JP2005231909A - Method for vapor growth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for vapor growth which is capable of growing well-reproductively an epitaxial layer of a compound semiconductor such as InGaAsP on a semiconductor substrate such as InP in a desired element composition and of manufacturing stably a semiconductor element with a definite PL wavelength. <P>SOLUTION: The method for vapor growth of growing the epitaxial layer on a semiconductor substrate comprises growing the epitaxial layer by measuring previously the concentration of a carrier of the semiconductor substrate at a room temperature and then by controlling a set temperature of the substrate responding to the carrier concentration at the room temperature so that a real surface temperature of the substrate may become a desired temperature regardless of the carrier concentration of the semiconductor substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vapor phase growth method for growing an epitaxial layer on a semiconductor substrate, and more particularly to a technique for growing an epitaxial layer made of a compound semiconductor with a desired composition to improve the peak wavelength of photoluminescence.

Conventionally, for the use of a semiconductor element for an optical device, an epitaxial layer made of a compound semiconductor such as an InGaAs layer, an AlGaAs layer, an AlInAs layer, an AlInGaAs layer, or an InGaAsP layer is formed on an InP substrate by metal organic chemical vapor deposition (MOCVD method). Semiconductor devices grown by the above are widely used. Among these, In _1-x Ga _x As _y P _1-y can be lattice-matched with the InP substrate relatively easily, and can be said to be suitable for obtaining a semiconductor element having excellent element characteristics.

  On the other hand, for use in applications such as semiconductor lasers, it is desirable that the peak wavelength of photoluminescence (hereinafter abbreviated as PL peak wavelength) is constant, but the quaternary compound semiconductors such as InGaAsP described above, InGaAs, AlGaAs In a ternary compound semiconductor such as AlInAs, the PL peak wavelength tends to fluctuate depending on the composition of the constituent elements. Therefore, it is extremely important to grow it while controlling the composition of the constituent elements to be constant.

As a technique for growing a thin film having a uniform composition, for example, the present inventors have proposed a vapor phase growth method in which the surface temperature of at least a part of a substrate holder on which a substrate is placed is controlled to be equal to or higher than the decomposition temperature of the source gas. (Patent Document 1).
JP 2001-220288 A

  However, when an epitaxial layer made of a compound semiconductor such as an InGaAs layer, an AlGaAs layer, an AlInAs layer, or an AlInGaAs layer is grown on an InP substrate by a conventional vapor phase growth method such as the prior application technique, the growth temperature ( In spite of performing vapor phase growth under the same growth conditions including the set temperature of the substrate, a problem has arisen in that the PL peak wavelength of the obtained semiconductor element varies. This was thought to be due to the change in the elemental composition of the epitaxial layer grown on the substrate depending on the substrate used. Further, from the relationship between stability and controllability of the conventional vapor phase growth apparatus, it has been considered that the element composition of the grown epitaxial layer changes because the growth conditions vary slightly with each growth.

  However, in recent years, the controllability of the vapor phase growth apparatus has been greatly improved, and it has become possible to minimize the variation in growth conditions caused by the apparatus. It was found that the composition changes in a direction determined by the substrate even when the vapor phase growth apparatus is used.

  The present invention has been made to solve the above-mentioned problems. An epitaxial layer made of a compound semiconductor such as InGaAsP is grown on a semiconductor substrate such as InP with a desired element composition with good reproducibility. An object of the present invention is to provide a vapor phase growth method capable of stably manufacturing a semiconductor device having the same.

The process for completing the present invention will be briefly described below.
First, the inventors epitaxially grown In _{1 -x} Ga _x As _y P _{1 -y} layers on various types of InP substrates by metal organic vapor phase epitaxy. Specifically, InP substrates having different carrier concentrations were prepared by doping Fe, S, and Zn, and an InGaAsP layer was epitaxially grown on the substrate. And the photoluminescence characteristic was measured about the obtained semiconductor element. The result is shown in FIG. FIG. 2 shows the relationship between the carrier concentration of the InP substrate and the PL peak wavelength. In FIG. 2, □ marks are measurement results for epitaxial growth of InGaAsP using an Fe-doped InP substrate, ◯ marks are S-doped InP substrates, and △ marks are Zn-doped InP substrates (FIGS. 3 to 3). 5 is the same). FIG. 2 reveals that the PL peak wavelength varies depending on the carrier concentration of the substrate used, and this causes a change in the composition of the In _{1 -x 1} Ga _x As _y P _{1 -y} layer defined by the PL peak wavelength. It became clear that.

Next, in order to investigate this cause, after introducing various substrates into the growth furnace, an InP substrate was heated at the same set temperature, and an experiment was conducted in which the surface temperature of the substrate was directly measured with a pyrometer. As a result, when an S-doped InP substrate was used (carrier concentration 3 × 10 ¹⁷ to 8 × 10 ¹⁸ cm ⁻³ ), the surface temperature of the substrate was highest depending on the carrier concentration of the substrate, although the set temperature was the same. It turned out that it changes about 5 degreeC. Moreover, the result that surface temperature became low, so that carrier concentration was high was obtained.

Subsequently, an InGaAsP layer was grown on the InP substrate under growth conditions in which the set temperature of the substrate was intentionally changed in order to grasp the influence of the change in the surface temperature of the substrate on the epitaxial layer. Specifically, the InGaAsP layer was grown by changing the substrate temperature in the range of about 640 to 660 ° C. and 20 ° C. At this time, the substrate used was S-doped InP and the carrier concentration was constant at 3 × 10 ¹⁸ cm ⁻³ . And PL peak wavelength was measured about the obtained semiconductor element. FIG. 3 shows the substrate temperature dependence characteristics of the PL peak wavelength of the obtained semiconductor element. FIG. 3 shows that the PL peak wavelength becomes shorter as the substrate temperature becomes higher.

  From the above, it can be seen that if the carrier concentration of the substrate is high, the surface temperature of the substrate is low even at the same set temperature, and as a result, the PL peak wavelength becomes long. It became clear that there was a good correlation between them.

Further, the Ga composition X and As composition Y of the In _1-x Ga _x As _y P _1-y layer are calculated from the PL peak wavelength and lattice mismatch data, the composition of the InGaAsP layer, the carrier concentration of the InP substrate to be grown, and The relationship with the surface temperature of the InP substrate was examined. FIG. 4 shows the relationship between the carrier concentration of the InP substrate and the composition of the InGaAsP layer, and FIG. 5 shows the relationship between the surface temperature of the S-doped InP substrate and the composition of the InGaAsP layer. 4 and 5, the variation of the Ga composition X is relatively small, and the variation of the As composition Y is large. From this, even if the set temperature of the substrate when growing the InGaAsP layer is the same, the surface temperature of the substrate changes depending on the carrier concentration of the InP substrate, and as a result, the composition of As (or P) mainly changes. As a result, it was found that the PL peak wavelength was changed.

  Further, since the surface temperature of the substrate changes depending on the substrate thickness and the heating method, the surface temperature was measured for each type of substrate and carrier concentration.

  Based on the above research results, when epitaxially growing InGaAsP or the like on an InP substrate, if the set temperature is adjusted according to the carrier concentration of the substrate, the actual surface temperature of the substrate becomes constant. The present invention has been completed by obtaining the knowledge that the composition of the constituent elements can be made constant.

  That is, according to the present invention, in the vapor phase growth method for growing an epitaxial layer on a semiconductor substrate, the carrier concentration at room temperature of the semiconductor substrate is measured in advance, and the actual surface temperature of the substrate is desired regardless of the carrier concentration of the semiconductor substrate. The epitaxial layer is grown by controlling the set temperature of the substrate in accordance with the carrier concentration at the room temperature so that the temperature of the epitaxial layer grows. Also, since the surface temperature of the substrate varies depending on the substrate thickness and heating method (vapor phase growth apparatus used), the relationship between the set temperature for the carrier concentration of the semiconductor substrate and the actual substrate surface temperature should be grasped for each. If this is done, it is easy to set the temperature to bring the surface temperature of the substrate to a desired temperature.

The semiconductor substrate may be a compound semiconductor such as InP. In the case of an InP substrate, the epitaxial layer to be grown may be InGaAs, AlGaAs, AlInAs, AlInGaAs, InGaAsP or the like that can be lattice-matched relatively well with InP.
In the above-described vapor phase growth, a metal organic vapor phase growth method can be used.

  According to the present invention, in the process of vapor-phase growth of an epitaxial layer made of a compound semiconductor such as an InGaAsP layer on a semiconductor substrate such as InP, the substrate temperature is changed due to the carrier concentration of the substrate. By appropriately setting the temperature, the substrate temperature can be kept constant at a desired temperature. Therefore, the composition of the constituent elements of the compound semiconductor layer grown on the substrate can be made constant, and a semiconductor element having a constant PL peak wavelength can be produced stably.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Preferred embodiments of the invention will be described below with reference to the drawings.
First, (100) InP substrates having various carrier concentrations were prepared by doping Fe, S, and Zn by a liquid encapsulated Czochralski (LEC) method. Then, an undoped InP layer (thickness: 0.3 μm), an undoped In _1-x Ga _x As _y P _1-y layer (thickness: 0.3 μm), and an undoped InP layer (thickness: 0.3 μm) are formed on the substrate by metal organic vapor phase epitaxy. A semiconductor element having a target PL peak wavelength of 1285 nm was manufactured. The growth pressure at this time was 40 torr, and the target surface temperature of the substrate was 620 ° C.

In this embodiment, for an InP substrate having various dopants and carrier concentrations, the carrier concentration at room temperature of the substrate is measured in advance, and the actual substrate temperature is controlled to be constant at 620 ° C. based on the carrier concentration of the substrate. The InGaAsP layer was grown by adjusting the temperature. Specifically, when a Fe-doped InP substrate having a carrier concentration of about 1 × 10 ¹³ cm ⁻³ at room temperature is used, the set temperature of the substrate is set to 617 ° C. When using an S-doped InP substrate, the set temperature is set to 622 ° C. when the carrier concentration at room temperature is about 3 × 10 ¹⁷ cm ⁻³ , and the set temperature is set to about 8 × 10 ¹⁸ cm ^−3. The temperature was 627 ° C. When a Zn-doped InP substrate is used, the set temperature is 623 ° C. when the carrier concentration at room temperature is about 1 × 10 ¹⁸ cm ⁻³ , and the set temperature is 625 when the carrier concentration is about 1 × 10 ¹⁹ cm ^−3. C.

  Note that this temperature setting is effective in the present embodiment, and it goes without saying that the temperature setting varies depending on, for example, the vapor phase growth apparatus used. In other words, if the relationship between the set temperature for the carrier concentration of the semiconductor substrate and the actual substrate surface temperature is known for the vapor phase growth apparatus to be used, it is easy to set the temperature to bring the substrate surface temperature to the desired temperature. Can be determined. The same applies to the substrate thickness.

  On the other hand, for comparison, an InGaAsP layer having a carrier concentration similar to that described above was used, and an InGaAsP layer was grown under the condition that the set temperature of the substrate was constant at 620 ° C.

  About the semiconductor element obtained by the method described above, PL peak wavelength and lattice mismatch were measured, and the composition of each element of the undoped InGaAsP layer was calculated based on the measurement results. The result is shown in FIG. In FIG. 1, □ marks are Fe-doped InP substrates, ◯ marks are S-doped InP substrates, and Δ marks are Zn-doped InP substrates, and the set temperature is adjusted so that the actual substrate temperature is constant at 620 ° C. The measurement results for the epitaxially grown InGaAsP layer (this embodiment) are as follows: ■ is a Fe-doped InP substrate, ● is an S-doped InP substrate, and ▲ is a Zn-doped InP substrate. It is a measurement result about what grown InGaAsP layer epitaxially (comparative example) by making 620 constant at 620 degreeC.

  From FIG. 1, in the semiconductor element obtained by the vapor phase growth method of the present embodiment, the PL peak wavelength variation is 2 nm or less, whereas in the semiconductor element obtained by the comparative example, the PL peak wavelength variation. Is a maximum of 15 nm.

  In this way, in the process of vapor phase growth of an epitaxial layer made of a compound semiconductor such as an InGaAsP layer on a semiconductor substrate such as InP, the carrier concentration of the semiconductor substrate at room temperature is measured in advance, and according to the carrier concentration of the semiconductor substrate. By controlling the set temperature of the substrate, it is possible to stably manufacture a semiconductor element having a constant PL peak wavelength.

As mentioned above, although the invention made by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.
For example, in the present embodiment, an example in which an InGaAsP layer is grown on an InP substrate by metal organic vapor phase epitaxy has been described, but the temperature is set according to the carrier concentration of the substrate and the actual substrate temperature is constant at a desired temperature. Thus, the same epitaxial growth method can be expected regardless of the type of epitaxial layer to be grown. Also, the type of substrate used and the growth method are not limited, and it is apparent from the above description that the present invention can be applied to other substrates and growth methods.

It is a graph which shows the carrier concentration of an InP substrate, and the PL peak wavelength of the epitaxial layer obtained by the growth method which concerns on this invention, and the conventional growth method. It is a graph which shows the relationship between the carrier concentration of an InP substrate, and the PL peak wavelength of the epitaxial layer obtained by the conventional growth method. It is a graph which shows the substrate temperature dependence characteristic of PL peak wavelength. It is a graph which shows the relationship between the carrier concentration of an InP substrate, and the composition of an InGaAsP layer. The relationship between the surface temperature of the InP substrate and the composition of the InGaAsP layer is shown.

Claims (4)

In a vapor phase growth method for growing an epitaxial layer on a semiconductor substrate,
The carrier concentration at room temperature of the semiconductor substrate is measured in advance, and the set temperature of the substrate is controlled in accordance with the carrier concentration at room temperature so that the surface temperature of the substrate becomes a desired temperature regardless of the carrier concentration of the semiconductor substrate. A vapor phase growth method characterized by growing an epitaxial layer.   The vapor phase growth method according to claim 1, wherein the semiconductor substrate is a compound semiconductor.   The vapor phase growth method according to claim 2, wherein the semiconductor substrate is an InP substrate.   4. The vapor phase growth method according to claim 1, wherein the epitaxial layer is grown using a metal organic vapor phase growth method.

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