JPH04348022A - Cell for molecular beam epitaxy - Google Patents

Abstract

PURPOSE:To acquire a cell for molecular beam epitaxy wherein an element contained in a crucible is uniformly heated and an element which has once evaporated does not attach to an end opening part of the crucible as a liquid drop. CONSTITUTION:A first heater 4 is provided to an area near an end opening part of a crucible 2 having a bottom with a raised part, and a second heater 8 is inserted to the raised part of the bottom to heat the crucible 2. It is possible to form a crystal layer of good crystallinity which is free from crystal defects with good reproducibility.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a cell for molecular beam epitaxy used for crystal growth of compound semiconductors used in semiconductor devices, and in particular, it houses component elements of the compound semiconductor and heats the elements. The present invention relates to a cell for molecular beam epitaxy that uses evaporation.

0002

[Prior Art] Conventionally, in the crystal growth process of compound semiconductors using the molecular beam epitaxy method, P
BN (Pyroritic Boron Nitrid)
A cell equipped with a plurality of crucibles shaped like e) is used, and group III elements such as Ga and Al, and group V elements such as As are placed in the crucibles, and each element is melted in an ultra-high vacuum. In general, each crucible containing crucibles is heated and controlled to an appropriate temperature, and a crystal layer with a predetermined elemental composition is grown on the substrate while keeping the ratio of the amount of evaporation of each component element constant. It is being said.

FIG. 2 is a schematic cross-sectional view showing the structure of a conventional cell for molecular beam epitaxy.
2 is a crucible made of PBN or the like, 13 is Ga as an evaporation source, 14 is a heater, 15 is a thermocouple, 16 is a shutter that temporarily blocks the evaporated elements, 17 is the upper end of the crucible 12 This is a cap for holding the opening in the heat radiation prevention cylinder 11.

Next, using the above cell, GaAs was deposited on the substrate.
The process of growing a crystal will be explained.

A heater 14 is provided from the center of the crucible 12 to the periphery of the top, and the temperature of the crucible is adjusted to a desired temperature while being detected by a thermocouple 15 disposed near the bottom. Then, the Ga 13 stored in the crucible 12 gradually begins to evaporate due to heating, and the evaporated elements are temporarily blocked by the shutter 16. Further, cells containing other component elements (not shown) have a similar structure, and the elements contained in the crucible are evaporated by heating, and the evaporated elements are blocked by a shutter (not shown).

Next, on the cell containing each component element,
A heated substrate (not shown) is placed in a state where crystal growth occurs, other conditions necessary for crystal growth are set, the shutter 6 and the shutters of the cells containing other component elements are opened, and the substrate is heated. evaporate each component element onto the substrate
Grow an aAs crystal.

[0007]

[Problems to be Solved by the Invention] By the way, in the crystal growth process using the above cell for molecular beam epitaxy,
The elements stored in the crucible are gradually consumed as the number of growth increases. For this reason, conventional problems have occurred in that the growth rate slows down as the number of times the crystal grows increases, and the crystal composition of the growing crystal gradually changes.

Therefore, when trying to increase the capacity of the crucible 12 so as to accommodate a large amount of elements to prevent a decrease in the growth rate due to an increase in the number of growths, the contained elemental solution has a temperature distribution over the entire liquid surface. As a result, the temperature at the tip opening of the crucible becomes lower than other parts, and some of the elements that have evaporated become droplets and adhere to the tip opening of the crucible. Re-evaporation of attached elemental droplets sometimes caused crystal defects called oval defects in the crystal layer.

Furthermore, when the capacity of the crucible 12 containing the elements is increased, the evaporation rate changes because it is not possible to maintain a uniform temperature of the large amount of elements accommodated in the crucible 12, and the resulting crystal layer still deteriorates. Problems such as changes in the crystal composition have occurred.

The present invention was made to solve the above-mentioned problems, and it reduces the adhesion of elemental droplets to the opening at the tip of the crucible, and also creates a crystal layer with no crystal defects and a good crystal composition. The purpose of the present invention is to provide a cell for molecular beam epitaxy that can grow with good reproducibility.

[0011]

[Means for Solving the Problems] A cell for molecular beam epitaxy according to the present invention has a crucible having a raised bottom, and a first heating heater provided near the opening at the tip of the crucible. The second part is placed on the raised part of the bottom.
A heating heater is inserted.

0012

[Operation] In this invention, the first heating heater is provided at the tip opening of the crucible, and the second heating heater is provided at the raised bottom part of the crucible, so that both the first and second heating heaters are provided. The heater can evenly heat the area around the crucible, and the first heating heater can set the opening at the tip of the crucible to a higher temperature than other parts.
The entire elemental solution contained in the crucible is heated uniformly and the evaporation rate becomes constant, and the elements once evaporated do not adhere as droplets to the opening at the tip of the crucible.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a cell for molecular beam epitaxy according to an embodiment of the present invention, and in the figure, 1
2 is a crucible made of PBN or the like; 3 is Ga as an evaporation source; 4 is a first heater; 5 is a thermocouple; is a shutter that temporarily blocks the evaporated elements, 7
A cap 8 for holding the upper end opening of the crucible 2 in the heat radiation prevention cylinder 1 is a second heater.

Next, a GaAs crystal growth process using the above cell will be explained. Ga element is contained in a crucible 2 having a W-shaped cross section and a raised bottom.A first heater 4 is provided around the opening at the tip of the crucible 2. A second heater 8 is inserted into the raised part of the bottom. Ga 3 stored in the crucible 2 is uniformly heated and evaporated by the first and second heaters 4 and 8, and the evaporated Ga is temporarily blocked by the shutter 6.

Here, the second heater 8 is controlled at an appropriate temperature in order to control the amount of evaporated Ga that reaches the substrate (not shown) on which the crystal grows. Further, the first heater 4 is set slightly higher than the second heater 8 so that once evaporated Ga does not adhere to the opening at the tip of the crucible 2.

Next, a cell containing another element (As) has the same structure as the above cell, and the crucible is heated to the optimum temperature by the first and second heaters.
The contained element (As) evaporates, and the evaporated element is temporarily blocked by the shutter.

Thereafter, as in the conventional case, a heated substrate (not shown) is placed on the cell containing each element so that crystal growth occurs, and other conditions necessary for crystal growth are set, and then the shutter is closed. By opening the shutter of the cell containing 6 and other elements and evaporating each component element toward the substrate, a GaAs crystal is sequentially grown.

As described above, the molecular beam epitaxy cell of this embodiment includes the crucible 2 having a raised bottom portion, the first heater 4 is provided around the opening at the tip of the crucible 2, and A second heater 8 is inserted into the raised part of the bottom of the crucible 2, and the crucible 2 is heated evenly from the periphery and the stored Ga(
Since the tip opening of the crucible 2 is heated to a higher temperature than other parts by the first heater 4, the evaporated Ga( Elements) do not adhere as droplets to the opening at the tip of the crucible, and as a result, good crystals with no crystal defects and a uniform crystal composition can be grown with good reproducibility.

[0019]

As described above, according to the present invention, a crucible having a raised bottom is provided, a first heater is provided in the vicinity of the opening at the tip of the crucible, and the crucible has a raised bottom. Since the second heater is inserted, even if the internal volume of the crucible is increased to increase the amount of elements filled, the elements in the crucible are uniformly heated and the evaporation rate is stabilized. Since the heater 1 can suppress the adhesion of element droplets to the opening at the tip of the crucible, it is possible to grow a good crystal with no crystal defects and a uniform crystal composition with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a cell for molecular beam epitaxy showing an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of a conventional cell for molecular beam epitaxy.

[Explanation of symbols]

1 Heat radiation prevention tube 2 Crucible 3 Ga 4 First heating heater 5 Thermocouple 6 Shutter 7 Cap 8 Second heating heater 11 Heat radiation prevention tube 12 Crucible 13 Ga 14 Heating heater 15 Thermocouple 16 Shutter 17 Cap 18 Ga droplet

Claims (1)

[Claims] Claim 1: A cell for molecular beam epitaxy that accommodates elements forming a compound semiconductor inside and evaporates the elements by heating, comprising: a crucible having a raised bottom; A cell for molecular beam epitaxy, comprising a first heater provided and a second heater inserted into the raised bottom of the crucible.