principal surface of the single-crystal silicon substrate; Performing a heat treatment in an atmosphere. 3. A deposition temperature t ° C. in the epitaxial growth of the silicon film, the heat treatment in the heat treatment under the same conditions in the oxidizing atmosphere, the dopant concentration is 10 ¹⁹ cm ^-3 or less of (100) single crystal silicon substrate thickness t _h n of the oxide film formed went against
and m is, log (t _h) The method of manufacturing a semiconductor device according to claim 1 or 2, characterized by satisfying the relation of ^{≧ -1.2 × 10 -3 × t +} 1.56.