Epitaxial growth device, production method for epitaxial wafer, and lift pin for epitaxial growth device

Abstract

An epitaxial growth device includes; a chamber; a susceptor; a supporting shaft, having a main column located coaxially with the center of the susceptor and supporting arms; and a lift pin, at least the surface layer region of the lift pin is made of a material having a hardness lower than the susceptor, the lift pin has a straight trunk part upper region configured to pass through the through-hole of the susceptor and having a surface roughness of from not less than 0.1 μm to not more than 0.3 μm, and the lift pin has a straight trunk part lower region configured to pass through the through-hole of the supporting arm and having a surface roughness of from not less than 1 μm to not more than 10 μm.

Claims

1. An epitaxial growth device comprising: a chamber; a susceptor for placing a silicon wafer thereon within the chamber; a supporting shaft for supporting the susceptor from below, having a main column located coaxially with a center of the susceptor and supporting arms radially extending from the main column; and lift pins configured to be inserted through both through-holes provided in the susceptor and through-holes provided in the supporting arms, and arranged movably in a vertical direction so that the silicon wafer is attached and detached on the susceptor by ascending and descending the lift pins, each of the lift pins having a rod-shaped straight trunk part and a head part having a diameter larger than the straight trunk part and the through-hole of the susceptor, wherein a straight trunk part lower region has a surface roughness larger than a surface roughness of a straight trunk part upper region, at least a surface layer region of each of the lift pins is made of glassy carbon having a hardness lower than a hardness of the susceptor, the straight trunk part of each of the lift pins comprises the straight trunk part upper region configured to pass through the through-hole of the susceptor and having the surface roughness of from not less than 0.1 um to not more than 0.3 um, and the straight trunk part of each of the lift pins comprises the straight trunk part lower region configured to pass through the through-hole of the supporting arm and having the surface roughness of from not less than 1 um to not more than 10 um.

2. The epitaxial growth device according to claim 1, wherein at least the surface layer region of each of the lift pins is made of glassy carbon, at least a surface layer region of the susceptor is made of silicon carbide, and the supporting arm is made of quartz.

3. The epitaxial growth device according to claim 1 or 2, wherein each of the lift pins comprises a rounded lower end part.

4. The epitaxial growth device according to claim 1, wherein the straight trunk part upper region has a surface roughness of 0.15 um to 0.3 um.

5. The epitaxial growth device according to claim 1, wherein the straight trunk part lower region has a surface roughness of 1 μm to 2 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This disclosure will be further described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a view illustrating a typical epitaxial growth device;

(3) FIG. 2 is a view illustrating an epitaxial growth device according to this disclosure:

(4) FIG. 3 is a view illustrating the peripheral region of a lift pin in an epitaxial growth device according to this disclosure;

(5) FIG. 4 is a view illustrating a relationship between the surface roughness of the straight trunk part lower region of a lift pin to be passed through a through-hole of a supporting arm and the ascending/descending defect occurrence rate; and

(6) FIG. 5 is a view illustrating a relationship between the surface roughness of the straight trunk part upper region of a lift pin configured to pass through a through-hole of a susceptor and average number of LPDs per wafer.

DETAILED DESCRIPTION

(7) Below, with reference to the drawings, this disclosure will be described in detail.

(8) FIG. 2 illustrates an epitaxial growth device 1 according to this disclosure having a supporting shaft 17. Moreover, FIG. 3 illustrates the peripheral region of a lift pin 15 in the epitaxial growth device 1. It should be noted that the same reference numeral refers to the same configuration, and the description will be omitted. As illustrated in FIG. 2 and FIG. 3, the epitaxial growth device 1 according to this disclosure has lift pins 15 made of a material having a harness lower than the susceptor 4, i.e., a soft material, and the lift pins 15 are configured to be inserted through respective through-holes 4h of the susceptor 4 and respective through-holes 17h of supporting arms 17b, and are arranged movably in the vertical direction.

(9) As illustrated in FIG. 3, each lift pin 15 has a rod-shaped straight trunk part 15a and a head part 15b having a diameter larger than the straight trunk part 15a and the through-hole 4h, and the head part 15b is configured to be engaged with a diametrically enlarged part 4w of the through-hole 4h of the susceptor 4. Additionally, the shape of each lift pin is not necessary to be limited, as long as the lift pin has a head part directly supporting a silicon wafer in the tip end of the rod-shaped straight trunk part, and therefore is not limited to the illustrated shape.

(10) As described above, each lift pin 15 is made of a material having a hardness lower than the susceptor 4, i.e., a soft material. Thereby, occurrence of contact scratches to the back surface of the wafer W can be substantially reduced. For the lift pin 15, specifically, glassy carbon, graphite, quartz, aluminum nitride, forsterite, cordierite, yttria, steatite, etc. can be used. Among them, glassy carbon is excellent in molding, and has high purity, and excellent heat resistance and acid resistance. It should be noted that it is not necessary to make the entire lift pin 15 of the above materials, as long as at least the surface layer region is made of a material softer than the surface material of the susceptor. For example, each lift pin 15 can be made of a base material having a high hardness such as SiC coated with the above materials on the surface.

(11) As the susceptor 4, from the perspectives of high purity, heat resistance durable for the use under a high temperature environment, and acid resistance, a carbon base material coated with SiC on the surface, a base material made of SiC itself, or the like is usually used.

(12) In this disclosure, it is important that a region 15c on the straight trunk part 15a of each lift pin 15 configured to pass through the through-hole 17h of the supporting arm 17b, which region is hereinbelow referred to as “straight trunk part lower region”, has a surface roughness of not less than 1 μm. As described above, in the case of making each lift pin of a material softer than the susceptor, some were found out to be caught within the through-holes of the supporting arms when descended downwards by descending the ascending/descending shaft.

(13) Although the cause of being caught is not necessarily apparent, it is presumed that larger surface roughness of the lift pin 15 decreases the area in contact with the wall surface defining the through-hole of the supporting arm, therefore increases slidability within the through-hole, and as a result, can prevent occurrence of being caught.

(14) Thus, in this disclosure, the surface roughness of the straight trunk part lower region 15c of each lift pin 15 configured to pass through the through-hole 17h of the supporting arm 17b is not less than 1 μm. Here, when the surface roughness of the straight trunk part lower region 15c was less than 1 μm, occurrence of being caught as described above could not be sufficiently prevented.

(15) Moreover, the upper limit of the surface roughness of the straight trunk part lower region 15c of each lift pin 15 configured to pass through the through-hole 17h of the supporting arm 17b is not particularly limited in terms of preventing occurrence of being caught as described above, but is desirably not more than 10 μm in terms of easy processing to adjust the surface roughness. It should be noted that “surface roughness” in this disclosure means arithmetic average roughness Ra regulated in JIS B 0601, 2001.

(16) Such surface roughness of each lift pin 15 can be adjusted by polishing treatment such as machining. Moreover, the surface roughness of a wall surface 17s within the through-hole 17h of the supporting arm 17b is generally adjusted by machining, etching, quenching, blast treatment, etc., and is adjusted to be a surface roughness of approximately not more than 0.5 μm.

(17) Furthermore, in this disclosure, a region 15d on the straight trunk part 15a of each lift pin 15 configured to pass through the through-hole 4h of the susceptor 4, which region is hereinbelow referred to as “straight trunk part upper region”, has a surface roughness of from not less than 0.1 μm to not more than 0.3 μm. In this disclosure, since each lift pin 15 is made of a material softer than the susceptor 4, by making the surface roughness of the straight trunk part upper region 15d of each lift pin 15 configured to pass through the through-hole 4h of the susceptor 4 to be not more than 0.3 μm, the above mentioned effect of preventing dust generation can be achieved. Moreover, by making the surface roughness to be not less than 0.1 μm, occurrence of dust generation can be effectively prevented without increasing the processing cost.

(18) Additionally, since the lower surface part of the head part 15b of each lift pin contacts the diametrically enlarged part 4w of the through-hole 4h of the susceptor 4, the surface roughness of the lower surface part of the head part 15b is preferable to be not more than 0.3 μm.

(19) Thus, each lift pin 15 according to this disclosure has different surface roughness between the straight trunk part upper region 15d configured to pass through the through-hole 4h of the susceptor 4 and the straight trunk part lower region 15c configured to pass through the through-hole 17h of the supporting arm 17b, and the surface roughness of the straight trunk part lower region 15c is made to be larger than the surface roughness of the straight trunk part upper region 15d.

(20) In addition, the surface roughness of the wall surface 4s defining the through-hole 4h of the susceptor 4 is also preferable to be from not less than 0.1 μm to not more than 0.3 μm. Thereby, the effect of preventing dust generation can be further enhanced.

(21) Moreover, it is preferable that each lift pin 15 has a rounded lower end part. As described above, the lift pin 15 is inserted through both the through-hole 4h of the susceptor 4 and the through-hole 17h of the supporting arm 17b, and is configured to be able to move in the vertical direction. In this regard, a slight gap or clearance is provided between each lift pin 15 and the corresponding through-holes 4h and 17h, so that the lift pin 15 can move smoothly within the through-holes 4h and 17h.

(22) Therefore, when a lift pin 15 performs the ascending/descending motion, the lift pin 15 may be inclined and deviate from the trajectory of the ascending/descending motion. However, by rounding the lower end part of each lift pin 15 to have roundness, each lift pin 15 can recover to the trajectory of the ascending/descending motion. This setup makes it possible to prevent dust from being generated by sliding between each lift pin 15 and the susceptor 4 due to deviation from the trajectory.

(23) Thus, according to this disclosure, occurrence of scratches to the epitaxial silicon wafer back surface can be reduced, and also attachment of particles to the wafer surface can be prevented.

EXAMPLES

Preparation of Lift Pins

(24) Eight types of lift pins were prepared for Examples 1 to 4 and Comparative Examples 1 to 4. For each case, the surface roughness of the straight trunk part upper region and the straight trunk part lower region are indicated in Table 1. All of these lift pins were made of glassy carbon.

(25) TABLE-US-00001 TABLE 1 Lift pin Surface roughness of Surface roughness of straight trunk part straight trunk part upper region (μm) lower region (μm) Example 1 0.2 1 Example 2 0.2 2 Example 3 0.15 1 Example 4 0.3 1 Comparative 0.2 0.2 Example 1 Comparative 0.2 0.7 Example 2 Comparative 0.5 1 Example 3 Comparative 1 1 Example 4

(26) Lift Pin Ascending/Descending Defective Motion Observation Experiment

(27) The lift pins prepared for Examples 1 to 4 and Comparative Examples 1 to 4 were respectively applied to the epitaxial growth device 1 illustrated in FIG. 2, and subjected to the motion observation experiment for observing whether or not defective motion occurred, when the lift pins were ascended and descended in a state of placing the silicon wafer W on the susceptor. This motion observation experiment was conducted at room temperature with the upper dome 11 of the epitaxial growth device 1 being open, and occurrence of defective motion was visually observed. The number of the ascending/descending motions was 100 times, counting a round-strip motion as one.

(28) FIG. 4 illustrates a relationship between the surface roughness of the straight trunk part lower region and the ascending/descending defect occurrence rate. As apparent from FIG. 4, the ascending/descending defect occurrence rate of the lit pin decreased as the surface roughness of the straight trunk part lower region increased, and when the surface roughness was not less than 1 μm, no defects occurred in the ascending/descending motion of the lift pins. Contrarily, when the surface roughness of the straight trunk part lower region was less than 1 μm, defects were observed in the ascending/descending motion of the lift pins. Thus, it is clear that occurrence of defects in the ascending/descending motion of the lift pins can be prevented, when the surface roughness of the straight trunk part lower region is not less than 1 μm.

(29) Epitaxial Wafer Production Experiment 1

(30) Epitaxial wafers were produced by applying the lift pins for Examples 1 and 2, and Comparative Examples 1 and 2 to the epitaxial growth device 1 illustrated in FIG. 2. Here, as the susceptor 4, a carbon base material coated with SiC on the surface was used. Moreover, as the substrate of epitaxial wafers, a boron doped silicon wafer W having a diameter of 300 mm was used.

(31) For producing an epitaxial wafer, firstly the silicon wafer W was introduced into the epitaxial growth device 1, and placed on the susceptor 4 using the lift pins 15. Then, hydrogen baking was performed under a hydrogen gas atmosphere at a temperature of 1150° C., and a silicon epitaxial film was grown on the surface of the silicon wafer W by 4 μm at 1150° C., to obtain an epitaxial silicon wafer. Here, trichlorosilane gas was used as a raw material source gas, diborane gas as a dopant gas, and hydrogen gas as a carrier gas. For each of the Examples and Comparative Examples, 50 epitaxial wafers were produced.

(32) Evaluation of Surface Quality

(33) For the obtained epitaxial wafers, the number of epitaxial defects formed in the epitaxial layer was evaluated. Specifically, the epitaxial layer surface was observed and evaluated using a surface defect inspection device, manufactured by KLA-Tencor: Surfscan SP-2, in DWO mode (Dark Field Wide Oblique mode), and an occurrence state of LPD (Light Point Defect) having a size or diameter not less than 0.25 μm was examined. This evaluation was carried out on each set of 50 wafers prepared for Examples 1 and 2, and Comparative Examples 1 and 2, and the number of LPDs per wafer was obtained. The results were that for Examples 1 and 2 in which the surface roughness of the straight trunk part lower region was more than 1 μm, sudden LPD increase was not observed, and it can be assumed that defects did not occur in the ascending/descending motion of the lift pins. For these Examples 1 and 2, the number of LPDs observed in all the produced epitaxial wafers was not more than 1/wf.

(34) Contrarily, for Comparative Examples 1 and 2 in which the surface roughness of the straight trunk part lower region was less than 1 μm, sudden LPD increase was observed, and it can be assumed that defects occurred in the ascending/descending motion of the lift pins. For these Comparative Examples 1 and 2, the number of epitaxial wafers having more than 10 LPDs/wf observed was 2 for Comparative Example 1, and 2 for Comparative Example 2.

(35) Epitaxial Wafer Production Experiment 2

(36) Similarly to Examples 1 and 2, and Comparative Examples 1 and 2, epitaxial wafers were produced by applying the lift pins for Examples 3 and 4, and Comparative Examples 3 and 4 to the epitaxial growth device 1 illustrated in FIG. 2. Here, the production conditions were all the same as the cases of Examples 1 and 2, and Comparative Examples 1 and 2.

(37) When the above epitaxial wafers were produced, for any of Examples 3 and 4, and Comparative Examples 3 and 4, since the surface roughness of the straight trunk part lower region was not less than 1 μm, sudden LPD increase was not observed. FIG. 5 illustrates a relationship between the surface roughness of the straight trunk part upper region and the average number of LPDs per wafer, regarding Examples 1, 3, and 4, and Comparative Examples 3 and 4. From FIG. 5, it is clear that Example 1 having the surface roughness: 0.15 μm, Example 3 having the surface roughness: 0.2 μm, and Example 4 having the surface roughness: 0.3 μm, in which the surface roughness of the straight trunk part upper region of each lift pin was not more than 0.3 μm, achieved the average number of LPDs not more than 1/wf, while Comparative Example 3 having the surface roughness: 0.5 μm and Comparative Example 4 having the surface roughness: 1 μm, in which the surface roughness of the straight trunk part upper region of each lift pin was more than 0.3 μm, could not achieve the average number of LPDs not more than 1/wf.

INDUSTRIAL APPLICABILITY

(38) This disclosure can reduce occurrence of scratches to the epitaxial silicon wafer back surface, and also reduce attachment of particles to the wafer surface, and thus is useful in the industry of semiconductor wafer production.

REFERENCE SIGNS LIST

(39) 1, 100 Epitaxial growth device 2 Chamber 4 Susceptor 4h, 7h, 17h Through-hole 4s, 17s Wall surface 4w Diametrically enlarged part 5, 15 Lift pin 6 Ascending/descending shaft 7 Supporting shaft 7a, 17a Main column 7b. 17b Supporting arm 11 Upper dome 12 Lower dome 13 Dome mounting body 14 Heat lamp 15a Straight trunk part 15b Head part 15c Straight trunk part lower region 15d Straight trunk part upper region 31 Gas supply opening 32 Gas exhaust opening W Silicon wafer