JP3227083B2 - Method for manufacturing bipolar transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for growing an ultra-high-speed bipolar transistor using a III-V compound semiconductor.

[0002]

2. Description of the Related Art A heterojunction bipolar transistor (HBT) using a wide gap semiconductor for an emitter layer is disclosed in US Pat.
It has excellent characteristics as a high-speed, high-frequency element, and is expected to be used in various applications. In the case of configuring an HBT, the configuration of a semiconductor material based on a combination of GaAs and AlGaAs or a combination of InP and InGaAs has the highest importance from a practical point of view and is widely used.

[0003] Carbon C, which is a Group IV atom, has attracted attention as a p-type dopant in recent years because it has characteristics such as a low diffusion constant in a crystal and high-concentration doping. Several methods have been used to grow a semiconductor layer to which carbon is added as an impurity. Among them, a vapor phase growth method such as MOCVD or VPE is easy in that an apparatus can be enlarged and a material can be easily replenished. MBE and LP in terms of
It is superior to other growth methods such as E and is widely used industrially. Generally, hydrogen is often used as a carrier gas for vapor phase growth because of its characteristic that a gas having a higher purity than other gases can be obtained. In addition, hydrides such as AsH ₃ and PH ₃ are often used as group V raw materials in vapor phase growth of III-V semiconductors. Therefore, dissociated active hydrogen exists in a high concentration in the growth chamber. This situation is due to TMAs, TBAs, TM
Even when an organometallic material such as P or TBP is used, dissociated hydrogen is generated, which is also generated. As one of the adverse effects of hydrogen on carbon impurities, the problem of inactivation by dopant hydrogenation is known. This is a phenomenon in which hydrogen existing in a high concentration in the growth atmosphere bonds with carbon impurities in the crystal to terminate the carbon bond, thereby offsetting the supply of carriers from carbon. When this phenomenon becomes apparent, most of the impurity carbon is inactivated by hydrogenation when a high concentration of C is added to the semiconductor layer, and the low efficiency of the carbon-added layer increases. There was a point.

[0004]

It is known that heat treatment in nitrogen is effective as a method for reactivating carbon inactivated by hydrogenation. However, HBT
Even after annealing after growing the structure, the highly doped n-type emitter and n-type cap layer remain
Since it is present on aAs, the elimination of hydrogen out of the crystal is hindered by the influence of positively charged space charges in the n-type layer, and there has been a problem that dehydrogenation cannot be performed effectively.
Also, it is considered that the heat treatment is performed in nitrogen while the growth is interrupted up to the base layer. , Hydrogenation of the carbon-added layer (base layer) occurs again, resulting in a problem that the resistivity of the carbon-added layer cannot be lowered.

An object of the present invention is to provide a method for growing a heterojunction bipolar transistor having a base layer containing carbon as an impurity in order to solve the above-mentioned problems, and to obtain a technique for reducing the hydrogenation rate of carbon impurities. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a collector layer on a semiconductor substrate and a p-type semiconductor having carbon added as an impurity.
In the method of manufacturing a bipolar transistor in which a base layer of n-type and a first emitter layer of n-type are sequentially deposited by a vapor deposition method, after growing the base layer to which the carbon is added, an n-type emitter layer and n Type or i-type first
After sequentially depositing a cap layer, the semiconductor layer structure is subjected to a carbon impurity activation heat treatment in an inert gas atmosphere,
This can be achieved by sequentially regrowing the n-type second emitter layer and the n-type second cap layer.

[0007]

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1 (a), an n-InGaAs collector electrode layer 5, i
-InGaAs collector layer 4, C-doped p-InGaAs
The layer structure in which the s base layer 3, the first n-InP emitter layer 2, and the first i-InGaAs cap layer 1 are sequentially grown by MOCVD is subjected to a heat treatment at 550 ° C. for 5 minutes in a nitrogen atmosphere. Hydrogen remaining in carbon-added InGaAs by heat treatment in an inert gas is reduced to the first n-
The crystal is separated from the crystal through the InP emitter layer 2 and the first i-InGaAs cap layer 1, and the activation rate of carbon is 1
Improve to nearly 00%. Next, the first i-InGaAs
After the s cap layer 1 was removed by etching, the wafer was put into the growth apparatus again, and the second n-InP emitter layer 7 and the second n-InGaAs cap layer 8 were removed as shown in FIG.
The growth is performed as shown in FIG.
By setting the temperature to not more than ° C., the hydrogen permeability of the n-InP layer can be kept low, and the hydrogenation of the carbon-doped base layer can be prevented. In other words, in this step, by performing regrowth at a temperature lower than a certain temperature than the dehydrogenation step,
The first emitter layer 2 functions as a barrier against hydrogen.

The inventor has determined that the conditions under which dehydrogenation can be effectively performed in the heat treatment step, that is, the conditions under which the hydrogen permeability of the n-InP emitter layer 7 can be kept high, are the first emitter layer thickness, the first cap Considering that there is a deep correlation with the layer thickness, the carrier concentration of the first emitter layer, the heat treatment temperature and the heat treatment time, the result of careful examination shows that the first emitter layer 2 and the first cap layer 1 The total film thickness is 1000 ° or less, and the total sheet impurity concentration of the first emitter layer 2 and the first cap layer is 5 × 10 5
^{It is in the range of 10} / cm ² to 2 × 10 ¹³ / cm ² , and it is confirmed that the heat treatment is effective when the heat treatment temperature is 520 ° C. or more as shown in FIG. 2 and the process is 1 minute or more. did. On the other hand, regarding the conditions for regrowth, at the stage where the first cap layer 1 was removed, the sheet impurity concentration of the first InP emitter layer 2 was 5 × 10 ¹⁰ / cm ² to 2 × 1
0 ¹³ / cm ² and the growth temperature is 480
It was confirmed that when the temperature was lower than or equal to ° C., intrusion of hydrogen into the crystal could be prevented, and the hydrogen permeability of the n-InP emitter layer could be kept low (FIG. 2).

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a growth process of InP / InGaAs.HBT will be described with reference to FIG.
A layer structure as shown in FIG. 1A is grown by MOCVD. In the figure, 1 is a first i-InGaAs cap layer, 2 is a first n-InP emitter layer, 3 is a C-doped p-InGaAs base layer, 4 is an i-InGaAs collector layer, and 5 is an n-InGaAs collector electrode. Layer 6 is an InP substrate. Here, the film thickness and carrier concentration of the n-InP emitter layer 2 are 200 ° and 3 × 10 ¹⁷ / cm ³ (sheet carrier concentration of 6 × 10 ¹¹ / cm ³ ).
cm ² ), and the thickness of the i-InGaAs cap layer 1 is 50
Å Next, the wafer is taken out of the growth apparatus and heat-treated at 550 ° C. for 5 minutes in a nitrogen atmosphere. By performing heat treatment under these conditions, hydrogen remaining in the InGaAs to which carbon is added is desorbed from the crystal through the i-InP emitter layer 2 and the i-InGaAs layer 1, and the activation rate of carbon as an acceptor is almost 100%.
%. In the sample used here, the carrier concentration immediately after the growth was about 1 × 10 ¹⁹ / cm ³ , but 550
Carrier concentration of 4 ×
It improved to about 10 ¹⁹ / cm ³ as shown in FIG.
Next, the first i-InGaAs cap layer 1 is removed by etching as shown in FIG. At this time, by using an appropriate solution (for example, a mixed solution of sulfuric acid, hydrogen peroxide, and water), only InGaAs can be selectively etched, and InGaAs / InP
Etching can be stopped at the interface with good controllability. This i-InGaAs layer is provided in order to suppress the deterioration of the crystal surface due to the heat treatment. By removing this layer by etching, a high-quality crystal surface can be exposed.

Next, the wafer is again introduced into the growth apparatus, and the second n-InP emitter layer 7 and the second n-InGa
The As cap layer 8 is regrown as shown in FIG. At this time, by setting the growth temperature to 480 ° C. or less, n
-The hydrogen permeability of the InP layer can be kept low (FIG. 2), and the hydrogenation of the carbon-doped base layer 3 can be prevented. That is, in this step, the first emitter layer 2 acts as a barrier against hydrogen by performing regrowth at a temperature lower than a certain temperature in the dehydrogenation step.

In this embodiment, the wafer is once taken out of the growth apparatus, subjected to heat treatment and etching, and then introduced into the growth apparatus again for regrowth. However, a part or all of the steps are continuously performed in the growth chamber. You can also do it. That is, annealing in a nitrogen atmosphere by introducing a nitrogen gas or the like into the growth chamber and InGaAs using a chlorine-based gas or the like.
Dry etching of the s layer and the InP layer can be performed. In this embodiment, the first InGaAs cap layer 1 is used as the surface protection layer. However, the layer structure to be grown in the first step is up to the first InP emitter layer 2, and after annealing, the first emitter layer 2 is formed. A process of removing a part by etching can be used instead. Furthermore, it is also possible to suppress the deterioration of the crystal surface quality during annealing by annealing conditions, the combined use of a solid phosphorus source, and the like. In this case, the step of removing a part of the first InP emitter layer by etching is omitted. Sometimes. InP for the collector layer
May be used, and the second cap layer may be composed of InP. On the other hand, regarding material systems, InP / I
The case of nGaAs-HBT was described, but InAl
(Ga) As / InGaAs, AlGaAs / (Al)
GaAs, InGaP / GaAs, InAlAs / Ga
It can be widely used for HBTs using other materials such as AsSb and InP / GaAsSb. Although the case where nitrogen is used as the atmosphere gas used for the heat treatment has been described, the same effect can be obtained by using another inert gas such as argon or helium.

[0012]

As described above, the method for fabricating a bipolar transistor according to the present invention comprises the steps of: providing a collector layer on a semiconductor substrate;
In a method for manufacturing a bipolar transistor in which a p-type base layer to which carbon is added as an impurity and an n-type first emitter layer are sequentially deposited by a vapor deposition method, after growing the base layer to which the carbon is added, After sequentially depositing an n-type emitter layer and an n-type or i-type first cap layer, the semiconductor layer structure is subjected to a carbon impurity activation heat treatment in an inert gas atmosphere, and then an n-type second The emitter layer and the n-type second cap layer are sequentially re-grown to activate the carbon in the base layer when growing an HBT using a compound semiconductor in which carbon is added as an impurity to the base layer. Therefore, the device characteristics can be improved by realizing a higher base layer carrier concentration.

[Brief description of the drawings]

FIGS. 1A to 1C show an embodiment in which the present invention is applied to an InP / InGaAs.HBT, and FIGS.

FIG. 2 is a diagram showing a heat treatment temperature dependency of a carrier concentration in a C-doped InGaAs layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st cap layer 2 1st emitter layer 3 Base layer 4 Collector layer 6 Semiconductor substrate 7 2nd emitter layer 8 2nd cap layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/331 H01L 21/205 H01L 21/324 H01L 29/205 H01L 29/73

Claims (3)

(57) [Claims] 1. A method for manufacturing a bipolar transistor, comprising: sequentially depositing a collector layer, a p-type base layer doped with carbon as an impurity, and an n-type first emitter layer on a semiconductor substrate by a vapor deposition method. After growing the carbon-added base layer, an n-type emitter layer and an n-type or i-type first cap layer are sequentially deposited, and the semiconductor layer structure is activated with carbon impurities in an inert gas atmosphere. After the heat treatment, the n-type second emitter layer and n-type
A method for manufacturing a bipolar transistor, comprising sequentially regrowing a second cap layer of a mold. 2. A following total thickness 1000Å of said first emitter layer and the first cap layer, and the sheet impurity concentration of the total has from 5 × 10 ¹⁰ in the range of 2 × 10 ¹³ cm ^-2 2. The method according to claim 1, wherein the activation heat treatment is performed at 520 ° C. or more for 1 minute or more, and the regrowth is performed at 480 ° C. or less. 3. The method according to claim 1, wherein the semiconductor substrate is InP, and the base layer is InP.
2. The method according to claim 1, wherein the collector layer is made of InGaAs or InP, the first and second emitter layers are made of InP, and the first and second cap layers are made of InGaAs.